Four-Way Receive Diversity

Four-Way receive diversity 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.

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

BSS Four-Way receive diversity

Contents

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 Four-Way receive diversity.............................................................................2-1 3 Technical Description ..............................................................................................................3-1 3.1 Technical Principle......................................................................................................................... 3-1 3.2 Four-Way Receive Diversity Algorithms ........................................................................................ 3-1

4 Parameters .................................................................................................................................4-1 5 Counters......................................................................................................................................5-1 6 Glossary ......................................................................................................................................6-1 7 Reference Documents .............................................................................................................7-1

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BSS Four-Way receive diversity

1 Introduction

1 Introduction 1.1 Scope This document describes the working principle and algorithms of four-way receive diversity.

1.2 Intended Audience This document is intended for: z

Personnel who need to understand Four-Way receive diversity

z

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: z

Feature change: refers to the change in the Four-Way receive diversity feature of a specific product version.

z

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: z

02 (2009-09-30)

z

01 (2009-06-30)

02 (2009-09-30) This is the second commercial release of GBSS9.0. Compared with issue 01 (2009-06-30), issue 02 (2009-09-30) incorporates the changes described in the following table. Change Type

Change Description

Parameter Change

Feature change

None.

None.

Editorial change

The structure of the document is optimized.

None.

01 (2009-06-30) This is the first commercial release of GBSS9.0. Compared with issue 01 (2009-04-30) of GBSS8.1, issue 01 (2009-06-30) of GBSS9.0 has no change.

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BSSBSS Four-Way receive diversityFour-Way receive diversity

2 Overview of Four-Way receive diversity

2 Overview of Four-Way receive diversity In radio communication environment, the TX signals tend to be affected by the shadow fading, buildings, and landforms. The TX signals from the MS arrive at the BTS through various paths, such as line-of-sight (LOS), reflections, and dispersions. As the MS moves around, Rayleigh fading occurs when the TX signals passing through various ways are combined. To suppress Rayleigh fading, four-way receive diversity is implemented in the TRX board, that is, four receive paths receive the same signal separately. Then, the four RX signals are combined into one according to the specified algorithm. In this way, a strong useful signal is obtained, and the uplink gain is enhanced. To ensure that the diversity antennas receive signals separately from each other, the distance between diversity antennas must be greater than 10 times the radio signal wavelength or the polarization diversity is adopted. Four-way receive diversity helps to suppress Rayleigh fading and provide better signal quality on the uplink, thus improving the quality of service (QoS). In addition, four-way receive diversity can be used to improve the uplink performance in wide coverage scenarios.

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BSSBSSBSS Four-Way receive diversityFour-Way receive diversity

3 Technical Description

3 Technical Description 3.1 Technical Principle Figure 3-1 shows the working principle of four-way receive diversity. The four RX signals (RXM1, RXD1, RXM2, and RXD2) are sent to one carrier in the TRX board. You should set Receive Mode to Four Diversity Receiver to enable four-way receive diversity. The following takes the Double-Transceiver Unit (DTRU) as an example to describe the working principle of four-way receive diversity. With four-way receive diversity, only one carrier in the DTRU is used. Figure 3-1 Working principle of four-way receive diversity

TX1 TX IN1 TCOM

TRX0

Combiner

IN2 TX2

RXM1

Divider

RXD1

Divider

TX RXM2 TRX1 RXD2

3.2 Four-Way Receive Diversity Algorithms There are two types of four-way receive diversity algorithms: Interference Cancellation Combining (ICC) and Maximal Ratio Combining (MRC). MRC does not consider the correlation of interference on the combining diversities. Therefore, MRC is an optimum option in the case of restricted noise and no interference. In the actual network, the interference on different diversity antennas comes from the same interference source. Therefore, the interference has a certain correlation. ICC uses this correlation to eliminate some interference. ICC is a combining algorithm developed on the basis of MRC. MRC can be regarded as a special case of ICC.

