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GSM BSS

GBSS14.0

Robust Air Interface Signaling

Feature Parameter Description

Issue 02

Date 2013-04-12

HUAWEI TECHNOLOGIES CO., LTD.


2/23

Copyright Huawei Technologies Co., Ltd. 2013. All rights reserved.

No part of this document may be reproduced or transmitted in any form or by any means without prior written

consent of Huawei Technologies Co., Ltd.

Trademarks and Permissions

and other Huawei trademarks are trademarks of Huawei Technologies Co., Ltd.

All other trademarks and trade names mentioned in this document are the property of their respective holders.

Notice

The purchased products, services and features are stipulated by the contract made between Huawei and the

customer. All or part of the products, services and features described in this document may not be within the

purchase scope or the usage scope. Unless otherwise specified in the contract, all statements, information,and recommendations in this document are provided "AS IS" without warranties, guarantees or representations

of any kind, either express or implied.

The information in this document is subject to change without notice. Every effort has been made in the

preparation of this document to ensure accuracy of the contents, but all statements, information, and

recommendations in this document do not constitute a warranty of any kind, express or implied.

Huawei Technologies Co., Ltd.

Address: Huawei Industrial Base

Bantian, Longgang

Shenzhen 518129

People's Republic of China

Website: http://www.huawei.com

Email: [email protected]

Issue 02 (2013-04-12) Huawei Proprietary and Confidential

Copyright Huawei Technologies Co., Ltd.

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Contents

1 Introduction....................................................................................................................................1

1.1 Scope..................................................................................................................................................................1

1.2 Intended Audience..............................................................................................................................................1

1.3 Change History...................................................................................................................................................1

2 Overview.........................................................................................................................................3

2.1 Introduction........................................................................................................................................................3

2.2 Benefits...............................................................................................................................................................4

3 Technical Description...................................................................................................................5

3.1 Repeated Downlink FACCH..............................................................................................................................5

3.1.1 Overview...................................................................................................................................................5

3.1.2 Implementation in the BSS........................................................................................................................5

3.2 Repeated SACCH...............................................................................................................................................6

3.2.1 Overview...................................................................................................................................................6

3.2.2 Implementation in the BSS........................................................................................................................6

4 Related Features.............................................................................................................................8

4.1 Prerequisite Features...........................................................................................................................................8

4.2 Mutually Exclusive Features..............................................................................................................................8

4.3 Impacted Features...............................................................................................................................................8

5 Network Impact.............................................................................................................................9

5.1 System Capacity.................................................................................................................................................9

5.2 Network Performance.........................................................................................................................................9

6 Engineering Guidelines.............................................................................................................106.1 When to Use Robust Air Interface Signalling..................................................................................................10

6.2 Required Information.......................................................................................................................................10

6.3 Planning............................................................................................................................................................10

6.4 Deployment......................................................................................................................................................11

6.5 Performance Monitoring...................................................................................................................................11

6.6 Parameter Optimization....................................................................................................................................12

6.7 Troubleshooting................................................................................................................................................13

7 Parameters.....................................................................................................................................14

8 Counters........................................................................................................................................17

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Robust Air Interface Signaling Feature Parameter

Description Contents



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9 Glossary.........................................................................................................................................18

10 Reference Documents...............................................................................................................19

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1Introduction

1.1 Scope

This document describes the GBFD-113721 Robust Air Interface Signalling feature, including

its implementation principles, parameters, related features, network impact, and engineering

guidelines. This feature consists of two functions: Repeated Downlink FACCH and Repeated

SACCH.

1.2 Intended Audience

This document is intended for personnel who:

l Need to understand the Robust Air Interface Signalling feature

l Work with Huawei GSM products

1.3 Change History

This section provides information about the changes in different document versions.

There are two types of changes, which are defined as follows:

l Feature change: refers to a change in the Robust Air Interface Signalling feature of a specificproduct version.

l Editorial change: refers to a change in wording or the addition of information that was not

described in the earlier version.

Document Issues

The document issue is as follows:

l 02 (2013-04-12)

l 01 (2012-04-28)

l Draft A (2012-02-15)

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02 (2013-04-12)

This is the second release of GBSS14.0.

