Feature Description Huawei

Chapter 1 BSS Solution ..................................................................................

1-1

1.1 GSM/GPRS System ............................................................................... 1.1.1 GSM System .................................................................................. 1.1.2 GPRS System ................................................................................ 1.2 BSS System features ............................................................................. 1.3 BSC ........................................................................................................ 1.3.1 Overview ........................................................................................ 1.3.2 Features ......................................................................................... 1.4 PCU ........................................................................................................ 1.4.1 Overview ........................................................................................ 1.4.2 Features ......................................................................................... 1.5 BTS Series ............................................................................................. 1.5.1 BTS30 ............................................................................................ 1.5.2 BTS312 .......................................................................................... 1.5.3 BTS30A.......................................................................................... 1.5.4 BTS3001C ..................................................................................... 1.6 Operation & Maintenance ....................................................................... 1.6.1 Operation & Maintenance of BTS .................................................. 1.6.2 Operation & Maintenance of BTS .................................................. 1.6.3 Traffic statistics console ................................................................. 1.6.4 Dynamic Data Configuration Management .................................... 1.6.5 LMT ................................................................................................ 1.6.6 OMC ............................................................................................... 1.6.7 Telnet terminal ...............................................................................

1-1 1-1 1-2 1-3 1-5 1-5 1-7 1-9 1-9 1-10 1-10 1-11 1-13 1-16 1-18 1-19 1-19 1-21 1-24 1-24 1-27 1-27 1-28

Chapter 2 BSS Functions ................................................................................

2-1

2.1 Basic Functions ...................................................................................... 2.1.1 Overview ........................................................................................ 2.1.2 Channel.......................................................................................... 2.1.3 System Information ........................................................................ 2.1.4 Idle Mode Behavior ........................................................................ 2.1.5 PLMN Selection ............................................................................. 2.1.6 Cell Selection and Reselection ...................................................... 2.1.7 Location updating........................................................................... 2.1.8 Access ........................................................................................... 2.1.9 Paging ............................................................................................ 2.1.10 Immediate assignment ................................................................. 2.1.11 Assignment .................................................................................. 2.1.12 Authentication .............................................................................. 2.1.13 Ciphering ......................................................................................

2-1 2-1 2-2 2-9 2-15 2-17 2-19 2-23 2-31 2-32 2-34 2-43 2-44 2-47

2.1.14 DTX .............................................................................................. 2.1.15 Frequency hopping ...................................................................... 2.2 Extended Functions ................................................................................ 2.2.1 Handover ....................................................................................... 2.2.2 Power Control ................................................................................ 2.2.3 Extended Cell................................................................................. 2.2.4 IUO ................................................................................................. 2.2.5 Satellite Transfer ............................................................................ 2.2.6 Diversity Receiving ........................................................................ 2.2.7 Aggressive Frequency Reuse Pattern ........................................... 2.2.8 Multiband Network ......................................................................... 2.2.9 Carrier Mutual-assistance .............................................................. 2.2.10 Cell Broadcast.............................................................................. 2.2.11 Radio Channel Allocation ............................................................. 2.2.12 Half Rate ...................................................................................... 2.2.13 E1 Ring Topology ........................................................................ 2.2.14 GSM900/GSM1800 Co-cell ......................................................... 2.2.15 Multi-MNC .................................................................................... 2.2.16 E-GSM/R-GSM ............................................................................ 2.3 GPRS Function ...................................................................................... 2.3.1 Supported Packet System Information .......................................... 2.3.2 Supported GPRS MS Modes ......................................................... 2.3.3 Supported RLC Modes .................................................................. 2.3.4 Supported Channel Coding Scheme ............................................. 2.3.5 Supported Network Control Modes ................................................ 2.3.6 Supported Network Operation Mode ............................................. 2.3.7 Supported QoS .............................................................................. 2.3.8 Supported Assignment ................................................................... 2.3.9 Supported Paging .......................................................................... 2.3.10 Timing Advance ........................................................................... 2.3.11 Measurement Report ................................................................... 2.3.12 Supported Flow Control ............................................................... 2.3.13 Supported Dynamic Handover between TCH and PDCH............ 2.3.14 Supported Packet Access Function .............................................

2-51 2-54 2-59 2-59 2-73 2-85 2-87 2-92 2-94 2-96 2-101 2-112 2-114 2-117 2-121 2-123 2-125 2-127 2-131 2-133 2-133 2-137 2-139 2-139 2-143 2-144 2-145 2-146 2-146 2-148 2-148 2-149 2-150 2-150

Chapter 3 Interface Description .....................................................................

3-1

3.1 A Interface .............................................................................................. 3.1.1 Overview ........................................................................................ 3.1.2 Protocols on the A-Interface .......................................................... 3.1.3 A-Interface Management at BSS Side ........................................... 3.2 Um Interface ...........................................................................................

3-2 3-2 3-3 3-11 3-20

3.2.1 Overview ........................................................................................ 3.2.2 Layer 1 - Physical Layer ................................................................ 3.2.3 Layer 2 - Data Link Layer............................................................... 3.2.4 L3 ................................................................................................... 3.3 Abis interface.......................................................................................... 3.3.1 Overview ........................................................................................ 3.3.2 Protocols on the Abis Interface ...................................................... 3.3.3 Characteristics of Abis Interface .................................................... 3.4 Gb interface ............................................................................................ 3.4.1 Overview ........................................................................................ 3.4.2 Protocols on the Gb Interface ........................................................ 3.4.3 Characteristics of Gb Interface ...................................................... 3.5 G-Abis Interface ..................................................................................... 3.5.1 Overview ........................................................................................ 3.5.2 Interface Features .......................................................................... 3.5.3 Physical Layer/Transmission Media .............................................. 3.5.4 G-TRAU Frame Structure .............................................................. 3.5.5 G-Abis Characteristics ................................................................... 3.6 Pb Interface ............................................................................................ 3.6.1 Overview ........................................................................................ 3.6.2 Internal Structure of Pb Interface ................................................... 3.6.3 Pb Interface Management .............................................................. 3.6.4 Characteristics of Huawei Pb Interface .......................................... 3.7 Operation & Maintenance Interface ........................................................ 3.7.1 Overview ........................................................................................ 3.7.2 Feature ...........................................................................................

3-20 3-21 3-28 3-32 3-37 3-37 3-42 3-49 3-54 3-54 3-55 3-57 3-58 3-58 3-58 3-59 3-60 3-61 3-62 3-62 3-63 3-64 3-67 3-68 3-68 3-69

Appendix A Abbreviations ..............................................................................

A-1

HUAWEI 1. BSS Solution 2. BSS Function Description 3. BSS Interfaces

M900/M1800 Base Station Subsystem Feature Description V300R002

M900/M1800 Base Station Subsystem Feature Description Manual Version

T2-032111-20030701-C-6.00

Product Version

V300R002

BOM

31210011

Huawei Technologies Co., Ltd. provides customers with comprehensive technical support and service. Please feel free to contact our local office, customer care center or company headquarters.

Huawei Technologies Co., Ltd. Address: Administration Building, Huawei Technologies Co., Ltd., Bantian, Longgang District, Shenzhen, P. R. China Postal Code: 518129 Website: http://www.huawei.com Email: [email protected]

Copyright © 2003 Huawei Technologies Co., Ltd.

All Rights Reserved No part of this manual may be reproduced or transmitted in any form or by any means without prior written consent of Huawei Technologies Co., Ltd.

Trademarks

, HUAWEI, C&C08, EAST8000, HONET,

, ViewPoint, INtess, ETS, DMC,

TELLIN, InfoLink, Netkey, Quidway, SYNLOCK, Radium, M900/M1800, TELESIGHT, Quidview, Musa, Airbridge, Tellwin, Inmedia, VRP, DOPRA, iTELLIN, HUAWEI OptiX, C&C08 iNET, NETENGINE, OptiX, SoftX, iSite, U-SYS, iMUSE, OpenEye, Lansway, SmartAX are trademarks of Huawei Technologies Co., Ltd. All other trademarks mentioned in this manual are the property of their respective holders.

Notice The information in this manual is subject to change without notice. Every effort has been made in the preparation of this manual to ensure accuracy of the contents, but all statements, information, and recommendations in this manual do not constitute the warranty of any kind, express or implied.

About This Manual Version The product version that corresponds to the manual is M900/M1800 Base Station Subsystem V300R002.

Organization of the Manual The manual consists of 3 chapters that brief the solution, function, interfaces of BSS. Chapter 1 is a brief introduction of the BSS solution that contains the networking of BSS, the network element of BSS, the characteristic of BSS. Chapter 2 introduces in detail the feature of BSS, contains basic feature, extended feature, and GPRS feature. Chapter 3 introduces all interfaces of BSS.

Target Readers The manual is intended for the following readers: z

Marketing staff

z

Installation engineers & technicians

z

Operation & maintenance personnel

Conventions This document uses the following conventions:

I. General conventions Convention

Description

Arial

Normal paragraphs are in Arial.

Arial Narrow

Warnings, cautions, notes and tips are in Arial Narrow.

Terminal Display

Terminal Display is in Courier New; message input by the user

via the terminal is in boldface.

II. Command conventions Convention

Description

italic font

Command arguments for which you supply values are in italics.

[]

Elements in square brackets [ ] are optional.

{ x | y | ... }

Alternative keywords are grouped in braces and separated by vertical bars. One is selected.

III. Symbols Eye-catching symbols are also used in this document to highlight the points worthy of special attention during the operation. They are defined as follows:

Caution, Warning, Danger: Means reader be extremely careful during the operation. Note, Comment, Tip, Knowhow, Thought: Means a complementary description.

Feature Description M900/M1800 Base Station Subsystem

Table of Contents

Table of Contents Chapter 1 BSS Solution ................................................................................................................ 1-1 1.1 GSM/GPRS System .......................................................................................................... 1-1 1.1.1 GSM System ........................................................................................................... 1-1 1.1.2 GPRS System ......................................................................................................... 1-2 1.2 BSS System features......................................................................................................... 1-3 1.3 BSC.................................................................................................................................... 1-5 1.3.1 Overview ................................................................................................................. 1-5 1.3.2 Features .................................................................................................................. 1-7 1.4 PCU ................................................................................................................................... 1-9 1.4.1 Overview ................................................................................................................. 1-9 1.4.2 Features ................................................................................................................ 1-10 1.5 BTS Series....................................................................................................................... 1-10 1.5.1 BTS30 ................................................................................................................... 1-11 1.5.2 BTS312 ................................................................................................................. 1-13 1.5.3 BTS30A ................................................................................................................. 1-16 1.5.4 BTS3001C............................................................................................................. 1-18 1.6 Operation & Maintenance ................................................................................................ 1-19 1.6.1 Operation & Maintenance of BTS ......................................................................... 1-19 1.6.2 Operation & Maintenance of BTS ......................................................................... 1-21 1.6.3 Traffic statistics console ........................................................................................ 1-24 1.6.4 Dynamic Data Configuration Management ........................................................... 1-24 1.6.5 LMT ....................................................................................................................... 1-27 1.6.6 OMC ...................................................................................................................... 1-27 1.6.7 Telnet terminal....................................................................................................... 1-28 Chapter 2 BSS Functions ............................................................................................................. 2-1 2.1 Basic Functions.................................................................................................................. 2-1 2.1.1 Overview ................................................................................................................. 2-1 2.1.2 Channel ................................................................................................................... 2-2 2.1.3 System Information ................................................................................................. 2-9 2.1.4 Idle Mode Behavior ............................................................................................... 2-15 2.1.5 PLMN Selection..................................................................................................... 2-17 2.1.6 Cell Selection and Reselection ............................................................................. 2-18 2.1.7 Location updating .................................................................................................. 2-23 2.1.8 Access................................................................................................................... 2-31 2.1.9 Paging ................................................................................................................... 2-32 2.1.10 Immediate assignment ........................................................................................ 2-34 2.1.11 Assignment.......................................................................................................... 2-43

i


Table of Contents

2.1.12 Authentication...................................................................................................... 2-44 2.1.13 Ciphering ............................................................................................................. 2-47 2.1.14 DTX ..................................................................................................................... 2-51 2.1.15 Frequency hopping ............................................................................................. 2-54 2.2 Extended Functions ......................................................................................................... 2-59 2.2.1 Handover............................................................................................................... 2-59 2.2.2 Power Control........................................................................................................ 2-73 2.2.3 Extended Cell ........................................................................................................ 2-85 2.2.4 IUO ........................................................................................................................ 2-87 2.2.5 Satellite Transfer ................................................................................................... 2-92 2.2.6 Diversity Receiving................................................................................................ 2-94 2.2.7 Aggressive Frequency Reuse Pattern .................................................................. 2-96 2.2.8 Multiband Network .............................................................................................. 2-101 2.2.9 Carrier Mutual-assistance ................................................................................... 2-112 2.2.10 Cell Broadcast ................................................................................................... 2-114 2.2.11 Radio Channel Allocation.................................................................................. 2-117 2.2.12 Half Rate ........................................................................................................... 2-121 2.2.13 E1 Ring Topology.............................................................................................. 2-123 2.2.14 GSM900/GSM1800 Co-cell............................................................................... 2-125 2.2.15 Multi-MNC ......................................................................................................... 2-127 2.2.16 E-GSM/R-GSM.................................................................................................. 2-131 2.3 GPRS Function .............................................................................................................. 2-133 2.3.1 Supported Packet System Information ............................................................... 2-133 2.3.2 Supported GPRS MS Modes .............................................................................. 2-137 2.3.3 Supported RLC Modes........................................................................................ 2-139 2.3.4 Supported Channel Coding Scheme .................................................................. 2-139 2.3.5 Supported Network Control Modes ..................................................................... 2-144 2.3.6 Supported Network Operation Mode .................................................................. 2-144 2.3.7 Supported QoS.................................................................................................... 2-145 2.3.8 Supported Assignment........................................................................................ 2-146 2.3.9 Supported Paging ............................................................................................... 2-147 2.3.10 Timing Advance ................................................................................................ 2-148 2.3.11 Measurement Report ........................................................................................ 2-148 2.3.12 Supported Flow Control .................................................................................... 2-149 2.3.13 Supported Dynamic Handover between TCH and PDCH ................................ 2-150 2.3.14 Supported Packet Access Function .................................................................. 2-150 Chapter 3 Interface Description ................................................................................................... 3-1 3.1 A Interface.......................................................................................................................... 3-2 3.1.1 Overview ................................................................................................................. 3-2 3.1.2 Protocols on the A-Interface.................................................................................... 3-3 3.1.3 A-Interface Management at BSS Side .................................................................. 3-11 3.2 Um Interface .................................................................................................................... 3-20

ii


Table of Contents

3.2.1 Overview ............................................................................................................... 3-20 3.2.2 Layer 1 - Physical Layer........................................................................................ 3-21 3.2.3 Layer 2 - Data Link Layer...................................................................................... 3-28 3.2.4 L3 .......................................................................................................................... 3-32 3.3 Abis interface ................................................................................................................... 3-37 3.3.1 Overview ............................................................................................................... 3-37 3.3.2 Protocols on the Abis Interface ............................................................................. 3-42 3.3.3 Characteristics of Abis Interface ........................................................................... 3-49 3.4 Gb interface ..................................................................................................................... 3-54 3.4.1 Overview ............................................................................................................... 3-54 3.4.2 Protocols on the Gb Interface ............................................................................... 3-55 3.4.3 Characteristics of Gb Interface.............................................................................. 3-57 3.5 G-Abis Interface ............................................................................................................... 3-58 3.5.1 Overview ............................................................................................................... 3-58 3.5.2 Interface Features ................................................................................................. 3-58 3.5.3 Physical Layer/Transmission Media...................................................................... 3-59 3.5.4 G-TRAU Frame Structure ..................................................................................... 3-60 3.5.5 G-Abis Characteristics .......................................................................................... 3-61 3.6 Pb Interface...................................................................................................................... 3-62 3.6.1 Overview ............................................................................................................... 3-62 3.6.2 Internal Structure of Pb Interface .......................................................................... 3-63 3.6.3 Pb Interface Management..................................................................................... 3-64 3.6.4 Characteristics of Huawei Pb Interface................................................................. 3-67 3.7 Operation & Maintenance Interface ................................................................................. 3-68 3.7.1 Overview ............................................................................................................... 3-68 3.7.2 Feature .................................................................................................................. 3-69 Appendix A Abbreviations ...........................................................................................................A-1

iii


Chapter 1

BSS Solution

Chapter 1 BSS Solution 1.1 GSM/GPRS System Huawei's GSM/GPRS mobile communication series cover all products in the network (except for MS). The comprehensive mobile communication solution includes the network construction at service layer, transport layer and supporting layer, etc. Huawei provides the best sustainable network solution and integrated system solution adaptable to different wireless environment according to the size, capacity, coverage and investment scope of the mobile network, satisfying the carriers' different requirements on products and services. GSM/GPRS network is illustrated in Figure 1-1.

GSM/GPRS BSS

Um

GSM NSS

R/S MSC

BTS BSC LMT

PCU LMT

GPRS NSS SGSN

LAN/WAN

R

OMC Server OMC W S OMC WS GSM/GPRS OMC

Telnet Terminal

GSM/GPRS OMS

Figure 1-1 Huawei GSM/GPRS network

1.1.1 GSM System M900/M1800 GSM serial products include the Mobile Switching System (MSC/VLR and HLR/AUC/EIR), mobile Base Station System (BSC and BTS), operation and maintenance center (OMC), GMSC, TMSC and SMC. VLR is integrated in MSC as a built-in device. HLR is the equipment with functions of AUC and EIR integrated. OMC

1-1


Chapter 1

BSS Solution

implements centralized management and unified maintenance for the entire network via LAN or WAN. Besides Huawei also provides Short Message Center (SMC). The SMC introduced here is integrated with Voice Mailbox (VM). M900/M1800 GSM system is in complete conformity with ETSI GSM standard, supporting the service and function defined in Phase 1, Phase 2 and Phase 2+. It includes indoor/outdoor macro BTS and integrated mini BTS. It also supports different antenna feeder systems such as dual band and dual polarization antenna and spaced antenna.All equipment support the two bands of GSM900/1800 M900/M1800 GSM provides services including: z

Voice, G3 fax, data service and various supplementary services to satisfy the basic needs of mobile subscribers.

z

CAMEL Phase 2 mobile intelligent service combines the technologies of GSM and intelligent network, upgrading the mobile communication network with advanced technologies.

z

General Packet Radio Service (GPRS) provides high-speed packet data service for the user. It is an important step for the smooth upgrading from GSM to 3G, which to the best extent protects the investment.

z

Other new services, such as Completion of Calls to Busy Subscribers (CCBS), Explicit Call Transfer (ECT), Support Optimized Route (SOR), Call Deflection (CD) and Unstructured Supplementary Service Data, make up the new profit maker for the carriers.

1.1.2 GPRS System Huawei GPRS is realized by adding GPRS Supporting Node and Packet Control Unit as well as the corresponding software to the GSM network.The major NEs include Service GPRS Supporting Node (SGSN), Gateway GPRS Supporting Node (GGSN), GSN Operation and Maintenance Center (OMC-G), border gateway, charging gateway, PCU, BSC, BTS, DNS and fire wall, etc. The theoretical maximum access speed of GPRS is 171.2 kbit/s, which is desirable for the high-speed mobile data service access. Its open system structure supports smooth capacity expansion. The standardized interface guarantees the equipment capacity, and supports QoS feature and the dynamic allocation of radio resources. In addition, the flexible networking and configuration function can save a great amount of initial investment of GPRS system for the carriers. M900/M1800 GPRS is able to provide various packet services such as mobile internet access, e-business (e.g. e-bank, e-currency, etc.), group management, remote control/test, service reservation system (e.g. hotel, theater, flight, etc.) and services base on group-call (e.g. stock information broadcasting), etc.

1-2


Chapter 1

BSS Solution

The high-speed mobile packet data service of GPRS effectively prolongs the life cycle of GSM improves the utilization of radio resources and paves the way for the emergence of 3G mobile communication. Huawei GPRS supports the smooth upgrading to 3G system, which is important in protecting the investment of the carriers.

1.2 BSS System features BSS is designed mainly to connect the Mobile Station (MS) to the Mobile Switching Center (MSC) of the GSM network or the Serving GPRS Support Node (SGSN). BSS also shares part of mobility management such as handover management. BSS is the subsystem in GSM/GPRS related to the concepts of radio cells. BSS communicates with MS through Um interface and handles radio link management and connection through it. On the other side BSS communicates with MSC and SGSN through A- and Gb interfaces respectively. Figure 1-2 illustrates Huawei BSS solution. BSS includes BSC, PCU, serial BTSs and O&M system.

SDH

BSC MS

MSC

MS

PCU SGSN

BSS

MS Integrated mini BTS

Indoor BTS

Outdoor BTS

Figure 1-2 Huawei BSS solution Supporting M900 BTS and M1800 BTS as well as M900/M1800 integrated BTS and dual-band MS access.

1-3


Chapter 1

BSS Solution

Currently, Huawei GSM supports not only PDH, SDH, HDSL, microwave transmission, but also satellite transmission, providing a comprehensive and completely compatible solution. Huawei M900/M1800 BSS provides complete GSM/GPRS solution with following salient features.

I. Serial BTSs which support seamless coverage z

A complete range of BSS products offers flexible networking and easy installation with seamless coverage supported. As regards capacity, the selection ranges from the integrated small BTS supporting one TRX, to macro cell supporting 12 TRXs. As regards usage environment, there is the indoor macro cell BTS, outdoor macro cell BTS, integrated small BTS and the mobilized BTS applicable to movable site.

z

Huawei BSS employs the layered cellular architecture to boost the coverage and service quality of the system.

z

Supporting 900MHz, 1800MHz and mixed 900MHz/1800MHz GSM frequency bands.

II. Flexible networking z

There are multiple transmission modes supported between BTS and BSC: E1, SDH, PON, HDSL, microwave and satellite, etc.

z

There are multiple transmission networking modes between BTS and BSC: star networking, chain networking, tree networking and hybrid networking.

z

The tree networking between PCU and BSC is supported.

z

The SMUX interface provides 4:1 link multiplexing (one 64kbit/s TS transmits 4 information channels) and the Abis interface provides a variety of multiplexing modes like 10:1, 12:1 and 15:1 (TRX: E1) and increases the transmission link utilization.

III. Multiple services supported z

A variety of services is provided: point-to-point short message service, cell broadcast short message service, data services and fax services of various kinds in addition to common voice services. Except for the voice services, these services can be both based on circuit switching and on packet switching (GPRS).

z

Easy upgrading from GSM to GPRS network. To deliver GPRS services based on the M900/M1800 BSS, simply update the software of the original BTS and BSC and then add PCU.

1-4


Chapter 1

BSS Solution

IV. Powerful and easy maintenance function: z

The operation & maintenance of the BSS is performed through centralized OMC system and a consistent operation & maintenance interface, which makes operation and maintenance easier and simpler.

z

Development-oriented architecture is adopted. All entities support downloading software, which simplifies the upgrading.

z

The OMC provides friendly user interface for easier operation.

z

The system supports dynamic data configuration, online data modification and online capacity expansion.

V. Stable and reliable performance z

Huawei BSS reduces the power consumption by supporting uplink power control, DRX (paging discontinuous reception) technology and VAD/DTX (voice activity detection/discontinuous transmission) technology.

z

High reliability: key components (e.g. main processor, switching network and BS interface equipment) operate in 1+1 hot backup and common parts runs with N+1 protection.

z

Self-check and switchover features enhances the system performance.

z

High availability of the system is ensured by using the excellent overload / congestion control algorithm and fault recovery strategy.

z

The leading-edge handover, power control and channel allocation algorithms make the system performance outstanding.

z

BCCH carrier frequency mutual-assistance, baseband frequency hopping & carrier frequency mutual-assistance and LAPD link mutual-assistance empower the system with a fault-prevention capability.

z

Supporting 120 km extended cell.

1.3 BSC 1.3.1 Overview With the use of switching, photoelectric, micro-electronic, computer and radio technologies, Huawei M900/M1800 BSC drives the mobile communication network to evolve towards digitalization, integration, intelligence and personalization. Based on an open network platform, it integrates an array of cutting-edge technologies in switching, transmission and radio management, and supports all the services delivered by GSM900 and GSM1800. M900/M1800 BSC mainly performs radio resources management, BTS management, power control, handover control, traffic statistics, etc. It plays a pivotal role in radio access and network optimization.

1-5


Chapter 1

BSS Solution

The M900/M1800 BSC, whose system structure is shown in Figure 1-3, is comprised of the following five modules:

I. Administration Module/ Communication Module AM/CM is a centre for speech channel switching and information exchange in the BSC. It implements the communication between various BMs.

II. Basic Module This module is mainly responsible for call processing, signaling processing, radio resources management, radio link management, and circuit maintenance, etc.

III. TransCoder & Sub-Multiplexer TCSM implements the transcending / rate adaptation and sub-multiplexing functions.

IV. Cell Broadcast Database (CDB) CDB is a traffic-processing centre, supports the broadcast short message service.

V. Back Administration Module (BAM) The BAM frame is a bridge between BSC and OMC. The latter performs the operation & maintenance of the BSC via OMC.

1-6


Chapter 1

AM/CM

BM BTS

Abisinterface

BSS Solution

BIE

GOPT

GFBI

GMEM GMC2

CDB GNET BIE

GNOD GLAP /LPN7

TCSM

GMPU

GALM

Ater-interface E3M

PCU Pb-interface BITS

OMC-R

ext.CBC

OMC interface (LAN/WAN)

ext.CBC interface (LAN/WAN/X.25)

GCTN GCKS

GSNT

BAM

GMEM CDB ... GMEM GMCCM GMCCS GMEM

GALM

Figure 1-3 BSC structure To communicate with BTS, MSC and PCU in the GSM/GPRS system, M900/M1800 BSC offers three external interfaces: A-interface, Abis interface and Pb interface. A-interface is a standard open interface. Pb and Abis interfaces are self developed interfaces. Complying respectively with ETSI GSM 08.08, ETSI GSM 04.08 & ETSI GSM 08.58, Huawei Pb interface protocol, and compatible with the specifications of GSM Phase 1 and GSM Phase 2, the three interfaces provide GSM Phase 2 + functions like GPRS.

1.3.2 Features The performance and features of the M900/M1800 BSC are: z

Standard A-interface ensures the interconnection and interworking with the equipment of other manufacturers.

z

M900/M1800 BSC can be expanded smoothly from 1 BM to 8 BMs.

z

Each BM can provide 8 A-sub interfaces or Pb interfaces, 64 Abis interfaces, 8 SS7 signaling ports and 192 LAPD ports at the most.

1-7

Feature Description M900/M1800 Base Station Subsystem z

Chapter 1

BSS Solution

One BM can control 128 TRXs (transceiver) at the most, the switching matrix is 4K × 4K.

z

At most 1024 Cell or 1024 TRX can be managed.

z

SMUX (sub-multiplexer) enables the multiplexing of terrestrial lines between MSC and BSC, and saves the investments on terrestrial lines. Each SMUX enables the 4:1 line multiplexing.

z

Base station Interface Equipment (BIE) enables the 15:1 line multiplexing. Supporting star, chain and tree networking topologies of BTS.

z

Transmission on the Abis interface can be implemented through terrestrial, satellite, microwave or optical fiber.

z

Supporting a maximum traffic of 6400Erl

z

Max. BHCA: 800K

z

Strong system processing capability. In full configuration and normal traffic model, GMPU load <25%. The processing capacity for future services is reserved. Powerful processing capability and support of high traffic load.

z

High reliability GMPUs in hot backup mode. The switching network and BIE use the 1+1 backup mode. SMUX uses the N+1 backup mode, where N is the total number of SMUX cards in the system. LAPD uses the N+1 backup mode.

z

Traffic adjustment: Optimized channel allocation mode enables the adaptive adjustment of the network according to the changes of cell traffic loads and radio environment.

z

Priority queuing function: The queuing of multiple priority levels for paging and channel allocation satisfies the requirements of different subscribers.

z

Handover function supports synchronous, asynchronous and dual-band handovers.

z

Multi-level traffic control mechanisms are provided on A- and Abis interfaces.

z

Resource verification and TRX cooperation mechanism: auto-fault clearing and auto-protection, which is intended for system normal operation.

z

Centralized OMC: Centralized network management is responsible for real-time management and control of the BSC & BTS, and provides detail interface tracing, radio resources configuration, and traffic statistics.

z

Supporting GSM900 BTS and GSM1800 BTS as well as M900/M1800 integrated BTS and dual-band MS access.

z

Synchronization mode uses active/standby synchronization mode.

z

Reasonable and flexible allocation of functions among modules based on a multi-level distributed and group-CPU control.

1-8


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BSS Solution

High integration, superb engineering and high reliability using state-of-the-art large scale integrated circuits (ASIC/EPLD/FPGA).

z

Low power consumption, only 3300W are required for maximum configuration.

z

Light & compact architecture, i.e. less room space is occupied.

z

The system supports dynamic data configuration, online data modification and system expansion.

z

BCCH radio carrier mutual assistance, baseband FH radio carrier mutual assistance and LAPD link mutual assistance ensure reliable system running.

z

Supporting GPRS packet services.

1.4 PCU 1.4.1 Overview Packet Control Unit (PCU) is a device introduced by BSS to support the GPRS. M900/M1800 PCU is fully designed according to GPRS standard protocols. It is responsible for z

Packet radio resource management functions.

z

Packet call control function.

z

Transmission of data packet on Um interface and Gb interface.

z

Providing Gb, G-Abis and Pb interfaces.

Based on a modular structure, M900/M1800 PCU is made up of several superimposed PCU frames. The hardware structure of PCU is quite simple, as shown in Figure 1-4. It consists of three modules: z

POMU (Packet O&M Unit) module, responsible for the operation & maintenance of the whole PCU frame.

z

RPPU (Radio Packet Processing Unit) module, which delivers all the traffic handling functions of PCU and supports operation & maintenance.

z

HSC (Hot Swappable Control) module, a pure hardware module used for the hot backup function.

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1+1

BSC

RPPU

RPPU

SGSN

BSC

RPPU

RPPU RPPU

SGSN

. . .

. . .

RPPU

RPPU

BSC

POMU

HSC

LAN Switch

WS

SGSN

OMC Server

PCU

Figure 1-4 PCU hardware architecture

1.4.2 Features M900/M1800 PCU owns the following performance and features: z

Modularized structure and smooth expansion of the network.

z

Large capacity and strong processing capability.

z

Preprocessing of measurement.

z

Uplink power control.

z

Excellent G-Abis interface solution, supports Um port synchronization. Support of CS-3 and CS-4 upgrading.

z

CS (Coding Scheme) dynamic adjustment algorithm.

z

Dynamic conversion of PDCH (Packet Data Channel).

z

Flexible networking modes.

1.5 BTS Series The BTS is the radio equipment serving one cell, which will be distributed over the whole radio service area. Based on customer’s current and future requirements, Huawei has developed a series of BTS products including indoor and outdoor products so that network deployment and coverage become very easy.

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Huawei BTS series include BTS30, BTS312, BTS30A and BTS3001C, etc. Among them, BTS30 and BTS312 are the indoor BTS, while BTS30A is the outdoor BTS, and BTS3001C is the integrated small BTS.

1.5.1 BTS30 BTS30 adopts modular structure, i.e. all circuits (including baseband processing part, RF part, power amplifier and power supply) that take care of one carrier are integrated in one plug-in TRX module. This greatly simplifies system configuration and facilitates installation, maintenance and expansion, as well as introduction of new hardware. BTS30 cabinet is a 19-inch standard cabinet based on IEC297 standards, with dimensions 1600 mm % 600 mm % 450 mm (H % W % D).

I. Features and functions BTS30 is capable of the following features and functions.

1)

Performance characteristics.

z

Supporting GSM900 and GSM1800 TRXs in the same cabinet.

z

The maximum output power of 900MHz and 1900MHz amplifiers is 40W.

z

Build-in transmission equipment (supporting E1, SDH, PON, etc.) saves carriers’ investment in transmission equipment.

z

Supporting various networking modes, including star, tree, chain and mixed topologies.

z

One cabinet provides up to 8 E1 interfaces.

z

15 TRXs share one E1 for transmission on the Abis interface (15:1)

z

Supporting large capacity flexible configurations: Omni cell: 1~18 TRXs, 2-sectors: 1/1~18/18 TRXs, 3-sectors: 1/1/1~18/18/18 TRXs.

z

Low power consumption (max. power consumption of a cabinet is 1200W) and light weight (a cabinet in full configuration weighs about 180kg).

z

Build-in power

supply system, 220VAC/-48VDC/24VDC

power

supplies

available. z

Centralized power supply to cabinets, and distributed supply to various modules, which enhances system reliability.

z

Modular structure, which facilitates installation, maintenance and capacity expansion.

2)

Functions

z

Supporting both 900MHz and 1800MHz dual-band systems

z

Supporting Phase 1 / Phase 2 / Phase 2+ compatible LAPDm protocol.

z

Supporting Phase 1 / Phase 2 / Phase 2+ compatible system messages and resources indication.

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Providing basic service functions required by the system, including location update, MTC and MOC.

z

Supporting synchronous, asynchronous and pre-synchronous handovers.

z

Supporting short message cell broadcast and point-to-point short message broadcast.

z

Calculation of timing advance.

z

Supporting diversity receiving and soft decision demodulation functions.

z

Supporting paging queuing.

z

Supporting data services specified in Phase 2.

z

Supporting detection of random access collision.

z

Supporting baseband hopping and RF hopping.

z

Supporting A5 encryption/decryption.

z

Supporting GPRS: routing area/location area update, uplink/down link TBF.

z

Supporting the CS-1/CS-2/CS-3/CS-4 radio channel coding schemes.

z

Supporting dynamic configuration of basic data.

z

Supporting dynamic resources management.

z

Supporting preprocessing of measurement report.

z

Supporting immediate assignment and paging combination to increase the radio channels utilization.

z

Supporting static and dynamic power control of the base station.

z

Supporting omni and sector cells.

z

Supporting cell layering, concentric cell and microcell applications.

z

Internal bus technique facilitates future expansion.

z

Providing both power supply and battery management functions.

z

Supporting locked, holdover, fast pull-in, and free-run clock modes.

z

BTS room environment monitoring function achieves unattended operation.

z

Use of triplex tower-top amplifier improves the receiving sensitivity.

z

Supporting bipolarization antennas, reducing antennas in a cell.

z

RF indices conform to GSM 05.05 specifications.

z

Supporting 120km extended cell.

II. Technical indices z

Dimension H % W % D = 1600 mm % 600 mm % 450 mm

z

Power supply 220V AC: 150~280 V AC / 45~65Hz, -48V DC: -40~-60VDC, 24 V DC: 19~29 V DC,

z

Operational temperature (normal): -5ÿC~+45ÿC

z

Operational humidity: 5%~85%

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Weight (fully configured): 180kg

z

Bearing requirement: 250kg/m

z

Power consumption / cabinet Max load: 1200W

z

Receiving sensitivity:

BSS Solution

2

-110 dBm (GSM900), -109 dBm (GSM1800) z

Tx Power: 40W (46 dBm)

1.5.2 BTS312 I. Performance characteristics. The BTS312 is an indoor macro BTS, featured by large capacity, high integration, and low power consumption. Single rack can support up to 12 TRXs (radio carriers). It is designed as a typical all-in-one BTS by taking full consideration of capacity, configuration, installation, power supply, transmission, and services requirements. BTS312 features:

1)

Mature technology and reliable RF performance

z

Large-scale application of Huawei radio base station equipment spawns on the maturity and stability of the RF technology.

z

Supporting both RF hopping and base band hopping with excellent performance in application.

z

Advanced digital RF technology improves the consistency, massive productivity, and reliability of the product.

2)

Large capacity & low power consumption BTS312 supports 24/24/24 configuration. A single rack supports up to 12 TRXs, consuming 2400W in total, on average each TRX consumes only 200W.

z

50% floor space needed comparing the regular 6-TRX BTS, thus greatly saving the equipment room space.

z

With a low power consumption design, the requirements for power supply and air conditioners are reduced.

z

The integrated transmission equipment supports multiple transmission modes, saving the investment on transmission equipment.

3)

The 15 TRXs on Abis interface share one E1 interface for transmission (15:1) For example The BTS whose configuration is S(5/5/5) occupies only one E1 at the Abis interface. This saves tremendously the transmission leasing expenses. The use of advanced flow control algorithm can accomplish the statistical multiplexing of the Abis signaling, as a result, it effectively improves the signaling density. This technique saves up to 50% transmission links compared to the normal 10:1 or 12:1 multiplexing.

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The E-Abis provides powerful anti-error code performance, synchronization performance and anti-delay capability. It supports satellite, SDH, E1/T1 and microwave transmission modes.

E-Abis technology includes the following aspects: z

The high precision and unique software phase lock technology can solve problems such as SDH clock phase jitter and satellite transmission clock signals out-of-sync.

z

-4

It tolerates a transmission BER of up to 10 , much higher than the conventional BER requirements, so it is suitable for the unstable transmission modes like microwave, xDSL and satellite.

z

It allows transmission flash interruption, that is, it can tolerate transmission interruption of less than 2s, which makes it suitable for unstable transmission.

z

Protection against long transmission delay on the Abis.

5)

Integrated optical transmission equipment Huawei is the first one in the telecom industry to integrate the SDH, PON equipment to provide "FTTB (Fiber To The Base station)", accomplishing the broadband wireless access at one swoop.

6)

Integrated RF components This technique protects the existing investment and ensures 100% usage of the old equipment during capacity expansion. The existing antenna system including the CDU, SCU, antenna, feeder and tower-top amplifier (optional) need not be replaced during expansion. In the expansion from S(1/1/1) to S(8/8/8) of broadband combining, each sector needs only one bipolarization antenna.

z

Modular structure: RF components are integrated in the CDU, which reduces the line connections and improves system reliability. Installation and maintenance also becomes easy.

z

Powerful maintenance functions: including the 2-level standing wave ratio alarm, low-noise amplifier divider alarm, tower-top amplifier alarm, tower-top amplifier power supply alarm, etc.

z

Intelligent CDU: in case of fault with the LNA (Low Noise Amplifier), this unit is powered off remotely so as to make a LNA bypass and ensure the normal working of the system. When the antenna incurs different losses, the gain of the divider unit can be adjusted remotely so as to ensure the sensitivity of the receiving system.

7)

Reliable power supply system BTS 312 supports three kinds of input voltages (+24DC, -48DC and 220V AC). Hot standby, centralized management and distributed power supply improve the system’s security and reliability.

8)

Supporting S (24/24/24) synchronous BTS configuration, completely meeting the requirement of future development 1-14


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A cell can hold 24 synchronous TRXs, and the maximum networking capability is S (24/24/24) (synchronous site). Synchronous inter-cell handover can be achieved even in the case of S (10/10/10) configuration or higher, thus shortening the handover time consumption, shortening the call-drop rate and improving the operation index of the entire network.

9)

Quick 1-minute startup and easy maintenance.

z

In case of any fault or failure, system can reload itself automatically without any delay.

z

After power failure BTS can automatically resume working quickly when power supply returns normal.

z

All software has been pre-installed before shipment from the factory, so there is no need to load it again from BSC. This facilitates BTS testing and cutover.

z

Software loading does not interrupt services.

10) Supporting GPRS II. Functions z


z

Supporting Phase 1/Phase 2 compatible LAPDm protocol.

z

Supporting Phase 1/Phase 2 compatible system messages and resources indication.

z


z

Supporting

synchronous,

asynchronous,

pseudo-synchronous

and

pre-synchronous handovers. z


z


z


z


z


z


z


z

Supporting EFR voice coding scheme, which ensures a better voice quality.

z

Supporting DTX which minimizes interference.

z


z

Supporting basic services and functions of GPRS, routing area or location area update, and uplink/downlink TBF.

z

Supporting the CS-1/CS-2/CS-3/CS-4 radio channel coding schemes.

z


z


z


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z


z


z

Internal bus technique facilitates expansion.

z


z

Supporting locked holdover, fast pull-in, and free-run clock modes.

z

BTS room environment monitoring function achieves unattended operation.

z


z


z


III. Technical indices z

Dimension H % W % D = 1880 mm % 650 mm % 500 mm

z

Power supply 220V AC: 150~280VAC/45~65Hz; -48V DC: -40~-60VDC; 24V DC: 19~29VDC.

z

Operational temperature (normal): -5ÿC~+45ÿC

z

Operational humidity: 15%~85%

z

Weight: Single cabinet full configuration 330kg Bearing requirement: 400kg/m

2

z

Power consumption / cabinet Max load: 2400W

z

Receiving sensitivity: -110dBm (GSM900), -109dBm (GSM1800)

z

Tx Power: 40W (46dBm)

1.5.3 BTS30A I. System overview BTS30A is an outdoor BTS of Huawei GSM product series. As outdoor equipment, it is characterized by excellent protection against wind, sands, rain, sunshine and burglary. It has minimum requirements for environment. The outdoor/indoor BTS and integrated small BTS make up the comprehensive solution for the construction of seamless wireless coverage.

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II. Performance characteristics. z

Supporting GSM900 and GSM1800 modules in the same cabinet.

z

The maximum output power of 900MHz and 1900MHz amplifiers is 40W.

z

Build-in transmission equipment (supporting E1, SDH, PON, etc.) saves network operators’ investment in transmission equipment.

z

Supporting various networking modes, including star, tree, chain and mixed topologies.

z

One cabinet provides up to 8 E1 interfaces. 15 TRXs share one E1 for transmission on the Abis interface (15:1)

z

Embedded power supply system, 220VAC applied.

z

Centralized power supply to cabinets, and distributed supply to various modules, which enhances system reliability.

z

Perfect

environment

monitoring

system

enables

remote

operation

&

maintenance. z

Powerful temperature regulation increases the system’s adaptability to environment.

z

Modular structure, which facilitates installation, maintenance and capacity expansion.

III. Functions z


z

Supporting Phase 1 / Phase 2 / Phase 2+ compatible LAPDm protocol.

z

Supporting Phase 1/Phase 2/ Phase 2+ compatible system messages and resources indication.

z


z

Supporting

synchronous,

asynchronous,

pseudo-synchronous

and

pre-synchronous handovers. z


z


z


z


z


z


z


z


z

Supporting GPRS.

z


z


z


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z


z


z

Supporting cell layering, concentric cell and microcell applications.

z

Internal bus technique facilitates future expansion.

z


z

Supporting locked holdover, fast pull-in, and free-run clock modes.

z

Unattended operation. Provides BTS room environment monitoring function.

z


z


z


z

Conforming to IP55 outdoor equipment protection standard.

IV. Technical indices z

Dimension -H % W % D = 1800 mm % 1200 mm % 800 mm -Internal available space = 1075 mm % 1001 mm % 725 mm

z

Power supply -220V AC: 150~280 V AC / 45~65 Hz,

z

Operational temperature: -33 ÿC~+55 ÿC (Environmental requirement),

z

Operational humidity: 5%~100%,

z

Weight (fully configured): 550 kg,

z

Power consumption / cabinet: max. 3200W,

z

Receiving sensitivity: -110 dBm (GSM900), -109 dBm (GSM1800)

z

Tx Power: 40 W (46dBm)

1.5.4 BTS3001C I. Overview iSite BTS3001C is highly adaptable to complicated climate and electro-magnetic environment. It features flexible addressing and easy installation. It is mainly used to improve the network capacity and to eliminate the blind spot of the macro cell coverage, thus realizing the continuity of the coverage and lower the cost on coverage. In places where the macrocells cannot cover, the microcell base stations can be installed to improve the network coverage and quality of service.

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II. Features BTS3001C features: z

Star networking and chain networking supported. In chain networking, the maximum serial connection levels are 5 levels,

z

Wide working temperature (-33ÿC ~+55ÿC). In high temperature environment, the cooling fins on the inner container will radiate the heat. In low temperature environment, internal heating device will be started to ensure a suitable working temperature.

z

All parts are fixed and little noise will be generated.

z

BTS22C can be installed on the walls, pillars or towers.

z

Flexible antenna configuration. Internal directional antenna and external omni / directional antennas are supported.

z

Supporting GPRS.

z

Closed structure in full compliance with IP55 outdoor equipment protection standard. All operations cannot be done until the locked operation cavity is opened. The operation cavity at the lower part of the integrated small BTS provides the maintenance interface and the indicators showing the working condition of the inner container.

z

The input voltage range is 150~300 V AC, which makes adaptable to the areas with highly fluctuating voltage.

1.6 Operation & Maintenance 1.6.1 Operation & Maintenance of BTS The BTS maintenance module of BSC provides rich BTS maintenance functions. Through these operations, subscribers can guarantee the highly efficient, stable and reliable operations of BTSs. The operation costs will be reduced and communication service quality will be improved.

I. BTS software loading management Normally a BSC controls multiple BTSs, which are distributed widely with no personnel on their duty. Some of them are even located at the areas with poor transportation, such as the mountaintop. There it is very complicated to replace the BTS board software at the location. As a solution to this problem, BSC supports the function of remote loading BTS software. It is possible to load all software at OMC. Multiple software can be loaded at one time, thus realizing the convenient upgrading of the BTS software.

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II. BTS data configuration management The BTS will be initialized once the data configuration is finished to ensure the normal operation of the BTS. The functions of online configuration and modification are supported. During normal running, operation parameters are issued by BSC to BTS. The BTS maintenance module in BSC enables the BTS data configuration process and configures such information as BTS parameters cell parameters, frequency parameter, channel parameters alarm threshold and BTS software & hardware configurations. In addition, BSC needs to configure the BTS network structure data to ensure the BTS functioning in different network topologies.

III. BTS equipment operation management The BTS management module of M900/M1800 BSC helps the subscribers to check the status of BTS equipment and objects. It also provides necessary maintenance measures. BTS maintenance is object-oriented. These objects include BTS, cells, BT (Baseband Transceiver), RC (TRX), channels, and boards.

IV. BTS test management To enable the long-term, continuous and stable operation of the system, the use of testing and diagnosis functions are necessary for the maintenance of the whole system. M900/M1800 BSC provides powerful test and diagnosis function for BTS maintenance. BTS maintenance module of BSC provides powerful test and diagnosis function. During normal running, BTS boards execute self-check instantly, and generate the alarms automatically or perform switchover in case of serious fault or abnormality. On the other hand, test tasks can be initiated from the BTS maintenance console.

V. BTS alarm management BTS alarm management of M900/M1800 BSC is another function of BTS maintenance management. If any abnormality or fault occurs during BTS running, BTS boards will instantly report and inform the fault-handling program to handle it. At the same time, various alarm messages and signals will be generated in the alarm system. Whenever the alarm is generated, the alarm processing module shall send the fault message reported from BTS to the maintenance and operation terminal. The alarm will also be sent to the alarm box through the alarm box interface board. Alarm box generates the sound and light indications to inform the maintenance personnel about the alarm. The alarm sent to the maintenance and operation terminal will be displayed on the terminal and also stored in the hard disk to be queried.

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VI. TRX mutual-assistance management 1)

In case of BCCH fault in a cell, another TRX in the cell can be started to provide service in place of the TRX where the original BCCH is located. Meanwhile, the TRX can be restored by clearing the fault. If the original TRX can not be restored, service provisioning will be interrupted. If the original TRX can not be restored, it will quit service provisioning.

2)

In case of fault with a certain baseband hopping TRX during the normal running process in a cell, this BTS will report the fault. The baseband frequency hopping TRX fault processing function will delete the faulty baseband frequency hopping TRX from the corresponding frequency hopping group so that the other frequency hopping boards can work normally. After the faulty TRX has been recovered, frequency hopping will no longer be available.

VII. Support of GPRS service 1)

BSS supports the dynamic conversion between PDCH and TCH. During the conversion, the property of the related channel will be issued from BSC to BTS. The dynamic conversion can be activated by BSC, and the conversion threshold can be set.

2)

The channel connection will be reestablished when the packet channel encoding mode is changed.

3)

Message transference between PDCH and TCH.

VIII. Other management processing Other management processes mainly include circuit/channel blocking, active/standby switchover of GMPU boards, alarm filtering, transfer of idle burst, BTS log report, and resource check.

IX. BTS Emergency Operations In the case of power failure, BTS will use the spare storage battery for power supply to maintain the normal operation of the BTS. If the BTS is over heated, BSC will automatically stop the power amplifying unit to avoid damaging BTS.

1.6.2 Operation & Maintenance of BTS The operation and maintenance system of M900/M1800 BSC is mainly used to receive the OMC maintenance commands and perform routine maintenance, control start, tracing & monitoring, overload management and memory operations. It is also used to return the operation results to OMC.

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I. Routine maintenance The routine maintenance involves software version checking and module status viewing so as to ensure normal and smooth system running.

II. Control startup The control startup function involves circuit control, LAPD link maintenance, immediate active/standby switchover, hierarchical resetting, board inquiry control, HDLC link status, BSC system reset, resources check and GLAP software loading.

III. Tracing & monitoring The maintenance management part of the BSC system features powerful tracing & monitoring functions, including interface tracing and system performance monitoring.

IV. Memory operations. The operations in the maintenance management of the BSC system on the memory include memory inquiry and memory dumping.

V. Overload management 1)

Conventional concept

When the traffic are more than BSS can handle, then the system is called in Overload State. To avoid such occurrence, overload control mechanism is introduced so that the system can detect overload timely and take effective measures. The BSS traffic comes from MS and MSC. Mobility management, call control, radio frequency management and measurement data processing are the primary traffic at the MS side. The traffic from the MSC includes call handling, handover request, resources request/indication and the allocation function. The overload control mechanism

includes traffic detection and preventive

mechanisms. The traffic is monitored in BTS, MSC and BSC. When overload is detected, the overload message will be sent to the BSC, which will take preventive measures automatically to reduce the calls. Once the overload is released, the measures will gradually be cancelled.

2)

BSC processor overloaded

The CPU of the BSC has a limited processing capability. When the traffic of the CPU crosses a certain level, the CPU may halt and system may be down if no measures are taken to reduce the traffic. The congestion and overload threshold can be set through the OMC terminal. When the CPU occupation ratio exceeds the CPU overload start threshold, the system is congested and it will generate alarms. When the CPU occupation ratio is lower than the CPU overload threshold, the system is 1-22


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recovered to the normal state and generates recovery reports. The start and end values of the congestion are higher than the overload start and end values. The default values of CPU congestion and overload threshold in M900/M1800 BSC are CPU overload start value 90%. CPU overload end value 70%. CPU congestion start value 95%. CPU congestion end value 80%.

3)

Radio interface overload

The basic strategy to control radio interface overload is to cut down the traffic on the CCH until overload is released. -AGCH overloaded AGCH is a unidirectional downlink channel shared by all the mobiles in the cell. This channel is used to setup the MS calls. If overload occurs on the AGCH, new calls can not be accepted and MS will probably access, the adjacent cells and this will consequently cause deterioration to the system. After acknowledging the overload status, BSC will start the following preventive measures: z

All the affected paging messages of BTS will be discarded.

z

Notifying to the MSC about the overload messages and points out the cause: CCCH overload and cell flag.

z

Phased reduction of service access.

-PCH overloaded The Paging Channel (PCH) sends the messages to MS in downlink direction. BTS monitors the load status of PCH. When the threshold is overstepped, BTS will notify BSC, and BSC starts the following protection measures: z

The paging message to the overload cells will be discarded.

z

Notifying to the MSC about the overload messages and points out the cause: CCCH overload and cell flag.

-RACH overloaded The Random Access Channel (RACH) is an uplink channel, designed to request dedicated channels for MS. BTS monitors the load status of RACH. When the threshold is overstepped, BTS will notify BSC of the overload message. Since the RACH capacity is no bottleneck, no measures need to be taken.

4)

MSC overloaded

MSC might also undergo overload. In this case, it sends the overload message to BSC, the reason being “CPU overload”. BSC will prohibit access by subscribers depending on the actual situation and MSC will also reduce paging and external handover (between MSCs).

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1.6.3 Traffic statistics console Traffic statistics is an important function of BSS, which measures and monitors the whole system and helps to improve and stabilize the network. The traffic statistics module receives the performance measurement tasks from the OMC traffic statistics console and dispatches them in a unified way. It informs corresponding module to start/stop measurement and collects the measurement results to send to the OMC traffic statistics console. The traffic statistics module routinely monitors the key resources of the system including CPU, message queue, Abis interface receive/transmit queue, and CCB list. It regularly monitors the traffic levels of cells and system flow levels to provide appropriate controls over other application modules. In addition, it monitors the radio network quality, radio resource, connection, and handover quality.

1.6.4 Dynamic Data Configuration Management Dynamic data configuration is also called online data configuration, that is, modifications of system configuration data and system attribute data can be done without resetting the BSC. This is very important for smooth expansion of the system capacity and network planning & optimization. If a BSC is in operation and a user wants to modify its data, reset of BSC means interruption of BSC and its BTS services. Dynamic data configuration facilitates the implementation of data modification and minimizes the impact on the current service.

I. Operation method OMC data management console provides a dynamic data configuration mode. This mode adopts wizard interface which realizes step by step dynamic data modification. The system handles data validity, consistency, integrity, and tolerance check automatically, which simplifies the process of dynamic data configuration and greatly improves the efficiency and security of dynamic data configuration.

II. Functions 1)

Sites addition/removal: This function can add (or delete) the sites in various networking modes, and even the cells, TRXs, and BTS boards. This function does not affect other working sites and the circuit-based and packet-based services that have been set up.

2)

Cells addition/removal: This function can add (or delete) the GSM900 and GSM1800 cells, and even the TRXs and BTS boards. This function does not affect other working cells or the circuit-based and packet-based services that have been set up.

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TRXs addition/removal: This function can add (or delete) the GSM900 and GSM1800 TRXs, and corresponding BTS boards. This function does not affect other working TRXs or the circuit-based or packet-based services that have been set up. It adds anti-collision mechanism to the fault handling function for BCCH mutual-assistance and baseband hopping TRX to ensure that there is no negative impact even if the TRXs are switched over.

4)

BTS boards addition/removal: This function can add (or delete) most boards at the BTS side.

5)

Modification of cell system information: It is possible to modify the system message to be sent to the cell. This function can modify TRX static power level, saturation threshold and DC bias voltage threshold.

6)

Modification of handover parameters: After the modification, handover can be performed based on the new parameters. This function does not affect the normal working of the cell and the established circuit-based and packet based services.

7)

Modification of cell power control parameters: It has no effect on the established circuit service and packet service. It is possible to optimize the network by modifying the handover parameter and power control parameter to improve the session quality.

8)

Configure the BIE data at site side: When adding/deleting the cascading sites, as well as their cells and TRXs, it is used to modify the multi-point connection data between the sites of upper and lower level.

