Tx diverstity & rx diversity Huawei

WCDMA RAN

TX Diversity and RX Diversity Feature Parameter Description

Copyright © Huawei Technologies Co., Ltd. 2011. 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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WCDMA RAN TX Diversity and RX 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 TX Diversity and RX Diversity .......................................................................2-1 2.1 RX Diversity................................................................................................................................... 2-1 2.2 TX Diversity ................................................................................................................................... 2-1

3 Technical Description ..............................................................................................................3-1 3.1 RX Diversity................................................................................................................................... 3-1 3.2 TX Diversity ................................................................................................................................... 3-2 3.2.1 Open Loop TX Diversity ....................................................................................................... 3-2 3.2.2 Closed Loop TX Diversity ..................................................................................................... 3-3

4 Engineering Guidelines...........................................................................................................4-1 4.1 RX Diversity................................................................................................................................... 4-1 4.2 TX Diversity ................................................................................................................................... 4-1 4.2.1 STTD .................................................................................................................................... 4-1 4.2.2 Closed Loop TX Diversity ..................................................................................................... 4-1

5 Parameters .................................................................................................................................5-1 6 Counters ......................................................................................................................................6-1 7 Glossary ......................................................................................................................................7-1 8 Reference Documents .............................................................................................................8-1

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1 Introduction

1 Introduction 1.1 Scope This document describes the TX Diversity and RX Diversity feature and related functions on which TX Diversity and RX Diversity is based, and furthermore provides parameters associated with this feature.

1.2 Intended Audience This document is intended for: 

Personnel who are familiar with WCDMA basics



Personnel who need to understand TX Diversity and RX Diversity.



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 TX Diversity and RX Diversity.



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 (2011-04-30)



Draft B (2011-03-30)



Draft A (2010-12-30)

01 (2011-04-30) This is the document for the first commercial release of RAN13.0. Compared with issue Draft B (2011-03-30) of RAN13.0, this issue has no change.

Draft B (2011-03-30) This is the draft of the document for RAN13.0. Compared with Draft A (2010-12-30) of RAN13.0, this issue optimizes the description.

Draft A (2010-12-30) This is the draft of the document for RAN13.0. Compared with issue 01 (2010-03-30) of RAN12.0, this issue optimizes the description.

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2 Overview of TX Diversity and RX Diversity

2 Overview of TX Diversity and RX Diversity 2.1 RX Diversity Radio waves are subject to multipath propagation as a result of reflection and diffraction. The signals on radio channels reach the receiver through multiple paths. If the signals are combined by the receiver, fading can be reduced to a great extent. Receive (RX) diversity is a radio reception technology that aims to reduce signal fading and interference. Based on this technology, multiple frequencies of one signal source or one frequency of multiple receivers and antennas can be monitored. RX diversity can be used to promote the UL receiver performance of the NodeB. When the feature is enabled, one signal is received by multiple antennas. From the signals received by the antennas, the receiver selects signals with relatively great strength and combines them into one signal, thus reducing the fading. In this manner, better UL receiver sensitivity and expanded UL coverage of the NodeB can be achieved, which decreases the investment cost of operators. RX diversity–capable NodeBs do not require additional equipment to support the feature. The channel resources involved in 2-way RX diversity (MRFD-210604 2-Way Antenna Receive Diversity) are twice the channel resources involved in 1-way reception, and channel resources involved in 4-way RX diversity (WRFD-010209 4-Antenna Receive Diversity) are twice the channel resources involved in 2-way RX diversity.

2.2 TX Diversity Transmit (TX) diversity (WRFD-010203 Transmit Diversity) is a technology based on which signals are transmitted to the receiver in space redundancy mode through multiple independent antennas or an antenna array. When the technology is applied, the signal fading can be reduced. In scenarios where NodeBs in TX diversity mode are deployed, signals are transmitted to UEs from different NodeBs or from different antennas of one NodeB. As the signals are not correlated, RAKE RX diversity-capable UEs can receive the signals and combine them together. Thus, the system performance can be significantly improved. TX diversity enables the NodeB to provide twice the quantity of RF DL channel resources compared with a non-TX diversity NodeB, and effectively improves the reception performance of the UE. TX diversity can improve UE performance especially in scenarios where multipath effect is insignificant and the UE moves at a low speed. With TX diversity, the DL capacity and coverage of the NodeB can be remarkably improved when the QoS is ensured. In such cases, the CAPEX and OPEX can be cut down. UEs that are capable of RX diversity are required to implement TX diversity.

