AMR-EFR

Enhanced Speech Codecs: AMRand EFR

DN9814098Issue 11-1 en

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2 (76) # Nokia Corporation DN9814098Issue 11-1 en

Enhanced Speech Codecs: AMR and EFR

Contents

Contents 3

List of tables 4

List of figures 5

Summary of changes 7

1 Overview of Enhanced Speech Codecs: AMR and EFR 9

2 Technical description of AMR and EFR 13

3 Functionality of AMR and EFR 193.1 Adaptive multirate codec inband control and link adaptation 243.2 Radio resource management with Enhanced Speech Codecs 30

4 Effect of AMR and EFR on interfaces 41

5 Schemes in AMR and EFR 455.1 Assignment 455.2 External handover 525.3 Internal handovers 605.4 In call modification and FACCH call set-up 69

6 User interface of AMR and EFR 73



Contents

List of tables

Table 1. Pools that support EFR 19

Table 2. Pools that support AMR 21

Table 3. Description of THR and HYST parameters. 28

Table 4. Mapping of the THR values between 0 and 63 to normalised C/I. 29

Table 5. Mapping of the HYST values between 0 and 15 to C/I. 29

Table 6. The basic codec sets for AMR FR 35

Table 7. The basic codec sets for AMR HR 35

Table 8. Example handover from a Talk-Family BTS 67

Table 9. Example handover from an UltraSite BTS 68



List of figures

Figure 1. The AMR FR and the AMR HR performance (3GPP specification 26.075version 1.0.0) 10

Figure 2. A high-level block diagram of the complete AMR system 24

Figure 3. An example of the AMR link adaptation 26

Figure 4. Definition of Threshold and Hysteresis for codec mode adaptation 28

Figure 5. An example of TCH allocation optimisation 37

Figure 6. Assignment procedure, basic scheme 46

Figure 7. Assignment procedure, switching of A interface circuit pool 50

Figure 8. External HO, source BSC 52

Figure 9. External HO, target BSC, basic scheme 54

Figure 10. External HO, target BSC, switching of A interface circuit pool 58

Figure 11. Internal HO, intra-cell 60

Figure 12. Internal HO, inter-cell (async) 63

Figure 13. Internal inter-cell handover, switching of A interface circuit pool 68

Figure 14. In call modification and FACCH call set-up 69



List of figures



Summary of changes

Changes between document issues are cumulative. Therefore, the latest documentissue contains all changes made to previous issues.

Changes made between issues 11-1 and 11-0

Added information on establishing a unidirectional connection in interalhandovers to Functionality of AMR and EFR.

Changes made between issues 11-0 and 10–1

Added information on TCSM3i and BSC3i 1000/2000 to Technical description ofAMR and EFR.

Added new pools (28 and 32) supported by TCSM3i and interworkinginformation with Single Antenna Interference Calculation to Functionality ofAMR and EFR.

Added DTM-related messages to Effect of AMR and EFR on interfaces.

Added AMR RX Quality Measurement to User interface of AMR and EFR.


Editorial changes.


Added information about AMR HR licensing and a reference to licensingdocument Licensing in BSC.

The document has been revised throughout to comply with the latestdocumentation standards.



Summary of changes


Radio resource management with Enhanced Speech Codecs

Modifications made due to “Remove or relax codec dependency for AMR HRpacking”.



1 Overview of Enhanced Speech Codecs:AMR and EFR

Adaptive multi-rate (AMR) and enhanced full rate (EFR) are speech codingalgorithms that give better speech quality than full rate (FR) coding.

EFR, AMR full rate (FR), and AMR half rate (HR) are application softwareproducts of the BSC. You can use either AMR FR, AMR HR or both.

AMR HR is a licence-based software. The type of the licence is ON/OFF. Formore information on licensing, see Licensing in BSC.

Benefits of AMR and EFR

AMR and EFR offer quality that is better than or comparable to adaptivedifferential pulse code modulation (ADPCM).

AMR is also capable of adapting its operation optimally according to theprevailing channel conditions, because AMR consists of a family of codecs(source and channel codecs with different trade-off bit-rates) operating in theGSM FR and HR channels. Codec mode adaptation for AMR is based on thereceived channel quality estimation in both the MS and the BTS, followed by adecision on the most appropriate speech and channel codec mode to apply at agiven time.

In high-error conditions, more bits are used for error correction to obtain errorrobust coding, while in good transmission conditions only a small number of bitsis needed for sufficient error protection and more bits can therefore be allocatedfor source coding. The figure below illustrates AMR FR and AMR HRperformance.



Overview of Enhanced Speech Codecs: AMR and EFR

Figure 1. The AMR FR and the AMR HR performance (3GPP specification26.075 version 1.0.0)

1.0

2.0

3.0

4.0

5.0

No Errors 16 dB C/I 13 dB C/I 10 dB C/I 7 dB C/I 4 dB C/I

EFR

AMR FR

AMR Full Rate performance compared to

Full Rate EFR in Clean Speech

1.0

2.0

3.0

4.0

5.0

No Errors 19 dB C/I 16 dB C/I 13 dB C/I 10 dB C/I 7 dB C/I 4 dB C/I

FR

AMR HR

AMR Half Rate performance compared to

Full Rate in Clean Speech

MOS (Mean Opinion Score)

MOS (Mean Opinion Score)



The BSC provides the basic AMR codec mode sets for the MS and the BTS vialayer 3 signalling. The MS supports all speech codec modes of AMR, althoughonly a set of up to 4 speech codec modes is used during a call. The BSC supportsall speech codec modes, except 7.95 kbit/s on a HR channel, and it has onedefault set for each channel mode per BTS. The default codec sets also include adefault set of thresholds and hysteresis for the above-mentioned codec modeadaptation.

EFR and AMR can use the state-of-the-art FR traffic channel, which means thatthe source codec rate EFR is 12.2 kbit/s and AMR is up to 12.2 kbit/s. AMR canalso use HR traffic channel (TCH) used by the basic HR, offering an increase ofcapacity in terms of TCHs at the BTS. To achieve this, AMR HR requires HR ordual rate (DR) channel configuration on the radio interface. The support for EFRor AMR in a network does not require nor imply support for the basic HR andvice versa.

Submultiplexing on highway PCM (Ater interface) for AMR FR and AMR HR is16 kbit/s (for AMR HR the other half of 16 kbit/s is unused). Therefore, nosavings in terrestrial transmission can be achieved with EFR or AMR whencompared to FR.

Related topics in Enhanced Speech Codecs: AMR and EFR

. Technical description of AMR and EFR

. Functionality of AMR and EFR

. Effect of AMR and EFR on interfaces

. Schemes in AMR and EFR

. User interface of AMR and EFR

Other related topics in BSC/TCSM documentation

. Descriptions. Functional Area Descriptions

. Radio Network Performance. Radio Channel Allocation

. Feature Descriptions. Radio Network Performance

. Half Rate in BSC

. Test and Activate. Radio Network Performance

. BSS10004: AMR. Activating and Testing AMR



Overview of Enhanced Speech Codecs: AMR and EFR

. Value Added Services. BSS6071: EFR

. Activating and Testing EFR

. Reference. Commands

. MML Commands. EA - Adjacent Cell Handling. EE - Base Station Controller Parameter Handling in

BSC. EH - Handover Control Parameter Handling. EQ - Base Transceiver Station Handling in BSC. ER - Transceiver Handling. EU - Power Control Parameter Handling. WG - Transcoder Configuration. WO - Parameter Handling

. Counters/Performance Indicators. 1 Traffic Measurement. 4 Handover Measurement. 14 RX Quality Statistics Measurement. 51 BSC Level Clear Code (PM) Measurement. 107 AMR RX Quality Measurement

. Parameters. BSS Radio Network Parameter Dictionary. PRFILE and FIFILE Parameter List

Related topics in GSM/EDGE BSS system documentation

. System feature descriptions. Radio Network Performance

. Adaptive Multi Rate Codec



2 Technical description of AMR and EFRRequirements

. BTS

The software-upgraded BTSs are capable of supporting EFR and AMRcodings dynamically.

Each radio timeslot (RTSL) configured to support a full rate (FR) channelcan be activated either as an EFR or as an AMR FR traffic channel (TCH)on a call.

Each RTSL configured to support a dual rate (DR) channel can beactivated either as an EFR, as an AMR full rate, or as two AMR half rate(HR) TCHs.

A RTSL configured to support a HR channel rate can be activated only asan AMR half rate TCH.

An inband signalling channel is defined for AMR which enables the MSand the BTS to exchange messages on applied or requested speech andchannel codec modes. This operation is called AMR link adaptation (LA).The BTS commands the MS to apply a particular speech codec mode in theuplink, but the MS can only request the BTS to apply a particular speechcodec mode in the downlink because the BTS has an option to override theMS's request.

. BSC

EFR and AMR can be used even if HR is not in use in the network inquestion.

Handovers between all speech coding algorithms are possible, whenneeded. The BSS has many parameters which have a direct or indirectimpact on the speech quality, and the optimisation and fine tuning of thesecan be carried out for the network to improve the speech quality. Forexample, it is possible to prohibit handovers between speech codingalgorithms.



Technical description of AMR and EFR

Channel rate is the primary requirement in assignment and in externalhandover if alternatives (for example channel rate or speech coding) aregiven. Additional requirements are also taken into account in all handoversfrom one TCH to another. Such a requirement can be the prohibition of ratechanges after the first channel allocation. If channel rate or speech codecchanges are allowed and a change is needed because of channelconfiguration in the BTS, speech codecs are changed primarily inside thechannel rate and secondarily between channel rates.

The BSC also supports the use of A interface circuit pools, if needed. Withpools the BSC makes checkings to ensure that the requirements on theTCH in question coincide with the properties of the pool before anassignment continues.

Note

No configuration at the Abis interface is needed for EFR or AMR. Forexample, any TCH configured to support FR at the Abis interface can beactivated with EFR and AMR FR depending solely on the properties of theBTS.

. TCSM

TCSM2s can be software-upgraded or added or TCSM3is added to handleextensions and the additional EFR or AMR capability.

TCSM2/TCSM3i equipment allows dynamic switching between differentspeech coding algorithms, when configured to support more than onechannel rate or speech coding algorithm.

If TCSM2 is used, dynamic switching between AMR and non-AMRspeech coding algorithms is not possible, because the only AMR pool thatTCSM2 supports (pool 23) is not capable of any other speech coding thanAMR. Pool switching is needed to enable switching between AMR andnon-AMR speech codings. For example the speech coding for one circuitcarrying one TCH may vary between FR, EFR and HR (as a result ofhandovers for the MS) at the Ater interface during one speech call.

With TCSM3i, pools 28 and 32 support all speech codecs.

. MSC

The support for EFR and AMR in the MSC mainly requires the capabilityto select appropriate resources based on the information received from theMS and relaying that information to the BSS. Since remote transcoders arein use in the Nokia BSS, the pool concept is supported.

. Transmission lines



From the transmission point of view, an EFR or AMR TCH is like any FRTCH. In the Nokia GSM system, the BSS provides flexible transmissionsolutions and effectively uses the capacity of PCM lines (2 Mbit/s)available. The optimisation of the use of 2 Mbit PCM lines can be realisedon both the A interface (BSC-MSC) and the Abis interface (BSC-BTS),thus using the network resources efficiently.

