amr presentation

AMR (Adaptive Multi Rate) Optimization Guidelines

Presented byPresented by Aamir NaveedAamir Naveed(LCC-North)(LCC-North)

AMR Overview

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. Below are the AMR FR and the AMR HR performancefigures.

AMR HR

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 utilise the state-of-the-art FR traffic channel, which meansthat the source codec rate EFR is 12.2 kbit/s and AMR is up to 12.2 kbit/s. AMRcan also utilise HR traffic channel (TCH) used by the basic HR, offering anincrease of capacity in terms of TCHs at the BTS. To achieve this, AMR HRrequires HR or dual rate (DR) channel configuration on the radio interface. Thesupport for EFR or AMR in a network does not require nor imply support for thebasic HR and vice versa.Submultiplexing on highway PCM (Ater interface) for AMR FR and AMR HRis 16 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.

Before & After AMR Before AMR the GSM operator had available on the air interface:

2 different Channel Type (Full Rate & Half Rate) 2 different channel Coding (1 @ Full Rate & 1 @ Half Rate)

With the introduction of AMR the GSM operator have available on the air interface:

2 Different Channel Type (Full Rate / Half Rate) 14 Different Channel Coding (8 @ Full Rate & 6 @ Half Rate)

The reason of the introduction of 2 different Channel Type is

Exploit where possible the capacity of the TRX Cope w/ temporary increase of the traffic

The reason of the 14 different Channel Coding is to use in every moment of the conversation the best trade off between Channel Coding and Speech Coding.

Increased Speech Coding ~ Increased Voice Reconstruction Accuracy Increased Channel Coding Increased Robustness Good FER in poor C/I environment

AMR Idea

The AMR idea is based on the fact that in soft limited RF environments (poor C/I)

Speech coding can be decreased in order to improve channel coding Overall result is an improved voice quality (in terms of FER) For AMR, the speech and channel coding data rates are dynamically adapted to

best fit the current RF channel conditions.

AMR consists on a family of codec with different Channel Coding operating in GSM Full Rate (FR) and Half Rate (HR). The aim is to improve channel (FR/HR) quality by adapting the most appropriate channel codec based on the current radio conditions.

With AMR, the speech capacity is increased by using the half rate (HR) mode and still maintaining the quality level of current FR calls.

The idea behind the AMR codec concept is that it is capable of adapting its operation optimally according to the prevailing channel conditions.

0

5

10

15

20

25

FR12.2

FR10.2

FR7.95

FR 7.4 FR 6.7 FR 5.9 FR5.15

FR4.75

HR7.95

HR 7.4 HR 6.7 HR 5.9 HR5.15

HR4.75

AMR codec mode

Ch

an

ne

l b

it-r

ate

(k

bit

/s)

Channel coding

Speech coding

Speech Speech QualQual

RobustnessRobustness

GSM FR/EFR channel gross bit-rate is 22.8 kbps in GSM FR/EFR:

13 kbps speech coding 9.8 kbps /channel coding

Note that HR channel gross bit rate 11.4 kbps

For AMR case, different codec use different bit rate to encode speech (source coding). The rest of the gross bit-rate is used for channel protection

AMR Codec

Algorithms Related to AMR

Set of Codecs

Channel Mode Adaptation

Codec Mode Adapt.

AMR

Codec Mode Adaptation Algorithm = Link Adaptation Algorithm

It select the best codec

Channel Mode Adaptation Algorithm

It changes the channel rate between FR and HR codec.

AMR CodecsFull Rate Half rate

12.2 10.2 7.95 7.95 7.4 7.4 6.7 6.7 5.9 5.9 5.15 5.15 4.75 4.75

Voice quality

Robustness

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

MOS (Mean Opinion Score)

EFRAMR 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/I16 dB C/I 13 dB C/I10 dB C/I 7 dB C/I 4 dB C/I

AMR HRAMR FR

MOS (Mean Opinion Score)

AMR Half Rate performance compared toFull Rate in Clean Speech

Quality loss of ~ 0.2 between AMR HR and FR

New AMR family of codec tolerate 6 dB higher interference than current GSM EFR codec

Can be directly utilized for higher capacity with Frequency Hopping Higher interference tolerance Reduced time slot occupancy