Compared with Issue 01 (2012-04-28) , 02 (2013-04-12) incorporates the changes described in

the following table.

Change Type Change Description Parameter Change

Feature change None None

Editorial change Optimized the descriptions

throughout the document.

None

01 (2012-04-28)

This is the first release of GBSS14.0.

Compared with issue draft A (2012-02-15) of GBSS14.0, issue 01 (2012-04-28) of GBSS14.0

has no change.

Draft A (2012-02-15)

This is the draft release of GBSS14.0.

Compared with issue 01 (2011-01-15) of GBSS13.0, issue Draft A (2012-02-15) of GBSS14.0

has no change.

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2Overview

2.1 Introduction

On networks with tight frequency reuse, strong interference, and poor radio transmission

performance, signaling messages sent using fast associated control channel (FACCH) or slow

associated control channel (SACCH) messages may be lost because of the high bit error rate

(BER) on the Um interface. Huawei addresses this issue through the Robust Air Interface

Signalling feature, which enables the BTS and MSs to repeatedly send FACCH and SACCH

messages, making FACCH and SACCH links more immune to interference and the BSC and

MSs more likely to successfully receive signaling messages.

Robust Air Interface Signalling consists of the following functions:

l Repeated Downlink FACCH

If an MS supports Repeated Downlink FACCH and the receive quality in the downlink

measurement report (MR) sent by the MS is lower than a specified threshold, the BTS will

retransmit FACCH messages to increase the probability that the MS will receive signaling

messages.

FACCH signaling messages are retransmitted using stolen frames. Therefore, Repeated

Downlink FACCH slightly affects voice quality.

l Repeated SACCH

NOTE

Repeated SACCH requires support from 3GPP Release 6 MSs (hereafter referred to as R6 MSs).If the BTS fails to correctly decode SACCH messages from an MS that supports Repeated

SACCH, it instructs the MS to retransmit the last SACCH message. If the MS fails to

correctly decode SACCH messages, it requests the BTS to retransmit the last SACCH

message.

If the radio transmission quality is poor:

Downlink signaling message retransmission reduces the number of call drops caused

by decoding failures.

Uplink signaling message retransmission increases the probability that uplink MRs can

be decoded, thereby making handover and power control decisions more accurate.

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2.2 Benefits

Robust Air Interface Signalling provides the following benefits:

l Repeated Downlink FACCH increases the FACCH performance of common MSs by about

2 dB and the FACCH performance of R6 MSs by about 4 to 5 dB.

l Repeated SACCH increases the SACCH performance of R6 MSs by about 4 to 5 dB.

l The improvements in FACCH and SACCH performance reduce the call drop rate and make

handover and power control decisions more accurate.

NOTE

For more information about the capability of R6 MSs to support Robust Air Interface Signalling, see 3GPP

TS 44.006.

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3Technical Description

3.1 Repeated Downlink FACCH

3.1.1 Overview

During a call, a great number of messages must be transmitted over the FACCH, for example,

messages during the voice group call service (VGCS) notification, dual tone multiple frequency

(DTMF) protocol control, and handover procedures. The retransmission of handover commands

during the handover procedure is especially important because these commands carry

information about the target cell and the encryption information about services. Whether MSs

can receive and correctly decode the handover commands is central to a successful handover.

Repeated Downlink FACCH applies to networks with a tight frequency reuse pattern and a high

BER on the Um interface. After the Repeated Downlink FACCH function is enabled, the BTS

retransmits downlink FACCH messages to MSs if the downlink quality is poor. This increases

the probability that MSs will correctly receive messages on the downlink FACCH.

3.1.2 Implementation in the BSS

The BSS implements Repeated Downlink FACCH as follows:

1. The REPEATDLFASETparameteris set to YES(Yes)so that the cell supports Repeated

Downlink FACCH.

2. When activating full-rate or half-rate channels, the BTS obtains the value of the RepeatedACCH Capability bit of an MS by decoding the Repeated ACCH Capability field contained

in the Channel Active information element (IE). The value of this bit indicates the capability

of the MS to support Robust Air Interface Signalling.