. Nokia NetAct

EFR as a speech coding algorithm sets no special requirements for NokiaNetAct. The needs of EFR can be handled with existing procedures.However, EFR causes changes in the interpretation or explanation of someexisting parameters, and these are reflected in the user interface of NokiaNetAct.

AMR introduces some new parameters for handover control and powercontrol and also new AMR coding sets for FR and HR.

. MS

New generation MSs capable of supporting EFR and/or AMR as defined inthe specification are needed to use the enhanced speech codingfunctionalities.

Software requirements for AMR

BTS: Talk-family BTS SW release DF6 or later

PrimeSite BTS SW release DF6 or later

MetroSite BTS SW release CXM3.0 or later

UltraSite BTS SW release CX3.0 or later

Flexi EDGE BTS any SW release

2nd generation BTS and Nokia InSite do not supportAMR.

TCSM: TCSM2 or TCSM3i

MSC: M10 or later

A interface circuit pool support is required.

BSC: S10 or later

MS: An AMR-capable phase 2 MS

There are no hardware or firmware effects.

Software requirements for EFR

BTS: 2nd generation BTS SW release B9.0 or later

Talk-family BTS SW release D2.1 or later




PrimeSite BTS SW release F2.1 or later

TCSM: TCSM2 or TCSM3i

MSC: M7-B or later

A interface circuit pool support is required.

BSC: S6 or later

MS: An EFR-capable phase 2 MS

There are no hardware or firmware effects.

Capacity

. BSC2i:

Up to 512 TRXs, if RTSLs are configured as FR channels.

Up to 256 TRXs, if RTSLs are configured as HR or DR channels.

. BSC3i 660:



. BSC3i 1000:



. BSC3i 2000:



Interworking

. Enhanced TRX priorisation

With the TRX priority in TCH allocation parameter, you candirect AMR calls primarily to non-BCCH TRX and non-AMR callsprimarily to BCCH TRX.

. Common BCCH Control and Multi BCF Control

In segment environment, if the AMR codec set of the BCCH BTS of thecell is disabled, it must also be disabled in the other BTSs of that cell.Similarly, if it is enabled, it must also be enabled in the other BTSs of thatcell.



AMR FR and AMR HR codec sets can be disabled or enabled separately.

For more information, see Common BCCH Control in BSC and Multi BCFControl in BSC.

. Direct Access to Desired Layer/Band (DADL/B)

To support 2nd generation BTSs in AMR environment and BTSs in whichAMR is disabled, DADL/B is used to hand over AMR calls to co-locatedAMR-capable cells during the call set-up phase. Both intra-BSC and inter-BSC DADL/B handovers are possible, preferably within one frequencyband as the failure probability is much higher with DADL/B handoversbetween bands.

TCH assignment vs. DADL/B handover start:. If an AMR call is the aim and there are no TCHs available in the

accessed cell, Directed Retry due to congestion, with or withoutqueuing, is made.

. If there are TCHs available in the accessed cell and there areadjacent cells defined as DADL/B handover target cells with theparameter AMR target cell of direct access to desiredlayer, a DADL/B handover is applied. Adjacent cells are notverified according to the MS capabilities (single band, dual band ortri-band), but they have to meet the current signal level requirementsto be considered as target cells for a DADL/B handover. The currentmethod for sorting the target adjacent cells is used.

. If there are no DADL/B handover target cells defined, the TCH isallocated from the accessed cell and another speech codec thanAMR is chosen.

. The default is No, meaning that the DADL/B handover is notapplied to the adjacent cell.

For more information, see Direct Access to Desired Layer/Band.

. Handover algorithm and preference order of target cells

To support AMR call continuation also after an internal or externalhandover, the handover target cell list is manipulated so that the AMR-capable cells in which the load is low are on top. The candidate cells on thetarget list are already pruned by the adjacent cell parameter HO marginpbgt. The AMR-capable cells are verified by the adjacent cell parameterAMR target cell of direct access to desired layer andthose AMR-capable adjacent cells that are below the threshold of the BTSparameter BTS load threshold are prioritised. Prioritisation is madeonly when an AMR call is the current call type.

The BSC drops cells from the candidate list according to the TCHconfiguration, resource situation and speech codec support of the targetcells.




. Intelligent Frequency Hopping and Intelligent Underlay-Overlay

AMR-specific good and bad C/I thresholds are specified for AMR HR andAMR FR.

The threshold values for AMR HR also serve the basic HR.

The following Handover Control parameters continue to serve the basicFR:. super reuse good C/I threshold (GCI), Px (GPX), Nx

(GNX). super reuse bad C/I threshold (BCI), Px (BPX), Nx

(BNX)

With the AMR-specific thresholds you can select the type of speech callsthat are preferred to enter the super layers cells.

Note that the BTS must support AMR for the super reuse layer to work.

For more information, see Activating and Testing Intelligent FrequencyHopping and Intelligent Underlay-Overlay.

. Single Antenna Interference Cancellation

When Single Antenna Interference Cancellation (SAIC) is used in thenetwork together with AMR, the SAIC-specific counters are updated inAMR RX Quality Measurement.

For an overview, see Overview of Enhanced Speech Codecs: AMR and EFR.



3 Functionality of AMR and EFRA interface circuit pools

A circuit pool is a group of circuits supporting a set of channel modes and relatedspeech codec algorithms. There may be several circuit pools per one BSS.

In assignment or external handover, the MSC selects a circuit from the circuitpool, which corresponds as well as possible to the requested radio channel type.The assignment procedure or the handover procedure is successful when the Acircuit is compatible with

. the current traffic channel (TCH) radio resource configuration and

. the resource situation in the BTS.

On the other hand, during the completion of assignment or handover, the BSCcan send the circuit pool information to the MSC with which it is able to find outthe possible circuit pool type mismatches. There can be a more suitable pool inrelation to the allocatable radio resources although the current A circuit would becompatible with the allocated TCH type.

The A interface speech circuits (CIC) are divided into pools (CIP) according tothe TCSM capabilities. The main factors when dividing the circuits into pools isthe channel rate and the speech codecs supported.

Table 1. Pools that support EFR

Coding Pool Supported channels and speech codingalgorithms

0000 0101 5 FR speech version 1

FR speech version 2

FR data (12, 6, 3.6 kbit/s)



Functionality of AMR and EFR

Table 1. Pools that support EFR (cont.)


FR speech version 2


HR speech version 1


FR speech version 2


HR speech version 1

HSCSD max 2 x FR data (12, 6 kbit/s)


FR speech version 2


HR speech version 1

HSCSD max 4 x FR data (12, 6 kbit/s)


FR speech version 2

FR data (14.5, 12, 6, 3.6 kbit/s)

HR speech version 1


FR speech version 2

FR data (14.5, 12, 6, 3.6 kbit/s)

HR speech version 1

HSCSD max 2 x FR data (14.5, 12, 6 kbit/s)

EDGE FR data (29.0 kbit/s)


FR speech version 2

FR data (14.5, 12, 6, 3.6 kbit/s)

HR speech version 1


EDGE max 2 x FR data (29.0 kbit/s)

EDGE FR data (43.5 kbit/s)



Table 1. Pools that support EFR (cont.)

00011100 28 (TCSM3i only) FR speech version 1

FR speech version 2

FR speech version 3

FR data (14.5, 12, 6, 3.6 kbit/s)

HR speech version 1

HR speech version 3


FR speech version 2

FR speech version 3

FR data (14.5, 12, 6, 3.6 kbit/s)

HR speech version 1

HR speech version 3


Pools 5 and 7 are primarily used for speech calls and pools 10, 13, 20-22, 28, and32 are primarily used for High Speed Circuit Switched Data (HSCSD)connections. If the EFR option is included in the software build, you can also usepool numbers 5 and 7.

Table 2. Pools that support AMR

Coding Pool Supported channels and speech codingalgorithms


HR speech version 3


FR speech version 2

FR speech version 3

FR data (14.5, 12, 6, 3.6 kbit/s)

HR speech version 1

HR speech version 3




Table 2. Pools that support AMR (cont.)


FR speech version 2

FR speech version 3

FR data (14.5, 12, 6, 3.6 kbit/s)

HR speech version 1

HR speech version 3


Because of the memory consumption of AMR codec modes, TCSM2 can supportsimultaneously only AMR-related codings (pool number 23). This means thatwhen AMR is introduced to the network, either a current pool is modified tosupport AMR or a new one is introduced for AMR use only. If the AMR option isincluded in the software build, you can also use pool number 23.

TCSM3i supports all speech codecs simultaneously on pools 28 and 32.

The circuit pool information is located on the PCMCON. This information isgiven with MML commands of the Transcoder Configuration when the ETs ofthe TCSM are connected on the A interface. The PCMCON can be accessed withCIC via the S7PCMF file.

In the initial case, the MSC selects a circuit from some circuit pool and offers thatto the BSC in an ASSIGNMENT REQUEST or HANDOVER REQUESTmessage. When the BSC receives the CIC, it reads the CIP information from thePCMCON, and then checks if the capabilities of the CIP are suitable bycomparing them to the capabilities of the received channel type:

. If the offered CIC is compatible with the required channel type (that is, theCIP supports at least one of the channel rates and speech coding algorithmsrequired) the BSC proceeds with the assignment or the handover request. Ifthe procedure is successfully completed, ASSIGNMENT COMPLETE orHANDOVER REQUEST ACKNOWLEDGE messages include a circuitpool element to indicate the pool from which the circuit was allocated.

. If the offered CIC is compatible with the required channel type but achannel cannot be reserved for the preferred channel mode, an attempt ismade to switch the pool to support the channel allocation for the otherchannel mode. The BSC sends the ASSIGNMENT FAILURE orHANDOVER FAILURE message with the cause Switch Circuit Pool andthe 'circuit pool list' element. Pool switching is not made for achieving amore advanced codec for the call. The pool switching lists are defined inA-Interface Hunting Order Handling (EYM MODIFY SPEECH CODECPOOL LIST).



. If the offered CIC is not compatible with the required channel type (that is,the CIP does not support any of the channel rates or speech codingalgorithms required), the BSC sends an ASSIGNMENT FAILURE orHANDOVER FAILURE message with the cause Circuit Pool Mismatch, ifthere is another pool that supports at least one requested channel rate/speech codec. If there is no other pool that supports at least one requestedchannel rate/speech codec, the BSC sends an ASSIGNMENT FAILURE orHANDOVER FAILURE message with the cause Requested Transcoding/Rate Adaption Unavailable in case of a data call, or the cause RequestedSpeech Version Unavailable in case of a speech call. The BSC includes thecircuit pool element in the message to indicate the pool to which theoffered CIC belongs in the BSC. The BSC also indicates its preferredcircuit pools with a circuit pool list element in these failure messages.

For more information, see General principles in TCH allocation.

. If there is a circuit pool mismatch between the BSC and the MSC, theMSC clears it. The MSC can compare the pool it has selected with the poolindicated by the BSC in the ASSIGNMENT COMPLETE andHANDOVER REQUEST ACKNOWLEDGE messages and correct itstables (CIC/CIP).

The circuit pool element is returned in an ASSIGNMENT COMPLETE or in aHANDOVER REQUEST ACKNOWLEDGE message to the MSC when severalcircuit pools are present on the MSC-BSS interface.

