ROBUSTAMRSIGNALLING.pdf

Robust AMR Signalling

DN70284148Issue 1-0 en27/02/2008

# Nokia Siemens Networks 1 (16)

BSC3153Nokia GSM/EDGE BSS, Rel. BSS13, BSC andTCSM, Rel. S13, Product Documentation, v.1

2 (16) # Nokia Siemens Networks DN70284148Issue 1-0 en27/02/2008


Contents

Contents 3

1 Overview of Robust AMR Signalling 5

2 Requirements for Robust AMR Signalling 7

3 Technical description of Robust AMR Signalling 9

4 Functionality of Robust AMR Signalling 114.1 Triggering conditions for FACCH/SACCH repetition and power

increment 114.2 Measurement reporting and averaging parameters with SACCH

repetition 12

5 Effect of Robust AMR Signalling on interfaces 13

6 User interface of Robust AMR Signalling 15

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Contents



1 Overview of Robust AMR Signalling

Low-rate AMR FR codecs provide satisfactory speech quality in radiochannels whose carrier-to-interference ratio (C/I) is up to 4 dB worse thanthat needed to give reliable operation of the FACCH and SACCH controlchannels. This results in calls being dropped even though their speechquality is still acceptable.

The effective C/I for downlink FACCH and uplink/downlink SACCH can beimproved by increasing the base station (BTS) Tx power for FACCH, or byrepeating the FACCH/SACCH block.

Robust AMR Signalling (BSS20872) is a licence-based applicationsoftware product that consists of four separately controlled features:

. FACCH and SACCH repetition for repeated ACCH capable mobileson AMR

From 3GPP Release 6 onwards, the mobile stations (MSs) andBTSs can ask for SACCH frames to be repeated exactly on transmit,so that the original frame and its repeat can be decoded togetherusing incremental redundancy (soft combining) type decode, similarto the incremental redundancy defined for EGPRS data. Thetransmit repeat and incremental redundancy on decode can also beused with downlink FACCH frames.

FACCH and SACCH repetition improve the C/I up to 4 dB.

. FACCH repetition for legacy mobiles on AMR FR

. FACCH repetition for legacy mobiles on AMR HR

For legacy MSs (Release 5 or older), the downlink FACCH can berepeated to give the MS two chances to decode the FACCH beforeeach link timeout and retry of the protocol.

. FACCH power increment

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Overview of Robust AMR Signalling

For legacy MSs (Release 5 or older), the BTS Tx power for downlinkAMR FACCH bursts can be increased by 2 dB up to the maximumtransmission power of the BTS (Pmax).

FACCH repetition and power increment together provide animprovement of up to 4 dB in C/I for FACCH decode.

Benefits of Robust AMR Signalling

. reduced dropped call rate in heavily loaded networks

. increased coverage, including in-building coverage, in lightly loadednetworks

. FACCH and SACCH repetition improve the C/I by up to 4 dB.

Related topics

. Feature descriptions. Radio network performance

. Enhanced Speech Codecs: AMR and EFR

. Install and upgrade. Software

. Licensing in BSC

. Test and activate. Radio network performance

. Activating and Testing BSS20872: Robust AMRSignalling

. Reference. Commands

. MML commands. EE - Base Station Controller Parameter Handling

in BSC. Counters/performance indicators

. Call control measurements (CS). 112 AMR Signalling Measurement

. Parameters. BSS Radio Network Parameter Dictionary



2 Requirements for Robust AMRSignalling

Software requirements

Table 1. Required software

Network element Software release required

BSC S13

Nokia Flexi EDGE BTSs EP2.0

Nokia UltraSite EDGE BTSs CX6.0

Nokia MetroSite EDGE BTSs CXM6.0

Nokia Talk-family BTSs Not supported

Nokia InSite BTSs Not supported

MSC/HLR Not applicable

SGSN Not applicable

Nokia NetAct OSS4.2

Table Required software shows the earliest version that supports RobustAMR Signalling.

Hardware requirements

Table 2. Required hardware

Network element Hardware requirements

BSC No requirements.

BTS UltraSite and MetroSite TRXs have tobe EDGE-capable or equipped with anEDGE-capable baseband unit.

TCSM No requirements.

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Requirements for Robust AMR Signalling

Table 2. Required hardware (cont.)

Network element Hardware requirements

SGSN No requirements.

Frequency band support

The BSC supports Robust AMR Signalling on the following frequencybands:

. GSM 800

. GSM 900

. GSM 1800

. GSM 1900

End-user equipment

3GPP Release 6 compliant MS is required for SACCH repetition. Althoughany MS can be used for FACCH repetition, only a Release 6 compliant MScan derive the full benefit from it.



3 Technical description of Robust AMRSignalling

Interworking

AMR Full Rate and AMR Half Rate

Although you can enable the four features that comprise Robust AMRSignalling whenever the Robust AMR Signalling feature has beeninstalled, they are in use only if AMR Full Rate, AMR Half Rate, or both areenabled, as illustrated in the following table.

Table 3. Relationship between Robust AMR Signalling features and AMR FR/HR

Feature AMR requirement

FACCH repetition for legacy mobiles on AMR FR AMR FR

FACCH repetition for legacy mobiles on AMR HR AMR HR

FACCH and SACCH repetition for repeated ACCHcapable mobiles on AMR

AMR FR or AMR HR(or both)

FACCH power increment AMR FR or AMR HR(or both)

FACCH repetition is possible only if the codec mode 4.75 kbit/s is thelowest one in the active AMR HR codec set and either 4.75, 5.15, or 5.9 isthe lowest one in the AMR FR codec set.

