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Copyright 2010 Huawei Technologies Co., Ltd. All rights reserved.

GSM Multiple RateAlgorithm

Copyright 2010 Huawei Technologies Co., Ltd. All rights reserved. Page1

Objectives Upon completion of this course, you will be able to:

Understand the multiple rate algorithm function and types.

Master the parameters of multiple rate algorithm.

Be able to configure the data of multiple rate algorithm.

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Full Rate

Traffic Channel (TCH) carries coded voice data. The full-

rate TCH is initially adopted to carry information at the

gross rate 22.8Kbit/s. The information contains the source

coding rate of 13Kbit/s.

As technologies develop, the enhanced full rate, half rate,

multiple rate and other coding are introduced.


Speech Version Speech version indicates the voice coding technology.

Full RateFull Rate

Speech Version1 FR

Speech Version2 EFR

Speech Version3 AMR

Half RateHalf Rate

Speech Version1 HR

Speech Version2 /

Speech Version3 AMR

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Circuit Pool Function

Circuit pool number actually represents the circuit type,

indicating the support capability of the voice codec.

Different circuit pool numbers can support different voice rates.


Circuit Pool FunctionCircuit Pool

NumberSupported Rate

1FR speech version 1FR data (12, 6, 3.6Kbps)

2 HR speech version 1HR data (6, 3.6 Kbps)

3FR speech version 1FR data (12, 6, 3.6Kbps)HR speech version 1HR data (6, 3.6 Kbps)

4FR speech version 2FR data (12, 6, 3.6Kbps)

5FR speech version 1FR speech version 2FR data (12, 6, 3.6 Kbps)

6

FR speech version 2FR data (12, 6, 3.6

Kbps)HR speech version 1HR data (6, 3.6 Kbps)

7

FR speech version 1FR speech version 2

FR data (12, 6, 3.6 Kbps)HR speechversion 1HR data (6, 3.6 Kbps)

Circuit PoolNumber

Supported Rate

23FR speech version 3HR speechversion 3

24FR speech version 3FR data (12, 6,3.6 Kbps)HR speech version 3

25

FR speech version 1FR speechversion 2FR speech version 3FR data (12, 6,3.6 Kbps)HR speech version 3

27

FR speech version 1FR speechversion 2FR speech version 3FR data (12, 6,3.6 Kbps)HR speech version 1HR speechversion 3HR data (6, 3.6 Kbps)

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Call Signaling Processing

BSC

ASS REQ

Channel ACT

Channel ACTACK

ASS CMD

SABM

UA

ESTIND

ASS CMPASSCMP

MS MSCBTS

Setup


Call Signaling MessageSetup Message

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Call Signaling MessageASS REQ Message


Call Signaling MessageChannel Act Message

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Call Signaling MessageASS CMD Message


Call Signaling MessageASS CMP Message

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Contents

1. EFR

2. HR

3. AMR


The Function of EFR The Enhanced Full Rate (EFR) is a speech coding scheme with

an enhanced full rate. Using this coding scheme, you can provide

services with better speech quality.

In the wireless communications system, the EFR applies to only

speech services and is irrelevant to data services or signaling

services.

The EFR function adopts the CELP( Code Excited Linear

Predictive Coding) coding scheme, thus improves the quality of

the speech signal.

When EFR is adopted, the transmission rate of the speech

signal of an MS on the air interface is 12.2 kbit/s.

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EFR Call Set-up Flow

Common call (FR)

EFR call

Speech version in the

assignment request is EFR

Start

Finish

Yes

NoWhether support EFRin the current cell?



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Call Signaling Processing

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EFR Data Configuration Configure Cell Attributes/Call Control/Advanced/Access Control

/Speech Version


Contents1. EFR

2. HR

3. AMR

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The Function of HR The half rate voice coding uses a new voice coding algorithm

called VCELPVCELP ((VectorVector--Sum Excited Linear PredictionSum Excited Linear Prediction)) to reduce

the voice coding rate to half that of full rate voice service. Thus,

one physical channel that can only support one call under the

full rate can support two calls under half rate.

If the half rate service is used, the voice capacity expands twice

without adding TRXs. By adopting half rate service, the operator

can fully use the current network to expand the system capacity.