The circuit pool element is returned in an ASSIGNMENT FAILURE or in aHANDOVER FAILURE message to the MSC when several circuit pools arepresent on the MSC-BSS interface.

The circuit pool list element is returned in an ASSIGNMENT FAILURE or in aHANDOVER FAILURE message to the MSC when the cause is either CircuitPool Mismatch or Switch Circuit Pool.

BTS speech codec support handling

The BSC is able to handle both BTSs that support AMR and those that do notsupport it. This functionality requires no input from the operator, because theBSC automatically checks the AMR capability of the BTS when the BTS is beingreset. This is important if all of the BTSs have not been updated to support AMR.

The BSC finds out the type and the version of the BTS from the BTS softwarepackage. The information is conveyed to BSDATA for storage.

The BSC derives the BTS speech codec support during the channel allocationprocedure against the speech codec requirements of the MSC. The BTS speechcodec support is further taken into account in channel activation towards the BTS.




3.1 Adaptive multirate codec inband control and linkadaptation

The figure below illustrates the AMR system.

Figure 2. A high-level block diagram of the complete AMR system

The system consists of the major components TRAU and BTS on the networkside and the MS. On the network side, speech encoder (SPE) and channel encoder(CHE) as well as channel decoder (CHD) and speech decoder (SPD) areconnected via the serial Abis interface. For each link, quality information isderived by estimating the current channel state. Based on the channel state, thecodec mode control, which is located on the network side, selects the codecmodes to be applied. The codec mode information, which has to be transmittedon each link, consists of:

. Mode Indications and Mode Commands in the downlink

. Mode Indications and Mode Requests in the uplink

Their tasks are:

SPE

SPD CHDspeech data

UL codec mode (received)

SPE

SPDCHD

DL Mode Request(received)

networkcontrol

UL-

meas

DL codec mode

DL-Mode Ctrl

UL-ModeCtrl

speech data

TRAU BTS MS

CHE

CHE

DL-Req.Gen

DL-Meas

UL ModeCommand

UL QualityIndicator

DL Mode Request

DL Quality Indicator

DL codec mode(received)

UL Mode Commandreceived)



. Mode Indications: inform the receiver about the currently applied codecmode

. Mode Commands: inform the MS about the codec mode to be applied onthe uplink

. Mode Requests: inform the BTS about the preferred codec mode on thedownlink

Codec mode information is transmitted inband in the speech TCH, using parts ofthe transmission capacity dedicated to speech data transmission.

The network controls the channel mode to be used (TCH/F or TCH/H). Uplinkand downlink always apply the same channel mode.

For codec mode adaptation (LA), the receiving side performs link qualitymeasurements of the incoming link. The measurements are processed yielding aQuality Indicator.

For uplink adaptation, the Quality Indicator is directly fed into the uplink modecontrol unit. This unit compares the Quality Indicator with AMR codec setthresholds and generates, when necessary, a Mode Command indicating thecodec mode to be used on the uplink. The Mode Command is then transmittedinband to the MS where the incoming speech signal is encoded in thecorresponding codec mode.

For downlink adaptation, the DL Mode Request Generator compares the DLQuality indicator with the same AMR codec set thresholds as the BTS andgenerates, when necessary, a Mode Request indicating the preferred codec modefor the downlink. The Mode Request is transmitted inband to the network sidewhere it is fed into the DL Mode Control unit in BTS. This unit grants therequested mode. The resulting codec mode is then applied for encoding of theincoming speech signal.

In the case of both uplink and downlink, the presently applied codec mode istransmitted inband within the Mode Indication together with the coded speechdata. At the decoder, the presently used codec mode is applied for decoding of thereceived speech data. The figure below illustrates an example of AMR linkadaptation.




Figure 3. An example of the AMR link adaptation

See also 3GPP 45.009 version 4.2.0.

Inband signalling

The following convention applies for the coding of the codec modes for theinband signalling (Mode Indications, Mode Commands, and Mode Requests).

00 CODEC_MODE_1 Represents the lowest codec mode (lowestbitrate).

01 CODEC_MODE_2 Represents the second lowest mode, if thecodec mode set includes more than one mode.

10 CODEC_MODE_3 Represents the third lowest mode, if the codecmode set includes more than two modes.

11 CODEC_MODE_4 Represents the highest mode, if the codecmode set includes four modes.

0 5 10 15 20 25 30

Time[s]

5

10

15

20

25

30

[dB]

12.2 kbit/s

7.4 kbit/s

5.9 kbit/s

4.75 kbit/s

C/I AMR

EFR operationC/I AMR mode



If less than 4 codec modes are used, the unused Mode Indications and ModeCommands/Mode Requests are not signalled. The inband signalling decoder doesnot detect the unused codec modes.

Codec modes are constrained to change only every second speech frame. ModeCommands or Mode Requests are sub-sampled so that they occur only everysecond frame. It is also possible to limit the Mode Commands to occur only onSACCH frame interval. For more information, see 3.2.1 AMR link adaptationfrom the BSC viewpoint.

The MS applies the corresponding mode at the reception of a Mode Command.The MS applies the signalled mode for the speech frame transmitted eightTDMAframes after the reception of the last TDMA frame containing the ModeCommand. The BTS should apply the requested mode for the earliest possiblespeech frame, unless the BTS intends to override the MS Mode Request.

Codec mode adaptation

Channel quality measurement:

Codec mode adaptation is based on a normalised one-dimensional measure of thechannel quality, called the Quality Indicator. For reference purposes, the QualityIndicator is defined as an equivalent carrier to interferer ratio, C/Inorm. The MSand the BSS continuously update the Quality Indicator estimates.

The Quality Indicator is derived from an estimate of the current burst bit errorprobability (BBEP), which is calculated from burstwise soft values in EqualizerDigital Signal Processor (EQDSP). The (logarithmic) BBEP values are sent toChannel Digital Signal Processor (CHDSP) and they are handled by a filter,which smooths out the BBEP signal (the sequence of BBEP values) and controlsfast codec changes, if needed. After that the filtered BBEP value is mapped to theC/I value.

Definition of Mode Command and Mode Request decision thresholds:

For codec mode adaptation, the channel Quality Indicators are mapped to ModeCommands/Requests. Hysteresis in the mapping from Quality Indicators to ModeCommands/Requests should be used to prevent undesirable fast switching ofMode Commands and Mode Requests. The degree of hysteresis is controlled byappropriately setting the upper and lower decision thresholds. For reasons ofchannel error robustness of the codec mode information, both Mode Commandsand Requests are restricted to change at maximum to their nearest neighbours.This means that mode switches to modes that are not direct neighbours to theprevious transmitted mode are prohibited.




The Mode Command and Mode Request decision thresholds are defined at callset-up and/or handover by layer 3 signalling. The AFS and AHS have their ownthresholds and hysteresis limits of codec modes. For each pair of neighbouringcodec modes in the codec mode set, a threshold and a hysteresis value in terms ofnormalized carrier to interference ratio (C/Inorm) is defined. The lower decisionthreshold for switching from mode j to mode j-1 is given by the signalledthreshold. The threshold is referred to as THR_MC_Dn(j) or THR_MR_Dn(j).

The sum of the signalled threshold and hysteresis constitutes the upper thresholdbetween the codec modes, referred to as THR_MC_Up(j-1) or THR_MR_Up(j-1). The figure below illustrates the definition of the decision thresholds, and theoperational range of the codec modes.

Figure 4. Definition of Threshold and Hysteresis for codec mode adaptation

The network gives the switching thresholds in a consistent order:

. THR_1 ≤ THR_2 ≤ THR_3,

. THR_1 + HYST_1 ≤ THR_2 + HYST_2 ≤ THR_3 + HYST_3

Table 3. Description of THR and HYST parameters.

Parameter name Description Range Bits

THR_1/2/3 Lower thresholds for switching betweenmode j and j-1

0-63 6

CODEC MODE 3

CODEC MODE 2

CODEC MODE 4

CODEC MODE 1

C/l

THR 3 + HYST 3 =THR MX Up(3)



THR 3 =THR MX Dn(4)

=THR MX Dn(3)

=THR MX Dn(2)THR 1

THR 2



Table 3. Description of THR and HYST parameters. (cont.)

HYST_1/2/3 Hysteresis values to obtain the higherthresholds for switching between mode jand j+1

0-15 4

A threshold (THR) is given as an absolute value in 0.5 dB steps.

Table 4. Mapping of the THR values between 0 and 63 to normalised C/I.

THR 1/2/3 0 = 0.0 dB

THR 1/2/3 1 = 0.5 dB

THR 1/2/3 2 = 1.0 dB

THR 1/2/3 :

THR 1/2/3 :

THR 1/2/3 62 = 31.0 dB

THR 1/2/3 63 = 31.5 dB

Note

The threshold for codec mode j should be set to a normalised C/I value so thatcodec mode j starts to degrade and that a frame error rate (FER) of less than1% is observed. The hysteresis range is defined in 0.5 dB steps.

Table 5. Mapping of the HYST values between 0 and 15 to C/I.

HYST 1/2/3 0 = 0.0 dB

HYST 1/2/3 1 = 0.5 dB

HYST 1/2/3 2 = 1.0 dB

:

:

HYST 1/2/3 14 = 7.0 dB

HYST 1/2/3 15 = 7.5 dB




Initial codec mode selection at call set-up and handover

The initial codec mode to start the speech call at call set-up and after handovermay be signalled within the AMR codec set, in which case it is used by the BTSand the MS.

If the Initial Codec mode is not signalled, which is the default operation mode ofthe BSC, the initial codec mode used by the BTS and the MS is given by thefollowing rule:

. if the codec mode set contains 1 mode, it is the Initial Codec mode

. if the codec mode set contains 2 or 3 modes, the Initial Codec mode is themost robust mode of the set with the lowest bit rate.

. if the codec mode set contains 4 modes, the Initial Codec mode is thesecond most robust mode of the set with the second lowest bit rate.

3.2 Radio resource management with EnhancedSpeech Codecs

General principles in TCH allocation

The Channel Type information element (IE) received initially in theASSIGNMENT REQUEST or HANDOVER REQUEST message from the Ainterface primarily determines the radio channel to be allocated for a call.

In the assignment and external handover request, the preferred channel rate is theprimary requirement if the alternative channel rates are given. The additionalrequirement concerning the prohibition of channel rate and speech codec changesafter the first channel allocation is taken into account in all handovers from atraffic channel (TCH) to another TCH. In handovers based on the Directed Retryprocedures, the channel rate requirements are treated as in a normal assignment.If BSS/BTS parameters allow channel rate/speech codec changes, a change isneeded because of channel configuration in a BTS, the speech codecs arechanged primarily within the channel rate and secondarily between channel rates.

Besides the Channel Type IE, the type of the pool from which the MSC hasallocated the A interface circuit (the CIP information) is a significant parameterfor TCH allocation. The channel rate of the allocated TCH must coincide with theChannel Type and the CIP type of the A interface circuit. The CIP information isinitially received from the BSC which has coded it according to the type of thecircuit identified in the Circuit Identification Code (CIC) IE received from the Ainterface in the ASSIGNMENT REQUEST or HANDOVER REQUESTmessage.



