UMTS Overview

UMTS Overview

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UMTS UMTS Overvi Overv i ew

Contents 1 1.1 1.2 1.3 2 2.1 2.2 3 4 5 6 7

Cellular System First Steps and first generation (1G) Second Generation (2G) Third generation (3G) UMTS UMTS development Mobile communication market Standardization UMTS Evolution Comparison with mobile technologies Exercises Solution

TM51101EN03GLA2 © 2010 Nokia Siemens Networks

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Cellular System


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In the following section, we will discuss the principle of cellular system and the advantages of it moving towards digital technology. There are three different generations as far as mobile communication is concerned as discussed below: 1. First Generation (1G) 2. Second Generation (2G) 3. Third Generation (3G)

1.1

First Steps Steps and first fir st generation generation (1 (1G) G)

The first generation, 1G, is i s the name for the analogue or semi-analogue (analogue radio path, but digital switching) mobile networks established after the mid-1980s, such as Nordic Mobile Telephone (NMT) and Advanced Mobile Phone System (AMPS). These networks offered basic services for t he users, and the emphasis was on speech and services related matters. 1G network were mainly national efforts and very often they were specified after the networks were established. Due to this, the 1G network was incompatible with each other. Mobile communication was considered some kind of curiosity, and i t added value service on top of the fixed networks in those times. The history of mobile communication starts with the transmission of information via High Frequency (HF) in the late 19th century. Even after HF speech transmission became possible in the first decade of the 20th century, it needed further 40 years, before the first mobile networks for private user started operation.

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1.1.1

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Simplex/Duplex

Simplex transmission means to be a communication "one-way street". Transmission in only one direction (to or from the mobile user) is possible at a certain time. Simplex transmission is used e.g. for radio and TV transmissions. Simple mobile communication systems use the so-called Semi-Duplex Transmission, i.e. at a certain time it is only possible to transmit data in one direction, but the direction can be changed (used in ancient mobile systems and walkie-talkies). Duplex transmission is used for simultaneous, bi-directional information exchange. Modern telecommunication systems are based on duplex transmission.


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1.1.2

Single cell system

The first mobile networks offering duplex transmission car phone telephone service to private user started operation in the late 1940's in the USA and in Europe during the 1950's. These systems have been created as Single Cell Systems. Single Cell Systems provide service in the service area (cell) of several Base Stations BSs, but every cell is far remote from others to prevent interference between different users (resulting in disruption of the connections). Every single cell was totally independent from the others. This caused the several problems, for example: •

low system capacity

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no "Handover" possible

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no seamless service areas

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no call toward the mobile user without knowledge of his current location

The following problems were also encountered by the first mobile services: •

poor service and speech quality

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manual switching (operator needed)

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heavy, cumbersome, massive, expensive equipment (only for car phone)

Single Cell Systems have been used until the m1990's, becoming less and less important with the introduction of the cellular systems at the end of the 1970's.

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TM511101EN03GLA01 1

© N ok i a S i em en s N et w or ks

Fig 1 Single cell system

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1.1.3

Principle of cellular system

According to a cellular principle a large number of Base Stations (BS) that provide full service coverage, their cell areas overlap each other significantly. To prevent interference between subscribers using the same frequency, only part of the available frequency range is used in a cell. The same frequency range is only permitted to be used in another cell sufficiently distant from this first cell (re-use distance). The area in which the entire "set of frequencies" is once used is known as the cluster. The number of calls that can be made at the same time in a particular area is no longer determined by the available frequency range but by the size of the available cells. Cellular Systems are the prerequisite for: •

Roaming

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Handover

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Enhanced network capacity

Cellular Systems were tested in many countries at the end of the 1970's. In 1979, AMPS started commercial operation in the USA and the Nippon Telegraph & Telephone Company - Mobile Telephone System (NTT-MTS) in Japan. Both systems operated in the 800-MHz range. In the beginning of the 1980's, the NMT system was launched. NMT was the first cellular system allowing International Roaming. In 1985 the Total Access communication System (TACS) was introduced in Great Britain in the 900MHz range. Some of the European Countries where NMT and TACS Systems were introduced in the 450- MHz range are: Italy: The RTMS system. Germany: The C450 system France: The Radiocom2000 system The introduction of the cellular system principle for mobile communication in the late 1970's made it possible to increase the number of mobile subscriber from less than 1 million world-wide to more than 500 million between 1980 and 2000.