9)

Modification of BS color code and network color code: This function does not affect the normal working of other cells and the established circuit-based and packet-based services.

10) Modification of cell state: Through this function a user can change the cell state from equipped to unequipped state and vice versa. It is similar to the cell addition/removal function except that the originally configured data does not need to be configured. This function does not affect the normal working of other cells and the established circuit-based and packet-based services.

11) Modification of cell attributes: It is possible to modify the thresholds of interference band, saturation threshold and DC offset threshold. This will not affect the normal working of this cell or the established circuit-based and packet-based services.

12) Modification of cell alarm threshold: This function does not affect the normal working of the cell and the established circuit-based and packet based services.

13) Modification of carrier frequencies: This function can modify the frequencies of the GSM900 and GSM1800 TRXs. Modifying the TRX frequencies of non-active BCCH of non-baseband hopping cell will not affect the calls already set up, but will affects the packet-based service.

14) Modification of cell's frequency hopping attributes: The software of the BSC supports timeslot hopping and can dynamically modify the hopping parameters

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of various channels in the cell, including MA table, MAIO, TSC, and HSN. As for the RF hopping cell, this function can modify the number of frequencies involved in hopping. For the baseband hopping cell, the function can modify the frequency values involved and change the cell from a hopping cell to non-hopping one and vice versa. This function does not affect the normal working of other cells and the established circuit-based and packet-based services.

15) Modification of TRX attributes: This function can modify the static power level, saturation threshold and DC bias voltage threshold of the TRX. This function can modify TRX static power level, saturation threshold and DC bias voltage threshold.

16) Modification of channel types: It is possible to convert any non-BCCH into TCH, SDCCH into PDCH. It has no effect on the established circuit service. If the modification of channel type involves the PDCH before and afterwards, this will affect the packet-based service.

17) Configuration of the antenna feeder uplink TTA and the power attenuation factor: It is used to dynamically configure the antenna feeder uplink TTA and the power attenuation factor.

18) Modify the encryption algorithm setting: It is used to dynamically modify the encryption algorithm of the cell.

19) 20) 21) 22) 23)

Configure the base band frequency hopping TRX switchover on failure. Configure the cell BCCH cooperation. Screen/de-screen BSC alarm. Open/close EFR function. It is used to modify the voice version data. Configure call control data. It is used to dynamically modify the call control parameter of the cell.

24) Modify the cell broadcast DRX property. Dynamic modification to the DRX property of a cell is supported.

25) Modify CGI. Dynamic modification to CGI is supported. 26) Modify the visibility of the BIE. The modification to the visibility of the BIE is supported. The value range of visibility of BIE is Visible/Invisible. After BIE has changed from "Invisible" to "Visible", it is possible to add more sites to the BIE.

27) Modify BSC interface Phase 1dentifier. The dynamic data configuration to the BSC interface Phase 1dentifier is supported. BSC interface Phase 1dentifier includes A interface Phase 1dentifier, Abis interface Phase 1dentifier and Um interface Phase 1dentifier.

28) Configure cell's effective frequency. Adding/deleting the effective frequency allocated to cells are supported.

29) Configure channel management data. It is used to modify the channel management parameter of the cells.

30) Modify the visibility of GLAP. The modification to the visibility of GLAP is supported. The value range of GLAP includes Visible/Invisible. After GLAP has

1-26


Chapter 1

BSS Solution

changed from "Invisible" to "Visible", it is possible to allocate more LAPD link on GLAP.

31) Modify external cell description data. III. Dynamic data configuration reliability In addition to the reliability check mechanisms provided by the OMC the BTSM provides such mechanisms as timed retransmission, added response, and alarming so that data can be configured correctly and completely in the BTS. In case of BTS maintenance link fault, the dynamic data configuration commands to the BTS can not be sent, this will cause inconsistency between the data at the site and that in the BSC, which will affect the working quality of the system. At this time, the BTSM will periodically re-send dynamic data commands to the BTS and send alarms to the OMC LMT can perform local maintenance on BSC, BTS or PCU, while the OMC and Telnet terminal are mainly used to perform remote maintenance on the BSS. Huawei OMC includes OMC-R and OMC-S, which manage respectively BSS and NSS. They can be provided either separately or along with BSS and NSS. When Huawei BSS and NSS are used at the same time, only a suite of OMC is required. OMC connects to BSS via the LAN or WAN.

1.6.5 LMT LMT is a desktop or portable PC providing local maintenance operations. The LMTs for BSC, PCU and BTS are identical and run the WINDOWS 95 or WINDOWS 98. The only difference is the application software for operation and maintenance. PCU runs Telnet or the Hyper Terminal simulator program while the local maintenance program on the BSC and BTS is the one with a graphic interface offered by Huawei.

1.6.6 OMC I. Operational function OMC conducts the operation & maintenance of the GSM network and effective management of network capacity and coverage area expansion. For instance, a user can expand the channel capacity and adjusts the initial coverage range based on the actual needs. OMC can optimize the utilization of the resources based on the network resources data acquired and decide whether to carry out capacity expansion. Network planning plays a pivotal role in the construction and development of the network. Network planning tools interact with OMC to acquire the network resources

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Chapter 1

BSS Solution

information via OMC, make analysis of these data, and revise the network plan. The implementation of this revised plan or expansion can be implemented through OMC easily. A user can send commands and view the responses through WS. It involves network configuration data management and network real-time feedback data management. The former is the prerequisite for ensuring the normal operation of the network and the latter contains some measurement results for network planning and optimization.

II. OMC platform Huawei OMC includes OMC Sever and WS. OMC Server runs on Unix operating system and the WS runs on Windows. OMC Sever connects to the WS through LAN and the OMC system communicates with BSS through LAN or WAN. The capacity of OMC depends on the number of connected network elements, system hardware and the number of connected subscribers. Both OMC Server and WS can be upgraded based on the requirements.

1.6.7 Telnet terminal A Telnet terminal is a command line terminal mainly used for the operation and maintenance of PCU.

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Chapter 2 BSS Functions

Chapter 2 BSS Functions BSS is a bridge between MS and NSS, which performs mainly the management of radio links and conversion of radio links and wire links. It is responsible for the communication of MS. BSS system functions can be divided into basic functions, extended functions and GPRS functions.

2.1 Basic Functions 2.1.1 Overview Figure 2-1 illustrates the GSM Protocol. MS

L3 L2 L1

MSC

BSC

BTS

CM

CM

MM

MM

RR

RR RR

LAPDm Sign. Layer1

BTSM

BTSM

LAPDm LAPD Sign. Sign. Layer1 Layer1

LAPD Sign. Layer1

Um

Abis

BSSMAP

B BSSMAP SCCP

SCCP

MTP

MTP

A

MS: Mobile Station BTS: Base Transceiver Station BSC: Base Station Controller RR: Radio Resource Management MSC: Mobile services Switching Centre, Mobile Switching Centre MTP: Message Transfer Part (MTP) SCCP: Signaling Connection Control Part LAPD: Link Access Procedure on the D channel MM: Mobility Management LAPDm: Link Access Procedure on the Dm channel CM: Connection Management BSSMAP: Base Station Subsystem Management Application Part BTSM: Base Transceiver Station Site Management

Figure 2-1 GSM protocol stack According to GSM 04.07, the functions of BSS on layer 3 and related sub-layers on the radio interface (Um) are classified into:

1) 2) 3)

RR: Radio Resource Management MM: Mobility Management CM: Communication Management

Where the functions on the MM and CM sub-layers are supported by the DTAP between A- and Um interfaces. The functions of RR sub-layer that include the 2-1



maintenance and release of radio resources are mainly carried out by BSS. There are corresponding communication management protocol for A interface and Abis interface to realize the air interface between GSM network and MS. The other functions of BSS are also essential for establishing communication between the GSM network and MS. The functions (RR) that BSS involves are mainly as follows: z

Radio channel management

z

Channel coding/decoding

z

Transcoding & Rate Adaptation

z

Full-rate & half-rate coding of speech and enhanced full-rate coding

z

Encryption/Decryption

z

Frequency hopping

z

Antenna Diversity

z

RF Power control and handover management

2.1.2 Channel I. Types of Radio Channels According to GSM/GPRS specifications, the radio channels fall into two major categories, which are Traffic Channel and Control Channel. A traffic channel s further divided into Speech Traffic Channel, Circuit Data Traffic Channel and Packet Data Traffic Channel, while the Control Channel is subdivided into Broadcast Channel, Common Control Channel and Dedicated Control Channel. Logical channel

CCH

TCH

DCCH BCCH

CCCH

SDCCH Downlink

SCH FCCH BCCH (BCCH1) (BCCH2) (BCCH3)

PCH

ACCH

Uplink

AGCH

RACH

SACCH

FACCH

Downlink Downlink/Uplink

Figure 2-2 GSM/GPRS channel classification 2-2



Figure 2-2 illustrates the logical channels. Below is the introduction.

II. Traffic Channel 1)

Speech traffic channels In the latest GSM 05.02, the speech traffic channels are divided into:

z

TCH/FS: full rate traffic channel for speech.

z

TCH/HS: half rate traffic channel for speech.

z

TCH/EFS: enhanced full rate traffic channel for speech.

z

TCH/AFS: adaptive full rate traffic channel for speech.

z

TCH/AHS: adaptive half rate traffic channel for speech.

Huawei BSS currently supports two types of traffic channels for speech: TCH/FS and TCH/EFS.

2)

Circuit data traffic channel In the most updated GSM 05. 02, the circuit data traffic channels are divided into:

z

TCH/F9.6: full rate traffic channel for 9.6 kbit/s user data.

z


z

TCH/H4.8: half rate traffic channel for 4.8 kbit/s user data.

z

TCH/H2.4: half rate traffic channel for 2.4 kbit/s user data.

z


z

TCH/F14.4: full rate traffic channel for 14. 4 kbit/s user data.

z

E-TCH/F28.8: enhanced circuit switched full rate traffic channel for 28.8 kbit/s user data.

z


z


Huawei BSS currently supports TCH/F14.4, TCH/F9.6, TCH/F4.8 and TCH/F2.4.

3)

Packet Data Traffic Channel

There are two rates for the PDTCH: PDTCH: full-rate PDTCH. With GMSK modulation it can carry packet data whose momentary rates are 0~22.8 kbit/s, while PDTCH with an 8PSK modulation system can carry packet data whose momentary rates are 0~69.6 kbit/s. PDTCH is a one-way channel and categorized by the direction as: z

PDTCH/D: downlink PDTCH, for MS terminated packet transmission.

z

PDTCH/U: uplink PDTCH, for MS originated packet transmission.

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III. Broadcast Channel (BCH) BCH is used to transmit broadcast messages to the MS in down link direction. It includes the following logical channels:

1)

FCCH (Frequency Correction Channel): This channel is responsible for transferring the frequency correction signals to the MS so that the MS can be adjusted to the corresponding frequency.

2)

SCH (Synchronization Channel): This channel is responsible for transmission of the frame synchronization number (TDMA frame number) and the Base Station Identity Code (BSIC) to the MS.

3)

BCCH (Broadcast Control Channel): This channel transmits the information common to all cells, such as Location Area Identity (LAI), cell maximum allowable output power, BCCH carrier frequency of the adjacent cells, and packet service system parameters.

4)

PBCCH (Packet Broadcast Control Channel): This channel transfers the messages related to packet services.

5)

Cell Broadcast Channel (CBCH): This channel is used for the cell broadcast short message services. It uses the same physical channels as SDCCH.

The channels introduced above are downlink channels.

IV. Common Control Channel (CCCH) CCCH are classified into the following four channels:

1)

Paging Channel (PCH): Downlink channel. MS tunes to and receives the information from this channel to check for any call from MSC at regular intervals.

2)

Random Access Channel (RACH): Uplink channel, through which an MS accesses the network and requests for allocating SDCCH.

3)

Access Grant Channel (AGCH): Through which the network notifies the MS about the allocation of the dedicated channel.

4)

NCH (Notification Channel): Downlink channel used for Voice Group Call Service (VGCS) and Voice Broadcast Service (VBS).

V. Packet Common Control Channel (PCCCH) PCCH includes the following four channels:

1)

PPCH (Packet Paging Channel): Downlink packet paging channel. MS tunes to the PPCH channel at a regular interval to check if there is any call from SGSN.

2)

PRACH (Packet Random Access Channel): Uplink packet random access channel. MS requests to access the network via the PRACH channel.

3)

PAGCH (Packet Access Grant Channel): Downlink channel. The network notifies the MS of the allocation of the packet data traffic channels via the PAGCH channel.

2-4


4)


PNCH (Packet Notification Channel): Downlink channel, designed for point-to-multipoint multicast call.

Huawei BSS supports PPCH, PRACH and PAGCH.

VI. Dedicated Control Channel (DCCH) DCCH consists of the following channels:

1)

SACCH (Slow Associated Control Channel): Associated with the SDCCH or TCH. This channel is designed for MS to send received signal quality and signal intensity of adjacent BTSs to the network, and meanwhile receives the system information including transmission power, power adjustment and timing advance.

SACCH can be further divided into: z

SACCH/TF: SACCH associated with TCH/F.

z

SACCH/TH: SACCH associated with TCH/H.

z

SACCH/C8: SACCH associated with SDCCH/8.

z

SACCH/C4: SACCH associated with SDCCH/4.

z

SACCH/M: SACCH associated with TCH/F for multi-TS configuration.

2)

FACCH (Fast Associated Control Channel): FACCH implements transmission by occupying a part on TCH, mostly for transmitting handover command.

FACCH can be further divided into: z

FACCH/F: FACCH associated with TCH/F;

z

FACCH/H: FACCH associated with TCH/H.

3)

SDCCH (Standalone Dedicated Control Channel): it serves to transmit the signaling such as short message information, location updating information, etc. between the MS and the network, prior to the call setup.

z

SDCCH/8SDCCH/8

z

SDCCH/4SDCCH/4

VII. Packet Dedicated Control Channel 1)

PACCH (Packet Associated Control Channel): Downlink channel serving to transmit the signaling, including response messages and power control messages, to the MS. PACCH can also transmit the resources allocation and re-allocation messages. PACCH shares the resource with the PDTCH currently allocated to MS. When MS is in transmission mode, SGSN can page the MS via PACCH to initiate CS service.

2)

PTCCH/U (Packet Timing Advance Control Channel Uplink): PTCCH/U sends the timing advance by way of random access burst when the MS operates in a transmission mode.

3)

PTCCH/D (Packet Timing Advance Control Channel Downlink): PTCCH/D is designed to send transmission timing advance to several MSs. One PTCCH/D corresponds to several PTCCH/Us.

2-5



VIII. Radio channel management Radio channel management involves the management of diverse radio channels in the GSM/GPRS. This process occurs in the phase of connection setup, maintenance, modification and release.

IX. Radio channel combination As per the logical channel types as listed above, a user can configure the following channel combinations in the M900/M1800 BSS. z

TCH/F+FACCH/F+SACCH/TF

z

SDCCH/8+SACCH/C8

z

FCCH+SCCH+BCCH+CCCH

z

FCCH+SCCH+BCCH+CCCH+SDCCH/4+SACCH/C4

z

BCCH+CCCH

z

BCCH+CBCH

z

SDCCH+CBCH

z

PBCCH+PCCCH+PDTCH+PACCH+PTCCH

z

PCCCH+PDTCH+PACCH+PTCCH

z

PDTCH+PACCH+PTCCH

X. Traffic channel management BSS is in charge of all the configured traffic channels. When a call is established, MSC sends the channel type, channel code and other parameters regarding the call to BSS, which chooses a traffic channel based on the messages. BSS also assumes the task for the measurement and release of these traffic channels.

XI. Dedicated control channel management BSS manages all the available dedicated control channels. After MS has sends a random access request via RACH or PRACH, BSS will allocate a DCCH for the MS. Besides, BSS is also responsible for monitoring and releasing the link of DCCH.

XII. Broadcast channel and common control channel management The management of the available broadcast channels and common control channels by the BSS involves DRX management, paging message dispatching, AGCH and PAGCH control, RACH and PRACH control, and BCCH message broadcast.

XIII. Terrestrial channel management The management of terrestrial channels between BSS and MSC is to keep the terrestrial circuit states at BSS and MSC consistent so that an idle circuit can be

2-6



available when MSC makes a call (“assign circuit”) and when MS performs handover (“assign terrestrial circuit”). This is to ensure the success for the call and the handover. Procedures included in the A-interface circuit resource management are Circuit Block/Unblock, Circuit Group Block/Unblock, Unequipped Circuit, and Reset Circuit. General principles of the circuit control includes: z

Circuit management message is normally initiated by BSC. While resetting circuit can be initiated either by MSC or BSC,

z

MSC can only block or unblock its circuits without affecting the circuits at the BSS side.

z

The BSS can not change the circuit state that has been changed at the local end of the MSC. For circuits blocked on the maintenance console at MSC side, the BSS has no authority to unblock or reset the circuit.

XIV. Channel Coding & Decoding The messages are encoded/decoded before being transmitted on the radio channel to avoid radio channel interference. There are various coding and interleaving methods for different logical channels (speech, data and signaling). For a detailed description of the coding methods for various channels, please refer to the specifications GSM 05. 03.

XV. Transcoding & Rate Adaptation Transcoding (TC) and Rate Adaptation provides an interface between the standard 64 kbit/s transmission at NSS side and the lower rate transmission at BSS side. The conventional voice-coding mode is PCM with a rate of 64 kbit/s. It is widely applied to PSTN. Pulse Code Modulation (PCM) is used for normal speech in PLMN, at a rate of 64 kbit/s whereas in GSM, RPE-LTP or CELP coding with much lower rate (16 kbit/s) is used due to the limitation of radio channel resources. To further improve the voice quality, EFR (Enhanced Full Rate) is introduced. To implement EFR, newly designed algorithms are used but it does not affect the coding rate on the Um interface. When adopting EFR, the compression algorithm for the MS and Transcoder & Rate Adaptor Unit (TRAU) must be modified. Generally, 3.6 kbit/s and 6 kbit/s data rates on the Um interface are arranged for the 8 kbit/s or 16 kbit/s channel (for transmission either on the full-rate channel or the half-rate channel), while the 12 kbit/s rate is for the 16 kbit/s channel. If a PSTN subscriber wants to call an MS, rate adaptation must be performed for the voice. The TRAU is introduced to complete this function. When the BTS and the TRAU are physically detached, these conversions will be especially important. A detailed description of the conversions on the interfaces is given in the related GSM specifications. 2-7



Since the rate of each channel of existing terrestrial lines is 64 kbit/s, it is a waste if one channel is used to carry one 16 kbit/s GSM channel. To save terrestrial line resources, sub-multiplexer (SMUX) is used between MSC and BSC to multiplex 4 % 16 kbit/s channels to transmit four speech channels over one terrestrial channel. In general, TRAU and SMUX are integrated in one unit called TCSM, i. e., it handles both rate conversion and multiplexing. Table 2-1 introduces the full-rate coding/decoding process and enhanced full-rate coding/decoding process. Table 2-1 Voice coding comparison FR (Full Rate)

EFR (Enhanced Full Rate)

RPE-LTP algorithm (regular impulse excitation-long term prediction) TRAU converts the voice signal received from MSC into frames in the format of 20 ms/fr. A frame of voice data contains 160 PCM sampling Coding points, making up 1280 bit. The output Process parameters after encoding are 260 bit, making up the 320 bit TRAU frame together with the synchronous header and control parameter. Decoding is a reverse process of coding. After TRAU receives the TRAU frames sent from the Decoding BSC, it restores them into speech data by Process applying decoding algorithm before sending them to MSC. Algorithm

ACELP algorithm (arithmetic code book excitation linear prediction) TRAU converts the voice signal received from MSC into frames in the format of 20 ms/fr. A frame of voice data contains 160 PCM sampling points, making up 1280 bit. The output parameters after encoding are 244 bit, making up the 320 bit TRAU frame together with the synchronous header and control parameter. Decoding is a reverse process of coding. After TRAU receives the TRAU frames sent from the BSC, it restores them into speech data by applying decoding algorithm before sending them to MSC.

In the occasion of MS-MS session, the TRAU coding / encoding can be omitted. As the coding / encoding process will degrade the voice quality, it is possible to improve the voice quality by removing TRAU coding/decoding with Tandem Free Operation (TFO). TFO is implemented by FTC via in-band signaling to reduce the primary coding/decoding during MS-MS session and improve the voice quality. To set up TFO status, the following should be realized: Both parties of the session should subscribe to the same service (i.e. both to FR or EFR service). The FTCs seized by the two MSs should support TFO function. There should be no other equipment that is capable of changing the PCM signal on the PCM link between the FTCs of the MSs, i.e., it should be a direct link, because TFO message and frame are transmitted with the low bit of the PCM sampling value. If these conditions are not satisfied, FTC will perform the normal coding/decoding. TFO features: Realized in the occasion of MS-MS session; TFO can improve the voice quality of both FR and EFR, especially the former with the MOS can be improved by 0.5 points (totally 5 points).

2-8



2.1.3 System Information I. Overview System information contains the major wireless network parameter on the air interface, including network identifier parameter, cell selection parameter, system control parameter and network function parameter. By receiving system information, MS can be properly accessed and perform network selection so that it can make full use of the services and cooperate with network. There are two modes for the transmission of system information: broadcast message and channel associated message. In idle mode, MS communicates with the network via the broadcasting of system information. The network sends system information to MS so that MS knows its current position and the service type available. Some parameters can also control the cell reselection of MS. When MS is establishing calls, the communication between network equipment is realized with the channel associated system information. Network equipment sends some contents in the channel-associated message to MS so as to control the behaviors such as transmission, power control and handover of MS. The broadcast system information is closely related to the channel-associated message. The content in the broadcast system information can overlap with that in the channel associated message. While the content in the channel associated message can be inconsistent with that in the broadcast system information, because the channel associated message has the effect on only one MS, while the broadcast system information affects all MSs in idle mode.

II. Types and content of system information There are totally 13 types: 1, 2, 2bis, 2ter, 3, 4, 5, 5bis, 5ter, 6, 7, 8 and 9. Among them, 1, 2, 2bis, 2ter, 3, 4, 7, 8 and 9 are broadcast information transmitted via BCCH under idle mode; 5, 5bis, 5ter and 6 are channel associated information transmitted via SACCH in active mode. Type 1: Cell channel description + RACH control information (optional) Cell channel description: all frequencies used by this cell, including BCCH frequencies and FH frequency to provide the frequency reference for MS Frequency Hopping (FH). RACH control information: parameters such as maximum times of retransmission (MAX RETRANS), number of transmission timeslots (TX Integer), Cell Bar Access, bit allowed for call reestablishment (RE), bit allowed for emergency call (EC) and access

2-9



restricted user level (AC). These parameters are used to control the behavior of MS in the initial access. Type 2: Adjacent cell BCCH frequency description + Network color code allowed + RACH control information (mandatory) Adjacent cell BCCH frequency description: the BCCH frequency used by the adjacent cell. Network color code allowed: NCC allowed for the MS test on the BCCH carrier in the cell. Type 2bis: Adjacent extended cell BCCH frequencies description + RACH control information (optional) Extended adjacent cell BCCH frequency description: the number of frequencies described in the frequency allocation table in system information type 2 is limited, therefore system information type 2bis contains the information of other frequencies in BA1 which are in the same frequency segment as system information type 2. RACH control information: contains the maximum times of parameter retransmission (MAX RETRANS), number of retransmission timeslot (TX Integer), Cell Bar Access, bit allowed for call reestablishment (RE), Restricted user level, bit allowed for emergency call (EC) to control the MS behavior during initial access. Type 2ter: Attached multi-frequency information + extended cell BCCH frequency description 2 (optional) Attached multi-frequency information: Number of the multi-frame measurement needed. Extended adjacent cell BCCH frequency description 2: describes the extended frequency allocation table of the adjacent cell (part of BA1 table). The frequency contained in this information is located at the different frequency segment as the current cell. Therefore, only the multiband MS can read this information. The single-band GSM 900 of GSM 1800 MS will skip this information. Type 3:Cell ID + LAI + control channel description + cell option + cell selection parameter + RACH control information (mandatory) Cell ID: identifier of the current cell. LAI: location area identifier of the current cell. Control channel description: contains the MS attach/detach allowed indication (ATT, Attach-Detach Allowed), number of blocks reserved for AGCH (BS AG BLKS RES), common control channel configuration (CCCH CONF), number of 51 TDMA multi-frames reserved for the same paging group in the paging information (BA PA MFRMS) and the interval of periodic location update.

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Cell option: includes the power control indication (PWRC), discontinuous transmission (DTX) and radio link timeout value (Radio Link Timeout). Cell selection parameter: includes the cell reselection hysteresis value, maximum Tx power level allowed for MS access to the cell (MS TXPWR MAX CCH) and minimum access level allowed for MS to access system (RXLEV Access MIN). RACH control information: contains the maximum times of parameter retransmission (MAX RETRANS), number of retransmission timeslot (TX Integer), Cell Bar Access, bit allowed for call reestablishment (RE), Restricted user level, bit allowed for emergency call (EC) to control the MS behavior during initial access. System information type 3 rest bytes: cell reselection parameter information and type 3 MS control information. Type 4: LAI + cell selection parameter + RACH control information + CBCH description + CBCH dynamic allocation information (mandatory) LAI: the location area identifier of the current cell. Cell selection parameter: includes the cell reselection hysteresis value, maximum Tx power level allowed for MS access to the cell (MS TXPWR MAX CCH) and minimum access level allowed for MS to access system (RxLEV Access MIN). RACH control information: contains the maximum times of parameter retransmission (MAX RETRANS), number of retransmission timeslot (TX Integer), Cell Bar Access, bit allowed for call reestablishment (RE), Restricted user level, bit allowed for emergency call (EC) to control the MS behavior during initial access. CBCH description: includes the channel type and TDMA offset (which type of dedicated channel combination), timeslot No. (TN), training sequence code (TSC), FH channel indication (H), mobile allocation index offset (MAIO), FH serial No. (HSN) and absolute RF channel No. (ARFCN). CBCH mobile allocation information: the relation between the sequence of frequencies used for FH and cell channel description. System information types 4 rest bytes: cell reselection parameter. Type 5: Adjacent cell BCCH frequency description (mandatory) Adjacent cell BCCH frequency description: the BCCH frequency used by the adjacent cell. Comparing with system information type 2, the difference is that MS can get the frequencies described in system information type 5 in active mode, and report the related information of the adjacent cell in the measurement report as the reference of handover. Similarly, the GSM900 MS in Phase 1 recognizes only the adjacent cell frequencies described in system information type 5 and ignore those contained in 5bis and 5ter.

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Type 5bis: Extended adjacent cell BCCH frequency description (optional) Extended adjacent cell BCCH frequency description: the number of frequencies described in the frequency allocation table in system information type 5 is limited, therefore system information 5bis contains the information of other frequencies in BA2 which are in the same frequency segment as system information 5. Type 5ter: Attached multi-frequency information + extended cell BCCH frequency description 2 (optional) Attached multi-frequency information: Number of the multi-frame measurement needed. Extended adjacent cell BCCH frequency description 2: describes the extended frequency allocation table of the adjacent cell (part of BA2 table). The frequency contained in this information is located at the different frequency segment as the current cell. Therefore, only the multiband MS can read this information. The single-band GSM 900 of GSM 1800 MS will skip this information. Type 6: Cell ID + LAI + cell option (mandatory) Cell ID: identifier of the current cell. LAI: the location area identifier of the current cell. Cell option: includes the power control indication (PWRC), discontinuous transmission (DTX) and radio link timeout value (Radio Link Timeout). Type 7: Cell reselection parameter Cell reselection parameter: includes cell reselection indication (PI), Cell Bar Qualify (CBQ), Cell Reselect Offset (CRO), Temporary Offset (TO) and Penalty Time (PT). Type 8: Cell reselection parameter Cell reselection parameter: includes cell reselection indication (PI), Cell Bar Qualify (CBQ), Cell Reselect Offset (CRO), Temporary Offset (TO) and Penalty Time (PT). Type 9: RACH control information + broadcast channel parameter RACH control information: contains the maximum times of parameter retransmission (MAX RETRANS), number of retransmission timeslot (Tx Integer), Cell Bar Access, bit allowed for call reestablishment (RE), Restricted user level, bit allowed for emergency call (EC) to control the MS behavior during initial access. Broadcast channel parameter

III. Meaning and function of wireless network parameter 1)

Network identification parameters

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Network identification parameters include CGI and BSIC. CGI consists of LAI and CI. LAI is composed of MCC, MNC and LAC. System information type 3,4 and 6 include all or part of CGI information. MS decodes the system information to get the CGI. MS decides whether to connect to the network in this cell according to the MCC and MNC indicated by CGI. It is also used to check whether the current location area has changed so as to initialize the location updating process. MCC, consisting of three decimal digits, is allocated worldwide in unified way. MNC, consisting of two decimal digits, is allocated by the country in unified way. LAC and CI, both consisting of 2 bytes, are arranged by GSM carrier in unified way. Note that the value range of CI is 0X0001~0XFFFE, while 0X0000 and 0XFFFF are reserved. BSIC identifies the local color code of each BTS in the GSM system. In GSM system, frequencies are multiplexed to different extents according to the different requirements in network plan. MS differentiates two cells' same frequency with their BSICs. Therefore, it is necessary to guarantee the uniqueness of BSICs of the cells using the same BCCH carrier frequency. BSIC is transmitted on the SCH of each cell. It consists of NCC (3 bits) and BCC (3 bits). Note that the TSC described in system information type 4 is the BCC of the current cell.

2)

System control parameter

System control parameter is transmitted to MS with system information via air interface by BTS. It serves to keep contact between MS and BTS. Besides, these parameters have the direct effect on the service bearing and signaling flow of various part of system. Therefore, reasonable setting of these parameters is important in maintaining of the normal operation of GSM system. IMSI attach and detach allowed (ATT) is used to notify MS whether the local cell allows IMSI attach/detach process. It is transmitted in control channel description in the system information type 3. ATT has 1 bit. "0" stands for IMSI attach/detach process not allowed, and "1" stands for the process allowed. CCCH CONF decides the integration mode of the CCCH in the cell. It is transmitted in the control channel description in the system information type 3. CCCH CONF is a 3 bit code. For details, see Table 2-2. Table 2-2 CCCH code meaning CCCH CONF 000 001 010 100

Meaning CCCH uses a basic physical channel which is not shared with SDCCH. CCCH uses a basic physical channel which is shared with SDCCH. CCCH uses two basic physical channels which are not shared with SDCCH. CCCH uses three basic physical channels which are not shared with 2-13

Number of CCCH information blocks in BCCH multiframe 9 3 18 27


110 Others


SDCCH. CCCH uses four basic physical channels which are not shared with SDCCH. Reserved

36

Note: The CCCH CONF setting of a cell should be in line with the actual setting of the cell's CCCH. It is decided by the traffic module of the cell.

BS AG BLKS RES is transmitted in the control channel of system information type 3. It is used together with CCCH CONF to decide the number of information blocks in each BCCH of the current cell. After setting CCCH CONF, BS AG BLKS RES will be used to arrange the occupancy ratio between AGCH and PCH on CCCH. It is possible to adjust this parameter to achieve the bearing balance between AGCH and PCH. BS PA MFRAMS is transmitted in the control channel description in system information type 3. It decides how many multiframes making up a cycle of a page sub-channel. This parameter actually decides how many sub-channels the PCH of a cell will be deviled into. BS PA MFRAMS is a 3 bit code. The value range is 0~7, respectively meaning that the number of multi-frame of a paging group cycled on the PCH is 2~9. Periodic location updating timer (T3212) decides the frequency of periodic location updating. It is transmitted in the control channel description in system information type 3. It is an 8-bit code. The value range is 0~255, each unit of which is the duration of six minutes, and 0 means no location updating. Cell Channel Description, transmitted in system information type 1, describes the RF channel No. of the local cell. It is used in frequency hopping. Note that the maximum number of channels configured in cell channel description is 64. Neighbor Cells Discretion, transmitted in system information type 2, 2bis, 2ter, 5, 5bis and 5ter, describes the absolute channel No. of the BCCH TRX of the cell adjacent to the current cell. Huawei BSS supports at most 32 adjacent cells. Extension Indication, transmitted in system information type 2 and 5, indicates whether there are still extended adjacent cells to be transmitted in system information type 2bis and 5bis. It is a 1-bit code. "0" means that system information type 2 and 5 contains the complete BA table, and "1" means that type 2 and 5 contains part of BA table. BA Indication transmitted in system information type 2 and 5. It is a 1-bit code, used for MS to select the data in BA 2 before or after modification. In another word, if the adjacent cell relation of the current cell and the BA2 table is changed during a session, the BA Indication in system information type 5 will be 1 instead of stead of 0. This 2-14



indicate that MS perform decoding in the adjacent cell indicated in the system information type 5 again. Multiband Reporting (MBR), transmitted in system information type 2ter and 5ter. It is a 2-bit code, indicating MS to report adjacent cell information on multiple frequency bands. It is applicable to multiband MS only. The details are listed below.

2.1.4 Idle Mode Behavior I. Overview A powered on mobile station (MS) that does not have a dedicated channel allocated is defined as being in idle mode. The purpose of the tasks performed in the idle mode is to be able to access the system and be reached by the system from any location in the network. When a mobile is powered on, it immediately attempts to make contact with a GSM Public Land Mobile Network (PLMN). The particular PLMN contacted may be selected either automatically or manually. The MS will look for and select a suitable cell of the chosen PLMN. It will then tune to the control channel of the cell to receive information about the available services provided by the PLMN. This selecting is known as “camping” on a cell. When an MS is in idle mode it will always try to camp on the best cell according to a signal level based criterion. The idle mode behavior is managed by the MS. It can be controlled by parameters which the MS receives from the base station on the Broadcast Control Channel (BCCH). All the main controlling parameters for idle mode behavior are transmitted on the BCCH carrier in each cell. When the MS is powered on but neither making nor receiving any calls (idle mode) there has to be a mechanism that always selects the best cell on which to camp. Moreover, to be able to access the system from anywhere in the network, regardless of where the MS was powered off, it has to be able to select a specific GSM base station, tune to its frequency and listen to the system message informations transmitted in that cell. It must also be able to register its current location to the network so that the network knows where to route incoming calls. The PLMN selection mechanism, the cell selection and reselection algorithms in addition to the location updating procedure are the core of the idle mode behavior. The purpose is to always ensure that the mobile is camped on the cell where it has the highest probability of successful communication.

II. Usage 1)

High signal level when accessing the system

The MS will at all times try to obtain the highest possible signal level when accessing the system. This is achieved by means of the idle mode cell selection and reselection

2-15



algorithms. These algorithms will enable the MS to choose the most suitable cell to camp on, based on signal level. A cell is suitable if certain criteria are satisfied. Camping on the most suitable cell provides the MS with a high probability of good communication with the system. The cell selection and reselection algorithms are governed by parameter settings. Using these parameters an operator can, on a per cell basis, make a specific cell more or less attractive to camp on for the MS. This makes it possible for the operator to achieve similar behavior for MSs in idle mode as in active mode. Well-designed parameter settings for cell selection and reselection in idle mode, will make the MS to camp on the cell that would have been chosen if the MS had been in active mode.

2)

Control of the paging load

In idle mode the MS will notify the network whenever it changes location area by the location updating procedure. Thus, the network will be kept updated concerning which location area the MS is presently in. When the system receives an incoming call it knows in which location area it should page the MS, and does not need to page it throughout the whole MSC service area. This reduces the load on the system. If the MS does not respond to the first paging information, then the network can send a second paging information. The MS can also, periodically and when powered on or off, notify the network of its present status by the location updating procedure. This prevents the network from doing unnecessary paging of MSs that have been powered off or left the coverage area. This would otherwise cause unnecessary load on the system.

3)

Low idle mode power consumption

In idle mode, the MS only occasionally monitors the system information being transmitted in the current cell or does measurements on neighboring cells to see if a cell change should be initiated. However, most of the time it will be in “sleep mode”. Hence, the power consumption during idle mode will be low. This is also referred to as discontinuous reception (DRX).

III. Technical description While the MS is in idle mode it will continuously make measurements on the BCCH-carriers of serving and neighboring cells to decide on which cell to camp on. It will also, if necessary, register its presence in the location area of the chosen cell by performing a location updating. The purpose of camping on a cell is threefold:

1) 2)

It enables the MS to receive system information from the PLMN The MS can initiate a call by accessing the network on the Random Access Channel (RACH) of the cell on which it is camped,

2-16


3)


The PLMN will know the location area of the cell in which the MS is camped (unless the MS has entered a limited service state) and can therefore page the MS when an incoming call is received.

The idle mode task can be subdivided into four processes: z

PLMN selection

z

Cell selection

z

Cell reselection

z

Location updating.

The relationship between these processes is illustrated in Figure 2-3. Service indication to User

Automatic/Manual Mode Selection User Selection of PLMN Indication to User

PLMN Selection PLMN Selection

PLMN Available Cell Selection

New Location Area

Initial Cell Selected Cell Reselectin Location Updating Responses

Cell & Location Area Changes Periodic Registration

Location Updating

Figure 2-3 Overall idle mode processes

2.1.5 PLMN Selection I. Overview The MS will select a PLMN when it is powered on or upon recovery from a lack of coverage. It will first try to select and register on the registered PLMN if one exists. If registration on a PLMN is successful, the MS indicates this PLMN (the “registered PLMN”) and is capable of making and receiving calls on it. If there is no registered PLMN, or if the registered PLMN is unavailable, the MS will try to select another PLMN either automatically or manually depending on its operating mode, The MS normally 2-17



operates on its home PLMN. However, another PLMN may be selected if, for example, the MS loses coverage. The MS will register on a PLMN if the MS finds a suitable cell to camp on and if a location-updating request is accepted. Registration has to be successful in order for the MS to be able to access that network. However, it does not need to perform location updating if it is in the same location area belonging to the same PLMN as it was before it entered the inactive state. The MS can select and register on another PLMN of its home country than its home PLMN if national roaming or international roaming is permitted. However, the MS will then do periodical attempts to return to its home PLMN. This is controlled by a timer. The interval between attempts is stored in the Subscriber Identity Module (SIM). Only the service provider is able to set the timer value for return to home PLMN. There are two modes for PLMN selection; automatic and manual. The automatic mode utilizes a list of PLMNs in an order of priority whereas the manual mode leaves the decision to the user and only indicates which PLMNs that are available.

II. Automatic mode In automatic mode, the MS will select PLMN if available and allowable, in the following order if no registered PLMN exists or is available: Home PLMN

1)

Each PLMN that has been stored in the Subscriber Identity

Module (SIM) in priority order 2) 3)

Other PLMNs with received signal level above -85 dBm in random order All other PLMNs in order of decreasing signal level.

III. Manual mode In manual mode, the MS will first try to select the registered PLMN or home PLMN (if no registered PLMN exist). If this registration fails or if the user has initiated a PLMN reselection the MS will indicate to the user all available PLMNs. The user can then select a desired PLMN which causes the MS to initiate a registration on this PLMN. If the selected PLMN is not allowable, an indication to the user to select another PLMN will be made. The user can at any time request the MS to initiate reselection and registration onto an alternative available PLMN. This is done either using automatic or manual mode, depending on the mode selected by the user.

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2.1.6 Cell Selection and Reselection I. Overview The purpose of cell selection and reselection is to enable MS to find a most suitable cell on which MS can reliably decipher the downlink data and maintain a high communication rate on uplink (so as to realize various telecom services). Once MS has selected a cell as its serving cell, its communication with the network becomes possible on this cell. MS will tune to the BCCH to receive the paging message and the system information broadcast on BCCH and use the RACH to send access request after it has selected this cell. MS implements cell reselection according to the message in BA table in the system broadcast information from the serving cell. There are two BA tables in GSM network. One is transmitted in the system information via BCCH. It includes the BCCH carrier used in a certain physical area for the MS in idle mode to implement cell selection and reselection. The other one is transmitted in the system information via SACCH. It is used to indicate the MS in active mode about the BCCH carrier for handover monitoring. In active mode, MS obtains the information of adjacent cell BCCH frequency through BA (BCCH). The process will not stop until MS receives the first BA (SACCH) information.

II. Cell selection procedure When MS is powered on and move from blind spot of coverage to the serving area, it will search for all available frequencies in the PLMN and select the suitable cell to camp on. This is the procedure of "cell selection". Cell selection procedure in the case of no BCCH information in MS MS first searches the 124 RF channels of GSM 900(if the MS is a multiband one, MS searches 374 GSM 1800 RF channels), and compares the signal level on the channels to calculate the average level. The entire measurement procedure lasts 3~5 s, during which, at least five sampling points will be extracted from different RF channels. After MS has tuned to the maximum carriers of the receiving level, it will first judge which one is the BCCH carrier (by searching FCCH burst). If so, MS will attempt to decode SCH to obtain the BCCH system broadcast information synchronous with this carrier. If the MS can properly decode BCCH data, and make sure that this cell belongs to the selected PLMN, parameter C1>0, and this cell has no access barring, MS can camp on this cell. Otherwise, MS will keep tuning to the next highest carriers until it reaches the available cell. 2-19



If no suitable cells are found after searching 30 RF channels with the highest level, MS will monitor the level of all channels and search for the BCCH of C>0 and no access barring. After finding this carrier, MS will camp on this cell without considering its PLMN ID. In this occasion, only emergency call can be implemented. Case 1: If the access level of the MS is barred at the cell, the cell selection algorithm will not be affected, i. e., when the cell satisfies the criterion, MS will still camp on it. Case 2: If the cell selected by MS belongs to PLMN, but access is barred (parameter CBA is set as "bar") or algorithm C1<0, MS will use the BA table obtained from this cell to search for these BCCH carriers. Cell selection procedure in the case of BCCH information already stored in MS If the BCCH carrier information has been stored in MS during the last powering off, MS will first search the stored BCCH carrier. If MS can decode the BCCH data of the cell, but cannot camp on it. MS will check the BA table of this cell. If no suitable cells found after all BCCH carriers have been searched, the previous procedure will be implemented. C1 is the path loss criterion as the reference of cell selection and reselection. C1 of the serving cell should be larger than 0. The formula is as follows: C1 = RxLEV − RxLEV _ Access _ MIN − MAX ((MS _ TxPWR _ MAX _ CCH − P ),0 )

See Table 2-3 for formula explanation. Table 2-3 Name of powers Name RxLEV RxLEV Access MIN MS TxPWR MAX CCH P

Meaning (Unit d Bm) Average level MS received Maximum receiving level allowed for MS to access Maximum transmitting power level allowed for MS to access the system Maximum output power of MS

C1 algorithm is used during cell selection procedure, as shown in Figure 2-4.

Cell1

Cell2

C1=15

C1=8

Figure 2-4 Cell selection

2-20



MS select the suitable cell to camp on according to the priority and C1. The selected cell is the main serving cell Figure 2-4, MS will select Cell 1 as the main serving cell to if the priorities are the same.

III. Cell reselection procedure After MS has selected a serving cell, it will camp on this selected cell and continue the monitoring on all BCCH carriers configured in the adjacent cell frequency configuration table indicated in the BCCH system information of the serving cell if the conditions are not changed greatly. When monitoring these BCCH carriers, the measurement of their receiving level should base on at least the average of 5 sampling points, and the number of measured sampling points extracted from all BCCHs should be the same. The sampling points allocated to each carrier should be as even as possible in each measurement period. The six strongest BCCH carriers should be refreshed at least once per minute. To lower the power consumption of MS, MS should measure the receiving level of each carrier in BA table when performing decoding page group. It is possible to obtain some BCCH frequencies and sample values of receiving level on the BCCH frequency of the serving cell during the appearance of MS page group. The MS routine measurement program also includes the measurement of the BCCH carrier of the current serving cell. MS should attempt to decode all system informations broadcast on BCCH of the serving cell at least every 30 s. MS should implement decoding of BCCH data block to the BCCH carriers of the six strongest non-serving cells at least every 5 min. This data block contains the parameter concerning cell reselection. After MS has found a new BCCH carrier as one of the strongest carriers, it will decode the BCCH data of the new carrier within at least 30 sums. MS should check the BSIC of one of the six strongest carriers within at least 30s to verify that the monitored objective is the same cell. If BSIC is changed, MS will regard the carrier as a new one, and decode the BCCH data again. During the process above, MS tries not to interrupt the monitoring to PCH. Under the following occasions, the procedure of cell reselection will be initiated. (If C2 algorithm has not been activated, C2 = C1). MS finds that the C2 value of a cell (in the same location area as the serving cell) has been larger than that of the serving cell for 5 seconds. MS finds that the C1 value of a cell (not in the current location area) has been larger than the sum of the C2 value of the serving cell and the cell selection hysteresis for five seconds. The current cell barred.

2-21



MS finds the downlink failure: the criterion of downlink signaling failure is based on the downlink signaling failure counter DSC. If MS has selected a cell, DSC is set as [90/BS PA MFRMS] round number. BS PA MFRMS is the number of multiframes of the 51 TDMA frame for the BTS transmission paging information for the MSs of the same paging level. Therefore, when MS is decoding on the PCH, if succeeded, add 1 to DSC; if failed, subtract 4 from DSC. When DSC = 0, there is downlink signaling failure. The value of C1 has been smaller than 0 for 5 s. During random access, MS fails to register at the retry after maximum retransmission. Note that after MS reselection and camping on the cell, MS should decode all of the BCCH data of the new cell to check whether the parameter concerning cell reselection has changed. If it is changed, MS will decide whether this change satisfies the criterion of cell reselection. If the criterion is satisfied, MS will camp on this cell. If MS finds that LAI has changed, it will initialize location updating. C2 algorithm is used in cell reselection, as shown in Figure 2-5 Cell1

Cell2

C2=4

C2=18

Figure 2-5 Cell Reselection MS selects the cell to camp on according to the priority and C1 value. The camped-on cell becomes the main serving cell. See Figure 2-5. With the same priority, MS will select Cell 2 as the main serving cell if reselection hysteresis and the reselection time are both satisfied.

IV. The impact of the network to the MS in idle mode Network side is responsible for completing system informations broadcast and paging task for idle MSs in downlink. System information type 2~4 and the optional type 1, 2bis, 7 and 8 are broadcast periodically from the network via BCCH. The MSs in idle mode decides whether and how to access the network according to these information. MS of GSM 900 supports the band of GSM 900 only. It regards the EXT IND bit described in adjacent cell in system information type 2 as the standby bit. If the

2-22



information sent from the multiband network is received, MS will regard that the information unit in system information type 2 contains the complete BA table and will ignore the system information type 2bis.

V. Definition of discontinuous receiving mode (DRX) and PCH If MS in idle mode has selected its serving cell, it is ready to monitor the paging information from this cell. To lower the power consumption of MS, the GSM specification adopts the discontinuous receiving mechanism, i. e., each subscriber (IMSI) corresponds to a dedicated paging group. Each group corresponds to a paging sub-channel of the cell. MS recognizes its paging group and the corresponding paging sub-channel according to the last three digits of the IMSI. MS in idle mode uses its own paging sub-channel to receive the paging information (or to monitor the receiving level of the BCCH carrier of the non-serving cell). MS ignores the information from other paging sub-channel or even shuts down the power of some hardware to lower its power consumption during the broadcasting of other paging sub-channels. But MS must measure the network information task periodically. The number of the paging sub-channels can be calculated according to the configuration type and BS AG BLKS RES (how many AGCH blocks for 51 multiframes), BS PA MFRMS (how many 51 multiframes to make up a cycle of the paging sub-channel). Common Control Channel (CCCH) includes AGCH and PCH. It is used to transmit the immediate assign information and paging information. CCCH can be bearded by a physical channel or shared by multiple physical channels. CCCH can share the same physical channel with SDCCH. The combination mode of CCCH is decided by the parameter CCCH CONF. The configuration of CCCH CONF should be consistent with that of CCCH. For the cell with one TRX, the recommended CCCH configuration is sharing one physical channel with SDCCH (3 CCCH information blocks in this case). For some location area with very heavy paging traffic, only one physical timeslot is insufficient to transmit the paging information. Therefore, the GSM specification allows configuring extra CCCHs on the TS0, TS2, TS4 and TS6 of the carrier.

2.1.7 Location updating Location updating is an important task of Mobile Management (MM).

I. Location Area To locate MS, each GSM PLMN domain is divided into locations areas covering one or more cells. The location area of each MS is recorded by the network as the location reference for paging this MS. With the introduction of the concept of location area, the paging MS can be implemented with a location area instead of all cells controlled by 2-23



MSC, thus lowering the paging load. Each location area is assigned with a Location Area Code (LAC), which is broadcast with the system information via BCCH. The size of a location area has a great effect on the system. The design of location area is very important in network planning. If the coverage of a location area is too small, the location updating of MS will trigger frequently, which will increase the signaling flow of system. On the other hand, if the coverage of a location area is too large, the load of PCH and the signaling flow on Abis interface will increase since one single paging information will be broadcast in all cells of this location area. Therefore, optimization of location area is a very important task in network planning. When designing the location areas, it is necessary to lessen the frequency of location updating on the basis of no overweigh paging load, so as to avoid waste of network resource.

II. Location updating When MS roams from one location area to another, it is to be registered in the new location area. In other words, once driven by certain needs or finding that the LAI stored is different from that of the current cell, MS will notify the network to change the stored location area. The procedure is called location updating. If the MS in idle mode triggers cell reselection when moving within the same location area, MS will not notify the network about this change although the serving cell has changed. If the two cells before and after reselection are not in the same location area, MS will notify the network about this change. This is "forced register". According to the labels of location updating in the network, there are three types of location updating: generic location updating (i.e. inter-location area location updating), periodic location updating (T3212 timeout) and IMSI attach (MS powered on). Their specific differences are whether only one VLR is involved in the location updating process and whether IMSI is used in the process.

III. Generic location updating Generic location updating is for the purpose of updating the actual MS's location registered in the network. The information unit of type of location updating in "location updating" should be indicated as generic location updating. If the network indicates that the status of MS in VLR is unknown, the generic location updating will also be initiated as a response to the request of MM connection setup.

1)

Intra-VLR location updating

This is the simplest location updating process, in which, MS does not need to provide its IMSI. It is implemented within the current VLR, and HLR will not be notified about the process.

2-24



During the initialization process, the access cause indicated in the initialization information contained in SABM frame sent from MS to the network is Location updating Request. This information also contains MSTMSI and LAI noted as for generic location updating. After receiving this information, MSC will send MAP Update Location Area to VLR. VLR, after receiving this information, will implement the location updating. It will update the location information of the MS and store the new LAI and then allocate a new TMSI for MS if necessary (TMSI can also be absent in the TMSI reallocation command. In this case, MS uses the former TMSI). After receiving TMSI Reallocation Complete from MS, VLR sends Location updating Accept to MS, and then release the channel to end the process.

IV. Inter-VLR location updating If MS roams to a cell whose LAI is different from the current one, it will send the old LAI and stored TMSI via MSC to VLR in the process of location updating If TMSI cannot be identified, MS can also be identified with its IMSI. See Figure 2-6. D A

B MSC

MS

D PVLR

VLR

HLR

Location Update Request MAP Update Location Area MAP Update Location MAPCancel Location MAPCancel Location ACK

MAP Insert Subscriber Data MAP Insert Subscriber Data ACK MAP Update Location ACK MAP Update Location Area ACK Location Update Accept

Figure 2-6 Interfaces and process of inter-VLR location updating

1)

Update with TMSI

If VLR finds that the TMSI is unknown after receiving MAP Update Location Area from MSC, it will label the "VLR Location Information Acknowledge" as "Unacknowledged" for the subsequent updating in HLR. If the subscriber has not registered in that VLR, 2-25



"HLR Location Information Acknowledge" will be labeled as "Unacknowledged". And then, according to the address of the previous VLR (PVLR) indicated in TMSI and LAI, VLR will send MAP Send Identification to PVLR to request for IMSI and authentication parameter, and as a response PVLR will return the IMSI and authentication parameter to the new VLR. If the new VLR fails to get the IMSI, it will then sends Identity Request to MS to request for its IMSI. After receiving IMSI, VLR will send the information of location updating of MS to HLR. This information contains the identification of MS and other related information for HLR the query the data and set up the path. If the new MSC/VLR has the normal service authority, HLR will store the new VLR No., and sends MAP Cancel Location to HLR. After receiving this information, PVLR will delete all information related to this MS, and sends MAP Cancel Location ACK to HLR. The new VLR continues to handle the processes of authentication, ciphering and TMSI reallocation. When these processes are done, HLR sends MAP Insert Subscriber Data to VLR to provide the subscriber information needed, including authentication information. After receiving the response from VLR, HLR will send Location updating Ark to that VLR.

2)

Update with IMSI

If the identification of the subscriber is IMSI, VLR will check whether this subscriber is unknown. If so, it will be labeled the "HLR Acknowledge" as "Unacknowledged", and then initializes HLR updating. If the IMSI is a known one, VLR will check whether the previous LAI provided in the information from MSC belongs to this VLR. If not, it will label "HLR Acknowledge" as "Unacknowledged", and then initialize HLR updating. Authentication is needed in these two cases.

V. IMSI attach and detach process IMSI attach and detach means to attach a binary mark to the subscriber record in MSC/VLR. The former one is marked as access granted, and the latter one is marked as access denied. IMSI attach and detach is an option of system. If the cell where MS is powered on supports this function, it will notify its power-on status to the network, i. e. sending the information of "IMSI Attach" to notify the network about the change of its current status. When the network receives this indication, it will note down the subscriber status in the system data so as to initialize the paging process when there is an paging information of this MS. If MS finds that the stored LAI is the same as the current LAI when powered on, it will initialized the process of IMSI attach. The process is almost the same as INTRA VLR Location Updating. The only difference is that the type of location updating marked in Location Updating Request is IMSI attach.

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VI. Periodic location updating Periodic location updating is used to periodically notify the network about the accessibility of MS. MS sends Location Updating Request to the network, in which the information unit of the type of location updating is periodic location updating. In the following cases, network will lose contact with MS: A powered on MS roams to the area beyond network coverage (blind spot). Since the network is not notified about the current status of MS, it still considers the MS in the status of IMSI attach.

1)

When MS is transmitting "IMSI Detach", if there is interference to the radio uplink path, the network may not be able to decode this information. This means that system still regards this MS in the IMSI attach status.

2)

In the case of MS power failure, MS cannot notify the network about its current status, resulting in the loss of contact with the network. If the above cases happen and the MS is paged, system will still sends the paging information to the location area where the subscriber registered. This paging will sure end up with paging timeout, and system resources are wasted.

