12-AMR

AMR

Adaptive MultirateAdaptive Multirate

Why AMR?

Improved speech quality at low C/I Apply tighter frequency reuse in a network with high AMR

capable MS penetration Possible to change speech codec during the call,

depending on interference conditions

AMR FR performance without background noise

Adaptive Multi Rate (AMR)

Quality and capacity gain

~ double capacity with tighter frequency reuse

– Dependent on AMR MS penetration

– AMR MS availability?

AMR HR performance without background noise

AMR Half Rate

Speech quality between EFR and FR

Theoretically: – double speech capacity

But:– C/I performance limit

gain

Concepts

Active Codec Set (ACS) A set of up to four different codec modes (all using the same channel rate)

Codec Mode A codec rate used within a codec set. The actual bit rate on Air-interface

Speech VersionVersion of speech coding. Sub pools in TRA pool.

FR SPV 1 = “normal Full Rate”

FR SPV 2 = “enhanced Full Rate”

FR SPV 3 = “AMR Full Rate”

HR SPV 1 = “normal Half Rate”

HR SPV 3 = “AMR Half Rate”

Channel Rate Full Rate (22,8 kbps gross bit rate on air interface) and Half Rate (11,4 kbps gross bit rate)

AMR transcoders

There are 8 different codec modes available:– 12,2 kbps– 10,2 kbps– 7,95 kbps– 7,40 kbps– 6,70 kbps– 5,90 kbps– 5,15 kbps– 4,75 kbps

An Active Codec Set may contain up to 4 codec modes, all using the same channel rate

12,2 kbps and 10,2 kbps can only be used in FR channels and the other six can be used in both FR and HR channels

Totally 22.8 kbit/s (Full Rate)

10.2

7.95

7.40

4.75

6.70

5.90

5.15

Data Error Correction

12.2 = GSM EFR 8 codec modes for FR

• 5 codec modes for HR (7.95 would require 16k A-bis)

• Up to 4 codec modes in one Active Codec Set

AMR - Codec Modes

Codec mode adaptation

Channel rate selected by network at call setup Active Codec Set communicated to the MS and BTS The codec modes in an ACS is defined as:

CODEC_MODE_1 - Represents the codec mode with the lowest bit rate

CODEC_MODE_2 - Represents the second lowest mode (if ACS includes more than one mode)

CODEC_MODE_3 - Represents the third lowest mode (if ACS includes more than two modes)

CODEC_MODE_4 - Represents the highest mode (if ACS includes four modes)

Thresholds for a codec set

THR_1/2/3 is given as integer values between 0 and 63 (unit: 0,5 dB)

HYST_1/2/3 is given as integer values between 0 and 15 (unit: 0,5 dB)

Thresholds and hysteresis values are used to determine which codec mode to use for a certain channel quality (C/I)

Predefined Codec Sets AMR Full Rate (AFR)

Full Rate Codec Set 1

CODEC_MODE_1 4,75 kbps









Decision thresholds and hysteresis values for FR Codec Set 1

Threshold Value (dB) Hysteresis Value (dB)

THR_1 6 HYST_1 1

THR_2 10,5 HYST_2 1,5

THR_3 10,5 HYST_3 1,5



THR_1 6 HYST_1 1

THR_2 8,5 HYST_2 1,5

THR_3 12,5 HYST_3 1,5

Predefined Codec Sets AMR Half Rate (AHR)

Half Rate Codec Set 1





Half Rate Codec Set 2




Decision thresholds and hysteresis values for HR Codec Set 1


THR_1 11,5 HYST_1 1,5

THR_2 14 HYST_2 2

THR_3 16 HYST_3 2

Decision thresholds and hysteresis values for HR Codec Set 2


THR_1 11,5 HYST_1 1,5

THR_2 15,5 HYST_2 2

AMR FR codec set 5








THR_1 6 HYST_1 1

THR_2 8 HYST_2 1

THR_3 12,5 HYST_3 1,5

This codec set, together with the Half Rate Codec set 2 satisfies the AMR FR and AMR HR interoperation in an optimal way for TFO connections. With these two codec sets it will be possible to run TFO on the three lower modes (7.4 - 5.9 - 4.75) since they are common.

• EFR calls get very bad speech quality at C/I ~7dB• AMR calls get very bad speech quality at C/I ~2 dB• EFR and AMR calls drop due to signalling at C/I ~4 dB

• Call drop occur when signalling channel is too disturbed (same for EFR and AMR)

• AMR and EFR use the same signalling channel (SACCH)

C/I (dB) 20 10 7 4 2 0

EFR

AMRCall drop

EFRBadSpeech

Area where EFR users may hang up due to bad quality, but AMR users may go on and eventually drop the calls (while still talking)

Good radio conditions Bad radio conditions

Behaviour of AMR vs. EFR

AMR Radio Link Timers on UL and DL

Separate AMR FR- and AMR HR- values for the parameters RLINKT and RLINKUP exists

It is recommended to put these parameters to higher values that RLINKT and RLINKUP

AMR HR

AMR FR

RLINKTAFR

RLINKUPAFR

RLINKTAHR

RLINKUPAHR

Non AMR

RLINKT

RLINKUP

AMR Related Statistics

There are a number of STS counters related to AMR:– SQI counters, belong to object types CELLSQI and

CELLSQIDL. – Codec mode utilization counters (uplink and downlink),

belong to object types CLTCHFV3C and CLTCHHV3C. – FER counters, belong to object types CELLFERF,

CELLFERH, CELLAFFER and CELLAHFER. – Dropped call counters, belong to object types CELTCHF,

CELTCHH, CLTCHDRAF and CLTCHDRAH. – Traffic level counters, belong to object types CELTCHF and

CELTCHH.

Inband signalling (BTS <-> MS)

Parameter summary

AMRFRSUPPORT Indicates if the AMR FR is turned ON or OFF and also which full rate codec set codec set that shall be

used within the BSC AMRHRSUPPORT Indicates if the AMR HR is turned ON or OFF and

also which full rate codec set codec set that shall be used within the BSC

SET Indicates which of the codec sets for a specific channel rate that shall be modified.

MODE Specifies the codec modes that shall be included in the codec set.

THR Specifies the thresholds between the codec modes in the codec set.

HYST Specifies the hysteresis values for the threshold in the codec set.

Parameters

Parameter Default value

Rec. value Value range

AMRFRSUPPORT 0 - 0=off

1=Full rate codec set 1





AMRHRSUPPORT 0 - 0=off

1=Half rate codec set 1




SET - - FR3, FR4, HR3, HR4

MODE - - 1 to 8

THR - - 0-63 (in steps of 0.5 dB)

HYST - - 0-15 (in steps of 0.5 dB)

Documents

12-AMR