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1EN0 3GLA01 © Nokia Siemens Networks

Fig 2: Cellular System

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1.1.4

Limitations of 1G

Cellular 1G systems transfer analogue information over the radio or air interface. Shortly after introduction of the first "analogue" mobile communications systems, it became evident that the exponential growth in subscriber numbers in mobile communications would quickly saturate the capacity. A further problem entailed the frequently poor speech quality and service availability of the "analogue" systems. The large numbers of historically evolved, incompatible analogue standards in Europe at the end of the 1980's also represented a barrier in a converging European market. As early as the beginning of the 1980's it became clear that a new, uniform cellular system/standard at European level had to be developed. The first system in the so called second mobile communications generation (2G) deriving f rom this initiative was the GSM Standard. The 2G systems differs from the 1G system in the respect that the 2G systems transmit digital information.

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1.2 1.2.1

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Second Generation (2G) 2G cellular systems

Global System for Mobile Communication (GSM) In 1990 the GSM Standard was ratified as first 2G standard. Commercial operation of GSM systems started in late 1991. Originally planned as a European system, GSM spread all over the world, serving 2/3 of all mobile subscriber in 2001. The GSM radio interface uses FDD for duplex transmission and FDMA/TDMA for multiple access. GSM systems are existing in the 900, 1800 and 1900 MHz frequency range. Digital Advanced Mobile Phone System ( D-AMPS) D-AMPS (also referred as IS-136 or US-TDMA) was conceived in 1991/1992 in America as an enhancement of the 1G AMPS standard. The D-AMPS radio interface uses FDD for duplex transmission and FDMA/TDMA for multiple access. The 800MHz band (824-849/869-894 MHz) is used in conjunction with AMPS. D-AMPS was extended in 1995 to the 1900-MHz frequency range. AMPS and D-AMPS serve some 10% of the world-wide mobile subscriber in 2001. Japanese Digital Cellular ( JDC) / Personal Digital Cellular (PDC) PDC, originally titled as JDC is used in Japan only. Commercial operation started in1993/1994. The PDC radio interface uses FDD for duplex transmission and FDMA/TDMA for multiple access. PDC is used at the 900-MHz band (810-826/940956 MHz) and 1500-MHz band (1429-1441, 1501-1513). In 200 some 70 million subscriber used PDC in Japan. Interim Standard-95 ( IS-95 ) IS-95 CDMA was developed at the beginning of the 1990's on the basis of CDMA technology. Commercial operation started 1995. The IS-95 radio interface uses FDD for duplex transmission, which is different to GSM, D-AMPS, and PDC CDMA for multiple access frequencies in the 800-MHz and 1900-MHz bands are used globally and also in the 1700-MHz band in Korea. IS-95 CDMA are used all over the world, serving some 100 million subscriber in 2001.


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1.2.2

Development of GSM Standard

In 1978, the Conférence Européene des Postes et Télecommunication (CEPT) reserved 2 x 25 MHz in the 900-MHz band for a future European mobile communications system. A team of experts – the “Groupe Special Mobile” (GSM) – was set up in 1982 to develop this standard. The objective was to create a binding, international standard for cellular mobile communications systems in Europe. In 1988, the new-founded European Telecommunication Standard Institute (ETSI) took over standardization work and finished work on t he standard, which has been renamed to Global System for Mobile communication (GSM). The standardization of GSM900 and GSM1800 is finished in year 1990 and 1991 respectively. Commercial operation started late 1991. In the following 10 years, GSM became the quasi-world standard for mobile communication, serving some 2/3 of all mobile subscribers in 2001 (some 550 million).