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3 Technical Description

3 Technical Description 3.1 RX Diversity RAKE Receiver In WCDMA, channel bandwidth is much higher than the flat fading bandwidth of the channel. The modulation technology in the WCDMA system adopts spreading codes that bear correlation and is different from the modulation technology in other systems that require equalization algorithm to help eliminate interference between symbols. Therefore, the latency spreading that occurs on radio channels is considered as signal retransmission. If the latency between signals on different paths exceeds the length of a chip, the RAKE receiver will consider the signals as irrelevant noises. In such cases, the latency equalization is not required. To efficiently extract useful information from signals on multipaths, the RAKE receiver improves the signal-to-noise ratio (SNR) of the signals by collecting the signals through correlators and combining the signals together. Figure 3-1 shows the operating principle of a RAKE receiver. First, the channel estimator estimates the channel condition using pilot symbols. Then, the phase rotator removes the information of channel condition from the received symbols. Then, the latency equalization compensates for the time-lag between the symbols of the received signals on each path. Finally, the RAKE combiner accumulates the symbols after channel compensation. In this manner, the fading is reduced, and a combined signal accumulated from signals on multipaths is generated. The matched filter shown in Figure 3-1 is used to detect and update the latency information of the multipaths on the current channel and to ensure that the signal strength of the RAKE receiver always reaches its maximum. Figure 3-1 Operating principle of the RAKE receiver

The RAKE receiver is adopted in WCDMA to receive radio signals. It uses several sub-receivers to individually process signals on multipaths. The signals are individually decoded and then combined

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together. In this manner, the transport channels are fully utilized, and the multipath fading is reduced. This helps increase the SNR or Eb/No in a multipath environment.

3.2 TX Diversity TX diversity in WCDMA is of two types, that is, open loop TX diversity and closed loop TX diversity.

3.2.1 Open Loop TX Diversity Open loop TX diversity is categorized into Time Switched Transmit Diversity (TSTD) and Space Time Transmit Diversity (STTD). Huawei NodeBs mainly adopt the STTD mode.

Time Switched TX Diversity TSTD applies only to synchronization channels (SCHs). In TSTD, the transmission is switched between different antennas at a specified interval, as shown in Figure 3-2. Figure 3-2 Transmit structure of SCHs in TSTD mode

In Figure 3-2, Cp indicates Primary Synchronization Code (PSC) and csi,k indicates Secondary Synchronization Codes (SSC), where i (= 0, 1, …, 63) indicates number of the scrambling code groups, and k (= 0, 1, …, 14) indicates the slot number. In even-numbered slots, both PSC and SSC are transmitted through antenna 1. In odd-numbered slots, both PSC and SSC are transmitted through an antenna 2. TSTD is the simplest TX diversity mode in WCDMA. The manner in which UEs receive TSTD signals in TX diversity scenario is the same as the manner in which UEs receive signals in a non-TX diversity scenario. Thus, the UE needs not to detect whether the TSTD is applied.

Space Time TX Diversity STTD uses the space-time block code at the NodeB to reduce deep channel fading. Channel coding, rate matching, and interleaving are performed similar to non-diversity mode. Figure 3-3 and Figure 3-4 show two STTD encoders. In QPSK modulation mode, the STTD encoder works on four symbols, that is, b0, b1, b2, and b3, as shown in Figure 3-3.

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Figure 3-3 STTD encoder in QPSK modulation mode

In 16QAM modulation mode, STTD works on blocks of eight consecutive symbols, that is, b0, b1, b2, b3, b4, b5, b6, and b7, as shown in Figure 3-4. Figure 3-4 STTD encoder in 16QAM modulation mode

3.2.2 Closed Loop TX Diversity In closed loop TX diversity mode, the UE periodically reports the estimated value of optimal transmit power (referred to as feedback in the WCDMA system) on the UL DPCCH, and the NodeB adjusts the TX power based on the feedback and transmits signals at the adjusted TX power. There are two modes in closed loop TX diversity, that is, mode 1 and mode 2. In mode 1, the NodeB adjusts only the phase on the DL physical channel. In mode 2, the NodeB adjusts both the phase and the amplitude on the DL physical channel. Huawei NodeBs mainly adopt mode 1. Figure 3-5 shows the operating principle of closed loop TX diversity.

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Figure 3-5 Receiver and transmitter in closed loop TX diversity mode

The UE periodically calculates the weights according to the information obtained from pilot signals. The weights are quantified and then sent to the NodeB on the reverse control channel. The NodeB adjusts the TX power according to the feedback weights so that the UE can receive signals at the highest RX power. If the feedback mechanism in closed loop TX diversity mode adequately tracks the conditions of the DL channels, the maximum SNR in closed loop TX diversity mode can be greater than that in STTD mode. Generally, closed loop TX diversity provides the greatest possible gain when the UE moves at a low speed. Open loop TX diversity, however, boosts the performance of the UE that moves at a high speed and provides less gain when the UE moves at a low speed.