AMR codecs:8 for FR and 6 for HR

6 dB gain inperformance

AMR Channel and Speech CodecChannel mode

Channel codec

Mode

Source coding bit-rate, speech

Net bit-rate, in-band channel

Channel coding bit-rate, speech

Channel coding

bit-rate, in-band

CH0-FS 12.20kbit/s (GSMEFR) 0.10 kbit/s 10.20 kbit/s 0.30 kbit/s

CH1-FS 10.20 kbit/s 0.10 kbit/s 12.20 kbit/s 0.30 kbit/s


TCH/FR CH3-FS 7.40 kbit/s (IS-641) 0.10 kbit/s 15.00 kbit/s 0.30 kbit/s





CH8-HS 7.95 kbit/s (*) 0.10 kbit/s 3.25 kbit/s 0.10 kbit/s

TCH/HR CH9-HS 7.40 kbit/s (IS-641) 0.10 kbit/s 3.80 kbit/s 0.10 kbit/s

CH10-HS 6.70 kbit/s 0.10 kbit/s 4.50 kbit/s 0.10 kbit/s




(*) Requires 16 kbit/s TRAU. Therefore it is not seen as a feasible codec mode and will not be supported by Nokia BSS10.

In high-error conditions more bits are used for error correction to obtain error robust coding, while in good transmission conditions a lower

amount of bits is needed for sufficient error protection and more bits can therefore be allocated for source coding

Codec Mode (Link) Adaptation Codec Mode Adaptation or Link Adaptation (LA) is the algorithm that selects which codec has to be used each moment by the MS (in UL) or by the network (in DL direction).

The basic AMR codec mode sets for MS and BTS are provided by BSC via layer 3 signalling

Both the MS and the network implement their own independent LA algorithms

There are two link adaptation (LA) modes:

ETSI specified fast LA Inband codec mode changes on every other TCH frame = 40 msec Nokia proprietary slow LA Changes only every SACCH frame interval = 480 msec

The suggested LA rate is the fast one.

LA algorithms are vendor dependant / proprietary

Advanced

1.-Which DL Radio Conditions?

2.-Request a codec for DL

3.- Network decides which codec to use for DL

4.-DL codec used

DL LA

1.-Which UL radio conditions?

2.-Command a codec for ULUL LA

3.-MS uses the codec commanded by the network for

UL

Procedure for Codec Mode (Link) Adaptation

Advanced

CMI, CMC

DL

UL SF 1

SF 2

SF 3

SF 4 SF 6

SF 5

SF 3SF 1

SF 7

SF 7SF 5

CMR

SF 2 SF 4 SF 6 SF 8

time

8 TDMA

frames

CMR

CMI CMI CMI CMI CMI CMI CMI CMI CMI

CMICMICMICMICMICMICMICMICMI

CMC CMC CMC CMC CMC CMC CMC CMC CMC

CMR CMR CMR CMR CMR CMR

SF 9

CMR, CMI

In band signaling

SF= Speech Frame CMC = Codec Mode Command

CMI = Codec Mode Indicator CMR= Codec ModeRequest

Advanced

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 (UL) adaptation, the Quality Indicator is directly fed into the UL 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 (DL) 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.

Channel Mode Adaptation is an HO algorithm that aims at select the correct channel rate (FR or HR).The selection of the channel rate depends on 2 main factors: load and quality

Channel Mode Adaptation

loadload Good Good QualityQuality

CodecCodec

FRFR HRHR

HRHRFRFRBad Bad

QualitQualityy

packingpacking

unpackingunpacking

Advanced

The Quality Indicator is derived from an estimate of the current burst bit error probability (BBEP), which is calculated from burstwise soft values in Equalizer

Digital Signal Processor (EQDSP). The (logarithmic) BBEP values are sent to Channel Digital Signal Processor (CHDSP) and they are handled by a filter,

which smooths out the BBEP signal (the sequence of BBEP values) and controls fast codec changes, if needed. After that the filtered BBEP value is mapped to the

C/I value.

Definition of Mode Command and Mode Request decision thresholdsFor each pair of neighbouring codec modes in the codec mode set, a threshold and a

hysteresis value in terms of normalized carrier to interference ratio (C/Inorm ) is defined. The lower decision threshold for switching from mode j to mode j-1 is given by the signalled threshold.

Initial codec mode selection at call set-up and handoverThe 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.

AMR parameter setting for Channel & Coded Adaptation

Channel Adaptation - RTSL parameters to decide Following the BSC level AMR feature activation and the addition of circuit pool 23,

AMR FR will be functioning on all sites with default parameters settings.

To configure the RTSL for half rate support, the existing FR only configuration (TCHF) must be changed to Dual Rate (TCHD) depending upon the traffic need and blocking on the site.