To tackle this problem, the corresponding measure is taken in GSM system to make the MS automatically reports its current location information to the network periodically. N this way, the network can have the timely information of the current location status of MS. This process is called periodic location updating. BSS sends the period of periodic location updating (T3212) to all subscribers in the cell with system broadcast system via the cell's BCCH, so that MS will automatically initialized location updating request to the network when the timer times out. After cell selection or cell reselection, MS will read T3212 from the system information of the serving cell, and then activate this timer and store it in SIM. After that, whenever T3212 times out, MS will automatically initialize location updating. At NSS side, the network will periodically query the subscribers marked as IMSI attach in its VLR to mark those without any contact with it witting this period as implicit power-off in order to avoid paging these MSs and wasting system resources. Periodic location updating is an important measure to keep the contact between the network and MSs, therefore, the more frequent periodic location updating is, the better overall performance of network can be achieved. However, frequent periodic location updating has two drawbacks: Increase of signaling flow which may lower the processing power of MSC/BSC/BTS and the utilization of radio resources if the situation is serious; Increase of MS power consumption which will shorten the standby time of the MSs served by this system. Therefore, the setting of T3212 should be based on the actual situation.

2-27



In the following cases, T3212 will be reset to 0: When receiving "Location Updating Request" or "Location Updating Refuse", Ciphering mode complete when receiving the first MM message, or MM connection being established. MS responds to its paging, and after which, it receives the first correct L3 message (excluding RR message). T3212 timed out. MS deactivated (equipment powered off or SIM removed). When T3212 times out, MS will initialize periodic location updating. If T3212 times out when MS is in the status of "no available cell", or "service restricted" or "searching for PLMN, MS will delay location updating will be delayed until these status changed. If BCCH information indicates periodic location updating not applied, this process will not be activated. T3212 timeout value is broadcast in the CCH description in "system information type 3". In the status of "no available cell", "service restricted" and "searching PLMN", T3212 cannot be changed. MS, after cell reselection, may find that the T3212 of the new cell is different from the previous one (sharing the same LAC) or the broadcast T3212 of the current cell is manually changed). In this case, assumed that "t1" is the new T3212 timeout value and "t" is the current value of T3212, the timer of MS will be restarted with the value of t mod t1. If MS is in the activated status, or it is necessary to change T3212 value, and the timer is not running, then the new timer will be started with a random number whose value range is 0~t1 ("t1" is new T3212 timeout value. The signaling flow of periodic location updating is the same as that of generic location updating.

VII. Generic location updating (specification) MS initialize location updating If there is no RR connection available when initializing location updating, MM sub-layer of MS will request RR sub-layer to establish RR connection. MS sends "Location Updating Request" to the network, and start T3210. The information unit of location updating type in this message will indicate the type of this location updating. On this occasion, the network can initialize the type querying procedure (e. g. to get the ciphering capability of MS). If the network cannot obtain the

2-28



IMSI according to TMSI and LAI, the network can initialize the identification process. After receiving "Location Updating Request" from MS, the network will initialize the authentication process. If it is necessary to reallocate TMSI, the network will initiate the process of ciphering mode setting.

1)

Attempt counter

To restrict the frequency of location updating attempt, the attempt counter is recommended in the specification. It is used to count the number of consecutive unsuccessful location updating. When a location updating failure occurs, the counter will add one. The attempt counter will be reset in the following cases: z

MS powered on.

z

SIM inserted.

z

Location update successfully completed, and the service statuses switch from Attempting to Update.

z

MS roaming into a new location updating area.

z

T3212 timeout.

z

Location update initiated by CM sub-layer.

Attempt counter is used to decide whether to implement another attempt after T3212 timeout.

2)

Location update accepted by the network

If the network accept location updating, it will send "Location Updating Accept" to MS. When authenticating the validity of security, TMSI reallocation is a part of location updating process. "Location Updating Accept" contains the TMSI allocated for MS and the current LAI. In this case the network will initialize T3250. If the network needs to prolong the RR connection so that MS can initialize MM connection (e.g. MS sends a request subsequent to "Location Updating Request"), the network will attach "Continue" to "Location Updating Accept" and initiate T3255. After receiving "Location Updating Accept", MS stores LAI, terminates T3210, restarts the attempt counter, and sets the status in SIM as Updated. If what contained in the message is IMSI, MS will delete the corresponding TMSI stored in SIM. If the message contains TMSI, MS will store it in the SIM and send "TMSI Reallocation Complete" to the network. If neither of them can be received, MS will delete the original TMSI stored in SIM. If the LAI or PLMN identifier in "Location Updating Accept" is one of "Barred series", all of original input will be deleted. After that, MS will use "Continue" to direct it action. If this unit exists, and MS has the underway CM service request, it will send "CM Service Request" to the network.

3)

Location update denied by the network

If location updating is denied, the network will send "Location Updating Denied" to MS. After receiving this message, MS will terminate T3210, store the reject cause, activate T3240, enter location denied status and wait for the network to trigger RR connection release. 2-29



a) If the reject cause is IMSI unknown to HLR, invalid MS, invalid ME. MS will set the location updating status as Roaming not Allowed, and store it in SIM. Delete TMSI, stored LAI and ciphering SN and regard the SIM as an invalid one until MS powered off or SIM removed. b) If the reject cause is : PLMN not allow, location area not allow, international roaming not allowed in this location area. MS will delete any LAI, TMSI and ciphering serial key, reset the attempt counter, and set the update status as "Roaming not Allowed". If MS receives "domestic roaming not allowed in this location area", it will return to MM Idle and then implement PLMN selection instead of cell selection. Other situations will be treated as abnormal ones.

4)

RR connection release after location updating

After location updating, MS will set T3240, enter "wait for network command phase" and wait for the release of RR connection. If MS cannot receive RR connection release command from the network within a period of time (controlled by T3240), it will terminate RR connection. No matter RR connection is released by MS or the network, MS will enter "idle status".

5)

Abnormality at MS side

a) Access denial controlled by access level, unable to initiate location updating. MS camps on the current serving cell, and implements normal cell reselection. Try to initiate before denial status ends or cell changed. b) Random access delayed (after receiving Immediate Allocation Denied): unable to initiate location updating. MS stays in the selected cell and initializes normal cell selection. When changing, initialize location updating before T3122 timeout. c) Random access failed: activate T3213. Activate location updating after it times out. d) RR connection failure: terminate location-updating process. e) T3210 timeout: terminate location updating process and RR connection. f) RR released before normal termination: terminate location-updating process. g) Location update denied caused by other reasons: MS waits for RR connection release. For (d) ~ (g) and random access occurring for many times, MS will terminate T3210. When T3210 times out, RR connection will be canceled, and attempt counter adds 1. The action afterwards is decided by LAI and the record of the attempt counter: a) The update status is "Updated", the stored LAI equals to the one received from the previous cell, and the record of attempt counter is four. MS will maintain the "Updated" 2-30



status. The MM idle status after RR connection release is "Normal Service". MS stores the type of location updating. After RR connection release, T3211 will be activated. After T3211 timeout, MS will reinitiate location-updating process (adopting the stored type). b) If the update status is not "Updated", or the stored LAI is different from the one received from BCCH, or the record in the attempt counter is larger than 4. After RR connection release, MS will delete LAI, TMSI, ciphering SN in SIM, set the update status as "Not updated", and enter MM idle sub-status "Attempt update". If the record in attempt counter is smaller than four, T3211 stored in MS will be initiated during RR connection release, otherwise the stored T3212 will be initiated.

6)

Abnormality at NSS side

a) RR connection failure If the RR connection failure occurs successively when there is a common program, the network should implement according to the common program description. If RR connection failure occurs successively and there is no common program, the location updating process should be terminated. b) Protocol error If protocol error exits in "Location Updating Request", the network should return "Location Updating Denied". The reject cause is z

Mandatory information unit incorrect

z

Information unit not exist or unable to be realized

z

Invalid information unit content

z

Protocol error, not regulated

When these errors occurs, the network will initialize the process of channel release.

2.1.8 Access I. Circuit service access An MS can be either in "active" state or in "idle" state. In idle mode, MS is not allowed to implement any transmission. In the "dedicated/active" mode, the MS can make effective transmission to the network through an allocated channel. In idle mode, MS gives the access cause and analysis of the cause in the 8-bit information during access request, and gets the channel for access after channel allocation. If the network cannot select the suitable channel type with limited cause analysis, it will allocate an SDCCH by default. If there is no available channel during channel allocation, the network will notify the MS to implement access attempt after a period of time with the command "Immediate Assign Denied". After the channel

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activation via Abis interface, the network sends "Immediate Assign" to MS. After receiving "Immediate Assign", MS sets up a dedicated channel to the network with "Setup Indication" and enters active mode. After receiving the setup indication reported by the MS, BSC analyzes the contents of the setup indication, including the processing of MS class mark, power control record, and encryption information. Then BSC transmits the setup indication reported by the MS to MSC.

II. Packet service access When no PCCCH is configured in the serving cell, packet service is accessed on the CCCH. The BSC transfers the packet paging messages coming from the PCU to the MS on the PCH of the CCCH. The channel request message issued from the MS is transferred to the BTS via the RACH of the CCCH and then reported via the BTS to the BSC. If the channel request message is for packet access (corresponding to the MOC), the BSC will not process it and will transfer it to the PCU. At the same time, the BSC receives the packet immediate allocation message from the PCU, transfers it to the MS and completes the packet call access. If mobile channel request message is for Paging Response (corresponding to the MTC), the BSC will first allocate the DCCH and enter the active mode. On the reception of EST_IND of RR_INITIALITION_REQ message, the BSC will transfer it to the PCU. And it will receive the PDCH message of the PCU, and transfer it to the MS, completing packet call access. If the MS accesses packet service via the PCCCH, then the packet call process is transparent to the BSC. After receiving packet paging message, MS will initialize the process of uplink Temporary Block Flow setup, and then sends the paging response packet in data form to PCU via the air interface. PCU forwards the packet to SGSN. After receiving the paging response, SGSN is ready to transmit downlink data.

2.1.9 Paging Paging means that when a call is routed to the destination office, GSM/GPRS network initializes the call at the current location area or routing area of the called MS. Packet paging is mainly implemented at routing area, but location area is available. This is decided by SGSN. There are two types of paging, i.e. packet paging and circuit paging, which will be examined respectively below.

I. Packet service paging When there are downlink data that shall be sent to the MS, SGSN needs to initiate a packet paging call. The paging request message originated by the SGSN is sent through Gb interface to PCU, which converts it into the packet paging request of the air interface (Um interface) before sending. If the PCCCH channel is configured for the BSS system, the message will be sent on the PPCH directly. If PCCCH is not

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configured for the system, PCU will send the message via the Pb interface to the BSC, which sends it on the PCH. On receipt of the packet paging message, MS starts access procedure.

II. Circuit service paging 1)

Overview

When a call reaches the MSC where the subscriber is located, the MSC sends a paging message to all cells in that location area according to the registered location area of MS. In the GSM network, the concept of Location Area (LA) is introduced to reduce waste of resources. A LA contains a small group of cells. An MS belongs to a LA at specific time. The LA information is stored in VLR from which MSC can query them. A paging process is completed jointly by MSC, BSC and BTS as follows: When a call is routed to the serving MSC of the called MS, MSC first figures out the location area of MS, and then sends the paging message to all BSCs in this location area. The paging message contains the information that can be used to identify the subscriber (IMSI or TMSI). BSC determines which BTS to page according to the LA, and determines the paging channel of the MS according to the IMSI, and sends them to the BTS. BTS will transmit the paging message of the MS on the specified PCH. The configuration of the PCH can be changed as the traffic increases or decreases. The PCH configuration information of each cell must be notified to each MS in the cell. When the configuration changes, BSC must modify the broadcast messages accordingly so that the MS in the cell can wait on the specified PCH sub-channel to answer the paging message. To enhance the signaling efficiency, a group of paging request combinations, called paging group, can be sent together. A page is generally sent three times. When flow control is allowed, the BSC can automatically adjust the configuration of PAGCH. If the GPRS/GSM system runs in network operation mode 1 and there exists a Gs interface, the circuit paging of the GSM service can be sent on the GPRS channel. In other words, if an MS is GPRS-attached, its circuit paging shall go from MSC to SGSN and then to PCU through the Gs and Gb interfaces, and PCU will determine on which channel to transmit the paging. If the system is configured with PCCCH, the paging message of the circuit will be sent directly by PCU on the PPCH or PACCH channel. If the MS is already allocated to PDCH, it shall be sent by priority on the PCCH. If the MS is not allocated to the PDCH, it shall be sent on the PPCH.

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If the system is not configured with PCCCH, PCU transfers the paging message to BSC through Pb interface, which then transmit the paging message on the PCH. After receiving the circuit-paging message, MS accesses the RACH and starts the circuit connection setup process. MS will initiate the GPRS SUSPEND process to suspend the GPRS services and will not recover the GPRS service till the circuit is released.

2)

Paging mode

The GSM network defines three commonly used paging modes: z

“Ordinary” paging mode: The paging messages are only transmitted on the channel defined by PCH configuration and IMSI.

z

“Complete” paging mode: When a notice is given to an MS group in this mode, it indicates that the paging messages of this subscriber group might be transmitted on any PCH at the same time slot. When the PCH configuration is modified dynamically, this mode can be used to avoid the loss of paging messages.

z

“Spaced” paging mode: BSS attaches a group of paging messages to another paging channel for transmission. This is to avoid temporary overload. In other words, the MS that receives an “ordinary” paging on the paging channel N can receive the paging message on the paging channel N+2.

M900/M1800 BSS supports all the three paging modes: "ordinary" paging mode, "complete" paging mode and “spaced” paging mode. Therefore, in PAGCH channel adjustment due to traffic flow, subscribers in the serving cell will not lose the paging message. Once a paging message is received by MS, the access allocation and allocation initialization process is started. If an MS is GPRS-attached in network operation mode 1, circuit paging to this MS will go through Gs interface, Gb interface, and Pb interface, and reach the BSC by way of MSC-SGSN-PCU. Then, there are three possibilities that the paging message will be transmitted to the MS, which are described according to their priorities. z

If the MS has been allocated with a PDCH, the message is transmitted on the PACCH.

z

If the serving cell has been allocated with a PCCCH, the message is transmitted on the PPCH.

z

If the serving cell is not configured with the PCCCH, the message is transmitted on the PCH.

2.1.10 Immediate assignment I. Overview Immediate assignment is for the purpose of establishing the wireless connection, i. e. RR connection with MS at Um interface. When MS needs to set up a connection, the

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immediate assignment process will allocate a channel necessary for the signaling interaction of establishing this connection. This channel can be either a SDCCH or a TCH. Huawei BSC supports the immediate assignment of SDCCH and immediate assignment of TCH at the level of cell.

II. Technology description 1)

Channel request

The process of initialization is actually the process of random access. Whenever MS needs to set up connection with the network, it has to send a message to the network via RACH to request for a signaling channel. The network will decide the type of the channel to be allocated according to the channel request. This message sent via RACH is called Channel Request. In this message, there is only 8 bits of meaningful signaling message. In which, 3 bits are used to the minimum indication of the access cause (in Phase 1, the cause occupies only 3 bits; in Phase 2, due to concept of half rate, the bit occupied by the cause is not a fixed, and the maximum one can be 6 bit). Such as emergency call, location updating, response to paging or caller request, etc. In the case of network congestion, system can implement different processing (which type of call will be accepted or denied) to the channel request of different access purposes according to this rough indication, and allocate the most suitable channels for them. In this indication, due to the capacity limit of the channel, it is impossible to transmit all information to be transmitted, such as the specific cause of channel request, subscriber identity and the feature of mobile equipment (all transmitted in SABM) to the network. The other 5 bits is the identification code selected by MS at random (for Phase 1 standard). It is not used to notify the network about the MS's location but to enable the network to identify the request initialized by different MSs. After that, the network will send "Immediate Assign Command" (includes the information of the allocated channel) to MS. The identification code will be returned to MS in this message. MS judges whether the information is for it by comparing the identification code it sent and the one returned from the network. But it has only 5 bits, which can be used to differentiate 32 MSs simultaneously. Two MSs initializing calls simultaneously do not necessarily have the random identification codes different from each other. To further differentiate MSs initializing calls simultaneously, the response messages on Um interface are used as another reference. The channel request message is processed only within BSS. All MSs with SIMs belong to a level among Level 0~9. The access level is stored in SIM. MS can also belong to one of the 5 special access levels (Level 11~15). Such level is also stored in SIM. In BCCH system information, the information, such as the access levels and special access levels allowed by the network, and whether all MS or only those of special levels is allowed to initiate emergency calls, will be broadcast.

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If the setup cause requested by MM is not emergency call, then only when MS belongs to the access level or special access level, can its access be grated. If the setup cause requested by MM is emergency call, then only when all MSs in the cell are allowed to initialize emergency call, or belongs to the allowed special access level, can their access be grated. Since the network cannot control the access time of MS, the event of two MSs contending for the same RACH timeslot will inevitably happen in the areas with heavy traffic. This is called the collision. The collision leads to two results: the network will receive a burst level from this timeslot obviously higher than the other. In this case, the network will process the random access request with higher level. The other one is that the network can receive neither of them due to their mutual interference. With the increase of traffic, the possibility of loss of message due to collision will become higher. This will become the major problem of network capacity. Therefore, it is necessary to introduce the mechanism of retranslating channel request. MS figures out that it allowed to transmit "Channel Request" via RACH for at most M + 1 times with the following methods: z

The timeslot No. Between the assign process and a "Channel Request" (not including the timeslot containing the information itself) is selected at random from {0, 1 MAC (T, 8)-} with the same probability.

z

The timeslot No. between the two consecutive "Information Request" of MS is selected at random from {S, S + 1, , S + T – 1} with the same probability.

T is the parameter "Tx integer" broadcast on BCCH; M is "Max Retrans"; the value of S depends of the configuration of CCCH. See Table 2-4. Table 2-4 Value of Parameter S Tx

Non-combined CCCH

Combined CCCH/SDCCH

3, 8, 14, 50 4, 9, 6 5, 10, 20 6, 11, 25 7, 12, 32

55 76 109 163 217

41 52 58 86 115

If the immediate assign command is not received even after Max Retrans, MS will return to idle mode. After transmitting initial channel request, MS will activate T3120 and stay on the entire downlink CCCH (to receive answer) and BCCH. When T3120 times out while RACH retransmission times has not exceeded "Max Retrans", MS will retransmit the channel request message containing a new random reference, and activate T3120 with a new value.

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When T3120 times out, and the Max Retrans is reached, MS will activate T3126, and then wait for a period of time and allow network to give up. If no network response received after T3126 timeout, MS will give up request attempt and perform cell reselection.

2)

The allocation of the initial channel

After correctly decoding the Channel Request of MS, BTS will send Channel Required to BSC via Abis interface. This message contains important attachment information and the estimation to TA that is important to activating timer advance control. After receiving this message, BSC will select a corresponding idle channel for MS according to the judgement to the existing radio resources. However, the availability of the allocated channel and the related terrestrial resources is to be acknowledged with the response from BT. This process is realized by sending "Channel Active" from BSC to BTS to query the availability of corresponding terrestrial resources (e. g. transmission circuit). This message indicates all properties needed in activating the channel, including channel type, working mode, physical feature and initial lead. When the corresponding resources are ready, BTS will return "Channel Active ACK" as a response to BSC. a) Immediate assignment After BSC receive Channel Active ACK from BTS, will send Immediate Assignment or Extended Immediate Assignment to allocate dedicated signaling channel for MS in the non-acknowledge mode, via the CCCH for MS receiving Channel Request. Immediate Assignment contains the assignment information of only one MS, while Extended Immediate Assignment contains the assignment information of two MSs. BTS can send Immediate Assignment or Extended Immediate Assignment on any message block of downlink CCCH. Therefore it is necessary for MS to monitor all information block on CCCH. The allocated channel type (TCH or SDCCH, channel mode is set as signaling) is decided by the carrier. Normally, if there is an idle SDCCH available that can satisfy the access request, BSC will allocate SDCCH. The process of requesting for SDCCH connection includes location updating, IMSI detach, supplementary service, short message at non-session status and services only supported by SDCCH. MS initializes access request, and BSC allocates a SDCCH for this call. This channel seizes 1/8 sub-timeslots of a timeslot. The signaling interaction necessary for call establishment is implemented on that channel. The signaling flow of SDCCH immediate assignment is illustrated in

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Figure 2-7.



BTS

MS Channel Request

MSC

BSC Channel Required Channel Active Channel Active ACK Immediate Assignment

Immediate Assignment SDCCH: SABM SDCCH: UA

Establishment Indication

Complete Layer3 Informaiton

SDCCH: Authentication Request SDCCH: Authentication Response SDCCH: Ciphering Mode Command

Encryption Command

SDCCH: Ciphering Mode Complete SDCCH: Setup SDCCH: Call Proceed

SDCCH: Assignment Command TCH: SABM TCH: UA TCH: Assignment Complete TCH: Alert TCH: Connect TCH: Connect ACK

Channel Active Channel ACK Assignment Command

Ciphering Mode Command

Assignment Request

Assignment Complete

Figure 2-7 Immediate assignment If TCH has been allocated before immediate assignment, there is no need to reallocate TCH during the process of assignment. Mode conversion process can be used to change the function of TCH from signaling transfer to voice transmission. Signaling flow of TCH immediate assignment is illustrated in Figure 2-8.

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Chapter 2 BSS Functions BTS

MS Channel Request

MSC

BSC Channel Required Channel Active Channel Active ACK

Immediate Assignment TCH: SABM TCH: UA

Immediate Assignment Establishment Indication

Complete Layer3 Informaiton

TCH: Authentication Request TCH: Authentication Response TCH: Ciphering Mode Command

Encryption Command

Ciphering Mode Command

TCH: Ciphering Mode Complete TCH: Setup TCH: Call Proceed

TCH: TCH:

Mode Modify Mode Modify ACK Channel Mode Modify Channel Mode Modify ACK

TCH: Alert TCH: Connect TCH: Connect ACK

Assignment Request

Assignment Complete

Figure 2-8 Immediate assignment Messages of immediate assignment or extended immediate assignment contain: z

Description of assigned channel.

z

Information field of channel request and abbreviated frame No. of the received channel request frame (abbreviated frame No. is a frame No. with narrow value range calculated from the TDMA frame No. received by BTS during channel request.)

z

Initial lead; Start time indication (optional).

The random reference and abbreviated frame No. are directly related to the MS channel request. They are used to reduce the conflict of request among MSs. TA is the initial lead calculated from equalizing the channel request information received by BTS on RACH. MS figures out the next initial lead for transmitting according to TA. After receiving immediate assignment or extended immediate assignment, MS switches to the channel assigned by the network, sets the channel modes as signaling only and sends the SABM with information field via the allocated channel to establish the main signaling link.

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Immediate assignment or extended immediate assignment message, containing the start time and description of possible alternative channel, can be used to indicate the frequency change in the process. If the received immediate assignment or extended immediate assignment message contains only the description of the channel used after start time, MS will access to the channel during the time waiting for start. If it misses the time, MS will immediately switch to this channel after receiving the message. If the message contains the description of the channel used after indication time as well as that before the indication time, MS will access the channel after receiving the message. If MS is ready for access to the channel upon the indicated time, MS will first access to the channel used before the indication time, and switch to the one after the indication time when the time comes (new frequency series, MAIO and HSN). If MS is ready after the specified time it will access the channel after the indication time. If MS has already sent the channel requests for maximum allowed times RR entity will start T3126. After T3126 timeout, immediate assignment process will be terminated. If the random access program is initiated by MM, system indicates failure of random access to MM. After sending the first channel request message, MS starts to monitor the system message on BCCH as well as the CCCH timeslot corresponding to its paging group, i. e. immediate assignment command may appear in any CCCH message block in 51 multiframe. Therefore it is necessary for MS to monitor the entire CCCH block after sending channel request, i. e. decode the messages of the entire paging sub-channel for response from the network. If the network adopts FH, MS will decode MA with the CA got from BCCH system message. CA refers to all the frequencies used in the cell (including FH frequencies). MA refers to all FH frequencies used in the cell. b) Immediate assignment denied If there is no available channel for BSC to allocate, the network can send the immediate assignment denied message in non-acknowledge mode to MS via CCCH. The reject cause can be MSC traffic closed, radio resources shortage, TA value exceeding limit, channel activation no response and BSC traffic overload. But system does not specify the part on downlink CCCH for immediate assignment denied transmission. The message of immediate assignment denied contains request reference and waiting indication. After receiving Immediate Assignment Denied, as the response to one of the last three channel requests, MS terminates T3120, activates T3122 with the specified value and returns CCCH idle mode. MS cannot start RR connection attempt until T3122 timeout. MS is not allowed to initialize another call attempt except for emergency calls until

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T3122 timeout. Emergency call attempt can be established in the same cell before T3122 timeout as long as no "Immediate Assignment Denied" of RR emergency attempt received. It corresponds to the immediate assignment extension. In order to improve AGCH efficiency, the format of extended immediate assignment denied is introduced. The message of extended immediate assignment denied can contain information of rejecting at most four MSs. The value of the wait indication information unit (T3122) depends on the cell receiving this message. After T3122 timeout, MS will not respond to paging but sends "Channel Request" instead till MS receives "Paging Request". c) Signaling channel assignment overlap The system may have a slow response to the channel request of MS, which results in request retransmission. In this case, system do not know whether a channel request message is a retransmitted one, so it may send the immediate assignment command to the MS for multiple times. MS will use the channel in the first assignment message it decoded. The others are regarded invalid ones. But according to the specification, MS should receive the last three network response messages to the channel request. This is called allocation overlapping. It is possible to cope with CCCH congestion caused by to many overlapped allocations by reducing the retransmission of MS or shorten T3101. This measure can avoid the waste of system resources.

3)

Initialization message

After receiving immediate assignment command, MS will decode this message. If the random identification code and the abbreviated frame No. satisfy the requirement, MS will tune its transceiver equipment to the specified channel and start to transmit signaling according to TA specified by BSC and maximum transmitting power (defined in the parameter "MS TxPWR MAX CCH" in BCCH system broadcast message). The first task for MS on the allocated SDCCH/TCH is to send a SABM frame to establish asynchronous balance mode (service access point type: SAPI = 0) so as to establish signaling message link connection in acknowledge mode. In GSM specification, SABM has a signaling message, i. e. initialization message. On Um interface, SABM frame is a message requesting for the establishment of a multiframe response operation mode on LAPDm. This message contains the L3 service request message. The reason for different standards about standard HDLC is to guarantee the correctness of MS receiving. If two MSs send the channel requests with the same message content at the same (possible in the case of high load), BSS will repines to one of them only. While these two MSs can both be allocated with the same dedicated channel. To settle this problem, there should be a mechanism judging such contention. According to the specification, the cell will send a UA frame (no No. verification) with the content

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completely the same as that of SABM frame after the cell has received the SABM frame. MS compares it and the SABM information. If the content is completely the same, the access will proceed. Otherwise, it will give up this channel and repeat the immediate allocation process. Only when the consistency is guaranteed, will MS stay on the channel. According to different request causes, the initialization messages in SABM can be divided into four types: CM service request (call establishment, short message, supplementary service management), location updating request (generic location updating, periodic location updating, IMSI attach), IMSI detach and paging response. All these messages contain the identity of MS, detailed access cause and Classmark of MS (used to indicate some key features of MS, such as transmission power level, ciphering algorithm, short message capability and frequency capability). Upon receiving SABM frame, BTS will send a message "Establishment Indication" to BSC. On Abis interface, this message is used to notify LAPDm that the connection has been established. It is a response to the immediate assignment message. After receiving the indication message of establishment, BSC will send a L3 service request message (Complete Layer3 INFO) to MSC. To be specific, this message is Location Updating Request, CM Service Request, Paging Response and IMSI Detach. This message contains the SCCP connection request (SCCP CR), cause of CM service request (e.g. MO call, emergency call, location updating and short message service), ciphering key sequence No., LAC, CI, physical information of this MS (e.g. transmitting power level, ciphering algorithm support, pseudo-synchronous capability and short message capability) and the ID of MS. Although the MTP connection at An interface has been established before the session, there should still be a SCCP connection on L2 for each call. This establishment request message will be transmitted in the SCCP CR message via A interface. If the request is permitted, the first downlink message at An interface will be contained in the CC frame at SCCP layer. For SCCP layer, the exchange between CR and CC is the exchange between original reference address and destination reference addresses. For different calls, the same SPC may refer to different original addresses and destination addresses. If SCCP cannot be established, MSC will send the message SCCP Refused. The access ends at this step. The signaling link between MS and MSC has been established, MSC at this phase is able to control the transmission feature of the RR management, and BSS is in the status of monitoring transmission quality and ready for handover.

4)

Phase1 and Phase2 MS

BSC cannot differentiate whether a call is for voice, data or signaling completely according to MS establishment cause. In the case of Phase 2 MS, BSC can obtain the access request cause more detailed than that of Phase1 MS. For Phase 2 MS, BSC is able to recognize the information unit "Channel Needed" in the paging message. This

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information unit indicates whether the current channel is for voice/data or signaling. MS selects a suitable establishment cause to response according to its own capability. Huawei BSC supports the information unit "Channel Needed" in the paging message.

III. Parameter Huawei BSC controls the function of immediate TCH assignment with the switch of "Immediate assign TCH. The detailed configuration process, as well as the data table and parameters involved are listed below: [Cell/Modify Cell's Call Control Parameter/Modify Cell Call Parameter/Call Control] Parameter: Immediate Assignment of TCH If “Immediate Assignment of TCH” is set as “No”, this indicates that the function of immediately assigned TCH is disabled. All call access requests use SDCCH. If “Immediate Assignment of TCH” is set as “Yes”, this indicates that the function of immediately assigned TCH is enabled. For emergency call and call re-establishment, BSC will preferentially assign TCH for them. If no idle TCH is available, the BSC assigns SDCCH for them. For other the channel access request of calls, SDCCH will be preferentially assigned and then TCH.

2.1.11 Assignment I. Overview BSS switches MS to TCH by means of assignment. Normally, the assignment is finished at the cell where the call is initialized. Huawei BSC supports the function of direct retry, which can assign MS to other cells.

II. Working principle After MS initializes service request, BSC will assign the MS to TCH by means of the assignment process. If BSC figures out that there is idle TCH in the cell where MS initialized the call, it will assign the MS to that TCH. Huawei BSC provides two algorithms of channel selection: "Huawei Channel Algorithm I" and "Huawei Channel Algorithm II". The channel allocation algorithms of Huawei guarantee that the currently allocated channel is the best one. If BSC has already assigned the MS to TCH during immediate assignment, it will not assign the MS to a new TCH, but to the old one. If there is no idle TCH in the cell of the MS, the function of directed retry can be used to assign the MS to other cells with idle TCH and go on with the service. BSC can select

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the best cell among the adjacent cells with the measurement reports as the destination cell in directed retry.

III. Parameter BSC decides whether to use the function of directed retry with the parameter "Directed retry permitted". The detailed data table and parameters involved are listed below: [Cell/Modify

Cell's

Call

Control

Parameter/Modify

Cell

Call

Control

Parameter/Call Control] Parameter: Directed Retry Perm. If parameter “Directed Retry Perm” is set as “No”, this indicates that the cell does not enable function of directed call retry. During assignment, if the current cell has no idle TCH, the assignment failure is returned. The reason is "No available radio resource". If this parameter is set as “Yes”, this indicates that the cell uses the function of directed call retry. During assignment, if the current cell has no idle TCH, BSC will try to assign MS to adjacent cells.

2.1.12 Authentication One of GSM system's advantages comparing with analog system is security system. It has the following improvements: on access network: AUC authenticates the subscriber; on radio path: communication information ciphering; EIR identifies the mobile equipment; IMSI is protected by TMSI; SIM is protected with PIN. The authentication process is one of the common processes of Mobility Management (MM) process. The common processes of MM includes authentication process, identification process, TMSI reallocation process and IMSI detach process initialized by MS. Other common processes will also be mentioned in this chapter.

I. Authentication process 1)

Authentication triplet

Authentication and ciphering process is realized with the triplet allocated by the system. The triplet is generated in the Authentication Center (AUC). After subscribing to GSM service, each MS will be allocated with a MSISDN and IMSI. IMSI is written to the SIM of the subscriber with SIM writer. Together with this IMSI, the authentication key Ki uniquely corresponding to the IMSI is also stored in the SIM and in AUC. In AUC, there is a pseudo-random code generator used to generate a unpredictable pseudo-random code RAND (randomly selected from 0~2128-1). The GSM specification also defines the algorithms of A3, A8 and A5 used in authentication and ciphering process. In AUC,

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SRES is generated by processing RAND and Ki with A3, and Kc is generated by processing RAND and Ki with A8. RAND, Kc and SRES make up the triplet, which will be transmitted to HLR and be saved in the database of that subscriber. Normally, AUC transmits five triplets at a time to HLR. HLR can store 10 triplets. When MSC/VLR requests HLR for triplet, HLR will transmit five triplets to it. MSC/VLR uses one triplet each time. When there is two triplets left, it will request HLR for triplets again. Below is the detailed introduction to the process of parameter transference.

2)

Authentication process

There are two purposes for authentication: one is to check whether the identification provided by MS is effective, and the other is to allocate a new ciphering key for MS. After the establishment of RR layer between MSC and BSS, the network is able to decide whether to trigger the authentication process to verify the identification of the mobile subscriber. Whether to trigger the authentication process depends on Kc at network side (stored after the previous processing of the MS service) is the same as that stored in the MS accessing currently. If they are the same, system will skip authentication and go to ciphering process with Kc stored in MS. Otherwise, Kc has to be calculated with authentication process. To enable the ciphering in the case of initializing RR connection without authentication process, the concept of ciphering key sequence number is introduced. It is called CKSN in the specification. CKSN is stored in SIM as well as in MSC/VLR together with Kc and is processed by the network. In the first L3 message (e. g. location updating, CM service request, paging response, MS will indicate the CKSN to the network. CKSN = 0 means no Kc allocated. The calculation of Kc is illustrated in Figure 2-9.

RAND

Ki

A8

Kc

Figure 2-9 Kc calculation After receiving Complete Layer3 INFO, MSC will send "Process Access Request" to VLR for authentication and ciphering. VLR will return the message of "Process Access Accepted". And then, MSC/VLR will send the message “Authentication Request” to MS to trigger the authentication process. At the same time, T3260 will be activated. "Authentication Request" contains a RAND and a CKSN. RAND is 128 bit. MS will send

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the message "Run GSM Algorithm" to SIM after receiving this message. A 32-bit SRES will be generated by processing Ki stored in SIM and this SRES with A3. Meanwhile, a 64-bit Kc is calculated by processing Ki and RAND with A8. MS will store it and CKSN to the suitable position SIM for the future activation of ciphering transmission. If RR connection exits, MS should respond to the authentication request message. MS will sends the SRES to the network with the message Authentication Response. After receiving "Authentication Response", the network will terminate T3260 and check the validity of the SRES. Since Ki is stored in VLR or HLR as a subscriber data, the A3 and A8 will also be carried out to generate a SRES and Kc and store them in VLR. System compares these two SRESs. If they are the same, the authentication will succeed and access to network will be grated, see Figure 2-10. And after that MSC proceeds ahead with the ciphering process. If they are different, authentication failed, and system will reject the access of the MS. The authentication process ends at this step.

AUC

RAND

Ki

Ki

RAND

A3

A3

Equal

SRES

SRES Network

MS Authentication succeeded

Figure 2-10 Authentication algorithm A3 and A8 can be executed either in MSC/VLR or in HLR/AUC. But it will be complicated for MSC/VLR, but simple for HLR/AUC for it stores Ki. Furthermore, it is a better way to achieve security and roaming. However, it causes the increase of signaling traffic between HLR and MSC, for each authentication, HLR/AUC will send RAND, SRES and Kc to MSC/VLR.

3)

Unsuccessful authentication

If the authentication failed, the network can use the subscriber's identification.

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a) MS uses TMSI If MS uses TMSI, the network can initiate the identification process. If the TMSI does not correspond to the IMSI, authentication will be restarted. b) MS uses IMSI If MS uses IMSI or the network decides not to initiate identification program, then "Authentication Denied" will be sent to MS. After sending this message, all MM connection in process will be released, and then the network will initialize the RR connection release process. After receiving "Authentication Denied", MS will set the status of SIM as "Roaming Denied", and delete the existing TMSI, LAI and CKSN, and regards SIM invalid until MS powered off or SIM removed.

4)

Abnormality handling during authentication process

a) RR connection failure If RR connection is detected before receiving "Authentication Response", the network will release all MM connection and terminate all running MM special process. b) T3260 timeout If T3260 timeout, the network will release RR connection. In this case, the network will terminate the authentication process and all ongoing MM process, releases all MM connection and initializes RR connection process.

2.1.13 Ciphering I. Overview The feature of wireless transmission has a negative effect on the security and interest of the subscribers. The analog mobile communication has always been the victim of interception and misappropriation. The digital transmission of GSM guarantees excellent security. The encryption function deals with the security for information exchange between MS and BTS, including signaling information and user information. It is up to the radio resources management to decide whether to adopt the encryption mode or not. The encryption function is implemented in the BTS to encrypt user data. The related parameters must be sent to the encryption program. The ciphering key Kc, generated by AC and stored in the MSC/VLR, is sent to the BTS before encryption starts.

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II. Technical description In order to achieve a general understanding of the encryption/decryption process of GSM, we will examine it here from three perspectives: TMSI, encryption process and Kc generation.

1)

TMSI (Temporary Mobile Subscriber Identity)

IMSI is the identity for mobile subscriber. Due to the importance of IMSI it is not transmitted on the radio link repeatedly. VLR allocates a TMSI to the subscriber during the MS registration. Afterwards TMSI is used in place of IMSI to protect the IMSI for the sake of subscriber security. The relation between TMSI and IMSI is not fixed. TMSI is valid only in a VLR area.

2)

Ciphering and deciphering processes

a) Initializing ciphering mode setting After authentication process, MSC will send "Ciphering Mode Command" to BSC. This message contains Kc. BSC sends Ciphering Mode Command to MS to indicate whether ciphering is necessary, and if needed, which type of dedicated resources are to be adopted. b) Ciphering mode setting complete Once MS receives the valid "Ciphering Mode Command", it will send the Kc stored in SIM to the mobile equipment. The valid "Ciphering Mode Command" are as follows: z

"Initialize Ciphering" is indicated when MS is in the status of "Non-ciphering".

z

"Non-ciphering" is indicated when MS is in the status of "Non-ciphering".

z

"Non-ciphering" is indicated when MS is in the status of "Ciphering".

MS will regard the "Ciphering Mode Command" of other type received as an incorrect one. It will respond with "RR Status", and the cause value is "Error: protocol not defined". After receiving the indication of "Ciphering Mode Command" and the ciphering process, MS should initiate the Tx and Rx in ciphering mode. After MS has activated the actions of "Ciphering Mode Command", it will returns "RR Ciphering Mode Complete" to the network. If the field "Ciphering Response" in the information unit of ciphering response message "IMEI shall be included", then MS will include its IMEI in "RR Ciphering Mode Complete". After receiving "Ciphering Mode Complete", the network will initialize the transmission in ciphering mode. BTS and MS carry out the encryption/decryption of the radio path. The process of encryption and decryption is shown in Figure 2-11.

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（TDMA（

Kc

Kc

A5

（TDMA（

A5

Data flow

Data flow

Mod 2+1

Mod 2+1

TX

RX

Data not ciphered

Data not ciphered

Figure 2-11 Process of ciphering and deciphering The algorithm for generating the ciphering code is called A5. Using the Kc consistent in MS and the network (64 bits) and the current pulse string frame number (22 bits), it calculates result is the 114-bit ciphering sequence (the data flow in Figure 2-11), which then performs "exclusive or" operation together with the burst 114 bit (the data not ciphered in Figure 2-11). The frame No. code consists of three values (T1, T3 and T2). If the communication lasts as long as the period of hyper frame (about 3 and half hours), the ciphering sequence will appear repetitiously. On uplink and downlink, the network uses the same ciphering sequence. For each burst, one sequence is used for the ciphering in MS and the deciphering sequence of BTS, the other one is for the ciphering of BTS and deciphering of MS. According to the system configuration, MS can decide whether to report the processing power of MS after Authentication Request. The name of this message is Classmark Change. Its content is the same as that in the establishment indication, and is more detailed in the description of ciphering algorithm at MS side. The establishment indication states whether A5/1, A5/2 and A5/3 are supported, while the Classmark Change further states whether A5/4~A5/7 are supported. After receiving this message, the network first response with the message MS PWR CTRL to describe the power range available for MS and the transmitting power of the TRX corresponding to this MS.

3)

Generation of Kc

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RAND generator RAND

Ki

Ki

A8

A8 Kc

Kc storing KC

storing KC

MS

NSS

Figure 2-12 Generation of Kc Ciphering key (Kc) is produced by A8 algorithm as shown in the Figure 2-9. Here Ki is a user authentication key. After registering in the network, a subscriber obtains the Ki, which is stored in the authentication centre and the SIM card. The MS and the network use the same Ki and random number (which is generated by the network and transmitted to the MS) so that the same Kc can be obtained.

III. Parameter Condition: MSC support ciphering, all kinds of ciphering algorithm and authentication in service access procedure. Huawei BSS supports both A5/1 and A5/2. The data configuration involved is as follows:

1)

BSC [BSC/Modify BSC Interface Phase Flag] A Interface Version: GSM_Phase_2 Um Interface Version: GSM_Phase_2 Abis Interface Version: GSM_Phase_2

2)

BSC [Cell/Modify Cell's system information/Modify Cell Configuration Data]

Encryption Algorithm Setting: Encryption Not Support, A5/1, A5/2

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Note: 1) This manual only introduces the related parameters. All data configuration of BSC is realized with auto data configuration console. For details, see M900/M1800 Base Station Controller Data Configuration Manual. 2) For the configuration of ciphering algorithm, it is recommended select ciphering option not selected for BSC. This is because BSC software selects ciphering algorithm from the intersection of algorithms allowed in MSC data configuration, algorithms allowed in BSC data configuration and algorithms supported by MS. If the intersection contains multiple algorithms, the one with the largest algorithm No. will be selected. The meaning of algorithm No.: 1 (No ciphering), 2 (A5/1), 3 (A5/2)… 8 (A5/7).

2.1.14 DTX I. Overview In the process of communication, only 40% of time of the mobile subscriber is engaged in session. Most of the time is not engaged in the transmission of voice message. If all information during the non-session period is sent to the network, not only the system resources are wasted, but also the intra-system interference will be worsened. To tackle the above problems, GSM adopts Discontinuous Transmission (DTX). When there is no session, the transmitting channel is closed to lower the interference level and improve the system efficiency. In addition, this function also saves the power consumption of MS. When transferring data, this function cannot be applied. DTX affects the transmission of TCH frame. There are two types of voice transmission in GSM system: one is normal mode, the voice stream is encoded as 13kbit/s regardless of the MS's session status, and the other is DTX mode. Only one mode can be selected in one session. When both parties of the communication are GSM subscribers, DTX will have a negative effect on the communication quality. Therefore, DTX mode is not allowed on the occasion.

II. Technologies description If DTX mode is adopted, the voice coding of 13 kbit/s will be used in voice activation period, and that of 500 bit/s (for transmitting the feature parameter of comfort noise only) in non-voice activation period.

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MS

IRAU VAD MSC

Voice coding

Voice frame replacing

Information DTX Processing

SP Information

BTS

SID

VAD: Voice Activity Detection TAF: Time Adjust Flag

BFI

DTX

SID

Processing

TAF

SID: Silence Indicator BFI: Bad Frame Indication

Voice decoding CN

CN: Comfort Noise SP: Speech Flag

Figure 2-13 Principle of DTX

1)

Voice Activity Detection

Voice Activity Detection (VAD) indicated the time to use DTX. When DTX is activated, it is used to detect whether voice or noise is transmitted. VAD algorithm and voice coding/decoding algorithm is closely related. This algorithm judges whether voice or noise is contained in the output frame by comparing the filter signal and the configured threshold. It also indicates whether the auxiliary bit of this frame is transmitted. This judgement is based on the principle of the energy of noise being lower than that of voice. VAD generates a group of threshold values in each voice block of 20 ms for judging whether the next voice block of 20 ms is voice or noise. If the background noise is too loud, it will be transmitted as the voice signal.

2)

Silence descriptor

The noise coding process is similar to that of voice coding process: after sampling and quantization, each 20 ms will be encoded as a noise block. The encoded noise block will also become a block of 260 bits like the voice block. This is a Silence Descriptor (SID). SID frame is applied to channel encoding, interleaving, ciphering and modulating like voice frame to become a field containing noise message and be transmitted in the 8 consecutive bursts. A complete SACCH message block on TCH has four 26-multiframe (480 ms). To enable the peer end to differentiate the voice frame and SID frame, these 8 consecutive bursts are fixedly arranged at the beginning of the third multiframe. Other frames (excluding SACCH) within the same period will not be used to transmit any message.

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Caution 1) The SID frame generated from 20 ms noise block completes the process of interleaving together with the SID frames before and after it. 2) The first SID frame completes the interleaving together with the voice frame before it and the SID frame after it.

The DTX functions are optional, independent in the direction of uplink/downlink and based on the control unit of a cell. The uplink and downlink DTXs are two processes independent to each other, and are activated by system parameters respectively. There measurement methods in GSM system: z

Global measurement: average the levels and quality of the 100 timeslots within the entire period (totally 4 TCHs of 26-multiframe, idle frame not included)

z

Partial measurement: average the levels and quality of 12 timeslots, including 8 consecutive TCH bursts and 4 SACCH bursts containing measurement report. To ensure the consistency, no matter whether the uplink or downlink activates DTX, BTS and MS should both complete these two types of measurement. Since each SACCH measurement report of BTS and MS indicates whether DTX is used, BSC can select whether to use global measurement or partial measurement to judge according to according to the measurement report.

Note: No matter whether DTX is used, the uplink and downlink will proceed with global and partial measurement.

DTX, which is applicable for voice and non-transparent data transmission, involves the operations of MS and TRAU. No matter whether DTX is used or not, the decision-maker is MSC and the executor is BSC.

III. Parameter [Cell/Modify Cell's System Message/Modify Cell System Message/Bsic Data] Parameter: Discontinuous Transmission Indication

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2.1.15 Frequency hopping I. Overview The purpose of frequency hopping (FH) is for obtaining better security and anti-interference capability. There are fast FH and slow FH. Fast FH means that the change rate of frequency is faster than modulation rate of signal. In GSM system, it is required that the frequency should remain unchanged within a burst period. Therefore, the FH in GSM system belongs to slow FH. It involves frequency diversity and interference diversity technologies. The frequency occupied by channel in the Um interface of GSM system is changed regularly. The frequency of changing frequency is about 217 times per second. The FH can avoid the attenuation caused by multi-path transmission and same frequency interference, and improve the average C/I of the interference restriction system (especially in cities), thus greatly improving the quality of session, strengthening the capability of high-density multiplexing and increasing the system capacity. Adopting FH can improve the transmission quality of the slowly moving MS by 6, 5 dB. Besides, FH can also improve the security of communication.

II. Technology description 1)

FH modes

FH means that the carrier containing meaningful information hops under the control of a sequence. This sequence is called frequency-hopping sequence (HSN). An HSN is an array of all frequencies in a frequency set uniquely defined with HSN, Mobile Allocation Index Offset (MAIO) and Frame No. (FN) by using certain algorithms. Channels on different timeslots (TN) can use the same HSN. Different channels on the same timeslot in the same cell should use different MAIOs. FH mode can be divided into frame FH and timeslot FH by the concept of time-domain. z

Frame FH: Frequency changes for each TDMA frame. In the mode, each carrier can be regarded as a channel. The TCH of the TRX which bears BCCH cannot be used for FH while other different TRXs should have their own MAIO. This is the expiation of timeslot FH.

z

Timeslot FH: Frequency changes for each timeslot of each TDMA frame. The TCH of the TRX which bears BCCH can be used for FH. But currently it is realized only on the occasion of base band FH.

FH mode can be divided into and into RF FH and base band FH by carrier realization mode. z

RH FH: Both Tx and Rx can be both used in FH. In a cell, the number of FH frequencies engaged in FH can be larger than the number of TRX.

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The RF FH of the M900/M1800 BTS is enabled through real-time switchover between two frequency synthesizers. There are two advantages for this implementation: first, lower speed requirements of the frequency synthesizer can be practical, i. e. the speed requirements are easier to implement; second, one of the two frequency synthesizers serves as the standby when there is no FH to enhance system reliability. Huawei BTS adopts dynamic loop bandwidth and Ping-Pong handover to solve the inconsistency between fast FH and signal quality, and realize the unrestricted FH in GSM 900 bandwidth of 25 MHz and DCS 1800 bandwidth of 75 MHz. All FH indices satisfy the requirements in GSM protocols. Dynamic loop band width technologies: local oscillation signal is mainly decided by reference clock (phase discrimination frequency), voltage controlled oscillator and loop bandwidth, etc. The phase noise of local oscillation within the loop bandwidth is decided by reference clock, and that beyond loop bandwidth is decided by collage controlled oscillator.

During the operation of Huawei BTS, loop bandwidth needs to be dynamically adjusted along with the needs of system. If the system is not in the working status, loop bandwidth changes back to best bandwidth, so that the output signal can be the best, and the best performance of the system can be guaranteed. Ping-Pong handover: Two identical oscillators are designed on the circuit. A switch is in charge of selecting between these two oscillators. When one oscillator is working, the other one locks on the next frequency quickly. Switching to another oscillator is realized with a switch between two timeslots. This avoids the instant performance worsening at the beginning and end of the timeslot. z

Base band FH: Each transmitter works on a fixed frequency. Tx is not involved in FH. The transmitting FH is realized by switching the base band signal. Rx is involved in FH. Therefore the number of FH frequencies in a cell cannot be larger than number of the TRXs of the cell. When a TRX is faulty, the system can skip it when implementing FH.

Huawei BTS adopts the technology of (FH_BUS), which implement FH on the basis of timeslot exchange. Each transmitter is tuned to a fixed frequency, and has a fixed ID. The coder of transmitter encodes the downlink signal to convert the data to burst format. It calculates the channel (i. e. TRX) to be modulated for the burst according to FH algorithm, and adds the attached information related to power control to generate a special data packet. The coder transmits the data packet periodically (sub-timeslot). Modulator checks the TRX ID of the data packet from each sub-timeslot. If the TRX ID is different from the local TRX, it will receive that from the next sub-timeslot. If the TRX IDs are the same, it will accept the data packet, and delay for a timeslot and then transmitted to the air interface. Base band FH has a very high requirement on the real-time identification of the ID of TRX. Huawei base band FH technology realizes fast and reliable TRX ID identification on the basis of the ASIC.

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Huawei BSS realizes the base band FH at timeslot level, RF FH at timeslot level, base band FH at frame level and RF FH at frame level.

2)

FH algorithm

Parameters involved: z

CA: Cell allocation table, i. e. the collection of frequency ID used in the cells.

z

FN: TDMA frame No., broadcast on the synchronous channel. BTS and MS achieve synchronous with FN (0~2715647).

z

MA: the radio frequency ID collection for MS FH, a subset of CA. M contains N frequency Ids, 1 ≤ N ≤ 64.

z

MAIO: Mobile Allocation Index Offset (0~N-1). During communication, the radio frequency ID adopted on air interface is an element in MA. MAI (Mobile Allocation Index, 0~N-1): indicating an element in MA, In other words, the frequency actually used is decided by MAI. MAIO is an initial offset of MAI. Its purpose is avoid multiple channels contends the same carrier.

z

HSN: FH serial No. (generator) (0~63). If HSN = 0, it will be cycle FH, and if HSN ≠ 0, it will be random FH.

The process of calculating the actual working frequency on each FH timeslot is as shown in Figure 2-14.

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MAI (m0~mN-1)

MAIO (0~N-1)


HSN (0~63)

FN T3(0~50)

NBIN bit

6bit

FN T1(0~2047)

FN T2(0~25)

11bit

6bit

T1R= T1 MOD 64

5bit Represent in 7 bit

6bit

7bit

Exclusive OR 6bit Addition 7bit Look-up table 7bit Addition 8bit T=T3 mod 2^NBIN

M'=M mod 2^NBIN NBIN bit

NBIN bit N

S=(M'+T) mod N

M'
Y

S=M'

NBIN bit MAI=(S+MAIO) mod

N

NBIN bit RFCN=MA(MAI)

Figure 2-14 FH algorithm In the figure above: z

MAI = (S + MAIO) MOD N (S is the result after calculating the frame No.)

z

RFCHN = MA (MAI)

z

mod: MOD

z

^: power

z

NBIN: INTEGER(log2N + 1)

z

Table: see Table 2-5.

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Table 2-5 "Table" meaning table Address 000~009 010~019 020~029 030~039 040~049 050~059 060~069 070~079 080~089 090~099 100~109 110~113

3)

Content 48 0 101 80 55 87 82 77 117 16 91 129

98 64 47 34 111 19 58 108 114 49 15 99

63 25 118 127 75 3 40 122 4 7 21 17

1 81 85 13 38 68 107 37 90 79 24 123

36 76 18 6 109 110 32 60 43 119 46

95 59 56 89 71 26 5 66 52 61 39

78 124 96 57 112 33 106 121 53 22 93

102 23 86 103 29 31 92 42 113 84 105

94 104 54 12 11 8 62 51 120 9 65

73 100 2 74 88 45 67 126 72 97 70

Concept synchronous cell

The concept of synchronous cell plays an important role in planning FH strategy and lowering intra-network interference. BTS and MS achieve synchronization through their agreement on FN. In synchronous cell, since the FNs of all TRXs are completely the same, it is possible for different FH groups to use the same HSN. Adjust MAIO to avoid the collision between cells and the adjacent frequencies of the same cell.

III. Parameter FH data configuration sequence: CAξMAξHSNξMAIO Four parameters of FH algorithm: MA = {f1, f2,↑,fN}, HSN, MAIO, FN The data tables and parameters involved in configuration are detailed below. [Cell/Modify Cell's FH Property/Modify Cell FH] Parameter: FH Mode Parameter: FH Group Assignment Table [Cell/Modify Cell's FH Property/Modify Cell FH /Configure MA Group] Parameter: MA Frequencies Assigned Parameter: Current MA Group No. Parameter: FH Sequence No. Parameter: Training Sequence No. (TSC)

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2.2 Extended Functions 2.2.1 Handover I. Overview Handover is a very important function in a cellular mobile communication network. Handover enables the continuous session of subscribers while moving around different cells. Besides, handover can also adjust the traffic of the cell, thus optimizing the overall performance. The overall handover process is implemented in the MS, BSS and MSC. Measurement of radio subsystem downlink performance and signal levels received from surrounding cells, is made in the MS. These measurements are send to the BSS for assessment. The BSS measures the uplink performance for the MS being served and also assesses the signal level of interference on its idle traffic channels. Initial assessment of the measurements in conjunction with defined thresholds and handover strategy may be performed in the BSS. Assessment requiring measurement results from other BTS or other information resident in the MSC, may be performed in the MSC. In the above handover process, handover decision algorithm is the most important part because it determines the service quality and frequency efficiency.