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4 Engineering Guidelines

4 Engineering Guidelines This chapter provides engineering guidelines regarding the configuration of RX diversity and TX diversity.

4.1 RX Diversity Huawei NodeBs support both RX diversity and non-RX diversity. In RX diversity mode, the NodeB can be configured with 2 antennas (2-way), or 4 antennas (4-way) through the parameter ANTM. If ANTM is set to 1, non-RX diversity is configured. RX diversity-capable NodeBs do not require additional equipment to support the feature. The channel resources involved in 2-way RX diversity are twice the channel resources involved in 1-way reception, and channel resources involved in 4-way RX diversity are twice the channel resources involved in 2-way RX diversity. The number of RX channels depends on the settings of the antenna connectors on top of the cabinet. 

If ANTM is set to 1, then the NodeB is in non-RX diversity mode. In this case, only Antenna Channel No.1, the associated cabinet number, and the subrack number need to be set.



If ANTM is set to 2, then the NodeB is in 2-way RX diversity mode. In this case, Antenna Channel No.1, Antenna Channel No.2, the cabinet number, and the subrack number associated with each antenna need to be set.



If ANTM is set to 4, then the NodeB is in 4-way RX diversity mode. In this case, Antenna Channel No.1, Antenna Channel No.2, Antenna Channel No.3, Antenna Channel No.4, the cabinet number, and the subrack number associated with each antenna need to be set.

The number of RX antennas is associated with DEMMODE, that is, the demodulation mode of NodeB. The following demodulation modes are available: 2-Channel Demodulation Mode (DEM_2_CHAN), 4-Channel Demodulation Mode (DEM_4_CHAN), and Economical 4-Channel Demodulation Mode (DEM_ECON_4_ CHAN). In economical 4-channel demodulation mode, the signals on the random access channel are received from two antennas, while the signals on the dedicate channel are received from four antennas. NodeBs in economical 4-channel demodulation mode support a maximum coverage radius of 200 km, while NodeBs in 4-channel demodulation mode support a maximum coverage radius of only 30 km.

4.2 TX Diversity 4.2.1 STTD To enable the STTD mode of other channels, run the ADD UCELLSETUP command to set the cell as an STTD-supportive cell and set the transmit diversity mode of each channel to STTD. For the AICH, PICH, and S-CCPCH, also run the commands ADD UAICH, ADD UPICH, and ADD USCCPCHBASIC to set the parameter STTDInd to TRUE. If a cell is configured to support the STTD mode, ensure that the associated local cell on the NodeB side supports TX diversity. ON the NodeB side, the TX diversity capability of the cell needs to be enabled through the parameter TTW.

4.2.2 Closed Loop TX Diversity To enable the closed loop TX diversity mode 1 (CP1) mode of other channels, run the ADD UCELLSETUP command to set the cell as an CP1-supportive cell and set the transmit diversity mode of each channel to CP1.

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4 Engineering Guidelines

If a cell is configured to support the CP1 mode, ensure that the associated local cell on the NodeB side supports TX diversity. ON the NodeB side, the TX diversity capability of the cell needs to be enabled through the parameter TTW. In the case of closed loop TX diversity, 3GPP defines two modes of reporting closed loop feedback information, that is, j+1 and j+2. The modes are set through the parameters: ClosedLoopTimeAdjustMode. 

In j+1 mode (OFFSET1), the feedback information of timeslot j is reported after (j+1) mod 15 timeslots.



In j+2 mode (OFFSET2), the feedback information of timeslot j is reported after (j+2) mod 15 timeslots.

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5 Parameters

5 Parameters Table 5-1 Parameter description Parameter ID

NE

MML Command

Description

ANTM

NodeB

ADD SEC

Meaning: Indicates the magnitude of antennas in the sector. GUI Value Range: 1, 2, 4 Actual Value Range: 1, 2, 4 Default Value: None

STTDInd

BSC6900

ADD USCCPCHBASIC(Optional)

Meaning: This parameter indicates whether the SCCPCH shall use STTD or not. For detailed information of this parameter, refer to 3GPP 25.346. GUI Value Range: TRUE, FALSE Actual Value Range: TRUE, FALSE Default Value: FALSE

TTW

NodeB

ADD LOCELL MOD LOCELL

Meaning: Indicates the Two Tx Way of the Local Cell. GUI Value Range: FALSE(FALSE), TRUE(TRUE) Actual Value Range: FALSE, TRUE Default Value: FALSE(FALSE)

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6 Counters

6 Counters There are no specific counters associated with this feature.

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7 Glossary

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

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8 Reference Documents

8 Reference Documents None.

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Tx diverstity & rx diversity Huawei

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