adjustment of adaptive timing advance

Adjustment of Adaptive Timing Advance Feature Parameter Description

Copyright © Huawei Technologies Co., Ltd. 2010. 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 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 the warranty of any kind, express or implied.

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

BSS Adjustment of Adaptive Timing Advance Contents

Issue 01 (2010-01-12) Huawei Proprietary and Confidential Copyright © Huawei Technologies Co., Ltd

iii

Contents 1 Introduction ................................................................................................................................1-1

1.1 Scope ............................................................................................................................................ 1-1 1.2 Intended Audience ........................................................................................................................ 1-1 1.3 Change History.............................................................................................................................. 1-1

2 Overview of Adjustment of Adaptive Timing Advance ...................................................2-1

3 Technical Description ..............................................................................................................3-1

4 Parameters .................................................................................................................................4-1

5 Counters......................................................................................................................................5-1

6 Glossary ......................................................................................................................................6-1

7 Reference Documents .............................................................................................................7-1

BSS Adjustment of Adaptive Timing Advance 1 Introduction


1-1

1 Introduction 1.1 Scope This document describes the feature of adjustment of adaptive timing advance of Huawei Global System for Mobile communications (GSM) Base Station Subsystem (BSS).

1.2 Intended Audience This document is intended for:

Personnel who need to understand adjustment of adaptive timing advance Personnel who work with Huawei products

1.3 Change History This section provides information on the changes in different document versions.

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

Feature change: refers to the change in the adjustment of adaptive timing advance feature of a specific product version.

Editorial change: refers to the change in wording or the addition of the information that was not described in the earlier version.

Document Issues The document issues are as follows:

01 (2010-01-12)

01 (2010-01-12) This is the initial issue of GBSS9.0.

BSS Adjustment of Adaptive Timing Advance

2 Overview of Adjustment of Adaptive Timing Advance


2-1

2 Overview of Adjustment of Adaptive Timing Advance In the GSM system, an uplink is a radio link for transmitting signals from an MS to a BTS while a downlink is for transmitting signals from a BTS to an MS. The Time Division Multiple Access (TDMA) frame of an uplink is later than that of a downlink by three bursts, that is, about 1730 µs. Transmission delay between the MS and the BTS, however, changes due to MS mobility. To compensate for transmission delay jitter, the MS must transmit signals to the BTS by a certain time period in advance. The time period is referred to as a Timing Advance (TA). An MS in dedicated mode must transmit signals in an appropriate TA. Otherwise, the synchronization between the MS and the BTS loses. In the GSM system, adjustment of adaptive timing advance is applied to ensure that each MS in dedicated mode uses an appropriate TA. Thus, the signals transmitted by the MSs that have different distances from the BTS can arrive at the BTS in sequence to avoid signal conflict and MS intervention.

BSS Adjustment of Adaptive Timing Advance 3 Technical Description


3-1

3 Technical Description By means of adjustment of adaptive timing advance, the TA offset of an MS can be reduced to +1 or -1 time length of a symbol.

In the GSM system, TDMA technology is applied over the Um interface. Each MS must transmit signals in the assigned timeslot, and the BTS must receive the signals in the corresponding timeslot. Figure 3-1 shows the delay offset of signals received by the BTS when the MS is traveling away from position P1, to P2, and then to P3.

It is assumed that the MS originally occupies timeslot 1 (TS1). That is, the signals transmitted by the MS are expected to arrive at the BTS in TS1, as shown in Figure 3-1. When the MS is close to the BTS, the transmission delay is short, and the BTS can receive signals from the MS right in TS1. As the MS travels away from the BTS, the transmission delay is prolonged and the signals transmitted by the MS may arrive at the BTS in a later TS if the TA is not adjusted. For example, as shown in Figure 3-1, when the MS moves to P3, some signals from the MS arrive in TS2. These signals are overlapped by the signals that are from other MSs and also arrive in TS2, and thus they cannot be decoded appropriately.

Figure 3-1 Signal reception with TA unchanged

P1 P2 P3

Ts0 Ts1 Ts2 Ts3 Ts4 Ts5 Ts6 Ts7

Ts1 Ts2Ts1 Ts2 Ts1 Ts2

To avoid this problem, the base station subsystem (BSS) monitors the required transmission time of each signal from the MS to the BTS and informs the moving MS of TA adjustment. Then, the MS transmits signals with the adjusted TA. This ensures that all signals from the MS can be received by the BTS in TS1, as shown in Figure 3-2.

A TA value ranges from 0 µs to 233 µs. The TA value affects the radio coverage of cells.

3 Technical Description BSS

Adjustment of Adaptive Timing Advance

3-2 Huawei Proprietary and Confidential Copyright © Huawei Technologies Co., Ltd

Issue 01 (2010-01-12)

Figure 3-2 Signal reception with adjusted TA

P1 P2 P3

Ts0 Ts1 Ts2 Ts3 Ts4 Ts5 Ts6 Ts7

Ts1 Ts2 Ts1 Ts2 Ts1 Ts2

In the GSM system, the TA value is an integer ranging from 0 to 63. It refers to the time required for transmitting 0- to 63-bit data. If the TA value is 0, the MS need not transmit signals in advance; if the TA value is 63, the distance between the MS and the BTS is the maximum, that is, approximately 35 km. If the MS transmits signals at a distance greater than 35 km, the signals arrive at the BTS in the next timeslot and cannot be decoded appropriately. By means of adjustment of adaptive timing advance, the TA offset of the MS can be reduced to +1 or -1 time length of a symbol. By setting Max TA, the BSC can specify the maximum TA value of MSs in each cell. It is recommended that Max TA of MSs in common cells be set to 62.

BSS Adjustment of Adaptive Timing Advance 4 Parameters


4-1

4 Parameters This chapter describes the parameters related to AEC.

For the description of each parameter, see Table 4-1. For the default value, value ranges, and MML commands of each parameter, see Table 4-2.

Table 4-1 Parameter description (1)

Parameter Description

Max TA Maximum time advance (TA).

Table 4-2 Parameter description (2)

Parameter Default Value

GUI Value Range

Actual Value Range

Unit MML Command Impact

Max TA 62 0~255 0~255 None SET GCELLBASICPARA Cell

BSS Adjustment of Adaptive Timing Advance 5 Counters


5-1

5 Counters For the counters,see the BSC6900 GSM Performance Counter Reference.

BSS Adjustment of Adaptive Timing Advance 6 Glossary


6-1

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

BSS Adjustment of Adaptive Timing Advance 7 Reference Documents


7-1

7 Reference Documents 3GPP TS 45.002: “Multiplexing and multiple access on the radio path” BSC6900 Feature List BSC6900 Optional Feature Description BSC6900 GSM Parameter Reference BSC6900 GSM MML Command Reference