HSUPA Interference Cancellation

WCDMA RAN

Interference Cancellation Feature Parameter Description

Copyright © Huawei Technologies Co., Ltd. 2011. All rights reserved.

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WCDMA RAN

Interference Cancellation Contents

Issue 02 (2011-06-30) Huawei Proprietary and Confidential

Copyright © Huawei Technologies Co., Ltd

ii

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 IC ........................................................................................................................... 2-1

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

3.1 Overview ....................................................................................................................................... 3-1

3.2 Multi-User Detection Technique .................................................................................................... 3-1

3.3 Classification of Multi-User Detection Technique .......................................................................... 3-2

3.4 Parallel Interference Cancellation ................................................................................................. 3-3

3.4.1 Basic Data Flow of Parallel Interference Cancellation ......................................................... 3-3

3.4.2 Interference Cancellation Objects ........................................................................................ 3-4

3.4.3 Control Channel Parallel Interference Cancellation ............................................................. 3-4

3.4.4 E-DPDCH PIC ...................................................................................................................... 3-5

4 Engineering Guidelines ........................................................................................................... 4-1

4.1 HSUPA UL Interference Cancellation ............................................................................................ 4-1

4.1.1 When to Use HSUPA UL Interference Cancellation ............................................................. 4-1

4.1.2 Feature Monitoring ............................................................................................................... 4-1

5 Parameters ................................................................................................................................. 5-2

6 Counters ...................................................................................................................................... 6-1

7 Glossary ...................................................................................................................................... 7-1

8 Reference Documents ............................................................................................................. 8-1

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Interference Cancellation 1 Introduction



1-1

1 Introduction

1.1 Scope

This document provides an overview of the interference cancellation (IC) feature. It also describes the functions of the IC feature.

This document includes the information about the following features:

WRFD-010691 HSUPA UL Interference Cancellation

WRFD-010210 Control Channel Parallel Interference Cancellation (CCPIC)

1.2 Intended Audience

This document is intended for:

Personnel who are familiar with WCDMA basics

Personnel who need to understand IC

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 IC feature.

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:

02 (2011-06-30)

01 (2011-04-30)

Draft B (2011-03-30)

Draft A (2010-12-30)

02 (2011-06-30)

This is the document for the second commercial release of RAN13.0.

Compared with issue 01 (2011-04-30) of RAN13.0, this issue adds the engineering Guidelines about HSUPA UL parallel interference cancellation. For details, see 4.1 “HSUPA UL Interference Cancellation.”

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 issue Draft A (2010-12-30) of RAN13.0, this issue optimizes the description.

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Interference Cancellation 1 Introduction



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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.

WCDMA RAN

Interference Cancellation 2 Overview of IC



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2 Overview of IC

The inherent self-interference in a WCDMA system has a serious impact on system capacity and coverage range. The parallel interference cancellation (PIC) methods, including Control Channel Parallel Interference Cancellation (CCPIC) and HSUPA UL Parallel interference cancellation (E-DPDCH PIC), are introduced in to eliminate interference signals on the DPCCH and E-DPDCH. PIC helps achieve higher signal-to-interference ratio (SIR) in demodulation and further improve uplink capacity of the UMTS system. In addition, E-DPDCH PIC implements inter-board IC and intra-board IC. In this way, other boards benefit from the IC technique. IC is a multi-user detection technique.

WCDMA RAN

Interference Cancellation 3 Technical Description



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3 Technical Description

3.1 Overview

The WCDMA system is also a self-interference system. Its capacity and performance are affected by interference from other subscribers, known as multiple access interference (MAI). In addition, the far-near effect problem still exists. That is, as the distances from subscribers to base stations increase and the signals fade, strong signals may suppress weak signals. As a result, the subscribers with relatively weak signals cannot be detected properly.

The Multi-user Detection (MUD) technique provides associated detection methods for subscribers or reduces interference from received signals to eliminate MAI and inter-code interference. This technique effectively combats the far-near effect, greatly improves system performance, and increases capacity of the WCDMA system.

IC is one of the MUD techniques.

3.2 Multi-User Detection Technique

In the scenario of single user, the noise for the user includes background noise, Inter-symbol interference (ISI), and exterior interference (including neighboring cell).

