Connected Mode Parameters
CONNECTED MODE PARAMETERS
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Connected Mode Parameters
CONNECTED MODE PARAMETERS Defining RRC Connected Mode LTE IRAT Interactions RRC Reconfiguration Message Measurement Configuration Measurement Objects Reporting Configurations Measurement Identities Other Parameters Measurement Objects E-UTRA Measurement Objects IRAT (UMTS) Measurement Objects IRAT (GSM) Measurement Gap Settings LTE Measurement Reporting Configuration LTE Measurement Report Trigger Events IRAT Measurement Reporting Configuration IRAT Mobility Triggers LTE Speed Scale Factors Measurement Reports Measurement Report for UMTS Cells Measurement Report for GSM/GERAN
4 6 8 10 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
Measurement Report for CDMA2000 Cells Inter-eNB Handover Procedure IRAT Handover Procedure UMTS Measurement Settings UMTS Event Triggers UMTS Measurement Report UMTS IRAT Handover Procedure Discontinuous Reception (DRX) Procedures Uplink Power Control Timing Advance CQI Reporting
42 44 46 48 50 52 54 56 58 60 62
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Connected Mode Parameters
Defining RRC Connected Mode The LTE RRC connected state is defined in TS 36.331 as shown in the diagram. It is similar to connected mode in other 3GPP technologies, but in LTE there is no dedicated channel. All signalling and traffic transfer between the UE and the eNB is handled through scheduling of the uplink and downlink shared channel resource. To avoid the need for continuous monitoring of the PDCCH for prolonged periods of time while in connected mode, the use of DRX, a feature normally associated with idle mode, is introduced. Note the UE is also required to maintain awareness of system information. Another key differentiator from idle mode is that mobility is under control of the network. Network behaviour in this respect is driven by parameters and mode settings broadcast in system information that are either part of manual or SON-based optimisation activities.
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E-UTRA RRC CONNECTED
3GPP TS 36.331 defines connected mode with the following:
• Transfer of unicast data to/from UE • At lower layers, the UE may be configured with a UE specific DRX • Network controlled mobility, i.e. handover and cell change order with optional network assistance (NACC) to GERAN • The UE: – monitors a Paging channel to detect incoming calls, system information change; for ETWS capable UEs,
–
– – – –
ETWS-notification; and for CMAS-capable UEs, CMAS notification monitors a Paging channel and/or System Information Block Type 1 contents to detect system information change, for ETWS capable UEs, ETWS notification, and for CMAS capable UEs, CMAS notification monitors control channels associated with the shared data channel to determine if data is scheduled for it provides channel quality and feedback information performs neighbouring cell measurements and measurement reporting acquires system information
Fig. 1 – E-UTRA RRC Connected Mode © Informa Telecoms & Media
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Connected Mode Parameters
LTE IRAT Interactions LTE standards define handovers and cell reselection between the E-UTRAN and both UMTS and GSM/GPRS networks. Transition from LTE in idle mode is primarily through cell reselection, with the exception of GPRS, which may employ CCO (Cell Change Orders). In RRC_Connected mode, the E-UTRAN decides which cell a UE should hand over to in order to maintain the radio link. The diagram shows the state transition model for UMTS and GSM/GPRS. A UE will be either Connected or Idle with respect to the E-UTRAN. The substates CELL_PCH, URA_PCH and Cell FACH do not exist in LTE. Handovers will occur between cell DCH and LTE connected. However, a UE in the UMTS states CELL_PCH and URA_PCH would return to LTE through cell reselection. Similarly, real-time traffic will probably handover to/from GSM, whilst non-real-time traffic using GPRS will probably utilise CCO with NACC (Network Assisted Cell Change).
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UMTS
LTE
GSM/GPRS
GSM Connected CELL_DCH
Handover E-UTRA RRC Handover Connected GPRS Packet transfer mode
CELL_FACH
CCO with optional NACC
CELL_PCH URA_PCH
Connection establishment/ release
Idle
Connection establishment/ release Reselection
Connection establishment/ release
CCO, reselection
Reselection
E-UTRA RRC Idle
Reselection CCO, reselection
GSM_Idle/ GPRS Packet_Idle
Fig. 2 – LTE IRAT Interactions © Informa Telecoms & Media
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Connected Mode Parameters
RRC Reconfiguration Message The RRCConnectionReconfiguration message is a multi-purpose message, using many sub headers to control a UE’s behaviour whilst in connected mode. Only relevant information elements will be included for mobility control, which will be investigated in detail throughout this section. The main information element that controls a connected mode UE is measConfig, which is used to set up, modify or remove measurement commands. In a similar manner to UMTS, a UE will be instructed to start measuring, and then when certain triggers or events occur, send measurement reports. Alternatively, measurement reports may be periodical.