3. The BTS compares the receive quality in the downlink MR with the value of the

REPEATDLFATHREDparameter to determine whether to retransmit downlink FACCH

messages.

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NOTE

According to 3GPP TS 44.006, the BTS retransmits FACCH messages according to the following rules:

l For MSs whose Repeated ACCH Capabilityis set to 0, the BTS retransmits only LAPDm command

frames carried in an FACCH message, not LAPDm response frames. For MSs whose Repeated ACCH

Capabilityis set to1, the BTS retransmits both types of frames.l FACCH messages are retransmitted in the following way: If the first burst of the first FACCH message

is sent in TDMA frame M, the first burst of the retransmitted FACCH message is sent in TDMA frame

M+8 or M+9 (the latter corresponds to cases where the two FACCH messages are separated by either

an SACCH message or an idle frame).

3.2 Repeated SACCH

3.2.1 Overview

The MS transmits link quality reports and MRs that contain the signal strengths of the servingcell and its neighboring cells to the BSC over the uplink SACCH. These reports are crucial to

MS handovers because the BSC determines which target cell to hand over an MS to according

to these reports. The downlink SACCH transmits information about power control and timing

advance (TA) values.

Adaptive multirate (AMR) FR speech frames are more robust than SACCH messages, that is,

AMR FR speech frames have better performance than SACCH messages when the radio channel

quality is poor. Therefore, after the AMR feature is enabled, calls may drop because of signaling

transmission failures on the SACCH before calls are terminated by subscribers due to poor

speech quality.

After Repeated SACCH is enabled, MSs or the BTS may retransmit SACCH messages to the

peer end, thereby increasing the success rate of message transmission.

Repeated SACCH applies when the AMR feature is enabled.

NOTE

After AMR is enabled, the call drop rate on the traffic channel (TCH) may increase. For details, see "Impact

on KPI" inAMR Feature Parameter Description.

3.2.2 Implementation in the BSS

The BSS implements Repeated SACCH as follows:

1. The REPEATSASETparameter is set to YES(Yes)so that the cell supports RepeatedSACCH.

2. When activating full-rate channel or half-rate channel, the BTS obtains the capability of

an MS to support Robust Air Interface Signaling by decoding the Repeated ACCH

Capability in the Channel Active IE.

3. Repeated SACCH is triggered in the following case:

l If the BTS fails to decode the SACCH frame correctly, it sets the SACCH Repetition

Order(SRO) in the downlink SACCH to 1 and instructs the MS to retransmit the last

SACCH frame.

l If the MS fails to decode the SACCH frame correctly, it sets the SACCH Repetition

Request(SRR) in the uplink SACCH frame to 1 and requests the BTS to retransmit themessage on the SACCH.

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SRR and SRO are IEs in SACCH messages. For more information about the two IEs, see 3GPP

TS 44.004. Table 3-1describes the values and meanings of SRR and SRO.

Table 3-1Values of the SRR and SRO

Value Description

0 Repeated SACCH not required

1 Repeated SACCH required

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4Related Features

4.1 Prerequisite Features

None

4.2 Mutually Exclusive Features

None

4.3 Impacted FeaturesNone

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5Network Impact

5.1 System Capacity

None

5.2 Network Performance

Repeated Downlink FACCH

l Reduces call drops due to failures in decoding the handover command by MSs and increases

the handover success rate. This is true when the carrier-to-interference ratio (CIR) is lowor greatly fluctuates.

l Slightly affects voice quality because stolen frames are used.

Repeated SACCH

l Reduces call drops caused by expiry of a radio link timer.

l Increases the probability of interpreting uplink MRs, making handover decisions more

accurate.

l Makes power control more effective when the CIR is low.

NOTE

Below is an instance of how Robust Air Interface Signaling affects network performance. After Robust

Air Interface Signaling is enabled at a site on a live network, the call drop rate decreases by 0.05% and the

handover success rate increases by 0.2%. The specific gains depend on various factors, such as the network

KPIs, whether AMR services are used, and the R6 MS penetration rate.

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6Engineering Guidelines

6.1 When to Use Robust Air Interface Signalling

Enable Repeated Downlink FACCH when the Um interface quality is poor and the interference

is strong, for example, in top 10 cells with poor LQIs.