II. Technology description Huawei handover algorithm includes cell sequencing and handover judgements.

1)

Cell sequencing

The cell sequencing can be divided into two parts: basic sequencing and network feature adjustment. a) Basic cell sorting. Huawei handover algorithm adopts the M principle and K principle based on level comparison in stead of L principle based on path loss. With M principle and K principle, the serving cell and all adjacent cells are sequenced according to their levels to obtain the standby cell list on the basis of levels. M principle: check whether the downlink receiving level of the adjacent cell is higher than the minimum receiving level while taking uplink and downlink balance compensation. Only the cell with receiving level lower than the minimum receiving cell, i. e. RxLEV > MS Rx MIN + MAX (0, Pa), can enter the standby cell list. In that formula Pa = MS TxPWR MAX - P. z

RxLEV is the MS receiving level for this cell.

z

MS Rx MIN is the minimum receiving level of MS required by the cell.

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z

MS TxPWR MAX is for restricting the maximum transmitting power of MS.

z

P is the maximum transmitting power of the MS.

K principle:

K _ rank (n ) = RxLEV (n ) − RxLEV (o ) − K _ BIAS (o, n ) K _ BIAS (n ) = RxSUFF (n ) − (RxSUFF (o ) − KOFFSET − KHYST )

After removing KOFFSET (offset) and KHYST (Hysteresis). The formula of K sequencing:

K _ rank (n ) = (RxLEV (n ) − RxSUFF (n )) − (RxLEV (o ) − RxSUFF (o )) In this formula, (RxLEV(n) – RxSUFF(n)) shows the difference between the adjacent cell receiving level RxLEV (n) and adjacent cell minimum receiving level threshold RxSUFF (n). (RxLEV(o) – RxSUFF(o)) shows the difference between the serving cell receiving level RxLEV(o) and serving cell minimum receiving level threshold RxSUFF(o). These two differences decide the position of an adjacent cell in the standby cell list. z

RxSUFF(n) is adjacent cell minimum receiving level threshold

z

RxLEV(o) is serving cell receiving level

z

RxSUFF(o) is serving cell minimum receiving level threshold

Note: The purpose of hysteresis is to avoid Ping-Pong handover. The communication may be handed over back and forth due to the unstable signal at the edge of the cells. This causes much increase in the load to the system. Applying hysteresis is like enlarging the coverage radius of the serving cell while shortening the coverage of the coverage radius of adjacent cell. In this way, handover will not be easily triggered, and the Ping-Pong handover can be eliminated.

b) Adjustment according to network features Network feature adjustment uses the network information except for the power level to decide the position of each cell in the standby cell list, thus providing the ultimate standby cell list for handover judgement. z

Implemented according to the load of the cell. The cell with less load has the higher priority.

z

Implemented according to whether BSC/MSC is the same. The cell controlled by the same BSC or MSC has the higher priority.

z

Implemented according to the layer and level of the cell. The cell of lower layer or level has the higher priority.

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With basic sequencing of cell and network feature structure adjustment, it is possible to have a best cell list on broad sense. In other words, regardless of the cause that triggers handover, a cell ranking first in the list is not a result of certain processing based on certain criteria. c) Layers and levels of the cell Hierarchical classification of the network can fulfill the demands of both coverage and hot spot traffic. This is a mandatory function to be realized. Normally, the macro cell settles the problem of coverage, while the micro cell tackles the problem of hot spot traffic. The basic frame of Huawei network hierarchy has four layers. They are Umbrella, Macro, Micro and Pico. In the multiband network, the top layer GSM 900 is usually set as Umbrella, and the major layer of GSM900 is Macro. The major layer of GSM 1800 is Micro and micro cell of GSM900/GSM1800 is Pico. Besides, it is also possible to differentiate the priority of GSM900/GSM1800 band according to the cell's layer. There are 16 levels of priority at each layer. In the network planning following this mechanism, the network is first considered according to the layers. The lower layer has higher property. In the same layer, according to the needs of network planning, the GSM 900 and GSM 1800 can be set with different priority. The smaller priority level has the higher priority. Umbrella Cell

Layer 4

GSM 900

GSM 900

GSM 900

GSM 900

Macro Cell

Layer 3

GSM 1800 GSM900

GSM 1800 GSM900

GSM900

GSM 1800 GSM900

GSM900

Micro Cell GSM1800

Pico Cell

GSM1800 GSM1800 GSM1800 GSM1800

GSM900

GSM900

GSM900

GSM900

GSM1800

GSM1800

GSM1800

GSM1800

Layer 2

Layer 1

Figure 2-15 Layers and levels of the cell

2)

Operation types

a) TA handover TA can be regarded as a criterion for controlling the size of a cell. BSC judges whether the TA of the current MS exceeds the maximum Timing Advanced LIMit (TALIM). If so, it

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will initiate an emergent handover. The value range of TA is 0~63. The step length of each bit is 553. 5 m, the TA setting can compensate for a distance 35 km over 63 steps. If the serving cell satisfies the requirement of TA handover. After a successful handover, the original cell will be punished so as to avoid this MS handover back to it for other causes. b) BQ handover The BER values used to define a quality band are the estimated error probabilities before channel decoding. BSC assesses the quality of radio link according to the quality level in the measurement report. The correspondence between quality level and actual BER is shown in Table 2-6. Table 2-6 BER corresponding to quality level Quality level 0 1 2 3 4 5 6 7

BER range Less than 0. 2% 0. 2% to 0. 4% 0. 4% to 0. 8% 0. 8% to 1. 6% 1. 6% to 3. 2% 3. 2% to 6. 4% 6. 4% to 12. 8% Greater than 12. 8%

Assumed value 0. 14% 0. 28% 0. 57% 1. 13% 2. 26% 4. 53% 9. 05% 18. 10%

Calculated value 14 28 57 113 226 453 905 1,810

The cause of BER increase could be signal power too low or channel interference. When the receiving quality in the serving cell is lower than the BQ handover threshold, BQ handover will be started so that the MS can maintain transmission quality of a certain level. If the serving cell satisfies the requirement of BQ handover. After a successful handover, the original cell will be punished so as to avoid this MS hands over back to it for other causes. c) Signal level rapid dropping handover Handovers such as edge handover and PBGT adopt methods such as averaging filter and P/N judgements. However it is not sensitive to short term signal level rapid dropping, FIR (Finite Impulse Response) filter to original receiving signal level is used to settle this problem. This kind of filter has a quick response to the rapid dropping slope of the original receiving signal level signal.

Note: Since the parameter setting of level rapid dropping handover algorithm is rather complicated, it is not easy to obtain experience point. Therefore, this function is usually not used.

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d) Interference handover When the receiving level in the serving cell is high, but the receiving quality deteriorates to a certain extent, interference handover is started so that the MS can maintain transmission quality at the certain level. Difference between interference handover and bad quality handover: in the former case, the quality is not low enough to affect session, and the receiving level is still high. When the active channel quality is affected by little interference in the serving cell, but they still can sustain the ongoing communication. At the same time, the receiving level in the serving cell is higher. There is possibility less interference on other channels in the serving cell, so intra-cell handover can be carried out. The parameters of interference handover algorithm: Qual_Thr and Lev_Thr. This to decide whether to trigger interference handover. If RxLev > Lev_Thr and RxQual > Qual_Thr, the interference handover is triggered. Interference handover is illustrated in Figure 2-16. Receiving quality (dtqu)

Qual_Thr

0

Receiving level

Lev_Thr

Figure 2-16 Interference handover zone The shadowed part in the figure stands for zones within which interference handover occurs. e) Edge handover This is a level-based handover and is rescue handover. If edge handover is to be triggered, the level of the destination cell is required to be higher than that of serving cell for at least one hysteresis value (inter-cell handover hysteresis). The criterion for triggering edge handover: When the receiving level of the serving cell is lower than the edge handover threshold, and fulfilling the P/N criterion within a certain measurement period, the edge handover will be triggered to ensure the communication quality. Edge handover is illustrated in Figure 2-17.

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Cell1

Cell2 -97dBm

-85dBm

Figure 2-17 Edge handover f) PBGT handover PBGT also belongs to better cell handover, a handover based on path fading. PBGT handover algorithm searches for the cell with lower path loss and satisfying the system requirement on real-time basis so as to judge whether handover is needed. Difference from other handover algorithms: the trigger condition is path loss and receiving power. Triggering condition of PBGT handover: The path loss of the adjacent cell is smaller than the threshold of the serving cell and the P/N criterion is satisfied within a period of measurement time. P/N criterion is that there are P satisfying the criterion during N measurements. PBGT(n) > PGBT_HO_Margin (n) In the inequality above, P, N and PBGT_HO_Margin (n) are configured at data configuration console. PBGT (n) calculates according to the control parameter and the information reported by BTS. The method of calculating PBGT (n): PBGT (n ) = (Min(MS _ TxPWR _ MAX , P ) − RxLEV _ DL − PWR _ C _ D ) − (Min(MS _ TxPWR _ MAX (n ), P ) − RxLEV _ NCELL(n ))

Meanings of the parameters: z

MS TxPWR MAX: maximum transmitting power allowed in the serving cell

z

MS TxPWR MAX (n): maximum transmitting power allowed in the adjacent cell n

z

RxLEV_DL: downlink receiving power of the serving cell

z

RxLEV_NCELL (n): downlink receiving power of the adjacent cell n

z

PWR_C_D: difference between the maximum downlink transmitting power caused by power control and the actual downlink transmitting power of the serving cell.

z

P: maximum transmitting capability of MS

PBGT handover occurs only between cells of the same layer and same level. g) Load handover

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There may be cells with heavy load while their upper layer cell and the adjacent cell bears less load. To achieve load balance between cells by sharing the load with upper layer and adjacent cell, the traffic load handover is applied. Its aim is to hand over part of the traffic in the heavily loaded cell to less loaded cells, and preventing the traffic of the adjacent cells being handed over to this cell. Load handover can be implemented between cells within the same BSC. Load handover is illustrated in Figure 2-18.

High traffic cell Low traffic cell

Low traffic cell Heavy traffic cell

High traffic cell

Low traffic cell Low traffic cell

Figure 2-18 Load handover The method of realizing load share: by heightening the edge handover threshold towards that of the serving cell, the traffic at the cell edge will be handed over those with less traffic. The basis for judging the traffic of a cell is the cell flow (i. e. TCH occupation rate) and the preset threshold. If the cell flow of a cell is higher than the heavy traffic load threshold (Load HO Start Threshold ), this cell is consider to have a heavy traffic load, and the load handover algorithm needs to be activated. If the cell flow of a cell is lower than the low traffic threshold (Load HO Rx Threshold), it is consider having a low traffic load, and is allowed to accept the traffic handed over from other heavy traffic load cells. Since the load handover mechanism is likely to trigger a good number of handovers, the situation of system CPU load should be taken into consideration before triggering handover, i. e. system flow level. In addition, to avoid too many handovers happening simultaneously, the load handover is implemented step by step, i. e. edge handover threshold will increase by certain step length (CLS_Ramp) and period (CLS_Period). The increase ends when the threshold reaches the load handover bandwidth (CLS_Offset). Load handover is illustrated in Figure 2-19.

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Load HO zone

Normal HO border

Cell A

Cell B

CONF_HO_RXLEV

CONF_HO_RXLEV+CLS_Offset

CONF_HO_RXLEV+CLS_Ramp

Figure 2-19 Load handover h) Hierarchical handover The GSM network is classified into layers, so as to flexibly direct its traffic and fulfill the needs of different network structure. If a cell has a high priority and its signal level is higher than a threshold (Inter-layer HO Threshold) and satisfy the P/N criterion, the traffic will be handed over to this cell even if the serving cell can still provide normal services. The purpose of hierarchical handover is to direct the traffic to the cell with higher priority so that the traffic can be distributed more reasonably. i) Fast moving handover This kind of handover is carried out for fast moving MS to reduce the number of handover and hence reduced call drop rate. If MS is moving quickly with micro cell as the reference, it will be handed over to the macro cell. If the fast moving MS registered in the macro cell, time penalty will be implemented to the micro cell so that the MS will stay in the macro cell. Fast moving handover is illustrated in Figure 2-20.

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Umbrella Cell Micro Cell

Figure 2-20 Fast moving handover There are two principles for fast moving handover: z

If the MS is moving fast with the micro cell as the reference, it will be handed over to the macro cell.

z

To avoid the fast moving MS registered in macro cell enter the micro cell, time penalty will be implemented to micro cell.

If the duration of MS camping in a cell is lower than a certain threshold (Fast Moving Time Threshold), this MS is considering to be moving fast with this cell as the reference. To avoid miscarriage of justice, P/N measurement will be implemented to several cells. If the criterion of fast moving is satisfied, this MS will be handed over the macro cells. For MS registered in macro cell, the method of "timer + penalty" is applied. Before the speed sensitive timer of a certain micro cell times out, this receiving level of this micro cell will be punished, so that the position of this micro cell in the cell sequencing will be lowered. Fast moving handover algorithm can only perform accumulation judgement to the MS within the same BM and same BSC. When MS moves to another BM, it is necessary to re-judge. j) Other handovers Other handovers include IUO handover, directed retry, forced handover, and extended cell handover.

3)

Handover procedure

Handover decision algorithm enables the preprocessing of the input MR and decides whether handover should be done and which type of handover it should be (intra-cell handover, inter-cell handover in the same BSC, outgoing BSC handover, etc.) according to the various conditions. Handover decision algorithm sends the message of decided handover result to call process module, which will complete handover-signaling process together with BTS, MSC and MS. If a handover fails for a

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certain reason, call process module will notify the handover result to the algorithm, which will decide how to further process this handover. Handover process is as shown in Figure 2-21.

MR preprocessing Handover decision algorithm starting decision MR averaging procesing Penalty processing of cell measurement value

Basic cell sorting Adjustment according to network features Handover decision Sending handover commands to the call handling module Call control Processing of handover results

Figure 2-21 Handover decision process flow chart Each phase of the process is described as follows. a) MR preprocessing. MR provides basic parameters needed in handover decision. MS measures the receiving quality (RxQual) and receiving level (RxLev) of the downlink of the serving cell as well as the downlink RxLev of the BCCH carrier frequency of adjacent cells (best six adjacent cells average). Then MS sends these measurement results to BTS through SACCH once every 480ms. If SACCH is used for the transmission of other signals, MS sends the measurement results once every 960ms. BTS measures the RxQual and RxLev of the corresponding uplink. BTS combines the uplink measurement value and the downlink measurement value to form a MR message.

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Note: If messages transmitted on the uplink SACCH do not include the MR (transmitted by MS), the uplink measurement result will indicate that the MR transmitted by MS is lost.

MR should be preprocessed so that it can have a better reflection of radio links. MR preprocessing process can be realized in both BTS and BSC and controlled by OMC. The preprocessing of the MR includes the following three procedures: MR interpolation processing: When discontinuous MRs are received by BTS or BSC, lost MRs should be interpolated so as to guarantee the continuity of the whole MR processing process. This procedure is called MR interpolation. If the number of lost MRs exceeds a limit, previously received MRs will be regarded as invalid ones and re-collection is needed. To eliminate the uncertainty in handover decision, it is necessary to perform smooth processing over the MRs, or filtering. A simple and practical algorithm is weighted filtering. Different filter lengths can be respectively defined for different types of measurement values like the receiving level, receiving quality and TA, or different channel types like signaling channels, speech and data channels. The receiving level (RxLev) and receiving quality (RxQual) use corresponding assumed value for calculations, as shown in Table 2-7, and Table 2-8. Table 2-7 Receiving level calculation assumed value RxLev number 0 1 2 … 62 63

Implication < -110dBm -110dBm~109dBm -109dBm~-108dBm … -49dBm ~ -48dBm > -48dBm

Assumed value -110dBm -109dBm -108dBm … -48dBm -47dBm

Table 2-8 Receiving quality calculation assumed value RxQual number 0 1 2 3 4 5 6 7

BER range

Assumed value

< 0. 2% 0. 2% ~ 0. 4% 0. 4% ~ 0. 8% 0. 8% ~ 1. 6% 1. 6% ~ 3. 2% 3. 2% ~ 6. 4% 6. 4% ~ 12. 8% > 12. 8%

0. 14% 0. 28% 0. 57% 1. 13% 2. 26% 4. 53% 9. 05% 18. 10%

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Calculated value 0 10 20 30 40 50 60 70



The MR represents the condition of radio channels in the previous measurement cycle, so it is of hysteresis to some extent. The prediction algorithm is mainly responsible for MR values for the next cycle(s) based on the radio environment changes prediction. MR prediction is a process that can be selected by the operator. When the multiplexing on the Abis interface is 15:1, every 4 signaling links multiplex a 64kbit/s timeslot statistically. MR is transmitted through RSL. In order to minimize signaling transmission error bit, when Abis interface multiplexing mode is 15:1, MR processing mode requires that MR should be a preprocessed one instead of the original one. Moreover, MR reporting frequency can adopt interval reporting. It can be realized with data configuration: in [Cell/Modify Cell's Handover parameter/Modify Handover Parameter/HO Control Data], modify [BTS Measurement Report Preprocessing], [Transfer Original Measurement Report] and [Report Freq. of Preprocessed Measurement Report]. Accordingly, the emergency handover due to fast level dropping is decided by BTS. And the BSC will forward the decision. For other handovers completed within BSC, handover decisions and processing are still carried out in the BSC. b) Handover decision algorithm starting decision Judge whether basic conditions for handover are satisfied, such as whether there are enough MRs. If conditions are satisfied, handover decision algorithm is started. c) MR averaging processing Filter MRs according to a certain algorithm, cancel their noise, and smooth MRs, thus to prevent incorrect handovers due to individual interference. d) Penalty processing of cell measurement value Practically there is a possibility that a handover can not be successful. In case the handover to the selected target cell fails, the MS will stick to the original serving cell. After the cycle of a handover decision is finished, the system might try to hand over the MS to the above-mentioned target cell again, which might cause invalid handover attempt or handover failure, or even interruption. Therefore, the target cell shall be punished, which is to reduce the receiving power of the corresponding cell by a set penalty value for a period (called the penalty time). Penalty types include the penalty of the forsaken cell due to TA value, penalty of the forsaken cell due to bad quality (BQ), penalty to the failed cell due to ordinary handover failure, and fast-moving penalty (this is a penalty imposed on the microcell in the candidate queue in order to prevent frequent handover when the fast moving MS accesses a cell of small coverage). e) Basic cell sorting.

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Adjacent cells that have been imposed penalty and the serving cell are sorted through a certain algorithm, thus the position of each cell is located. This is to get ready for final handover. f) Adjustment according to network features To adjust candidate queue through a certain algorithm according to hierarchical network, cell priority, speed sensibility, and the specific network environment. g) Handover decision Handover decision algorithm is used to decide the time to start handover and the target cell to be handed over. Confirm the candidate cell queue list, adjust cells adjusted in last procedure and finalize a uniform clear list of cells that are ready to be handed over. h) Sending handover commands to the call handling module After making the handover decision with the algorithm and deciding to execute the handover, BSC sends handover message containing the type of incoming handover to the call-handling module, then the latter starts the signaling procedures for this handover. i) Processing of handover results After the call handling module has processed handover signaling, it returns the result to the handover decision module. If the handover fails, the handover decision module will start penalty to the cell responsible for the failure. If the handover is successful, the module will set a new handover interval timer to avoid frequent handovers.

III. Parameter 1)

TA Handover

“TA Thrsh ” in [Handover\Emergency Handover Table] “Filter Length for TA ” in [Handover\Filter Table] “Penalty Time after TA HO ” in [Handover\Penalty Table] “Penalty Level after TA HO ” in [Handover\ Penalty Table]

2)

BQ Handover

“UL Qual. Thrsh ” in [Handover\Emergency Handover Table] “DL Qual. Thrsh ” in [Handover\ Emergency Handover Table] “Filter Length for TCH Level ” in [Handover\Filter Table] “Filter Length for SD Qual ” in [Handover\Filter Table] “Penalty Level after BQ HO ” in [Handover\Penalty Table]

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“Penalty Time after BQ HO ” in [Handover\Penalty Table]

3)

Level rapid dropping handover

“Rx_Level_Drop HO Allowed ” in [Handover\Handover Control Table] “Filter parameter A1~A8 ” in [Handover\Emergency Handover Table] “Filter parameter B ” in [Handover\Emergency Handover Table]

4)

Interference handover

“UL Qual. Thrsh. for Interf. HO ” in [Handover\Emergency Handover Table] “DL Qual. Thrsh. for Interf. HO ” in [Handover\Emergency Handover Table] “UL RX_LEV Thrsh. for Interf. HO ” in [Handover\Emergency Handover Table] “DL RX_LEV Thrsh. for Interf. HO ” in [Handover\Emergency Handover Table]

5)

Edge handover

“Edge HO UL RX_LEV Thrsh ” in [Handover\Normal Handover Table] “Edge HO DL RX_LEV Thrsh ” in [Handover\Normal Handover Table] “Edge HO watch time” in [Handover\Normal Handover Table] “Edge HO valid time” in [Handover\Normal Handover Table] “Inter-cell HO Hysteresis” in [Handover\Adjacent Cell Relation Table]

6)

PBGT handover

“PBGT HO Allowed” in [Handover\Handover Control Table] “PBGT HO Thrsh” in [Handover\Adjacent Cell Relation Table] “PBGT Watch Time” in [Handover\Normal Handover Table] “PBGT Valid Time” in [Handover\Normal Handover Table]

7)

Load handover

“load HO Allowed ” in [Handover\Handover Control Table] “System Flux Thrsh. for Load HO” in [Handover\Load Handover Table] “Load HO Thrsh” in [Handover\Load Handover Table] “Load Req. on Candiate Cell” in [Handover\Load Handover Table] “Load HO Bandwidth” in [Handover\Load Handover Table] “Load HO Step Period” in [Handover\Load Handover Table] “Load HO Step Level” in [Handover\Load Handover Table]

8)

Layered and hierarchical handover.

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“Layer of The Cell” in [Handover\Cell Description Table] “Cell Priority” in [Handover\Cell Description Table] “Inter-layer HO Thrsh” in [Handover\Cell Description Table] “Inter-layer HO hysteresis” in [Handover\Cell Description Table] “Layer HO watch time” in [Handover\Normal Handover Table] “Layer HO valid time” in [Handover\Normal Handover Table]

9)

Fast Moving handover

“MS Fast Moving HO Allowed” in [Handover\ Handover Control Table] “MS Fast-moving Watch cells” in [Handover\Fast-moving handover Table] “MS Fast-moving Valid cells” in [Handover\Fast-moving handover Table] “MS Fast-moving time Thrsh” in [Handover\Fast-moving handover Table] “Penalty on MS Fast Moving HO” in [Handover\Cell Description Table] “Penalty Time on MS Fast moving HO” in [Handover\Cell Description Table]

2.2.2 Power Control I. Overview As an important method to control radio link, power control adjusts the transmit power of MS and BTS according to the expected value configured in OMC data management system, the receiving level (including uplink and downlink) from BTS and the MR of receiving quality. Basic rules for power control are:

1)

When the level or signal quality is higher than the expected value, the power should be decreased accordingly.

2)

When the level or signal quality is lower than the expected value, the power should be increased accordingly.

3)

The level and signal quality should be both considered so as to improve the accuracy and effectiveness.

The nature of a cellular system requires that the output power of the BSC and MS should be set as low as possible. With the limited resource of the RF spectrum cellular systems depend upon the reuse of the RF channels. The reuse distance between these channels mainly upon the subscriber density in a particular area, the greater the density the shorter the reuse distance. By keeping the MS and BSC at the minimum acceptable power output it reduces the chances of interference, particularly co-channel.

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Another benefit of effective power control is that the battery of MS is extended, thus maximizing available talking time. Huawei BSS offers three different algorithms for the implementation of power control, which is GSM 0508 power control algorithm, and Huawei I (HW_I) and Huawei II (HW_II) algorithms. Any algorithm can be selected among these three algorithms. HW_I and HW_II algorithms are recommended due to their flexible configurations, effectiveness, easy operations and easy command. These Huawei-developed algorithms are compatible nicely with the GSM900 and GSM1800 systems.

II. Technical description 1)

Power control classification

Power control comprises uplink and downlink power controls, which are executed separately. The uplink power control is for MS while the downlink power control is for BTS. a) MS power control The purpose of MS power control is to adjust the MS output power in order to achieve the stable receiving signal so as to reduce the interference from subscribers of adjacent channels, decrease the saturation degree of BTS multicoupler and reduce MS power consumption. The MS power control is divided into two adjusting stages, i.e., the stable adjusting stage and the initial adjusting stage. The stable adjusting is the normal method for performing the power control algorithm, while the initial adjusting is used in the time when the call connection is initially started. When a connection is performed, MS is output as the nominal power of the cell where it is located (the nominal power indicates that the MS transmitting power is the MS maximum transmitting power MS_TXPWR_MAX_CCH in the broadcast system messages on the BCCH channel of the cell where it is located. If MS does not support this power class, the supported power class that is nearest to it will be utilized, such as the maximum output power class supported by the reported MS Classmark in the establishment indication message). However, since BTS may simultaneously support multiple calls, the receiving signal intensity should be reduced in a new connection as quick as possible, otherwise, the quality of other call supported by this BTS may be deteriorated due to the saturation of the BTS multi-coupler, and the call quality of other cells may be affected due to the high interference. Therefore, the purpose of the initial stage power control adjusting is to reduce the MS transmitting power as quick as possible until the stable measurement report is obtained, so that the MS can be adjusted according to the stable power control algorithm. The parameters that must be selected in the uplink power control, such as the expected desirable uplink receiving level, desirable uplink receiving quality, etc. , are all set by the

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O&M data management console, the data configuration can be dynamically carried out according to the actual situations of the cell. After a given number of the uplink measurement reports is received, by the processing methods such as interpolation and filtering, the actual uplink receiving level and the receiving quality are obtained, then they are compared with the desirable uplink receiving level and the receiving quality, with the power control algorithm, the power class to which the MS should be adjusted is calculated; if it is different from the current MS output power class and meets a given application restricted conditions (such as the power adjusting step length restriction, MS output power range restriction), the power adjusting command is sent. The essence of the uplink power control adjusting is to enable the actual uplink receiving level and receiving quality obtained from interpolation and filtering to progressively approach the desirable uplink receiving level and receiving quality set by O&M. The purpose for the interpolation and filtering of the measurement reports is to process the lost measurement report, clear the temporary nature (spiffiness), so as to ensure the stability of the power control algorithm. The difference between power controls in initial phase and stable phase is that their expected uplink receiving levels and receiving qualities, filter lengths are different, and the former one only adjusts downwards. b) BTS power control The BTS power control is an optional function. The base station power control is basically identical to the MS power control, except that the base power control utilizes only the stable power control algorithm. The parameters that must be selected in the power control include the receiving level threshold (lower limitation) to be performed the power control and the receivable maximum sending level threshold (upper limitation). The receiving level RXLEV is divided into 64 classes, with numbers from 0 to 63, class 0 of the receiving level is the lowest, while the class 63 of the receiving level is the highest. The base station power control is divided into the static power control and the dynamic power control, the later is the fine adjusting based on the former. The GSM 05.05 protocol specification specifies that the base station static power class is divided into 6 (2dB/per class), when the maximum power output by the base station is 46dBm (40W), the class 6 is 34 dBm. The static power level is defined in the cell attribute table of the data management console, i. e., the maximum output power value Pn of the current dynamic power control is specified. As the dynamic power control classes are set to 15, the range of the dynamic power control is Pn-Pn-30dB. If the requirements cannot be satisfied when the dynamic power control reaches its maximum value, the static power control classes should be adjusted to increase the maximum output power value Pn of the dynamic power control. enable the actual uplink receiving level and receiving quality obtained from interpolation and filtering to progressively approach the desirable uplink receiving level and receiving quality set by O&M. The purpose for the interpolation and filtering of the measurement reports is to process the lost

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measurement report, clear the temporary nature (spilliness), so as to ensure the stability of the power control algorithm.

2)

Execution process of power control

There are 3 MR cycles from sending command to execution, as shown in Figure 2-22. In the 26 multiframe the 12th frame is for Report period of SACCH: sending SACCH 26× 4＝104 frame (480ms) SA0

SA1 SA2

SA3

BTS transmifs the command of adjust power and TA at SACCH header

SA0

SA1

SA2 SA3

SA1 SA2

SA3

MS starts to send the messurement report of the previous multi-frame

MS adopts new powerand TA

MS obtains SACCH block

SA0

MS Generates new SACCH BTS receives the header to report new TA and measurement report power control message

Figure 2-22 Power control execution process a) In the first MR cycle, MS receives the power regulation message carried by SACCH header on dedicated channel and the first layer header carried by a downlink SACCH message block. MS will execute the power control command in next cycle instead of upon the receipt of these headers in first cycle. b) In the second MR cycle, power control is executed. The maximum rate of change of MS power is 2dB/13 frame (60ms). If the regulation step length is 8, i. e. 8×2=16dB. It needs 104 frames (i. e. 480ms, one MR cycle) to complete power regulation. If the regulation step length is 16, i. e. 16×2=32dB. It takes 2 MR cycleS to complete power regulation. c) In the third cycle, the current transmit power (refers to the power level used by the last burst pulse of SACCH MS cycle) is stored, which will be reported to BTS in next SACCH uplink MR.

3)

Power Control Algorithm

BSC can dynamically implement power control on each MS and BTS Three algorithms can be adopted as power control algorithm: GSM 0508 algorithm, HW_I algorithm and HW_II algorithm. Algorithm process is as shown in Figure 2-23

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MR Preprocessing

Power Control Algorithm selection

GSM0508 power control algorithm

HW_I Power control algorithm

HW_II Power control algorithm

Figure 2-23 Power control algorithm selection Power control algorithm is specified in the 0508 protocols (for further details refer to the related specifications). For uplink, upper limit and lower limit thresholds are set for the receiving signal level and the receiving signal quality. Counters P' and N' are used to count the MR and the values of these counters can be set through OMC. When N' MRs in the consecutively received P' MRs exceeds the above threshold, power regulation will be executed. Usually the steps for power control are: z

MR preprocessing

z

Power calculation

z

Power control decision

z

Adjustment by sending power control commands

4)

Huawei HW_I algorithm

Huawei HW_I has following features: z

Compared with protocol algorithm, the initial state regulation is added.

z

Data configuration is rather complicated. The power control adjustment involves many parameters and complicated calculation.

z

Power control decision is the sum of the level and quality, and the expected value is just a specified value instead of a range. Once the adjustment results of the receiving level and receiving quality are contrary, the power control will never stop and the level fluctuates with the expected value.

Power control decision process HW_I algorithm power control decision process is as shown in Figure 2-24.

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MR pre-processing

Y

Satisfying power control target N Power control calculation and regulation cinitial state and stable state

Figure 2-24 HW_I algorithm power control decision process b) Measurement Report In order to implement power control decision, various kinds of information about the current communications status from MS and BTS should be collected, including receiving signal level, and communication quality etc. Network side on SACCH will receive MRs from MS and BTS every 480 ms, in which various kinds of information needed for power control decision are contained. The process of MS reporting is as shown in Figure 2-25.

MR

MR

MR

MR Uplink measurement

Downlink measurement

Figure 2-25 Reporting MR

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An example of BSS MR is shown in Figure 2-26.

Figure 2-26 MR example c) MR preprocessing. Interpolation: each MR has a serial number. If the serial numbers of received MRs are found not continuous, this means that there are some MRs gets lost. In this case, network will add all lost MRs according to interpolation algorithm. Filtering: Several continuous MRs results will be used to reflect the state of MS in a period of time thus to avoid the one-sidedness caused by judging the state of MS according to only one MR result. d) Power control decision Number of transmit power to be adjusted (Expected stable signal level - current receiving signaling level) × uplink (downlink) compensating factor + (current actual receiving uplink (downlink) quality – expected uplink (downlink) quality) × 10 × uplink (downlink) quality compensating factor

Caution: The last regulated power level cannot exceed the maximum power control step length.

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Actual stable level equals to the sum of current actual level and transmit power to be regulated During the process of judging power control level to be adjusted, it needs to search tolerance table according to the level of current transmit power. If the final power regulation level is with the tolerance range, the regulation is unnecessary. GSM1800 tolerance table is shown in Table 2-9. Table 2-9 GSM1800 tolerance table Level

0

1

2

3

4

5

6

7

8

9

1 0

1 1

1 2

1 3

1 4

1 5

1 6

1 7

1 8

1 9

Tolerance

2

2

2

2

2

2

2

2

2

3

3

3

3

3

4

4

4

2

2

2

GSM900 tolerance table is shown in Table 2-10. Table 2-10 GSM900 tolerance table Level

0

1

2

3

4

5

6

7

8

9

1 0

1 1

1 2

1 3

1 4

1 5

1 6

1 7

1 8

1 9

Tolerance

2

2

2

4

4

4

4

4

4

4

4

4

4

4

4

4

6

6

6

6

The similarities and difference of HW_I algorithm uplink power control and downlink power control is as follows: Similarities: z

In order to avoid the fluctuation caused by power controls, the interval between two continuous controls is specified for both uplink and downlink.

z

In order to not being affected by unexpected factors, all MRs should be filtered.

z

Both uplink and downlink power controls have power control on level and quality respectively.

z

Both have maximum power control step length and compensating factor.

Difference: z

MS has power control not only for stable state but also for initial connecting phase before a call is connected. The purpose is to lower MS transmit power as soon as possible.

z

Uplink has measures to improve transmit power in the case of MS handover failure.

z

Downlink has the restriction for both maximum and minimum MS transmit power.

5)

Huawei HW_II algorithm

Compared with HW_I, HW_II has following advantages: z

MR compensation, which makes the power control decision more accurate.

z

MR prediction, which reduces power control delay.

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Adaptive power control, which sufficiently guarantees the algorithm stability and high efficiency.

z

Keep power control target within the range between upper limit and lower limit so as to avoid power control fluctuation.

z

Easy and flexible data configuration, which guarantees effective regulation of network optimized parameters.

a) Power control decision process HW_II power control decision process is as shown in Figure 2-27.

MR pre-processing

Power control requested by receiving level

Power control requested by receicing quality

Conprehensive decision of power control

Figure 2-27 HW_II power control decision process b) Request power control according to level z

After the preprocessing of MR, power control module compares the current receiving level with expected value.

z

Then the transmit level step length is calculated. The regulation is to make the receiving level closer to the expected value.

z

When receiving level regulates transmit power, variable step length can be adopted so that the quick power control can be obtained.

c) Request power control according to receiving quality After the preprocessing of MR, power control module compares the evaluation value of the current receiving quality with expected value. z

Calculate the transmit step length to be regulated

z

Improving transmitting power for low receiving quality.

z

Decreasing transmitting power for high receiving quality.

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Do not adjust the transmitting power when the receiving quality fallsbetween the upper/lower thresholds.

d) Comprehensive decision of power control Comprehensive decision of power control is shown in Table 2-11. Table 2-11 Table of comprehensive decision of power control Receiving level power control regulation οAdjStep_Lev οAdjStep_Lev οAdjStep_Lev µAdjStep_Lev µAdjStep_Lev µAdjStep_Lev No action No action No action

Receiving quality power control regulation οAdjStep_Qul µAdjStep_Qul No action οAdjStep_Qul µAdjStep_Qul No action οAdjStep_Qul µAdjStep_Qul No action

Comprehensive decision of power control οMAX(AdjStep_Lev, AdjStep_Qul) No action οAdjStep_Lev µAdjStep_Lev µMAX(AdjStep_Lev, AdjStep_Qul) µAdjStep_Lev οAdjStep_Qul µAdjStep_Qul No action

e) MR compensation Power control module will extract the receiving level and receiving quality of some history MRs when it implements power control decision. These MRs might be obtained in different transmit powers. In order to guarantee the accuracy of receiving level to be used, if the transmit powers in these MRs are different, the receiving level value of history MRs should be compensated. The interpolated and compensated MRs are filtered so as to make control power decision more effective. f) Predict filtering The power control is a process of transmitting power control based upon the current received level and the receiving quality. The sending and transmission of power control command and power adjustment will take certain period of time, so there will exist certain hysteresis between the receiving change and corresponding transmitting power adjustment.Filtering prediction enables MR on which power control decision is based to get closer to the state of power regulation so as to erase delay effectively. MR filtering prediction is implemented in a very short time and changes of receiving level and quality are likely to be continuous. N MRs before the current time are used for weighted filtering, then 0~3 MRs of after the current time are predicted. Generally, there are 3 MRs between power control decision and power regulation, which is about 1.5 second. As a consequence, the accuracy of prediction is guaranteed. Power control decision is made after the filtering of predicted MRs, interpolated MRs, and compensated history MRs. g) Dual threshold power control algorithm

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Dual threshold power control algorithm adopts the following three strategies: Adjust power control step length according to receiving level: The final purpose of power control is to obtain the best communication quality at the lowest level. However, due to the instability of radio link and the external interference, transmit power cannot be lowered greatly. Therefore, HW_II adopts the power control strategy of dual threshold so as to try to keep receiving within two thresholds. Adjust power step length according receiving quality: Generally, the change of receiving quality is associated with interference. The main interference of GSM comes to same frequency interference generated from frequency multiplexing. This interference is interactive. One call increases its power means that it exerts a stronger interference on the other call. Therefore, the power regulation caused by the change of receiving quality should avoid the group effect of increasing transmit power due to bad quality. Receiving quality threshold is also set with dual thresholds. Receiving quality with the range between two thresholds needs not to adjust transmit power. While receiving quality beyond the range should be adjusted. For the power regulation caused by quality factor should use fixed step length to avoid. Considering both power control strategies of receiving level and receiving quality regulation. Considering the requirements of both level and quality. On one hand, both requirements should be satisfied as much as possible; on the other hand, in the case that the requirements are not consistent or completely contrary, the stability should be fully considered to prohibit the unstable regulation process. Therefore, the effect on power control caused by level and quality should be both considered. h) Variable step length power control When variable step length regulation is adopted, if that the level or quality is greatly different from its expected value, use the larger step length to quickly adjust power; in the case that the level or quality is slightly different from its expected value, use the smaller step length to adjust power. Thus, quick and accurate power regulation is achieved. i) Adaptive power control Adaptive power control is to change power control strategy according different communication environments. This fact leads to a more effective and more stable power control. This is reflected in following two aspects: z

Power control adjustable maximum step length can be adjusted automatically according to the different communication environments.

z

The different power control strategies are adopted for different communication environments.

(j) Adjustment of upper threshold of signal strength

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Double-threshold power control algorithm is adopted for power control. For level, there are upper threshold of uplink (downlink) signal strength and lower threshold of uplink (downlink) signal strength. When the receiving quality is rather poor, the value of upper threshold can be increased furthermore. When the receiving quality is good, the lower value of upper threshold can be adopted so as to reduce the transmit power of mobile phone or base station. When the receiving quality is rather poor, the higher value of upper threshold can be adopted so as to improve the communication quality.

III. Parameter 1)

HW_I algorithm parameters

“Initial RX_LEV Expected ” in [Power\MS Power Control Table] “Stable RX_LEV Expected ” in [Power\MS Power Control Table] “Uplink RX_LEV Compensation ” in [Power\MS Power Control Table] “UL Qual. Expected ” in [Power\MS Power Control Table] “UL Qual. Compensation ” in [Power\MS Power Control Table] “Max PC Step ” in [Power\MS Power Control Table]

2)

HW_II algorithm parameters

“Filter Length for UL RX_LEV ” in [Power\HWII Power Control Table] “Filter Length for DL RX_LEV ” in [Power\HWII Power Control Table] “Filter Length for UL Qual ” in [Power\HWII Power Control Table] “Filter Length for DL Qual ” in [Power\HWII Power Control Table] “MR Compensation Allowed ” in [Power\HWII Power Control Table] “UL M.R. Number Predicted ” in [Power\HWII Power Control Table] “DL M.R. Number Predicted ” in [Power\HWII Power Control Table] “PC Interval ” in [Power\HWII Power Control Table] “UL RX_LEV Upper Thrsh ” in [Power\HWII Power Control Table] “UL RX_LEV Lower Thrsh ” in [Power\HWII Power Control Table] “UL Qual.Upper Thrsh ” in [Power\HWII Power Control Table] “UL Qual. Lower Thrsh ” in [Power\HWII Power Control Table] “DL RX_LEV Upper Thrsh ” in [Power\HWII Power Control Table] “DL RX_LEV Lower Thrsh ” in [Power\HWII Power Control Table] “DL Qual. Upper Thrsh ” in [Power\HWII Power Control Table] 2-84



“DL Qual. Lower Thrsh ” in [Power\HWII Power Control Table] “MAX Adj. Value for Qual. Zone 0 ” in [Power\HWII Power Control Table] “MAX Adj. Value for Qual. Zone 1 ” in [Power\HWII Power Control Table] “MAX Adj. Value for Qual. Zone 2 ” in [Power\HWII Power Control Table] “Adj. PC Value by RxQual ” in [Power\HWII Power Control Table] “UL Qual. Bad TrigThrsh ” in [Power\HWII Power Control Table] “UL Qual. Bad UpLEVDiff ” in [Power\HWII Power Control Table] “DL Qual. Bad TrigThrsh ” in [Power\HWII Power Control Table] “DL Qual. Bad UpLEVDiff ” in [Power\HWII Power Control Table]

2.2.3 Extended Cell I. Overview In GSM specifications, the TA of cell has a restriction of 63 bit at the radio interface, which results that the cell coverage radius should be within 35km. In regions such as vast land, with scattered subscribers, with low traffic, and the infrastructure facilities such as transmission and power supply are hard to be constructed or unavailable, the cell with radius over 35km should be provided. The extended cell breaks the restriction of radius within 35km. Supported by BTS hardware, it can cover a range with radius of 120km under its ideal state. Carriers can use this technology to fast construct their GSM networks with fewer stations and at lower cost, and to attract the mobile subscribers in special regions so as to improve profit.

II. Technical description When the cell coverage radius exceeds 35km, signal delay will exceed the duration corresponding with the maximum value 63 bit specified in GSM specifications. If an MS reaches the ordinary coverage verge, it will transmit at the maximum TA allowed by system; if the MS continues to move outside of cell range, the system is no longer able to implement adaptive regulation on TA value due to the TA has reached its maximum, and part of signaling transmitted by MS will reach BTS receiver at next time slot. It is this principle that extended cell uses to realize the cell extension, i. e. two continuous time slots in BTS are specified for each MS call, and the receiving window of BTS receiver is also extended to a width of two time slots thus the cell coverage radius is extended to over 35km. In order to enable MSs in extended range to initiate call at any time, two time slots should be always distributed to BCCH, CCCH and SDCCH.

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The frame TDMA of GSM radio interface is composed of 8 time slots. Each time slot is a channel. Normally, the system uses TA to make the uplink signals of MSs with different distances reach within the corresponding local time slot. TA supports a maximum of 63 bit. In order to support the extended MS signals over 63 bit, dual time slot solution binds odd and even time slots and regards each TDMA frame as only with four channels: 0/1, 2/3, 4/5, 6/7. . For MS, only channel 0, 2, 4, and 6 are distributed. The MS in the range 0~35km, its TA value changes within the range 0~63. The TA value of MS with radius over 35km is always maintained as 63. While BTS demodulates uplink data in two continuous time slots. TA value of TA in MS has a maximum of 63+156. 25 = 219. 25 bit. The principle of extended cell delay regulation is as shown in Figure 2-28. unlink data

DELAY<=63

demodulation range After TA adjustment

TS2

TS1

TS0

delay>63

After TA adjustment

TS0

TS2

TS1 Dual times lot extendend cell

Figure 2-28 Principle of extended cell delay regulation If all carrier frequencies in a cell are set as ordinary ones, this is called cell level dual time slot solution. If part of carrier frequencies in a cell are set as ordinary ones and other carrier frequencies are configured as dual time slot ones, and BCCH is located in dual time slot carrier, then this is called carrier level dual time slot solution. When carrier level dual time slot extended cell is adopted, there are ordinary carrier and dual time slot ones. BCCH in dual time slot guarantees the random access of any areas. The calls within TA value accessed randomly being within 35km radius are distributed to ordinary carrier; while the calls within 34~120km radius and the incoming handovers are distributed to dual time slot carrier. For the incoming handovers to be found as 0~35km ones, the system can handover them again to ordinary carrier. When the calling MS crosses 35 km line, this will lead to an intra-cell handover, which is from 2-86



the dual time slot frequency to the ordinary one or from the ordinary to dual time slot frequency. The conversion of carrier frequencies between ordinary one and dual time slot one can be set through BSC data configuration

III. Parameter “Cell Extension Type ” in [Cell\Cell Attribute Table] “CH Type ” in [Local Office\Radio Channel Configuration Table]

“TA Thrsh ” in [Handover\Emergency Handover Table]

“TA Thrsh ” in [Handover\Concentric cell Handover Table] “TA Hysteresis ” in [Handover\ Concentric cell Handover Table]

2.2.4 IUO I. Overview With the development of GSM network, the number of subscribers increases gradually, so the contradict between short frequency resource and great demand is particularly obvious. In order to increase capacity, the technology of aggressive frequency reuse should be used to improve the frequency utilization. However, the aggressive frequency reuse increases the radio interference greatly and even to affect the communication quality seriously. Under the circumstance of aggressive frequency reuse, the IUO technology can be used to avoid or decrease radio interference so as to guarantee communication quality. The IUO technology divides an ordinary cell into two service layers: OverLaid subcell and UnderLaid subcell. For the MS in the UnderLaid subcell, try to distribute the less reuse frequency, such as BCCH frequency; for the MS in the OverLaid subcell, try to distribute the more reuse frequency, such as frequency except BCCH. The frequency inside the OverLaid subcell adopts aggressive frequency reuse mode, which can improve system capacity effectively.

II. Technical description IUO refers to the different carrier circle cells formed by different carrier frequencies in a cell with difference on coverage. Logically, OverLaid subcell and UnderLaid subcell can be regarded as two cells because their coverage areas are different, The OverLaid subcell is the main traffic carrier layer because it has many channels. Its function is to absorb the most subscribers within the cell coverage area. UnderLaid subcell solve the

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problem of coverage and provide service for the areas not covered by overlaid cell. e The technical description of IUO is as shown in Figure 2-29. UnderLaid subcell Cell A

Cell B

OverLaid subcell

Signal

Interference

Figure 2-29 Aggressive Frequency Reuse of IUO cell As shown above, the IUO divides the cell coverage into OverLaid subcell and UnderLaid subcell. The carrier frequencies of OverLaid subcell and UnderLaid subcell can adopt different multiplexing modes. For the OverLaid subcell cell, it adopts more reuse frequency mode such as 1x3 due to its small coverage. For the UnderLaid subcell cell, it adopts less reuse frequency mode such as 4x3. After the IUO technology is employed, compared with Multiple Reuse Pattern (MRP), it can greatly increase the network capacity and guarantee the network quality because the OverLaid subcell employs of aggressive frequency reuse mode. In some special cases, the UnderLaid subcell is configured with only one carrier BCCH with the multiplexing mode of 4x3 being adopted and the rest TCH carrier frequencies are configured in OverLaid subcell with the multiplexing mode of 1x3 being adopted, then the IUO cell is completely the same as the cell with the multiplexing mode of 1x3 adopted and the average frequency multiplexing ratio is the same as that of 1x3 multiplexing. Therefore, in this case, the IUO can effectively reduce the interference for the whole network and obtain the better network quality than 1x3 multiplexing without the decrease of network capacity. The wider coverage can be realized through having the carrier in which BCCH is used large power amplifier. The power that provided by BCCH carrier is greater than other carriers, so the coverage distance of different carrier is different. While the cell coverage area depends on the carrier of smaller coverage, so the coverage area is greatly restricted. When the IUO technology is employed, the carrier with wide coverage can be used to serve as UnderLaid subcell to realize the far end coverage of site; while the carrier with small coverage can be used to serve as OverLaid subcell to increase the near end capacity of site. In this way, the cell coverage area can be increased.

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Underlaid Overlaid

Figure 2-30 IUO coverage After the employment of the IUO cell, the cell coverage area can be greatly increased. The theoretically added coverage of various typical stations with different combining modes is shown in Table 2-12. Table 2-12 Coverage changes for typical sites after the employment of IUO cell Number of cell carrier frequencies

Combining mode

3 4,5 4,5 5,6

CDU+CDU CDU+CDU+SCU CDU+CDU+CDU CDU+CDU+SCU

Loss of low loss carrier 1. 0dB 1. 0dB 1. 0dB 4. 5dB

Loss of high loss carrier 4. 5dB 8. 0dB 4. 5dB 8. 0dB

Added coverage area after the employment of IUO 27% 60% 27% 27%

The division of OverLaid subcell and UnderLaid subcell is based on the MS downlink receiving level, downlink receiving quality and TA, as shown in Figure 2-31.

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Figure 2-31 Division of OverLaid subcell and UnderLaid subcell in a IUO cell

Note: The division foundation of OverLaid subcell and UnderLaid subcell is as follows: OverLaid subcell: Receiving Level>= RX_LEV Thrsh. + RX_LEV Hysteresis and TA=TA Thrsh + TA Hysteresis or Receiving Quality >= Receiving Quality Thrsh.

RX_LEV Thrsh., Receiving Quality Thrsh. and TA Thrsh. can be adjusted through data configuration. Therefore, under the precondition of without affecting the network performance indexes, the boarders of UnderLaid subcell and OverLaid subcell can be adjusted flexibly to let OverLaid subcell and UnderLaid subcell rationally share the traffic.

1)

Channel assignment technology of IUO cell

This technology can adopt different assignment strategies in various channel assignment cases in fully consideration of features of IUO. The following are the main cases: a) Immediate assignment There is no reference receiving level, receiving quality and TA for immediate assignment. In order to guarantee the service quality, the SDCCH of UnderLaid subcell

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is assigned preferentially. Only when there is no signaling channel available in the UnderLaid subcell, will the signaling channel in the OverLaid subcell be assigned. b) Assignment The channel assignment strategy of IUO is used to assign channels. The OverLaid subcell channel will be assigned as far as possible when the subscriber is in the OverLaid subcell coverage. The UnderLaid subcell channel will be assigned when no OverLaid subcell channel is available. Similarly, the UnderLaid subcell channel will be assigned as far as possible when the subscriber is in the UnderLaid subcell coverage. The OverLaid subcell channel will be assigned when no UnderLaid subcell channel is available. Select the suitable service layer to serve the subscriber. c) Intra-BSC handover Intra-BSC handover is applicable to the non-IUO handover and the handover from the OverLaid subcell directly to an adjacent cell. Use the IUO channel assignment strategy to assign channels and select the suitable service layer to serve the MS. d) Inter-BSC handover Being unable to get the receiving level, receiving quality and TA of adjacent cells, the system selects the preferential UnderLaid subcell, or preferential OverLaid subcell, or non-strategy mode through switch.

2)

IUO cell handover technology

Huawei handover algorithm has the IUO handover judgement function to realize the ordinary IUO technology. When the MS crosses the boundary between OverLaid subcell and UnderLaid subcell, the IUO handover can be initiated to enable the MS to setup a call at a suitable service layer. If the object handover layer is congested, the handover will not be initiated. With the IUO cell handover technology, BSC can intelligently direct the traffic so as to utilize the frequency resource effectively.

III. Parameter Parameters in [Handover/ Concentric Cell Handover Table]: "Direction for IUO HO – UL to OL HO Allowed" "Direction for IUO HO – OL to UL HO Allowed" "Criterion for IUO HO – Rx_Lev for UO HO Allowed" "Criterion for IUO HO – Rx_Qual for UO HO Allowed" "Criterion for IUO HO – TA UO HO Allowed" "UO signal intensity difference " "RX_LEV Thrsh." 2-91



"RX_LEV Hysteresis" "Receiving Quality Thrsh." "TA Thrsh." "TA Hysteresis" "IUO HO Watch Time" "IUO HO Valid Time" "Assign optimum layer" "Assign-optimum-level thrsh." "Incoming-to-BSC HO optimum layer" "Pref. subcell in HO of intra-BSC " Parameters in [Handover/Penalty Data Table]: "Penalty time after IUO HO Fail." Parameters in [Handover/Cell Description Data]: "Cell Type" Parameters in [Site/Carrier Configuration Table]: "HW-IUO Property"

2.2.5 Satellite Transfer I. Technical description Satellite communication is the development and the special form of microwave communication, the supplement and backup to conventional communication means. Satellite communication features wide coverage, little effected by landform, fine mobility, and flexible link calling. Meanwhile, it has the problems such as delay, jitter, and bit error, which leads to the Abis interface of ordinary GSM equipment not supporting satellite transfer. Huawei BSS adopts dedicated satellite transfer equipment to realize the satellite transfer of Abis interface according to the features of satellite transfer. The solution principle is described as follows:

1)

LAPD protocol processing

During the LAPD protocol process, the timer duration is prolonged and the value of slide window is increased to resist delay.

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2)


TRAU frame algorithm

The adjustment algorithm of the TRAU frame is modified from fixed cycle adjustment to self-adaptive adjustment.

3)

BTS clock work mode

The transmission between BSC and BTS can only occupy 19 time slots of DDN circuit (TS1~18, TS31) and the time slot 0 of DDN circuit is used for the synchronization of DDN instead of transmitting service. Therefore, BTS can only use the clock of DDN. However, the accuracy of DDN clock is only 10E-7, which cannot satisfy the requirement of GSM protocol. BTS adopts internal clock, which accuracy meets the requirement of GSM protocol.

4)

Voice quality

When the transmission bit error is less than 10E-6, the Voice quality is not affected. Usually, the transmission bit error of satellite circuit is less than 10E-8. As the link lease is very expensive and the quality is particularly sensitive to environments, the solution of Abis interface transmission by using satellite transfer should be positioned for the special areas where the ordinary transmission means is dissatisfactory and for the emergency communication. When the satellite transfer is used for networking, the star networking mode is usually adopted. The typical satellite transfer networking diagram is shown in Figure 2-32.

Satelite

Earth Station

MSC

Earth Receiving E1 Station BTS BSC BTS SDH/PDH /HDSL/Microware /E1 BTS

Earth Receiving E1 BTS Station

Figure 2-32 Typical satellite transfer networking diagram Satellite communication is composed of satellite and ground station.