Early classmark sending

The BSC has to know the repeated ACCH capability of the MS beforesending a CHANNEL ACTIVATION message to the BTS. The capability isindicated in the Mobile Station Classmark 3 information element that theMS sends on the SDCCH if the value of the segment-specific parameterearly sending indication (ESI) is Y (Yes).

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Technical description of Robust AMR Signalling

If the BSC does not receive the information before sending the CHANNELACTIVATION message, it considers the MS to be incapable of ACCHrepetition.



4 Functionality of Robust AMR Signalling

4.1 Triggering conditions for FACCH/SACCH repetitionand power increment

FACCH repetition and FACCH power increment for legacy MS

FACCH repetition and/or power increment is triggered if the MS requeststhe lowest downlink codec, which for AMR FR calls is either 4.75, 5.15, or5.9 kbit/s, and for AMR HR calls 4.75 kbit/s.

The retransmission of the PHYSICAL INFORMATION message, followingthe expiry of the timer T3105, is also a trigger.

Note that FACCH repetition is enabled separately for AMR HR and AMRFR.

Power increment only applies when the Tx power used for the call is lessthan the maximum power capability of the TRX (TRXmax). Furthermore,since the BCCH carrier power level must remain constant, the powerincrement applies only to FACCH bursts sent on non-BCCH carriers.

If the BCCH power level is less than TRXmax, then the FACCHs may besent at a power level that is 2 dB higher than the BCCH power level.

FACCH repetition for Rel. 6 compliant MS

FACCH repetition is triggered if the MS requests the lowest downlinkcodec, which for AMR FR calls is either 4.75, 5.15, or 5.9 kbit/s, and forAMR HR calls 4.75 kbit/s. For AMR HR calls, the expiry of the timer T200for the frame is also required.

The retransmission of the PHYSICAL INFORMATION message, followingthe expiry of the timer T3105, is also a trigger.

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Functionality of Robust AMR Signalling

SACCH repetition for Rel. 6 compliant MS

In the downlink direction, SACCH repetition is triggered if a Rel.6compliant MS requests for SACCH frames to be repeated.

In the uplink direction, triggering SACCH repetition depends on thenumber of uplink SACCH single decode block errors and the value of theSACCH Repeat Window (SRW) parameter.

If the value of the parameter is 1, a decoding failure of a SACCH blockmeans that a repeat command is sent to the MS in the next downlinkSACCH block. Values 2 to 15 can be used to define the number ofconsecutive SACCH blocks that can contain two decoding failures beforea repeat command is sent to the MS. For example, if the value is 3 and theBTS fails to decode two of the preceding three blocks, it commands theMS to repeat a SACCH block.

4.2 Measurement reporting and averaging parameterswith SACCH repetition

When the BTS fails to decode the uplink SACCH and therefore cannotreceive the MEASUREMENT REPORT message from the MS, it sendsonly the uplink measurements to the BSC in the MEASUREMENTRESULT message for that SACCH period.

With uplink SACCH repetition, the MS resends the sameMEASUREMENT REPORT message during the next SACCH period.Because the BTS cannot determine whether the message sent by the MSis the same or a new one, it always sends the MEASUREMENT REPORTmessage to the BSC when it is correctly decoded. This may cause thesame report to be used twice in the averaging of serving and adjacentcells.



5 Effect of Robust AMR Signalling oninterfaces

Radio interface

The Repeated ACCH Capability field of the Mobile Station Classmark 3information element in the CLASSMARK UPDATE message indicateswhether the MS supports FACCH/SACCH repetition.

Abis interface

The optional ACCH Control information element in the CHANNELACTIVATION message is used by the BSC to inform the BTS whether itcan use FACCH/SACCH repetition or FACCH power increment during thecall.

The AMR Signalling Data Information field in the Uplink Measurementsinformation element in the MEASUREMENT RESULT message containsinformation on the preceding SACCH period. This information includes thefollowing:

. whether uplink SACCH was decoded using soft combining

. whether the MS requested downlink SACCH repetition

. whether the BTS ordered uplink SACCH repetition

. whether the BTS repeated a downlink SACCH frame

. the number of downlink FACCH blocks that were repeated

. the number of downlink FACCH blocks that were not repeated.

The Uplink Measurements information element also contains the BTS'sestimation whether the MS used discontinuous transmission (DTX) in thereporting period and information on the validity of the estimation.

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Effect of Robust AMR Signalling on interfaces

A interface

No effect.

Gb interface

No effect.



6 User interface of Robust AMR SignallingParameters

The following BSC radio network object parameter is used for handlingRobust AMR Signalling:

. SACCH repeat window (SRW)

MMLs

. Base Station Controller Parameter Handling in BSC (EE)

The following commands are used for handling Robust AMRSignalling: EEO, EEQ

. Licence and Feature Handling (W7)

Counters

112 AMR Signalling Measurement contains the counters related to RobustAMR Signalling. These counters are updated according to the informationreceived in the AMR Signalling Data Information field in the UplinkMeasurements information element in the MEASUREMENT RESULTmessage

Number Name

112000 TCH SEIZURES FOR REP ACCHCAPABLE MS

112001 UL SACCH FRAME SOFT COMBININGS

112002 REPEATED DL SACCH FRAMES

112003 UL SACCH REPETITION REQUESTS

112004 REPEATED DL FACCH BLOCKS

112005 NON REPEATED DL FACCH BLOCKS

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User interface of Robust AMR Signalling

For more information, see 112 AMR Signalling Measurement underReference/Counters/performance indicators in the PDF view.



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ROBUSTAMRSIGNALLING.pdf