In addition to the TCH rate requirement, speech codec requirement and the pooltype, the channel configuration and speech codec support of the BTS aresignificant in the TCH allocation procedure:

1. If the A interface circuit fully supports the channel rate and speech codecrequirement of the resource request, the BTS resource situation and theBTS speech codec support are the only reasons for success or failure in theTCH allocation attempt. In a failure case, the return code of the channelallocation algorithm is No radio resource available for BTS resourcesituations and Requested Speech Version Unavailable for BTS speechcodec support cases.

2. If the A interface circuit only supports the preferred channel rate, that is, atleast one of the speech codecs specified as preferred in the resourcerequest, the following takes place, depending on the TCH configuration ofthe BTS and the BTS speech codec support:. When the pool does not support the preferred codec, but the BTS

has the preferred channel rate type of TCH resources free, thepreferred type of TCH is allocated and another codec is used. This isdone although there is a suitable pool on the A interface and the BTSsupports the preferred speech codec of that channel rate. The reasonfor not switching the pool is because this way a more advancedcodec for the call is achieved. It is only applied when a channelcannot be reserved for the preferred channel mode. The pool is thenswitched to support the allocation of channel for the other channelmode.

. If the BTS has only the non-preferred channel rate type of TCHresources free and the BTS supports at least one of the speechcodecs of that channel rate, the TCH allocation attempt fails with thecause Switch Circuit Pool. If the indicator allows the immediate Ainterface pool switching, both the queuing of the TCH resource andthe Directed Retry are denied.

. If the non-preferred channel rate type of TCH resources are alloccupied and the BTS supports at least one of the speech codecs ofthat channel rate, the TCH allocation attempt fails with the causeSwitch Circuit Pool. Both the queuing of the TCH resource and theDirected Retry are allowed.

. If the BTS has only the non-preferred channel rate type of TCHresources free or configured, but the BTS does not support therequested speech codecs of that channel rate, the TCH allocationattempt fails with the cause Requested Speech Version Unavailable.

. If the BTS has only the preferred channel rate type of TCH resourcesconfigured, but not free, the TCH allocation attempt fails with thecause No Radio Resource Available. Both the queuing of the TCHresource and the Directed Retry are allowed.




3. If the A interface circuit only supports the non-preferred channel rate, andif there is at least one of the speech codecs of non-preferred channel rate inthe resource request, the following takes place, depending on the BTSconfiguration and the BTS speech codec support:. If the BTS has the preferred type of working TCHs free and it

supports at least one of the preferred speech codecs, the TCHallocation attempt is immediately interrupted with the cause SwitchCircuit Pool. Both the queuing of the TCH resource and the DirectedRetry are denied.

. If the BTS has the preferred type of working TCHs free, but itsupports none of the preferred speech codecs or when the BTS hasno preferred type of working TCHs free, but it supports at least oneof the preferred speech codecs, the following takes place, dependingon the TCH configuration and speech codec support of the BTS:. When the pool does not support the preferred codec of the

non-preferred channel rate and the BTS has the preferredchannel rate type of TCH resources free, the non-preferredtype of the TCH is allocated and another codec is used. Thisis done although there is a suitable pool on the A interface,because the reason for pool switching is not to achieve a moreadvanced codec for the call.

. If the BTS has the preferred channel rate type of workingTCH resources and it supports at least one of the preferredspeech codecs, the TCH allocation attempt fails with thecause Switch Circuit Pool. Both the queuing of the TCHresource and the Directed Retry are denied.

. If the BTS has the preferred channel rate type of workingTCH resources free, but the BTS supports none of thepreferred speech codecs, the TCH allocation attempt failswith the cause No Radio Resource Available. Both thequeuing of the TCH resource and the Directed Retry areallowed.

. If the BTS has no working preferred channel rate type of TCHresources configured at all, the TCH allocation attempt failswith the cause No Radio Resource Available. Both thequeuing of TCH resource and Directed Retry are allowed.

Traffic channel allocation and speech codec selection

The TCH rate to be allocated is determined initially in the ASSIGNMENTREQUEST message, or in the HANDOVER REQUEST message in an externalhandover procedure case. As an attachment to channel rates, there is also a list ofpreferred speech codecs. The expected rate can be specified to be uniquely eitherFR or HR. However, FR or HR can be set to be only the preferred rate; if thepreferred channel type is not available at the moment, a channel of the other rateis accepted, too. The latter case also contains information on whether the channel



rate is allowed to be changed or not as a result of a new request after the first TCHallocation. You can override this constraint and set the AMR FR as the morepreferred speech codec over AMR HR during assignments and handovers, exceptin the case of FACCH call set-up and an intra-cell handover.

You can prohibit the channel rate and the speech codec changes during internalhandovers within the BSS area and during external handovers using the MMI.Additional constraints for channel rate and speech codec selection in internal andexternal handovers can be defined both on BSS and BTS level. In the case ofAMR, it is also possible to define which AMR codec sets the BSC prefers duringan external handover. The choices are:

. the AMR codec set of the BTS

. the currently used one coming from the MSC

The A interface circuit type allocated by the MSC brings an additional constraintto the channel allocation procedure. The type of the traffic channel that is going tobe allocated must match the type of the A circuit. If it does not, the BSC can try tochange the A interface circuit by sending an ASSIGNMENT or a HANDOVERFAILURE message with a cause value which indicates to the MSC that the Ainterface circuit type should be changed. The BSC always first determines thetype of the TCH to be allocated. This is done on the basis of the following:

. the TCH rate and speech codec requirements received from the MSC

. the TCH configuration and resource situation of the BTS

. the actual A interface circuit pool configuration

The supported speech codec that is the primary choice is selected, unless AMRFR is selected because it is preferred over AMR HR.

If the MSC has initially allocated the circuit from an unsuitable type of pool, anattempt is made to change the A interface circuit to a suitable one matching thetype of the TCH after the decision of the TCH to be allocated has been made. Thecircuit pool type restricts the selection of the TCH radio resource when it is notfully matching the TCH type requirement and there is no other type of A interfacecircuit free.

Channel rate and speech codec control in internal and external handovers

Channel rate and speech codec control in handovers are controlled with thefollowing parameters:

. TCH rate internal handover

. TCH rate intra—cell handover




For more information, see Half Rate in BSC, section Channel rate and speechcodec control in handovers.

The BSC-specific parameter AMR configuration in handovers controlsthe selection of the AMR codec set during internal and external handovers.

The BSC-specific parameter AMR set grades enabled controls the codecmode set downgrades during internal inter-cell handovers and upgrades afterinternal inter-cell handovers. The source side downgrade is used to align thesource side codec set with the one chosen for the target side, to use the uni-directional downlink connection for the target side. The use of uni-directionaldownlink connection decreases the amount of muting experienced in the speechpath connection during an internal handover. The target side upgrade is made touse the original AMR codec set of the target BTS which was not chosen for thetarget side because of target side alignment with the source side during an internalhandover. The reason for this alignment is the same as in the downgrade case.

By default, downgrades and upgrades are not enabled. For more information, seealso section Schemes in Enhanced Speech Codecs, AMR Codec Set DowngradesAnd Upgrades During Internal Inter-Cell Handovers.

Handling of AMR FR and AMR HR codec sets

There are some restrictions related to the content of AMR HR codec set:

1. The AHS 7.4 mode should not be used alone in the AMR HR codec set. Atleast one codec mode lower than 6.7 should be included.

2. The use of AHS 6.7 mode alone or together with the 7.4 mode is notrecommended in the AMR HR codec set. At least one codec mode lowerthan 6.7 should be included.

3. If the ICM field in the AMR HR codec set is taken into use, the 7.4 modeshould not be used as the ICM mode. It is not recommended to use the 6.7mode as the ICM mode.

The restrictions are based on 3GPP specification 48.061 In-band control ofremote transcoders and rate adaptors for half rate traffic channels, chapter FrameSyncronisation/8 kbit/s Submultiplexing/For Adaptive Multi-Rate Speech.

The frame synchronisation for the speech frames for codec mode 6.70 Kbit/s isobtained by a 6-bit pattern, which is indicated by all the bits set to binary '0' orbinary '1'. This codec mode may be used for Initial Synchronisation, but thepreferred solution is to use a lower code mode or No_Speech frames. InitialSynchronisation is started after resource allocation and after a loss ofsynchronisation.



The frame synchronisation for the speech frames for codec mode 7.40 kbit/s isobtained by a 6-bit pattern, which is indicated by all the bits set to binary '0' orbinary '1'. This codec mode should not be used for Initial Synchronisation; therecommended solution is to use a lower code mode or No_Speech frames.

AMR FR and AMR HR codec sets are handled with parameters AMR FR codecmode set and AMR HR codec mode set.

AMR sets include AMR codec mode set (1-4 codecs), their threshold andhysteresis values and initial codec mode definition. The radio network databaseobject for codec sets is the BTS. A set is disabled by setting codec mode setparameter as 0. If AMR is not included in the software build, the modificationcommand for codec sets is not visible. However, default AMR sets are entered tothe BTS during the BTS creation (EQC command). AMR codec set modificationdoes not require the locking of the BTS.

Table 6. The basic codec sets for AMR FR

CodecMode Threshold (C/I) Hysteresis (C/I)

12.2 11 1

7.4 7 1

5.9 4 1

4.75

Table 7. The basic codec sets for AMR HR

CodecMode Threshold (C/I) Hysteresis (C/I)

7.4 14 1

5.9 11 1

4.75

By default, the BSC does not give the element Initial Codec Mode. Instead, it isdefined by the implicit rule provided in 3GPP 45.009. The default sets above arebased on the support of Nokia Talk-Family BTS.




Channel rate for AMR calls

By default, a channel for an AMR call is allocated as for any other speech call.Another option is to allocate a full rate channel for an AMR call, if possible,despite the original rate preference (full rate must be allowed), the cell load andthe constraints set for handovers.

If it is not possible to allocate a full rate channel for an AMR call, the allocationprocedure is continued as usual and the restrictions mentioned earlier are takeninto account.

This function is applied in call setup (except in FACCH call setup), internal inter-cell handover and external handover. The reason behind this function is that thesignal quality may not be sufficient for a half rate AMR call setup.

This function is controlled by the BSC-level parameter initial AMRchannel rate. The parameter can be handled with commands EEM and EEO.

. Channel rate control in handovers

The constraints set for handovers do not restrict the allocation of a full ratechannel for an AMR call if the parameter initial AMR channel ratestates that the full rate is preferred for AMR calls.

. Channel rate selection based on cell load

Cell load based channel rate selection does not restrict the allocation of afull rate channel for an AMR call if the parameter initial AMRchannel rate states that the full rate is preferred for AMR calls.

TCH allocation optimisation based on the cell load

The function is based on intra-cell HOs between AMR channel rates and iscontrolled with the following parameters:

. lower limit for FR TCH resources: determines the limit value forthe decreasing amount of available FR TCH resources of a cell from whichexisting AMR FR calls are handed over as AMR HR calls

. upper limit for FR TCH resources: determines the limit value forthe increasing amount of available FR TCH resources of a cell when thehanding over of AMR FR calls as AMR HR calls is stopped

The parameters can be handled at both BSS-level (HRL and HRU) and BTS-level(FRL and FRU). The default values for the lower and upper limit are set so thatTCH allocation optimisation is off.