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Generally, the satellite communication adopts synchronous satellite, i.e. the satellite orbit plane is on the equator plane, the satellite is 35786. 6km from the earth surface, the flying direction is the same as the earth rotation, and the duration of satellite rotation cycle is the same as that of the earth. The satellite consists of control system, communication system (antenna and trunk equipment), telemetry system, power supply system and temperature control system. The ground station consists of antenna system, transmitter, receiver, channel terminal equipment (modem), communication control system and power supply system. The ground station of ordinary satellite communication is a kind of large-sized international or European standard communication station. It has such features as high transmission rate, antenna of large caliber, and expensive cost of equipment. The subscriber data are connected to the ground station through the ground communication network to complete communication. The subscribers in VSAT system form a dedicated network to communicate through satellite respectively. This mode is featured by its low cost of equipment, antenna of small caliber, and flexible application.

II. Parameter 1) 2) 3) 4) 5)

“Transfer Mode ” in [Site\Site Description Table] “Immediate Assignment opt ” in [Cell\Cell Call Control Table] “MS MAX retrans ” in [Cell\System Information Table] “Tx-integer ” in [Cell\System Information Table] “CCCH_CONF ” in [Cell\System Information Table]

2.2.6 Diversity Receiving I. Technical description In radio waves propagation, fading (including slow fading and fast fading) may impact on the communication quality and may even interrupt the communication. In this technique, the system receives two or more input signals, which carry identical information but irrelevant random fading features. To minimize these impacts and enhance the transmission quality, diversity technique is used. It is an effective approach to overcome fading, encompasses frequency diversity, time diversity, polarization diversity and space diversity.

1)

Space diversity

Space diversity is implemented by providing two sets of stand-alone receiving equipment concurrently, including antenna, tower amplifier (optional), feeder, DMUX and receiver. The receiver is made up of two completely independent paths. The input signals of the two channels come from the master and diversity antennas. The two 2-94



signals of space diversity receiving have different propagation environments and different kinds of fading so they have the feature of coherence or little coherence. It lowers the impact of propagation factor to adopt diversity combining technology and make it output powerful useful signals. In the mobile communication, the wider spacing interval, the more different multipath propagation, and the less relativity. The interval between antennas can be either vertical or horizontal. The vertical interval has a poor performance of diversity, so it is rarely used. In the same BTS or cell, if two sets of antennas with an interval of dozens of wavelength are used to receive the same signal, the most powerful signals or combined signals with minimum fading can be selected through diversity combining technology. The diversity gain can be used to indicate the improvement of space diversity, which value is related with adopted combing technology. However, the improvement depends on the ratio between the effective height of diversity antenna (he) and level interval (d), and the incoming wave angle α. When the frontal signal (i. e. α=0o) is received, the signal coherence coefficient on two sets of antennas is the smallest one and the gain is the greatest one; when the lateral signal (α=90o) is received, the coherence coefficient is the greatest one and the gain is the smallest one. Space diversity is the most effective and most common mode in the mobile communication.

2)

Time diversity

Time diversity can be used to send the same message through a certain delay, or send a part of message at different times within the allowed range of delay. Interleaving technology is used to realize time diversity.

3)

Frequency diversity

Frequency diversity is realized through frequency hopping.

4)

Polarization diversity

It can get a better diversity gain to set two sets of antenna to form a certain angle. Moreover, the two sets of antenna can be integrated as one set of antenna. Therefore, for a sector, only one set of Tx antenna and one set of Rx antenna are needed. If the duplexer is used, only one set of antenna integrated by Tx and Rx antennas is needed. Huawei BTS uses dual polarization antenna to realize polarization diversity. This can realize the combination of antenna, tower top amplifier (optional), feeder, and divider. When the complicated radio transmission conditions result in deterioration in a path of the received signals, another path of received signals may vary in signal quality as they are from an irrelevant transmission path. The BTS receives two paths of signals: main and diversity signals, demodulates and combines them. This gives 3~5dB diversity gain. It has been proven that for the space diversity, a better diversity can be achieved when the distance between 2 sets of antenna is greater than 10 wavelengths. For the 2-95



polarization diversity, it has the advantage of convenient antenna extension and saving hoist space and is increasedly used.

II. Parameter The system needs no extra data configuration to realize the diversity receiving.

2.2.7 Aggressive Frequency Reuse Pattern I. Aggressive Frequency Reuse With the development of network, the subscribers increase gradually, the contradict between short frequency resource and great demand is particularly obvious. In order to increase capacity, the technology of aggressive frequency reuse should be used to improve the frequency utilization. According to the actual network circumstance and requirements, the system can adopt hierarchical aggressive frequency reuse and 1x3 multiplexing technology. The comparison of adopting different aggressive frequency reuse is as shown in Table 2-13. Table 2-13 The maximum configuration under different bandwidths Frequency band 6MHz 10MHz

4x3 multiplexing S(2/2/2) S(4/4/4)

Hierarchical multiplexing S(3/3/3) S(6/6/6)

1x3 multiplexing S(4/4/4) S(8/8/8)

Note: 1) S(4/4/4) indicates three synchronous cells with each carrier number being 4. 2) In 4x3 multiplexing, 4 indicate four sites, 3 indicates three cells, and totally there are twelve cells as frequency cluster. Different cells in the same cluster have different frequencies; while cells of other clusters reuse one certain group of frequency in these twelve frequency clusters.

II. Advanced aggressive frequency reuse technology 1)

Hierarchical aggressive frequency reuse

Hierarchical aggressive frequency reuse supports that there can be several different frequencies multiplexing modes working simultaneously in the same GSM network. For example BCCH adopts 4x3 multiplexing mode and TCH adopts 3x3 and 2x3 modes. The nature of hierarchical aggressive frequency reuse is a method of frequency planning. It has no special requirements of software and hardware for equipment. Hierarchical aggressive frequency reuse divides all available frequencies into several

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groups and each group serves as a carrier layer. The principle of hierarchical aggressive frequency reuse is as shown in Figure 2-33.

(1,2,3,4,...36,37) 1 2 3 4 5 6 7 8 9 10 11 12 BCCH BCCH

TCH1 TCH1

TCH2 TCH2

TCH3

MICRO

Figure 2-33 Principle of hierarchical aggressive frequency reuse After the hierarchical aggressive frequency reuse is used, frequency hopping, DTX and dynamic power control should be started to improve C/I thus to satisfy the requirement of C/I>12dB. The frequency hopping can get the frequency diversity gain and interference diversity gain. For example: the maximum configuration S (4/4/4) packet mode can be divided into: BCCH, TCH1, TCH2 and TCH3. There are two modes of carrier packet: z

Continuous packet: The ARFCNs of frequencies assigned in the same layer are continuous.

z

Interval packet: The ARFCNs of frequencies assigned in the same layer have intervals.

The following examples illustrate these two packets. Provided that frequency range is 512~561, totally 50 frequencies. 12 frequencies are assigned for BCCH, 38 for TCH. a) Continuous packet mode BCCH (12): 512~523; TCH (38): 524~561. b) Interval packet mode BCCH (12): 512, 514, 516, 518, 520, 522, 524, 526, 528, 530, 532, 534; TCH: 513, 515, 517, 519, 521, 523, 525, 527, 529, 531, 533, 535~561. Both these two packet modes have their advantages and disadvantage. The comparison is made as follows. In the case of continuous packet, the interference between BCCH carrier layer and TCH carrier layer is little. However, both same frequency and adjacent frequency interference should be considered as a restriction for the planning of BCCH layer. 2-97



Meanwhile, BCCH layer and TCH layer are quite independent and there is only one frequency between BCCH and TCH layers, therefore, BCCH layer can be easily modified without interference to TCH layer. The employment of interval packet mode can guarantees that there is no adjacent frequency interference between BCCHs. Moreover, the planning of BCCH carrier layer is relatively easy since the same frequency interference is considered as a main restriction. However, the interference between BCCH and TCH layers is strong. Therefore, the planning of TCH layer after the planning of BCCH layer becomes difficult. Under the condition of the same number of frequencies, the continuous packet mode of BCCH carrier layer is more difficult than the interval packet mode, for more consideration should be given to the restriction of adjacent frequency interference. (In the system with frequency hopping adopted, the less consideration can be given to the restriction of adjacent frequency interference. The principle for different carrier layer multiplexing ratios: Assign frequency layer by layer, try to apply different multiplexing ratios for different layers, and realize aggressive frequency reuse layer by layer. General principle: BCCH>TCH1>TCH2>TCH3 When multiple frequency multiplexing is adopted, C/I value will be decreased due to the aggressive frequency reuse being adopted for each TCH layer. Then the requirement that the same frequency interference C/I is greater or equal to 12dB in GSM system is not guaranteed. Moreover, the different frequencies have different interference situations. The less frequencies in the layer, the more serious interference. If frequency hopping and other measures are not adopted, the above-mentioned interference between frequencies will take place thus the communication quality is not guaranteed. Therefore, the system must adopt measures such as frequency hopping, discontinuous transmission, and dynamic power control to minimize these kinds of interference. Frequency hopping can get the frequency diversity gain and interference diversity gain so as to avoid Rayleigh fading and same frequency interference. It should be noted that the purpose for different carrier layers using different multiplexing ratios is to avoid interference at most. This is shown in the flowing aspects. Under the circumstance of non-uniform network sites, it is not the case for every cell to use the TRX of last layer or the most last layers. So the TRX of last layer or the most last layers can realize a higher aggressive frequency reuse ratio (even without the employment of frequency hopping). Since the system tries to s are tried to use different multiplexing modes for each carrier layer, frequencies of any two cells in network are not completely the same, i. e. there is no the real same frequency cell. After multiple frequency multiplexing is realized, though interference is increased, the TRX also increased. This makes more frequencies to participate in frequency hopping and the gain is increased. If the 2-98



frequency with weak interference and frequency with strong interference coexist in the same cell, they will be mixed after frequency hopping is adopted. The system can still use the interfered frequencies according to the feature of decoder. So for each burst, C/I is changeable. But for a specified connection, its quality depends on C/I equalizing value and the equalizing value is not fluctuated.

III. 1x3 frequency multiplexing technology 1x3 frequency multiplexing technology is a kind of aggressive frequency reuse. The following is a simple example to illustrate the principle of 1x3 frequency multiplexing. Provided that the maximum configuration site is S (8/8/8) in a certain area, the available frequency band is 14. 4MHz, 9 frequencies are reserved for micro-cellar, 12. 6MHz is left, and there are totally 63 frequencies. Among these 63 frequencies, 15 are assigned for BCCH carrier (the assignment on the frequency is continuous), and 48 TCH frequencies are left. Then frequencies are divided into 3 groups (combiner hopping mode is adopted): Group 1: 29, 32, 35, 38, 41, 44, 47, 50, 53, 56, 59, 62, 65, 68, 71, 74; Group 2: 30, 33, 36, 39, 42, 45, 48, 51, 54, 57, 60, 63, 66, 69, 72, 75; Group 3: 31, 34, 37, 40, 43, 46, 49, 52, 55, 58, 61, 64, 67, 70, 73, 76. 1x3 frequency multiplexing has the advantage of high frequency efficiency, easy planning method, and easy assignment of frequency. Meanwhile, HSN and MAIO should be carefully planned and the BTS should support radio frequency hopping. In large cities, there are many BTSs and the site is complicated. The employment of 1x3 frequency planning method can greatly reduce workload and good performance can be achieved in the case of small multiplexing ratio. 1x3 multiplexing uses the principle that the number of FH frequencies is greater than the number of carrier frequencies in the cell to avoid interference and to reduce same frequency collision probability. For a specified connection, its quality depends on C/I equalizing value. It has been proven that whether the C/I is good or not depends on same frequency collision probability after radio frequency hopping. And the collision probability is only related with the frequency utilization. 1x3 frequency multiplexing mode is as shown in Figure 2-34.

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Figure 2-34 1x3 frequency multiplexing mode The frequency planning of 1x3 frequency multiplexing is easy and practical, as well as some disadvantages. For example: when sites are distributed irregularly and the landforms are greatly different, the collision probability will be greatly increase Moreover, in the network in which 1x3 planning is implemented, there is also requirement for network load. When TCH multiplexing ratio is over 40% and the load is over 80%, the network quality will be decreased rapidly. If the TCH multiplexing ratio is higher, for example, over 50% and the load is over 60% or 70%, the network quality will also be decreased rapidly.

IV. Applied conditions for aggressive frequency reuse To adopt aggressive frequency reuse to improve the frequency utilization and the network capacity, a series of anti-interference measures should be taken to reduce the same frequency and adjacent frequency interference caused by aggressive frequency reuse. According to the specifications, carrier interference ratio index (engineering value) is: Same frequency carrier interference ratio: C/I is greater than or equal to 12dB; Adjacent frequency carrier interference ratio: C/I is greater than or equal to-6dB; Carrier interference ratio when carrier has an offset of 400 kHz: C/I is greater than or equal to -38dB. Currently, the following measures are taken to improve the network anti-interference capability so as to satisfy the carrier interference ratio index: Frequency hopping, DTX and power control. The following introduces the effect on improvement of network same frequency C/I and adjacent frequency C/I by frequency hopping. Frequency hopping has two functions: frequency diversity and interference diversity. The frequency diversity gain of frequency hopping depends on propagation environment, MS speed, frequency number of frequency hopping sequence number,

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and the inter-frequency relativity. It is no greater than 6dB. When MS has a high, frequency hopping has no function of frequency diversity. Generally, the electromagnetic wave of mobile communication consists of direct wave component and scattered wave component. When direct wave is in a dominant position, the frequency diversity of frequency hopping is not obvious. Its gain is about 0~3dB. On the contrary, when scattered wave in a dominant position, the gain is obvious, which is about 3~6dB. For a typical environment in which propagation environment, MS speed, and interval between frequencies are satisfied to achieve the maximum FP frequency gain, the maximum gain for three-frequency hopping reaches 3. 3dB, 6dB for four-frequency hopping, no greater than 5.5dB for 9-frequency hopping. The maximum gain of frequency diversity is no greater than 6dB. The interference diversity capability of frequency hopping is related to interference distribution, frequency number of frequency hopping sequence number, and the inter-frequency relativity. Generally, for the narrow band interference, interference diversity functions apparently; for the broadband interference, it does not function apparently. It has been proven that when interference is distributed as narrow band and the number of FH frequencies is 3, 5, 7, the interference diversity gain for interfered frequency is 3.2 dB, 4.6 dB , 5.5 dB respectively. The function of interference diversity is shown on the equalization of interference. Therefore, the interference diversity gain for a single frequency is 0 by default and is sent in the system information

2.2.8 Multiband Network I. Overview The multiband network is a network combined GSM900 and GSM1800 In the multiband network, GSM multiband MS can communicate in either GSM900 frequency band or GSM1800 frequency band. Each cell in a multiband network has frequencies from only one frequency band. The multiband network allows cell reselection, distribution and handover between GSM900 cell and GSM1800 cell. The application of multiband network is as shown in Figure 2-35.

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GSM900

GSM1800

MSC BSC

BSC

MSC BSC

BSC

GSM900 Cell GSM1800 Cell Figure 2-35 GSM900/GSM1800 multiband network The multiband network can be used to utilize the abundant frequency resources in GSM1800 frequency band, to absorb network traffic, and to satisfy the increasing demand of network capacity.

II. Technical description To guarantee the stable operation of multiband network, it is of utmost importance to correctly configure the parameters related with the multiband network operation at the stage of network commissioning. Given below is a description of the technical principles governing the multiband network.

1)

MS Classmark

In the GSM system, MS Classmark represents the MS services, supported bands, power, and encryption capability. The Classmark of the mobile station falls into three categories: Classmark1, Classmark2 and Classmark3. The network can interrogate the Classmark of MS and realize its capabilities. In addition, the network can request the mobile station to report its Classmark3 immediately after creating a link by setting the parameter “Early Classmark Sending Control”. Since the important messages in Classmark3 are created specially for multiband applications, it is required that in the multiband network the equipment should support the processing of MS Classmark. Huawei BSS supports ECSC, processing of MS Classmark3, etc.

2)

BA list

In the GSM system, the BA (BCCH Allocation) list is a set of all the carrier channel numbers of adjacent cells of each cell. The network carries out compatibility handling for various types of MSs through system information control. It also guides the MSs to access and handover correctly so that good services of the radio network can be guaranteed.

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BA defines the absolute channel numbers used by carrier of all adjacent frequency cell BCCHs, which is used for cell selection and handover. It is the system that informs MS the BA list through system information. There are two types of BA list: z

The BA1 mainly contains the list of adjacent cells searched by the MSs in idle mode. It is transmitted periodically in the system information type 2, 2bis or 2ter, and used for cell re-selection in the idle mode.

z

The BA2 mainly contains the list of adjacent cells searched by the MSs in active mode. It is transmitted in the system information 5, 5bis or 5ter, and used for handover in active mode.

When an MS is in active mode, It extracts the parameters of adjacent cells from the associated channel system information type 5, 5bis or 5ter on the SACCH, instead of from the system information type 2, 2bis and 2ter. In accordance with the actual network status, the BA list in the system information type 5, 5bis and 5ter can be either identical to or varied with that in the system information type 2, 2bis and 2ter. The BA list shall be set in accordance with the network design requirements and the actual status of adjacent cells. Otherwise, there might be inappropriateness in handover or cell re-selection, or even handover failure. In this case, it may impact the services provided by the network. The number of adjacent cells on each BA list shall not exceed 32.

3)

Support of system Information for multiband network

The network carries out compatibility handling of MSs of various classes through system information (type 2 / 2bis / 2ter and 5 / 5bis / 5ter). The radio network controls the MSs to access and handover correctly and guarantees good services. Huawei GSM system carries out thorough compatibility processing of Phase 1 and Phase 2 900 MSs, Phase 1 and Phase 2 1800 MSs and multiband MSs, and supports system information type 2 / 2bis / 2ter and 5 / 5bis / 5ter. The BA1 list is sent in system information type 2 for re-selection. The BA2 list is sent in the system information type 5 for handover. In GSM900 system, the frequency channels are numbered from 1 to 124. Coding can be done on one list without 2bis / 2ter / 5bis / 5ter when the bitmap format is used. However, this should be adjusted after the multiband system is employed. For the GSM900 cells, the GSM1800 frequency channels on its adjacent cell list are for multiband MSs. They are transmitted via the system information type 2ter / 5ter. Only a multiband MS supports the system information type 2ter / 5ter. Whereas the frequency channels of its GSM900 adjacent cells are placed in the system information type 2 / 5 and can be coded in the bitmap format. The Phase 1 MS recognizes the bitmap format only. This ensures compatibility with Phase 1 GSM900 MSs.

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For the GSM1800 cells, they are handled in a similar way. The 900M frequency channels on the list of its adjacent cells are for multiband MSs, transmitted through the system information type 2ter / 5ter. Whereas the frequency channels of its GSM1800 adjacent cells are placed in the system information type 2/5. As they cannot be coded on one list, the BA list needs to be split into two parts, transmitted respectively in the system information type 2 (or 5) and 2bis (or 5bis). The system information type 2bis (5bis) is for single-band M1800 MSs and multiband MSs only. For the multiband network, it is required that the equipment should support the system information type 2ter/5ter.

4)

ECSC (Early Classmark Sending Control)

ECSC indicates whether MS is required to report the MS Classmark3 voluntarily and early. For further details refer to the protocol 0408. On receipt of the Classmark change message, MS will send the additional Classmark message to the network as early as possible. Classmark3 information includes the power messages of various frequency bands of multi-frequency MS. In the handover between different frequency bands, power level should be correctly described. It is essential to know the Classmark3 message when making a paging call or sending the BA2 list in different bands. The sampling range of the ECSC is as follows: ECSC=1, transmission required. ECSC=0, transmission not required. This function comes into beings for the multiband-networking situation. And the information in Classmark3 is for multiband application. In case of single-band networking, it is advisable to set this parameter to 0. In case of multiband networking, the recommended value of ECSC is 1 so that signaling flow can be reduced. The parameter ECSC is transmitted in system information type 3.

5)

MBR (Multi-Band Report)

MBR serves to help the network to notify the MS that the 6 adjacent cells reported must cover multiple bands. In the single-band GSM system, when the MS reports the adjacent cell measurement results to the network, it need only report the 6 adjacent cells with strongest signals in a band. When there is a multi-band network, the operator will usually expect the MS to have the priority to enter a band in time of handover depending on the actual status of the network. Therefore, the MS is expected to report the measurement results based not only on the level of the signals but also on the band of the signals. The system parameter “Multi-band Report”, therefore, serves to notify the mobile station to report the multi-band adjacent messages.

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In the multiband network, the following situation often occurs because the propagation loss in the 1800 MHz band is larger than that of the 900MHz band: among the 6 adjacent cells with strongest signals as reported by MSs, none of them is a GSM 1800 cell. This will affect the absorption of traffic by the GSM1800 network. In this case, the network can request the multiband MSs to send the MR about the adjacent 1800MHz cells by setting the MBR value. By setting different values for MBR, the MSs can report the messages of the adjacent cells of different bands as required when submitting the MRs of 6 best adjacent cells. MBR is represented in decimal digits, with the ranges from 0 to 3. Its implication is shown in Table 2-14. Table 2-14 MBR implication MBR 0 1

2

3

6)

Implication MS shall report the measurement results of 6 adjacent cells with strongest signals known and allowed by NCC depending on the signal level of the cells, regardless of which band the cells are in. MS shall report the measurement results of an adjacent cell in each band with strongest signals, which are known and allowed by NCC on the adjacent cell list. Then it shall report the adjacent cells in the band used by the current service area in the remaining space of the report. If there is still space left, it shall report the status of the other adjacent cells, regardless of which band they are in. The MS shall report the measurement results of two adjacent cells in each band with strongest signals known and allowed by NCC on the adjacent cell list. Then it shall report the adjacent cells in the band used by the current service area in the remaining space of the report. If there is still space left, it shall report the status of the other adjacent cells, regardless of which band they are in. The mobile station shall report the measurement results of three adjacent cells in each band with strongest signals known and allowed by NCC on the adjacent cell list. Then it shall report the adjacent cells in the band used by the current service area in the remaining space of the report. If there is still space left, it shall report the status of the other adjacent cells, regardless of which band they are in.

PI (Cell Reselection Parameter Index)

PI is used to notify MS whether to adopt C2 as cell reselection parameter and to calculate whether the parameter of C2 exist. Value range of PI: Y or N. Y indicates that MS should extract parameters from broadcasting of system information in cell to work out C2 value and use the value to serve as the standard of cell reselection; N indicates that MS should use C1 to serve as cell reselection standard (i. e. C2 = C1). Generally, PI is set as Y in multiband network.

III. Traffic guide strategy in multiband network In the multiband networking, one of the most important purposes is to try to let GSM1800 network absorb or share traffic so as to satisfy the increasing requirement of network capacity and quality. The following principles should be followed. z

In the early stage of multiband network construction, try to let GSM1800 cells absorb multiband subscribers.

z

Realize the continuous coverage of GSM1800 network in hot spot areas. 2-105



When the number of multiband subscribers reaches a certain level, use different bands to share traffic thus to reduce handover and provide better service.

The carrier can realize different traffic control strategy through real-time adjustment of related parameters. Different traffic control methods are used for different MS states. GSM1800 cell can have higher priority or better adjacent cell measurement comparison value through the configuration of system parameters. So when the subscriber turns on the mobile to select cell in idle mode or reselects cell in standby state, GSM1800 cell can be more likely to be the serving cell for multiband subscribers. In this way, the subscriber is more likely to wait at GSM1800 before a call connection; during the connection of MS call, the traffic distribution can be adjusted by directed retry. In connected state, try to connect as much as possible traffic to high level GSM1800 cells in lower layers through cell hierarchy and specifying different hierarchical cell structures (HCS); the multiband traffic handover can be used to make traffic load more rational. The following describes in detail the cell selection, cell reselection, directed retry, cell hierarchy and specifying HCS, and multiband handover.

1)

Cell Selection and Cell Reselection

In idle mode, the system guides the traffic absorption by controlling the process of MS cell selection and cell reselection. When MS turns on, it first needs to select cell so that to confirm its serving cell. Principle of cell selection: cells allowing to be accessed and cells with high priority are first selected; for the cells with the same priorities, the cell with maximum C1 value is first selected. The C1 value of selected cell should be greater than zero. C1 value is calculated as follows: C1 = RxLEV − RxLEV _ Access _ MIN − MAX ((MS _ TxPWR _ MAX _ CCH − P ),0 )

RxLEV Access MIN range: 0~63, 0 is corresponding with -110dBm, 63 is corresponding with -47dBm. MS TxPWR MAX CCH value range: z

GSM900: 0~19 available, 0 is corresponding to 43dBm, 1 is corresponding to 41dBm. The value of higher level is 2dB greater than that of lower level.

z

GSM1800: 0~15 available, 0 is corresponding to 30dBm, 1 is corresponding to 28dBm. Step is 2dB.

In the multiband network, owing to the strong fading of signals in GSM1800 frequency band, signals in GSM900 frequency band is stronger. In order to enable MS can be accessed to GSM1800 system, the cell selection priority can be controlled by setting value of cell bar qualify (CBQ) and cell bar access (CBA). The signals in GSM1800 cell are generally weaker than that in GSM900 cell. To enable the multiband MS to select

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GSM1800 cell preferentially, GSM1800 cell can be set as Normal and GSM900 cell as Low. Table 2-15 Cell selection/reselection hierarchy Case 1 2 3 4

CBQ

CBA

0 0 1 1

0 1 0 1

Cell selection Normal Barred Low Low

Cell reselection Normal Barred Normal Normal

When selecting cell, GSM900 cell is set as CBQ=1, CBA=0 and GSM1800 is set as CBQ=0, CBA=0. This enables GSM1800 cell to have a higher priority. After MS completes cell selection, it should reselect cell in standby state in order to select a better serving cell. The parameter that decides cell reselection is C2. MS reselection principle is to select the cell with maximum C2 value as the serving cell. C2 depends on the following factors: z

C2=C1+CRO-TO×H(PT-T) (PT<31)

z

C2=C1-CRO

(PT=31)

Where, the value Cell Reselection Offset (CRO) decides the difficulty of cell reselection and Temporary Offset (TO) functions within penalty time (PT). CRO value can be 0, 1, ↑ 63 with grade as unit, which are corresponding to 0=0dB; 1=2dB; 63=126dB respectively. TO value can be 0, 1, and 7, which are corresponding to 0=0dB; 1=10dB; 6=60dB; 7=infinite respectively. PT value can be 0, 1, and. 31, which are corresponding to 0=20s, 1=40s, and 30=620s respectively. H ( ) = 0 if PT-T<0 H ( ) = 1 if PT-T>0 C1 indicates the quality of radio channel. The greater C1 value, the better quality of channel. C2 is corrected manually. C2 value of each cell can be adjusted through CRO value. So the C2 value can be calculated according to CRO, TO, and PT so as to confirm the cell reselected for MS. That is to say, C2 value of GSM1800 cell can be greater than that of GSM900 cell by setting parameters that can affect C2 value, such as CRO. Therefore, though signals in GSM1800 cell are weaker that of GSM900 cell, GSM1800 cell can still be reselected for MS by setting parameters. Parameters of cell selection and reselection can be flexibly used to control MS to select GSM1800 network as required in network planning; under the precondition that

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network quality is guaranteed, these parameters can be used to make MS establish calls in GSM1800 network so as to share the load of GSM900 network.

2)

Directed retry

Provided that the process to initiate a call by an MS has completed switching, connection, control of some signaling and it is time to for SDCCH to assign TCH so as to connect the speech channel of both parties. However, it is found that the TCH of this cell is full. In this case, directed retry can be used to assign TCH of adjacent cells for MS from SDCCH thus to guarantee the successful connection. At the same time, the traffic is shared.

3)

Layers and levels of network

Under the connected state, traffic between frequency bands can be distributed rationally through abundant Huawei multiband handover This is the core of multiband traffic guide and control strategy. Huawei hierarchy handover algorithm divides a cell into 4 layers each layer with 16 levels. This meets the need of complicated networking circumstances. The design concept of this hierarchy has fully considered the collaboration with the current network equipment and the requirement of future network development. The cell layers and levels are as shown in Figure 2-36. Umbrella Cell

GSM900 Cell

GSM 1800 Cell

Layer 4

GSM 900

GSM 900

GSM 900

GSM 900

Layer 3

GSM 1800

GSM1800

GSM1800

Layer 2

GSM900

GSM900

GSM900

GSM1800

GSM1800

GSM1800

GSM900

Layer 1

Micro Cell GSM1800

Figure 2-36 Cell layers and levels The GSM system covering the same area is divided into 4 layers. The high layer is the fourth layer, i. e. umbrella-like cellular, which is generally is a GSM900 cell with wide coverage. It has two functions: covering and quick connection of MS. The middle layer consists of GSM900 macro cells. These are the main cells of the system and most of subscribers gather in this layer. The followed layer consists of GSM1800 micro cells with small coverage. This layer is the main target for capacity expansion so as to solve the problem of short resource of frequencies. The bottom layer consists of GSM1800

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Pico cells, which is to meet the requirements of hot spot and blind spot areas. For the priority, the cell in lower layer has a higher priority. Considering the future network development, to make network planning and optimization more detailed and more flexible, the layer should combine with level division, that is to say, each layer should be divided into several levels. Each layer of these four layers is divided into 16 priorities. For the description of handover, please refer to 2.3.6 .

IV. Features of GSM1800 1)

Propagation characteristics of GSM1800

The working frequency of GSM1800 is two times as that of GSM900. According to COST-231 model and practical experience, the propagation loss of GSM1800 inside stadia is 6dB greater than that of GSM900 and the propagation loss of GSM1800 outside stadia is 10dB greater than that of GSM900. The propagation loss inside buildings is 5~17dB higher (it varies from material to material). The fast fading of GSM1800 is a disadvantage to realize the fine coverage of GSM1800 and the condition of GSM1800 coverage is directly related with the performance of network. Moreover, electromagnetic diffraction of GSM1800 is poorer that than of GSM900.

2)

GSM1800 coverage requirements

a) Outdoor coverage The outdoor coverage can be easily realized if the distance between sites is not too far. If necessary, besides the installation of GSM1800 equipment on the site of original GSM900 site, the new sites should be installed in proper places. b) Indoor coverage In order to guarantee the fine indoor coverage of GSM1800, the distance between BTSs in the city should not exceed 1000m. In the city with buildings in reinforced concrete structure, which penetration loss is very great, so it is recommended that the distance between BTSs should be 500~800m.

3)

GSM1800 coverage mode

There are three coverage modes for GSM1800 network in multiband network: Fine continuous coverage, continuous coverage of hot spot areas, scattered coverage of hot spot areas. a) Fine continuous coverage This coverage mode has the following advantages: GSM1800 is easy to absorb traffic and has less handovers and high quality of operation; the frequency planning and network optimization is easy to be realized and the traffic distribution is easy to be controlled; after sites are constructed, if capacity expansion is needed, it is only needs to configure carrier instead of constructing new sites; and it is convenient to be 2-109



constructed and maintained. The disadvantage is that the investment is large and it is hard to select sites in one time. b) Continuous coverage of hot spot areas This coverage mode has the following disadvantages: the traffic absorption of GSM1800 is limited and there are frequent multiband handovers; strict requirement for locating traffic hot spot; it is hard to plan frequencies and optimize network due to the irregular distribution of GSM1800 BTSs. The construction and maintenance is complicated. The advantage is that the site in highly intense areas can be gradual constructed so as to save the investment. c) Scattered coverage of hot spot areas This coverage mode has the following disadvantages: the traffic absorption of GSM1800 is low and there are frequent multiband handovers; strict requirement for locating traffic hot spot; it is hard to plan frequencies and optimize network due to the irregular distribution of GSM1800 BTSs. The construction and maintenance is complicated. The advantage is that the initial investment is small.

V. Multiband networking modes There are three modes for multiband networking: standalone MSC networking, shared MSC/standalone BSC networking, and shared BSC. In general, the former two modes are called standalone networking and shared BSC network is also known as mixed networking.

1)

Standalone MSC networking

Standalone MSC networking refers to that GSM900 and GSM1800 use different MSCs for networking respectively, as shown in Figure 2-37.

BTS BSC

MS

M S C /V L R

BTS

E IR OMC H L R /A U C

SMC BTS MS

BSC

M S C /V L R

BTS

G SM 900

G SM 1800

Figure 2-37 Standalone MSC networking mode

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The standalone MSC networking has the following features: z

No impact on original network

z

Clear network planning, clear network data configuration, and easy to construct.

z

Satisfy the requirement of long-term capacity expansion.

z

Convenient to manage the whole network and develop new services.

z

The initial investment of network is relative large but the investment for each subscriber is the smallest.

z

Introduce competition so as to lower equipment investment and improve quality of service.

Besides the above features, the standalone MSC networking increases the inter-office handovers and position updates, thus the load of signaling link is increased. In addition, the standalone MSC networking has the problem of collaboration of equipment of different providers. In a long-term view, it is better than mixed networking.

2)

Shared MSC / standalone BSC networking

Shared MSC / standalone BSC network refers to GSM900 and GSM1800 network adopts the same MSC and different BSCs for networking, as shown in Figure 2-38.

BTS MS

BSC BTS EIR

OMC MSC/VLR SMC

HLR/AUC

BTS MS

BSC BTS

GSM1800

GSM900

Figure 2-38 Shared MSC/standalone BSC networking Shared MSC/standalone BSC networking has the following features: z

It has impact on the original network.

z

It needs to plan NSS again and it is hard to be constructed.

z

It is hard to expand its capacity. As network develops, construction and maintenance might become difficult.

z

The initial investment of network is relative small and the investment for each subscriber is small.

z

Introduce competition so as to lower equipment investment and improve quality of service.

z

BSC has backup function so the network security is good.

3)

Shared BSC networking 2-111



Shared BSC networking refers to that BTSs of GSM900 and GSM1800 access the same BSC or multiband mixed BTS accesses BSC, as shown in Figure 2-39. BTS MS

BTS

BSC

BTS

EIR

OMC MSC/VLR SMC

HLR/AUC

BTS MS

BTS

BSC

BTS GSM900

GSM1800

BTS GSM1800/GSM900

Figure 2-39 Shared BSC networking mode Shared BSC networking has the following features: z

It might impact on original network greatly, especially when BSC has a small capacity.

z

It needs to plan NSS and BSS again so the construction is difficult.

z

It is hard to expand its capacity. As network develops, construction and maintenance might become difficult.

z

Development of new services is restricted.

z

It cannot introduce competition thus it is hard to lower the cost and to improve service.

z

The initial investment of network is the smallest and the investment for each subscriber is the largest.

2.2.9 Carrier Mutual-assistance I. Overview In case of BCCH TRX failure or baseband frequency hopping TRX failure, the cell can handle it automatically through the TRX aiding function. Thus, the cell services can not be affected before the failed TRX is replaced.

II. Technical description TRX aiding contains BCCH TRX aiding and baseband frequency hopping TRX aiding. For the non-baseband frequency hopping cell, only BCCH TRX aiding will occur. For the baseband frequency hopping cell, both BCCH TRX aiding and baseband frequency hopping TRX aiding may occur.

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1) BCCH TRX aiding In the idle state, MS needs to know some information about the infrastructure of the network. BSC sends the generic broadcast message to BTS, and BTS broadcasts it on BCCH. BCCH is a low-capacity channel and can send a message of 23 bytes every 0.235s. The broadcast information includes cell selection information, adjacent cell information, access control information, private channel control information, cell identification code, location, system parameters of packet service, etc. When BCCH TRX of a cell is failed, all services of this cell will be interrupted. In order to ensure the cell services not to be affected, in case of BCCH TRX failure, another available TRX of the cell can substitute for the TRX that BCCH is originally on. Thus, the cell can continue to provide the services. After the fault of TRX that BCCH is originally on is removed, BCCH can be recovered (or, changed back) onto this TRX. This is the function of BCCH TRX aiding. 2) Baseband frequency hopping TRX aiding In the baseband frequency hopping cell, if a TRX participating in frequency hopping is failed, the conversations on this frequency hopping channel will lose some voice frames. Correspondingly, the communication quality will be decreased. In order to ensure the communication quality, in case of baseband frequency hopping TRX failure, BSC will start the TRX aiding function. It will automatically change the cell to the non-frequency-hopping mode. Thus, the failure of a TRX will not affect the communication quality of the entire cell. When the fault is removed, this cell can be restored to the frequency hopping mode. This is the function of baseband frequency hopping TRX aiding. When TRX aiding or TRX aiding recovery occurs, there will be corresponding alarms reported (all are event alarms): 198: BCCH TRX aiding alarm. 199: BCCH TRX aiding recovery alarm. 200: Baseband frequency hopping TRX aiding alarm. 201: Baseband frequency hopping TRX aiding recovery alarm.

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Note: 1) If BCCH TRX in a baseband frequency hopping cell is failed, except for BCCH TRX aiding, baseband frequency hopping TRX aiding will also occur. That is, the cell is changed to the non-frequncy-hopping mode. In addition, only when the faults of all TRXs participating in frequency hopping and the original BCCH TRX are removed, can the baseband frequency hopping TRX aiding recovery occur. That is, the cell is restored to the frequency hopping mode. 2) When TRX aiding or TRX aiding recovery occurs, the cell will be initialized again. 3) In the previous BSC versions of G3BSC32.10100.06.1120A, the TRX aiding function cannot be used together with the baseband timeslot frequency hopping function. From the version of G3BSC32.10100.06.1120A, this limitation is canceled. These two functions can be used at the same time. 4) If such adjustment as SDCCH dynamic adjustment, full-rate/half-rate dynamic adjustment or PDCH channel dynamic adjustment occurred in the cell, the dynamic adjustment channel on the TRXs involved in TRX aiding will be restored to the channel type configured originally. For BCCH TRX aiding, the involved TRXs contain the current BCCH TRX and TRX to be aided. For baseband frequency hopping TRX aiding, the involved TRXs are all TRXs in the entire cell.

III. Parameters The TRX aiding function only uses a parameter for controlling. The parameter is configured in [Cell Configuration Data Table], as shown in Figure 2-40. Figure 2-40 Description of parameter of Cell Configuration Date Table Parameter

Value range

TRX Aiding Not Allowed

TRX Aiding Function Control

Allowed, Recover Forbidden Allowed, Recover Immediately Allowed, Recover When Check Res (default value of the field).

Description TRX aiding is not allowed. That is, the TRX aiding function is closed. TRX aiding is allowed. However, after the fault TRX is restored, TRX recovery is forbidden. TRX aiding is allowed. After the fault TRX is restored, it can be recovered immediately. TRX aiding is allowed. After the fault TRX is restored, it will not be recovered immediately but recovered during resource check at 3:00 am.

2.2.10 Cell Broadcast I. Overview Cell broadcast is a specific service of the GSM system, broadcast information to all mobile stations in a specific area periodically. The MS supporting this service can monitor this broadcast information continuously and this information can be displayed

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on the MS terminals. The typical examples of cell broadcast are to broadcast traffic information and weather forecast. Short Message Service Cell Broadcast (SMSCB) allows short message to be broadcast to all mobile stations in certain areas. These areas may be one or several cells, even the entire PLMN area. The short message from Cell Broadcast Centre (CBC) is sent to BSC, and BSC will manage and dispatch the message, and send the received message to BTS, which can control the flow of short message broadcast. The architecture of cell broadcast system is as shown in Figure 2-41. WAN

OMC

CBC

Remote connection LAN connection LAN

CBC

CDB

CDB

BTS

GMEM GMEM ... GMEM GMEM ...

BSC

BTS

BTS BSC

Figure 2-41 Cell broadcast system architecture

II. Cell broadcast functions 1)

Receiving and storing of short messages

CDB receives and stores the short message from CBC. There are three kinds of commands to broadcast short messages sent from the CBC: send a new broadcast short message, delete an outdated message or a message that meet specified requirements, and replace an old message with a new one. CDB handles these three cases respectively and updates the memory of short messages, i. e., adding the new message to the short message database. On the reception of new command it deletes the older one, or deletes the older message before adding a new message after the reception of replacing message. If old message can not be deleted then the new message will not be added.

2)

Dispatching and transmitting of short messages

Every short message should be broadcast in specific areas, which correspond to one or more cells. In the meantime, every message has its own transmission requirements, i. e. the transmit times and frequencies are different. BSC should send each message to the specific area according to its transmit requirements. When a cell requests multiple short message, BSC should calculate the transmitting time sequence according to specific message dispatch algorithm, and send these messages to BTS in turn according to the assigned sequence. 2-115


3)


Responding to the query of cell broadcast centre

While storing and transmitting short messages, CDB will record the completion message, the number sent by each cell, message load conditions of each cell and the broadcast channel state of each cell. CBC can keep track of the current system running state by querying and monitoring the cell broadcast system. It can adjust and optimize the system to ensure satisfactory running. When fault occurs in cell, CDB will report it to CBC, which will stop sending short messages to this cell. When CBC identifies that a specific broadcast message is been sent, it will send a command to delete or replace this message from CDB to reduce its load.

III. Cell broadcast features 1)

Supporting MS DRX mode

If MS in idle mode has selected its serving cell, it is ready to monitor the paging message from this cell. To lower the power consumption of MS, the GSM specification adopts the discontinuous receiving mechanism (DRX), i. e. each subscriber (IMSI) corresponds to a dedicated paging group and each group corresponds to a paging sub-channel of the cell. MS recognizes its paging group and the corresponding paging sub-channel according to the last three digits of the IMSI and PCH allocation on service cell. MS in idle mode uses its own paging sub-channel to receive the paging message (or to monitor the receiving level of the BCCH carrier of the non-serving cell). MS ignores the message from other paging sub-channel or even shuts down the power of some hardware to lower its power consumption during the broadcasting of other paging sub-channels. But MS must measure the network messages task periodically. The BSC supporting DRX mode needs to send scheduling messages to satisfy the requirement of the discontinuous receiving by MS. One dispatch message contains the information of the short messages to be sent one after another in a cell. The cycle occupied by short messages in one dispatch message is called dispatch cycle. Dispatch message contains the descriptions of each short message to be broadcast according to the transmit sequence, and indicates the message position in dispatch cycle. Mobile subscriber can read concerned short message in less time by reading dispatch message, thus minimizing power consumption.

2)

Supporting traffic control for BTS

Transmit sequence of short messages in each cell is dispatched by BSC and transmitted by BTS. Each TRX maintains one message buffer and sends short message periodically to MS through specific channel. Thus, there will be an asynchronous state of sending short messages between BSC and BTS. In this case, BTS will report this asynchronous state to BSC in the form of load indication message. If a specific TRX receives too many short messages and can not send them in time, BSC will temporarily stop sending short messages of this TRX. If a TRX barely receives short messages, BSC will send out some short messages so that the time sequence for sending short message in this cell will be met. By sending broadcast messages to BTS 2-116



to control traffic, CDB can schedule the balance of the broadcast system of the whole cell. Thus the requirement of sending broadcast messages is satisfied as much as possible.

2.2.11 Radio Channel Allocation BSC is responsible for the allocation of circuit channel and PCU for the allocation of packet data channel.

1)

Radio channel allocation requirements

Radio channel allocation is based on the following requirements: z

Initial channel allocation: An idle MS enters active mode during MOC, paging response, or location updating.

z

Connection allocation: The channels allocated can not meet the requirements. For example, MS has been allocated SDCCH, but if need to transfer speech or data.

z

Handover: Due to the subscriber mobility or the change in the interference level, it is necessary to hand the MS call to another channel.

For the dedicated channel allocation management of the BSC system, VEA (Very Early Allocation) and EA (Early Allocation) are used in a combined manner as an allocation strategy. VEA refers to the allocation of TCH at initial stage. EA refers to the allocation of TCH after the initial allocation of SDCCH. During channel allocation in the BSC, the VEA is used for some special calls. For common calls, the EA technique is used, which can effectively improve channel utilization efficiency.

2)

Radio channel allocation algorithm

BSC channel allocation algorithm selects the channel for allocation by considering channel interference, configuration, history record, load distribution, MS transmitted power, etc., and based on the specific call event and environment. Channel interference directly determines such critical traffic statistic indices as the quality of communication completion ratio and call drop rate on the channel. It is the most important factor to be considered during the channel allocation. The measurable interference includes uplink interference of the idle channel and the uplink / downlink interference of the occupied channels. The rule for the interference-based channel allocation algorithm is to select the channel of lower interference for allocation. But there are two special cases. The first is that for a high-level call or user, the MSC may have an interference limit for channel allocation. The channel with interference higher than this limit can not be allocated. The second is the specific call environment in which the maximum transmitting power capacity of MS and path loss are considered. The call with better receiving level can be allocated with 2-117



a channel having severer interference. The channel with lower interference is reserved for the call of poorer receiving level and thus the call completion ratio and communication quality can be improved. The channel allocation algorithm based on channel configuration is based on the following factors: whether the carrier of the channel is that of BCCH, the frequency reuse distance of the TRX, whether the channel use frequency hopping, and the number of frequency in the frequency hopping group. Proper frequency allocation based on channel configuration helps to reduce the interference of network, and improve the quality of network. The channel allocation algorithm based on channel history record is characterized by the memory function. The history record includes the channel seizure success or failure and call drops, and it needs to verify whether the cause of seizure failure and that of call drop lies in the radio channel itself. Such history records can provide reliable facts for the current channel allocation. The channel allocation algorithm based on load balancing is characterized by even distribution of the carrier frequencies, Time Slots (TS) and sub-TSs during the channel allocation. It can reduce adjacent-channel interference and same frequency interference. On the other hand, it also helps to avoid the risk caused by calls being concentrated on a few carriers. There are also special allocation methods for specific call events such as intra-cell handover and IUO handover. For example, intra-cell handover is mainly caused by the quality problem of the speech channel, which indicates that the carrier where the original channel is located has suffered interference. If the original channel frequency hops, then some frequency bands in the frequency-hopping group of the original channel may have suffered severe interference. In case of intra-cell handover, the allocation of new channel may select the carrier and frequency hopping group that are different from those of the original channel.

3)

Queuing

Channel allocation algorithm used in the BSC supports queuing. In case of initial allocation, no queuing takes place because an MS will resend the channel request. Queuing is mainly applied to connection allocation and handover, where the MSC decides if queuing is allowed in the allocation request or handover request. If no allocable radio channel is available and queuing is allowed, then the M900/M1800 BSC will queue the allocation requests. Try to allocate traffic channel with the allowed period of time so as to reduce the subscriber’s wait time.

4)

Allocation by priority

The channel allocation algorithm in the M900/M1800 BSC supports different priority levels, that is, channel allocation can be carried out according to the preset priority

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levels. In some cases, the request of higher priority can be forcibly implemented and can occupy the channel, which is being used by a user of lower priority.

5)

Dynamic allocation of SDCCH

a) Purpose The objective of SDCCH dynamic allocation is to optimize the usage of traffic channels and signaling channels, reduce the occurrence of congestion on the SDCCH, and lower the impact of the initial configuration of the SDCCH on the system performance. The number of SDCCHs required is based on the traffic model, that is, the current traffic distribution and statistical data about handover. An increase of short message service will lead to the increase of requirement for the SDCCHs, which makes the prediction of the SDCCHs requirement very difficult. There may be the case that the number of users in a cell suddenly increases, and many users can not access the network just because they fail to request the SDCCH. In this case, TCHs have to be converted into SDCCHs so as to ensure that most of the users can access the network and communication can be implemented through directed retry function, which improves the call success rate. b) Advantages It's not necessary to work out the exact number of SDCCH in advance after implementing SDCCH dynamic allocation. SDCCH dynamic allocation increases the system capacity and improves the call completion ratio. The disadvantage of SDCCH dynamic allocation is increased intra-cell handover traffic. It can be overlooked on account of its advantages. c) Approach SDCCHs are allocated with the cell as a unit. The following should be configured in the data management console: dynamic/static allocation of SDCCH, idle SDCCH threshold, and maximum number of cell SDCCHs, minimum time for TCH recovery, etc. If SDCCH allows dynamic allocation and satisfy the following conditions: z

When number of SDCCHs is less than or equal to idle SDCCH threshold;

z

And number of existing SDCCHs in the cell is less than the maximum number of SDCCHs;

z

Number of idle TCHs is greater than 4 or greater than the number of configuration carriers.

The system will automatically select a TCH and turn it into SDCCH. At the same time, BSC delivers configuration command to BTS to configure this TCH as SDCCH and update the channel list of internal BSC.

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When there are many idle SDCCHs, the SDCCH channels are dynamically converted into TCHs.

6)

Dynamic allocation of PDCH

a) Introduction To support GPRS service, two types of channels are introduced, i. e. , static PDCHs and dynamic PDCHs. Static PDCHs are used for packet service only. Dynamic PDCH is initialized as a TCH and controlled by BSC. When the static PDCHs are not sufficient, the PCU will apply for dynamic PDCHs from the BSC. When the PCU is granted with the control authority, dynamic PDCHs are used for packet service. On the contrary, if TCHs are insufficient, the BSC can request dynamic PDCHs from the PCU. When the BSC is in control, the dynamic PDCHs serve as TCHs. According to the protocol, following channel combinations are provided. z

PBCCH+PCCCH+PDTCH+PACCH+PTCCH

z

PCCCH+PDTCH+PACCH+PTCCH

z

PDTCH+PACCH+PTCCH

z

PBCCH+PCCCH

Huawei BSS supports the first three combinations. b) Approach The dynamic PDCH control is based on cell, the following two items should be configured: Idle TCH threshold N1; application TCH decision period T (minute). Set a Count for each cell with initial value being 0. Count value ranges -T~T. Adjust Count every one minute. If the number of the current channels is greater than N1, then 1 is added to the counter value, if the number of the current idle TCHs is less than or equal to N1, then 1 is subtracted from the counter value. If the counter value is less than -T/2 after adjustment, then the BSC requests dynamic PDCHs from the PCU. After the BSC acquires the control power, dynamic PDCHs serve as TCHs. If any change takes place to the current type of a dynamic PDCH, it is necessary to issue a configuration command to the BTS so as to configure this channel as the current type and update the channel list in the BSC. c) Note: It is difficult to predict the packet traffic of the cell. The introduction of dynamic PDCH can improve the utilization of the channels. Channel allocation follows the principle that circuit switching service being preferred to packet switching service. The PCU will automatically release the dynamic PDCH when the number of idle PDCH is enough.

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2.2.12 Half Rate I. Function Description Increasing BSS capacity. With the half rate function, a TRX can provide a maximum of 16 half rate traffic channels (TCHs) and can simultaneously support a maximum of 16 MSs. This makes the BSS capacity almost doubled. Raising call proceeding rate. With the half rate function, a half rate channel can be assigned via the immediate assignment procedure. This raises the call proceeding rate. Since the BSS system can provide more TCHs, there is no need to worry about channel congestion even though the TCH is assigned during the immediate assignment procedure.

II. Technical Description 1)

Call procedure

The fundamental principle of the half rate function is that two logical half rate TCHs are multiplexed in a timeslot of a physical TDMA frame as two logical channels. The hardware provides a more advanced speech coding/decoding algorithm to make the speech QoS on a half rate channel close to that on a full rate channel. The BSC deals with the same call signaling procedures as before after the half rate function is performed. However, the contents of some signaling messages may change because a different channel type is selected. For example, that BSC allocates a half rate TCH to MS may be reported to the MSC in an Assignment Complete or Handover Complete message. The BSC shall select a speech version (in the case of speech transmission) or data rate (in the case of data transmission) for the current call after allocating a TCH. Due to the FTC capability limitation, the BSC does not support half rate data services by default. The operator may enable the corresponding software parameter switch (see "Parameter") to enable the BSC to support the half rate data services. The BSC always select the first data rate the MSC allows. For selecting a speech version, a multi-module BSC takes into consideration the speech version the MSC allows, the rate type of the current channel, the speech version supported by the circuit pool of the A interface circuit of the current call and the capability of the FTC bearing the current circuit. Then the BSC fetches the intersection of the above four sets. It selects the latest one among the speech versions (if so) in the intersection. A single-module BSC differs from a multi-module BSC in speech version selection. The single-module BSC does not take the capability of the FTC bearing the A interface circuit into consideration. Therefore, the A interface circuit configuration in a single-module BSC should comply with the principle that the speech version set supported by the circuit pool should be a subset of that supported by the FTC.

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The dynamic switchover between a full rate TCH and a half rate TCH makes it possible to optimize the TCH configuration according to the current capacity situation on the existing resource basis. This lessens the possibility of TCH congestion and makes it no longer a problem that the initially configured full rate TCHs and half rate TCHs cannot satisfy the actual traffic requirement.

2)

MSC channel rate selection policy

When the requested channel type is "Only select full rate channel" or "Only select half rate channel ", only a channel at a fully matched rate can be allocated. When the requested channel type is "Select full rate channel priority", a full rate TCH shall be allocated if other conditions are satisfied and there is a full rate TCH in the cell. When the requested channel type is "Select half rate channel priority ", a half rate TCH shall be allocated if other conditions are satisfied and there is a half rate TCH in the cell. This rigid channel allocation as per MSC's rate assignment is difficult to get the system capacity and speech QoS into the optimum status. To break down this limitation, Huawei introduces a BSC channel rate selection policy. The MSC channel rate selection policy is still provided in order that the A interface interconnection test may prove that channel allocation can be implemented as per MSC's assignment.

3)

BSC channel rate selection policy

When the requested channel type is" Only select full rate channel " or " Only select half rate channel ", only a channel at a fully matched rate can be allocated. When the requested channel type is " Select full rate channel priority " or " Select half rate channel priority ", a full rate TCH is preferred to guarantee the speech QoS if there are many idle full rate TCHs and a half rate TCH is preferred to guarantee the system capacity if there are few full rate TCHs. This is the basic principle of BSC channel rate selection. In practice, a full rate TCH is preferred when the number of idle full rate TCHs > Idle Thrsh for TCH/F Priori in the current cell and a half rate TCH is preferred when the number of idle full rate TCHs ≤ Idle Thrsh for TCH/F Priori in the current cell.

III. Parameter 1)

Channel Management Parameter

"TCH Rate Adjust Allowed" in [Channel\Radio CH management ctrl. table]. "TCH Rate Adjust Traffic Thrsh" in [Channel\Radio CH management ctrl. table] "MIN Recovery Time of TCH/H (s)" in [Channel\Radio CH management ctrl. table] "Idle Thrsh for TCH/F Priori" in [Channel\Radio CH management ctrl. table]

2)

Networking Parameter

The 34BIE has to be used to support the half rate function. Since the 34BIE applies a different exchange mode from before, the following networking parameters are added or modified.