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BSSBSS Four-Way receive diversityBSSFour-Way receive diversity


With four-way receive diversity, superimposed antenna thermal noise and co-channel interference occur when the TX signals arrive at the diversity antennas through different radio paths. Thus, the demodulation performance of the BTS is affected. The noise of the diversity antennas has no correlation, but the co-channel interference has a certain correlation. The ICC algorithm takes into account the correlation between interference signals. In this way, co-channel interference is suppressed, and the demodulation performance of the BTS is improved. See Figure 3-2. Figure 3-2 ICC algorithm Noise and W1 interference RX channel 1

RX signal r1 (k )

S1 (k ) Noise and interference W2

RX channel 2

RX signal r2 ( k )

S2 (k ) Noise and interference

Signal x(k) RX channel 3

RX signal r3 ( k )

RX signal r4 ( k )

y(k)

S3 (k ) Noise and interference

RX channel 4

W3

W4

S4 (k )

As shown in Figure 3-2, the ICC algorithm procedure is described as follows: 1. Through four receive paths, the signal x(k) arrives at the diversity antennas, marked r1(k), r2(k), r3(k), and r4(k). With interference and noise added, the signals are marked S1(k), S2(k), S3(k), and S4(k). 2. Based on the maximum signal-to-noise ratio criterion, the adaptive combining coefficients W1, W2, W3, and W4 are calculated and the output signal is obtained through the formula: y(k) = W1 x S1(k) + W2 x S2(k) + W3 x S3(k) + W4 x S4(k). z

When W1, W2, W3, and W4 are equal to 1, y(k) is the output signal calculated through the MRC algorithm.

z

The four receive paths shown in Figure 3-2 correspond to two pairs of main and diversity paths.

Huawei four-way receive diversity algorithms consist of the MRC algorithm and the ICC algorithm with blind detection. The ICC algorithm with blind detection avoids the negative gain obtained by the ICC algorithm in the case of restricted noise and no interference in comparison to the MRC algorithm. The ICC algorithm with blind detection is scenario-adaptive. The choice of the MRC or ICC algorithm for the signal received on each timeslot is made according to the following rules: z

For the interference-restricted scenario, the ICC algorithm is used.

z

For the noise-restricted scenario, the MRC algorithm is used.

The ICC algorithm with blind detection processes useful signals and interference signals based on the maximum signal-to-noise ratio criterion. Therefore, the ICC algorithm features high capability to suppress multipath fading and co-channel interference, and the receiver sensitivity is improved.

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The interference on the signals received by multiple antennas has both spatial correlation and temporal correlation. The ICC algorithm uses only the spatial correlation to eliminate the interference. The enhanced ICC (EICC) algorithm, however, takes into account these two types of interference and constructs the multi-dimensional combining coefficient matrix to combine the signals according to the maximum signal-to-noise ratio criterion. The EICC algorithm is most applicable to the networks where tight frequency reuse pattern is adopted and the traffic volume is high. Currently, the EICC algorithm supports only two-way receive diversity, namely, main and diversity.

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4 Parameters

4 Parameters This chapter describes the parameters related to Four-Way receive diversity. For the meaning 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

Receive Mode

RF receiving mode of the TRX

Table 4-2 Parameter description (2) Parameter

Receive Mode

Defaul t Value

GUI Value Range

None

INDEPEN DENT(Inde pendent Receiver), DIVIDING( Dividing Receiver), FOURDIV ERSITY(F our Diversity Receiver), MAINDIVE RSITY(Mai n Diversity), NONE(No ne)

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Actual Value Range

INDEPEN DENT, DIVIDING, FOURDIV ERSITY, MAINDIVE RSITY, NONE

Unit

Non e

MML Comm and

SET GTRX DEV(O ptional )


Impact

TRX

4-1


5 Counters

5 Counters None.

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6 Glossary

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

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BSSBSS Four-Way receive diversityFour-Way receive diversity

7 Reference Documents

7 Reference Documents z

BSC6900 Feature List

z

BSC6900 Optional Feature Description

z

GBSS Reconfiguration Guide

z

BSC6900 GSM Parameter Reference

z

BSC6900 GSM MML Command Reference

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Four-Way Receive Diversity

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