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RRC Connection Reconfiguration Message • Measurement Configuration
•
Mobility Control Information
•
Dedicated Information NAS List
•
Security Configuration
•
Non-Critical Extensions
eNB RRC Connection Reconfiguration DCCH/DL-SCH Periodical or event-
RRC Connection Reconfiguration Complete
based measurement process started
Trigger Event
DCCH/UL-SCH
Measurement Report DCCH/UL-SCH
Fig. 3 – RRC Reconfiguration © Informa Telecoms & Media
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Connected Mode Parameters
Measurement Configuration The measConfig IE (information element) consists of the following IE sets: • • • •
Measurement Objects Reporting Configurations Measurement Identities Additional parameters
Measurement Objects Measurement objects define either LTE, UMTS, GSM or CDMA2000 neighbours to measure. Each command is assigned a unique-per-UE measurement identity, and may include up to 32 neighbours per RAT/frequency layer.
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RRC Connection Reconfiguration Message Measurement Configuration
measConfig Measurement Objects
•
Mobility Control Information
•
Dedicated Information NAS List
measObjectToRemoveList measObjectId
List As Required
measObjectToAddModList
• •
Security Configuration Non-Critical Extensions
measObjectId
List As Required
measObject
LTE, UMTS, GSM or CDMA2000
1…n (Max =32)
Fig. 4 – Measurement Objects © Informa Telecoms & Media
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Connected Mode Parameters
Reporting Configurations Triggers or events for reporting are contained within the Reporting Configuration IE. Reports may be set to event based or periodical. Appropriate timers and hysteresis values will also be conveyed to a UE. A report configuration ID is used for each defined configuration message.
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RRC Connection Reconfiguration Message Measurement Configuration
measConfig Reporting Configurations
•
Mobility Control Information
•
Dedicated Information NAS List
• •
Security Configuration Non-Critical Extensions
reportConfigTo RemoveList
List As Required
reportConfigToAddModList reportConfigId reportConfig Rat
List As Required
1…n (Max =32)
Event or Periodical and Details
Fig. 5 – Reporting Configurations © Informa Telecoms & Media
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Connected Mode Parameters
Measurement Identities Measurement Identities are used to bind together combinations of reporting configurations and measurement objects.
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RRC Connection Reconfiguration Message Measurement Configuration
measConfig Measurement Identities
•
Mobility Control Information
•
Dedicated Information NAS List
• •
Security Configuration Non-Critical Extensions
measIdTo RemoveList
List As Required
measIdToAddModList measId
List As Required
1…n (Max =32)
measObjectId measConfigid
Fig. 6 – Measurement Identities © Informa Telecoms & Media
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Connected Mode Parameters
Other Parameters Other parameters which may be used are contained here including speed scaling, measurement gaps, measurement filter coefficients and serving cell quality thresholds. These will be covered later in this section.
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RRC Connection Reconfiguration Message Measurement Configuration
measConfig Other Parameters
•
Mobility Control Information
•
Dedicated Information NAS List
• •
Security Configuration Non-Critical Extensions
Quality confi guration Meas. filter by type 0–9 and RAT 11, 13, 15, 17, 19 Measurement Gap
Gp1
0…39
Configuration S-Measurements
Gp2 Serving Cell Quality threshold
0…39 0–97 (–140 to – 44dBm)
–
–
preRegistrationInfo HRPD Speed Parameters t-Evaluation
30, 60, 120, 240 seconds
T-HystNorm
30, 60, 120, 240 seconds
N-cellChange Medium
1…16
N-cellChangeHigh 1…16 speedStateScale Factors Sf-Medium
0.25, 0.5, 0.75, 1.0
Sf-High
0.25, 0.5, 0.75, 1.0
Fig. 7 – Other Parameters © Informa Telecoms & Media
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Connected Mode Parameters
Measurement Objects E-UTRA The diagram shows an example of the parameters which may be used to control measurements on LTE cells. It is possible to instruct a UE to measure a frequency layer only (from 1.4 MHz to 20 MHz). The inclusion of the optional cellsToAddMod list allows more precise targeting of specific cells. Note that if the cellsToAddMod list is not included, cells may still be barred from the measurement command using black lists.