In the scenario of multiple users, interference between users should be considered as noise too. This type of interference is called Multiple User Interference (MUI) or Multiple Address Interference (MAI).

Noise type

Description

NO Background noise

ISI Inter-symbol interference (ISI) is a form of distortion of a signal in which one symbol interferes with subsequent symbols. This is an unwanted phenomenon as the previous symbols have similar effect as noise, thus making the communication less reliable. ISI is usually caused by multipath propagation or the inherent non-linear frequency response of a channel causing successive symbols to "blur" together. The presence of ISI in the system introduces errors in the decision device at the receiver output. Therefore, in the design of the transmitting and receiving filters, the objective is to minimize the effects of ISI, and thereby deliver the digital data to its destination with the smallest error rate possible. Ways to fight inter-symbol interference include adaptive equalization and error correcting codes.

MAI MAI is caused by multiple access technology. Scrambling codes are used to distinguish UEs in the uplink. Scrambling codes are not orthogonal. So the users interfere with each other in the uplink and cause Multiple Access Interference (MAI).

When SF is large and subscriber number is small, the MAI is approximate to Gaussian white noise and has little impact on performance. But when SF is small or subscriber number is large, the MAI can not be taken as Gaussian white noise and affects performance greatly.

A traditional detection technique uses a matched filter to despread the received signals and is followed by an information bit decision. A common receiver does not perform combined signal processing because it does not consider the MAI from other subscribers. That is, it does not use transmission information from other subscribers.

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Compared with the common detection technique, the multi-user detection (MUD) technique uses signal information from all subscribers that have generated MAI to detect signals of a single subscriber. The MUD technique improves the anti-interference capability of the system, solves the near-far effect problem, efficiently uses the spectrum resource in the uplink (UL), and also increases system capacity.

3.3 Classification of Multi-User Detection Technique

The MUD technique can be classified into optimal MUD and suboptimal MUD.

Optimal MUD is implemented by using a matched filter and the Viterbi algorithm to detect the transmit sequence with the maximum posterior probability for the received signals. This technique is also called maximum likelihood sequence (MLS) detection. The Viterbi algorithm has excellent performance. The MLS detection uses the amplitude and phase of the received signals, which are obtained through estimation. The computational complexity of the estimation increases exponentially with the number of users and therefore the optimal MUD actually cannot be implemented in reality.

Suboptimal MUD is classified into two types: linear MUD and non-linear MUD. The IC technique is one of the non-linear MUD techniques. It estimates the MAI produced by different subscribers, through decision and reconstruction, and then eliminates part of or all interference from the received signals. The interference canceller (IC) need not include the calculation of correlated matrix. It can be expanded without increasing the calculation complexity. In addition, the interference canceller can improve the reception performance of low-power signals. Therefore, the IC technique is often preferred in a third-generation (3G) communications system.

The basic idea of IC is to estimate the MAI in the received signals through decision and reconstruction and then to eliminate part of or all interference before the decision. The main IC methods are as follows:

Parallel interference cancellation (PIC)

PIC performs decision and reconstruction on signals of multiple subscribers simultaneously to reduce the impact of MAI between subscribers. Currently, the IC method used in Huawei products is PIC.

Successive interference cancellation (SIC)

SIC performs decision and reconstruction on signals of a single subscriber at each level and then eliminates interference from the received signals to reduce the impact of MAI on other subscribers at lower levels. Generally, the operations by levels are performed in descending order of power of received signals. That is, the SIC operation is performed on subscribers in sequence from strong power to low power. Therefore, subscribers with lower power benefit most from the method.

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Figure 3-1 MUD methods

3.4 Parallel Interference Cancellation

Based on different scenarios, Huawei provides the following PIC methods:

Control channel parallel interference cancellation (CCPIC)

HSUPA UL interference cancellation (E-DPDCH PIC)

In addition to the principles of IC, differences and characteristics of the PIC methods are described in the subsequent sections.

3.4.1 Basic Data Flow of Parallel Interference Cancellation

Figure 3-2 shows the basic data flow of PIC.