TCH allocation optimisation is triggered by any new channel allocation, unlessthe previous optimisation case is unfinished. After a new channel allocation anintra-cell HO is performed for a certain number of AMR FR calls. The number isdefined so that the number of free full rate resources increases by one whencompared to the situation before the new channel allocation. Handovers areperformed for AMR FR calls whose quality is above the intra HOthreshold Rx qual AMR FR threshold for AMR FR. Queuing is forbidden forthe packing procedure. The figure below is an example of TCH allocationoptimisation. Packing in the figure refers to the handovers from AMR FR toAMR HR.

Figure 5. An example of TCH allocation optimisation

Channel rate change restrictions from the MSC do not prevent optimisation. Butthe channel rate and speech codec controlling parameters TCH rate internalhandover and TCH rate intra-cell handover cause the followingrestriction for applying the cell load threshold parameters: if the channel rate andspeech codec changes are denied totally, they will not be allowed due to the cellload dependent conditions.

Free FR TCHs

Upper limit for freeFR TCHs

Lower limit for freeFR TCHs

TimePacking of

AMR FR calls

No packing ofAMR FR calls

No packing ofAMR FR calls




AMR HR calls are handed over back to AMR FR calls when the quality of anAMR HR call degrades below the intra HO threshold Rx qual AMR HRthreshold for AMR HR or when the signal strength of an AMR HR call degradesbelow the HoThresholdsLevDL or HoThresholdsLevUL and at the sametime the quality of an AMR HR call degrades below the intra HO thresholdRx qual AMR HR threshold for AMR HR. Cell load does not have an effect.Queuing is allowed while AMR HR calls are handed over back to AMR FR callsand channel rate change restrictions from the MSC do not prevent it.

For more information, see Half Rate in BSC, section Channel rate selectionbased on cell load.

When the speech codec is changed during an internal handover, such as an intra-cell handover between AMR channel rates, there is a short break in the downlinkspeech path because, in this case, a unidirectional connection cannot beestablished. However, the BSC can change these handovers to external handoversin order to enable a unidirectional connection and in this way avoid downlinkmuting. For more information, see Radio Channel Allocation, section TCH ratein internal handover.

AMR link adaptation from the BSC viewpoint

The BSC-specific parameter slow AMR LA enabled controls the AMR linkadaptation (LA) mode within the BSS. Alternatives are the fast and the slow LA.During the fast LA mode, the BTS allows the inband codec mode changes onevery other TCH frame. During the slow LA mode, the BTS allows inband codecmode changes only on SACCH frame interval.

The slow LA mode offers the best flexibility with handover and power controlalgorithms (with mode reporting), and better mapping between the used codecmode and the experienced quality on the network. By default, the slow LA modeis not enabled, which means that the fast LA mode is used.

For more information on AMR counters for FR and HR codec modes used onuplink and downlink with different RxQual classes, see 107 AMR RX QualityMeasurement.

At the end of the Multirate Configuration IE, the BSC indicates to the BTS whichLA mode is used. This is done during the channel activation procedure. The BTSindicates in the MEASUREMENT RESULT message the first and the last usedcodec mode and the average quality during the last measurement interval. Thisindication is valid during both LA modes and it covers both uplink and downlink.Reactions to these measurements in RX quality cases of power control (PC) andhandover (HO) algorithms are the following:



. If the quality is below the lower AMR-specific thresholds, either morepower or HO is triggered depending on whether the PC or the HO limit istriggered first. If the quality is above the lower AMR-specific thresholds,nothing is done.

. If the quality is above the upper AMR-specific thresholds, less power istriggered. If the quality is below the upper AMR-specific thresholds,nothing is done. The above cases are valid only in quality HOs, not forexample in power budget HOs.

For an overview, see Overview of Enhanced Speech Codecs: AMR and EFR.






4 Effect of AMR and EFR on interfacesA interface

Informationelement Description Used in messages

Channel Type Contains all the information that the BSC needsto determine the required radio resource(s).

Includes the permitted speech codecs and thechannel rate preference.

ASSIGNMENT REQUEST

HANDOVER REQUEST

Circuit Pool Indicates the circuit pool of a circuit or a group ofcircuits.

ASSIGNMENT COMPLETE

HANDOVER REQUEST ACK

ASSIGNMENT FAILURE

HANDOVER FAILURE

Circuit Pool List Defines a list of BSC-preferred circuit pools in theorder of preference.

HANDOVER REQUIRED

ASSIGNMENT FAILURE

HANDOVER FAILURE

Chosen Channel Contains a description of the channel allocated tothe MS in the target BSS.

Channel Mode field indicates the use of thechannel: signalling, speech, or data.

Channel field indicates the channel: SDCCH orTCH.

ASSIGNMENT COMPLETE

HANDOVER PERFORMED


Speech Version Indicates the speech version being used in thesource BSS and the one chosen in the targetBSS.

The used speech version is coded in the sameway as the permitted speech version identifier inthe Channel Type element.

ASSIGNMENT COMPLETE

HANDOVER PERFORMED

HANDOVER REQUIRED

HANDOVER REQUEST


Current ChannelType 1

Contains a description of the channel being usedin the source BSS.

Channel Mode field indicates the use of thechannel: signalling, speech, or data.

Channel field indicates the channel: SDCCH orTCH.

HANDOVER REQUIRED

HANDOVER REQUEST



Effect of AMR and EFR on interfaces


Old BSS To NewBSS

General container for passing Field Elementstransparently between BSSs via the MSC.

The MultiRate Configuration Information fieldcontains the AMR codec set being used in thesource BSS.

HANDOVER REQUIRED

HANDOVER REQUEST

Abis interface


Channel Mode Gives information on the mode of coding/decoding and transcoding/rate adaption of achannel.

Includes the chosen speech codec and channelrate.

CHANNEL ACTIVATION

MODE MODIFY

MultiRateConfiguration

Gives a description of the multirate speechcodec configuration, that is, AMR codec set, tobe applied.

CHANNEL ACTIVATION

MODE MODIFY

Cause The following cause value is significant duringchannel activation and channel mode modifyprocedures:

Mandatory Information Element Error: If anattempt is made to activate a radio channel for acall with a speech codec not supported by theBTS.

CHANNEL ACTIVATION NACK

MODE MODIFY

Radio interface


Channel Mode Gives information on the mode on coding/decoding and transcoding.

Includes the chosen speech codec.

The chosen channel rate is defined moreprecisely in the Channel Description 2 element.

ASSIGNMENT COMMAND

DTM ASSIGNMENT COMMAND

HANDOVER COMMAND

CHANNEL MODE MODIFY

CHANNEL MODE MODIFY ACK

MultiRateConfiguration

Gives all parameters related to a multi-ratespeech codec, that is, AMR codec set.

ASSIGNMENT COMMAND

DTM ASSIGNMENT COMMAND

HANDOVER COMMAND

CHANNEL MODE MODIFY



Related topics

. Overview of Enhanced Speech Codecs: AMR and EFR

. Activating and Testing AMR




Effect of AMR and EFR on interfaces



5 Schemes in AMR and EFR

5.1 Assignment

In a mobile-originating call, the MS indicates the preferred speech codecs in theBearer Capability Information Element (IE) for the SETUP message.

In a mobile-terminating call, the CALL CONFIRMED message indicates thepreferred speech codecs. The MSC/VLR can limit the possible speech codecsbased on subscriber data and operator settings.

Assignment procedure, basic scheme



Schemes in AMR and EFR

Figure 6. Assignment procedure, basic scheme

disc

ua

MS BTS BSC MSC

assignment_request1

physical_context_request2

physical_context_confirm3

channel_activation4

channel_activation_ack5

assignment_command6

sabm7

establish_indication8

ua9

assignment_complete10


**** CONVERSATION PHASE ****

**** RELEASE OF A CALL ****

clear_command12

channel_release13

deactivate_sacch14

15

16release_indication

17rf_channel_release

18rf_channel_release_ack

19clear_complete

20rlsd

21rlc

22



1. The MSC starts the assignment procedure by sending anASSIGNMENT REQUEST message to the BSC. In themessage, the MSC indicates the permitted speech codec(s)in the order of preference in Channel Type IE. The BSCuses this information in the selection process and stores itfor the duration of the call.

2. The BSC checks that the Permitted Speech VersionIdentifiers are valid and correspond to the channel raterequirements. If not, the assignment procedure isinterrupted with the A interface cause invalid messagecontents.

The BSC removes all non-supported speech codecs fromthe Channel Type IE list and checks if the enhancedspeech codecs are allowed to be used in the BSC. If theyare not allowed to be used and the MSC offers them andpossibly other non-supported codecs, an ASSIGNMENTFAILURE message with the cause requested speechversion unavailable is sent to the MSC.

The BSC checks the compatibility of the TCH type andthe speech codecs initially presented in the Channel TypeIE of the ASSIGNMENT REQUEST with the pool of theA interface circuit implied by the circuit identificationcode (CIC) IE of the ASSIGNMENT REQUEST message:

. If there is no circuit pool on the A interface able tosupport the requested type of TCH and speechcodec, the ASSIGNMENT FAILURE message withthe cause requested speech version unavailable issent to the MSC.

. If there is a circuit pool on the A interface which isable to support the requested type of TCH andspeech codec but the pool implied by the CIC iscontradictory with the TCH type and speech codecrequirement, the ASSIGNMENT FAILUREmessage with the cause circuit pool mismatch issent to the MSC. The message contains the CircuitPool IE which indicates the pool of the A interfacecircuit implied by the CIC and the Circuit Pool ListIE.

The BSC expects a new ASSIGNMENTREQUEST or CLEAR COMMAND message fromthe MSC. If the pool of the A interface circuitimplied by the CIC of the new ASSIGNMENT




REQUEST message is still contradictory with theTCH type and the speech codec, an ASSIGNMENTFAILURE message with the cause circuit poolmismatch is again sent to the MSC.

The BSC stores all the preferred and supported speechcodecs.

4. In the channel allocation procedure, the BSC always firstdetermines the TCH type to be allocated on the basis of theTCH rate and speech codec requirements received fromthe MSC. After that, the BSC determines the TCHconfiguration and resource situation of the BTS, thespeech codec support of the BTS and the actual Ainterface circuit pool configuration. During the TCHselection, the supported speech version that is the primarychoice is selected. However, if AMR HR is preferred andthe parameter initial AMR channel rate prefersAMR FR, it is selected, if available, despite the otherrequirements. The parameter initial AMR channelrate is not valid if only AMR HR is allowed in therequest. AMR is not selected if the AMR codec set of thetarget channel rate is disabled. In that case, anothersupported speech codec is selected.

In case of AMR, the codec set must also be selected. Inassignment, it is always the one defined for the targetchannel rate in the BTS.

After carrying out the channel allocation, the BSCacknowledges the chosen channel and the chosen speechcodec and sets the chosen speech codec to be sent to theBTS in the CHANNEL ACTIVATION message.

The chosen speech codec is included in the Channel Modeelement of the CHANNEL ACTIVATION message. Incase of AMR, the chosen codec set and the LA mode arealso included.

In all the procedures, the BSC maps the A interface codecvalue to the Abis interface codec value on the principlethat the same types and versions of codecs are used. Forexample, FR version 2 on the A interface is FR version 2on the Abis interface.

The BTS then continuously informs the TCSM by TRAUframe about the use of the selected codec.