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RRC Connection Reconfiguration Message measConfig Measurement Objects measObjectToRemoveList measObjectId
List As Required
measObjectToAddModList
Measurement Configuration •
Mobility Control Information
•
Dedicated Information NAS List
•
Security Configuration
•
Non-Critical Extensions
measObjectId
List As Required
measObject
LTE, UMTS, GSM or CDMA2000
1…n (Max =32)
Measurement Objects EUTRA example CarrierFrequency
EARFCN
allowedmeasBandwidth
6, 15, 25, 50, 75, 100 rbs
presenceAntennaport1
True/false (MIMO)
Ncell configuration
MBSFN or TDD info
OffsetFrequency
–24…24dB
Cells to remove list
Indicies as requested
Cells to add or modify list Cellindex
1…n(Maximum32)
PhysicalcellID
0…503(PCI)
Individual cell offset Black cells to add list
–24…24 dBm 1…32
Black cells to remove list Cellindex
1…n(32max)
Physical cell range Start
0…503 (PCI)
Range
1,4,8,16,24,32,48,64, 84…504
CelltoreportCGI
0…503(PCI)
Fig. 8 – Measurement Objects EUTRA © Informa Telecoms & Media
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Connected Mode Parameters
Measurement Objects IRAT (UMTS) The measObject information element may include UMTS cells, as shown in the diagram. Up to 32 UMTS cells may be defined in each UMTS frequency layer. A UARFCN and cell code, corresponding to the primary scrambling code, is defined for UMTS neighbours.
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RRC Connection Reconfiguration Message measConfig Measurement Objects measObjectToRemoveList measObjectId
List As Required
measObjectToAddModList
Measurement Configuration •
Mobility Control Information
•
Dedicated Information NAS List
•
Security Configuration
•
Non-Critical Extensions
measObjectId
List As Required
measObject
LTE, UMTS, GSM or CDMA2000
1…n (Max =32)
Measurement Objects UTRA example CarrierFrequency
EARFCN
Offsetfrequency
–15…15dB
Cells to remove list
Indicies as required
Cells to add or modify list
FDD or TDD
Cellindex
1…n(Maximum32)
PhysicalcellID
FDD0…511 TDD 0…127
CelltoreportCGI
Asabove
Fig. 9 – UMTS Neighbour Definition © Informa Telecoms & Media
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Connected Mode Parameters
Measurement Objects IRAT (GSM) The measObject information element may include GSM neighbour cells, as shown in the diagram. Up to 32 GSM cells may be defined by listing ARFCNs. Note that no BSIC is included for GSM neighbours. However, the use of NCC permitted may be used restrict unwanted PLMN measurements.
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RRC Connection Reconfiguration Message measConfig Measurement Objects measObjectToRemoveList measObjectId
List As Required
measObjectToAddModList
Measurement Configuration •
Mobility Control Information
•
Dedicated Information NAS List
•
Security Configuration
•
Non-Critical Extensions
measObjectId
List As Required
measObject
LTE, UMTS, GSM or CDMA2000
1…n (Max =32)
Measurement Objects GERAN example StartingARFCN
ARFCN
Bandindicator
900/1800
Following ARFCNc ListofARFCNs ARFCN spacing
1…n(Maximum32) 1…8
Number of following ARFCNs 0…31 ARFCN bitmap Offset Frequency
Up tp 16 octetcs –15…15 dB (meas eval req)
NCCpermitted
8bit
CelltoreportCGI
BSIC
Fig. 10 – GSM/GERAN Neighbour Definition © Informa Telecoms & Media
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Connected Mode Parameters
Measurement Gap Settings Measurement gap parameters are used to define time periods when no uplink or downlink transmission will be scheduled for a specific UE, thus enabling a UE to take neighbour measurements. This is similar in concept to compressed mode in UMTS or Idle frames in GSM. LTE monitoring gap patterns occur in multiples of 10 ms, and have a duration of 6 ms. A single monitoring pattern is defined for both LTE neighbours and Inter-RAT. Note that the 6 ms gap period should be sufficient to allow a UE to synchronise onto LTE neighbours for cell identification. (PSS and SSS every 5 ms). However, careful selection of gap repetition must be employed to allow a UE to decode a GSM synch burst to obtain BSIC and the SFN.
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Neighbour
Neighbour
Neighbour
MGL
Measurement Gap Length
MGRP
(Measurement Gap Repetition Period) measGapConfig Defines start position
eNB (Serving Cell)
Gap Pattern ID
MGL (MS)
MGRP (MS)
0
6
40
1
6
80
Fig. 11 – Measurement Gap Settings © Informa Telecoms & Media
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Connected Mode Parameters
LTE Measurement Reporting Configuration The diagram shows the parameters and trigger events a UE may be instructed to perform on neighbouring LTE cells. Depending on measurement type, a UE may measure and report serving cell, listed cells or any cells detected on a listed frequency. A UE can trigger a report based on either RSRP or RSRQ. However, both may be included in any report. The E-UTRAN can influence the UE report entry condition by setting configurable parameters such as offsets and hysteresis. For any event to be triggered the entry condition must be met for at least the ‘Time-to-Trigger’ value.