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"Connection mode" in [Local Office\BSC BIE description table]. "BIE networking configuration" in [Local Office\Site BIE config. table]. "Site ID 1 ~ Site ID 30" in [Local Office\BSC BIE active/stby. group table]. "Belong to BIE group No.1 ~ Belong to BIE group No.8" in [Site\Site description table]. "BSC BIE Port No " in [Local Office\Radio channel config. table]. "BSC BIE E1Timeslot No " in [Local Office\Radio channel config. table]. "BSC BIE port No " in [Local Office\LAPD semi-perm. connection table]. "BSC BIE E1Timeslot No "in [Local Office\LAPD semi-perm. connection table]. A [BSC BIE semi-perm. connection table] is added to support semi-perm. connection establishment. It includes the following fields: "Module No."in [Local Office\BSC BIE semi-perm. connection table] "Trunk circuit No."in [Local Office\BSC BIE semi-perm. connection table] "Transfer Rate "in [Local Office\BSC BIE semi-perm. connection table] "BIE Port No "in [Local Office\BSC BIE semi-perm. connection table] "E1 Timeslot No "in [Local Office\BSC BIE semi-perm. connection table]

2.2.13 E1 Ring Topology I. Overview E1 ring topology is a networking mode in which several sites are connected in a ring. All the sites work in the forward ring normally. In case the transmission ring is broken at one point, the sites before the breakpoint still work in the forward ring while those after the breakpoint are reinitialized and begin to work in the reverse ring. Compared with the normal chain topology, E1 ring topology has an advantage that the transmission ring can be automatically divided into two chains when it is broken at one point so that the sites before and after the breakpoint can both still work normally. This enhances the robustness of the system.

II. Technical Description To be specific, the E1 ring topology has the following functions: 1) Automatic rotate in case of ring breakage Normally all sites in a ring work in the forward ring as if they were in a normal chain. In case the transmission ring is broken at one point, the sites after the breakpoint

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automatically form a chain in the reverse direction and begin to work in the reverse ring after reinitialization. If the transmission in the reverse ring is normal, the sites do not automatically rotate back to the forward ring after the forward ring recovers. If the transmission in the reverse ring is interrupted, the sites automatically rotate back to the forward ring after the forward ring recovers. In the case of rotate (rotate-back), the BSC reports a ring rotate (rotate-back) alarm to the alarm system to notify the operator to examine and repair the transmission ring and so on. 2) Manual rotate/rotate-back If they work normally in the reverse ring, the sites do not automatically rotate back to the forward ring after the forward ring recovers from failure. The operator can forcedly rotate them back to the forward ring. The operator can also manually rotate the sites to the reverse ring in case the transmission quality in the forward ring is not good. The manual rotate/rotate-back for a site is performed by specifying port 1/port 0 of the site as a reset port in the site maintenance system during the site reset process. To realize a manual ring rotate, the operator shall begin with the site at the first level in the reverse ring to be rotated and then the one at the next level and so on. A site is successfully rotated to the reverse direction and then reinitialized before the next site is rotated. To realize a manual ring rotate-back, the operator shall begin with the site at the first level in the forward ring to be rotated and then the one at the next level and so on. 3) Dynamic rotate parameter configuration and query The operator may query the ring topology parameters and the current ring direction of a site in the site maintenance system. The operator may also dynamically modify those parameters in the data management system or auto data configuration system. 4) Dynamic data configuration The BSC still supports dynamic data configuration in the E1 ring topology, such as dynamic BTS adding/deletion, cell adding/deletion, TRX adding/deletion, etc. The dynamic BTS adding must be implemented in the forward ring at the time when the forward transmission is normal. All sites in a ring shall be reset after dynamic adding/deletion of BTS, cell, TRX or modification of channel type in the ring or tributary. 5) Involved Technology When it detects OML breakage, a site in a ring continuously tries to establish a chain via port 0 or port 1 till it succeeds. The MPU prepares two sets of data i.e., forward ring data and reverse ring data for each site. The BSC sends the forward ring data to a site when a chain is established for the site in the forward ring. Otherwise, the BSC sends the reverse ring data to the site when a chain is established in the reverse ring. The site is initialized and started after it receives the data.

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III. Parameter This parameter determined a group of BIE working under “Full Rate Ring Topology” or “Half Rate Ring Topology” Rotate parameters: 1) Auto rotate permit: It indicates whether a site is allowed to rotate automatically in case of transmission interruption. Its default value is Yes. 2) Waiting time before rotate: It indicates the time measured in seconds a site waits before it rotates to the reverse direction in case of transmission interruption. Its value range is 60~300. Its default value is 90. 3) Try rotating duration time: A site continuously tries to establish a chain via port 0 or port 1 after it begins to rotate. It turns to the other port if it has not established a chain via one port after the "Try rotating duration time". This time is measured in seconds. The value range of this parameter is 60~300 and the default value is 90.

2.2.14 GSM900/GSM1800 Co-cell I. Overview With the sharp increase in MS quantity, it has become an inevitable tendency to construct a dual band network. At present, there are three networking modes available to the construction of dual band network: standalone MSC, shared-MSC but standalone BSC, and shared-BSC. In any of the above networking modes, the inter-cell handover and cell reselection will be inevitable, as will inevitably reduce the network quality. A 900M/1800M co-cell is a networking mode in which the GSM900 and DCS1800 TRXs coexist in the same cell. The best advantage of using the 900M/1800M co-cell to construct a dual band network is that two frequency bands coexist in a cell and that the 1800M frequency band becomes a natural extension of 900M frequency band in this mode. This avoids cell reselection and inter-cell handover that are inevitable in other networking modes.

II. Technical Description A dual band MS can be freely handed over between the two frequency bands. Since the 900M is characterized by less propagation loss and larger coverage, it is recommended as the BCCH in this networking mode. The TRXs in the frequency band the BCCH belongs to shall be in the underlaid subcell and those in the other frequency band the BCCH does not belong to shall be in the overlaid subcell. A 900M/1800M co-cell is based on a concentric platform. So does a two-timeslot extended cell. However, the two types of cells have different application purposes: the

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former is used for continuous coverage and scattered coverage in hot spots while the latter for wide coverage. Therefore, a 900M/1800M co-cell repels a two-timeslot extended cell. That is, a 900M/1800M co-cell cannot be a two-timeslot extended cell, cannot be a 900M/1800M co-cell, and vice versa. Note: The GSM900 in this document includes P-GSM, E-GSM and R-GSM.

1)

900M/1800M Co-cell Channel Allocation

Since a 900M/1800M co-cell is based on a concentric platform, the 900M/1800M co-cell channel allocation shall comply with the concentric channel allocation strategy. However, the BSC shall distinguish the MS frequency band capability before performing channel allocation, for a single band MS may not support the frequency band in the overlaid subcell. Therefore, for an MS supporting the frequency bands in both overlaid and underlaid subcells, the channel allocation can be implemented as per the concentric channel allocation strategy. For other MSs, only the channels in the underlaid subcell shall be allocated. Details are given below: Immediate assignment: When immediate assignment is performed in a 900M/1800M co-cell, since no MS information is available for reference, an underlaid-preferred channel allocation strategy is adopted to guarantee the MS can most possibly initiate a call. That is, the channel in the underlaid subcell shall be preferred. Assignment: When the MS classmark 3 is not obtained or when the MS classmark 3 indicates only the frequency band of the underlaid subcell is supported, only the channel in the frequency band of the underlaid subcell can be allocated no matter how the Assign Optimum Layer is configured. When the MS classmark 3 indicates both frequency bands are supported, the channel can be allocated according to the Assign Optimum Layer configuration.

2)

Intra-BSC incoming cell HO:

When the MS classmark 3 is not obtained or when the MS classmark 3 indicates only the frequency band of the underlaid subcell is supported, only the channel in the frequency band of the underlaid subcell can be allocated no matter how the Pref. Subcell in HO of Intra-BSC is configured. When the MS classmark 3 indicates both frequency bands are supported, the channel can be allocated according to the Pref. Subcell in HO of Intra-BSC configuration.

3)

Inter-BSC incoming cell HO:

When the MS classmark 3 is not obtained or when the MS classmark 3 indicates only the frequency band of the underlaid subcell is supported, only the channel in the frequency band of the underlaid subcell can be allocated no matter how the Pref. Subcell in HO of Inter-BSC is configured. When the MS classmark 3 indicates both

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frequency bands are supported, the channel can be allocated according to the Pref. Subcell in HO of Inter-BSC configuration.

4)

900M/1800M Co-cell Handover

Since a 900M/1800M co-cell is based on a concentric platform, the 900M/1800M co-cell handover shall comply with the normal concentric handover strategy.

III. Parameters: "Cell system type " in [Local Office\BSC Cell Table] " HW-IUO property" in [Site\Carrier Configuration Table] Table name: [Handover\Concentric Cell HO Table] Parameter: All data in [Concentric Cell HO Table] are applicable to a 900M/1800M co-cell.

2.2.15 Multi-MNC I. Overview The multi Mobile Network Code (multi-MNC) function allows the operator to configure the cells which have different MNC in one BSC.

II. Technical Description 1)

System message processing

The system sends different system messages including different MNCs respectively to the multi-MNC cell and the normal cell, and then an MS can display the mobile network name it subscribes to as per the system message. (The BSC contains the same Cell Global Identification (CGI) for a cell as the MSC does if the MSC supports a multi-MNC cell. In this case, the BSC need not use the multi-MNC function parameter). The multi-MNC function is applied when two or more network operators are integrated or when some small operators rent equipment from a large operator. See Figure 2-42.

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A-MSC

B-MSC Operator A: MNC = 12 Operator B: MNC = 34

A-BSS

T R X 1

T R X 2

Cell 1: 460 12 1850 0001 Cell 2: 460 34 1810 0002

MS Display: 12

MS Display: 34

Figure 2-42 Multi-MNC diagram In this document, a multi-MNC cell is a cell whose CGI includes a MNC different from the MNC configured in the [Local Office Information Table].

2)

Handover strategy

System provides flexible handover control means. In different situations, mobile phones can be handed over to a cell with the same MNC or a cell with a different MNC. There are seven handover control means provided: normal handover, only the handover to a cell with the same MNC allowed, a cell with the same MNC first, a better cell with the same MNC first, a better cell with a different MNC first, a cell with a different MNC first, and only the handover to a cell with a different MNC allowed. Select a suitable multi-MNC handover control type according to the actual situation. The following will give an introduction to the control strategy and the possible applicable situation of each handover type. In the situations where multiple MNCs are used, configure "Multi-MNC handover judgement allowed" with "Y". "Multi-MNC handover type" can be configured with the expected types according to the actual requirements. The control strategy and applicable situation of each handover type are as follows: a) Normal handover Control strategy: Handover to a cell with better QoS (considering all such factors as level, quality, cell level, load, whether to share the same BSC (MSC), etc.).

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Applicable situation: The situations where mobile phones are expected to be handed over to a cell with better QoS. Not considering whether the object cell has the same MNC or a different MNC. b) Only the handover to a cell with the same MNC allowed Control strategy: Only the handover to a cell with the same MNC is allowed, including the service cell. Applicable situation: The situations where mobile phones are expected to be handed over to a cell in the same network. c) A cell with the same MNC first Control strategy: As long as the adjacent cell has the same MNC with the service cell and the received level is higher than "minimal downlink power of candidate handover cell" of this adjacent cell, mobile phones will be handed over to this adjacent cell, including the service cell. Applicable situation: As long as a cell in the same network can provide normal services, mobile phones are expected to be handed over to this cell. When mobile phones cannot be handed over to a cell in the same network (for example, no signal can be detected in a cell with the same MNC), they can be handed over to a cell with a different MNC. d) A better cell with the same MNC first Control strategy: If the adjacent cell and the service cell have the same MNC and the received level of the adjacent cell is higher than the inter-layer handover threshold of this adjacent cell, mobile phones can be handed over to this adjacent cell, including the service cell. Applicable situation: When a cell in the same network can provide good services (i.e., higher than the inter-layer handover threshold), mobile phones are expected to be handed over to a cell in the same network. If no cell that can provide good services is available in the same network, mobile phones will be handed over to a cell with the better QoS, regardless of whether the object cell with the same MNC or a different MNC. e) A better cell with a different MNC first Control strategy: If the adjacent cell has a different MNC from the service cell and the received level of the adjacent cell is higher than the inter-layer handover threshold, mobile phones will be handed over to this adjacent cell. Applicable situation: When a cell with a different MNC from the service cell can provide good services (i.e., higher than the inter-layer handover threshold), mobile phones are expected to be handed over to this cell. If no cell that can provide good

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services is available in other networks, mobile phones will be handed over to a cell with the better QoS. If there are only a few cell channels in this network but the coverage is satisfied, this control strategy can be selected in case of congestion and if traffic sharing is allowed in other networks. f) A cell with a different MNC first Control strategy: As long as the adjacent cell has a different MNC from the service cell and the received level of the adjacent cell is higher than "minimal downlink power of candidate handover cell", mobile phones will be handed over to this adjacent cell. Applicable situation: As long as a cell in another network can provide normal services, mobile phones are expected to be handed over to this cell. When mobile phones cannot be handed over to a cell in another network (for example, no signal can be detected in this cell), mobile phones can be handed over to a cell with the same MNC. If there are only a few cell channels in this network but the coverage is satisfied, this control strategy can be selected in case of congestion and if traffic sharing is allowed in other networks. g) Only the handover to a cell with a different MNC allowed Control strategy: Only the handover to a cell with a different MNC is allowed. Applicable situation: Mobile phones are expected to be handed over only to a cell in another network.

3)

Application note

a) The CGI allocated by the MSC to a normal cell should include a LAC different from the LAC in the CGI the MSC allocates to a multi-MNC cell. b) The MNC in the [Local Office Information Table] at the BSC side should be the same as the MNC configured at the MSC side. At the BSC side, the cell CGI is configured as the CGI over the Abis interface of the local BSC and the external cell CGI as the CGI over the Abis interface of the peer BSC. There should be only one difference between the multi-MNC cell CGI configured at the BSC side and the corresponding CGI at the MSC side i.e., different MNCs. c) For a BSC with the multi-MNC function, inter-BSC handover can be implemented only when the peer BSC is also designed as multi-MNC function supportable. d) The multi-MNC cell cannot support GPRS services presently and the normal cell can.

III. Parameter "Multi-MNC HO Allowed" in [Handover/ Handover Control Data] "Multi-MNC HO Type" in [Handover/ Handover Control Data]

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2.2.16 E-GSM/R-GSM I. Overview Along with the development of GSM in a large scale, the frequency resource becomes more and more insufficient and bottlenecks the further development of GSM. The current solution is to introduce new frequency bands. The introduction of E-GSM and R-GSM extended bands plays an important role in solving the shortage of frequency resource.

II. Technical description According to GSM 05.05 (version 8.5.0), there are four frequency bands: 1) GSM900 base band, P-GSM: The working frequencies of the GSM900 baseband are: 890 ~ 915MHz: For mobile phone sending and BTS receiving. 935 ~ 960MHz: For BTS sending and mobile phone receiving. 2) GSM900 extended band, E-GSM (including GSM900 base band): The working frequencies of GSM900 extended band are: 880 ~ 915MHz: For mobile phone sending and BTS receiving. 925 ~ 960MHz: For BTS sending and mobile phone receiving. 3) GSM900 railway band, R-GSM (including GSM900 base band and GSM900 extended band): The working frequencies of R-GSM900 are: 876 ~ 915MHz: For mobile phone sending and BTS receiving. 921 ~ 960MHz: For BTS sending and mobile phone receiving. 4) DCS1800 band: The working frequencies of DCS1800 band are: 1710 ~ 1785MHz: For mobile phone sending and BTS receiving. 1805 ~ 1880MHz: For BTS sending and mobile phone receiving. The internal between frequencies is 200kHz. The relations between frequency points and absolute frequencies are as follows. n: frequency point. Fl(n): uplink frequency corresponding to n. Fu(n): downlink frequency corresponding to n. Unit: MHz. 2-131



Table 2-16 Table 1 Relations between frequency points and absolute frequency P-GSM 900 E-GSM 900 R-GSM 900 DCS 1800

Fl(n) = 890 + 0.2*n Fl(n) = 890 + 0.2*n Fl(n) = 890 + 0.2*(n-1024) Fl(n) = 890 + 0.2*n Fl(n) = 890 + 0.2*(n-1024) Fl(n) = 1710.2 + 0.2*(n-512)

1<= n <=124 0<= n <=124 975<= n <=1023 0<= n <=124 955<= n <= 1023 512<= n <= 885

Fu(n) = Fl(n) + 45 Fu(n) = Fl(n) + 45 Fu(n) = Fl(n) + 45 Fu(n) = Fl(n) + 95

The newly introduced E-GSM 900 band and R-GSM 900 band belong to the same band with P-GSM. However, the frequency points are not continuous. Therefore, the E-GSM extended band and R-GSM extended band are introduced. The E-GSM extended band refers to the E-GSM band excluding the P-GSM band provided in the Protocol. The R-GSM extended and refers to the R-GSM band excluding the E-GSM provided in the Protocol. Huawei BSC can support four frequency bands: P-GSM, E-GSM, R-GSM, and DCS1800. Table 2-17 Table 2 Relations between frequency bands and frequency points Frequenc y band Frequenc y point

P-GSM

E-GSM

R-GSM

DCS1800

1~124

0~124,975~10 23

0~124,955~1023

512~885

E-GSM extended band 0, 975~1023

R-GSM extended band 955~974

Channel assignment technology of E-GSM\R-GSM For the cell configured with frequency points of the E-GSM extended band or the R-GSM extended band, the channel assignment technology can adopt different assignment strategies in different situations after fully analyzing the frequency band support capabilities of the mobile phone and channels. I generation algorithm of channel assignment: Before assignment, the system has obtained the classmark of the mobile phone. According to it, the system can work out the support capability of each channel for this mobile phone. And then the system can assign a channel from all channels supporting this mobile phone conforming to the polling strategy. For example, if a mobile phone supports E-GSM, the channel to be assigned can be a channel of P-GSM or E-GSM extended band. II generation algorithm of channel assignment: Before assignment, the system has obtained the classmark of the mobile phone. According to it, the system can work out the support capability of each channel for this mobile phone. In all channels supporting this mobile phone, the system gives the priority to the channel of the band outside the band intersection. For example, if the mobile phone supports E-GSM and the channels respectively support the P-GSM band and the E-GSM extended band. The channel of

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the E-GSM extended and will be assigned first. The band intersection P-SGM will be reserved for other mobile phones with poor support capability. For the immediate assignment, the system assigns the channel for the mobile phone according to the frequency band support capability of the host BCCH.

III. Parameters "Effective frequency points: 1~64" in [Carrier configuration table]

2.3 GPRS Function The GPRS functions supported by BSS include: Radio link management and radio resources management. Access control over the MS. Provision of routes for the transfer of packet data. The radio link management function involves mainly establishment, maintenance and release of the radio links. The radio resources management function involves mainly coding/decoding of radio packet channels, configuration of radio packet channels, multiplexing of radio channels, switchover of radio channels between the circuit switched traffic channel and the packet switched traffic channel and allocation of channels to the MS. The access control function serves primarily to solve the issue of channel contention and allocate radio resources to the MS according to the requested QoS. The routes serve to transfer the uplink data to Serving GPRS Support Node (SGSN) properly and receive the downlink data from the SGSN.

2.3.1 Supported Packet System Information I. Overview The packet system information broadcast in the cell serves mainly for the MS to access the network. If the cell supports GPRS, the System Information 13 (SI13) shall be added to the BCCH, if not, SI13 will not be broadcast. The cell can either be configured with the PBCCH channel or without it. This will be notified to the MS via SI13. The main message broadcast on the PBCCH are the dedicated packet system information of GPRS.

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II. Technical description There are following types of packet system information:

1)

Packet System Information Type 1 (PSI1)

This information is sent by the network on the PBCCH or PACCH, giving information for Cell selection, for control of the PRACH, for description of the control channel(s) and optional global power control parameters. This information shall not be segmented across more than one RLC/MAC control block.

2)


This information is sent by the network on PBCCH and PACCH, giving information of reference frequency lists, cell allocation, GPRS mobile allocations and PCCCH descriptions being used in the cell. PSI2 also contains Non-GPRS cell options applicable for non-packet access. This message shall not be segmented across more than one RLC/MAC control block.

3)


This information is sent by the network on the PBCCH or PACCH, giving information of the BCCH allocation (BA_GPRS) in the neighboring cells and cell selection parameters for serving cell and non-serving cells. This information shall not be segmented across more than one RLC/MAC control block.

4)

Packet System Information Type 3 bis (PSI3bis)

This information is sent by the network on the PBCCH and PACCH giving information of the BCCH allocation in the neighboring cells and cell selection parameters for non-serving cells. This information shall not be segmented across more than one RLC/MAC control block. If not all information fits into one instance of the PSI3bis, the PSI3bis can be repeated.

5)


This information is optionally sent by the network on the PBCCH and PACCH giving information directing the mobile station to make measurements on a list of serving cell PDCHs, during the idle frame of those PDCHs. This information shall not be segmented across more than one RLC/MAC control block.

6)


This optional information is sent by the network on the PBCCH giving information for measurement reporting and network controlled cell reselection. If not all information fits into one information, the remaining information will be sent in other instances of the PSI5. The information is sent on PBCCH only if so indicated in PSI1.

7)


This information may be broadcast by the network on the PACCH. The information provides the mobile station with GPRS cell specific access-related information. The information in this information shall be the same as provided in the PSI13 on BCCH.

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PSI1~PSI4 can either be broadcast on the PBCCH or sent on the PACCH. PSI5 can be broadcast only on the PBCCH. PSI13 can be sent only on the PACCH. When there is PBCCH in the cell, no PSI13 will be transferred on the PACCH, but PSI1 will be broadcast periodically on it. When there is no PBCCH in the cell, only the PSI13 will be broadcast periodically on the PACCH. M900/M1800 BSS can transfer all the GPRS-related packet system information, provide such functions as controlled re-transmission, high-speed re-transmission and low-speed retransmission, and control the transfer of packet system information on the PACCH based on the configuration of the PBCCH/PCCCH in a cell.

III. Parameter At present, the PBCCH and PCCCH are not configured. Therefore, PSI13 is usually broadcasted on PACCCH. The configuration of PSI13 is realized with the command pcu add gprs. The following parameters are involved.

1)

NMO

Description: network operation mode. Value range: 0~3. 0 - network operation mode I, 1 - network operation mode II, 2 network operation mode III, 3 – reserved. Default: At present, the GPRS network usually has neither Gs interface nor PCCCH configured. Therefore, this parameter is usually set as "1".

2)

T3168

Description: T3168 timer overtime value. The duration for MS to wait for the packet uplink assignment message. Value range: 500 ms, 1000 ms,↑, 4000 ms Default: 1000ms

3)

T3192

Description: T3192 timer overtime value. The duration for the MS to wait for TBF release after receiving the last data block. Value range: 500 ms, 1000 ms, 1500 ms, 0 ms, 80 ms, 120 ms, 160 ms and 200 ms Default: 500 ms

4)

DRXTimerMax

Description: maximum duration of non-DRX. The maximum duration for executing non-DRX mode when MS is switching from packet transfer mode to packet idle mode. Value range: no – enter DRX mode immediately, 1 s – 1 s, 2 s – 2 s, ↑64 s – 64 s

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Default: 4 s, i.e., enter DRX mode after 4 seconds

5)

AccBurst

Description: the access burst format used by MS in PRACH, PTCCH/U or packet control acknowledge message. Value range: 8 bit, 11bit Default: Some MSs do not support 11 bit access burst type, so it is recommended to set it as "8 bit".

6)

CtrlAckType

Description: control acknowledge message type. The format adopted by MS in the control acknowledge message. Value range: 0, 1. 0 – 4 access burst used (TA can be obtained without sending "polling" message), 1 - RLC/MAC control block used (TA can be obtained only after sending "polling" message). Default: 0

7)

BsCvMax

Description: maximum value of MS countdown timer Value range: 0~15 Default: 4

8)

PanDec

Description: PAN_DEC used by MS N3102 counter. When MS T3182 times out, N3102 will reduce the value of PAN_DEC. Value range: 0~7, nouse Default: 3

9)

PanInc

Description: PAN_INC used by MS N3102 counter. When MS activates T3182 and receives the corresponding acknowledge message from packet uplink, N3102 will increase the value of PAN_DEC. Value range: 0~7, nouse Default: 3

10) PanMax Description: PAN_MAX of MS N3102 counter, i.e. the maximum value of N3102. Value range: 4, 8, ↑ 32, nouse Default: 12

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2.3.2 Supported GPRS MS Modes I. GPRS MS types The integrated GPRS MS consists of ME and SIM. ME includes MT and TE. GPRS MS is divided into three classes:

1)

Class A GPRS MS

Class A GPRS MS can simultaneously be connected to both GSM and GPRS networks and activated in both networks, monitor information of each system and start them simultaneously, and provide GPRS service and GSM circuit-switched service simultaneously, including short message service. Class A MS subscriber can initiate/receive call in both services and handover automatically between packet data service and circuit service.

2)

Class B GPRS MS

Class B GPRS MS can be connected to both GSM and GPRS networks simultaneously. It can be used in GPRS packet service and GSM circuit-switched service separately but not simultaneously, i. e. in a certain moment, it uses either circuit-switched service or packet-switched service. Class B MS also can automatically handover.

3)

Class C GPRS MS

At a certain moment, Class C MS can be connected only GSM network or GPRS If it supports both packet-switched and circuit-switched services, the service handover should be completed manually. It cannot use both services simultaneously.

II. GPRS MS multislot hierarchy GPRS system can use the MAC layer function to provide a subscriber with the multislot mode. However, the corresponding MS should be capable to support this mode. The classification of MS under different multislot modes is listed as follows.

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Table 2-18 Classification of MS under different multislot modes Classification 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29

Max. number of time slots Rx 1 2 2 3 2 3 3 4 3 4 4 4 3 4 5 6 7 8 6 6 6 6 6 8 8 8 8 8 8

Tx 1 1 2 1 2 2 3 1 2 2 3 4 3 4 5 6 7 8 2 3 4 4 6 2 3 4 4 6 8

Sum 2 3 3 4 4 4 4 5 5 5 5 5 NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA NA

Min. number of time slots Tta 3 3 3 3 3 3 3 3 3 3 3 2 NA NA NA NA NA NA 3 3 3 2 2 3 3 3 2 2 2

Ttb 2 2 2 1 1 1 1 1 1 1 1 1 a a a a a 0 b b b b b b b b b b b

Tra 4 3 3 3 3 3 3 2 2 2 2 2 3 3 3 2 1 0 2 2 2 2 2 2 2 2 2 2 2

MS type Trb 2 1 1 1 1 1 1 1 1 1 1 1 a a a a 0 0 c c c c c c c c c c c

1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 1 1 1 1 1 1 1 1 1 1 1

a=1 indicates that FH is adopted; a=0 for not adopting FH; b=1 indicates that FH being adopted or MS changes frequency when it changes from receiving to transmitting; b=0 indicates that FH is not adopted and MS does not change frequency when it changes from receiving to transmitting; c=1indicates that FH is adopted and MS changes frequency when it changes from transmitting to receiving; c=0indicates that FH is not adopted and MS does not change frequency when it changes from transmitting to receiving . Rx indicates the maximum number of time slots used in an MS downlink in a TDMA frame. MS should support configurations of time slot numbers indicated by all integers from 0 to RX. The receiving time slots can be discontinuous by time. For the type 1 MS, its receiving time slots will be distributed in a receiving window with a size of RX. There is no transmitting time slot between receiving time slots in the TDMA frame. Tx indicates the maximum number of time slots used in an MS uplink in a TDMA frame. MS should support configurations of time slot numbers indicated by all integers from 0 to Tx The transmitting time slots can be discontinuous by time. For the type 1 MS, its transmitting time slots will be distributed in a transmitting window with a size of RX. There is no receiving time slot between transmitting time slots in the TDMA frame. Sum indicates the sum of all available time slots that can be used by MS in each TDMA frame. 1≤Rx + Tx≤Sum Tta relates to the time needed for the MS to perform adjacent cell signal level measurement and get ready to transmit. Ttb relates to the time needed for the MS to get ready to transmit. Tra relates to the time needed for the MS to perform adjacent cell signal level measurement and get ready to receive. Trb relates to the time needed for the MS to get ready to receive.

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Huawei’ BSS system supports z

MS of Type B

z

MS of Type C

z

MS with multi-slot capability ranging 1~12.

2.3.3 Supported RLC Modes I. RLC acknowledged mode Under RCL acknowledged mode, the transmission of RLC data block adopts retransmission method. The transmitting party numbers RLC data block through block sequence number (BSN), which can be used for retransmission and recombination. The receiving party can transmit “PACKET ACK/NACK” message to request retransmit RLC data block.

II. RLC non-acknowledged mode The transmission of RLC data block under RLC non-acknowledged mode does not support retransmission. But in the process of releasing uplink TBF, the last transmitted uplink block might be retransmitted. The BSN of RLC data block header numbers the RLC block data for recombination. The receiving party sends “PACKET ACK/NACK” to transmit other necessary control signaling. Huawei GPRS BSS supports RLC acknowledged mode and non-acknowledged mode.

2.3.4 Supported Channel Coding Scheme PDTCH defines four coding schemes: CS-1~CS-4. Except for PRACH and TPCCH/U, CS-1 is usually used for other packet control channels. For PRACH access burst, defines two coding schemes. All coding schemes are forced for MS. Only CS-1 is forced for network.

I. Channel coding: z

Channel coding of PDTCH

The radio block bearing RLC data block can use 4 types of coding schemes. Parameters of each coding scheme are shown in Table 2-19. Table 2-19 Coding parameter of coding schemes

z

Channel coding scheme

RLC/MAC data block size (octets)

Rate kbit/s

CS-1 CS-2 CS-3 CS-4

23 33 39 53

9. 05 13. 4 15. 6 21. 4

Channel coding of PACCH, PBCCH, PAGCH, PPCH, PNCH and PTCCH 2-139



PACCH, PBCCH, PAGCH, PPCH, PNCH and downlink PTCCH adopt CS-1, uplink PTCCH adopts the same coding scheme as PRACH. z

Channel coding of PRACH

There are two types of packet access burst in PRACH: 8bit and 11bit packet access burst. 8bit packet access burst bears 8 information bits. The same channel coding is adopted for uplink packet access burst and random access burst. The coding scheme of 11-bit packet access burst bears 11 information bit. Huawei BSS supports all these four CS and dynamically handovers between them according to radio transmission quality (RLC block retransmission rate of uplink /downlink TBF).

II. Dynamic Additional Sub-TS Under CS-1/CS-2, BSS is also based on the 16kbit/s link at the G-Abis interface. When CS-3 and CS-4 is adopted, the rate of a PDCH is 15.6 kbit/s and 21.4 kbit/s, therefore, when mapping the radio channels to the terrestrial channels, a PDCH is mapped to two 16 kbit/s links. However, the coding scheme adopted by PDCH is adjusted according to the change of the radio transmission environment of the MS that occupies it. Mapping a PDCH permanently onto two 16kbit/s links will greatly decrease the multiplexing ratio of the G-Abis interface, and thus greatly reduce the utilization ratio of the G-Abis interface transmission equipment. With dynamic additional sub-TS allocation, M900/M1800 GPRS BSS can resolve the transmission issue of CS-3 and CS-4 on the G-Abis interface perfectly. The dynamic attached sub-slot technology is to statically allocate a main 16 kbit/s sub-timeslot and dynamically allocate a attached 16 kbit/s sub-timeslot at the G-Abis interface for the CS-3/CS-4 PDCH. With the dynamic additional sub-TS technology, it is not necessary for GPRS BSS to upgrade the hardware of BTS, BSC or PCU for supporting CS-3 and CS-4. In addition, in its support for CS-3 and CS-4, the multiplexing ratio of the G-Abis interface is greatly improved, thus saving investments on the G-Abis interface transmission equipment. The dynamic additional sub-TS technology used by M900/M1800 GPRS BSS displays the following features: z

Any idle Sub-TS of the G-Abis interface can be used as additional sub-TS, so that each has maximum utilization.

z

Within a same site address, the additional sub-TSs can be dynamically attached to various main TSs to enhance the utilization ratio of this sub-TSs according to statistical multiplexing rules.

z

The locations of the additional 16kbit/s sub-TS are relatively flexible. They do not have to be adjacent to the main 16kbit/s sub-TS.

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It packs and unpacks the data packets through software to avoid hardware upgrading.

III. Parameter M900/M1800 BSS supports four types of coding schemes: CS-1~CS-4. The configuration related to channel coding schemes is realized with the command pcu add cspara. The following parameters are involved.

1)

UpFixCs

Description: CS fixedly adopted for uplink. Value range: cs1, cs2, cs3, cs4, unfixed Default: cs2

2)

UpDefaultCs

Description: Default CS adopted for uplink. If the uplink configured to adjust CS type dynamically, then the CS of the first TBF to transfer can be set by this parameter, the CS of other TBF is dynamically adjusted according to the signal transmission quality. Value range: cs1, cs2, cs3, cs4. Default: cs2

3)

UpThdCs1Cs2

Description: The resend rate conversion threshold, i.e. when the resend rate of the uplink TBF is smaller than or equals to this value, the coding scheme of it changes from CS-1 to CS-2. Value range: 0~100 Default: 5

4)

UpThdCs2Cs1

Description: Uplink TBF retransmission rate conversion threshold from CS-2 to CS-1, i.e. when the uplink TBF retransmission rate is larger than or equals to this value, the uplink TBF coding scheme changes from CS-2 to CS-1. Value range: 0~100 Default: 10

5)

UpThdCs2Cs3

Description: Uplink TBF retransmission rate conversion threshold from CS-2 to CS-3, i.e. when the uplink TBF retransmission rate is smaller than or equals to this value, the uplink TBF coding scheme changes from CS-2 to CS-3. Value range: 0~100

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Default: 10

6)

UpThdCs3Cs2


7)

UpThdCs3Cs4

Description: Uplink TBF retransmission rate conversion threshold from CS-3 to CS-4, i.e. when the uplink TBF retransmission rate is smaller than or equals to this value, the uplink TBF coding scheme changes from CS-3 to CS-4. Value range: 0~100 Default: 10

8)

UpThdCs4Cs3


9)

DnFixCs

Description: Fixedly adopted CS for downlink. Value range: cs1, cs2, cs3, cs4, unfixed. Default: unfixed

10) DnDefaultCs Description: Default CS adopted for downlink. If the downlink dynamically adjusts CS, then the CS of the first TBF can be set by this parameter, the CS type of other TBF is dynamically adjusted according to the signal transmission quality. Value range: cs1, cs2, cs3, cs4. Default: cs2

11) DnThdCs1Cs2 Description: Downlink TBF retransmission rate conversion threshold from CS-1 to CS-2, i.e. when the downlink TBF retransmission rate is smaller than or equals to this value, the downlink TBF coding scheme changes from CS-1 to CS-2. Value range: 0~100 2-142



Default: 5

12) DnThdCs2Cs1 Description: Downlink TBF retransmission rate conversion threshold from CS-2 to CS-1, i.e. when the downlink TBF retransmission rate is larger than or equals to this value, the downlink TBF coding scheme changes from CS-2 to CS-1. Value range: 0~100 Default: 10


14) DnThdCs3Cs4 Description: Downlink TBF retransmission rate conversion threshold from CS-3 to CS-4, i.e. when the downlink TBF retransmission rate is smaller than or equals to this value, the downlink TBF coding scheme changes from CS-3 to CS-4. Value range: 0~100 Default: 10


16) MaxFixCs34Pdch Description: The fixed maximum number of PDCH supporting CS-3/CS-4 in this cell. Value range: 0~255 Default: none

2.3.5 Supported Network Control Modes During the cell reselection required by network, the network requires MS to send MR so as to control the cell reselection. Here three network control modes are defined.

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z

NC0: MS controlled cell re-selection, no measurement reporting.

z

NC1: MS controlled cell re-selection, MS sends measurement reports.

z

NC2: Network controlled cell re-selection, MS sends measurement reports.

Huawei BSS supports NC0.

I. Parameter Network control mode parameter is configured with the command pcu add relatedinfo in PCU. Parameter: NCO Description: Network control mode. Value range: nc0, nc1, nc2 Default: Currently fixedly set as "nc0", meaning MS controlled cell re-selection, no measurement reporting

2.3.6 Supported Network Operation Mode GPRS network defines three network operation modes in order to uniformly coordinate the pagings of circuit-switched and packet-switched service.

I. Network operation mode I The network sends a CS paging message for a GPRS-attached MS, either on the same channel as the GPRS paging channel (i.e., the packet paging channel or the CCCH paging channel), or on a GPRS traffic channel. This means that the MS needs only to monitor one paging channel, and that it receives CS paging messages on the packet data channel when it has been assigned a packet data channel.

II. Network operation mode II The network sends a CS paging message for a GPRS-attached MS on the CCCH paging channel, and this channel is also used for GPRS paging. This means that the MS needs only to monitor the CCCH paging channel, but that CS paging continues on this paging channel even if the MS has been assigned a packet data channel.

III. Network operation mode III The network sends a CS paging message for a GPRS-attached MS on the CCCH paging channel, and sends a GPRS paging message on either the packet paging channel (if allocated in the cell) or on the CCCH paging channel. This means that an MS that wants to receive pages for both circuit-switched and packet-switched services

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shall monitor both paging channels if the packet paging channel is allocated in the cell. No paging co-ordination is performed by the network. Table 2-20 shows channels that deliver circuit paging message and packet paging message under various network modes. Table 2-20 Network operation mode Network operation mode

Circuit paging channel Packet Paging Channel CCCH Paging Channel Packet Data Channel CCCH Paging Channel

I II

CCCH Paging Channel

III

CCCH Paging Channel

GPRS paging channel Packet Paging Channel CCCH Paging Channel Not Applicable CCCH Paging Channel CCCH Packet Paging Channel CCCH Paging Channel

Paging coordination Yes No No

Currently, Huawei GPRS BSS system supports three network operation modes.

2.3.7 Supported QoS GPRS provides the subscriber with negotiable QoS configuration. GPRS QoS has five basic attributes: z

Precedence class;

z

Delay class;

z

Reliability class;

z

Peak throughput class

z

Mean throughput class.

Each attribute has multiple values available. The combination of different priorities enables the system to support various applications with different QoSs required. During the negotiation of QoS profile, MS can apply a value for every QoS attribute, including the default value stored in HLR and used to create new account. Network also needs to negotiate a priority for every attribute so that it can keep consistent with effective GPRS resources. Network always provides adequate resource to support the negotiated QoS profiles. RLC/MAC layer supports four radio priority levels, and whether the cause for the uplink access is user data or signaling message transmission. This information is used by the BSS to determine the radio access precedence and the service precedence. The radio priority levels to be used for transmission of MO SMS shall be determined by the SGSN and delivered to the MS in the Attach Accept message. The radio priority level to be used for user data transmission shall be determined by the SGSN based on the negotiated QoS profile and shall be delivered to the MS during the PDP Context Activation and PDP Context Modification procedures.

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Huawei BSS can satisfy MS QoS requirements as much as possible according to the state of current radio resources.

2.3.8 Supported Assignment When network side or MS requests to establish TBF for data transmission, GSM/GPRS network can assign some channel resources for data transmission or refuse the request according the multi-slot capability of MS and network resources state. Network can assign TBF resource from CCCH, PACCH or PCCCH. According to the direction of TBF data transmission, assignment can be divided into uplink and downlink assignment. When channel resource is in short or for other causes, network can refuse the request to establish TBF. When MS requests to establish TBF for uplink data transmission, network sends immediate assignment message on CCCH or packet uplink assignment message on PCCCH to assign channel resource. When MS requests to establish uplink TBF during its downlink TBF data transmission, network assigns packet uplink channel for MS on PACCH. MS transmits data according to assigned channel resource. When network requests to establish TBF for downlink data transmission, network can send immediate assignment message on CCCH or packet assignment message on PCCCH for MS to assign downlink channel resource. When MS requests to establish downlink TBF during its uplink TBF data transmission, network can assign packet uplink channel for MS through PACCH. MS transmits data according to assigned channel resource. Network assigns resource on different channels according to CCCH or PCCCH configuration. Meanwhile, network can perform different assignments such as single block assignment and packet resource assignment according to different access requests, such as two phases, one phase, and single block request. M900/M1800 BSS supports: z

Packet uplink resource assignment on PACCH

z

Packet downlink resource assignment on PACCH

z

Uplink immediate assignment for TBF establishment on CCCH.

z

Downlink immediate assignment for TBF establishment on CCCH.

2.3.9 Supported Paging In GPRS/GSM system, paging includes packet paging and circuit paging.

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I. Packet paging When there are downlink data that shall be sent to the MS, SGSN needs to initiate a packet paging call so as to locate MS accurately. The paging request message originated by the SGSN is sent through Gb interface to PCU, which converts it into the packet paging request of the air interface (Um interface) before sending. If the PCCCH channel is configured for the BSS system, the message will be sent on the PPCH directly. If PCCCH is not configured for the system, PCU will send the message via the Pb interface to the BSC, which sends it on the PCH. After receiving packet paging message, MS will initialize the process of uplink TBF establishment, and then sends the paging response packet in data form to PCU via the air interface. PCU forwards the packet to SGSN. After receiving the paging response, SGSN is ready to transmit downlink data.

II. Paging coordination When a call reaches the MSC where the subscriber is located, the MSC sends a paging message to all cells in that location area according to the registered location area of MS. If there is Gs interface between SGSN and MSC, GPRS/GSM system operates in network operation mode I and the paging service of GSM service can be sent through GPRS packet channel. In other words, if an MS is GPRS-attached, its circuit paging go from MSC to SGSN and then to PCU through the Gs and Gb interfaces, and PCU will determine on which channel to transmit the paging. In network operation mode I, if this MS has been assign with packet dedicated channel, then the circuit paging is sent on PACCH; if this MS has not assigned with packet dedicated channel and the system has not been configured with PCCCH, PCU forwards the paging message to BSC through Pb interface. Then BSC sends this message on PCH. If there is no Gs interface between SGSN and MSC, GPRS/GSM system can operate only in network operation mode II and mode III. In this case, the system sends circuit paging on CCCH. After receiving the circuit paging message, MS accesses the RACH and starts the circuit connection setup process. If MS is currently handling GPRS service, MS will initiate GPRS Suspend process to suspend GPRS service and it will not recover GPRS service until circuit connection is released. M900/M1800 BSS supports above-mentioned packet paging and paging coordination.

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2.3.10 Timing Advance Timing advance (TA) procedure is used to extract the correct TA value so that MS can transmit radio block on uplink. TA includes tow parts:

I. Initial TA estimation Initial TA estimation is based on a single access burst bearing packet channel. Request, packet uplink assignment or packet downlink assignment message, estimate TA and send to MS. MS uses this value for uplink transmission till a new value is provided.

II. Continuous TA update The MS in packet transmission mode needs continuous TA update. TA update is born by PTCCH assigned to MS. Uplink packet transmission uses packet uplink assignment message to assign TA index (TAI) and PTCCH to MS. And downlink packet transmission uses packet downlink assignment message to assign TA index (TAI) and PTCCH to MSTAI specifies the PTCCH sub-channel for MS. On uplink, MS sends access burst on assigned PTCCH. Network obtains TA from the burst. Then network analyses the received TA and provides new TAs for all MSs that perform TA update on this PDCH. New TAs is sent through downlink signaling message on PTCCH/D. Network also can send TA in packet TA/power control message and packet uplink acknowledged/negative message on PACCH. Huawei GPRS BSS supports: z

Continuous TA update procedure

z

Quick TA initial value

2.3.11 Measurement Report Network can request MS to send MR. There are two types of MR:

I. Network control (NC) MR Network carries relative network control parameters carried in PSI5 broadcast on PBCCH, SI13 on BCCH, and PSI13 on PACCH to control MS. Under NC1 or NC2 mode, MS should carry out NC measurement and indicate MR period in PSI5.

II. Extended MR Network can order MS to send extended MR. MS sending extended MR is controlled by XT Measurement Order parameter. This parameter is contained in PSI5 or order packet measurement message. Network broadcasts PSI5 on PBCCH, or sends order packet 2-148



measurement message on PCCCH or PACCH to address a specified MS. The value of parameter EXT Measurement Order should be EM0, EM1. When MS is under EM1 mode, it should carry out EM measurement. MR period is specified in field EXT Reporting Period in PSI5 or in order packet measurement message. After MS receives order of EM MR, it starts timer T3178 according to the instructed report period. When T3178 is active, MS can reselect a new cell which is in EM1 mode. If T3178 timeout duration is greater than the report period indicated in the new cell, MS should immediately use this period to restart T3178. If timer timeout duration is less than this period, then T3178 continues working. Uplink MR is supported. The priority and quality of uplink transmission signal from MS to site calculated by BTS is sent to PCU through inband signaling of Abis interface TRAU frame and is used to generate MR.

2.3.12 Supported Flow Control Gb interface and Um interface have different physical mediums and transfer protocols, which leads to their different transfer rates. The data transfer rate of Gb interface is greater than that of Um interface. Moreover, in downlink data transfer, the data transfer through Um interface is restricted by MS multislot capacity, radio quality, whether there is radio channel available in the cell. Thus the transfer rate is not constant and it is necessary to implement flow control for downlink data. When cell is in normal state, PCU starts flow control procedure: PCU periodically reports the cell bucket size and the cell bucket rate according to the state of radio packet channel in the cell, and reports MS bucket size and bucket rate according radio resource occupation state of MS. SGSN adjusts the downlink data rate of this cell/MS according to the reported parameters, which is the purpose of downlink data flow control.

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Note: 1). Cell bucket refers to the maximum packet data quantity that allowed being stored. It varies from the number of packet channels in the cell. 2). MS bucket refers to the maximum packet data quantity that allowed being stored. It varies from the number of packet channels assigned to MS. 3). Bucket rate is data transfer rater. Huawei PCU system can implement downlink data flow control, report the bucket size and bucket rate of the current cell/MS to SGSN, and adjust the reported parameters according to the changes of cell packet resource and MS resource occupation.

z

Uplink flow control supports refusal of immediate assignment on CCCH.

z

For downlink flow control, BVC downlink flow control and MS downlink flow control are supported.

2.3.13 Supported Dynamic Handover between TCH and PDCH At the early stage of GPRS service, GSM network is usually updated to support GPRS service due to the shortage of radio frequencies. In order to reduce the effect on original GSM circuit switched speech services caused by GPRS service, Huawei GPRS BSS supports the dynamic handover between TCH and PDCH.

1)

Supporting the handover from TCH to PDCH during the establishment of TBF.

Huawei GPRS BSS classifies channel attribute into fixed packet service channel, voice service channel and dynamic channel. Fixed packet service channel is dedicated for packet data service, such as PBCCH, PCCCH, and PDCH; voice traffic channel is dedicated for voice service, such as TCH, BCCH, SDCCH; and the dynamic channel is voice TCH at its initialization stage. It can be converted between TCH and PDCH. When there is more packet traffic and the speech channels are relatively idle, PCU will request the BSC to convert the dynamic channel into the dynamic packet data channel. Whereas when BSC determines the speech channels are busy, it can also request PCU to return the converted dynamic channel and use it again as speech channel. In this process, the speech service is given the priority over the packet service to guarantee the original speech services.

2)

Supporting inter-cell PDCH sharing on the same RPPU

2.3.14 Supported Packet Access Function When MS upper layers have data to be transferred, MS RLC/MAC will initiate packet access. MS packet access types are as follows: Short access, phase I access, phase II access, single block not establishing TBF access, paging response, cell update, mobility management.

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If the data to be transferred is less than 8 RLC blocks, the MS channel request type is short access. The number of data packets is calculated according to CS-1.

z

If the data to be transferred is more than 8 RLC blocks and RLC mode is required to be acknowledged mode, then MS channel request type is phase I access or phase II access.

z

If MS MR is to be transferred, then the channel request type is monolith not establishing TBF access.

z

For channel request type of paging response, cell update, and mobility management, they are usually processed as phase I or phase II access.

For short access and phase I access, radio resource is assigned for MS in the first time (such as TFI, dynamic assignment of USF or list of fixed assignment of radio block position list) For two-phase access channel request, the first request is for assigning a radio block for MS. MS sends packet resource request message on assigned sigle radio block for second resource assignment (including TFI, USF or radio block position list). Then MS begins to transfer data on assigned resource. The packet channel request is an access burst with 8 bit or 11 bit, so it carries a little of information. While the packet resource request is an RLC/MAC signaling packet with CS-1, it can carry relatively more information (including MS TLLI, MS multislot capacity, radio priority). These kinds of information are helpful in assigning appropriate resource for MS. M900/M1800 PCU supports all these access types. For access types such as paging response, cell update, and mobility management, it processes them by regarding them as two-phase ones.

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Chapter 3 Interface Description

Chapter 3 Interface Description M900/M1800 BSS offers standard external interfaces including Um interface between MS and BSS, A interface between BSS and MSC and Gb interface between BSS and SGSN. The interface protocols and interface procedures strictly follow the ETSI specifications. They guarantee Huawei BSS’s compatibility with the equipment of other manufacturers. The interfaces between BSS elements (BTS, BSC, and PCU) and between BSS and OMC are close interfaces. Although ETSI draws specification for these interfaces, the implementation of these interfaces is manufacturer-specific. It is the GSM protocol stack. Figure 3-2 illustrates the protocol stack of GPRS. MS

BSC

BTS

MSC

CM

CM

MM

MM

RR

RR L3

RR

BSSMAP BSSMAP

BTSM

BTSM

L2

LAPDm

LAPDm

LAPD

LAPD

L1

Sign. Layer1

Sign. Layer1

Sign. Layer1

Sign. Layer1

Um

BSC

Abis

SCCP

SCCP

MTP

MTP

A

MS: Mobile Station CM: Connection Management BSC: Base Station Controller MM: Mobility Management MSC: Mobile services Switching Centre, Mobile Switching Centre RR: Radio Resource Management BSSMAP: Base Station Subsystem Management Application Part LAPD: Link Access Procedure on the D channel LAPDm: Link Access Procedure on the Dm channel BTS: Base Transceiver Station SCCP: Signaling Connection Control Part MTP: Message Transfer Part (MTP) BTSM: Base Transceiver Station Site Management

Figure 3-1 GSM protocol stack

3-1



GMM/SM

GMM/SM LLC

LLC Relay

RLC

RLC

BSSGP

BSSGP

MAC

MAC

Network Service

Network Service

GSM RF

GSM RF

L1bis

L1bis

MS

Um

Gb

BSS

SGSN

GMM: GPRS Mobility Management

LLC: Logical Link Control

RLC: Radio Link Control

MAC: Medium Access Control

BSSGP: Base Station Subsystem GPRS Protocol

SM: Session Management

Figure 3-2 GPRS protocol stack

3.1 A Interface 3.1.1 Overview A-interface is the standard interface between BSS and MSC, so that M900/M1800 BSS can be easily deployed in any network in which the MSC of other vendor is being used. It is a standard GSM interface specified to achieve the following targets. The standard interface is adopted so as to: z

Support BSSs of different vendors in any PLMN

z

Support MSCs of different vendors in any PLMN

z

Use different BSSs in any PLMNs.

z

Use different MSCs in any PLMNs.

z

Ensure the independent developments of MSC and BSS technologies

z

Ensure the independent development of O&M functions

z

Enable lower speech coding rate

z

Support all GSM Phase II services

The reference model of A-interface signaling protocol in M900/M1800 BSC is shown in Figure 3-3, which describes the hierarchical structure of A-interface:

3-2



BSS

MSC

BSSAP

BSSAP

DTAP

BSSMAP

BSSMAP

DTAP

Allocation function

Allocation function

SCCP

SCCP

MTP

MTP

Physical layer A

DTAP: Direct Transfer Application Part MTP: Message Transfer Part (MTP) SCCP: Signaling Connection Control Part BSSAP: Base Station Subsystem Application Part BSSMAP: Base Station Subsystem Management Application Part

Figure 3-3 A-interface signaling protocol reference model

3.1.2 Protocols on the A-Interface I. Physical layer The physical layer of the A-interface is of 120-ohm symmetrical twisted pair or 75-ohm coaxial cable whose rate is 2 Mbit/s. The physical layer of A-interface has the following features: z

The 2 Mbit/s transfer rate complies with G.703.

z

Frame structure, synchronization and timing comply with G.705.

z

Fault management complies with G.732.

z

CRC4 check complies with G.704.

II. Message Transfer Part (MTP) The main function of MTP is to ensure reliable signaling message transfer in the signaling network. In case of system and signaling network faults, it can takes measures to avoid or reduce the loss. MTP protocols are defined in ITU-T Q.701~710 Recommendations. MTP comprises three functional levels: signaling data link function, signaling link function and signaling network function.

1)

Signaling data link function

Signaling data link (layer 1) is the channel used for signaling transmission. It comprises two data channels of the same data rate but two opposite working directions. A semi-permanent path between the signaling processing equipment of BSS and digital trunk equipment is established via the digital-switching network. The

3-3



former one occupies a timeslot to provide 64 kbit/s. The digital trunk equipment actually implements the first level function of MTP. The advantage of semi-permanent connection is, any TS (except synchronous TS) can be used as the signaling data link, which can be configured through the man-machine commands.

2)

Signaling link function

Signaling link function (layer 2) regulates the functions and procedures to send the signaling to the data link, and guarantees to provide reliable signaling message transfer between two directly connected signaling points. Functions of layer 2 include: signaling unit delimitation, signaling unit alignment, error detection, error correction, initial alignment, processor fault, level-2 flow control, and signaling link error rate monitoring. The BSS signaling processing equipment executes the above functions. In addition, different error control means can be set for it via the OMC. The basic error correction method applies to the terrestrial signaling links and the international signaling links whose unidirectional transmission delay is less than 15ms. The preventive cyclic retransmission mode applies to the international signaling links with the unidirectional transmission delay more than or equal to 15ms and to all the signaling links established through satellites.

3)

Signaling network function

Signaling network functions (level 3) refer to the functions and procedures that transfer management information between signaling points to guarantee the reliable transfer of signaling information when the signaling links and signaling transfer points in the signaling network fail. Signaling network functions include signaling message processing and signaling network management. Signaling message processing Signaling

message

processing

function

sends

signaling

messages

to

the

corresponding signaling links or user parts (such as TUP, ISUP and SCCP) on the basis of analyzing message flags. Signaling message processing functions comprise three parts: message routing (MRT), message discrimination (MDC) and message distribution (MDT), as shown in Figure 3-4.