This saves the cost and eases the spectrum use.


The Function of HR

T T T T T T T T T T T S T T T T T T T T T T T T IT

T T T T T T S T T T T T T

t t t t t t t t t t t t s

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The Function of HR

SingleWhen a timeslot is used as two TCH/H channels, one

TCH/H channel is busy and another is idle, this idle

TCH/H channel is called single channel or channel

fragment or fragment.


The Function of HR CoupleWhen a timeslot is used as two TCH/H

channels, and these two channels are both free,

this timeslot is called a couple.

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The Function of HR


Channel Assignment Strategies If the half rate function is used, when BSC receives the

assignment request from the MSC, it will decides to use the

channel allocation algorithm according to channel assignment

strategy specified in the data configuration.

MSC channel assignment strategy

Assign the channel according to the MSC request. If the request from MSC

is "TCHF preferred", assign the full rate channel preferentially. If it is

"TCHH preferred", assign the half rate channel preferentially.

BSC channel assignment strategy

When the assignment request sent from MSC is "Full rate TCH preferred"

or" Half rate TCH preferred", BSC assigns the proper channel according to

the availability of idle full rate channel in the cell and the allowance of MSC.

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Channel Assignment Strategies

The BSC channel allocation strategy is the default strategy. That is,

when the network is idle, the full rate is used, otherwise, the half

rate is used.

For the call that uses the half rate preferentially, the single channel

is assigned preferentially to reduce the fragment.

If a cell has multiple TRXs, the channels on the TRXs that do not

allow the rate adjustment are assigned preferentially.


Rate Adjustment Flow If the channel assignment request is to choose the full rate channel only:

When there is idle full rate channel, assign the channel directly.

When there is no idle full rate channel in the cell, but there is idle couple

channel, convert the couple channel to full rate channel and then assign the

converted full rate channel.

When there is no idle full rate channel and idle couple channel in the cell, but

there is idle single channel, check whether the number of single channel in

the cell is more than one. If yes, initiate intracell handover to form a couple

channel and then convert the couple channel to full rate to assign.

Otherwise, reject the assignment request.

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Rate Adjustment Flow

Yes

Yes

Yes

No

No

No

Assignment request

forTCHF only

Full rate available?

Couplechannel

available?

More than onehalf

rate channel?

Request reject

Assignfull rate channel

Convert couplechannel to full

rate channel andthen assign

the converted channel

Initiateintra-cellhandover to

form couplechannel, andthen

convert thecouplechannelto

fullrate channel to assign

Start

End


Rate Adjustment Flow If the channel assignment request is to half rate only :

When there is idle single channel in the cell , assign the idle half rate channel

on the single channel directly.

When there is no idle single channel in the cell, but there is idle couple channel

in the cell, assign the idle half rate channel on the couple channel.

When there is no idle single channel and idle couple channel in the cell, but

there is idle full rate channel in the cell, convert the full rate channel into couple

channel and then assign the idle half rate channel on the couple channel.

Otherwise, reject the request.

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Yes

Yes

Yes

No

No

No

Half rate only assignment request

Single channel available?

Couple channel available?

Full rate channel available?

Assignment fails

Assign half rate channel

Assign the half rate channel

on the couple channel

Convert the full rate channelinto couple channel and

then assign the half ratechannel on it

Start

End


Rate Adjustment Flow If the channel assignment request is to choose the full rate channel

preferentially:

When there is idle full rate channel in the cell, assign it directly.


in the cell, convert the couple channel into full rate channel and then assign it.

When there is no idle full rate channel and couple channel in the cell, check

whether the number of adjustable half rate channel in the cell is more than one.

If yes, initiate intracell handover to form a couple channel and then convert the

couple channel to full rate to assign

Otherwise, assign the idle half rate channel on the single channel.

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Yes

Yes

No

No

No

Yes

Assignrequest for full rate preferentially

Full rate available?

Couplechannelavailable?

More than onehalf rate channel?

Assignfull ratechannel

Convert the couplechannel

into fullrate channel to assign

Formcouple channel by intracellhandoverand thenconvertcouplechannel into fullrateto assign

Start

End

Assignhalf rate channel


Rate Adjustment Flow If the channel assignment request is to half rate preferentially:

When there is idle single channel in the cell , assign the idle half rate channel

on the single channel directly.


in the cell, assign the idle half rate channel on the couple channel.