1.2.3

GSM Evolutionary concept

The GSM Standard was originally intended to include all specifications on its ratification. However, in 1998 it became clear that not all planned services and half rate speech could be offered within the specified deadlines. This led to a crucial decision that GSM was not to be declared as a closed, immutable standard, and need to be further developed in phases. This evolutionary concept provides flexibility for modifications and technical innovations and allows GSM t o be adapted to market requirements and the latest technical developments. GSM Phase 1 The standardization ratified in 1990 for GSM900 and in 1991 for GSM1800 is referred to as GSM Phase 1. Phase 1 of the implementation of GSM systems includes all central requirements for the transmission of digital information. Speech data transmission is of core importance. Data transmission is likewise defined at rates of 0.3 to 9.6 kbit/s. GSM Phase 1 has only a few Supplementary Services (SS) such as call forwarding and barring. GSM Phase 2 Work on GSM Phase 2 was completed in 1995. In this phase, supplementary services, in particular, with features comparable to ISDN were added to the standard. Technical improvements were also specified such as half-rate speech. An important aspect of Phase 2 was the declaration of downward compatibility – i.e., all Phase 2 networks and terminal equipment must retain compatibility with the Phase 1 networks and terminal equipment. GSM Phase 2+ Phase 2+ indicates ongoing development. The GSM Standard will not be fully revised; instead, individual topics can be separately treated. The Standard has been updated annually since 1996 (Annual Releases '97 – '99). The current topics relate to new supplementary services, services for special user groups, improved voice codecs, IN applications and high data rate services.

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TM51101EN03GLA01 1

© Nokia Siemens Networks

Fig 3 Evolution of GSM

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1.2.4

Advantages of di gi tal transmission

Mobile communication followed the trend set in fixed networks in the mid-1980's under the term Integrated Services Digital Network (ISDN). Following are several advantages that are correlated with the introduction of 2G digital transmission: 1. Network Capacity: Compression of digitized speech information can considerably increase the capacity of mobile communication networks. Speech compression must be weighed against a reduction in speech quality however. Compression in speech from 64 kbit/s (digital fixed network transmission) to 2.4 – 13 kbit/s is used in the different 2G systems for transmission over the air interfaces. 2. Security Aspects: Unlike analogue signals, digital information can be very easily ciphered, preventing unauthorized eavesdropping of user data. 3. Supplementary Services: Digital data transmission greatly simplifies the transfer of signaling information thereby allowing the introduction of a wide range of supplementary services not confined to just pure speech and data transmission. 4. Cost Factor : Digital devices are less expensive to produce than analog devices thanks to better options for the use of large-scale integrated microelectronic components. Purchasing costs, as well as operating and maintenance costs, are lower and opened the way for the 2nd generation to the mass market. 5. Miniaturization: Microelectronics for digital information transmission allows a HW reduction that is relatively simple compared to analog HW elements. In this way, the size and weight of Mobile Stations MS could be reduced very much from 1G to 2G, allowing turning over from car phone to handhelds. The weight of handhelds decreased during the 1990's from more than 500g to less than 100g. 6. Transmission Quality: During transmission across the air interface the signals experience considerable fading, distortion and corruption. Digital signals can be treated easily with redundancy, can be better regenerated and offer therefore significantly better transmission quality than analogue signals. Analogue signals can only be amplified (including all disturbances).

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TM51101EN03GLA01 1

© N ok i a S i em en s N e tw o rk s

Fig 4 Advantages of Digital Transmission

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UMTS Overview

1.3

Third generation (3G)

The third generation, 3G, is expected to complete the globalization process of the mobile communication. Again there are national interests involved. Also some difficulties can be foreseen. Several 3G solutions were standardized, such as Universal Mobile Telecommunications System (UMTS), cdma2000, and Universal Wireless Communication-136 (UWC). The 3G system UMTS is mostly be based on GSM technical solutions due to two reasons. Firstly, the GSM as technology dominates the market, and secondly, investments made to GSM should be utilized as much as possible. Based on this, the specification bodies created a vision about how mobile telecommunication will develop within the next decade. Through this vision, some requirements for UMTS were short-listed as follows:

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The system to be developed must be fully specified (like GSM). The specifications generated should be valid world-wide.