Enable Repeated SACCH when AMR is enabled and R6 MSs are used.

6.2 Required Information

Before enabling Robust Air Interface Signalling, collect the following information:

l Coverage and Um interface interference level: The gains of this feature are significant in

scenarios with weak coverage or strong interference.

l TCH handover success rate: The gains of this feature are significant when the handover

success rate is low.

l TCH call drop rate: The gains of this feature are significant in scenarios with a high TCH

call drop rate.

l R6 MS penetration rate: When other conditions remain unchanged, the higher the R6 MS

penetration rate, the greater the gains of this feature.

l Whether the AMR feature is enabled: Repeated SACCH applies only to networks enabled

with AMR.

6.3 Planning

RF Planning

N/A

Network Planning

N/A

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Hardware Planning

N/A

6.4 DeploymentFor details about how to activate, verify, and deactivate this feature, see Configuring Robust

Air Interface Signalling.

6.5 Performance Monitoring

Feature performance can be monitored by counters. For details about these counters, see 8

Counters.

The gains provided by this feature can be monitored by counters related to the handover success

rate and call drop rate.

1. Counters related to the handover success rate

Compare the values of the counters listed in Table 6-2before and after Robust Air Interface

Signalling is enabled. After this feature is enabled, the handover success rate should

increase. The increased value depends on various factors, such as the Um interface quality,

original handover success rate, and R6 MS penetration rate.

Table 6-1Counters related to the handover success rate

Counter ID Counter Name Description

1278078483 CELL.HO.SUCC.RATE RH303:Handover SuccessRate

1278078484 CELL.RD.HO.SUCC.RA

TE

RH303A:Success Rate of

Radio Handover

1278077526 CELL.INTRABSC.HO.S

UCC.RATE

RH303B:Intra-BSC

Handover Success Rate

1278077527 CELL.INTRABSC.RD.H

O.SUCC.RATE

RH303C:Intra-BSC Radio

Handover Success Rate

1278080469 CELL.INTERBSC.INCEL

L.HO.SUCC.RATE

TH343:Success Rate of

Incoming External Inter-Cell Handovers

1278080482 CELL.INTERBSC.INTO.

CELL.RD.HO.SUCC.RA

TE

RH303D:Success Rate of

Incoming External Inter-

Cell Radio Handovers

1278081560 CELL.INTERBSC.OUTC

ELL.HO.SUCC.RATE

TH333:Success Rate of

Outgoing External Inter-

Cell Handovers

1278081578 CELL.INTERBSC.OUT.C

ELL.RD.HO.SUCC.RATE

RH303E:Success Rate of

External Outgoing Cell

Radio Handovers

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Counter ID Counter Name Description

1278078485 CELL.DOUBLE.FH.HO.S

UCC.RATE.900.1800

RH303F:Success Rate of

Dual-Band Handovers

(900/850/810-1800/1900)

1278078486 CELL.DOUBLE.FH.HO.S

UCC.RATE.1800.900

RH303G:Success Rate of

Dual-Band Handovers

(1800/1900-900/850/810)

2. Counters related to the call drop rate

Compare the values of the counters listed in Table 6-5 before and after Robust Air Interface

Signalling is enabled. After this feature is enabled, the call drop rate should decrease. The

decreased value depends on various factors, such as theUm interface quality, original call

drop rate, and R6 MS penetration rate.

Table 6-2Counters related to the call drop rate

CounterID

Counter Name Description

12780725

94

CELL.RATE.TCH.CALL.DROP.INCLUDE.H

O

ZTR304:Call Drop

Rate on TCH per cell

(including Handover)

12780725

95

CELL.RATE.TCH.CALL.DROP.EXCLUDE.H

O

ZTR304A:Call Drop

Rate on TCH per cell

(Excluding Handover)

12784734

73

CELL.RATIO.CALL.DROP ZTR308:Traffic Call

Drop Ratio per cell

12780725

96

CELL.TCH.RD.DROP RM333:Radio Drop

Rate of TCH

12780754

92

CELL.CALL.CMP.SUCC.RATE RA333B:Call

Complete

Establishment Success

Rate

6.6 Parameter Optimization

Repeated Downlink FACCH slightly affects voice quality because this function uses stolen

frames. The value of REPEATDLFATHREDdetermines the probability of FACCH message

retransmission. This parameter helps operators balance the voice quality, handover success rate,

and call drop rate.