When there is no idle single channel and idle couple channel in the cell, but

there is idle full rate channel in the cell, convert the full rate channel into couple

channel and then assign the idle half rate channel on the couple channel.

Otherwise, assign the idle full rate channel.

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Yes

Yes

Yes

No

No

No

Prefer half rate assignment request

Single channel available?

Couple channel available?

Full rate channel available?

Assignment TCH/F

Assign half rate channel

Assign the half rate channel

on the couple channel

Convert the full rate channelinto couple channel and

then assign the half ratechannel on it

Start

End



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HR Data Configuration

Configure Site Attributes\multiplexing mode(1:1 or 2:1 is recommended)


HR Data Configuration Configure Call Control\Advanced\Access Control

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Configure Cell Attributes\Other Parameter\Public Channel Control\

Support Half Rate


HR Data Configuration Configure Cell Attributes\TRX Attributes\Channel Attributes\

Channel Type

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HR Data Configuration Configure Cell Attributes\TRX Attributes\Device Attributes\

TCH Rate Adjust Allow


HR Data Configuration Configure Cell Attributes\Channel Parameter\Basic Channel

Management Parameters\Enhanced TCH Adjust Allowed

Configure Cell Attributes\Channel Parameter\Advanced\TCH

Traffic Busy Threthold

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Contents1. EFR

2. HR

3. AMR

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Contents

3. AMR

3.1 AMR Overview

3.2 AMR Impact on the Network Quality

3.3 AMR Call&Handover Procedure and Parameter Introduction

3.4 AMR Optimization and Maintenance Strategy


AMR Overview AMR (Adaptive Multi Rate) is a new voice coding technique after EFR,

FR, and HR.

Its core thought is to automatically select appropriate codec algorithm

and constantly select the voice coding rate according to change of the

uplink/downlink signal quality.

BER

MOS

Codec1

Codec2

Codec3

AMR

Different codec algorithms

produce voice code streams in

different rates so as to get the

optimal balance between voicequality and system capacity.

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AMR Overview

AMR is a collection of multiple voice codec algorithms. AMR allows the

BTS and the MS to select appropriate codec algorithms according to the

actual situation of the radio environment.

AMR is applicable only to the voice service of the wireless communication

system. It is not related to data service and signaling service.

You need to obtain license to use AMR. The license is applied on one cell.


AMR OverviewChannel

AMR Voice Coding Mode(Rates)

TCH/FRAMR

(8modes)

12.2 kbit/s (GSM EFR)

10.2 kbit/s

7.95 kbit/s

7.40 kbit/s

6.70 kbit/s

5.90 kbit/s

5.15 kbit/s

4.75 kbit/s

TCH/HRAMR

(6modes)

7.95Kbit/s

7.40 kbit/s6.70 kbit/s

5.90 kbit/s

5.15 kbit/s

4.75 kbit/s

AMR Voice Coding Mode (Rates)

Full-rate AMR supports eight voice

coding modes.

Half-rate AMR supports five voice

coding modes.

AMR Activated Voce Coding Set (ACS)

ACS defines the set of changes of the

voice coding rates during a call. Thisset contains one~four coding modes.

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AMR FRExperiment 1a - Test Res ults