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Event ID
measConfig
Event A1
Measurement Identities
A1 Threshold
Choice
Threshol d – RSRP
0…97 (maps to –140…–44 dBm)
Threshol d RSRQ
0…34 (maps to –19.5…–3 dB)
A2 Thre shold
Choice
Threshol d – RSRP
0…97 (maps to –140…–44 dBm)
Threshol d RSRQ
0…34 (maps to –19.5…–3 dB)
reportConfig Rat
List As Required
1…n (Max =32)
Event or Periodical and Details
measConfig
Event A3
Report onleave
List As Required
reportConfigToAddModList reportConfigId
Event A2
A3 Off set
reportConfigTo RemoveList
–30…3 0 True/false
Triggertype Event EventID
Event A4 A4 Thresh old
Choice
Threshol d – RSRP
0…97 (maps to –140…–44d Bm)
Threshol d RSRQ
0…34 (maps to –19.5…–3 dB)
A5 Thresh old 1
Choice
Threshol d – RSRP
0…97 (maps to –140…–44d Bm)
Threshol d RSRQ
0…34 (maps to –19.5…–3 dB)
A5 Thresh old 2
Choice
Threshol d – RSRP
0…97 (maps to –140…–44 dBm)
Threshol d RSRQ
0…34 (maps to –19.5…–3 dB)
Eventtriggerlist A1,A2,A3,A4,A5
Hysteresis
0…30in0.5bdsteps
Time to trigger
0, 40, 64, 80, 100…2560, 5120 ms
Periodical Purpose
Event A2
Choice
Trigger quantity Reportquantity Maxcellstoreport
Reportstrongestcells/ Report CGI RSRP/RSRQ RSRP/RSRQ 1to8
Report interval
120, 240, 480…102402ms 1, 2, 4, 60 minutes
Report amount
1, 2, 4, 8, 16, 32, 64, infinte
Fig. 12 – Measurement Reporting Configuration © Informa Telecoms & Media
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Connected Mode Parameters
LTE Measurement Report Trigger Events The diagram shows the event triggers defined for LTE. • • • • •
Event Event Event Event Event
A1 A2 A3 A4 A5
Serving cell becomes better than an absolute threshold. Serving cell becomes worse than an absolute threshold. Neighbour becomes better than an offset relative to serving cell. Neighbour cell becomes better than an absolute threshold. Serving cell becomes worse than an absolute threshold and neighbour cell becomes better than a second absolute threshold.
Remember that each event will have associated hysteresis and time-to-trigger values.
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Event A1
Event A2
Serving Cell Absolute Threshold
Absolute Threshold Serving Cell
Event A3
Neighbour cell
Offset Serving Cell
Even At4
Neighbour cell
Absolute Threshold
Even At5
Neighbour cell
Absolute 1 Threshold Absolute Threshold 2 Serving Cell
Fig. 13 – LTE Event Triggers © Informa Telecoms & Media
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Connected Mode Parameters
IRAT Measurement Reporting Configuration The parameters relevant for IRAT reports are shown in the diagram. Note that monitoring of IRAT neighbours will be performed during available monitoring gaps. The three UMTS physical channels required for identification and measurement are P-SCH, S-SCH and CPICH. GSM requires RSSI and BSIC decode. Events may be periodical or event based, and as with LTE reports, appropriate hysteresis values and time-to-trigger will be set by the E-UTRAN.
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Event ID
measConfig
Event B1
Measurement Identities
B1 Threshold UTRA
Choice
UTRA RSCP
–5 to 91(maps to –120…-25 dBm)
UTRAEc/No
0…49(maps to–24…0dB)
B1 Threshold GERAN
0…63 (maps to –110…–44 dBm)
Threshol d RSRQ
reportConfigTo RemoveList
List As Required
reportConfigToAddModList reportConfigId reportConfig Rat
0…63
List As Required
1…n (Max =32)
Event or Periodical and Details
Event B2 B2Threshold1
Choice
Threshol d – RSRP
0…97 (maps to –140…–44 dBm)
Threshol d RSRQ
0…34 (maps to –19.5…–3 dB)
B2Threshold2 B2 Threshold UTRAN
Choice Choice
UTRA RSCP
–5 to 91(maps to –120…-25 dBm)
UTRAEc/No
0…49(maps to–24…0dB)
B1 Threshold GERAN
0…63 (maps to –110…–44 dBm)
B1 Threshold CDMA2000
0…63
measConfig Triggertype Event Event ID
Choice Eventtriggerlist B1, B2
Hysteresis
0…30in0.5bdsteps
Time to trigger
0, 40, 64, 80, 100…2560, 5120 ms
Periodical Purpose
Maxcellstoreport
Reportstrongestcells/ Report strongest cells FOR SON/ Report CGI 1to8
Report interval
120, 240, 480…102402ms 1, 2, 4, 60 minutes
Report amount
1, 2, 4, 8, 16, 32, 64, infinte
Fig. 14 – IRAT Reporting Configuration © Informa Telecoms & Media
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Connected Mode Parameters
IRAT Mobility Triggers The diagram shows the two trigger events associated with IRAT mobility. • •
Event B1 Neighbour cell becomes better than an absolute threshold Event B2 Neighbour cell becomes better than an absolute threshold and serving cell becomes worse than an absolute threshold.