3-4



MTP user part

Message allocation Message to local office Message discrimination

Message to other SP

Message routing

MTP L3 signaling message processing

MTPL2 signaling message processing

Figure 3-4 Signaling message processing flow z

Message Routing

Message Routing function is used at each signaling point to determine the signaling link group and the signaling link to destination signaling point. The message route should be identified by the route flag and the service indicator in message signaling unit. The routing function is fulfilled by message routing part according to the network indicator in message, DPC and SLS in route flag, as well as the routing data of relevant destination signaling point. z

Message Discrimination (MDC)

Message Discrimination (MDC) part is designed to receive the messages from Layer 2 to ascertain whether the destination of the messages is the local signaling point. If the destination is the local signaling point, the MDC part will send the messages to the Message Distribution (MDT) part. If the destination is not the local signaling point, the MDC part will send the messages to the Message Routing (MRT) part. z

Message Distribution (MDT)

Message Distribution (MDT) part is designed to allocate the messages from the MDC part to the user part and the signaling network management and test & maintenance part accordingly. z

Signaling network management

Signaling network management is to re-construct the signaling network and to keep and recover the normal transfer ability of the signaling unit when the signaling network fails. Signaling network management includes three parts: signaling traffic management, signaling link management and signaling route management. z

Signaling Traffic Management (STM)

3-5



Signaling Traffic Management (STM) is used to transit the signaling flow from one link/route to another or multiple available links/routes when the signaling network fails. It is also used to temporarily reduce signaling traffic in case of congestion at the signaling point. z

Signaling link management

Signaling link management is used to recover or startup the signaling link in the signaling network or to exit from the signaling link, and to ensure the provision of certain pre-determined link groups. The connection between the signaling data link and the signaling terminal is normally established by the man-machine commands. Operations in the signaling system can not automatically change the above connection relationship. z

Signaling route management

Signaling route management is used to ensure the reliable exchange of signaling route availability information between signaling points so as to block or unblock signaling routes when necessary. It mainly comprises such procedures as transfer prohibited, transfer allowed, controlled transfer and restricted transfer, signaling route group test, and signaling route group congestion test. These procedures are used only when the signaling services from the originating point reach the destination through the signaling transfer point.

III. Signaling Connection & Control Part (SCCP) The purpose of SCCP is to provide complete network layer functions with the help of MTP. According to OSI model, network layer provides connectionless services and connection-oriented services. SCCP protocols are defined in ITU-T Q.711~716 Recommendations. The application of SCCP enables: z

Interconnection of signaling networks.

z

New services and functions in mobile communications, e.g., intelligent network and intelligent management.

z

ISDN supplementary services.

z

Data transfer between network management centres

In general, SCCP provides reliable services for any information exchange on the basis of MTP. SCCP not only provides network service functions, but also has certain routing functions and network management functions. The routing function of SCCP is mainly used in addressing with such information as DPC + SSN (destination signaling point code + subsystem No.) and GT (global title), etc.

3-6



SCCP network management function mainly executes signaling point state and subsystem

state

management,

active/standby

subsystem

switchover,

state

information broadcast and subsystem state testing.

1)

Basic services of SCCP

SCCP services can be classified into four classes: Basic connectionless service, in-sequence delivery connectionless service, basic connection-oriented service and flow control connection-oriented service. 0 and 1 are connectionless service, while 2 and 3 are connection-oriented. Various SCCP services are introduced as follows: -Connectionless service In connectionless service, users do not establish the signaling connection before data transfer, but use the routing function of SCCP and MTP to transfer data information directly in the signaling network. This service is flexible and simple and it applies to the transfer of a small amount of data. Class-0 service does not guarantee the sequential transfer of messages. Class-1 service guarantees the sequential transfer of messages depending on the coordination of SLS (Signaling Link Selection) and MTP. Connectionless services transfer user data by adopting the Unit Data Message (UDT) and Extended Unit Data Message (XUDT). UDT messages do not have data segmentation/concatenation capability and can transfer only a small amount of user data. XUDT messages have the segmentation/concatenation capability and can transfer up to 2 kbyte user data. -Connection-oriented service Connection-oriented services require the establishment of signaling connection (virtual connection) via the acknowledged mode between the originating point and the destination point before the transfer of signaling information. In such cases, there is no need to select routes by using the SCCP routing function when transferring data. Instead, the data is transferred through the established signaling connection. When the transfer of data is finished, the signaling connection need not be released. This class of service applies to the transfer of large volumes of data because the destination has confirmed to be able to receive data before the data is transmitted, and hence the invalid transmission of data batches can be prevented. At the same time, the pre-established connection results in no SCCP routing for the subsequent data transfer, so the transfer delay of data batches can be effectively curtailed.

2)

SCCP routing control

The SCCP routing control provides a powerful address translation function, which is required for connectionless and connection-oriented service. The following specific address information can be found in SCCP: 3-7


DPC

z

DPC + SSN or GT (or both)

z

GT + (SSN)


DPC is the destination point code used by MTP in addressing. SSN, the subsystem number, is used to identify different SCCP users in the same node, such as ISUP, MAP, TCAP, and BSSAP. It eliminates the disadvantages of the small number of MTP message users, and the addressing range can be expanded to meet the requirements of future new services. GT (Global Title) is a dialed number, such as international and national telephone numbers, ISDN numbers, and E.214 numbers that are unique in GSM. It does not represent directly routing information in the signaling network, and can be obtained only through GT code translation. GT codes differ from DPC. DPC is meaningful only in the designated signaling network while GT is meaningful in the global range. The address range of GT is far larger than that of DPC, which enables the transfer of information unrelated to circuits between any two signaling points in the global range. The powerful addressing capability of GT is an important feature of SCCP.

3)

SCCP management

SCCP management (SCMG) is to keep the network functionality by re-routing or adjusting traffic in case of network faults or congestion. This function is accomplished by transferring SCCP management messages and primitives. The management messages adopt class-0 UDT. SCCP management includes signaling point management, subsystem management, active/standby subsystem switchover, state information broadcast, and faulty subsystem state testing.

IV. BSSAP 1)

Protocol overview

The BSSAP protocol, which serves as A-interface specification, describes two kinds of messages: BSSMAP and DTAP message. The former, which is responsible for traffic flow control, needs to be handled by the internal functional module of the A-interface accordingly. For the latter, the A-interface is equivalent to a transmission channel. It is transported directly to the radio channel at the BSS side while it is transported to the corresponding functional processing units at the NSS side. BSSAP protocols are defined in ETSI GSM 08.08 and ETSI GSM 04.08 specifications.

2)

Typical message contents

-DTAP messages According to the functional units of the NSS that process the DTAP messages, the DTAP messages can be divided into Mobile Management (MM) messages and Call Control (CC) messages.

3-8



The MM messages consist of messages related to authentication, CM service request, identification request, IMSI detach, location update, MM state, TMSI re-allocation, etc. The call control messages consist of alerting, call proceeding, connection, setup, modification, release, disconnection, notification, state query, DTMF startup messages, etc. -BSSMAP messages The BSSMAP messages can be divided into connectionless and connection-oriented messages. z

The connectionless messages consist of Block/Unblock, Handover, Resource, Reset, Paging messages, etc. The Block/Unblock messages include Block & Block ACK messages and Unblock & Unblock ACK messages. The Circuit Group Block/Unblock messages include Circuit Group Block message, Circuit Group Block ACK message, Circuit Group Unblock and Circuit Group Unblock messages. Handover messages include Handover Candidate Enquire and Handover Candidate Enquire Response. The resources messages include Resources Request and Resource Indication messages. The Reset messages include Reset and Reset ACK messages.

z

The connection-oriented messages include Assignment, Handover, Clear and Cipher messages. The Assignment messages include Assignment Request, Assignment Complete and Assignment Error messages. The Handover messages include Handover Request, Handover Request ACK, Handover Command, Handover Complete and Handover Error messages. The Clear messages include Clear Request and Clear Complete messages. The Cipher messages include Cipher Mode Command and Cipher Mode Complete messages.

3)

BSSAP protocol functionality

The BSSAP protocol can deliver its own functions in connection-oriented mode and connectionless mode of SCCP. When MS needs to exchange service-related messages over radio resources with the network side while there is no MS-related SCCP connection between MSC and BSS, a new connection will be established. A new connection shall also be set up for external handover. There are two kinds of connection setup: 3-9



While MS sends the Access Request message on the RACH, BSS allocates a

z

dedicated radio resource (DCCH or TCH) to MS. After the L2 connection is set up on the SDCCH (or FACCH) where resources are allocated, BSS starts the connection setup. When MSC decides to execute an external handover (the target BSS might be

z

the original BSS), it must reserve a new DCCH or TCH from the target BSS. In this scenario, MSC starts the connection setup. The BSSAP protocol implements the functional flow as shown in Table 4-1 using the connection and connectionless messages. Table 3-1 Functions Serial number

Function

1

Assign

2

Block/Unblock

3

Resource Indication

4

Reset

5

Handover Request

6

Handover Resource Allocation

7

Handover Procedure

Description “Assign” is to ensure the dedicated radio resources are allocated or re-allocated properly to the MS. The initial MS random access and “immediate assignment” to a DCCH is processed automatically by BSS but not controlled by MSC. During circuit assignment, MSC selects an available terrestrial channel. If this channel is no longer available then BSS notifies it to MSC. The Block/Unblock procedure can carry out this function. Resource indication serves to notify MSC: Amount of the radio resource available for TCH in BSS, Amount of all available radio resource (i.e. able to provide service or have been specified) It is not easy to get this information from the MSC-controlled services. These must be considered when MSC decides an external handover. “Reset” is to initialize the BSS or MSC. For instance, if BSS goes faulty or loses all the reference messages about processing, BSS sends a Reset message to MSC, which releases the affected calls, deletes the affected reference messages and sets all the circuits related to the BSS to idle. If MSC or BSS is only locally faulty, the affected parts can be cleared using the Clear procedure. BSS may send a “handover request” to MSC requesting to perform handover of the MS, to which dedicated resources have been allocated, for the reasons as listed below: a) BSS detects a radio cause for handover. b) MSC starts the Handover Candidate Enquirer procedure. The MS is waiting for the handover. Due to congestion, the serving cell needs to be changed during the call setup such as directed retry. The Handover Request messages should be re-sent once in a while till one of the following situations occurs: Receive the "Handover Command" message from MSC Reset message is received All communications with MS will be interrupted and the processing is aborted Processing is over, such as call clearing. Handover Resources Allocation enables MSC to request for resources from BSS based on the handover request. The target BSS will reserve resources and wait for an MS to access this channel. This is the procedure in which MSC instructs MS to access the radio resources of another cell. When handover is carried out, the original dedicated radio resources and terrestrial resources are maintained all the time until MSC sends a Clear Command message or Reset occurs.

3-10

Feature Description M900/M1800 Base Station Subsystem Serial number


Function

8

Release of Radio Resources and Terrestrial Resources

9

Paging

10

Flow Control

11

Classmark Update

12

Cipher Mode Control

13

Queuing Indication

14

Load Indication

Description When processing is done, MSC sends a “Clear Command” to BSS to release radio resources. On receiving the command, BSS starts the Clear procedure at the radio interface, then sets the configured terrestrial circuit to idle and returns a Clearing Complete message to MSC, which in turn releases the terrestrial resources of the local end. If resources need to be released by BSS, BSS will send a “Clear Request” to notify MSC to start the release procedure to release the terrestrial and radio resources concerning MSC and BSS. The paging to MS is transported with the SCCP connectionless service via BSSMAP. If BSS receives the Paging Response message at the radio channel interface, it will establish an SCCP connection to MSC. The paging response message, which is loaded in the BSSMAP Full L3 Message, is transported on the signaling connection to MSC. Flow control can prevent the entities from receiving too much traffic. Flow control on the A-interface is implemented by controlling the traffic at the traffic source. Two levels of flow control are available. Flow control can be implemented based on subscriber classes. Classmark Update serves to notify the class messages received from MS to the receiving entities. Generally, BSS notifies MSC after receiving the class messages from MS. It is also likely that when handover is complete, MSC sends the corresponding MS Classmark messages to the new BSS via the A-interface. The Cipher Mode Control procedure allows MSC to transport the cipher mode control messages to BSS and start the subscriber equipment and signaling cipher equipment with a correct Kc. This procedure is designed to notify MSC that BSS wants to delay the allocation of necessary radio resources. This procedure is valid only when the queuing function is introduced for traffic channel assignment and traffic channel handover in the BSS. Load indication serves to notify the traffic state of a cell to all the adjacent BSSs so that an overall control over the handover services in an MSC can be exercised. In a certain valid period, the traffic state of the adjacent cells will be taken into account by the adjacent BSS during handover.

3.1.3 A-Interface Management at BSS Side An interface management in M900/M1800 BSC includes terrestrial channel management (or A interface circuit resource management), management of part of the radio resources, and so on.

I. A interface circuit resource management The purpose of the terrestrial channel management between BSS and MSC is to keep the states of terrestrial circuits at both ends consistent. An idle circuit can be found when the MSC "assigns circuit" in calling and assigns terrestrial circuit during MS handover to make sure a successful call/handover. Procedures included in the interface circuit resource management are Circuit Block/Unblock, Circuit Group Block/Unblock, Unequipped Circuit, and Reset Circuit. General principles of the circuit control includes:

3-11



z

The circuit management messages, except Reset Circuit, are initiated by BSC.

z

The MSC can only block/unblock the local circuits without affecting the circuit state of the BSS.

z

The BSS can not change the circuit state that has been changed at the local end of the MSC. For circuits blocked on the maintenance console at MSC side, the BSS has no authority to unblock or reset the circuit.

1)

Block Circuit

The process of blocking the circuit is shown in Figure 3-5. BSC

MSC Block circuit

Block ackonwledge

Figure 3-5 Process of blocking the circuit Circuit Block procedure means the circuits corresponding to the BSS and the MSC are blocked simultaneously. This procedure can be initiated by the maintenance console of the BSC or by the allocation of circuit during call process or during handover request. This procedure can be used in Phase I and Phase II. When there is no "Block ACK" message received by BSC for a certain period of time, this message will be sent again. Even if BSC does not receive Blocking ACK, the circuit at BSC side is still in the blocked state. When BSC is sending Block message, an alarm will generate at BSC. The Circuit Group Block procedure does not affect the circuits in service, that is, the busy circuit will not be blocked until the communication is completed.

2)

Unblock the Circuit

The process of unblocking the circuit is shown in Figure 3-6. BSC

MSC Unblock circuit

Unblock anknowledged

Figure 3-6 Process of unblocking the circuit

3-12



The purpose of Circuit Unblock is to unblock the circuit blocked by the BSC. This procedure can be originated by maintenance console or originated during equipment fault recovery. The Circuit Unblock procedure is generally started by the maintenance console and can be used by GSM Phase 2 and Phase 1. When there is no "Unblock ACK" message received by BSC for a period of time, this message will be sent again. Even if BSC does not receive the Unblock message, the circuit at BSC side is still in idle state. When BSC is sending the unblocking message, an alarm will be generated at BSC.

3)

Group-unblock the Circuit

The process of blocking the circuit is shown in Figure 3-7. BSC

MSC Group block

Group block acknowledged

Figure 3-7 Process of blocking the circuit The purpose of the Circuit Group Block is to block multiple A-interface circuits simultaneously. This procedure can be started by the maintenance console or by trunk equipment itself automatically. This procedure is used for Phase 2 only. When there is no "Group Block Ack" message received by BSC for a certain period of time, this message will be sent again. Even if BSC does not receive the message of Group Block ACK, the circuits at the BSC side are still in the blocked state. When BSC is sending Group Block message, an alarm will generate at BSC. The Circuit Group Block procedure does not affect the circuits in service, that is, the busy circuit will not be blocked until the communication is completed.

4)

Group-unblock the circuit

The process of unblocking the circuit is shown in Figure 3-8.

3-13


BSC


MSC Group unblock

Group unblock acknowleged

Figure 3-8 Process of blocking the circuit The purpose of the Circuit Group Unblock is to unblock multiple A-interface circuits simultaneously. This procedure can be started by the maintenance console or by trunk equipment itself automatically. This procedure is used for Phase 2 only. When there is no "Group Unblock ACK" message received by BSC for a period of time, this message will be sent again. Even if BSC does not receive the Group Unblock ACK message, the circuits at BSC side are still in the idle state. When BSC is sending the group-unblocking message, an alarm will be generated at BSC.

5)

Unequipped Circuit

The Unequipped Circuit procedure is shown in Figure 3-9. BSC

MSC Unequipped circuit

Unequipped circuit

Figure 3-9 Process of unequipped circuit The Unequipped Circuit procedure is used by BSC or MSC to inform the peer end that the circuit does not exist and cannot be used. This procedure can be initiated during any procedures related to circuits. This procedure is used for Phase II only. The unequipped circuit will not be sent again. When BSS or MSC sends Unequipped Circuit message, alarms will be generated.

6)

Reset circuit

The Reset Circuit procedure is shown in Figure 3-10.

3-14


BSC


MSC Reset circuit

Reset circuit acknowledged

Figure 3-10 The process of resetting the circuit The purpose of Reset Circuit is to recover the system resource information of the MSC and BSC when the fault (e.g. abnormal release of SCCP) affects only a small part of the equipment. Figure 3-10 shows the Reset Circuit procedure initiated by the BSC. When the MSC receives the Reset Circuit message, it clears the possible calls on the circuit and sets the circuit to idle state. Then it returns the Reset Circuit ACK message. The Reset Circuit procedure initiated by MSC is similar to the above figure, the only difference is the direction of the messages. If a BSC does not receive Reset Circuit ACK message and time is out, Reset Circuit message will be sent repeatedly. The repetition times can be set through software. Even if the BSC does not receive the Reset Circuit ACK message, the circuit at the BSC side is still in the idle state. When BSC is sending the resetting message, an alarm will be generated at BSC. Similar procedure is followed by MSC. The Reset Circuit can also be initiated through maintenance console to be used for maintenance and testing.

II. A-interface radio resources management A-interface radio resource management mainly includes Resource Indication and Clear procedures.

1)

Resource Indication

The Resource Indication procedure is shown in Figure 3-11. The purpose of the Resource Indication procedure is to inform MSC about the number of idle radio resources in BSS which can be used as traffic channels, as well as the total available radio resources (resources able to provide services or already assigned). The MSC may consider the relevant information when identifying the external handover.

3-15



BSC

MSC Resource indication request

Resource indication

Figure 3-11 Resource indication process at A interface There are four types of resource indications including automatic indication, single indication, periodic indication and no indication. No indication is the default mode. In the automatic indication mode, the cell corresponding to the BSS will continuously send Resource Indication messages to MSC according to the cycle set in the Resource Indication Request message when resource of the cell satisfies the conditions. In the single indication mode, the BSS instantly return a Resource Indication message about the corresponding cell to MSC. In the periodic indication mode, the BSS continuously sends Resource Indication Request message according to the cycle set in Resource Indication Request, until it receives the new Resource Request message or Reset message. The period shall be set by the MSC, and the actual period are 100ms multiply the original value. In the non-indication mode, the BSS immediately returns a single Resource Indication" message without any resource information, and the procedure is finished. For each idle channel, the BSS calculate the average value of the interference level within a period. And the average result shall divide the idle channel into 5 interference sections according to the interference level. The Resource Available Information Elements includes two pieces of information for each of the five interference bands: number of available half-rate traffic channels in the interference band and number of available full-rate traffic channels in the interference band.

2)

Clear process

The purpose of the Clear procedure is to release all relative terrestrial circuit resources and radio resources. This procedure includes two cases: Clear initiated by MSC and Clear initiated by BSS. The clear process originated by MSC is illustrated in Figure 3-12.

3-16


BSC


MSC Clear command

Clear complete

Figure 3-12 Clear procedure initiated by MSC The clear process originated by BSS is illustrated in Figure 3-13. BSC

MSC Clear request Clear command Clear complete

Figure 3-13 Clear procedure initiated by BSS

III. Other A-interface management procedures There are some other A-interface management procedures, which are Classmark Update, Reset, Flow Control, Queuing, Error Handling, SCCP Link Control and Load Indication.

1)

Classmark update

The purpose of Classmark update is to notify MSC about the class information received from MS. This process is applied when the power Classmark of a dedicated resource occupied by MS is changed. See Figure 3-14.

3-17



BSC

MSC

Classmark update

Figure 3-14 Process of Classmark update

2)

Reset process

Reset procedure is to initialize the BSS or MSC in the event of failure so that all resources can be released. Reset at BSS: BSS releases all resources and sends the Reset message to the MSC, which will release all calls and connection resources and set all circuits related to BSS as idle. After guard period T2 seconds, the MSC returns the Reset ACK message to the BSS, indicating that the reset is successful. See Figure 3-15. MSC

BSC Reset

Reset acknowledged

Figure 3-15 BSS reset process Reset at MSC: MSC releases all resources and sends the Reset message to the BSC, which will release all calls and connection resources upon the receipt of the message. After guard period T13 seconds, a Reset ACK message is returned to the MSC, indicating that the reset is successful. See Figure 3-16.

3-18



MSC

BSC Reset

Reset acknowledged

Figure 3-16 MSC reset process

3)

Flow Control Process

The purpose of Flow Control at the BSC side is, when the MSC is overloaded, the BSC can control the flows from MS. System malfunction or congestion will not be caused, and the flow of calls can be controlled within a reasonable range. When the MSC is overloaded, A-interface at the MSC side will generate the Overload message to inform the BSC to control the traffic flow. The control algorithm used is the flow control algorithm stipulated by the GSM specifications, which is executed by using the specific design developed by Huawei. That is, a dynamic sliding window is adopted, which is started in overloading, and the size of the window can be modified according to the size of the traffic so as to control the traffic. The window is invalid when the MSC is no longer overloaded. See Figure 3-17. BSC

MSC Overload

Overload

Overload

Figure 3-17 Flow Control Process

Note:

When BSC is overloaded, BSC will send "Overload" message to MSC. MSC implements flow control. BSC side also has the corresponding flow control measure.

3-19


4)


Load Indication

Load Indication procedure informs the traffic condition of a cell to all neighboring BSS. This procedure is used to control the handovers. After the MSC receives the Load Indication message, it forwards the information to the BSS, which contains this cell, according to the cell list attached to the message.

5)

SCCP Link Control

In case of the abnormal disconnection on the SS7 link, A-interface will stop sending control messages through software. When the SS7 link recovers, A-interface continues sending control messages. Due to the long-time disconnection, A-interface shall start clearing the resources as soon as the link is recovered to prevent the hang-up of resources.

6)

Error handling

As errors may occur on the transmission links, messages transferred may not be understandable. Therefore, A-interface shall omit the error messages and send selectively "confusion" messages (these messages are used in GSM Phase 2+).

3.2 Um Interface Um interface (air interface or radio interface) is defined as the communication interface between MS and BSS. It is for the communication between MS and the fixed part of GSM. Its physical link is the radio link. The information transmitted via this interface include radio resource management, mobility management and connection management.

3.2.1 Overview In a GSM/GPRS network, MS is connected through radio channels to the fixed network so that a call can be routed to the specific destination. To realize the inter-working between MS and BSS, it is necessary to standardize the transmission of the signals on the radio channel. The norm concerning the signal transmission on the radio channel is the radio interface, or Um interface. The Um interface is the most important interface in the GSM system. It is necessary to follow a standard interface so that a complete compatibility can be achieved between different of different manufactures, which is the basic condition for global roaming. The Um interface is specified by the following features: z

Channel structure and access capability

z

MS-BSS protocols

z

Maintenance and operation characteristics

3-20



z

Performance characteristics

z

Service characteristics.

The Um interface can be divided into 3 layers, as shown in Figure 3-18.

L3 L2 L1

Figure 3-18 Layered structure of Um interface The first layer is the physical layer at the bottom. It includes various channels, and provides basic radio channels for information transfer on higher layer. The layer 2 is the data link layer using the LAPDm protocol. It includes various data transmission structures, and controls data transmission. The layer 3 is the highest layer. It includes various messages and programs, and controls services. It includes 3 sub-layers, which are Radio Resources management (RR), Mobility Management (MM), and Connection Management (CM).

3.2.2 Layer 1 - Physical Layer I. Physical layer interface and services The interfaces between the physical layer (L1) and data link layer (L2), the physical layer (L1) and radio resources management sublayer (RR) of L3, the physical layer (L1) and other functional unit, are shown in Figure 3-19.

Radio resource management

L3

Data link Other functional unit

MPH Primitive

PH Primitive Physical layer

Figure 3-19 Physical layer interface

3-21

TCH



The physical layer provides the following services: Access capability: the physical layer provides a series of limited logical channels

z

for transmission service. The logical channel is multiplexed on the physical channel. Error code detection: Physical layer provides error protection transmission,

z

including error detection and correction. Ciphering:

z

II. Multiple access scheme Both FDMA and TDMA techniques are used by Um interface, along with frequency hopping. The transmission unit on Um interface is the burst consisting of about 100 modulated bits. It is called "BP (Burst Pulse). Each BP is of 200kHz wide with duration of 0.577ms (15/26ms) as shown in Figure 3-20. The time and frequency window it occupies is called slot. The duration of the slot is the timeslot. Frequency width occupied by the slot is called frequency slot. The frequency slot here is the RF channel in GSM specification. Frame consists of n consecutive timeslots. In GSM system, "n" is 8. The frame in this format is called a TDMA frame. A TDMA frame consists of 8 consecutive timeslots. Frequency

3

200 kHz

2 1

0

1

2

3

4

BP

5

6

7

8

Time

Slot

15/26ms

Figure 3-20 Concept of timeslot A physical channel is the burst sequence transported in the timeslots that occur at specific and periodic intervals. In the GSM system, the period is 8, namely, one TDMA frame. In other words, one RF channel contains 8 physical channels, which can be differentiated by serial numbers. This serial number is called time slot number. If a RF channel is not Frequency Hopping, it follows that its central frequency is constant, otherwise its central frequency changes in a unit of 200kHz.

3-22



Figure 3-21 illustrated the complete TDMA frame. 1 Hyper Frame=2048Super Frame=2715648TDMA Frame (3h28m53s760ms) 0 TCH SACCH/T FACCH

1

2

3

2044

2045

2046

2047 BCCH CCCH SDCCH

1 Super Frame=1326TDMA Frame (6.12s) 0

1

2

0

3

47

1

24

1

49

50 25

1 Multiframe=51TDMA Frame(3060/13ms)

1 Multiframe= 26TDMA Frame(120ms) 0

48

24

25

0

1

49

50

1TDMA Frame=8 Timeslot (120/26=4.615ms) 0

1

2

3

4

5

6

7

Figure 3-21 Frame structure of channel One TDMA frame has a duration of 4.615ms (120/26ms), consisting of 8 timeslots. Multiframe consists of 26 or 51 frames. Multiframe of 26 frames has duration of 120 ms and carries traffic channel, slow associated control channel and fast associated control channel. A Multiframe of 51 frames has duration of 235.365 ms and be used as control channel. One superframe consists of 51 traffic multiframes or 26 control multiframes and consists of 51×26 TDMA frames with a total duration of 6.12 seconds. The period of superframe is 6.12 s. A hyperframe contains 2048 superframes. Its period is 12533.76 s, i.e. 3h28m53s760ms. Each period of the hyper frame contains 2715648 TDMA frames, which are numbered from 0 to 2715647.

III. Physical channel and logical channel 1)

Physical channel

The physical channel is the combination of FDM and TDM and is composed of the slot stream between BTS and MS. The physical channel is a combination of frequency division and time division, so a physical channel must be described from two perspectives: z

Frequency band description

3-23



Table 3-2 GSM/GPRS frequency bands Item Working frequency band Duplexing interval Carrier interval

z

900 band Uplink (MS to BTS): 890~915 MHz Down (BTS to MS): 935~960 MHz 45MHz 200kHz

1800 band Uplink: 1710~1785 MHz Downlink: 1805~1880 MHz 95MHz 200kHz

Time description

TN: Timeslot No. FN: TDMA Frame No.

2)

Logical channel

The logical channel is obtained by multiplexing the physical channel in TDM. Different logical channels serve to transport different types of messages between BSS and MS. The logical channel is mapped to the physical channel as per certain rules. Different logical channels have different frame structure, but whatever the arrangement is, the frame structure of the logical channels are always periodic in time. Great effort has been made to design the frame structure of the logical channels in order to build a high-performance system in the GSM specifications. This results in a complicated frame structure system in the GSM system. The relation between logical channel and physical channel is detailed described in ETSI GSM 05.02 specification. z

Among all carriers of a cell, there is only one supporting BCCH (and CCCH). The cell is uniquely identified through this carrier. This carrier is defined as C0 in the protocol.

z

Carrier C0 must be transmitted on the same frequency with constant power. The frequency used by the C0 is called nominal frequency.

IV. The timing advance of uplink, downlink and MS In GSM/GPRS system, uplink refers to the link from MS to BTS, and downlink from BTS to MS. The size of the MS can be greatly reduced if the transmission and receiving can be completed in different time. To realize this, in the GSM system, the TDMA frame on the uplink always lags behind the TDMA frame on the downlink by 3 BP. For BTS, this delay is fixed, but to MS, it is a different issue. There is always some transmission delay during its passage to the BTS (serving cell) due to the mobility of MS and the transmission delay is generally not fixed. To make up the transmission delay between MS and BTS, the transmitting at MS side should be in advance. This is the timing advance. The range of timing advance is 0 ~ 233µs (corresponding TA: 0 ~ 63).

3-24



Therefore, the precision deviation of the uplink and downlink is 3BP minus the timing advance with respect to MS. The MS under the dedicated mode must do the transmission at any time in proper timing advance, or it will lose synchronization with BTS. In the GSM system, the “Adaptive Timing Adjustment” approach is introduced to ensure the MS in a dedicated mode uses proper timing advance.

V. Procedure from source data to radio wave The radio channel bears features totally different from the wireline channel. First, the radio channel exhibits remarkable time-varying features. Impacted by interference, multipath fading and shadow fading, the signals are characterized by high error codes. To address the problems brought about by radio channel transmission, a series of conversions and inverse conversions are needed to give necessary protection for the transmitted signals. These include the conversion from the primitive user data or signaling data to the messages carried by the radio wave, and that vise versa. These conversions

mainly

include

channel

encoding/decoding,

interleaving

and

de-interleaving, burst formatting, encryption and decryption, modulation and demodulation. For voices, the transformation procedure is shown in Figure 3-22. (This procedure is the same for other user data or signaling).

3-25



Voice

Voice

Digitalization and source coding

Source coding

Channel coding

Channel decoding

Interleaving

De-interleaving

Burst formatting

Burst formatting

Ciphering

De-ciphering

Modulation

Demodulation

Receiver

Transmitter

Figure 3-22 Procedure from source data to radio wave

1)

The operation process at the transmitting side

z

Channel coding

Redundancy is introduced to the message flow to detect and rectify errors in the transmission process. The result of channel encoding is a data block. The length of voice data is 456 bit. z

Interleaving

Interleaving means mixing several data blocks so that the neighboring bits in the modulated signals can be extended into these data blocks. In the message flow, the consecutive errors are correlated. If the correlation between the errors is eliminated, the channel encoding performance can be improved. The purpose of interleaving is to eliminate the correlating error and the location correlation in the data block. After interleaving, the message flow becomes the sequence of message block. Each channel burst pulse has a message block. The interleaving and encoding schemes of various transmission modes are listed in Table 3-3.

3-26



Table 3-3 Interleaving and encoding under various transmission mode Input bloc k

Input rate

Channel and transmission mode

kbit/s

TCH/F9.6 TCH/F4.8

12 6

240

TCH/F4,8

6

120

TCH/F2,4

3.6

72

Odd-even code (3bit) 1/2 convolutional code 1/2 convolutional code None 1/2 convolutional code Subtracting 1 bit from each 15 bit Add 32 "0" bits 1/3 convolutional codes 1/6 convolutional codes

TCH/F2,4

3.6

144

1/3 convolutional codes

Ia TCH/FS

50

Ib II

13

132 78

SCH

Odd-even code (10bit) 1/2 convolutional code Odd-even code (6bit) 1/2 convolutional code

25

RACH (+ Handover access) Fast Associated Control Signaling on TCH/F and TCH/H TCH/8, SACCH; BCCH, PAGCH

z

Output block

Code

8

184

224/184 Fire code 1/2 convolutional codes

Interleaving

456

On 8.5 burst pulse

456

Combined on 22 uneven burst pulse.

456

Same as the above

456

On 8.5 burst pulses Combined on 22 uneven burst pulses

456 78

On 1 S burst pulse

36

On 1 access burst pulse On 8 burst pulses

456 On 4 burst pulses

Format burst pulse

Add the training sequence to the message bit flow so that the receiving end can estimate the transmission feature of the channel, so as to restore the received signal. An ordinary burst contains two groups of 58bit, which are separated with a 26 bit training sequence. Three ends are all 0. They are added to the head and end of the burst. For the content of the ordinary burst, see Table 3-4. Table 3-4 Content of an ordinary burst Head

Information

Training sequence

Information

End

3

58

26

58

3

The access burst is the only short burst in GSM. It contains a 41 bit training burst, 36 bit information, 7 bit at the head and 3 bit at end. The content of the access burst is listed in Table 3-5. Table 3-5 Content of an access burst Head

Training sequence

Information

End

7

41

36

3

3-27



S burst is applicable to downlink SCH. Its length is the same as other ordinary bursts (142 bit). For its content, see Table 3-6. Table 3-6 Content of an ordinary burst Head

Information

Training sequence

Information

End

3

39

64

39

3

F burst is a long burst. Its only purpose is to enable the MS to find and modulate the S burst in the same cell. Its length is 148 bit, all 0. z

Ciphering

Modify the message flow with the ciphering mode recognizable to both MS and BTS to ensure the safety of the subscriber data. z

Modulate

Convert the burst sequence into RF analog signal so that it can be transmitted on the RF channel in the form of radio wave. The modulation adopts GMSK. BT = 0.3, the modulation rate is 2705/6 kbit/s.

2)

The operation process at the receiving end

z

Demodulate

When antenna receive radio signal, selects the useful signal according to multi address rule. Then it demodulates the signal and output binary bit stream. z

Decipher

Modify the received message bit flow by reversing the process of ciphering. z

Format burst pulse

Remove the training sequence in the message flow. z

De-interleaving

Restore the original locations of various bursts and reestablish the codes. z

Channel decoding

Use the attached redundancy information to check and correct the errors in the message flow as much as possible.

3.2.3 Layer 2 - Data Link Layer Data link layer is the second layer of the OSI model. It receives the service from the physical layer and provides service to L3. The data link Service Access Point (SAP) is the node that provides services for layer 3. SAP is identified through SAPI. Each SAP is associated with one or multiple Data Link Connection End Points (DLCEP). Viewed from layer 3, DLCEP is identified by Data Link Connection End Point Identifier

3-28



(DLCEPI). Viewed from layer 2, it is identified by the Data Link Connection Identifier (DLCI). The communication between data link layer entities is governed by a peer-to-peer protocol specific to the layer. For information exchange between two or more layer 3 entities, an association must be established between the layer 3 entities in the data link layer using a data link layer protocol. This association is called a data link connection. (DLC). Messages at the data link layer are transferred between entities at layer 2 of the physical layer. Layer 3 request services from the data link layer via service primitives. The same applies for the interaction between the data link layer and the physical layer. The link layer protocol used by the GSM system at the radio interface is the LAPDm protocol, which evolves from the LAPD protocol. Currently, two SAPI values are defined in the LAPDm protocol: 0 (main signaling) and 3 (short messages).

I. LAPDm 1)

Function

LAPDm transfers information between layer 3 entities through the radio interface on the Dm channel. LAPDm supports multiple layer 3 entities and physical layer entities, and signaling of BCCH, PCH, AGCH and DCCH.

Note:

The Dm channel is a generic term for all the signaling channels at the Um interface in the GSM system. For instance, the Dm channel can either be PCH or BCCH.

LAPDm includes functions for: z

The provision of one or more data link connections on a Dm channel. Discrimination between the data link connections is by means of a data link connection identifier (DLCI).

z

Allows for frame type identification.

z

Allows L3 message units to be transmitted transparently between L3s.

z

Exercises sequence control to maintain the order of frames that pass DLC.

z

Check on the format and operation errors on the data links.

z

Flow control.

z

Contention resolution when establishing a data link after an access request has been made on the RACH.

2)

Operation types

3-29



Two types of operation of the data link layer are defined for layer 3 information transfer: unacknowledged operation and acknowledged (multiple frame) operation. They may co-exist on a Dm channel. z

Unacknowledged operation:

In unacknowledged operation, layer 3 information is transmitted in Unnumbered Information (UI) frames. At the data link layer, the UI frames are not acknowledged. Flow control mechanisms and error recovery mechanisms are not defined. Unacknowledged operation is applicable to different types of control channels except for RACH. z

Acknowledged operation:

In unacknowledged operation, layer 3 information is transmitted in Unnumbered Information (UI) frames. The data link layer acknowledges the transmitted I frame. Error recovery procedures based on retransmission of unacknowledged frames are specified. In case of errors, which cannot be corrected by the data link layer, a report is issued to the layer 3 entity. Flow control procedures are also defined. Acknowledged operation is applicable to DCCH.

3)

Information transfer mode:

On different channels, information transfer modes are different. z

Information transfer on the BCCH: The BCCH exists only in the network to MS direction and is used for broadcasting radio sub-system information to MSs. Only UI frames are sent on the BCCH.

z

Information transfer on the PCH + AGCH: These channels exist only in the network to MS direction. On the PCH + AGCH only unacknowledged operation is possible.

z

Information transfer on the DCCHs: On the DCCHs both unacknowledged operation and multiple frame operation are possible. The type of operation required at any time is determined by layer 3.

4)

Release of data links:

Multiple frame operation may be released in the following ways: z

Normal release by exchange of commands/responses.

z

Local end release, i.e. without exchange of commands/responses, initiated and controlled by layer 3.

This type of release is initiated by layer 3.

II. Service characteristics. The data link layer provides services to layer 3 and uses the services provided by the physical layer. Interaction among them is accomplished by primitives. The primitive format between layer 2 and layer 3 is DL_XX_XXX. The primitive format between

3-30



layer 2 and the management layer is MDL_XX_XXX. And the primitive format between layer 2 and physical layer is PH_XX_XXX.

1)

Services provided to layer 3

Unacknowledged information transfer service The characteristics of the unacknowledged information transfer service are summarized in the following: z

Provision of a data link connection between layer 3 entities for unacknowledged information transfer of layer 3 message units;

z

Identification of data link connection endpoints to permit a layer 3 entity to identify another layer 3 entity.

z

Sending of frames in accordance with priority given to the message.

z

No verification of message arrival within the data link layer.

The primitives associated with the unacknowledged information transfer service are: DL-UNIT DATA-REQUEST/INDICATION The DL-UNIT DATA-REQUEST primitive is used to request that a message unit be sent using the procedures for unacknowledged information transfer service; DL-UNIT DATA-INDICATION indicates the arrival of a message unit received by means of unacknowledged information transfer. Acknowledged information transfer service One mode of acknowledged operation is defined, i.e. multiple frame operation. The characteristics of this service are summarized in the following: z

Provision of a data link connection between layer 3 entities for acknowledged information transfer of layer 3 message units.

z

Identification of data link connection endpoints to permit a layer 3 entity to identify another layer 3 entity.

z

Sequence integrity of data link layer message units in the absence of machine malfunctions.

z

Notification to the peer entity in the case of errors, for example, loss of sequence.

z

Notification to the layer 3 entity of unrecoverable errors detected by the data link layer.

z

Flow control.

z

Sending of frames in accordance with the indicated SAPI value.

z

Segmentation and concatenation control functions.

Primitives used for multiframe acknowledged information transfer include: DL_DATA_REQUEST/INDICATION: used to request that a message unit be sent using the procedures for multiframe acknowledged information transfer and the arrival of message units received by means of acknowledged information transfer.

3-31



DL_ESTABLISH_REQUEST/INDICATION/CONFIRM: These primitives are used to request, indicate and confirm the establishment of multiple frame operation between two data link layer entities. DL_RELEASE_REQUEST/INDICATION/CONFIRM: used for the termination of the multiframe mode. Random access procedure The

primitive

used

by

the

random

access

process

is

DL_RANDOM

ACCESS_INDICATION, which is used in the MS to request the transmission of a random access burst.

2)

Services required from the physical layer

The services provided by the physical layer are summarized in the following: z

Physical layer connection for transparent transmission of frames.

z

Indication of physical state of the Dm channel.

z

Transmission of data link layer message units in the same order as they were issued by the data link layer.

z

Provision of frame synchronization.

z

Provision of error protection to ensure a low residual bit error rate at the data link layer.

z

Transmission (in the MS) and reception (in the network) of random access bursts.

3)

Administrative services

Primitives used by management layer services: MDL_ERROR_INDICATION, used by the data link layer to indicate that there is an error in the data link layer procedures that cannot be resolved by normal exception handling procedures. MDL_RELEASE_REQUEST, used by the layer 3 entity to initiate abnormal local end release of a data link.

3.2.4 L3 I. Introduction The signaling layer 3 provides the functions to establish, maintain and terminate circuit-switched connections across a GSM PLMN and other networks to which the GSM PLMN is connected. It provides the necessary supporting functions related to supplementary services control and short messages service control. Furthermore it includes the functions necessary for mobility management and radio resource management.

3-32



The layer 3 body consists of many functional program blocks. These program blocks transfer message units carrying various kinds of information among all layer 3 entities and between layer 3 and neighboring layers. The objectives of the layer 3 are to provide the means for: z

The establishment, operation and release of a dedicated radio channel connection (RR).

z

For location updating, authentication and TMSI reallocation (MM).

z

For establishment, maintaining and termination of circuit-switched calls (CC).

z

Supplementary services support (SS).

z

Short messages service support (SMS).

Layer 3 consists of 3 sub-layers including Connection Management (CM), Mobility Management (MM) and Radio Resource management (RR). The functions of the signaling layer 3 are performed by means of the signaling layer 3 protocols between two systems which represent the Mobile Station side and the Network side of the radio interface as viewed by the Mobile Station. GSM 04.07 does not consider the distribution of signaling functions among the different network equipment. The functions of layer 3 and its supporting lower layers, therefore, provide the Mobile Network Signaling (MNS) Service to the upper layers.. Interaction between layer 3 and higher layers and between services interfaces of layer 2 as well as that between neighboring sub-layers in layer 3 can be described in primitives and parameters. Exchange of information between two peers of the signaling layer 3 is performed by means of the three sublayer protocols.

II. L3 Structure As have already introduced, the 3 sub-layers of layer 3 are further discussed here: Among them, the highest sub-layer is composed of three functional entities: Call Control (CC), Short Message Service support (SMS) and Supplementary Service support (SS). In total, there are five functional entities consisted in the layer 3 radio interface. Below is the brief introduction to these entities: z

Radio Resources (RR) management handles the establishment, maintenance, and release of physical channels and logical channels, as well as cross-cell transfer on the request of CM sub-layer.

z

Mobility Management (MM) deals with the all necessary functions of mobile features to support mobile subscribers. It notifies the network when the mobile station is activated and deactivated, or the location area is changed. It is also responsible for the security of activated radio channels.

z

CC deals with all necessary functions to establish or release the circuit-switched connections.

z

SS deals with all necessary functions to support GSM supplementary services.

3-33



SMS performs all necessary functions to support point-to-point short message services.

In addition, other functions are contained in layer 3 which are related to the transport of messages, e.g. multiplexing and splitting. Those functions are defined in the Radio Resource Management and Mobility Management. They have the task to route the messages according to the protocol discriminator (PD) and transaction identifier (TI) which are part of the message header. The MM routing function route the messages of the CM entities and the messages of the MM entity of its own sublayer towards the service access point of RR, and multiplex them in case of parallel transactions. The routing function of Radio Resource Management shall distribute the messages to be sent according to their protocol discriminator (PD) and the actual channel configuration. The messages provided at the different service access points of layer 2 are split by the RR routing function according to the protocol discriminator (PD). If PD equals to RR, this message will be transferred to RR at the local sub-layer. Other messages are provided to MM via the access point RR-SAP. The routing function of MM passes the messages according to the protocol discriminator (PD) and the transaction identifier (TI) towards the MM entity or towards the CM entities via the various MM-SAP's. Figure 3-23 illustrates the protocol model of L3 signaling. The RR sub-layer at the bottom receives services provided by layer 2 through various service access points (i.e., various types of channels) of layer 2, and provides services via RR-SAP to the MM sub-layer. The MM sub-layer provides services to the three entities (CC, SS and SMS) on the CM sub-layer through different service access points MMCC-SAP, MMSS-SAP and MMSMS-SAP respectively. The 3 independent entities on the CM sub-layer provide services to higher layers through MNCC-SAP, MNSS-SAP and MNSMS-SAP respectively.

3-34


Mobile Service


MNCC-SAP

MNSS-SAP

MNSMS-SAP

CC

SS

SMS

MMSS-SAP MMCC-SAP

MMSMSSAP

MMREG -SAP

MM

CC

Layer 3 Signaling

MM

SS

SMS

RR-SAP ..RR

RR PD RR

SDCCH SACCH

BCCH AGCH+PCH SDCCH SACCH FACCH

SAPI 3

RACH

SAPI 0

Figure 3-23 Um interface L3 protocol model

III. Service characteristics. 1)

Services provided by layer 3 on the MS side

z

Registration services, i.e., IMSI attach and detach operations.

z

Call Control services for normal and emergency calls including call related Supplementary Services Support services.

z

Call independent Supplementary Services Support.

z

Short Message Services Support.

Services provided by layer 3 on the network side z

Call Control Services, including call establishment, call maintaining, call termination and call related supplementary service support.

z

Call independent Supplementary Services Support.

z

Short Message Services Support.

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2)

Inter-layer services between the mobile station and network side

z

Services provided by Radio Resource Management entity. These services are provided to MM via RR-SAP. They are used for establishing control channel connections, establishing traffic channel connections, ciphering mode indication, releasing control channel connections, and control-data transfer. Services provided by mobility management entities (MM). These services

z

support call control, supplementary services and short messages services of connection management entities. MS

Network Side

MM

RR - Primitive RR SAP

corresponding layer protocol RR

Figure 3-24 Communication at RR

MS CC

SS

Network Side SM

CC

SS

Corresponding layer protocol MM

MM

Figure 3-25 Communication at MM

3-36

SM



3.3 Abis interface 3.3.1 Overview The Abis interface is the interface between Base Station Controller (BSC) and Base Transceiver Station (BTS). It is an internal interface of the BSS. At the beginning, ETSI hope to realize the complete standardization of Abis interface, so that the BTS can connect to the BSC of different supplier. However, the complete standardization of Abis interface has not been turned into reality. As a result ETSI only strictly define the service part of Abis interface in 08.52, 08.54, 08.56 and 08.58 of the GSM specification, and didn't define the O&M part. Therefore, the Abis interface can only be regarded as an internal interface. The interworking between different vendors' BTS and BSC has not been realized. The terrestrial traffic channels on the Abis interface and the radio traffic channels on the Um interface are in one-to-one correspondence with one another.

I. Protocol Model 1)

Protocol Model

The protocol model of the Abis interface is shown in Figure 3-26. BSC

BTS

RR BTSM

RR LAPDm

LAPD

Sign Layer1

Layer1

BSSAP

BTSM SCCP LAPD MTP Layer1

Abis

BTSM: Base Transceiver Station Management LAPD: Link Access Procedure on the D Channel RR: Radio Resource LAPDm: Link Access Procedure on the Dm Channel SCCP: Signaling Connection Control Part MTP: Message Transfer Part BSSAP: Base Station Subsystem Application Part

Figure 3-26 Protocol model of Abis interface z

Layer 1 of the Abis interface is hardware-based and responsible for receiving and transmitting data to the physical link.

z

The layer 2 protocol of the Abis interface is based on the LAPD. LAPD addresses TRX (or BCF) through TEI. Different logical links are used for traffic management message (RSL, Radio Signaling Link), network management

3-37



message (OML, Operation & Maintenance Link), and L2 management messages (L2ML, Layer 2 Management Link). z

RR (Radio Resource Management) messages are mapped onto the BSSAP (BSS Application Part) in BSC. In BTS, most of RR messages are handled as transparent messages. However, some of them have to be interpreted and executed by BTS (for example, cipher, random access, paging and assignment), these messages are processed by the BTSM (BTS Management) entities in BSC and by BTS.

z

BSC and BTS do not interpret CM (Connection Management) and MM (Mobility Management) messages. These messages are transferred over the A-interface by DTAP (Direct Transfer Application Part). At the Abis interface, DTAP messages are transferred as transparent messages.

2)

Abis interface related protocols:

z

GSM 08.52 defines the basic principles for the Abis interface specifications, and the traffic function division between BSC and BTS.

z

GSM 08.54 defines the physical structure of Abis interface.

z

GSM 08.56 defines the data link protocol of Abis interface.

z

GSM 08.58 defines the layer 3 procedures.

z

GSM 12.21 defines the transmission mechanism of the OM message on the Abis interface.

z

GSM 08.60 defines the in-band control protocol of the remote transcoder and rate adapters.

II. Structure of Abis interface The Abis interface can support three different internal BTS configurations (as illustrated in Figure 3-27): z

Single TRX.

z

Multiple TRXs are connected with the BSC via a common physical connection.

z

Multiple TRXs are connected with the BSC via different physical connections.

3-38



BSS Abis TRX

BTS1

BCF TRX TRX

A MSC

Abis

BTS2

TRX

BSC

BCF Abis TRX TRX

BTS3

TRX TRX BCF

Figure 3-27 Struction of Abis interface In Figure 3-27: z

TRX is the functional entity that supports 8 physical channels that belong to the same TDMA frame, which is defined in the PLMN.

z

The BCF (Base Control Function) is the functional entity that performs common control functions including BTS initialization, software loading, channel configuration, operation and maintenance.

There are two types of channels at the Abis interface, which are: z

Traffic channels with the rates of 8kbit/s, 16kbit/s and 64kbit/s respectively, carrying speech or data from radio channels.

z

Signaling channels with rates of 16kbit/s, 32kbit/s or 64kbit/s respectively, carrying signaling between BSC and MS, and between BSC and BTS.

Different Terminal Equipment Identifiers (TEI) are assigned to get unique addresses of TRXs. Three separate logical links are defined with each TEI (as shown in Figure 3-28): z

RSL: Radio Signaling Link used to support traffic management procedures, one for each TRX.

z

OML: Operation & Maintenance Link used to support network management procedures, one for each SITE.

z

L2ML, L2 management link, for transferring the management messages at L2.

3-39



BSC

BTS RSL SAPI=0 OML SAPI=62 L2ML SAPI=63

TRX

TEI1

BCF

LAYER 2

TEI

MANAGE-

RSL SAPI=0 OML SAPI=62 L2ML SAPI=63

TRX TEI2 BCF

RSL SAPI=0 OML SAPI=62 L2ML SAPI=63

MENT

TRX

TEI3

BCF OML SAPI=62 L2ML SAPI=63

BCF

TEI4

BCF

Figure 3-28 Abis interface layer 2 logical links

III. Functional division between BSC and BTS The BSS is composed of two functional entities, i.e. BSC and BTS. BTS is the radio part of the BSS under the control of the BSC, providing services for a specific cell. The BTS fulfills the interworking and mapping of the terrestrial channels and the radio channels, as well as the interworking of the MS and the network via the radio interface (Um interface). The BSC is the controlling part of the BSS, which manages the external and the internal interfaces, as well as the radio resource and radio interface parameters. The specific function division between the BTS and the BSC is shown in Table 3-7.

3-40



Table 3-7 Distribution of services and functions between BTS and BSC Location

Function

BTS

MSC-BSC channel Terrestrial channel management BSC-BTS channel

Channel allocation Blocking indication Channel allocation Blocking indication

BSC/MSC √ √ √

√

Channel configuration management

√

Frequency hopping

DCH management

Radio channel management

Remark

BCCH/CCCH management

Management Execution Channel allocation Link monitoring Channel release Idle channel observation Power control decision System information management System information broadcast Random access check Immediate assignment DTX paging management DTX paging execution

Channel coding/decoding Transcoding/rate adaptation

√ √ √ √ √ √ √

√

Note 1

√ √ √ √ √ √ √ √

Uplink measuremen t Processing measuremen t report Traffic measuremen t Calculation

Measurement

Timing advance

3-41

√ √ √ √

√

Note 2


Chapter 3 Interface Description Location

Function

BTS Indication to MS during random access Indication to MS during handover Indication to MS during session

Timing advance

Radio channel management LAPDm function

Remark

BSC/MSC √

√ √ √

Management

Ciphering

Execution Management Handover access check

Handover

√ √ √ √

Mobility Management

√

Calling Control

√

Note 1: The support of power control in BTS is optional Note 2: The initial measurement data is reported by BTS to BSC through Abis interface. As an option, the BSC/BTS may support preprocessing of the initial data in BTS, which reduces the load of BSC.

3.3.2 Protocols on the Abis Interface I. Physical layer Abis interface physical layer adopts the PCM link with the working rate at 2048 kbit/s to provide 32 channels at 64kbit/s. The electro-technicial parameter at the physical layer conforms to the CCITT G.703 recommendations. BSS is the connection point of the radio channel and terrestrial channel. Both kinds of channels have different transfer patterns and coding rates. In the radio channel of BSS, the transfer rate is 16kbit/s while it is 64kbit/s in the terrestrial channel. Therefore transcoding and rate adaptation is needed. This function is realized at the physical layer of Abis interface by the Transcoder & Rate Adaptation Unit (TRAU). TRAU can be located at BTS side, BSC side or MSC side. Given to the channel utilization at the Abis interface, M900/M1800 BTS does not support TRAU at BTS side, but the BSC or MSC instead. Data coding is described in GSM 08.20. The in-band control protocol of TRAU is stipulated in GSM 08.60.

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II. Data link layer 1)

Overview

The data link layer of Abis uses LAPD protocol. It utilizes the service on the physical layer, and provides connection-oriented or connectionless services for layer 3. The data link Service Access Point (SAP) is the point that provides services for layer 3. SAP is identified by Service Access Point Identifier (SAPI). A data link connection endpoint is identified by a data link connection endpoint identifier as seen from layer 3 and by a data link connection identifier (DLCI) as seen from the data link layer. For information exchange between two or more layer 3 entities, an association must be established between the layer 3 entities in the data link layer using a data link layer protocol. The communication between data link layer entities is governed by a peer-to-peer protocol specific to the layer. Messages at the data link layer are transferred between entities at layer 2 through physical layer. Inter-layer service request is implemented with service primitive.

2)

Function

The purpose of LAPD is to realize reliable end-to-end information transfer between layer 3 entities through the user-network interface by using the D-channel. To be specific, LAPD supports: z

Multiple terminal equipment between subscriber and interface,

z

Multiple L3 entities.