1.0

2.0

3.0

4.0

5.0

C ondi t ions

M OS

EFR

12.210.27.957.46.75.95.154.75

EFR 4.01 4.01 3.65 3.05 1.53

12.2 4.01 4.06 4.13 3.93 3.44 1.46

10.2 4.06 3.96 4.05 3.80 2.04

7.95 3.91 4.01 4.08 3.96 3.26 1.43

7.4 3.83 3.94 3.98 3.84 3.11 1.39

6.7 3.77 3.80 3.86 3.29 1.87

5.9 3.72 3.69 3.59 2.20

5.15 3.50 3.58 3.44 2.43

4.75 3.50 3.52 3.43 2.66

No Er ro rs C/I=1 6 dB C/I=1 3 d B C/I=10 dB C/I= 7 dB C/I= 4 d B C/I= 1 dB


AMR HR

1.0

2.0

3.0

4.0

5.0

Conditions

MOS

EFR7.957.46.75.95.154.75FRHR

EFR 4.21 4.21 3.74 3.34 1.58

7.95 4.11 4.04 3.96 3.37 2.53 1.60

7.4 3.93 3.93 3.95 3.52 2.74 1.78

6.7 3.94 3.90 3.53 3.10 2.22 1.21

5.9 3.68 3.82 3.72 3.19 2.57 1.33

5.15 3.70 3.60 3.60 3.38 2.85 1.84

4.75 3.59 3.46 3.42 3.30 3.10 2.00

FR 3.50 3.50 3.14 2.74 1.50

HR 3.35 3.24 2.80 1.92

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

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Contents

3. AMR

3.1 AMR Overview





Impact of AMR on Network Quality(1) Impact of AMR on Voice Quality

According to the simulation result, when C/I is greater than 6, the

voice quality performance in descending order is FR AMR, EFR, HR

AMR, FR, and HR. It can be seen that AMR can effectively improve

network quality.

The voice quality performance of HR AMR is the similar to FR,

However, radio bandwidth occupied by HR AMR in the Um interface

is only half of that of FR. Therefore, HR AMR can not only ensure the

good voice quality, but also increase the system capacity effectively.

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Impact of AMR on Network Quality(2) Impact of AMR on Network Coverage

AMR Network Coverage Performance

AMR has excellent anti-interference capability. Under the same FER,

AMR supports lower CIR than non-AMR. Therefore AMR has better

coverage performance.

AMR Coverage Bottleneck

In the actual coverage capability of AMR is determined by the coverage

capability of the SACCH.

In application, the data[RLT] and [SACCH Multi-Frames] should be

set to higher values for AMR channels to increase the robustness of the

SACCH. Thus the network coverage performance of AMR is improvedand the call drop rate is reduced.

Enhanced signaling link technique is available to improve it.


Impact of AMR on Network Quality(3) Impact of AMR on the Network Capacity

AMR can equivalently increase the total spectrum bandwidth

of the Radio System

AMR can tolerate lower C/I. With AMR, the number of cells in a

frequency reuse cluster is smaller and the spectrum reuse

degree is higher, compared with non-AMR.

AMR can reduce the radio bandwidth for a single user

When HR AMR is used, the number of channels doubles, while

the voice quality does not drop obviously.

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Impact of AMR on Network Quality(4) Impact of AMR on KPIs

Traffic volume

The voice codec of AMR has low requirement for CIR, so in weak coverage areas

where calls could not be made before, AMR calls can be made, thus reducing the

possibility of users hang-up. Therefore, AMR can improve network traffic volume.

Call drop rate

AMR only optimizes the performance of the voice f rames. In weak coverage areas,

because voice frames can be correctly decoded, users will not hand up a phone,

however, because the SACCH frames cannot be correctly decoded, the RLT times

out, leading to call drop. Therefore with AMR, the call drop rate can rise, while

enhanced signaling link technique is available to improve it.

Handover

AMR increases the width and depth of the network coverage. But C/I is low in these

weak coverage areas and the receive quality in the measurement report is poor,

triggering BQ handover. Therefore with AMR, the number of BQ handovers can rise.


Contents3. AMR

3.1 AMR Overview




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AMR Call&Handover Procedure andData Configuration In the BSC6000, the following AMR parameters need to be set

1. AMR basic data parameters

2. ACS and starting mode

3. Coding rate adjustment threshold and hysteresis (full rate)

4. Coding rate adjustment threshold and hysteresis (half rate)

5. Radio link timeout (RLT) and SACCH Multi-Frames

6. AMR radio channel management parameters

7. AMR handover parameters

8. AMR power control parameters


AMR Parameter Introduction(1)1. AMR basic data parameters

To active AMR, enable full-

rate speech coding

algorithm 3 and half-rate

speech coding algorithm 3

on the MSC side.

In addition, configure the

corresponding interface flag

as GSM_PHASE_2+.