As for the other event reports, hysteresis and time-to-trigger values may be employed.
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Event B1
Inter-RAT Neighbour cell Absolute Threshold
Event B2
Inter-RAT Neighbour cell
Absolute Threshold 2 Absolute Threshold 1 LTE Serving Cell
Fig. 15 – Inter RAT Mobility Triggers © Informa Telecoms & Media
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Connected Mode Parameters
LTE Speed Scale Factors In idle mode, it was seen that it is possible to apply hysteresis and scaling factors to a UE based on a number of cell reselections in a given time. The assessment of speed state whilst in connected mode is performed in a similar fashion. However, a UE will now count consecutive handovers. Based on a number of consecutive handovers a UE will apply a speed scaling factor to the time-to-trigger value, thus enabling better mobility management, especially in a hierarchical cell structure.
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Connected Mode Parameter Value Range
Idle Mode Parameter
t-Evaluation
30,60,120,240secs
TCRmax
t-HystNormal
30,60,120,240secs
TCRmaxHyst
n-CellChangeMedium
1…16
NCR_M
n-CellChangeHigh
1…16
NCR_H
Normal Mobility
No Action
Medium Mobility
Time-to-trigger x sf-Medium
High Mobility
Time-to-trigger x sf-Medium
Fig. 16 – Speed Scale Factors © Informa Telecoms & Media
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Connected Mode Parameters
Measurement Reports A periodical or event-based trigger will cause the UE to generate a measurement report. The specific contents of the report will vary dependent on the measurement command provided by the E-UTRAN. Only information elements specifically asked for in the measurement command will be reported by the UE. For example, Cell Global Identity may or may not be included. Usually the physical cell identity will suffice. The diagram shows an example report for LTE (E-UTRA).
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Measurement Report Triggertype measID
Choice 1…n(max=32)
measResultServingCell rsrp Result
0…97 (maps to –110…–44 dBm)
rsrp Result
0…34(maps to –19.5…–3dB)
measResultN-Cell
Choice
Result List E-UTRA
List as required
E-UTRA results
ResultUTRA
Listasrequired
PhysicalcellID
ResultGERAN
Listasrequired
cgi info
Result CDMA2000
CellGlobalID LAC plmnIDList
0…503
MCC+MNC+CID bit 16 Max=5
Measurement Results rsrpResult
0…97
rsrpResult
0…34 CSG information
Fig. 17 – Measurement Report E-UTRA © Informa Telecoms & Media
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Connected Mode Parameters
Measurement Report for UMTS Cells The diagram shows an example report for UMTS (UTRA) cells. Note that on receipt of the MobilityFromEUTRACommand message the UE will start timer T304 and attempt to connect to the new node. Expiry of this timer before a handover complete message will result in handover failure.
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Measurement Report Triggertype measID
Choice 1…n(max=32)
measResultServingCell rsrp Result
0…97 (maps to –110…–44 dBm)
rsrp Result
0…34(maps to –19.5…–3dB)
measResultN-Cell
Choice
Result List E-UTRA
List as required
ResultUTRA
Listasrequired
UTRA results
ResultGERAN
Listasrequired
PhysicalcellID
Result CDMA2000
FDD0…511 TDD 0…127
cgi info CellGlobalID LAC
MCC+MNC+CID bit 16
RAC
bit8
plmnIDList
Max=5
Measurement Results UTRA RSCP
–5…91 (maps to –120…–25dBm)
UTRAEc/No
0…49(maps to–24…0dB) CSG information
Fig. 18 – IRAT Measurement Report UMTS © Informa Telecoms & Media
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Connected Mode Parameters
Measurement Report for GSM/GERAN The diagram shows an example report for GSM/GERAN cells. Note that the MobilityFromEUTRACommand message will contain either a L3 signalling message from the destination BSS/GERAN or, in the case of CCO, a target cell and frequency.
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Measurement Report Triggertype measID
Choice 1…n(max=32)
measResultServingCell rsrp Result
0…97 (maps to –110…–44 dBm)
rsrp Result
0…34(maps to –19.5…–3dB)
measResultN-Cell
Choice
Result List E-UTRA
List as required
ResultUTRA
Listasrequired
ResultGERAN
Listasrequired
Result CDMA2000
GERAN results CarrierFrequency
ARFCN
PhysicalIdentity
BSIC
cgi info CellGlobalID RAC
MCC+MNC+CID bit8
Measurement Results RSSI
0…63(mapsto–110…–47dBm)
Fig. 19 – IRAT Measurement Report GERAN © Informa Telecoms & Media
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Connected Mode Parameters
Measurement Report for CDMA2000 Cells The diagram shows an example report for CDMA2000. For CDMA2000, additional procedures have been defined, using SRB1, to register a UE’s presence in the destination core prior to any handover procedure.