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The system must bring clear added value when comparing to the GSM in all aspects. However, in the beginning phase(s) the system must be backward compatible at least with GSM and ISDN.

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Multimedia and all of its components must be supported throughout the system.

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The radio access of the 3G must be generic


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UMTS


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2.1

UMTS development

The European Telecommunication Standard Institute (ETSI) Global Multimedia Mobility (GMM) Report from 1996 pointed the way for the development not only of UMTS, but also of GSM. GSM was to be further evolved in the GSM Phase 2+ in such a manner that its capabilities progressed toward UMTS. The GSM network and protocol structures were developed so that they can be used as a platform not only for high level GSM services, but also for UMTS. UMTS will continue the GSM success story. The existing infrastructure of the GSM operators will be more intensively used, and also for UMTS. This reduces the financial risks involved in the introduction of UMTS. In other words, the 2G investments will continue to be utilized. The experience gained by GSM with regard to the core network and the Protocols and procedures (for example, the MAP protocol, call control, mobility management, handover, etc.) will also be used either directly or in a modified form. Using these Protocols and procedures will also reduce the r isks involved in the 3G implementation. The introduction of dual and multimode terminals is of great importance. It will use the entire area serviced by GSM from the very beginning by handover between UMTS and GSM, thereby paving the way for UMTS (reduction of 3G risks). This new evolutionary plan gives 2G operators a chance to reconfigure their networks for upward compatibility, and UMTS operators can avail of the downward compatibility to assure successful UMTS launching. In this way GSM will slowly evolve along a migration path toward the original objectives of UMTS to obtain the smoothest possible transition from the 2nd to the 3rd generation of mobile communications.

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UMTS Overview

2.2

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Mobile communication market

Unlike the fixed network sector, which over the last decades only developed slowly and which is only recently gaining momentum again, many market studies indicate unrestricted expansion of the mobile communications sector even well beyond the year 2010. This growth is only likely to be overtaken by the forecasts for the Internet market. It is generally expected that the number of mobile communications subscribers will exceed those in fixed networks in the next years. This is already the case in particular in regions with a poorly developed fixed network infrastructure. About 4 billion subscribers are reached for the mobile communications market by the year 2008 according to the UMTS Forum Report. This growth is being experienced to a large extent in the current developing and threshold nations in the Asian/Pacific region. Forecasts indicate a 50% share of the global mobile communications market for this region by 2015. Similar growth rates are expected for Eastern Europe and Central and South America. The "classical industrial countries" in North America and Europe (EU15) will only have a slight increase in subscriber numbers from 2005 because, with penetration rates of more than 80%, saturation will be approached. North America and EU15 will only have shares of the world's subscribers of about 7% and 11% respectively by 2015 according to forecasts. One result of the immense growth rates will be a steep ri se in the demand for additional radio resources the necessity for very efficient usage of the radio resources. Trend: Speech to Data Transmission There is constant increase in global demand for data transfer, record growth in Internet links and access together. With the requirement to make these services in the fixed network sector as well in the mobile sector, all forecasts are predicting a steep rise in the volume of data transfers using mobile communication systems. Although the demand for mobile computing, Internet and intranet access already exists, expansion in these sectors was greatly hindered by cumbersome equipment, very low data transfer rates and overly expensive costs for the mobile transfer of data. All of these barriers are set to be overcome in GSM Phase 2+ and by the 3G systems. Against this background, the expert studies (for example, UMTS Forum) are predicting a considerably greater increase in the volume of data for transfer than for speech transmissions. While annual growth in speech transmission in industrialized nations in the coming years is predicated to be between 20% – 60%, a significant growth rate of more than 100% is expected for the volume of data to be transferred. Between the years 2005 and 2007, the data transfers are predicted to make up about 50% of the total traffic – with an upward trend in the years thereafter. This means that all forecasts envisage data transfers taking the lion's share in the medium term.