Figure 3-2 Basic data flow of PIC

The IC technique includes the following operations:

1. One-time demodulation or data regeneration: After the NodeB receives the antenna data (data of all subscribers), it demodulates the data of each subscriber and then modulates the data to obtain the modulated data of each subscriber, that is, regenerating subscriber data.

2. IC: The regenerated data is sent to the IC module.

3. NodeB demodulation: The NodeB demodulates the data after IC.

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3.4.2 Interference Cancellation Objects

The HSUPA function of the WCDMA system provides a new UL transport channel, called E-DCH. In contrast to HSDPA, HSUPA uses dedicated channels rather than shared channels. Each UE is assigned a dedicated E-DCH, which is independent from the DCH and channels of other UEs. At the same time, HSUPA uses various new physical channels, as shown in Figure 3-3.

Figure 3-3 shows all the physical channels required for running HSUPA, except the broadcast channel.

The E-DPDCH is a physical channel used for the UE to transmit bits (E-DCH processing results) to the NodeB. Subscriber data is carried on this channel. With the increase of the HSUPA rate, the UL interference increases.

The IC technique is developed to eliminate interference signals on the two types of channels. CCPIC is used to eliminate interference signals on the DPCCH. E-DPDCH PIC is used to eliminate interference signals on the E-DPDCH.

Figure 3-3 Physical channels required for HSUPA when the R99 DCH is used in the DL

E-HICH: E-DCH HARQ Acknowledgement Indicator Channel

E-RGCH: E-DCH Relative Grant Channel

E-AGCH: E-DCH Absolute Grant Channel

E-DPCCH: E-DCH Dedicated Physical Control Channel

E-DPDCH: E-DCH Dedicated Physical Data Channel

UE: User Equipment

3.4.3 Control Channel Parallel Interference Cancellation

Control Channel Parallel Interference Cancellation (CCPIC) is used to eliminate interference signals on the DPCCH.

Each subscriber has a control channel that is the major source for the interference, especially for low-rate and low-activity services. CCPIC is a simplified MUD technique of the receiver in the NodeB. It is used in the heavy-load scenario. By eliminating interference from the UL control channel signals in the baseband data and reducing UL interference, CCPIC improves system capacity and thus reduces the investment for operators.

The principle of CCPIC is as follows: After receiving baseband signals, the NodeB demodulates the signals. According to the multipath delay and fading signals, the data regeneration module regenerates DPCCH signals and sends them to the IC module for IC processing. The data on other channels such as the DPDCH, E-DPDCH, and E-DPCCH can be demodulated after IC is performed on the DPCCH.

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3.4.4 E-DPDCH PIC

HSUPA UL interference cancellation (E-DPDCH PIC) is used to eliminate interference signals on the UL high-rate E-DPDCH. This function is controlled by the parameter IC_MODE.

HSUPA provides UL high-rate services. The Radio Access Network (RAN), based on the wideband code division multiple access technology, is a typical self-interference system. With the increase of the HSUPA rate, the UL interference increases. The UL interference is a major factor affecting the UL capacity of the RAN.

E-DPDCH PIC greatly improves the UL capacity of the RAN system. When there are few high-throughput HSUPA subscribers and several low-throughput HSUPA subscribers in the system, high-throughput HSUPA subscribers generate serious UL interference to low-throughput HSUPA subscribers, and the rate of the original high-throughput HSUPA subscribers is also affected. E-DPDCH PIC can reduce the interference from high-throughput HSUPA subscribers on other subscribers. When E-DPDCH PIC is used, more subscribers using low-rate services such as VoIP can access the network, considering that the rate of the existing subscribers remains unchanged.

In the HSUPA application scenario, if there are some high-rate HSUPA subscribers, E-DPDCH PIC can be used to increase the SIR and the system capacity.

When E-DPDCH PIC is used, the NodeB demodulates the HSUPA UL E-DPDCH data and then performs IC based on the demodulated data and the original received baseband data. Then, the NodeB demodulates the baseband data again after IC. For the baseband data after IC, the interference from the E-DPDCH data is eliminated and the MAI is reduced. Therefore, the signal-to-noise ratio (SNR) of the data is improved.