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AMR Parameter Introduction(1)

1. AMR basic data parameters


AMR Call Set-up Procedure

Y

FinishesAMR call set up

BSC decides whether tosupport AMR function

Normal CallN

BSC receives the assigningrequest sent by MSC

BSC decides whether toassign channel that

supports AMR function

Relationship between voice type andvoice version

FR : Full rate /speech version 1EFR: Full rate /speech version 2FR AMR : Full rate /speech version 3

HR : Half rate /speech version 1HR AMR : Half rate /speech version 3Normal Call

N

Y

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2. ACS and Starting Mode

ACS should be set basing on the actual radio environment.

However, because of the complexity of the actual radio

environment and the randomness of users' behaviors, not all

of the coding modes can be listed. Generally, the worst

coding mode, the best coding mode, and two coding modes

between them are selected.

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3. Coding Rate Adjustment Threshold and Hysteresis (FR)


AMR Parameter Introduction(4)4. Coding Rate Adjustment Threshold and Hysteresis (HR)

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AMR Parameter Introduction(4) Principles of AMR Codec Mode Adjustment

The criteria for conversion of the voice codec mode is CODEC MODE 1~4

corresponding to THR_1~3 and HYST1~3

Assume that the active codec mode is CODEC_MODE_3 for example. When

C/I is greater than THR_3+HYST_3, the codec mode is switched to

CODEC_MODE_4; when C/I is smaller than THR_2, the codec mode is

switched to CODEC_MODE_2

CODEC_MODE_4

CODEC_MODE_3

CODEC_MODE_2

CODEC_MODE_1

C/I

THR_1 + HYST_1 = THR_MX_Up(1)

THR_1 = THR_MX_Dn(2)


THR_2 + HYST_2 = THR_MX_Up(2)


THR_3 + HYST_3 = THR_MX_Up(3) The adjustment of thepractical voice codecrate can only changesstep by step, while can

not jump over severalsteps for suddenchanging of C/I


Principle of AMR Coding Mode Adjustment The uplink coding mode is detected by the BTS.

If the BTS discovers that the configured threshold is achieved, it initiates

Coding Mode Change command.

After the conversion of the coding mode is completed, the MS responds with

a Coding Mode Indication message.

AMRFR/HRUL Codec Mode Adjustment

Coding Mode Change

Coding Mode Indication

BTS detects that RQI

reaches the threshold

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Principle of AMR Coding Mode Adjustment

The downlink coding is detected by the MS(The same algorithm is used).

When the MS detects that the threshold is achieved, it initiates Coding

Mode Request.

The BTS either ignores or immediately responds to the request

depending on the actual situation.

Upon completion, the BTS sends a Coding Mode Indication message

to the MS.

Coding Mode Request

Coding Mode Indication

MS detects that RQIreaches the threshold

AMRFR/HR DL Codec Mode Adjustment


AMR Parameter Introduction(5)5. Radio Link Timeout (RLT) and SACCH Multi-Frames

To increase the robustness of the SACCH channel, to

improve the AMR network coverage performance, and to

lower the call drop rate, in practice the RLT and SACCH Multi-

Frames should be set higher.

On the other side, Enhanced Signaling Link Technique is

available to improve it.

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Enhanced Signaling Link Technique

Repeated Downlink FACCH

Improve the probability of the

MS receiving the FACCH

frames in the poor radio

enviroment

Repeated SACCH

Improve the robustness of

SACCH links



Repeated Downlink FACCH Technical Principle

Enable BSS to transmit the FACCH frames repeatedly when the measurement

result of the downlink link is lower than the threshold configured.

The repetition mechanism is as follows

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Implementation of Repeated

Downlink FACCH Technical

1. Enable the cell-level switch


and configure Repeated

Downlink FACCH Threshold



Implementation of Repeated Downlink FACCH Technical

2. BSC decodes the capability of the MS support Repeated ACCH ,

and then informs BTS about the Repeated ACCH Capability of the

MS via Channel Active message when activizing TCH channel.

3. BTS determines whether to start to send repeated FACCH

messages by comparing the receive quality provided in the downlink

MR and the Repeated Downlink FACCH Threshold.

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Repeated SACCH Technical Principle

Add SRO(SACCH Repetition Order) indication bit on the downlink SACCH, and

SRR(SACCH Repetition Request) indication bit on the uplink SACCH.