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UMTS Overview

Current Market Demands Regarding Mobile Communications The demands currently made by the mobile communications market are varied and include the following: 1. Improved speech quality 2. User friendliness 3. Global accessibility 4. Special services for particular user groups (for example, Closed User Groups) 5. Flexible Service Creation 6. Everywhere the same services as in HPLMN 7. Fast transfer of large data volumes 8. Mobile Internet / Intranet Access 9. Multi Media capabilities 3G – Services & Required Data Rates Different services have different requirements regarding the appropriate data rate. Only a few kbit/s are required for conventional voice transmission with the use of efficient speech data compression functions. Data rates to the order of several 10 kbit/s are helpful and meaningful for convenient e-mail transfers. Greater bandwidth ranging from several kbit/s to more than 100 kbit/s is required for efficient general data transmissions, Internet access, mobile banking, shopping, etc. Even greater data rates from several 10 kbit/s to several 100 kbit/s are necessary for high-quality image transmission and video telephony. The highest requirements for data rates from 100 kbit/s to more than 1 Mbit/s are demanded by video conferences and video-on-demand applications, in addition to different multimedia applications. UMTS will be able to dynamically and flexibly provide these data rates ranging from 8 kbit/s to a maximum of 20 Mbit/s.

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TM51101EN03GLA01 1

© N ok i a S i em en s N et w or ks

Fig 5 Services provided by UMTS

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Standardization


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UMTS Overview

Specification bodies related are also global ones as discussed following section. In addition to the specification bodies, the specification process includes co-operation of operators and manufacturers. The following international standardization bodies are acting as “generators” for 3G specification work: International Telecommunication Union (ITU-T) This organization provides in practice all the telecommunication branch specifications that are official in nature. Hence, these form all the guidelines required by the manufacturers and country-specific authorities. ITU-T has finished its development process for, International Mobile Telephone – 2000 (I MT2000). IMT-2000 represents a framework on how the network evolution from a second to a third generation mobile communication system shall take place. Even more important, different radio interface scenarios were outlined for 3G systems. European Telecommunication Standard Institute (ETSI) This organizational body has had a very strong role when GSM Specifications were developed and enhanced. ETSI is divided into workgroups named SMG (number), and every workgroup has a specific area to develop. Because of the GSM background, ETSI is in a relatively dominant role in this specification work. Alliance of Radio Industries and Business (ARIB) ARIB conducts studies and R&D, establishes standards, provides consultation services for radio spectrum coordination, cooperates with other overseas organizations and provides frequency change support services for the smooth introduction of digital terrestrial television broadcasting. These activities are conducted in cooperation with and/or with participation by telecommunication operators, broadcasters, and radio equipment manufacturers. American National Standard Institute (ANSI) ANSI is the American specification body that has issued a license for a subgroup to define telecommunication-related issues in that part of the world. Because of some political points of view, ANSI’s role is relatively small as far as UMTS concerned. The ANSI subgroup is mainly concentrating on a competing 3G air interface technology selection called cdma2000. In order to maintain globalization and complete control of the UMTS specifications, a separate specification body called 3GPP (3rd Generation Partnership Project) was established to take care of the specification work in co-operation with the previously listed institutes. The outcome of the 3GPP work is a complete set of specifications defining the 3G network functionality, procedures, and service aspects.

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UMTS Overview

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UARFC UARFC UARFC UARFC UARFC UARFC UARFC UARFC UARFC UARFC UARFC UARFC Frequency Uplink Downlink