6. After receiving the CHANNEL ACTIVATION ACKmessage from the BTS, the BSC sends theASSIGNMENT COMMAND message to the MS. Thismessage includes the selected speech codec in the element



Channel Mode. In case of AMR, the selected codec set isalso included if the assigned configuration is new, that is,different from the configuration of a previously allocatedchannel. After receiving the ASSIGNMENT COMMANDmessage, the MS uses the Initial Codec Mode of AMRspecified in the Multirate Configuration IE, if present, orapply the implicit rule defined in 3GPP 45.009.

In all the procedures, the BSC maps the A interface codecvalue to the radio interface codec value on the principlethat the same types and versions of codecs are used. Forexample, FR version 2 on the A interface is FR version 2on the radio interface.

10. If the MS supports the indicated mode, it returns anASSIGNMENT COMPLETE message. In case of AMR,the link adaptation starts on the assigned channel betweenthe MS and the BTS, and it is independent of the powercontrol (PC) and handover (HO) control of the BSC.

If the MS does not support the indicated mode or theMultirate Configuration is inconsistent, the MS returns anASSIGNMENT FAILURE message with the causechannel mode unacceptable. It remains on the currentchannel and uses the old mode.

Also, if during the initial assignment of the multiratespeech the MS receives an ASSIGNMENT COMMANDmessage and the Multirate Configuration IE is not present,the MS returns an ASSIGNMENT FAILURE messagewith cause channel mode unacceptable. It remains on thecurrent channel and uses the old mode. AnASSIGNMENT FAILURE message is sent to the MSCwith the cause radio interface failure, reversion to oldchannel.




11. After receiving the ASSIGNMENT COMPLETE messagefrom the MS, the BSC indicates the chosen channel andthe chosen speech codec to the MSC in theASSIGNMENT COMPLETE message. The ChosenChannel is included when the MSC gives the BSC thepossibility to select the channel rate/type. A new element,Speech Version (chosen) is used to indicate the chosenspeech codec. Speech Version (chosen) is included whenthe MSC gives the BSC the possibility to select the speechversion.

The circuit pool of the A interface circuit implied by theCIC in the ASSIGNMENT REQUEST is sent to the MSCin the Circuit Pool element of the ASSIGNMENTCOMPLETE message when there is more than one poolon the A interface.

13. The BSC stores the preferred speech codecs for theduration of the call.

Assignment procedure, switching of A interface circuit pool

Figure 7. Assignment procedure, switching of A interface circuit pool

MS BTS BSC MSC

assignment_request1

assignment_failure2

assignment_request3



1. The MSC starts the assignment procedure by sending theASSIGNMENT REQUEST message to the BSC. In themessage, the MSC indicates the permitted speech codec(s)in the order of preference (in Channel Type IE).

2. The BSC can send an ASSIGNMENT FAILURE messagewith the cause switch circuit pool if the circuit poolimplied by the CIC is at least partially compatible with therequested TCH type and speech codec. The reason for thechanging of the pool is the actual traffic channel resourcesituation of the cell. The message contains the Circuit Poolelement of the A interface circuit implied by the CIC andthe Circuit Pool List element.

Note

The message can be delayed due to queuing for TCH resources, in otherwords received by the MSC after the QUEUING INDICATION message, orDirected Retry attempt.

3. The BSC expects a new ASSIGNMENT REQUEST orCLEAR COMMAND message from the MSC. If the poolof the A interface circuit implied by the CIC of the newASSIGNMENT REQUEST message is the same as in thefirst ASSIGNMENT REQUEST message, the TCH isallocated among those TCHs that the pool supports. AnASSIGNMENT FAILURE message with the cause noradio resource available is sent to the MSC if the allocationof the TCH is not successful.




5.2 External handover

External handover, source BSC

Figure 8. External HO, source BSC

MS BTS BSC MSC

HO measurements, HO decision and inquiry-evaluation -> external HO attempt

measurement_report1

measurement_result2

handover_required3

TCH reservation and activation in target BSC,HO command from MSC, signalling on FACCH-TCH

handover_command4

handover_command5

Signalling on FACCH-TCH in target BSC,disconnection, TCH release in source BSC

clear_command6

rf_channel_release7

rf_channel_release_ack8

clear_complete9



3. The source BSC starts the external handover by sendingthe HANDOVER REQUIRED message to the MSC. Inthe message the BSC indicates the currently used channel.It also indicates the currently used speech codec if it is aspeech call and the MSC has given the BSC the possibilityto choose the speech codec in the previous assignmentprocedure or external handover procedure. In case ofAMR, the currently used multirate configuration is alsoincluded.

The BSC sends the HANDOVER REQUIRED messagewith the cause switch circuit pool if an A interface circuitpool change is required during a handover. The message issent if the successful allocation of a suitable TCH andspeech codec in an intra-BSS handover requires a poolchange. The message contains the Circuit Pool List IE.The BSC expects a HANDOVER REQUEST messagewith the cause switch circuit pool or a HANDOVERREQUIRED REJECT message from the MSC.

4. The MSC delivers the radio interface HANDOVERCOMMAND to the source BSC in the HANDOVERCOMMAND message.

5. The radio interface HANDOVER COMMAND messageis sent to the MS. If the channel mode indicates that amultirate speech codec must be applied, and the MultirateConfiguration IE is not included in the HANDOVERCOMMAND message, the MS assumes that the multirateconfiguration has not changed. For the Initial Codec Modeof AMR, the MS uses the previously received InitialCodec Mode, if any, or applies the implicit rule defined in3GPP 45.009.

If the MS does not support the indicated mode or theMultirate Configuration IE is inconsistent, the MS returnsa HANDOVER FAILURE message with the causechannel mode unacceptable, remains on the currentchannel and uses the old mode. A HANDOVERFAILURE message is sent to the MSC with the causeradio interface failure, reversion to old channel.

7. The BSC stores the preferred speech codecs for theduration of the call.




External handover, target BSC, basic scheme

Figure 9. External HO, target BSC, basic scheme

ua

MS BTS BSC MSC

HO measurements and external HO decision madein the source BSC, the MSC sends HO request

handover_request1

TCH reservation and activation in target BTS

channel_activation2


handover_request_ack4

Signalling on FACCH-TCH in target BTS, connection

handover_access5

handover_detection6

handover_detect7

physical_information8

sabm9


11handover_complete

12

handover_complete13



1. The MSC sends a HANDOVER REQUEST message tothe target BSC and indicates the permitted speech codec(s)in the order of preference (in Channel Type IE) andoptionally the currently used speech codec (SpeechVersion (used) element), currently used channel (CurrentChannel element) (if received in the Handover Requiredmessage), and the currently used multirate configuration ifAMR is in question (if received in the Handover Requiredmessage).

2. The BSC checks that the Permitted Speech VersionIdentifiers are valid and correspond to the channel raterequirements. If not, the handover procedure is interruptedwith the A interface cause invalid message contents.

The BSC removes all non-supported speech codecs fromthe Channel Type IE list and checks if the enhancedspeech codecs are allowed to be used in the BSC. If theyare not allowed and the MSC offers them and possiblyother non-supported codecs, a HANDOVER FAILUREmessage with the cause requested speech versionunavailable is sent to the MSC.

The BSC checks the compatibility of the TCH type andthe speech codec, initially presented in the Channel TypeIE of the HANDOVER REQUEST message, with the poolof the A interface circuit implied by the CIC IE of theHANDOVER REQUEST message:

. If there is no circuit pool on the A interface which isable to support the requested type of TCH andspeech codec, a HANDOVER FAILURE messagewith the cause requested speech version unavailableis sent to the MSC.

. If there is a circuit pool on the A interface which isable to support the requested type of TCH andspeech codec but the pool implied by the CIC iscontradictory with the TCH type requirement, aHANDOVER FAILURE message with the causecircuit pool mismatch is sent to the MSC. Themessage contains the Circuit Pool element whichindicates the pool of the A interface circuit impliedby the CIC and the Circuit Pool List element.




The BSC expects a new HANDOVER REQUESTor CLEAR COMMAND from the MSC. If the poolof the A interface circuit implied by the CIC of thenew HANDOVER REQUEST is still contradictorywith the TCH type and speech codec, aHANDOVER FAILURE with the cause circuit poolmismatch is again sent to the MSC.

The BSC stores all the preferred speech codecs.

In the channel allocation procedure, the BSC always firstdetermines the TCH type to be allocated on the basis of theTCH rate and speech codec requirements received fromthe MSC. Then the BSC determines the TCHconfiguration and resource situation of the BTS, thespeech codec support of the BTS and the actual Ainterface circuit pool configuration.

During the TCH selection, the most preferred supportedspeech version is chosen. The Current Channel andSpeech Version (used) are used in the BSC to helpdetermine which channel to allocate for a call. Forexample, if BSS parameters define that the current channeltype and speech codec should be kept, a channel isallocated according to the Current Channel and SpeechVersion (used), if it is not contradictory with therequirements of the Channel Type IE. If it is contradictory,the radio channel is allocated according to therequirements of the Channel Type IE, if codec and ratechanges are allowed in the BSC.

If AMR HR is preferred and the parameter initial AMRchannel rate prefers AMR FR, it is selected ifavailable, despite the other requirements. The parameterinitial AMR channel rate is not valid if only AMRHR is allowed. AMR is not selected, if the AMR codec setof the target channel rate is disabled. In that case, anothersupported speech codec is selected.

In case of AMR, the codec set must also be selected. TheHANDOVER REQUEST message may contain thecurrently used AMR codec set. Depending on theparameter AMR configuration in handovers, it iseither the currently used one, which is selected if it isavailable and suitable for the target BTS, or the onedefined for the target BTS.



The speech codec is changed during a handover if the callis handed over for example from an EFR-supporting BTSto a BTS not supporting EFR or vice versa, or if the TCHis going to be changed from FR to HR or vice versa. Thistakes place if the channel type allows changes and BSS/BTS parameters allow changes between channel rates andspeech codecs.


The chosen speech codec is included in the Channel ModeIE of the CHANNEL ACTIVATION message. In case ofAMR, the chosen codec set and LA mode are alsoincluded.

The BTS then continuously informs the TC by TRAUframe about the use of the selected codec.

4. After receiving the CHANNEL ACTIVATION ACKmessage, the BSC indicates the chosen channel andchosen speech codec to the MSC in the HANDOVERREQUEST ACKNOWLEDGE message. The ChosenChannel is included when the MSC gives the BSC thepossibility to select the channel rate/type. Speech VersionIE is used to indicate the chosen speech codec. SpeechVersion IE is included when the MSC gives the BSC thepossibility to select the speech version.

The HANDOVER REQUEST ACKNOWLEDGEmessage contains the radio interface HANDOVERCOMMAND to the MS. The chosen speech codec isincluded in the element Channel Mode. In the case ofAMR, the chosen multirate configuration is also includedif the assigned configuration is new, that is, different fromthe configuration of a previously allocated channel.

The circuit pool of the A interface circuit implied by theCIC of the HANDOVER REQUEST message is sent tothe MSC in the Circuit Pool element of the HANDOVERREQUEST ACK message when there is more than onepool on the A interface.

12. In case of AMR, the link adaptation starts on the assignedchannel between the MS and the BTS and it isindependent of the power and handover control of theBSC.