ZERM:BTS=x,TRX=x, CHx=TCHD;

Configure AMR HR Packing triggers. The value depends upon how aggressive we want to deploy HR. The setting shall be in accordance with traffic/blocking and average C/I in the area.

ZEEM:HRU=x,HRL=x; ZEQY:BTS=x,IHRF=x,IHRH=X;

Channel Adaptation - Packing & Unpacking mechanism To trigger the packing of active Full Rate AMR calls to AMR Half Rate, traffic and quality threshold

must be set.

Spontaneous Packing of AMR FR to AMR HR calls is triggered: Free full rate resources reduces below the value of the parameter btsLoadDepTCHRate(HRL) At least 2 calls in which quality is above the amrHandoverFr(IHRF) and which uses the least

robust codec mode

Packing continues until the number of free full rate resources increases above the value of the parameter btsLoadDepTCHRate (HRU).

Spontaneous unpacking of AMR HR calls to AMR FR calls is triggered when the quality of a AMR HR call degrades below the amrHandoverHr(IHRH). Cell load does not have an effect.

HRL and HRU are set on BSC level but load evaluation is based on individual BTS.

btsspLoadDepTCHRate (FRL) and (FRU) are BTS specific parameters. They have priority over btsLoadDepTCHRate (HRL) and (HRU)

Voice Quality To ensure better Voice Quality it is important that in HR we start with the 2nd most

robust codec. By default HR starts with the most robust codec Implicit rule provided in 3GPP 45.009:

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 the most robust mode

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

mode of the set with the second lowest bit rate. To manually assign which codec to use in the initial assignment you need to change the

BTS parameter (ICMI) HRI. Then change the HRS parameter.

(ICMI) HRI = AMR HR INITIAL CODEC MODE INDICATOR (ICMI) 0 = Initial codec mode is defined by the implicit rule provided in GSM 05.09 (3GPP 45.009) 1 = Initial codec mode is defined by the Start Mode field (HRS)

HRS = AMR HR START MODE HRS Range => 00, 01, 10, 11 => Codec Mode 1, 2, 3, & 4

Proposed Values for AMR HR: ICMI HRI = 1 and HRS = 01 Impact => reduced AHS 4.75 codec usage.

Channel Adaptation - Packing & Unpacking mechanism Example:

HRL = 40% HRU = 60% IHRF = 2 IHRH = 4 Packing starts when free FR resources below 40% and calls with RxQual below 2, and stops when free FR

resources above 60% Unpacking when HR call’s RxQual below 4

Codec Adaptation - Parameters to decide

The parameters "amrConfigurationFr: codecModeSet" & "amrConfigurationHr: codecModeSet" (FRC) determine the set of codecs in used.

Dynamic code adaptation is based on C/I estimation. Threshold and hysteresis:

FRTx: AMR FR threshold x amrConfigurationFr: thresholdx, with x=1,2,3 FRHx: AMR FR hysteresis x amrConfigurationFr: hysteresisx, with x=1,2,3 HRTx: AMR HR threshold x amrConfigurationHr: thresholdx, with x=1,2,3 HRHx: AMR HR hysteresis x amrConfigurationHr: hysteresisx, with x=1,2,3

Trial ResultsHR CODEC DISTRIBUTION %

50%

55%

60%

65%

70%

75%

80%

85%

90%

95%

100%

02/2

8/0

5

03/0

2/0

5

03/0

4/0

5

03/0

6/0

5

03/0

8/0

5

03/1

0/0

5

03/1

2/0

5

03/1

4/0

5

03/1

6/0

5

03/1

8/0

5

03/2

0/0

5

03/2

2/0

5

03/2

4/0

5

03/2

6/0

5

03/2

8/0

5

03/3

0/0

5

04/0

1/0

5

04/0

3/0

5

04/0

5/0

5

04/0

7/0

5

04/0

9/0

5

04/1

1/0

5

04/1

3/0

5

04/1

5/0

5

04/1

7/0

5

HR 7.5 HR 5.9 HR 4.75

There was approximately 50% reduction in AMR HR 4.75 codec usage when the HRI (ICMI) and HRS were changed to start with AMR HR 5.9 codec. HR usage was about 65%.

HO and PC in AMR

HO and PC in AMR environment HOC and POC is done based on RX quality Following actions are taken based on Rx quality cases

of PC & HO algorithms in BSC:

If the quality is below lower thresholds then PC (more power) or HO is triggered depending on the current threshold values. Otherwise if quality is above lower thresholds, nothing is done.