TM51101EN03GLA01 1

© Nokia Siemens Networks

Fig 6 3GPP

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4



UMTS Evolution


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UMTS Overview

The following topic discuss about the evolutionary path of GSM to UMTS technology and list significant events in the evolution of CDMA networks. GSM & UMTS Evolution The original plans for GSM in the 1980's included all aspects of a 2G standard. In 1988 it became clear that this was not possible in the specified time frame. For this reason, GSM was released in a preliminary version in 1990/91 as GSM Phase 1. GSM Phase 1 Phase 1 contains everything required for the operation of GSM networks. Speech data transfer is the core focus. Data transfer is defined, too (0.3 - 9.6 kbit/s). Only a few supplementary services are included. GSM Phase 2 After Phase 1completion, the GSM Standard was fully revised. Phase 2 includes a wide range of supplementary services comparable with the ISDN standard. GSM Phase 2+ Phase 2+ enhances in Annual Releases (`96, `97, `98, `99) the GSM standard and prepares the UMTS introduction. Especially the GSM Core Network (CN) is enhanced to be used as UMTS CN at UMTS start. Major Phase 2+ aspects are IN services, flexible service definition, packet data transfer, high data rate transmission and improved voice codes. GSM is limited by the narrowband radio access, the radio resource efficiency and a lack of additionally available frequency bands. UMTS Release `99 (also: Release 3) With GSM Rel. `99, a handshake with the first UMTS Release (Rel`99 or Rel. 3) according to many CN and service aspects is performed. UMTS introduces a new, broadband radio access optimized for packet data transmission up to 2 Mbit/s. UMTS Release 4 Unlike GSM Phase 2+, the enhancement of UMTS is not performed in annual steps. Enhancements should be possible in flexible time schedules. Rel. 4 (March 2001) introduces for example, important CN modifications (bearer independent signaling flow) and the Low Chip Rate LCR TDD mode as a third radio access option. UMTS Release 5 For UMTS Rel. 5 major CN modifications, i.e. the IP Multimedia Subsystem (IMS) are planned. New network elements and protocol structures are defined. For the future modifications of the UMTS Terrestrial Radio Access Network (UTRAN) toward an All IP RAN, enhancements of the radio resource efficiency, new frequency ranges (WRC'2000) and many more enhancements toward 4G are expected.

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UMTS Overview

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UMTS Release 6 Rel-6 was published in 2005. It is also a major release featuring, among others, the following: . IMS supporting services The specification of services for mobile networks is the responsibility of the Open Mobile Alliance(OMA). 3GPP therefore standardized only a small number of supporting services, e. g. Push Service, Instant Message Service and Presence Service. . I-WL A N

AtrustedWLANAccess Network is defined as alternative access to the 3GPP Core Network. The WLAN and 3GPP Core Network communicate with each other using standard IETF Protocols. The I-WLAN, however, is neither architecturally nor functionally equivalent to a UTRAN or GERAN. For example, the I-WLAN does not support mobility. . GA N The goal of GAN is to attach a generic IP-based Access Network to the 3GPP Core Network via the A/Gb interface. This is achieved by using an additional network element, masking the GAN to the Core Network. A number of 3GPP-specific protocols is employed to this end. Functionally and architecturally, a GAN is equivalent to a GERAN. . Update of the ch arging arch itecture

A harmonized charging architecture was introduced for bearer-, subsystem- and service level. Pre-Rel-6, for each level and each domain an independent charging architecture had been developed. . Flow -based Chargin g

Until the advent of Flow-basedCharging, charging is only possible with the resolution of a bearer: when two or more service-level flows utilize the same bearer, they cannot be differentiated. Flowbased Charging supports service-specific charging on the bearer-level of any resolution and, furthermore, allows for the coordination of charging on the bearer- subsystem- and service-levels. . High Speed Uplink Packet Access

High Speed Uplink Packet Access (HSUPA) extends the downlink HSPA from Rel-5 by adding a dedicated uplink channel with bandwidth up to 5.76 Mb/s—since uplink a sufficient number of codes has been available, there is no need to introduce shared channels. HSUPA in Rel-6 is, however, specified only for FDD.