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Measurement Report TriggerType measID
Choice 1…n(max=32)
measResultServingCell rsrp Result
0…97 (maps to –110…–44 dBm)
rsrp Result
0…34(maps to –19.5…–3dB)
measResultN-Cell
Choice
Result List E-UTRA
List as required
ResultUTRA
Listasrequired
ResultGERAN
Listasrequired
Result CDMA2000
CDMA2000 results Physical Identity
0…511 (Pilot PN-Offset)
cgi info Cell Global ID
SID/NID = CID POSS. Sector ID
Measurement Results PilotPNhase Pilotstrength
0…32767 0…63
Fig. 20 – IRAT Measurement Report CDMA2000 © Informa Telecoms & Media
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Connected Mode Parameters
Inter-eNB Handover Procedure The diagram shows the air interface signalling flow for an Inter-eNB handover. The stages for handover are as follows: 1. The UE sends a measurement report. 2. The source eNB requests that the target cell prepares for handover. Note that in the case of X2-based handover either lossless or seamless handovers are defined. 3. If no X2 interface is available, an S1-based handover may be triggered by the source eNB. 4. The source eNB sends a RRCConnectionReconfiguration message to the UE, including mobility control IEs (new C-RNTI, Cell identity and, optionally, target cell frequency). 5. The UE will initiate the random access procedure and start timer T304. 6. After the successful random access procedure the UE stops timer T304.
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MME
eNB
eNB
1. Measurement report
2. X2 Handover prep
3. S1 Handover prep 4. HO Command RRCConnectionReconfiguration 5. Random Access (T304 Started)
6. HO Complete (Stop T304) RRCConnectionReconfigurationComplete
Fig. 21 – LTE Handover Procedure (Inter-eNB) © Informa Telecoms & Media
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Connected Mode Parameters
IRAT Handover Procedure The major difference between an Inter E-UTRA handover and IRAT handover is that the E-UTRA has no direct connection to the target radio network. These interactions have to be handled by the MME. Once the MME has relayed the appropriate inter-RAT cell information to the source eNB it can instruct the UE to hand over using the MobilityFromEUTRACommand message. On receipt of this message the UE will change to the appropriate radio technology and implement the handover procedure. RRC or RR handover complete messages will then be used for UMTS and GSM respectively.
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MME
Target CN
Target RAN
eNB Measurement report
Handover Prep
Handover Prep
Handover Prep
RRCConnectionReconfiguration Mobility from E-UTRA Command Handover Complete
Fig. 22 – LTE IRAT Handover Procedure © Informa Telecoms & Media
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Connected Mode Parameters
UMTS Measurement Settings The information elements contained in the diagram are passed to a UE in connected mode using RRC measurement control. For the purpose of LTE handover, the most relevant parameters will be the EARFCN and bandwidth information element. LTE itself is specified as a measurement object and no specific cell identities are defined. Note that a UE that is RRC connected and in the state Cell-DCH will be given compressed mode gap configuration information to enable inter-frequency measurements. Reporting criteria may be either event based or periodical and multiple events can be specified. The trigger points for events can be modified with time-to-trigger values and hysteresis.
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Measurement Control
New Frequency List (8 maximum)
MeasurementID
E-UTRACarrier
1…n(max=16)
EARFCN
Measurement Command
Setup/modify/release
Bandwidth to measure
6, 15, 25, 50, 75, 100 rbs
Report Mode
AM/UM and Event/Periodical
Blacklistedcells
Listasneeded
Measurementtype
Choice
Physical Cell ID
OCI(0…503)
Intra-Frequency Inter RAT
Measurement Report Criteria (8 maximum)
Etc…
InterRATEventID
EARFCN
Own System Threshold
6, 15, 25, 50, 75, 100 rbs
LTE Inter RAT
W
0to2in0.1steps(3aonly)
Measurement Objects
Other System Threshold
–115…0 dBm (3a, b, c only) Value - IE-25
Hysteresis
0…7.5in0.5steps
Time to Trigger
0, 10, 20, 40…640, 1280, 2560, 5000ms
InterRATCellInfo
N/A
E-UTRA Hz List Removal New Frequencies
List as Required
Max. num. of cells to report
1…12
Measurement Quantity Measurement quantity
RSRP/RSRQ
Filter coefficiant
1, 2, 9, 11, 13, 19
Report quality
Oneor both (RSRP/Q)
Number of cells to report
1…12
Periodical Report Criteria Amount or repo rts
1, 2, 4, 8, 16, 32, Infinite
Report interval
250, 500, 1000, 2000…32000, 64000 millisecs
Report Criteria Measurement report criteria Periodical report criteria No report
Fig. 23 – UMTS Measurement Settings © Informa Telecoms & Media
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Connected Mode Parameters
UMTS Event Triggers The diagram shows the inter-RAT events and can be defined as follows: •
Event 3a
• • •
Event 3b Event 3c Event 3d
UMTS active set quality becomes worse than an absolute threshold and an LTE neighbour becomes better than an absolute threshold. An LTE neighbour becomes worse than an absolute threshold. An LTE neighbour becomes better than an absolute threshold. Best LTE neighbour cell change.