Respectively, if the quality is above upper thresholds then PC (less power) is triggered. Otherwise if quality is below upper thresholds, nothing is done.

Above cases are valid only in quality HO, not for example in PBGT HO.

New RxQual HO thresholds are specified for FR and HR AMR and they are taken into account when making intra-cell handovers between FR AMR and HR AMR:

Intra HO threshold Rx Qual for AMR FR Intra HO threshold Rx Qual for AMR HR

All the information (codec usage and quality) goes to BSC statistics part for further processing.

Intra cell Handover process ( FR to HR packing ) is based upon BTS load , call quality and current codec being used

AMR Parameter Overview

Parameter Level Name Suggested Value

Comments

AMR Configuration FR Codec Mode Set BTS FRC 149 With this parameter you define the codec mode set for a full rate channel. If the parameter is defined as disabled, then the whole codec mode set is disabled. Codec set used is

12.2(128), 7.40(16), 5.9(4), 4.75(1) kbit/s

AMR Configuration FR Hysteresis 1 (dB)

BTS FRH1 1 With this parameter, together with AMR FR threshold 1, you define the threshold for swiTCHing from codec mode 1 (lowest bit-rate) to codec mode 2 (second lowest bit-rate).

Unused hysteresis is set as 0.







AMR Configuration FR Init Codec Mode BTS FRI 0 With this parameter you define whether the initial codec mode used by the mobile station is defined explicitly in the AMR codec mode set or is it implicitly derived by the mobile

station from the amount of codec modes in the AMR codec mode set.

AMR Configuration FR Start Mode BTS FRS 0 With this parameter you define explicitly the initial codec mode used by the mobile station.

AMR Configuration FR Threshold 1 (dB) BTS FRT1 9 With this parameter you define the threshold for swiTCHing from codec mode 2 (second lowest bit-rate) to codec mode 1 (lowest bit-rate). Unused threshold is set as 0.

AMR Configuration FR Threshold 2 (dB) BTS FRT2 12 With this parameter you define the threshold for swiTCHing from codec mode 3 (third lowest bit-rate) to codec mode 2 (second lowest bit-rate). Unused threshold is set as 0.

AMR Configuration FR Threshold 3 (dB) BTS FRT3 16 With this parameter you define the threshold for swiTCHing from codec mode 4 (third lowest bit-rate) to codec mode 3 (second lowest bit-rate). Unused threshold is set as 0.

AMR Configuration HR Codec Mode Set

BTS HRC 21 With this parameter you define the codec mode set for a full rate channel. If the parameter is defined as disabled, then the whole codec mode set is disabled.Codec set used is

7.40(16), 5.9(4), 4.75(1) kbit/s

AMR Handover FR Bad CI Ratio BTS BCIG 10 With this parameter you define the downlink C/I ratio on a super-reuse TRX for triggering the HO from the super-reuse TRX. Defined for AMR FR calls.

AMR Handover FR Good CI Ratio BTS BGIF 17 With this parameter you define the downlink C/I ratio on a super-reuse TRX for triggering the HO to the super-reuse TRX. Defined for AMR FR calls.

AMR BTS parameters (FR)

Parameter Level Name Suggested Value

Comments

AMR Configuration HR Hysteresis 1 (dB)

BTS HRH1 1 With this parameter you define the threshold for swiTCHing from codec mode 2 (second lowest bit-rate) to codec mode 1 (lowest bit-rate). Unused threshold is set as 0.





AMR Configuration HR Init Codec Mode

BTS HRI 0 With this parameter you define whether the initial codec mode used by the mobile station is defined explicitly in the AMR codec mode set or is it implicitly derived by the mobile station

from the amount of codec modes in the AMR codec mode set..

AMR Configuration HR Start Mode BTS HRS 0 With this parameter you explicitly define the initial codec mode used by the mobile station.

AMR Configuration HR Threshold 1 (dB)

BTS HRT1 14 With this parameter you define the threshold for swiTCHing from codec mode 2 (second lowest bit-rate) to codec mode 1 (lowest bit-rate). Unused threshold is set as 0.





AMR Handover FR Intra Threshold DI Rx Qual

BTS IHRF 2 With this parameter you define the threshold level of the signal quality downlink and uplink measurements for triggering the intra-cell handover process for an AMR FR call in order to

swiTCH it to an AMR HR call.

AMR Handover FR Threshold Dl Rx Qual

BTS QDRF 6 With this parameter you define the threshold level of the downlink signal quality measurements for the BTS power decrease. Defined for the default FR AMR set.