29

UMTS Overview

. Multim edia Broadc ast Multicast Service

As we already know, UMTS designers are somewhat concerned about saving resources on the radio interface. In scenarios such as multicast of sport events, multiparty conferencing or broadcast of emergency information it may happen that several UEs in a cell receive the same data stream. The Multimedia Broadcast Multicast Service (MBMS) [GPP 23.246] enables a resource efficient data transfer to many UEs in parallel: by means of an additional network element in the Core Network and new protocols, the data is sent only once to each cell and all UEs access the same channel for receiving it. Most of Rel-6 is currently in the trial phase. The exception is HSUPA of which a number of networks have already been deployed. UMTS Release 7 Rel-7 was published at the end of 2007.Among others, the following features are part of Rel-7: . PCC

Whereas in previous releases, the authorization of QoS in the PS Domain by the IMS (via SBLC) and Flow-based Charging relies on an independent mechanism, Policy and Charging Control (PCC) provides a single policy infrastructure in order to handle both kinds of policies. Furthermore, PCC is applicable to any IP-CAN, and to any service network. Together with the introduction of PCC, the COPS protocol between GGSN and PCF/PCRF was abandoned and replaced by Diameter. . HS PA þ

This is an enhancement of the HSPA technology, in particular towards higher bandwidth— 28 Mb/s downlink and 11 Mb/s uplink. This is achieved by employing 16-QAMand MIMO. . HSUPA fo r TDD

The specification of HSUPA has been extended to also work with TDD. . IMS supp ort of UEs behin d NATs

The original 3GPP idea is that of the UE as a single piece of equipment connected directly to the RAN. Of course, it is also possible for the subscriber to set-up a home network of devices, e.g. laptop and mobile phone, and to facilitate UMTS Network access for all devices via the mobile phone. In this case the UE consists of several pieces of equipment and one UICC. What is more, the subscriber may install a Network Address Translator (NAT) and a firewall between the UE and the UMTSNetwork. TheNAT separates the address spaces of the subscriber's home network and UMTS Network: In the home network a private address space is used, while towards the outside, the IP address assigned by the GGSN is employed. In other words, the NAT translates the IP address and may be even the port number of any packet traversing it. NATs are known to create considerable problems in cases where the IP address, respectively the port number, appears in “unexpected” places,

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UMTS Overview

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i.e. somewhere else than in the IP header, respectively the transport header: the NAT cannot translate them. For example, the payload of a SIP signaling message can contain the IP address of the originator of a session. AUE behind a NAT is not aware of its outside IP address and would of course include its local IP address. As a result, the recipient of the SIP message is unable to contact the UE. 3GPP specifies two solutions for this problem. One solution is employing an Application Level Gateway (ALG), as defined in [RFC 2663], co-located with the P-CSCF. The ALG performs deep packet inspection and has application-specific knowledge that allows it t o translate appropriately, e.g. IP addresses in session descriptions, possibly in interaction with the NAT.

TM51101EN03GLA01 1

© N o ki a S i em en s N e tw or ks

Fig 7 UMTS evolution


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Comparison with mobile technologies


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It is now time to look at the development of mobile telecommunications from a technical perspective. The table below shows the evolution from the 1st generation (1G) up to what is expected to come after 3G, the 4th Generation (4G). The first mobile user devices became available in the middle of the last century. They were the size of a car boot and were mobile because they indeed travelled in a car boot. Mobile user devices have since decreased in size dramatically. Bandwidth An important characteristic of mobile networks is the bandwidth available to a single user on the radio interface. The radio interface is naturally the bottleneck of the network. Note that ever more bandwidth per user is only of interest when services other than voice are being utilized. We observe a steady increase of bandwidth over time. In the end of 2006, 5 Gb/s were demonstrated in a field trial. Cell radius Another interesting aspect of evolution is the size of a single cell, i.e. the region covered by a single antenna. In early 1G Networks, it was not possible to perform a handover, i.e. to move out of the coverage of one antenna into the coverage of another, while maintaining an ongoing phone call. Furthermore, it was not possible to initiate a call to mobile users without knowing in which cell they were currently located. Interestingly, in today's WLANs support for handover and paging is only slightly better. In early 1G Networks the missing handover support was alleviated by making cell sizes as large as possible, for example in Germany with a radius up to 150 kilometers. This, however, decreased the overall capacity of the network because the overall capacity of a cell is (to some degree) independent of its size; in a given area, many small cells can serve more users than one big cell. In 2G, paging and handover no longer posed a technical challenge and consequently cell radii shrank down to a kilometer range. Cell radii in UMTS can be even smaller, down to meters if need be.