As UMTS is a CDMA system, a UE will potentially be involved in a soft handover and thus serving cell quality may be derived across an active set as follows: QUTRAN = 10•LogMUTRAN=W •10•Log •
• + (1-w)•10•logM
best
Where: Mi MBEST Na W
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Quality of ith cell in active set Quality measure of best cell in active set Number of cells in active set Weighting factor to manipulate sum of Mi and MBEST
© Informa Telecoms & Media
Event 3a
Inter-RAT LTE Neighbour cell
Event 3b
Absolute Threshold Other
Absolute Threshold
Absolute Threshold Own
Inter RAT LTE Neighbour cell UMTS Active set (QUTRAN)
Event 3c
Inter-RAT LTE Neighbour cell Absolute Threshold
Event 3d
Change of best n-cell
Inter-RAT LTE Neighbour cell 1
Inter RAT LTE Neighbour cell 2
Fig. 24 – UMTS Event Triggers © Informa Telecoms & Media
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Connected Mode Parameters
UMTS Measurement Report When the appropriate trigger conditions or period is met the UE will compose and send a measurement report. Note that prior to release 8, GSM CDMA2000 and intra-UMTS measurements could be reported. New information elements have been included in release 8 and a software upgrade in an existing UTRAN will be required to support LTE measurement reports.
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Measurement Report
E-UTRA Measured Results
Measurement Identity
1…n (maximum 16)
Measured results list
4x field entities non applicable for LTE
N/A
E-UTRACarrierHz
EARFCN
Measuredcelllist
Maximum4
Additiona l measured resu lts
Up to 4
E-UTRA measured results E-UTRA event results
Maximum 4
Physical Cell ID
PCI(0…503)
RSRP
0…97(mapsto-–40…–144dBm)
RSRQ
0…33(mapsto–19.5…–3dB)
UTRA CSG frequency info
E-UTRA Event Results IRAT event identity
E3a, E3b, E3c, E3d
Eventresultlist
Maximum4
CarrierHz
EARFCN
Reported cells list
Maximum 4
Physical cell ID
PCI (0…503)
Fig. 25 – UMTS Measurement Report © Informa Telecoms & Media
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Connected Mode Parameters
UMTS IRAT Handover Procedure A UE that is RRC connected to the UTRAN may not necessarily be in compressed mode. It would be usual for a UE to send a measurement report (1) based on an event trigger such as e6a or e1f (Serving cell RSCP reduction or UE Tx Power respectively). This would allow an RNC to send a Measurement Command and physical channel reconfiguration information (2) to the UE with gap parameters for compressed mode and new measurement commands for LTE Neighbours. Once in compressed mode (3), if the appropriate trigger event is met (Event 3a to 3d) a UE will send a measurement report (4) to the RNC. The source UTRAN may then retrieve appropriate LTE cell information for the target eNB (via core network) and issue a Handover from UTRAN (5) command to the UE. The UE will then attempt to reconnect (6) via LTE using the LTE random access procedure.
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UE Moving away from Node B
Node B
UE
eNB
1. Measurement report 2. Measurement command 3. UE in compressed mode 4. Measurement report 5. Handover command
6. Handover to LTE 7. Handover complete
A
B
C
Fig. 26 – UMTS IRAT Handover Procedure © Informa Telecoms & Media
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Connected Mode Parameters
Discontinuous Reception (DRX) Procedures DRX will be configured for a UE in connected mode so that a UE does not need to permanently monitor the PDCCH, thus saving battery life. The parameters for DRX have a trade-off between latency and battery life and are configurable for LTE. The onDurationTimer (Multiples of 1 ms) defines the amount of time the UE monitors downlink control channels whilst DRX is active. A short and long DRX cycle can be defined for LTE. If we take, for example, a UE involved in an active web browsing session, the long DRX cycle could be employed whilst a UE is RRC connected but no data is being received, and the UE will switch to the short DRX cycle when a web page has been downloaded to ensure no further data is immediately forthcoming. When a UE receives a scheduling message for its c-RNTI, it will start its DRX inactivity timer and begin to decode data. If instructed by a MAC control element, or if this timer expires, the UE will enter the short DRX cycle. If no data is received and the drxShortCycleTimer expires, then the UE may revert to the long DRX cycle.