Huawei NodeB can provide an IC resource pool to share signals generated after IC between the boards. The functions of the IC resource pool are as follows:

Intra-board IC: IC results cannot be shared between boards. IC results of an IC-capable board can be used within the board only but cannot be shared with other boards, irrespective of whether these boards are IC-capable.

Inter-board IC: IC results can be shared between all boards in the NodeB. That is ,when there are multiple IC-capable boards in a NodeB, IC-capable boards can share IC results with each other. In addition, IC-incapable boards in this NodeB can also share the IC results of IC-capable boards. As a result, users carried on IC-incapable boards can use the signals after IC rather than the original signals for demodulation. This improves the demodulation performance of users carried on IC-incapable boards and brings gain from IC.

Currently, only the 3800/3900 series base stations support inter-board IC. Other types of base stations support intra-board IC only.

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WCDMA RAN

Interference Cancellation 4 Engineering Guidelines



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4 Engineering Guidelines

4.1 HSUPA UL Interference Cancellation

4.1.1 When to Use HSUPA UL Interference Cancellation

HSUPA UL Interference Cancellation reduces uplink interference and improves uplink system capacity.

This feature yields notable gains in some scenarios. For example, if the system needs to support a small number of HSUPA users that require high throughput and a large number of HSUPA users that require low throughput, HSUPA UL Interference Cancellation can be used to prevent high-throughput users from inflicting too much interference on low-throughput users. Without HSUPA UL Interference Cancellation, the system supports only a limited number of low-throughput users (such as VoIP users) or has to lower the rates of high-throughput users.

The uplink rates of HSUPA UL Interference Cancellation users affect interference cancellation efficiency and uplink system capacity. Generally, this feature yields notable gains for high-throughput users on the uplink. Higher rates mean more gains. Therefore, HSUPA UL Interference Cancellation is recommended for HSUPA cells if the network has high-throughput users on the uplink.

When used together with HSUPA Adaptive Transmission (large retransmission state), HSUPA UL Interference Cancellation yields reduced gains, because a higher proportion of retransmissions leads to a lower efficiency of HSUPA UL Interference Cancellation.

4.1.2 Feature Monitoring

To determine whether HSUPA UL Interference Cancellation has taken effect, check the values of the following NodeB counters:

VS.HSUPA.Ic.MeanEff: average HSUPA UL Interference Cancellation efficiency in a cell within a measurement period

VS.HSUPA.Ic.MaxEff: maximum efficiency of HSUPA UL Interference Cancellation in a cell within a measurement period

HSUPA UL Interference Cancellation increases cell uplink throughput. To find out how much the cell uplink throughput has increased, compare the uplink throughput before the feature is enabled with the uplink throughput after the feature is enabled. The following NodeB counters indicate uplink throughput in a cell:

VS.HSUPA.Thruput: total number of bits in MAC-d PDUs successfully received from all users within a measurement period

VS.HSUPA.MeanBitRate: average bit rate of MAC-d data flows successfully received from all users within a measurement period

VS.HSUPA.MeanBitRate: average bit rate of MAC-d data flows successfully received from all users in data transmission within a measurement period

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Interference Cancellation 5 Parameters



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5 Parameters

Table 5-1 Parameter description

Parameter ID NE MML Command Description

IC_MODE NodeB ADD LOCELL

MOD LOCELL

Meaning:Indicates whether Interference Cancellation(IC) is supported by the cell

GUI Value Range:FALSE(FALSE), TRUE(TRUE)

Actual Value Range:FALSE, TRUE

Default Value:FALSE(FALSE)

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../NodeBMMLHtml/mml-mo-para/mml/add_locell.html

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Interference Cancellation 6 Counters



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6 Counters

Table 6-1 Counter description

Counter ID Counter Name Counter Description

Feature ID Feature Name

50331892 VS.HSUPA.Ic.MeanEff Average efficiency of IC in a cell


50341858 VS.HSUPA.Ic.MaxEff Maximum efficiency of IC in a cell


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Interference Cancellation 7 Glossary



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7 Glossary

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

Glossary.htm

WCDMA RAN

Interference Cancellation 8 Reference Documents



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8 Reference Documents

[1] HSUPA Feature Parameter Description

HSUPA.htm

HSUPA Interference Cancellation

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