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TM51101EN03GLA01 1

© N okia Siemens Networks

Fig 8 Comparison of Mobile Telecommunication Generations

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UMTS Overview

Analogue/Digital The early 1G Networks were of course completely analogue. The fixed part of the network later became digital. However the radio interface remained analogue. The transition to 2G is defined by the radio interface also becoming digital. Standards and Technology The table also shows the growing impact of standardization. 1G Networks were barely standardized. At the time, telecommunication operators were usually national monopolists, buying their equipment from a single manufacturer. This implied that all subscribers of this operator were delivered mobile phones made by the same manufacturer. What is more, for each subscription, mobile communication was restricted to a single country: Usually, neither equipment nor networks could interoperate between countries. Markets, however, became more open. It became desirable for operators to allow their users to attach to and use the networks of other operators, a feature known as roaming. For manufacturers it became desirable to be able to sell their equipment to all operators, even at the cost of increased competition from other manufacturers. Therefore, starting with 2G, mobile Telecommunication Networks became standardized on a large scale. With 3G, the standard even became open, i.e. accessible to everybody. Standardization, however, does not imply that it is possible to agree on a single world-wide standard. Rather, a number of incompatible regional standards exist, hampering global roaming. In 2G, Europe developed GSM, the US developed cdma One and D-AMPS and Japan developed PDC. For 3G, an attempt was made to develop a single worldwide standard on the basis of the International Mobile Telecommunications at 2000MHz (IMT-2000) family concept. This endeavor, however, did not succeed and in 3G we have, among others, UMTS, cdma2000 and—as the most recent addition—Mobile WiMAX. For 4G, a new approach to the problem promises worldwide roaming: the integration of heterogeneous standards such that inter-technology roaming is possible. Circuit Switched/Packet Switched Mobile Telecommunication Networks are direct descendants of circuit-switched fixedline telephony. Therefore, GSM is circuit-switched. This means that each call is reserved the one-size-fits-all identical bandwidth. This is perfect for voice with its constant bandwidth needs. However, with the broadening of supported services the picture changes: Data traffic tends to be bursty, and, moreover, it does not have realtime requirements: It is not crucial for an email to arrive within, say, 100 ms. Booking a constant bandwidth for data is therefore quite wasteful. Rather, data traffic is the perfect background traffic for filling up currently unutilized bandwidth when need be. Hence, for example, in “2.5G”, General Packet Radio Service (GPRS), packetswitching based on the IP protocol, and consequently bandwidth-sharing were introduced. This was the first, irreversible, step towards convergence of the telecommunications world and the Internet.

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TM51101EN03GLA01 1

© N okia Siemens Networks

Fig 9 Bandwidth comparison

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6

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Exercises

Exercise 1 From which generation are we able to make handover? 1G 2G 3G Exercise 2 Which techniques were newly used with 3G? WCDMA HSDPA GPRS Exercise 3 UMTS is based on which technology? GSM D-AMPS JDC Exercise 4 Which bit rate can be reached practically by UMTS? 100 kb/s 2 Mb/s 40 Mb/s 2 Gb/s Exercise 5 A cluster is: An area of cells, where the whole set of frequencies is set once Coverage area of Node B Coverage area of RNC Cellular network of one operator


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7

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Solution

Exercise 1 From which generation are we able to make handover? 1G 2G 3G Exercise 2 Which techniques were newly used with 3G? WCDMA HSDPA GPRS Exercise 3 UMTS is based on which technology? GSM D-AMPS JDC Exercise 4 Which bit rate can be reached practically by UMTS? 100 kb/s 2 Mb/s 40 Mb/s 2 Gb/s Exercise 5 A cluster is: An area of cells, where the whole set of frequencies is set once Coverage area of Node B Coverage area of RNC Cellular network of one operator


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