The larger the value of this parameter, the less likely the FACCH messages will be retransmitted

and the smaller impact Repeated Downlink FACCH will have on voice quality.

The smaller the value of this parameter, the more likely the FACCH messages will beretransmitted and the greater impact Repeated Downlink FACCH will have on voice quality.

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6.7 Troubleshooting

N/A

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7ParametersTable 7-1Parameter description

Parameter ID NE MMLCommand

Feature ID Feature Name Description

REPEATDLF

ASET

BSC6900 SET

GCELLCCBA

SIC

GBFD-113721 Robust Air

Interface

Signalling

Meaning:When

the cell supports

Repeated

Downlink

FACCH, the

BTS enables the

repeated

transmission of

FACCH framesif the measured

downlink

quality is higher

than "Repeated

Downlink

FACCH

Threshold".

GUI Value

Range:NO(No),

YES(Yes)

Unit:NoneActual Value

Range:NO, YES

Default

Value:NO(No)

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REPEATDLF

ATHRED

BSC6900 SET

GCELLCCBA

SIC


Interface

Signalling

Meaning:If the

cell supports the

Repeated

Downlink

FACCH

function and the

measured

downlink

quality is lower

than the

downlink

quality

threshold, the

BTS enables therepeated

transmission of

FACCH frames.

GUI Value

Range:0~7

Unit:None

Actual Value

Range:0~7

Default Value:5

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REPEATSASE

T

BSC6900 SET

GCELLCCBA

SIC


Interface

Signalling

Meaning:Wheth

er to support

Repeated

Downlink

SACCH in a

cell. Assuming

that a cell

supports

Repeated

Downlink

SACCH and an

MS in the cell

supports

RepeatedSACCH. If the

BTS cannot

correctly parse

SACCH frames,

it instructs the

MS to retransmit

the latest

SACCH frame.

If the MS cannot

correctly parse

SACCH frames,

it requests theBTS to

retransmit the

latest SACCH

frame.

GUI Value

Range:NO(No),

YES(Yes)

Unit:None

Actual Value

Range:NO, YES

Default

Value:NO(No)

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8CountersTable 8-1Counter description

Counter ID Counter Name CounterDescription

NE Feature ID Feature Name

1282431774 TRX.REPEAT.

FACCH.NUM

S4233A:Numbe

r of

Retransmitted

Downlink

FACCH Frames

BSC6900 GBFD-113721 Robust Air

Interface

Signalling


SACCH.NUM

S4233B:Numbe

r of

RetransmittedDownlink

SACCH Frames


Interface

Signalling


SACCH.IND.N

UM

S4233C:Numbe

r of Indications

to MS for

Retransmitting

SACCH Frames


Interface

Signalling

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9GlossaryFor the acronyms, abbreviations, terms, and definitions, see the Glossary.

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10Reference Documents1. 3GPP TS 44.001 "Mobile Station - Base Station System (MS - BSS) Interface General

Aspects and Principles"

2. 3GPP TS 44.003 "Mobile Station - Base Station System (MS - BSS) interface Channel

structures and access capabilities"

3. 3GPP TS 44.004 "Layer 1 General requirements"

4. 3GPP TS 44.005 "Data Link (DL) layer General aspects"

5. 3GPP TS 24.007 "Mobile radio interface signalling layer 3; General aspects"

6. 3GPP TS 44.018 "Mobile radio interface layer 3 specification; Radio Resource Control

Protocol"

7. 3GPP TS 45.002 "Multiplexing and multiple access on the radio path"

8. 3GPP TS 48.056 "Base Station Controller - Base Transceiver Station (BSC - BTS)interface; Layer 2 specification"

9. 3GPP TS 48.058 "Base Station Controller - Base Transceiver Station (BSC - BTS)

interface; Layer 3 specification"

GSM BSS


Description 10 Reference Documents

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