Repeated FACCH

GSM BSS GBSS14.0

Robust Air Interface Signaling Feature Parameter Description Issue

02

Date

2013-04-12

HUAWEI TECHNOLOGIES CO., LTD.

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.

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Website:

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Email:

[email protected]

Issue 02 (2013-04-12)

Huawei Proprietary and Confidential Copyright © Huawei Technologies Co., Ltd.

i

GSM BSS Robust Air Interface Signaling Feature Parameter Description

Contents

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.............................................................................................................10 6.1 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 Issue 02 (2013-04-12)


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Contents

9 Glossary.........................................................................................................................................18 10 Reference Documents...............................................................................................................19

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1 Introduction

1

Introduction

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 specific product 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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1 Introduction

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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2 Overview

2

Overview

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 Overview

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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3 Technical Description

3

Technical 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 REPEATDLFASET parameter is 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 Repeated ACCH 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 REPEATDLFATHRED parameter 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 Capability is set to 0, the BTS retransmits only LAPDm command frames carried in an FACCH message, not LAPDm response frames. For MSs whose Repeated ACCH Capability is set to 1, 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 serving cell 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" in AMR Feature Parameter Description.

3.2.2 Implementation in the BSS The BSS implements Repeated SACCH as follows: 1.

The REPEATSASET parameter is set to YES(Yes) so that the cell supports Repeated SACCH.

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 the message 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 3-1 describes the values and meanings of SRR and SRO. Table 3-1 Values of the SRR and SRO

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Value

Description

0

Repeated SACCH not required

1

Repeated SACCH required


7


4 Related Features

4

Related Features

4.1 Prerequisite Features None

4.2 Mutually Exclusive Features None

4.3 Impacted Features None

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5 Network Impact

5

Network 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 low or 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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6 Engineering Guidelines

6

Engineering 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 Issue 02 (2013-04-12)


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Hardware Planning N/A

6.4 Deployment For 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 6-2 before 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 6-1 Counters related to the handover success rate

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Counter ID

Counter Name

Description

1278078483

CELL.HO.SUCC.RATE

RH303:Handover Success Rate

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 InterCell Handovers

1278080482

CELL.INTERBSC.INTO. CELL.RD.HO.SUCC.RA TE

RH303D:Success Rate of Incoming External InterCell Radio Handovers

1278081560

CELL.INTERBSC.OUTC ELL.HO.SUCC.RATE

TH333:Success Rate of Outgoing External InterCell Handovers

1278081578

CELL.INTERBSC.OUT.C ELL.RD.HO.SUCC.RATE

RH303E:Success Rate of External Outgoing Cell Radio Handovers


11


2.


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)

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 the Um interface quality, original call drop rate, and R6 MS penetration rate. Table 6-2 Counters related to the call drop rate Counter ID

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 REPEATDLFATHRED determines 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 be retransmitted and the greater impact Repeated Downlink FACCH will have on voice quality. Issue 02 (2013-04-12)


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6.7 Troubleshooting N/A

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7 Parameters

7

Parameters

Table 7-1 Parameter description Parameter ID

NE

MML Command

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 frames if the measured downlink quality is higher than "Repeated Downlink FACCH Threshold". GUI Value Range:NO(No), YES(Yes) Unit:None Actual Value Range:NO, YES Default Value:NO(No)

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7 Parameters

Parameter ID

NE

MML Command

Feature ID

Feature Name

Description

REPEATDLF ATHRED

BSC6900

SET GCELLCCBA SIC

GBFD-113721


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 the repeated transmission of FACCH frames. GUI Value Range:0~7 Unit:None Actual Value Range:0~7 Default Value:5

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7 Parameters

Parameter ID

NE

MML Command

Feature ID

Feature Name

Description

REPEATSASE T

BSC6900

SET GCELLCCBA SIC

GBFD-113721


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 Repeated SACCH. 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 the BTS 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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8 Counters

8

Counters

Table 8-1 Counter description Counter ID

Counter Name

Counter Description

NE

Feature ID

Feature Name

1282431774

TRX.REPEAT. FACCH.NUM

S4233A:Numbe r of Retransmitted Downlink FACCH Frames

BSC6900

GBFD-113721


1282431775

TRX.REPEAT. SACCH.NUM

S4233B:Numbe r of Retransmitted Downlink SACCH Frames

BSC6900

GBFD-113721


1282431776

TRX.REPEAT. SACCH.IND.N UM

S4233C:Numbe r of Indications to MS for Retransmitting SACCH Frames

BSC6900

GBFD-113721


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9 Glossary

9

Glossary

For the acronyms, abbreviations, terms, and definitions, see the Glossary.

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10

10 Reference Documents

Reference Documents

1.

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"

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Repeated FACCH

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