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© Informa Telecoms & Media
On duration
Scheduling message reception
Inactivity timer or MAC CE reception
Short DRX cycle Timer expiry
Continuous reception
LongDRXcycle
Short DRX cycle
Long DRX cycle
RRC sends DRX parameters MAC CE activates DRX
eNB
Fig. 27 – Two Stage DRX Procedure © Informa Telecoms & Media
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Connected Mode Parameters
Uplink Power Control Uplink power control is needed in any mobile system, primarily to achieve a required Eb/No value at the eNB, but also to reduce overall system interference and preserve battery life. Detailed power control formulae are defined for LTE for the PUSCH, PUCCH and sounding reference signals. The formula for each channel follows the same basic principle and consists of a basic open-loop operating point (derived from static or semi-static parameters issued by an eNB) and dynamic offsets derived on a sub-frame basis. Note that a UE will never exceed maximum Tx power (23 dBm). The bandwidth element is derived from the number of scheduled radio blocks. The static/semi-static control point is derived from both the Po-PUSCH(j) (defined cell by cell from –126 dBm to +23 dBm) and Pl (an estimation of path loss made by the UE). TPC (Transmit Power Control) commands are transmitted on the PDCCH to individual UEs via a specific TPC_RNTI to control the dynamic closed loop offset. Note that a UE (for example capable of transmitting 23 dBm) must report power control headroom to the eNB. The eNB can then use this information to schedule uplink bandwidth to a UE. Power control headroom has a range +40 dBm to –23 dBm. The negative value would enable a UE to indicate that it has been allocated more radio blocks than it has power available to transmit in, thus enabling the eNB to reduce allocated uplink bandwidth.
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UE TX Power = min{PCMAX, 10log10(MPUSCH(i)) + PO_PUSCH(j) + α(j).PL +∆TF(i) +f(i)} dBm Power class Bandwith factor, Basic open 23 dBm no. of RBs loop operating point
Dynamic offset
Individual or Group TPC commands sent In PDCCH Power Headroom report sent in Uplink grant (–23....+40 dB)
eNB
Fig. 28 – Uplink Power Control © Informa Telecoms & Media
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Connected Mode Parameters
Timing Advance Like GSM, timing advance must be employed by LTE to ensure uplink transmission from multiple UEs arrives at the eNB orthogonally. Uplink timing advance utilises MAC control elements to update UE transmission time based on distance from the base station to counteract different propagation delays. Initial timing advance is set during the random access procedure, allowing an initial setting with granularity from 0.52 µs to 0.67 ms. Granularity of subsequent timing advance commands is again 0.52 µs (or 16 Ts). The command utilises a 6-bit MAC CE with a range of 0–63. Values 0–31 reduce timing advance, 31–63 increase timing advance.
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© Informa Telecoms & Media
eNB
eNB
DL symbol Txd at eNB
DL symbol RXd at UE, Tp1 propagation delay TP1
Tp1 2Tp1 Timing Advance = 2Tp1
UL transmitted symbol timing
UL symbol arrives at eNB. delay 2Tp1
2Tp1
Tp1
Fig. 29 – Timing Advance © Informa Telecoms & Media
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Connected Mode Parameters
CQI Reporting Link adaptation, or the process by which a transmitter should try to match the appropriate data rate for each user’s variable air interface characteristics, is utilised within LTE. The AMC process will define both the modulation scheme (from QPSK to 64QAM) and amount of error protection required for both uplink and downlink transmission. Uplink adaptation should be calculated by the source eNB based on measurements of uplink UE transmission, or, alternatively, an eNB may request a UE to transmit sounding reference signals. A UE can be configured to report CQI values in order to allow the eNB to determine an appropriate downlink Modulation and Coding Scheme (MCS) as seen in the diagram. Note that the CQI value is NOT a direct indication of SINR, but an indication of the highest MCS that it can decode with a transport block error rate probability not exceeding 10%.
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CQIIndex 0
Modulation Tx
No
CodeRateApprox –
SymbolEfficiency
–
1
QPSK
0.076
0.15
2
QPSK
0.12
0.23
3
QPSK
0.19
0.37
4
QPSK
0.3
0.60
5
QPSK
0.44
0.87
6
QPSK
0.59
1.17
7
16QAM
0.37
1.47
8
16QAM
0.48
1.91
9
16QAM
0.6
2.40
10
64QAM
0.45
2.73
11
64QAM
0.55
3.32
12
64QAM
0.65
3.90
13
64QAM
0.75
4.52
14
64QAM
0.85
5.11
15
64QAM
0.93
5.55
Downlink Adaptation based On UE CQI reporting
64QAM 16QAM
16QAM
QPSK
QPSK
eNB CQI 8
CQI 12
CQI 7
CQI 4
CQI …
Fig. 30 – CQI Reporting © Informa Telecoms & Media
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