Functions of LAPD includes: z

Establishes one or several data links on the D channel.

z

Delimits, locates and transmits transparently frames so that a string of bits transmitted on the D channel in the form of frames can be identified.

z

Implements sequence control to keep the order of the frames that pass the data link connections.

z

Checks the transmission errors, format errors and operation errors in the data link connections.

z

Makes recovery based on the detected transmission errors, format errors and operation errors.

z

Notifies the management layer entities of the unrecoverable errors.

z

Flow control.

Data link layer provides the means for information transfer between multiple combinations of data link connection points. The information may be transferred through point-to-point data link connections or via broadcast data link connections.

3-43



III. Traffic management of Layer 3 The traffic management part of the Abis interface layer 3 is mainly described in GSM 08.58 specifications. The procedures defined in this specifications has two major functions: z

Realizing the interworking of the MS and BSS/NSS on the Um interface.

z

Implementing part of the radio resource management functions under the control of BSC.

The traffic management message is divided into the transparent and non-transparent messages, as shown in Figure 3-29. z

The

transparent

message

refers

to

the

messages

forwarded

without

interpretation or being processed by the BTS. z

The non-transparent message refers to the messages processed and structured by the BTS.

The traffic management messages can also be divided into four groups in terms of functions, which are: z

Radio link layer management message, used for the management of the data link layer on the radio channel.

z

Dedicated channel management message used for the management of dedicated channels (SDCCH and TCH).

z

Common control channel management message used for the management of common control channels.

z

TRX management message used for TRX management.

Transparency and group of the message is determined by the message discriminator at the header of the message.

1)

Radio link layer management procedures

Radio link layer management procedures include: z

Link establishment indication procedure: BTS uses this procedure to indicate to BSC the success of setting up multi-frame link originated by the subscriber. BSC establishes a link from MSC to SCCP through the indication.

z

Link establishment request procedure: This procedure is used by BSC to request the establishment of a link layer connection in multi-frame mode on the radio channel.

z

Link release indication procedure: This procedure is used by BTS to indicate to BSC that a link layer connection on the radio channel has been released at the initiative of an MS.

z

Link release request procedure: This procedure is used by BSC to request the release of a link layer connection on the radio channel.

3-44



Transmission of a transparent L3-message on the Um interface in acknowledged mode: This procedure is used by BSC to request the sending of a transparent L3 message to MS on the Um interface in acknowledged mode.

z

Reception of a transparent L3-message on the Um interface in acknowledged mode: This procedure is used by BTS to indicate the reception of a transparent L3 message on the Um interface in acknowledged mode.

z

Transmission

of

a

transparent

L3-message

on

the

Um

interface

in

unacknowledged mode: This procedure is used by BSC to request the sending of a transparent L3 message to MS on the Um interface in unacknowledged mode. z

Reception of a transparent L3-message on the Um interface in unacknowledged mode: This procedure is used by BTS to indicate the reception of a transparent L3 message in unacknowledged mode.

z

Link error indication procedure: Through this procedure BTS indicates BSC incase of any abnormality in the radio link layer.

2)

Dedicated channel management procedures

The dedicated channel management principles includes: z

Channel activation procedure: This procedure is used to activate a channel at BTS for an MS which later will be commanded to this channel by an Immediate Assignment, an Assignment Command, an Additional Assignment or a Handover Command message.

z

Channel mode modification procedure: This procedure is used by BSC to request a change of the channel mode of an active channel.

z

Handover detection procedure: This procedure is used between the target BTS and BSC to detect the accessing of the MS being handed over.

z

Start of encryption procedure: This procedure is used to start encryption according to the procedure defined in Technical Specification GSM 04.08.

z

Measurement report procedure: It includes the necessary basic measurement report procedure and measurement report preprocessing procedure. BTS reports all parameters related to handover decision to the BSC through this procedure.

z

Deactivate SACCH procedure: This procedure is used by BSC to deactivate the SACCH at BTS according to the Channel Release procedure defined in Technical Specification GSM 04.08.

z

Radio channel release procedure: This procedure is used by BSC to release a radio channel that is no longer needed.

z

MS power control procedure: This procedure is used by BSS to set the MS power level or the parameters required by TRX. MS power control decision must be implemented in BSC, and as an optional procedure in BTS.

z

BTS Transmission power control procedure: This procedure used between BSC and BTS to set the TRX transmission power level or the parameters required by TRX. The BTS transmission power control decision should be implemented in BSC, or in BTS. 3-45



Connection failure procedure: This procedure is used by BTS to indicate to BSC that an active connection has been broken.

z

Physical context request procedure: This is an optional procedure which allows the BSC to obtain information on the "physical context" of a radio channel just prior to a channel change.

z

SACCH information modification procedure: BSC uses this procedure to instruct BTS to change the information (system information) filled in a specific SACCH channel.

3)

Common channel management procedures

Common channel management regulations include: z

Channel request by MS procedure: The procedure is initiated by TRX upon detection of a random access from an MS (Channel Request message from MS).

z

Paging principle procedure: It is used to page an MS on the specified paging sub-channel. The paging of an MS is initiated by BSC sending a Paging Command message to BTS. BSC determines the paging group to be used according to the IMSI of the called MS. The value of this paging group together with the identity of the mobile station is sent to BTS.

z

Immediate assignment procedure: When a mobile station accesses BTS, BSC uses this procedure to assign a dedicated channel for the mobile station immediately.

z

Delete indication procedure: This procedure is used by BTS to indicate that due to overload on the AGCH, an Immediate Assign Command has been deleted.

z

CCCH load indication procedure: This procedure is used by BTS to inform BSC the load on a designate CCCH. Indication period is also set by OM.

z

Broadcast information modification procedure: This procedure is used by BSC to indicate to BTS the new information to be broadcast on BCCH.

z

Short message cell broadcast procedure: Short Message Service Cell Broadcast messages are sent to BTS as SMS Broadcast Request messages.

4)

TRX management procedures

This type of procedure is used for TRX management. There are: z

SACCH filling information modify procedure: This procedure is used by BSC to indicate to BTS the new information to be used as filling information on SACCHs.

z

Radio resources indication procedure: This procedure is used to inform BSC on the interference levels on idle channels of a TRX.

z

Flow control procedure: This procedure is defined to give some degree of flow control. It can be used for TRX processor overload, downlink CCCH overload and ACCH overload.

z

Error reporting procedure: This procedure is used by BTS to report detected downlink message errors, which cannot be reported by any other procedure.

3-46



IV. Operation and maintenance part of Layer 3 1)

Operation and maintenance information model

z

Managed objects

There are four types of management objects: site, cell, carrier and channel. The basic structure is illustrated in Figure 3-29. SITE

CELL 0

CELL 1

CELL n

TRX0

TRX1

TRXm

TRX

CH0

CH1

CH7

Figure 3-29 Basic structure of management object z

Object addressing

Addressing of network management messages is realized by means of managed object types and cases. For each object case in BTS there is a complete L2 connection description. The setup of the first connection uses one (semi-) permanent default TEI. Subsequent connections use the TEIs provided when setting up TEI procedures. Object cases can also use layer 3 addresses. The mixed use of layer 2 and layer 3 addressing enables one BTS site have one or multiple physical links. z

Managed object state

Management status include management status, operation status and availability status. See Table 3-8, Table 3-9 and Table 3-10. The management state of managed objects is only controlled by BSC, and available state is the specific explanation of operative state. Table 3-8 Management status State Locked Shut down Unlocked

Description BSC has disconnected all calls through this managed object, and no new calls can be connected to this object. New services can not be connected to this managed object, but those existing calls will be maintained. New calls can be connected to this managed object.

3-47



Table 3-9 Operation status State Disabled Enabled

Description Resources are completely unavailable, and can no longer provide services to the users. All or part of resources are available and can be used.

Table 3-10 Availability status State ln test Failed Power off Off line Dependency Degraded Not Installed

2)

Description The resource is being tested. Its operational state is disabled. The source/object is not working due to some internal error. Its operational state is disabled. The resource needs power supply. Its operational state is disabled. The resource needs manual or automatic operations. Its operational state is disabled. Services provided by this resource are degraded in a certain sense, such as rate or operational capacity. Its operational state is disabled. Services provided by this resource are degraded in a certain sense, such as rate or operational capacity. Its operational state is disabled. Hardware or software of the managed objects is not installed. Its operational state is disabled.

Basic procedures

All procedures are based on formatted O&M messages. Most formatted O&M messages initiated by BSC or BTS require the peer layer 3 endpoint to give response or acknowledgment in the form of formatted O&M messages. Single formatted O&M messages that need not be responded are called a basic procedure. All formatted O&M messages are sent on layer 2 in the form of I frames. A group of procedures, called as structured procedures, are based on the combination of some basic procedures. For a specific object, if a certain basic procedure is not completed, the system will not start its subsequent basic procedures. When there is no response to the formatted operation and maintenance message from the peer layer 3 before L3 timeout, the basic procedure is regarded as “not completed”. When the previous basic procedure has not received any response (ACK or NACK) before layer 3 timeout, then no subsequent basic procedure is sent to this object case. The default timeout for layer 3 is 10s. If part of an original message is not understood or supported, the whole message is discarded. A ACK message returned by the object indicates affirm response, it is used to notify the message sender that the command has been executed or will be executed. A NACK message returned by the object indicates disaffirm response, it is used to notify the message sender that the command executed unsuccessfully and the corresponding failure cause. There are mainly the following types of basic procedures: z

Software loading management procedure

z

Abis interface management procedure

z

Transmission management procedure

3-48



z

Air interface management procedure

z

Test management procedure

z

State management and event reporting procedure

z

Equipment state management procedure

z

Other procedure

3.3.3 Characteristics of Abis Interface Huawei's Abis interface supports various services. It also supports the control over BTS and the allocation of frequency. Abis interface has the following characteristics: z

Supporting all the services as stipulated in the GSM 02 series.

z

Supporting smooth expansion of BTS capacity.

z

There are three types of multiplexing modes on Abis interface: 10:1, 12:1 and 15:1, meaning the ability to simultaniously transmit 10, 12 or 15 TRX data on the same E1 respectively.

z

The transmission modes on the Abis interface can be terrestrial, satellite, microwave or optical fiber.

I. Transmission Modes on the Abis Interface The transmission modes on the Abis interface can be terrestrial or satellite. These two types of transmission mode are selected in the BSC data configuration. For thinly populated and scattered areas where ordinary transmission technology is expensive and difficult to implement, Huawei offers connectivity through satellite. Figure 3-30 shows a typical example of networking through satellite.

Satelite

Earth Station

MSC

Earth Receiving E1 Station BTS BSC BTS SDH/PDH /HDSL/Microware /E1 BTS

Earth Receiving E1 BTS Station

Figure 3-30 Networking of satellite transmission

3-49



The networking implementation through satellite transmission is different from the land transmission due to long transmission delay. To get good quality transmission, following measures are taken: z

LAPD protocol is modified to overcome the impact of delay.

z

The adjustment algorithm of the TRAU frame is modified from fixed cycle adjustment to self-adaptive adjustment. The BTS clock works in internal clock mode.

z

II. Abis interface channel assignment Abis interface has three types of channels, including Traffic Channel (TCH), Radio Signaling Link (RSL) and Operation & Maintenance Link (OML). Each site corresponds to an OML, each TRX corresponds to an RSL, and a radio traffic channel corresponds to the traffic channel at the Abis interface. There are three multiplexing modes for Abis interface: 10:1, 12:1 or 15:1, respectively meaning that the data of 10, 12 or 15 TRXs can be simultaneously transmitted on one E1. In the following description, the row is the timeslot No., and the column is the sub-timeslot No. Which is calculated by 8kbit/s rate. Ti.j refers to the No. j sub-timeslot of the No. i TRX which occupys a 16kbit/s sub-timeslot on E1.

1)

Timeslot distribution of E1 in 10:1 multiplexing

Table 3-11 Sequence table under 10:1 mode Sub-TS

Sub-TS 0

Sub-TS1

Sub-TS2

Sub-TS3

TS 0

Synchronization

1

T0.0

T0.1

T0.2

T0.3

2

T0.4

T0.5

T0.6

T0.7

3

RSL0

4

T1.0

T1.1

T1.2

T1.3

5

T1.4

T1.5

T1.6

T1.7

6

RSL1

7

T2.0

T2.1

T2.2

T2.3

8

T2.4

T2.5

T2.6

T2.7

9

RSL2

10

T3.0

T3.1

T3.2

T3.3

11

T3.4

T3.5

T3.6

T3.7

12

RSL3

13

T4.0

T4.1

T4.2

T4.3

14

T4.4

T4.5

T4.6

T4.7

3-50

Feature Description M900/M1800 Base Station Subsystem Sub-TS


Sub-TS 0

Sub-TS1

Sub-TS2

Sub-TS3

TS 15

RSL4

16

T5.0

T5.1

T5.2

T5.3

17

T5.4

T5.5

T5.6

T5.7

18

RSL5

19

T6.0

T6.1

T6.2

T6.3

20

T6.4

T6.5

T6.6

T6.7

21

RSL6

22

T7.0

T7.1

T7.2

T7.3

23

T7.4

T7.5

T7.6

T7.7

24

RSL7

25

T8.0

T8.1

T8.2

T8.3

26

T8.4

T8.5

T8.6

T8.7

27

RSL8

28

T9.0

T9.1

T9.2

T9.3

29

T9.4

T9.5

T9.6

T9.7

30

RSL9

31

OML

In 10:1 multiplexing, each E1 carries 10 TRXs. Each signaling link occupies a 64kbit/s timeslot on the E1. If some sites cascad on one E1, , the E1 can carry 4 sites/9 TRXs or 7 sites/8 TRXs.

2)


Table 3-12 Sequence table under 12:1 mode Sub-TS

Sub-TS 0

Sub-TS1

Sub-TS2

Sub-TS3

TS 0

Synchronization

1

T0.0

T0.1

T0.2

T0.3

2

T0.4

T0.5

T0.6

T0.7

3

RSL0, RSL1

4

T1.0

T1.1

T1.2

T1.3

5

T1.4

T1.5

T1.6

T1.7

6

T2.0

T2.1

T2.2

T2.3

7

T2.4

T2.5

T2.6

T2.7

T3.2

T3.3

8 9

RSL2, RSL3 T3.0

T3.1

3-51



Sub-TS 0

Sub-TS1

Sub-TS2

Sub-TS3

10

T3.4

T3.5

T3.6

T3.7

11

T4.0

T4.1

T4.2

T4.3

12

T4.4

T4.5

T4.6

T4.7

TS

13

RSL4, RSL5

14

T5.0

T5.1

T5.2

T5.3

15

T5.4

T5.5

T5.6

T5.7

16

T6.0

T6.1

T6.2

T6.3

17

T6.4

T6.5

T6.6

T6.7

18

RSL6, RSL7

19

T7.0

T7.1

T7.2

T7.3

20

T7.4

T7.5

T7.6

T7.7

21

T8.0

T8.1

T8.2

T8.3

22

T8.4

T8.5

T8.6

T8.7

23

RSL8, RSL9

24

T9.0

T9.1

T9.2

T9.3

25

T9.4

T9.5

T9.6

T9.7

26

T10.0

T10.1

T10.2

T10.3

27

T10.4

T10.5

T10.6

T10.7

28

RSL10, RSL11

29

T11.0

T11.1

T11.2

T11.3

30

T11.4

T11.5

T11.6

T11.7

31

OML

In 12:1 mode, each E1 carries 12 TRXs, and every two RSLs share a 64kbit/s timeslot of E1. If some site cascaded on one E1, then the E1 can carry 3 sites/11 TRXs or 6 sites/10 TRXs.

3)


Table 3-13 Sequence under 15:1 mode Sub-TS

Sub-TS 0

Sub-TS1

Sub-TS2

Sub-TS3

TS 0

Synchronization

1

V1

V2

V3

V4

2

V5

V6

V7

V8

3

V9

V10

V11

V12

4

V13

V14

V15

V16

3-52



Sub-TS 0

Sub-TS1

Sub-TS2

Sub-TS3

5

V17

V18

V19

V20

6

V21

V22

V23

V24

7

V25

V26

V27

V28

8

V29

V30

V31

V32

9

V33

V34

V35

V36

10

V37

V38

V39

V40

11

V41

V42

V43

V44

12

V45

V46

V47

V48

13

V49

V50

V51

V52

14

V53

V54

V55

V56

15

V57

V58

V59

V60

16

V61

V62

V63

V64

17

V65

V66

V67

V68

18

V69

V70

V71

V72

19

V73

V74

V75

V76

20

V77

V78

V79

V80

21

V81

V82

V83

V84

22

V85

V86

V87

V88

23

V89

V90

V91

V92

24

V93

V94

V95

V96

25

V97

V98

V99

V100

26

V101

V102

V103

V104

27

V105

V106

V107

V108

TS

28

RSL11, 12, 13, 14

29

RSL7, 8, 9, 10

30

RSL3, 4, 5, 6

31

OML+RSL0, 1, 2

In 15:1 mode, each E1 carries 15 TRXs, and timeslots 1 to 27 contain 108 sub-timeslots of 16kbit/s for the use by traffic channels of 15 TRXs. Vi refers to the ith traffic channel of the site. The E1 can be configured with 16 signaling links, every 4 of which share a 64kbit/s timeslot. If all cascaded sites have the same 15:1 configuration, then a single E1 can carry 2 sites/14 TRXs or 4 sites/12 TRXs.

3-53



3.4 Gb interface 3.4.1 Overview The Gb interface is the standard open interface between BSS and SGSN. M900/M1800 BSS, which includes the PCU, can be connected with the SGSN from any other vendor. Through this interface SGSN communicates with BSS to implement such functions as packet data transfer, flow control, mobility management, etc. This is a mandatory interface in GPRS network. The location of Gb interface in GPRS system is similar to that of the A interface in GSM system. A interface is between BSS and MSC, while Gb interface is between BSS and SGSN. Their difference is that Gb interface is more suitable to provide packet service.

I. Layered Model of the Gb interface protocol Figure 3-31 describes the location of the Gb interface and the main structure of the interface protocol stack.

LLC RLC

RELAY

BSSGP

BSSGP

MAC

NS

NS

L1

L1

L1

BSS

Gb

SGSN

Figure 3-31 Protocol stack at Gb interface z

The L1 physical layer of the Gb interface, which is based on the Frame Relay (FR) protocol, can be actually implemented by means of point-to-point frame relay network connection or multipoint-to-multipoint frame relay network connection.

z

The Network Service (NS) L2 protocol of the Gb interface implements the transmission function of the NS SDUs at the Gb interface as well as configuration and state management of NS-VS, etc.

z

The BSSGP L3 protocol of the Gb interface is designed mainly to carry out such operation & maintenance functions as uplink and downlink transmission of the upper layer (LLC layer) signaling and data, downlink data flow control, and blocking/unblocking and restarting of BVC (BSSGP Virtual Connection).

3-54



II. Related protocols of the Gb interface Like the A interface, the Gb interface is also an open interface so it is strictly designed according to GSM specifications to ensure good interworking between the GPRS BSS and the GPRS core network of different manufacturers. The related protocols of the Gb interface include: GSM 03.60, which specifies the location definition and the protocol stack

z

structure of the Gb interface. GSM 08.14, which specifies that physical layer of the Gb interface between BSS

z

and SGSN should use the FR protocol. GSM 08.16, which specifies the details of the L2 protocol NS of the Gb interface

z

between BSS and SGSN. GSM 08.18, which specifies the details of the L3 protocol BSSGP of the Gb

z

interface between BSS and SGSN.

3.4.2 Protocols on the Gb Interface I. FR Frame Relay protocol introduced for the physical layer of the Gb interface and E1 or T1 is imported for the physical media. The frame relay module enables the interworking between sub-networks so that the two ends (PCU and SGSN) can connect with each other directly through dedicated link (in point-to-point mode) or through frame relay network (in an intermediate network mode). As shown in Figure 3-32 and Figure 3-33. Gb BSS (user)

SGSN (network)

Figure 3-32 Point to Point mode

BSS (user)

Gb

Gb

Frame Relay network

SGSN (user)

Figure 3-33 Intermediate network mode The Frame Relay is a mature and universal physical layer protocol, not limited to the GPRS Gb interface only.

3-55



II. NS Distributed over the two sides of the Gb interface, the NS protocol layer has symmetrical functions on both sides of the Gb interface. But as a whole it provides simple and clear interface services to the upper-level BSSGP. It delivers mainly three service functions as follows: z

Upper Layer SDU transfers: All messages transported in the BSSGP layer are transferred in the NS layer in the form of NS SDU. The normal operation of the NS layer affords a reliable channel and protection for the normal operation of the upper layer protocol.

z

Network congestion indication: When the NS layer detects congestion or congestion removed on the bottom layer link, it will notify the upper layer through the congestion indication message so that the latter can handle it accordingly.

z

Network state indication: When the NS layer finds the bottom layer link is faulty and it cannot transmit data or the bottom layer link fault has recovered, it will notify the specific faulty point (recovery point) message to the upper layer so that the latter can handle it accordingly.

III. BSSGP L3 protocol Distributed over the two sides of the Gb interface, the NS protocol layer has symmetrical functions on both sides of the Gb interface. Figure 3-34 describes the service model implemented by the BSSGP protocol at both ends i.e. BSS and SGSN. Service model in a BSS RELAY

GSM 03.64 RLC/MAC

GMM

RL

Service model in an SGSN

NM

GMM

LLC

NM

GMM

BSSGP

BSSGP

NM

GMM

NM

BSSGP

GSM 08.16 Netw ork service

GSM 08.16 Netw ork service

Figure 3-34 BSSGP service model It can be seen from the protocol service model that the functions offered by BSSGP to the upper layer fall into three major parts: z

NM BSSGP: This part performs the network management function at the Gb interface, involving downlink data flow control, blocking, unblocking and resetting of BVC (BSSGP Virtual Connection), and MS tracing.

3-56



GMM BSSGP: This part performs the GPRS mobility management function at the Gb interface, including network paging to MS, MS radio access capability, and suspending and resuming of the GPRS service.

z

Uplink and Downlink Data Transfer: Gb interface delivers the data transmission service at BSS and SGSN. Although they differ in their names (it is called RL BSSGP service at the BSS side and LLC BSSGP service at the SGSN side), they are fully identical in their function implementation. It also carries out transparent transmission of the uplink and downlink upper-layer data.

3.4.3 Characteristics of Gb Interface 1)

Flexible physical interface and LMI support

M900/M1800 PCU supports ITU-T standard E1 interface. The Local Management Interface (LMI) supports Annex A of ITUT Q933 as stipulated in the GSM protocol as well as Annex D of CISCO LMI and ANSI T1-617, making it easy to interwork with the equipment of other manufacturers in the network.

2)

Flexible FR BC bandwidth and NS-VC bandwidth

The bandwidth of the physical carrier channel of the FR layer of M900/M1800 PCU can be configured flexibly between 64x1kbit/s~64x31kbit/s. The bandwidth of NS-VC in the NS layer can be configured flexibly between 1kbit/s~1984kbit/s. This measure greatly facilitates the network planning.

3)

Load sharing on the NS layer

M900/M1800 PCU supports full load sharing between NS-VSs of an NSE. NS-VSs can be located on different boards. This is crucial in enhancing the transmission reliability and utilization of the Gb interface.

4)

BSSGP layer entity switchover

M900/M1800 PCU supports full switchover between BSSGP PTP entities and between BSSGP SIG entities. When a PTP entity is somehow unavailable, the services in the entity can be switched over automatically to another available PTP entity, regardless of whether or not the available PTP entity is in the same physical board as the faulty PTP entity. When a SIG entity is somehow unavailable, the services in the entity can be switched over automatically to another available SIG entity, regardless of whether or not the available SIG entity is in the same physical board as the faulty SIG entity. The entity switchover function in the BSSGP layer is vital in boosting the reliability of the BSSGP layer.

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3.5 G-Abis Interface 3.5.1 Overview G-Abis interface is an internal interface between PCU and BTS in Huawei’s GPRS BSS. Through this interface, PCU fulfils communication with BTS and handles packet signaling transfer, packet data transfer, in-band signaling transfer and block synchronization, etc. It is similar to the Abis interface between BSC and BTS. The difference lies in that G-Abis interface provides functions and features more suitable for packet switching service.

3.5.2 Interface Features A PCU can be located at three positions. But there is no substantial specification of the interface between BTS and PCU in the GSM/GPRS specifications, so the G-Abis interfaces of different manufacturers are implemented in different ways. Huawei’s G-Abis interface has maximum transmission bandwidth utilization and effectively supports the processing of packet data and signaling. The G-Abis interface has the following features: z

Packet switching services, data and signaling are transferred by G-TRAU frame.

z

Provide 16kbit/s band width to transmit packet data of CS-1/CS-2 code and 32kbit/s band width to transmit packet data of CS-3/CS-4 code.

z

G-TRAU frame format transfer is adopted, with abundant in-band signaling contents including a series of mechanisms such as BTS measurement, BTS power control, RLC/MAC block coding scheme indication, air interface block synchronization, etc.

The transmission parameter of GPRS encoding mode is listed in Figure 3-10. Table 3-14 Transfer parameters of coding schemes Coding scheme CS-1 CS-2 CS-3 CS-4

Coding rate 1/2 2/3 3/4 1

Code bits 456 588 676

Rate kbit/s 9.05 13.4 15.6 21.4

When CS-1/2 encoding mode is supported, the rate of G-Abis interface should be less than 16kbit/s. When CS-3/4 encoding mode is supported, G-Abis interface should be able to provide the rate of 32 kbit/s. BTS measures the strength and quality of the uplink radio signals and reports via the G-Abis interface the measurement results to PCU, which controls the uplink power based on the results. 3-58



PCU sends the BTS control parameters to BTS through G-Abis and provides control over the downlink power based on the parameters. The RLC/MAC block coding scheme is sent by PCU via G-Abis to BTS, which makes radio block coding for the downlink data and the uplink radio blocks based on the code. All the packet data channels (PDCH) used by GPRS take the structure of 52 multiframes and maintain a strict mapping relationship with the G-TRAU frames of the G-Abis interface. The frame number message of the air interface is transported between PCU and BTS via the in-band signaling. After a synchronization process, the data blocks sent by PCU to BTS can establish a precise time sequence relationship with the TDMA frame numbers of BTS, so that there is minimum time delay when the uplink and downlink data blocks are processed in BTS.

3.5.3 Physical Layer/Transmission Media Like the Abis interface, the G-Abis interface counts physically on the 2Mbit/s E1, which reaches BTS through BSC relay. The BSC functions only as a physical relay for the data of the G-Abis interface. There are packet traffic channel of the G-Abis interface and LAPD channel of the Pb interface in the E1 from PCU to BSC, as shown in Table 4-8. There are packet traffic channel of the G-Abis interface, circuit traffic channel of the Abis interface, RSL (circuit-switched radio signaling link) and OML (circuit-switched operation & maintenance link) link in the E1 from BSC to BTS. Depending on the usage of channel resources, the G-Abis interface and the Abis interface may share one E1. The sub-TSs in E1 occupied by the G-Abis interface and the Abis interface are shown in Table 4-9. Table 3-15 Sample of G-Abis interface TS configuration (in PCU-BSC section) TS

Sub-TS 0

Sub-TS1

Sub-TS2

Sub-TS3

0 1 n

0 4 4n

1 5 4n+1

2 6 4n+2

3 7 4n+3

m

4m

4m+1

4m+2

4m+3

31

124

125

126

127

3-59

Usage E1 synchronization TS Packet data channel Packet data channel Dynamic additional sub-TS, supporting additionally CS-3/CS-4 packet traffic channel LAPD channel



Table 3-16 Sample of G-Abis interface configuration (in BSC-BTS section) TS

Sub-TS 0

Sub-TS1

Sub-TS2

Sub-TS3

0

0

1

2

3

1

4

5

6

7

n

4n

4n+1

4n+2

4n+3

m 31

4m 124

4m+1 125

4m+2 126

4m+3 127

Usage E1 synchronization TS Circuit traffic channel or packet data channel Dynamic additional sub-TS, supporting additionally CS-3/CS-4 packet traffic channel RSL OML

The radio channel on the air interface can be dynamically allocated as TCH or PDCH to supports GPRS services. The sub-TSs at the E1 can be allocated dynamically to the Abis interface or the G-Abis interface. The sub-TSs for the Abis interface transport speech data with E-TRAU frames (GSM 08.60) and the sub-TSs for the G-Abis interface transport packet data with G-TRAU frames. In CS-1/CS-2, the PDCH with the rate of 16kbit/s can be carried by one sub-TS. Two type sub-TSs can convert each other. In CS-3/CS-4, the bandwidth of the PDCH exceeds 16kbit/s, so one sub-TS is not enough to carry the PDCH. This issue can be resolved with the additional sub-TS. This is made up of 16kbit/s main TSs configured for TCH by Abis interface, and the dynamic additional Sub-TS pool consisting of 16kbit/s idle TSs. When the data blocks of CS-3/CS-4 need to be transported between PCU and BTS, additional Sub-TS will be taken from the additional Sub-TS pool and attached to the main TS. After the data to be transmitted are decomposed by BTS, they are transmitted simultaneously in the main and additional Sub-TS. PCU is responsible for restoring the messages.

3.5.4 G-TRAU Frame Structure It transports a bi-directional G-TRAU frame between BTS and PCU in every 20ms for one PDCH. Each G-TRAU frame has the following fields as listed in Table 4-10. Table 3-17 G-TRAU structure G-TRAU frame field Frame Header Data Domain In-band signaling

Description Serves to synchronize G-TRAU frames between BTS and PCU. It is a group of special bit sequences designed to define G-TRAU frames. RLC/MAC data blocks generated during BTS decoding, or RLC/MAC data blocks sent by PCU to BTS after being encoded. Performs signaling interworking between PCU and BTS.

The signaling between PCU and BTS is in-band signaling. The G-TRAU frame in-band signaling contains a large variety of complicated mechanisms including BTS measurement, BTS power control, RLC/MAC block 3-60



coding scheme indication, synchronization of air interface blocks between BTS and PCU.

3.5.5 G-Abis Characteristics 1)

Half Standalone PCU and Flexible Physical Location

In GSM/GPRS specification, there is no concrete definition about the interface between PCU and BTS (G-Abis interface). Despite the fact that PCU is part of GPRS BSC, it can either be an embedded device or half stand-alone device. The M900/M1800 PCU, a half stand-alone device can be located in BSC or SGSN (or in MSC in a special networking mode) flexibly. The addition of PCU makes the smallest impact on the existing GSM circuit switching system. It makes possible for the existing BTS and BSC to support GPRS without hardware upgrading. It can meet the processing capacity requirements posed by packet-switched services to the greatest extent and cut the impact on the processing capacity of the already-planned BSS to the minimum.

2)

Dynamic Additional Sub-TS Technology

Abis interface is based on the 16kbit/s links (or called 16kbit/s sub-TS). M900/M1800 GPRS BSS is also based on the 16kbit/s link at the G-Abis interface. When CS-3 and CS-4 encoding mode is adopted, the rate of a PDCH is 15.6 kbit/s and 21.4 kbit/s, therefore, when mapping the radio channels to the terristrial channels, a PDCH is mapped to two 16 kbit/s links. However, the encoding mode adopted by PDCH is adjusted according to the change of the radio transmission environment of the MS that occupies it. Mapping a PDCH permanently onto two 16kbit/s links will greatly decreases the multiplexing ratio of the G-Abis interface, and thus greatly reduce the utilization ratio of the G-Abis interface transmission equipment. With dynamic allocation, M900/M1800 GPRS BSS can resolve the transmission issue of CS-3 and CS-4 on the G-Abis interface perfectly. The dynamic attached sub-slot technology is to statically allocate a main 16 kbit/s sub-timeslot at the G-Abis interface for the CS-3/CS-4 PDCH. With the dynamic additional sub-TS technology, it is not necessary for GPRS BSS to upgrade the hardware of BTS, BSC or PCU for supporting CS-3 and CS-4. In addition, in its support for CS-3 and CS-4, the multiplexing ratio of the G-Abis interface is greatly improved, thus saving investments on the G-Abis interface transmission equipment. The dynamic additional sub-TS technology used by M900/M1800 GPRS BSS displays the following features: z

Any idle Sub-TS of the G-Abis interface can be used as additional sub-TS, so that each has maximum utilization.

3-61



Within a same site address, the additional sub-TSs can be dynamically attached to various main TSs to enhance the utilization ratio of this sub-TSs according to statistical multiplexing rules.

z

The locations of the additional 16kbit/s sub-TS are relatively flexible. They do not have to be adjacent to the main 16kbit/s sub-TS.

z

It packs and unpacks the data packets through software to avoid hardware upgrading.

3)

Fast and stable time synchronization mechanism for the air interface blocks

With advanced synchronization mechanism and algorithm, PCU can stably synchronize CCU within one TDMA multiframe duration (240ms) in terms of cell-based air interface block after system initialization. The stable air interface block synchronization between PCU and CCU is of great significance for ensuring normal packet system information broadcast and high-efficiency radio transmission in GPRS cells.

4)

Scalable G-TRAU Frames

The issue of forward and backward compatibility is taken into full account in the definition of the structure of the G-TRAU frames, so it features good scalability. Three-bit version number is defined in the header of the G-TRAU frame so that it can support 8 different G-TRAU frames. M900/M1800 BSS, which features good forward and backward compatibility on the G-Abis interface, can smoothly evolve to next generation through the G-TRAU version mechanism.

3.6 Pb Interface 3.6.1 Overview Pb interface is the interface between PCU and BSC. Like other BSS systems available in market, Huawei’s own proprietary Pb interface is efficiently designed and implemented.

3-62


Chapter 3 Interface Description MSC BTS

BSC A

Um PCU Pb

BSS

Gb SGSN

Figure 3-35 Position of PCU PCU can be co-located with BSC or MSC or SGSN sites, even though it serves as part of BSS. Huawei-developed Pb interface satisfies all the requirements of BSC-PCU interface. It implements management functions between PCU and BSC for various kinds of shared resources such as cell, packet channel, E1 trunk and system information. Besides, it supports dynamic channel conversion, MS access to CCCH, etc. Figure 3-35 Location plan of PCU In actual practice, one PCU frame (with a maximum of 12 Radio Packet Processing Units RPPUs) can connect with several BSCs through E1, while one BSC can only connect with one PCU frame (or with several RPPUs concurrently).

3.6.2 Internal Structure of Pb Interface The Pb interface, as an internal protocol, has three layers. z

Layer 1 (physical layer) adopts sub-TS of the E1 line. In fact, the Pb interface and the G-Abis interface share the same physical link. One E1 is divided into 128 sub TSs of 16kbit/s where 4 sub-TSs serve for synchronization. Some of these sub-TSs are used for the physical link of the G-Abis interface, some for the physical link of the Pb interface and the rest might serve as idle sub-TSs or be multiplexed.

z

Layer 2 (link layer) is based on the LAPD protocol, which is a general data link layer protocol. It receives the data transfer service from the physical layer and delivers the connection-oriented or connectionless service to L3. LAPD aims to implement peer-to-peer reliable message transfer between L3 entities.

z

Layer 3 protocol consists of a series of self-defined signaling messages. It is the core of the Pb interface. It mainly manages of the messages regarding 3-63



GPRS-related resources between PCU and BSC, supports conversion of dynamic channels between the packet service, speech service, and provides functions of MS access to CCCH and speech paging message transmission. As the bottom layer is based on the standard LAPD protocol, the Pb interface protocol also refers specifically to its L3 signaling procedure.

3.6.3 Pb Interface Management The Pb interface management includes: management of the trunk circuits between the BSC and PCU, management of packet radio resources, packet service access support, transmission management, PbSL link management, etc.

I. Management of the trunk circuits on the Pb interface Management of the trunk circuits on the Pb interface helps to monitor the trunk circuits between BSC and PCU for smooth system running, so that the PCU can be assigned with an idle circuit when requesting the PDCH or dynamically modifying channel coding to ensure the data services. The procedures of Pb interface circuit resources management include Circuit Block/Unblock, Unequipped Circuit, and Reset Circuit. The causes that initiate the procedures include the OMC maintenance or change of the Pb interface equipment state. To simplify the design, the following rules are employed for Pb interface circuit management: z

A BSC only records the maintenance state of the circuit, not the usage of the circuit.

z

Circuit management messages are activated by the BSC.

z

The PCU can block/unblock and reset circuits at the local end, without affecting the circuit state at the BSC side.

z

The BSC can not change the state of the circuit determined by the maintenance console at the PCU side, i.e. BSC has no authority to unblock a circuit that is blocked at the maintenance console (PCU side).

The procedures of Circuit Block/Unblock, Unequipped Circuit, and Reset Circuit are almost the same as those on the A-interface. The only difference is that MSC is changed to the PCU and the trunk CIC (Circuit Identification Code) at the A-interface is changed to the trunk circuit PCIC at the Pb interface. For example, the Circuit Block procedure at the Pb interface is shown in Figure 3-37.

3-64


Chapter 3 Interface Description PCU

BSC

Block circuit

Block circuit acknowledgement

Figure 3-36 Process of group blocking the circuit

II. Packet radio resource management Radio resource management on the Pb interface refers to the management of radio resources related to the packet service. It has the following characteristics:

1)

All the radio resource information is configured at the data configuration console. The radio resource information of PCU is obtained from the BSC. Pb interface cell initialization process corresponds to this principle. It includes the cell resetting at both BSC and PCU sides, notification by BSC to PCU of the packet radio resource configuration of the cell, and start of packet system information broadcast.

2)

Circuit service and packet service shares the radio resources, which are allocated on demand. The circuit-based service will have the priority to be allocated. Dynamic allocation of resources on demand requires that the BSC allocate the radio resources in real-time to the circuit-based service or packet-based service according to the current application. This means a dynamic conversion between the TCH and PDCH. There are three channel conversion processes at Pb interface:

z

When there is more data traffic demand for more channel resources, PCU requests BSC to convert TCH into the PDCH. BSC decides the conversion according to the available resources. If there are many TCHs idle, then BSC will allow to converting TCHs into PDCHs and send the related information to the BTS.

z

When the BSC discovers TCHs are insufficient, it requires the PCU to hand over some PDCHs, which will be converted into TCHs. This requirement is mandatory according to the rule of circuit-based service having the priority.

z

When the PCU discovers there are too many PDCHs idle, it will automatically hand back some PDCHs, which will be converted into TCHs again. This is the rule of circuit-based service having the priority.

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3)


The BSC is responsible for assigning TCH, and the PCU is responsible for assigning PDCH.

After PCU has been assigned with a PDCH, the allocation and release of this PDCH is decided by PCU. Similar to GSM network, BSC is responsible for the allocation and release of TCH.

4)

The states of the radio resources at the BSC and PCU sides must be kept consistent.

To achieve the consistency between the states at both sides, the BSC need to notify the PCU of the impact of the change on the BTS and OMC operations on the radio resources. For example when the OMC blocks a certain packet channel, the BSC needs to notify the PCU to update the channel state.

III. Packet service access To support GPRS, it is necessary to broadcast system information type 13 on the BCCH, and at the same time modify system information type 3, system information type 7, etc, so that they include GPRS messages as GPRS Indicator. Based on these messages, MS decides whether it should access the current serving cell for data services or not. When no PCCCH is configured in the local cell, the MS will access the packet service through the CCCH. This mainly involves three procedures: packet call access initiated by the MS, packet call access terminated by the MS, packet service suspension and recovery for the Class-B MS.

IV. Other management procedures on the Pb interface 1)

Transmission management

In the TCH-to-PDCH conversion, the BSC needs to connect the trunk circuit on the Abis interface and that on the Pb interface. During the process of packet data transmission, the BSC needs to forward packet data among BTS-BSC-PCU. In the PDCH to TCH conversion, the BSC needs to release the original connection. In general, each PDCH corresponds to a 16kbit/s data channel. But if the transmission quality proves to be satisfactory by PCU, it can activate a more efficient channel coding method, like CS-3 or CS-4. At this time, the BSC needs to dynamically allocate one more 16kbit/s timeslot to the PDCH, that is, the 32kbit/s data channel corresponds to the PDCH.

2)

PbSL management

The Pb interface signaling link (PbSL) is a LAPD link. And PbSL management involves the transmission and reception of Pb interface message packets, link load sharing, link mutual-assistance function, etc.

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If there is no PCCCH in a certain cell, the disconnection of all the PbSLs will lead to the release of the resources of the cell at both sides of the Pb interface.

3)

Error handling

There may be errors during the process of transmission, so the Pb interface has the error handling function. By this function, error messages will be omitted and some "confusion" messages will be transmitted selectively.

3.6.4 Characteristics of Huawei Pb Interface I. Supporting dynamic conversion traffic channels

between packet traffic and the speech

In practice, the channels are classicified into three types according to their properties: fixed packet traffic channel, voice traffic channel and dynamic channel. The fixed packet channel is dedicated for packet service, such as PDTCH, PBCCH and PCCCH. Voice traffic channel is dedicated for voice service, such as TCH, BCCH and SDCCH. The dynamic channel is the voice TCH at the initialization stage. It can be converted between the former two types of channels. When there is more packet traffic and the speech channels are relatively idle, PCU will request the BSC to convert the dynamic channel into the dynamic packet traffic channel. Whereas when BSC determines the speech channels are busy, it can also request PCU to return the converted dynamic channel and use it again as speech channel. In this process, the speech service is given the priority over the packet service to guarantee the original speech services.

II. Supporting MS channel access request for CCCH As BTS cannot identify the access request message sent by an MS on the CCCH, it can make out that it is a packet access request only after the BSC analyzes the MS request and then transfers it to PCU. Accordingly, the immediate assignment message of PCU needs to be processed by BSC before it is sent to BTS. It can be seen from here that when a MS accesses the CCCH and the PCCCH, it is processed differently in the BSS. The MSs that support access to the CCCH are not complex, so they are also low in costs. Whereas the design of Huawei-developed Pb interface can enable PCU to support two kinds of access concurrently, thus enhancing tremendously the adaptability of the system.

III. Maintaining the consistency of resource data between BSC and PCU. PCU and BSC are located in two places, so the message data of all the shared resources (such as cells, channels, PCIC trunks and system information parameters) 3-67



should be consistent. This is also the major function of the Pb interface. The functions of the Pb interface involve the management & maintenance of some resources, such as cell parameter configuration, cell restarting, channel blocking/unblocking, PCIC blocking/unblocking,

PCIC

restarting,

packet

system

information

parameter

configuration and regular check of all the resources data.

IV. Sending speech paging messages. When the network operation mode is Mode 1, and there is no PCCCH. MSC sends the voice paging message via Gs interface (MSC-SGSN) and Gb interface (SGSN-PCU), and PCU transfers the message via Pb interface to BSC, which will transmit the message on CCCH. For details of network operation mode, refer to other relative chapters.

V. Supporting GPRS suspension and resume messages sent by Class-B MSs. Class-B MS cannot implement CS service and PS service simultaneously. Therefore, when the MS in packet transmission mode is engaged in traffic service, it will send the GPRS suspension request to BSC. BSC will transfer this message to PCU via Pb interface. When the circuit service of an MS is over, BSC will send a GPRS service recovery request to PCU again via the Pb interface. The capability of supporting the Class-B MSs by the system is enhanced while the Pb interface processes this kind of messages.

3.7 Operation & Maintenance Interface 3.7.1 Overview The operation & maintenance interface is an interface between the BSS and the Operation & Maintenance System. A subscriber can perform the maintenance and management over the BSS system through OMC console or the Telnet terminal, as shown in Figure 3-37.

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Chapter 3 Interface Description Telnet

MSC

O Interface

DCN

BSC

R

OMC Server

PCU

... SGSN

OMC Workstation

OMC Workstation

Figure 3-37 GPRS/GSM operation & maintenance interface Of the GSM equipment such as MSC, BSC, HLR, there is a BAM designed specifically as a bridge between the equipment and the OMC. It collects the equipment information and communicates with the OMC to implement the functions of the O interface. In the GPRS equipment such as PCU, SGSN, etc., no BAM exists due to variations in hardware implementation, so OAM module (OMC Agent Module) in the POMU serves as a bridge between the system equipment and the OMC. For different equipment, the OMC WSs are similar in interface, but are different in such implementation as message interpretation.

3.7.2 Feature Unlike the network bottom layer interfaces like Gb and Pb, the operation & maintenance interface is an application layer interface in nature, thus relatively simple in message structure and protocol layer. The lower layer of the operation & maintenance interface is based on the TCP/IP protocol, which enables the OMC system to acquire a very strong remote networking capability. As regards the system composition, the software system sturcture of the O&M interface is arranged as shown in Figure 3-38.

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OMA

BAM ...

PCU

BSC LAN/WAN

TCP/IP OMC SHELL

Communication Server

Traffic Statistic

...

Alarm Tracing

Database Server ... OMC Sercer/DB

WorkStation

Figure 3-38 Structural diagram of the O interface software system The O&M interface programs include OAM/BAM program, OMC Server/DB, OMC Shell and OMC application console. Below is the brief introduction to the function and feature: z

OAM and BAM differ in hardware and software implementation. Although different equipment manages different messages and information, they are the same in basic functions. The functionality of the OAM is mainly two-fold: first, it serves as a communication bridge between the OMC system and the network equipment, forwards the maintenance & operation command from the OMC to the FAM board and orients the response from the AM to the OMC terminals accordingly. On the other hand, it acts as a server in Client/Server models. Apart from the management of the database as well as the test task and traffic statistic task, the OAM also stores and forwards the charging messages, alarm messages and traffic statistic data. It stores all the vital data on the hard disk and dumps them to the CDs or OMC server if necessary.

z

OMC server is for running various service processes, such as communication server and database server, etc. Communication server is the core of the whole system, it connects other parts through application agents. The communication server assigns an ID to each application part that connects directly to it. In the process of message transmission, the communication server receives the messages from all parts, determines the destination for these messages and forwards the messages to the destination or makes proper processing. On the other hand, all the database servers interact with the database management system (DBMS) and manage all the data by answering the requests from the

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OAM/BAM or SPOS. Moreover, there are also some other application servers and management modules on the OMC server. z

OMC Shell is a user interface that manages, operates and maintains the GSM objects as well as a communication interface with all the SPOS programs. OMC Shell is used for visual management of NEs of the entire Huawei GSM system through WS. OMC Shell program consists of user interface module and communication module. User interface module provides visual operating interfaces such as tree-like list and map windows. On the interface, a user can view the state of the GSM objects or performs directly the operation, maintenance and management over the GSM objects. The communication module is mainly responsible for communication management.

z

OMC application console is a classified set of some service functions. For different equipment, the functions implemented in their application consoles will also change. The OMC application console of PCU mainly includes traffic statistics management console, alarm console and message tracing console. Since the overall system design is modularized by functions, it is possible to adjust the function of the application console according to the carrier's requirement.

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Appendix A Abbreviations

Appendix A Abbreviations A AC AC ACELP AGCH AM/CM ANSI APL ARFCN ASIC AUC B BA BAM BCC BCCH BCF BCH BER BHCA BIE BM BP BQ BSC BSIC BSS BSSAP BSSMAP BTS BTSM BVC C CA CAMEL CBA CBC CBCH CBQ CC CC CCBS CCCH CD CDB CDU CELP CGI CI CIC CIR CKSN CM CPU CR CRC CRO

Access Class (C0 to C15) Alternating Current Algebraic code excitation linear prediction Access Grant Channel Administration Module/ Communication Module American National Standard Institute Advanced Phase Locking Absolute Radio Frequency Channel Number Application Specific Integrated Circuit Authentication Centre BCCH Allocation Back Administration Module BTS Color Code Broadcast Control Channel Base Control Function Broadcast Channel Bit Error Rate Busy Hour Call Attempts Base station Interface Equipment Basic Module Burst Pulse Bad Quality Base Station Controller Base Station Identity Code Base Station System Base Station Subsystem Application Part Base Station Subsystem Management Application Part Base Transceiver Station Base Transceiver Station Management BSSGP Virtual Connection Cell Allocation Customized Applications for Mobile network Enhanced Logic Cell Bar Access Cell Broadcast Center Cell Broadcast Channel Cell Bar Qualify Connection Confirm Call Control Completion of Calls to Busy Subscribers Common Control Channel Call Deflection Cell Broadcast Database Combining and Distribution Unit Code Excited Linear Prediction Cell Global Identity Cell Identity Circuit Identification Code Carrier to Interference Ratio Ciphering Key Sequence Number Connection Management Central Processing Unit Connection Request Cyclic Redundancy Check Cell Reselect Offset

A-1

Feature Description M900/M1800 Base Station Subsystem CS D DBMS DC DCCH DCL DDN DL DLC DLCEP DLCEPI DLCI DNS DPC DRX DSC DTAP DTMF DTX E EA E-Abis EC ECSC ECT EFR EIR EM ETSI F FACCH FCCH FDMA FH FIR FN FR FTC FUC G G-Abis GGSN GLAP GMM GMPU GMSC GMSK GPRS GSM GSM900 GSM1800 GSN GT H HCS HDLC HDSL HLR HSC HSN HW I IEC IMEI


Coding Scheme Database Management System Direct Current Dedicated Control Channel Diagnostic Control Link Digital Data Network Downlink Data Link Connection Data Link Connection End Point Data Link Connection End Point Identifier Data Link Connection Identifier Domain Name Server Destination (Signaling) Point Code Discontinuous Reception (mechanism) Downlink Signaling fault Count Direct Transfer Application Part Dual Tone Multi Frequency Discontinuous transmission (mechanism) Early Allocation Enhanced Abis Emergency Call Early Classmark Send Control Explicit Call Transfer Enhanced full rate speech code Equipment Identify Register Extended Measurement European Telecommunication Standards Institute Fast Associated Control Channel Frequency Correction Channel Frequency Division Multiple Access Frequency Hopping Finity Impulsion Response Frame Number Frame Relay Full Rate Transcoder Frame Unit Controller GPRS Abis Gateway GPRS Support Node LAPD Protocol Process board GPRS Mobility Management Main Process Unit Gateway Mobile Switching Center Gaussian Minimum Shift-frequency Keying General Packet Radio Service Global System for Mobile communications GPRS Support Node Global Title Hierarchical Cell Structure High level Data Link Control High speed Digital Subscriber Line Home Location Register Hot Swap Controller Hopping Sequence Number Highway International Electrotechnical Commission International Mobile Equipment Identity

A-2

Feature Description M900/M1800 Base Station Subsystem IMSI IP ISDN ISUP ITU-T L L2ML LA LAC LAI LAPD LAPDm LLC LMT LNA M MA MAC MAIO MAP MBR MCC MDC MDT ME MM MNC MNS MDSL MR MRP MRT MS MSC MSISDN MT MTP N NC NCC NCH NM NS NSE NSS O OAM OMC OML OSI P PACCH PAGCH PBGT PBCCH PbSL PCCCH PCU PD PDP PDCH PDH PDTCH PIN


International Mobile Subscriber Identity Internet Protocol Integrated Services Digital Network Integrated Services Digital Network User Part/ISDN User Part International Telecommunication Union - Telecommunication Standardization Sector Layer 2 Management Link Location Area Location Area Code Location Area Identity Link Access Protocol on the D channel Link Access Protocol on the Dm channel Logical Link Control Local Maintenance Terminal Low Noise Amplifier Mobile Allocation Media Access Control Mobile Allocation Index Offset Mobile Application Part Multiband Report Mobile Country Code Message Discrimination Message Distribution Mobile Equipment Mobility Management Mobile Network Code Mobile Network Signaling Medium Bit-rate Digital Subscriber Loop Measurement Result Multiple Reuse Pattern Message Routing Mobile Station Mobile Switching Centre Mobile Station International ISDN Number Mobile Terminal Message Transfer Part Network Control Network Color Code Notification Channel Network Management Network Service Network Service Entity Network Sub System Operation Administration and Maintenance Operations & Maintenance Centre Operation and Maintenance Link Open Systems Interconnection Packet Associated Control Channel Packet Access Grant Channel Power Budget Packet Broadcast Control Channel PCU-BSC Signaling Link Packet Common Control Channel Packet Control Unit Protocol Discrimination Packet Data Protocol Packet Data Channel Plesiochronous Digital Hierarchy Packet Data Traffic Channel Personal Identity Number

A-3

Feature Description M900/M1800 Base Station Subsystem Phase I Phase II PLMN PNCH POMU PON PPCH PRACH PSI PSK PSTN PT PTCCH PTM-M PTP Q QoS R RACH RE RF RLC RPE-LTP RPPU RR RSL S SABM SACCH SAP SAPI SCCP SCH SCU SCMG SDCCH SDH SDU SGSN SID SIG SIM SLM SLS SMC SMS SMSCB SMUX SOR SRM SS SSN STM T TA TAI TBF TCH TDMA TCSM TE TEI TFI TLLI


Personal Identity Number Public Land Mobile Network Packet Notification Channel Packet Operation & Maintenance Unit Passive Optical Network Packet Paging Channel Packet Random Access Channel Packet System Information Phase Shift Keying Public Switched Telephone Network Penalty Time Packet Timing advanced Control Channel Point To Multipoint Multicast Point To Point Quality of Service Random Access Channel Reestablishment Radio Frequency Radio Link Control Regular Pulse Excitation-Long Term Prediction Radio Packet Process Unit Radio Resource Radio Signaling Link Set Asynchronous Balanced Mode Slow Associated Control Channel Service Access Point Service Access Point Identifier Signaling Connection Control Part Synchronization Channel Simple combining Unit SCCP Management Stand-alone Dedicated Control Channel Synchronous Digital Hierarchy Service Data Unit Serving GPRS Support Node Silence Descriptor Signaling Subscriber Identity Module Signaling Link Management Signaling Link Selection Short Message Center Short Message Service support Short Message Service Cell Broadcast Sub-Multiplexer Support Optimization Routing Signaling Route Management Supplementary Service support SubSystem Number Signaling Traffic Management Timing Advance Timing Advance Index Temporary Block Flow Traffic Channel Time Division Multiple Access TransCode & Sub-Multiplexer Terminal Equipment Terminal Equipment Identifier Transport Format Indicator Temporary Link Level Identity

A-4

Feature Description M900/M1800 Base Station Subsystem TMSC TMSI TN TO TRX TRAU TSC TUP U UA UDT UI USF USSD V VAD VBS VEA VGCS VLR VM VSAT W WS X xDSL


Tandem Mobile Switching Centre Temporary Mobile Subscriber Identifier Timeslot Number Temporary Offset Transceiver Transcoder & Rate Adaptation Unit Training Sequence Code Telephone User Part Unnumbered Acknowledge Unit Data Unnumbered Information (frame) Uplink State Flag Unstructured Supplementary Service Data Voice Activity Detection Voice Broadcast Service Very Early Allocation Voice Group Call Service Visitor Location Register Voice Mailbox Very Small Aperture Terminal Workstation x Digital Subscriber Line

A-5

Feature Description Huawei

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