External handover, target BSC, switching of A interface circuit pool

Figure 10. External HO, target BSC, switching of A interface circuit pool

MS BTS BSC MSC

HO measurements and external HO decision madein source BSC, MSC sends HO request

handover_request1

handover_failure2

handover_request3



1. The MSC sends a HANDOVER REQUEST message tothe target BSC and indicates the permitted speech codec(s)in the order of preference (in Channel Type IE) andoptionally the currently used speech codec, the currentlyused channel (if received in the HANDOVERREQUIRED message) and the currently used multirateconfiguration if AMR is in question (if received in the HOmessage).

2. The BSC can send a HANDOVER FAILURE messagewith the cause switch circuit pool if the circuit poolimplied by the CIC is at least partially compatible with therequested TCH type and speech codec. The reason forchanging the pool is the actual traffic channel resourcesituation of the cell. The message contains the Circuit PoolIE of the A interface circuit implied by the CIC and theCircuit Pool List IE.

Note

The message can be delayed due to queuing for TCH resources, in otherwords, the MSC receives the message after the QUEUING INDICATIONmessage.

3. The BSC expects a new HANDOVER REQUEST orCLEAR COMMAND message from the MSC. If the poolof the A interface circuit implied by the CIC of the newHANDOVER REQUEST message is the same as in thefirst HANDOVER REQUEST message, the TCH isallocated among those TCHs that the pool supports. AHANDOVER FAILURE message with the cause no radioresource available is sent to the MSC if the allocation ofthe TCH is not successful.




5.3 Internal handovers

Internal handover, intra-cell

Figure 11. Internal HO, intra-cell

MS BTS BSC MSC

HO measurements, HO decision and inquiry

measurement_report1

measurement_result2

Physical context information

physical_context_request3

physical_context_confirm4

TCH reservation and activation

channel_activation5


Signalling on FACCH-TCH (old)

assignment_command7

Signalling on FACCH-TCH (new), connection

sabm8


ua10


handover_performed12

TCH (old) release in BTS

rf_channel_release13




5. In the channel allocation procedure, the BSC always firstdetermines the TCH type to be allocated on the basis of theTCH rate and speech codec requirements originallyreceived from the MSC. After that, the BSC determinesthe TCH configuration and resource situation of the BTS,the speech codec support of the BTS and the actual Ainterface circuit pool configuration.

During the TCH selection, the most preferred supportedspeech version is chosen. The chosen channel and thechosen speech codec are used in the BSC to helpdetermine which channel to allocate for a call. Forexample, if BSS parameters define that the current channeltype and speech codec should be kept, a channel isallocated according to the chosen channel and the chosenspeech codec. The parameter initial AMR channelrate does not have an effect during internal intra-cellhandovers. AMR is not selected, if the AMR codec set ofthe target channel rate is disabled. In that case, anothersupported speech codec is selected, if codec changes areallowed in the BSC.

In case of AMR, the codec set must also be selected.Depending on the parameter AMR configuration inhandovers it is either the currently used one, which isselected if it is suitable for the target channel rate, or theone defined for the target channel rate.

The speech codec is changed during a handover if the callis handed over, for example, from an EFR-supporting BTSto a BTS not supporting EFR or vice versa, or if the TCHis going to be changed from FR to HR or vice versa. Thistakes place if the channel type allows changes and theBSS/BTS parameters allow changes between channel ratesand speech codecs. During an AMR call, however, thechannel rate can change from FR to HR and vice versa,although the Channel Type denies changes.

For more information, see Functionality of EnhancedSpeech Codecs, TCH allocation optimisation based on thecell load.

Note

Changing AMR FR to AMR HR or vice versa causes a short break in thespeech path connection.





The chosen speech codec is included in the Channel Modeelement of the CHANNEL ACTIVATION message. Incase of AMR, the chosen multirate configuration and LAmode are also included.


7. After receiving the CHANNEL ACTIVATION ACKmessage from the BTS, the BSC sends theASSIGNMENT COMMAND message to the MS. Thismessage includes the chosen speech codec in the ChannelMode IE. In case of AMR, the chosen multirateconfiguration is also included if the assigned configurationis new, that is, different from the configuration of apreviously allocated channel.

11. If the MS supports the indicated mode, it returns anASSIGNMENT COMPLETE message. If the channelmode in the ASSIGNMENT COMMAND indicates that amultirate speech codec must be applied and the MultirateConfiguration IE is not included in the ASSIGNMENTCOMMAND message, the MS assumes that the multirateconfiguration has not changed. For the Initial Codec Modeof AMR, the MS uses the previously received InitialCodec Mode, if any, or applies the implicit rule defined in3GPP 45.009. AMR link adaptation starts on the assignedchannel between the MS and the BTS and it isindependent of the PC and HO control of the BSC.

If the MS does not support the indicated mode or theMultirate Configuration IE is inconsistent, the MS returnsan ASSIGNMENT FAILURE message with the causechannel mode unacceptable. It remains on the currentchannel and uses the old mode. As a consequence theinternal handover fails.

12. After receiving the ASSIGNMENT COMPLETE messagefrom the MS, the BSC indicates the chosen channel andthe chosen speech codec to the MSC in the HANDOVERPERFORMED message. The Chosen Channel is includedwhen the channel rate/type changes during the internalhandover. A Speech Version element is used to indicatethe chosen speech codec. Speech Version IE is includedwhen the speech version changes during the internalhandover.



Internal handover, inter-cell (async)

Figure 12. Internal HO, inter-cell (async)

HO measurements, HO decision and inquiry

measurement_report1

measurement_result2

TCH reservation and activation in BTS2

channel_activation3


Signalling on FACCH-TCH in BTS1

handover_command5

handover_command6

Signalling on FACCH-TCH in BTS2, connection

handover_access7

handover_detection8

physical_information9

sabm10


12handover_complete

13handover_complete

14handover_performed

15

TCH release in BTS1

rf_channel_release16


ua

MS BTS1 BTS2 BSC MSC




3. In the channel allocation procedure, the BSC always firstdetermines the TCH type to be allocated on the basis of theTCH rate and speech codec requirements originallyreceived from the MSC. After that, the BSC determinesthe TCH configuration and the resource situation of theBTS, the speech codec support of the BTS and the actualA interface circuit pool configuration.

During the TCH selection, the supported speech versionthat is the primary choice is chosen. The chosen channeland the chosen speech codec are used in the BSC to helpdetermine which channel to allocate for a call. Forexample, if BSS parameters define that the current channeltype and speech codec should be kept, a channel isallocated according to the chosen channel and the chosenspeech codec. However, if AMR HR is requested and theparameter initial AMR channel rate prefers AMRFR and AMR FR is allowed, it is selected if available,despite the other requirements. AMR is not selected, if theAMR codec set of the target channel rate is disabled or thetarget BTS does not support AMR. In that case, anothersupported speech codec is selected. This requires Ainterface pool switching. The above is valid in bothdirections (from AMR to other codecs and vice versa).

In case of AMR, the AMR multirate configuration mustalso be selected. Depending on the parameter AMRconfiguration in handovers, it is either thecurrently used one which is selected, if it is suitable for thetarget BTS, the one defined for the target BTS. Theparameter AMR configuration in handovers hasno effect if AMR codec set downgrades and upgrades aredisabled.

The speech codec is changed during a handover if the callis handed over for example from an EFR-supporting BTSto a BTS not supporting EFR or vice versa, or if the TCHis going to be changed from FR to HR or vice versa. Thistakes place if the channel type allows changes and theBSS/BTS parameters allow changes between channel ratesand speech codecs.

Note

Changing AMR FR to AMR HR or vice versa causes a short break in thespeech path connection.



After carrying out the channel allocation, the BSCacknowledges the chosen channel and the chosen speechcodec and sets the chosen speech codec to be sent to BTS2(target BTS) in the CHANNEL ACTIVATION message.Before target side channel activation in the BTS2, anoptional source side AMR codec set alignment may betriggered. For more information, see 5.3.1 AMR codec setdowngrades and upgrades during internal inter-cellhandovers.

The chosen speech codec is included in the Channel Modeelement of the CHANNEL ACTIVATION message. Incase of AMR, the chosen codec set and LA mode are alsoincluded.


5. After receiving the CHANNEL ACTIVATION ACKmessage from BTS2, the BSC sends a HANDOVERCOMMAND message to the MS. The message includesthe chosen speech codec in the Channel Mode IE. In caseof AMR, the chosen multirate configuration is alsoincluded if the assigned configuration is new, that is,different from the configuration of a previously allocatedchannel.

13. If the MS supports the indicated mode, it returns aHANDOVER COMPLETE message. If the channel modein the HANDOVER COMMAND indicates that amultirate speech codec must be applied and the MultirateConfiguration IE is not included in the HANDOVERCOMMAND message, the MS assumes that the multirateconfiguration has not changed. For the Initial Codec Modeof AMR, the MS uses the previously received InitialCodec Mode, if any, or applies the implicit rule defined in3GPP 45.009. AMR link adaptation starts on the assignedchannel between the MS and the BTS and it isindependent of the PC and HO control of the BSC.

If the MS does not support the indicated mode or theMultirate Configuration IE is inconsistent, the MS returnsa HANDOVER FAILURE message with the causechannel mode unacceptable. It remains on the currentchannel and uses the old mode. As a consequence, theinternal handover fails.

15. After receiving the HANDOVER COMPLETE messagefrom the MS, the BSC indicates the chosen channel andthe chosen speech codec to the MSC in HANDOVERPERFORMED message. The Chosen Channel is included




when the channel rate/type changes during the internalhandover. A Speech Version element is used to indicatethe chosen speech codec. Speech Version IE is includedwhen the speech version changes during the internalhandover.

After the internal handover is completed, an optional targetside AMR codec set alignment may be triggered. For moreinformation, see 5.3.1 AMR codec set downgrades andupgrades during internal inter-cell handovers.

AMR codec set downgrades and upgrades during internal inter-cellhandovers

1. In the channel allocation procedure, the BSC alwaysdetermines the need for AMR codec set downgrades(during internal inter-cell HO on source BTS side) andupgrades (after internal inter-cell HO on target BTS side).By default, the BSC does not perform downgrades andupgrades.

Downgrades and upgrades are both performed via modemodify procedures, first MODE MODIFY to the BTS andthen CHANNEL MODE MODIFY to the MS. The ideabehind the downgrade is to allow the use of theunidirectional downlink speech path connection on thetarget BTS side to minimise the experienced muting onspeech during internal inter-cell handovers. The ideabehind the upgrade is to use the BTS-defined AMR codecset.

When an AMR call on the source side is also going to bean AMR call on the target side, and when the channel rateand the AMR codec sets (that is, those currently used onthe source side and the BTS-defined one on the targetside), are the same on both sides, there is no need toperform AMR codec set downgrades on the source side.The BSC can then use, without extra MODE MODIFYprocedures, the unidirectional downlink speech pathconnection on the target BTS side.

If the codec sets are different on the source and the targetBTS side although the channel rates are the same, one ofthe following takes place, depending on the situation:



1. The codec set defined on the target side differs fromthe current codec set, but it can be aligned with thesource side by selecting the current codec set. Thetarget side alignment depends on the codec modesupport of the target BTS. If the AMRconfiguration in handovers parameterprefers the codec set of the target BTS, the targetside is upgraded back to its original AMR codec setafter the handover if the parameter AMR setgrades enabled allows it.