AMR Handover FR Threshold Ul Rx Qual

BTS UDRF 6 With this parameter you define the threshold level of the downlink signal quality measurements for the BTS power decrease. Defined for the default FR AMR set.

AMR Handover HR Bad CI Ratio BTS BCIH 10 With this parameter you define the downlink C/I ratio on a super-reuse TRX for triggering the HO from the super-reuse TRX. Defined for AMR HR calls.

AMR Handover HR Good CI Ratio BTS GCIH 17 With this parameter you define the downlink C/I ratio on a super-reuse TRX for triggering the HO to the super-reuse TRX. Defined for AMR HR calls

AMR BTS parameters (HR)

Parameter Level NameSuggested

Value Comments

AMR Handover HR Intra Threshold Dl Rx Qual

BTS IHRF 4 With this parameter you define the threshold level of the signal quality downlink and uplink measurements for triggering the intra-cell handover process for an AMR FR call in order to

swiTCH it to an AMR HR call.

AMR Handover HR Threshold Dl Rx Qual

BTS QDRH 5 With this parameter you define the threshold level of the signal quality downlink measurements for triggering the handover. Defined for the default AMR HR set.

AMR Handover HR Threshold Ul Rx Qual

BTS QURH 5 With this parameter you define the threshold level of the signal quality uplink measurements for triggering the handover. Defined for the default AMR HR set.

AMR Power Control FR PC Lower Threshold DL Rx Qual

BTS LDRF 5 With this parameter you define the threshold level of the downlink signal quality measurements for the BTS power increase. Defined for the default FR AMR set.

AMR Power Control FR PC Lower Threshold UL Rx Qual

BTS LURF 5 With this parameter you define the threshold level of the downlink signal quality measurements for the MS power increase. Defined for the default FR AMR set.

AMR Power Control FR PC Upper Threshold DL Rx Qual

BTS UDRF 3 With this parameter you define the threshold level of the downlink signal quality measurements for the BTS power decrease. Defined for the default FR AMR set.

AMR Power Control FR PC Upper Threshold UL Rx Qual

BTS UURF 3 With this parameter you define the threshold level of the downlink signal quality measurements for the MS power decrease. Defined for the default FR AMR set.

AMR Power Control HR PC Lower Threshold DL Rx Qual

BTS LDRH 3 With this parameter you define the threshold level of the downlink signal quality measurements for the BTS power increase. Defined for the default HR AMR set.

AMR Power Control HR PC Lower Threshold UL Rx Qual

BTS LURH 3 With this parameter you define the threshold level of the downlink signal quality measurements for the BTS power increase. Defined for the default HR AMR set.

AMR Power Control HR PC Upper Threshold DL Rx Qual

BTS UDRH 1 With this parameter you define the threshold level of the downlink signal quality measurements for the BTS power decrease. Defined for the default HR AMR set.

AMR Power Control HR PC Upper Threshold UL Rx Qual

BTS UURH 1 With this parameter you define the threshold level of the downlink signal quality measurements for the MS power decrease. Defined for the default HR AMR set.

Limit For FR TCH Resources Lower (%) FRL

BTS FRL 20 With this parameter you define the percentage of full rate TCH resources that must be available for traffic channel allocation. Full rate TCHs are allocated until the number of free

full rate resources is reduced below the threshold given in the parameter. The half rate resources are then allocated.

Limit For FR TCH Resources Upper (%) FRU

BTS FRU 40 With this parameter you define the percentage of full rate TCH resources that must be available for traffic channel allocation. Full rate TCHs are again allocated when the number

of the free full rate resources increases above the threshold given by the parameter.

AMR HO & PC parameters

Parameter Level NameSuggested

ValueComments

TCH in handover BSC HRI 1

TCHRateInternalHo (HRI) is used to control the speech and channel type changes in handover when IAC=1. If set to 1, channel type and speech codec used in source BTS are primary allocated in target cell.

Lower limit for FR TCH resources

BSC HRL 20 btsLoadDepTCHRate (HRL) and btsLoadDepTCHRate (HRU) are considered in call set-up and handovers only when IAC=1. HR is to

be assigned if free resources go below HRL. FR is to be assigned if free resources go above HRU

Upper limit for FR TCH resources

BSC HRU 40

AMR configuration in handover

BSC ACH 1”1” = the currently used multirate configuration is preferred. ”2” = the multirate configuration of target BTS is preferred

Initial AMR channel rate for call setup and hand off

BSC IAC 1

”1” = Any rate. Channel type allocation depends on further network parameters/settings. ”2” = AMR FR. AMR FR is preferred over AMR HR and allocated despite of the values of the currently used information for channel allocation. IAC=2 overrides TCHRateInt

Slow AMR Link Adapation enabled

BSC SAL Noenable slow link adaptation. This is a proprietary algorithm where codec mode changes happen every SACCH period (480ms) instead of as fast as 40ms.

