zgo-03!05!005 incremental redundancy in dl fg 20101030

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ZGO-03-05-005 Incremental

Redundancy in DL

Feature Guide



ZGO-03-05-005 Incremental Redundancy in DL

ZTE Confidential Proprietary © 2010 ZTE CORPORATION. All rights reserved. I


Version Date Author Approved By Remarks

V1.00 2010-10-30 Not open to the Third Party

© 2010 ZTE Corporation. All rights reserved.

ZTE CONFIDENTIAL: This document contains proprietary information of ZTE and is not to bedisclosed or used without the prior written permission of ZTE.

Due to update and improvement of ZTE products and technologies, information in this document issubjected to change without notice.




ZTE Confidential Proprietary © 2010 ZTE CORPORATION. All rights reserved. 1

1 Feature Property

iBSC Version: [iBSC V6.20]

BTS Version: [For all BTS versions based on SDR]

Property: [Optional]

Related Network Elements and Requirements:

NE Name Related or Not Special Requirements

MS √

BTS √

BSC √

MSC -

MGW -

SGSN -

GGSN -

HLR -

Dependent Function: [None]

Exclusive Function: [None]

Note: [None]

2 Overview

2.1 Feature Introduction

IR (Incremental Redundancy) is one of the ways to control the EDGE link quality.In the IR

mode, when the RLC header is decoded successfully but one data block fails to be

decoded at the receiving end, this data block received but not decoded will be stored.

After the receiving end gives an answer message, the transmitting end uses another





Figure 3-1 Theoretical Transmission Rates of LA And IR

Incremental redundancy is a better coding mode than segmented retransmission

because the receiving end can receive more information bits and multi-transmitted

different information can be complementary.

3.2 IR Implementation

Incremental redundancy is a better retransmission method than segmented reassembly.

To understand its working principle, we should first know the coding process of EGPRS.

The first step of coding is to convolute the payload by 1/3. For example, a payload of 612

bits will be increased to 1836 bits after 1/3 convolution with the MCS9 coding scheme.

During this convolution process, 2/3 predefined protective codes are added. In the next

step called disintegration, the protective codes are deleted from the convolutional codes.

With different deleting methods, different code blocks are generated, and they are

respectively named P1 and P2 (MCS1~6) or P1, P2 and P3 (MCS7~9). Different code

blocks carry identical payload but different redundant information. Take the MSC6 coding

scheme for example. If a block coded by MCS6 needs to be retransmitted, the

retransmitted block still uses MCS6, but different code blocks are retransmitted. For





instance, if P1 is transmitted previously, P2 can be retransmitted, and so on. The

receiving end needs to retain the code stream that is not decoded, in order to perform

joint decoding together with the code stream retransmitted by the transmitting end. In this

way, the redundant code streams in different code blocks complement each other to

improve the probability of successful decoding. This following provides an illustration of

IR.

Figure 3-2 IR Example

For DL IR, the saving and joint decoding of DL abnormal blocks is completed by MS. MS

is supposed to support DL IR by default, which is informed to BSC through DL

confirmation. If the excessive abnormal blocks in MS cache leads to overflow or memory

recovery of MS, IR/LA handover will be informed. Under IR mode, BSC will judge whether

to use IR currently while resending NACK block. If IR should be used, the data block will

be retransmitted in the same coding scheme as that of the block sent previously but in

different perforation mode.

If the excessive abnormal blocks saved in MS cache leads to overflow of MS, MS will

inform BSC of this through DL confirmation. BSC will check the overflow label. If overflow

does happen and IR mode is used, handover to LA mode. If the overflow label indicates

that memory has recovered, handover to IR again and resend NACK data block.





4 Parameters and Configurations

Downlink IR is enabled by default, so its configuration interface is not needed.

5 Related Counters & Alarms

5.1 Related Counters

None.

5.2 Related Alarms

None.

6 Engineering Guidance

6.1 Application Scenarios

This feature applies to all scenarios as long as terminal supports IR in DL. IR mode

enjoys the highest priority when system resends in DL.

6.2 Configuration Description

This feature does not involve iBSC and BTS hardware configuration adjustment.

6.3 Impact on Network

After DL IR is switched on, the rate of successful decoding will be enhanced so that the

transmission rate will be enhanced to some extend.





This feature will impose no impact on iBSC capacity or BTS capacity.

7 Abbreviation

Abbreviations Full Characteristics

ARQ Automatic Repeat Request

BSC Base Station Controller

BTS Base Transceiver Station

EDGE Enhanced Data rates for Global Evolution

GERAN Gsm/Edge Radio Access Network

GSM Global System for Mobile communications

IR Incremental Redundancy

LLC Logical Link Control

MAC Medium Access Control

MRC Macro Ratio Combing

MS Mobile Station

MSC Mobile Switching Centre

OMC Operation & Maintenance Center

PS Packet Switched

QoS Quality of Service

RLC Radio Link Control

SGSN Serving GPRS Support Node

TBF Temporary Block Flow

8 Reference Document

[None]

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