Table Example handover from a Talk-Family BTSbelow shows an example handover from a Talk-Family BTS with the default codec set to anUltraSite BTS with an imaginary codec set. Thetable shows the codec set selected for the target sideduring a handover and also the result of a possibleupgrade after the handover.

2. The codec set defined on the target side differs fromthe current codec set, but it cannot be aligned withthe source side because of the target side codecmode support. That is why the source side is alignedwith the target side by triggering a downgradeprocedure on the source side, if the parameter AMRset grades enabled allows it. If thedowngrade is not allowed, use of the unidirectionaldownlink speech path connection on the target BTSside is not possible. Downgrades take place if theparameter AMR configuration inhandovers prefers the currently used codec set.

Table Example handover from an UltraSite BTSbelow shows an example handover from anUltraSite BTS with an imaginary codec set to aTalk-Family BTS with the default codec set. Thetable shows the codec set situation on the sourceside both before and after the downgrade and it alsoshows that the target side is kept as it is during thehandover.

Table 8. Example handover from a Talk-Family BTS

Source: Talk-Family

Target: NokiaUltraSite

Set selected fortarget

Set upgraded afterHO

12.2 12.2 12.2 12.2

7.4 10.2 7.4 10.2




Table 8. Example handover from a Talk-Family BTS (cont.)

5.9 6.7 5.9 6.7

4.75 5.15 4.75 5.15

Table 9. Example handover from an UltraSite BTS

Source: Nokia UltraSite(before downgrade)

Source: Nokia UltraSite(after downgrade)

Target: Talk-Family

12.2 12.2 12.2

10.2 7.4 7.4

6.7 5.9 5.9

5.15 4.75 4.75

Note

The mode modify procedure due to AMR codec set downgrades or upgradescauses a short break in the speech path connection.

Internal inter-cell handover, switching of A interface circuit pool

Figure 13. Internal inter-cell handover, switching of A interface circuit pool

MS BTS BSC MSC

Internal HO, pool switching is needed

handover_request2

handover_required1



1 If the current circuit pool does not support the speechcodec to be selected in the target BTS, the BSC proposespool switching. There are two cases that can lead to poolswitching during an internal HO:. AMR codec is used in the source BTS, but the

target BTS does not support AMR, and AMR codecis the most wanted one

. Another codec than AMR is used in the source BTS(due to lack of AMR support), although AMRcodec is the most wanted one, and the target BTSsupports AMR

The BSC initiates the pool switching procedure by sendingthe HANDOVER REQUIRED message to the A interfacewith the cause switch circuit pool. The message alsocontains a list of preferred pools (Circuit Pool List IE) andthe identifier of the cell candidate. The optional IEsCurrent Channel and Speech Version (used), whichcharacterise the source channel type and mode and theused speech version, can be included in the message.

2 The BSC expects a HANDOVER REQUEST from theMSC. If the pool of the A interface circuit implied by theCIC of the HANDOVER REQUEST is the same as thecurrently used one, the TCH is allocated among thoseTCHs that the pool supports.

5.4 In call modification and FACCH call set-up

Figure 14. In call modification and FACCH call set-up

MS BTS BSC MSC

assignment_request1

mode_modify2

mode_modify_ack3

channel_mode_modify4

channel_mode_modify_ack5





2. The BSC removes all non-supported speech codecs fromthe Channel Type IE list and checks if the enhancedspeech codecs are allowed to be used in the BSC. If theyare not allowed to be used and the MSC offers them andpossibly other non-supported codecs, an ASSIGNMENTFAILURE message with the cause requested speechversion unavailable is sent to the MSC.

The BSC selects the supported speech version that is theprimary choice when the TCH is modified from signallingto speech in FACCH call set-up or when the TCH ismodified from data to speech in in call modification. TheBSC takes into account the speech codec support of theBTS. AMR is not selected, if the AMR codec set of theused channel rate is disabled. In that case, anothersupported speech codec is selected.

The chosen speech codec is indicated to the BTS in theMODE MODIFY message in the Channel Mode IE. Incase of AMR, the chosen codec set and LA mode are alsoincluded.

Note

The BTS must support AMR, otherwise the AMR with FACCH call set-updoes not work.

4. The chosen speech codec is indicated to the MS in theCHANNEL MODE MODIFY message in the elementChannel Mode. In case of AMR, the chosen codec set isalso included. After receiving the ASSIGNMENTCOMMAND, the MS uses the Initial Codec Mode ofAMR, specified in the Multirate Configuration IE, if it ispresent, or applies the implicit rule defined in 3GPP45.009.

5. If the MS supports the indicated mode, it returns aCHANNEL MODE MODIFY ACKNOWLEDGEmessage with the indicated mode. In case of AMR, thelink adaptation starts on the assigned channel between theMS and the BTS and it is independent of the PC and HOcontrol of the BSC.



If the MS does not support the indicated mode, it retainsthe old mode and returns the associated channel modeinformation in the CHANNEL MODE MODIFYACKNOWLEDGE message. An ASSIGNMENTFAILURE message is sent to the MSC.

Related topics

. Radio Channel Allocation

. Half Rate in BSC

. Overview of Enhanced Speech Codecs: AMR and EFR






6 User interface of AMR and EFRMMLs and parameters

. Parameter Handling (WO). EFR:

EFR_SUPPORT_IN_BSC defines whether the BSC supports theEFR speech codec.

. AMR:

AMR_CODEC_USED defines whether the BSC supports the AMRfull rate (FR) option.

. Licence and Feature Handling (W7). AMR:

BSC supports AMR half rate (HR) if AMR HR feature state is ON.

. Base Transceiver Station Handling in BSC (EQ). TCH rate intra-cell handover (TRIH). AMR FR codec mode set (FRC). AMR HR codec mode set (HRC). lower limit for FR TCH resources (FRL). upper limit for FR TCH resources (FRU)

. Transceiver Handling (ER). The creation of RTSL types HR TCH and DR TCH (ERC command)

for the TRX is possible when the AMR option is active, despite thestate of the Half Rate option.

. The optional TRX half rate support parameter is valid incommands ERC, ERM, and ERO when the AMR option is active. Theparameter indicates the capability of the TRX hardware to supportHalf Rate. This parameter is used for Nokia 2nd generation BTSTRX hardware bookkeeping. All TRX hardware of other BTSgenerations supports Half Rate.

. Base Station Controller Parameter Handling in BSC (EE). TCH in handover (HRI). lower limit for FR TCH resources (HRL)



User interface of AMR and EFR

. upper limit for FR TCH resources (HRU)

. AMR configuration in handovers (ACH)

. initial AMR channel rate (IAC)

. slow AMR LA enabled (SAL)

. AMR set grades enabled (ASG)

. Handover Control Parameter Handling (EH). AMR FR and AMR HR specific parameters for handling the

entrance and exit relating to super-reused TRXs. Nx and Px valuesof C/I thresholds for basic FR and HR are used.

. AMR FR and AMR HR specific RxQual thresholds for internalinter-cell and external handovers. Nx and Px values of RxQualthresholds for basic FR and HR are used. If the AMR codec sets aremodified and the most robust one is replaced or removed, thecorresponding HO RxQual thresholds must be edited manually. Thesame applies to the least robust mode. Replacement or removal of amiddle mode on AMR codec set does not affect the AMR-specificHO thresholds.

. intra HO threshold Rx qual AMR FR (IHRF) and intraHO threshold Rx qual AMR HR (IHRH):

AMR FR and AMR HR specific RxQual thresholds for internalintra-cell handovers between AMR channel modes. Nx and Pxvalues of RxQual thresholds for basic FR and HR are used.

The radio network database object for handover parameters is the BTS.The parameters are created with their default values during BTS creation(EQC).

. Power Control Parameter Handling (EU). pc lower threshold dl Rx qual AMR FR (LDRF). pc upper threshold dl Rx qual AMR FR (UDRF). pc lower threshold dl Rx qual AMR HR (LDRH). pc upper threshold dl Rx qual AMR HR (UDRH)

AMR FR and AMR HR specific RxQual thresholds for power control. Nxand Px values of RxQual thresholds for basic FR and HR are used. If theAMR codec sets are modified and the most robust is replaced or removed,the corresponding PC RxQual thresholds must be edited manually. Thesame applies to the least robust mode. The replacement or removal of amiddle mode on AMR codec set does not affect the AMR-specific PCthresholds.

The radio network database object for power control parameters is theBTS. The parameters are created with their default values during BTScreation (command EQC).



. Adjacent Cell Handling (EA)

AMR target cell of direct access to desired layer(DADLA)

The radio network database object for the adjacent cell parameter is theSEG.

. Transcoder Configuration (WG)

Creation of EFR and AMR related TC PCMs (A interface pools).

Related topics:

. Functionality of AMR and EFR

. BSS Radio Network Parameter Dictionary

. Activating and Testing AMR


Counters

. Traffic Measurement. Seizures for TCH allocations on BTS level with either EFR or AMR

codec in use:

FULL TCH SEIZ SPEECH VER 2 (001109)

FULL TCH SEIZ SPEECH VER 3 (001110)

HALF TCH SEIZ SPEECH VER 3 (001113). Seizures for all internal handovers between FR and HR on BTS

level:

FULL TCH SEIZ INT HO CH RATE (001116)

HALF TCH SEIZ INT HO CH RATE (001117). Seizures for intra AMR HOs, that is, HOs between AMR channel

rates:

FULL TCH SEIZ INTRA AMR HO (001182)

HALF TCH SEIZ INTRA AMR HO (001183). TCH requests for AMR calls, that is, AMR codec is the most

preferred one:

TCH CALL REQ FOR AMR (001184). AMR codec mode set downgrades and upgrades:

SUCCESSFUL AMR CODEC SET DOWNGRADES (001185)

UNSUCCESSFUL AMR CODEC SET DOWNGRADES (001186)

SUCCESSFUL AMR CODEC SET UPGRADES (001187)

UNSUCCESSFUL AMR CODEC SET UPGRADES (001188)



User interface of AMR and EFR

. Handover Measurement. Number of HO attempts from AMR FR to AMR HR: HO ATT FOR

AMR TO HR (004142). Number of HO attempts from AMR HR to AMR FR: HO ATT FOR

AMR TO FR (004143)

. RX Quality Statistics Measurement. AMR FR and AMR HR codec modes (1-4) used on uplink and on

downlink with different RxQual classes (0-7). The counter AMRCODEC MODE SETS (014149) maps the codec modes 1-4 toactual codec mode rates (014021- 014148)

. Clear Code PM Measurement. Number of successful intra-cell HOs from AMR FR to AMR HR:

INTRA HO TO AMR HR (051133). Number of successful intra-cell HOs from AMR HR to AMR FR:

INTRA HO TO AMR FR (051134)

. AMR RX Quality Measurement. AMR FR and AMR HR bit rates used on uplink and on downlink

with different RxQual classes (0-7)

For more information on the counters, see

. 1 Traffic Measurement

. 4 Handover Measurement

. 14 RX Quality Statistics Measurement

. 51 BSC Level Clear Code (PM) Measurement

. 107 AMR RX Quality Measurement



Documents

AMR-EFR