Upon the failure to decode an SACCH frame, BTS sets the SRO to 1, requesting

MS to resend the SACCH frame.

Upon the failure to decode an SACCH frame, MS sets the SRR to 1, requesting

BTS to resend the SACCH frame.



Implementation of Repeated

SACCH Technical

1. Enable the cell-level switch


2. BSC decodes the capability of the

MS support Repeated ACCH ,

and then informs BTS about the

Repeated ACCH Capability of the

MS via Channel Active message

when activising TCH channel.

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Implementation of Repeated SACCH Technical

3. Suppose MS supports Repeated ACCH Capability

when BTS receives the uplink SACCH frame in which SRR=1, the BTS

will resend SACCH frames excluding short message unti l SRR=0

If BTS fails to decode an uplink SACCH, BTS sets SRO=1, requesting

MS to resend the uplink SACCH frame until SRO=0


AMR Parameter Introduction(6)6. AMR Radio Channel Management Parameters

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7. AMR Handover Parameters

AMR handover is the intra-cell handover between FR AMR and

HR AMR.

Via HR-FR channel conversion, which is based on RQI and

channel occupation ratio, control strategy for balancing between

the capacity and quality of the cell is provided.

When configure the handover parameters, [AMR TCH/H Prior

Allowed] and [AMR TCH/H Prior Cell Load Threshold] should

be taken into account.


AMR Handover Procedure AMR handover refers to the intra-cell handover between FR AMR and HR

AMR basing on the RQI.

The AMR handover provides control strategy of capacity-quality balance

within a cell.

The AMR handover is implemented through the intra-cell handover procedure.

If in P seconds of N seconds:RQI > [F2H HO Threshold], then intra-cell handover indication from FR AMR toHR AMR is initiated;

RQI < [H2F HO Threshold], then intra-cell handover indication from HR AMR toFR AMAR is initiated.

Relationship between RQI and C/IRQI = 2*C/I

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AMR Handover ProcedureBegin

Is [Intracell F-H HOAllowed] Yes ?

Yes

Is current channelTCH & version3?

No

A: Cell load > [AMR TCH/H Prior

Cell Load Threshold]

During [Penalty Timeafter AMR TCHF-H HO

Fail(s)]?

Yes

Yes

Is current channel FR?

Satisfy P/N rule?Trigger internal cell

AMR handover

Yes

NoEnd

RQI/2 >[F2H HO th] & A RQI/2

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7. AMR Handover Parameters


AMR Parameter Introduction(8)8. AMR Power Control Parameters

Different power control thresholds are set for AMR calls and non-AMR

calls. AMR calls are transmitted in lower power than non-AMR calls.

The setting principles are as follows:

Set lower AMR UL/DL RX_LEV Upper/Lower Threshold for AMR calls

than those for non-AMR calls.

Set higher AMR UL/DL Qual. Upper/lower Threshold for AMR calls than

those for non-AMR calls.

Keep other AMR power control parameters consistent with normal power

control parameters. In practice, need to consider the setting of normal power control

parameters to adjust the AMR power control parameters.

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8. AMR Power Control Parameters


AMR Parameter Introduction(8)8. AMR Power Control Parameters

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Contents

3. AMR

3.1 AMR Overview





AMR Optimization&Maintenance Strategy(1)

No. Performance Counters

1 Speech Version 1 Completed Assignments(Excluding Directed Retry)(TCHF)



4 Speech Version 1 Completed Assignments(Excluding Directed Retry)(TCHH)



Half rate speech version 2 actually does not exist. Therefore the half rate speech

version 2 TCH assignments (excluding direct retry) should be always zero

Traffic StatisticsAMR Call Ratio Calculation

If you need to calculate AMR (speech version 3) call ratio, according to

the number of TCH assignment successes of various speech versions

under full rate/half rate.

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AMR Optimization&Maintenance Strategy(2)

Adding cell-level AMR call counters.

Cell-level AMR call counters are added in the Call Measurement.

Radio quality indication (RQI) performance statistics

TRX-level RQI performance statistics function by TA distribution

is provided.


Summary In this course we have learned

The function of EFR, HR, AMR

The signaling assignment flow of EFR, HR, AMR

Data configuration of EFR, HR, AMR

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