AMR set grades enabled BSC ASG No

Y = downgrades and upgrades are applied N = downgrades and upgrades are not applied. If multirate configuration of source and target BTS are the same then ACH and ASG has no impact

AMR BSC parameters

Radio Link Timeout (RLT) in AMR

RLT Background 3GPP 05.08 states that Radio Link Failure (RLF) in the MS is determined by the success rate of

decoding messages on the downlink SACCH

The aim of determining RLF in the MS is to ensure that calls with unacceptable voice/data quality, which cannot be improved either by RF power control or handover, are either re-established or released in a defined manner

The Radio Link Timeout (RLT) parameter controls that a forced release (drop) will not normally occur until the call has degraded to a quality below that at which the majority of subscribers would have manually released it

The RLF procedure is implemented in the RRM at the BSC and is as follows:

After the assignment of a dedicated channel a counter is initialized to RLT When a SACCH message is unsuccessfully decoded the counter is decreased by 1 When a SACCH message is successfully decoded the counter is increased by 2 If the counter reaches 0 a RLF is declared Call is released

AMR Optimization Warnings

With the AMR HR implementation BSCs maximum channel capacity 4096 must be taken into the account in BSCs TRX amount dimensioning. For example, the BSC2i provides with 512 full-rate TRXs capacity or 256 half –rate TRXs.

Unpacking shall take place before any HO is triggered to other cells. better speech quality conservative PC setting shall be used.

HR shall be used aggressively in dense urban areas where C/I is good and traffic is very high whereas in rural area FR shall be preferred and HR shall be used conservatively based on traffic loads

Aggressive PC settings shall be used for higher capacity gain where as for better speech quality conservative PC setting shall be used.

HR shall be used aggressively in dense urban areas where C/I is good and traffic is very high whereas in rural area FR shall be preferred and HR shall be used conservatively based on traffic loads.

AMR Optimization Warnings

AMR Field Results

In-Door Trial Results

DL results – coverage improvement

PESQ 2.7AMR

PESQ 1.8Non AMR

UL results – coverage improvement

PESQ 3.6 non AMR

PESQ 3.2 AMR

PESQ 1.9non AMR

PESQ 3.0 AMR

PESQ 2.7

AMR FR voice quality coverage gain

AMR does not improve radio conditions (level, interference), it improves speech quality (MOS) in poor radio conditions.

Coverage gain will be the result of subscriber perception, meaning being able to continue the call in poor radio conditions with good voice quality due to AMR.

Results from trial:

Good Radio Conditions

Poor Radio Conditions

Good Radio Conditions

MOS 2.7

AMR

Non- AMR

Out Door Trial Results

MOS distribution vs. RxLev

DLDL DLDL

ULUL ULUL

MOS distribution vs. RxQual

DLDL DLDL

ULUL ULUL

MOS distribution vs. C/I

• C/I measured by scanner not by MS

DL DL

MOS scores per AMR codec

• Average AMR MOS = 3.3• Average non AMR MOS = 3.1

• Peak AMR MOS = 3.7• Peak non AMR MOS = 3.7

DL

AMR codec usage vs. RxQual

DL

9 sites were selected RVSDBSC16 to see the affect of changes in the FRT/HRT/FRH/HRH values.

Three set of parameters were tested as given in the following table. Parameter changes were made only for few hours for drive test purpose.

Trial on FRT/HRT

Parameter Current Value Case 1 Case 2 Case 3

AMR Configuration FR Hysteresis 1 (dB) 1 1 1 2



AMR Configuration FR Threshold 1 (dB) 9 11 7 9



AMR Configuration HR Hysteresis 1 (dB) 1 1 1 2



AMR Configuration HR Threshold 1 (dB) 14 16 12 14



DL Codec Usage

0

10

20

30

40

50

60

70

80

90

100

Current Value Drive 1 Drive 2 Drive 3

Higher threshold-

More channel coding

Lower threshold-

More speechcoding

Hysteresis changed

from 1 to 2 db

Current threshold

value

UL Codec Usage

0

10

20

30

40

50

60

70

80

90

100

Current Value Drive 1 Drive 2 Drive 3

No noticeable change in codec set usage

There is no noticeable change in DL FER with change in FRT/FRH values.

