Amr

Adaptive Multi Rate (AMR)Central II

Topics• AMR Overview

• AMR parameter setting for Channel & Coded Adaptation

• Drive Test in AMR

• AMR effect on KPIs, Capacity, Coverage

• AMR network doctor reports

AMR Overview

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– Improved Quality,where possible.

• 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.

• 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

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

Cha

nnel

bit-

rate

(kbi

t/s) Channel coding

Speech coding

Speech Qual

Robustness

AMR CodecsFull Rate Half rate

12.210.2

7.95

7.957.4

7.46.7

6.75.9

5.95.15

5.154.75

4.75

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/I 16 dB C/I 13 dB C/I 10 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

Channel coding

bit-rate, speech

CH0-FS 12.20kbit/s (GSMEFR) 10.20 kbit/s CH1-FS 10.20 kbit/s 12.20 kbit/s CH2-FS 7.95 kbit/s 14.45 kbit/s

TCH/FR CH3-FS 7.40 kbit/s (IS-641) 15.00 kbit/s CH4-FS 6.70 kbit/s 15.70 kbit/s CH5-FS 5.90 kbit/s 16.50 kbit/s CH6-FS 5.15 kbit/s 17.25 kbit/s CH7-FS 4.75 kbit/s 17.65 kbit/s CH8-HS 7.95 kbit/s (*) 3.25 kbit/s

TCH/HR CH9-HS 7.40 kbit/s (IS-641) 3.80 kbit/s CH10-HS 6.70 kbit/s 4.50 kbit/s CH11-HS 5.90 kbit/s 5.30 kbit/s CH12-HS 5.15 kbit/s 6.05 kbit/s CH13-HS 4.75 kbit/s 6.45 kbit/s

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 Supported• Note that the codec supported from the Nokia BTSs depends from the type of BTS

• These are the codec supported from the different NOKIA BTSs

• Mobile Shall Support all Speech Codec Modes, although a setup of four Speech Codec Modes is used during a call.

BTS AMR FR AMR HRTalk Family 4.75, 5.90, 7.40, 12.2

kbps4.75, 5.90, 7.40 kbps

Prime Site 4.75, 5.90, 7.40, 12.2 kbps

4.75, 5.90, 7.40 kbps

Ultrasite All All except 7.90 kbpsMetrosite All All except 7.90 kbps

AMR FR AMR HR

Default Value 4.75, 5.90, 7.40, 12.2 kbps 4.75, 5.90, 7.40 kbps

Link Adaptation(Algorithms)• Link Adaptation is a capacity of AMR Feature to very Codec Used according to

the Link Conditions.

• Both BTS for Downlink and Mobile for Uplink ,measure the radio conditions in each Link and take decisions which Codec should be applied to each way .

• Two Different Type Of Link Adaptation are Defined• Codec Mode Adaptation It select the best codec• Channel Mode Adaptation It changes the channel rate between FR and HR codec.

Set of Codecs

Channel Mode Adaptation

Codec Mode Adapt.

AMR

Codec Mode (Link) Adaptation• Codec Mode Adaptation 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

• 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

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

load Good Quality

Codec

FR HR

HRFRBad

Quality

packing

unpacking

AMR parameter setting for Channel & Coded Adaptation

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 Quality (2) 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)

• The feature is disable when set HRL > HRU or FRL > FRU• Real network behavior shows that if FRL > FRU, but HRL < HRU, the AMR

feature is enable

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

Initial Codec Mode Selection• amrConfigurationFR: codecModeSet and amrConfigurationHR: codecModeSet

specify which of the possible speech coding bit-rate are implemented in the serving Cell.

• The most robust codec available (less bit rate for speech) is recommended

• The Initial Codec mode to start the speech coding operation at call set-up and after handover may be signalled by layer 3 signalling

• amrConfigurationFr: initCodecMode, amrConfigurationFr: startMode, amrConfigurationHr: initCodecMode and amrConfigurationHr: startMode you can select a different codec mode from the default ones:

• If the initial codec mode is set to "0" (default) then the Initial codec mode is defined by the implicit rule provided in

GSM 05.0 "1" Initial codec mode is defined by amrConfigurationFr: startMode.

Parameter Codec Mode SetamrConfigurationFR 4.75, 5.90, 7.40, 12.2 kbpsamrConfigurationHr 4.75, 5.90, 7.40kbps

Initial Codec Mode Selection• amrConfigurationFr: startMode

00: Codec mode 1 (the most robust mode) 01: Codec mode 2 10: Codec mode 3 11: Codec mode 4

• With initAmrChannelRate parameter you define the initial channel in call set-up ,internal inter cell handover (HO) and external HO for an AMR call.

• Default Value can be any Rate ,the other option is AMR Full Rate. The reason behind this last parameter is that quality may not be sufficient for HR AMR call set-up

Code Mode Adaptation• Parameters which are taken into account for switching

between different Codec Modes are AMR Thresholds: amrConfigurationFr: threshold1

amrConfigurationFr: threshold2 amrConfigurationFr: threshold3

AMR HYSTERESIS: amrConfigurationFr: hysteresis1

amrConfigurationFr: hysteresis2 amrConfigurationFr: hysteresis3

AMR Thresholds And Hysteresis

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:

• 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.

• There is no change in codec usage in UL.

Change in FRT/HRT

Drive Test in AMR

• 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/ICodec 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/IHR 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

= 0

AMR HR Call, DL VQ =0 , good C/IHR 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/ICodec used 4.75 kbps

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 =6Codec used 5.3 kbps

Unpacking = HR FR (2/2)

Handover FR (1/3)• The slide

shows MS call on AMR FR

on codec set

12.2kbps and VQ =

0


Handover FR(2/3)


• The slide shows MS

call on AMR FR after HO

has switched to Codec

Mode 5.9kbps VQ = 0

HandOver FR(3/3)


• The slide shows MS

call on AMR FR after HO

has switched

back again to 12.2kbps

from Codec Mode

5.9kbps as VQ =

0

AMR effect on KPI, Capacity, Coverage

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.

• Quality -> better perceived speech quality.• With Frequency Hopping and AMR, BER becomes increasingly

meaningless and therefore alternative indicators are needed to benchmark the voice quality

• 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

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

Documents

Transcript of Amr