There is a change in codec usage in DL with change in the thresholds.

No noticeable change in codec usage in UL.

The overall C/I is good in the area chosen for the trial and mostly codec 12.2 and 7.4 are used.

The current threshold values are good as best codec in terms of speech is used most of the times.

Another area ( Trial area -1 ) is selected where the C/I is not as good so that we can see the affect of FRT/HRT values on the DL FER.

The DL FER is best when using the current set of FRT/HRT values and degraded in all other three set of values.

The current set of FRT/HRT values shall be used to have best DL FER.

Trial Summary

HOC, POC, BTS Optimization Settings

Parameter Setting Parameter Level Setting 1 Setting 2 Setting 3 Comments

AMR Configuration FR Hysteresis 1 BTS 1 2 2 -



AMR Configuration FR Threshold 1 BTS 12 18 18 -



AMR Configuration HR Hysteresis 1 BTS 1 2 2 -



AMR Configuration HR Threshold 1 BTS 22 28 28 -



AMR HO HR Threshold DL RxQual BTS 6 5 5 -

AMR HO HR Threshold UL RxQual BTS 6 5 5 -

AMR POC FR PCL Threshold DL RxQual BTS 5 4 4 -

AMR POC FR PCL Threshold UL RxQual BTS 5 4 4 -

AMR POC FR PCU Threshold DL RxQual BTS 1 3 3 -

AMR POC FR PCU Threshold UL RxQual BTS 1 3 3 -

AMR POC HR PCL Threshold DL RxQual BTS 4 2 2 -

AMR POC HR PCL Threshold UL RxQual BTS 4 2 2 -

AMR POC HR PCU Threshold DL RxQual BTS 1 0 0 -

AMR POC HR PCU Threshold UL RxQual BTS 1 0 0 -

PC Interval Poc 0 1 0 Setting 1 and 3 are very aggressive (low POC & HOC quality threshold) as AMR allow MS to

maintain good FER in low C/I

PC L T Qual DL RxQual POC 5 3 5

PC L U Qual DL RxQual POC 5 3 5

HO T Qual DL Rx Qual HOC 5 4 5

HO T Qual UL Rx Qual HOC 5 4 5

Composition of Calls

70% calls using AMR Codec

30 % calls using EFR Codec

This profile didn’t change in the different trial phases.

CODEC profile

Drive Test in AMR

Drive Test

Drive test was done using TEMS investigation to verify the following events:

Call packing from FR to HR Call unpacking from HR to HR Link adaptation depending upon channel

conditions

The slide shows MS call on AMR FR on codec set 12.2 and VQ = 0

AS VQ is good, depending upon load thresholds the call packs from FR 12.2 codec to HR 4.75 codec as shown in next slide

AMR FR Call, DL VQ =0, good C/I

Codec used 12.2 kbps

Packing = FR HR (1/3)

After packing from FR to HR the MS first selects most robust codec (4.75 kbps) on HR and then does the link adaptation to select another codec depending upon channel conditions.

The slide shows MS call on AMR HR on codec set 4.75 and VQ = 0

AS VQ is good, (good C/I ) MS does the link adaptation and changes from codec 4.75 to codec 7.4

AMR HR Call, DL VQ =0, good C/I

HR Codec used is 4.75 kbps


After packing from FR to HR the MS first selects most robust codec (4.75 kbps ) on HR.

AS VQ is good, (good C/I ) MS does the link adaptation and changes from codec 4.75 to codec 7.4

The slide shows MS call on AMR HR on codec set 7.40 kbps and VQ = 0AMR HR Call, DL VQ =0 , good C/I

HR Codec used is 7.40 kbps


The slide shows MS call on AMR HR on codec set 4.75 and VQ = 5, and bad C/I

AS VQ is bad, call unpacks from HR 7.4 codec to FR 5.3 codec as shown in next slide

AMR FR Call, DL VQ =5, bad C/I


Unpacking = HR FR (1/2)

The slide shows MS on HR on AMR FR on codec set 5.3 and VQ = 6

AMR FR Call, DL VQ =6

Codec used 5.3 kbps

Unpacking = HR FR (2/2)

AMR HR Call, DL VQ =0, good C/I


HR Link Adaptation (1/3) After packing from FR to HR the MS first selects most robust codec ( 4.75 kbps ) on HR.

The slide shows MS call on AMR HR on codec set 7.4 and VQ = 0 and good C/I.

AMR HR Call, DL VQ =6, bad C/I




AS VQ is good, ( good C/I ) MS does the link adaptation and changes from codec 4.75 to codec 7.4

AMR FR Call, DL VQ =6

Codec used 5.3 kbps



As VQ is good, ( good C/I ) MS does the link adaptation and changes from codec 4.75 to codec 7.4

AMR effect on HO, KPI, Capacity, Coverage

RXLEV and Power Budget HO parameters are identical for AMR and EFR

AMR call would handover at the same point as an EFR call.

Separate RXQUAL threshold settings for AMR

Default set to “worse” values than EFR. (e.g. EFR =4, AMR = 5) With these default settings AMR calls would be expected to have fewer HO due to quality

No difference in RXQUAL measurement method between EFR and AMR

EFR call and AMR call in identical location should show identical RXQUAL measurements

Packing/Unpacking

Unpacking from HR to FR is always based on RX quality In congested cell with no available TS for unpacking, Inter-cell HO required based on RXQUAL.

Improved robustness in AMR over EFR

AMR better able to handle poor radio conditions - low RXLEV, poor RXQUAL, low C/I

Optimization of separate AMR parameters is important to ensure no negative impact to HO. Different environments will need different parameter settings to optimise the performance. Other AMR parameters should have no negative impact in a network designed for EF

AMR effect on HO

AMR effect on KPIs The AMR feature itself will not impact the individual connections DCR, but it will affect the overall

system DCR since the interference generated in the network is lower due to the AMR power control settings.

Radio Link Timeout can be adapted to AMR in order for dropped calls to maintain the same correlation with voice quality degradation as with EFR

AWS National standard changed for Radio Link Timeout changed from 20 to 44 SACCHs.The new standard is due to the fact that the AMR calls may still have a good communication but radio link timeout is small and call is cleared based on RLT.

The new standard was implemented to Los Angeles market .Increasing the radio link timeout to 44 clearly improved the retainability in L.A. core area.

Quality -> better perceived speech quality. Traditionally, GSM voice quality has been usually benchmarked based on BER measurements With Frequency Hopping and AMR, BER becomes increasingly meaningless and therefore

alternative indicators are needed to benchmark the voice quality BSS10.5 brings FER based counters:

In UL, the system measures the UL FER and related counters are available In DL, the system estimates the DL Frame Erasure Probability (FEP) based on the rest of

information available

AMR provides a significant performance enhancement that can be translated into a tradeoff between quality and capacity

AMR feature impact and deployment strategy depends strongly upon the AMR capable mobile penetration

AMR gains:

Quality -> AMR maintains good speech quality in the situation where the connection faces low C/I or low signal level. Also due to retransmissions schemes used by these channels the probability of signaling success maintain very high even for very degraded conditions

Capacity -> HR utilization doubles the hardware capacity of the cell since two half-rate connections can be allocated to fill only one timeslot. Practically the gain is up to 150% higher capacity for the same quality

Coverage -> additional 3-4 dB effective coverage Cost (HR hardware efficiency) -> 20-40% lower number of TRXs Improved BCCH plan: tighter frequency reuse or better quality with same frequency

reuse, potentially releasing frequencies to be used on the non-BCCH layer

AMR effect on Capacity & Coverage

AMR Network Doctor reports

Network Doctor Reports

Following Network Doctor report are used to monitor and optimize the AMR codec utilization

ND-244: BER quality per CODEC type and rate. Reports total voice samples distributed across AMR and EFR for each CODEC rate

ND-245: Lists FER for both uplink and downlink separated for all CODEC types and rates

ND-246: Summary report for AMR KPI

ND-247: Call failure rate per CODEC type

ND-248: This report shows seizure and failure statistics for codec set modifications in internal HO

ND-249: AMR counters summary

AMR & “Soft Channel Capacity” feature (S11.1)

Soft Channel Capacity to help AMR deployment One of the NOKIA BSS practical limits that has been highlighted from the

customer is the fact that we can’t deploy all the BSC as HR

This is true till S10.5

In S11.1 Nokia is introducing the “Soft Channel Capacity” feature that allows to define all the RTSL in the BSS as Dual Rate

This will have in important (positive) impact on the OPEX and CAPEX savings for the customers.

As we write the feature is under trial in the AWS Los Angeles market but it very promising

Question & Comments

For questions and comments please contact:

amr presentation

Documents