6 Lte Eran6.0 Mimo Feature Issue 1.00

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Copyright © 2013 Huawei Technologies Co., Ltd. All rights reserved.

LTE eRAN6.0 MIMO Feature

Copyright © 2013 Huawei Technologies Co., Ltd. All rights reserved. Page3

Foreword

LTE MIMO feature include:

Benefits Provided by MIMO

Classification of MIMO in eRAN2.1

UL MIMO

DL MIMO


Objectives

Upon completion of this course, you will be able to:

Describe the benefits provided by MIMO

Describe the function of UL MRC and IRC receiver

Describe the function UL MU-MIMO

Describe the DL MIMO mode

Describe adaptive switch of DL MIMO

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Contents

1. MIMO Feature Overview

2. UL MIMO in eNodeB

3. DL MIMO in eNodeB

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Introduce of MIMO

Trend : Desire of higher throughput

Solution:

Higher bandwidth: Now 20MHz is supported and

further 100Mhz can be achieved in LTE advanced, but it

will be limited

Higher MCS scheme: Now 64 QAM is used and further

256 QAM will be introduced in LTE advanced, but it will

be limited

MIMO is technology based on spatial domain, achieve

the obvious improvement of throughput

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Benefit of MIMO

Spatial multiplexing gain

Improve system peak throughput

Diversity gain

Decrease probability of deep path feeding, thus get the

additional gain

Array gain

Improve SINR of cell edge

Co-channel interference reduction gain

Applicable for high interference scenario, gain is achieved from

interference mitigation

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Spatial Multiplexing Gain

Spatial multiplexing gain is a throughput gain

achieved by adding spatial channels (that is, by

adding antennas) without increasing the total

bandwidth and total TX power. RXTXRXTX

Multi-Path

Scatter


Diversity Gain

The probability of deep fading after signal combining

is reduced greatly, and the diversity gain is

achieved.


Array Gain

Array gain is a power gain achieved by combining

signals from different antennas based on the

correlation between signals and the non-correlation

between noises.


Co-channel Interference Reduction Gain Interference mitigation methods can achieve the co-

channel interference reduction gain by minimizing

the interference gain and maximizing the signal

gain.

Co-channel interference reduction gain is achieved

by using interference rejection combining (IRC) or

other interference mitigation methods.


Classifications of MIMO

LTE support variable MIMO scheme with different

aspect

Based on whether the transmitter feedback channel

information:

Open-loop MIMO : Just feedback CQI and rank(Optional)

Closed-loop MIMO: Beside CQI and rank, PMI is also

required

Based on the number of spatial data streams

transmitted at the same time:

Spatial diversity: only 1 data stream for each user,

rank=1

Spatial multiplexing: 1 or more streams for each user,

rank=1,2,3,4


MIMO Modes Supported by eRAN6.0(FDD) UL MIMO:

Receive diversity:

1x2 (Basic feature)

1x4

MU-MIMO :2x2 or 2x4

DL MIMO:

Open-loop transmit diversity (OL-TD)

Closed-loop transmit diversity (CL-TD)

Open-loop spatial multiplexing (OL-SM)

Closed-loop spatial multiplexing (CL-SM)


Device Configuration

RRU Configuration

Sector Configuration

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Contents


2. UL MIMO

3. DL MIMO

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Contents

2 . UL MIMO

2.1 Receive Diversity

2.2 MU-MIMO

Page16


Principle of Receive Diversity

Receive diversity is a diversity scheme in which each

UE uses one antenna for transmission and occupies

a time domain resource different from other UEs

while the eNodeB uses multiple antennas for

reception and combines signals from these

antennas.


Signal Combining in Receive Diversity The algorithms of signal combining in receive

diversity include MRC and IRC. Both provide the

diversity gain and array gain.

The MRC receiver and the IRC receiver are

applications of a theoretical model named MMSE

receiver in different interference environments.

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MRC and IRC

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MRC

The MMSE receiver is MRC receiver

when the interference and noise are

spatially white.

Assuming that both interference and

noise are spatially white, the MRC

receiver meets the MMSE criterion

by using the maximum ratio

combining algorithm.

When there is no spatially colored

interference, the eNodeB selects

MRC.

IRC

The MMSE receiver is IRC receiver

when there is high interference in the

environments.

Assuming that colored interference

exists, the IRC receiver meets the

MMSE criterion by mitigating

interference during signal combining.

When there is spatially colored

interference, the eNodeB selects IRC.


MRC/IRC Adaptive Switch

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Contents

2 . UL MIMO

2.1 Receive Diversity

2.2 MU-MIMO

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Principle of MU-MIMO

The number of UEs cannot exceed the number of

eNodeB RX antennas in MU-MIMO mode.

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UE Pairing in MU-MIMO UE pairing in MU-MIMO is a process in which the

eNodeB scheduler tries to select a pair of most

appropriate UEs for transmission.

The eNodeB performs UE paring in each TTI. The

phases are as follows:

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SINR measurement

Candidate UE selection

UE pairing

Scheduling


Adaptive Mode Selection and Switching

If the channel SINRs are high and the channels

are approximately orthogonal, the eNodeB

selects MU-MIMO. Otherwise, the eNodeB

selects receive diversity.

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Receiver Technology for MU-MIMO For 2x2 MU-MIMO

Default receiver: MRC

Optional receiver: PSIC (Parallel Soft Interference

Cancellation)

For 2x4 MU-MIMO

Same as UL diversity receive, both MRC and IRC could

be used

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PSIC Advanced Receiver (eRAN6.0 Enhancement) Gain of PSIC receiver

IUI(inter user interference) cancellation: Reduce the

interference between paired UEs. The interference

cancellation effect depends on the correlation between

users as well as the detection and decoding

performance.

ISI(inter symbol interference) cancellation: PSIC

reduces ISI, which is caused by frequency selective

fading, to improve demodulation performance. The

interference cancellation effect depends on the ISI

degree as well as the equalization and decoding

performance.Page26


Contents


2. UL MIMO

3. DL MIMO

Page27


Contents

3 . DL MIMO

3.1 DL MIMO Implementation

3.2 DL MIMO Introduction

3.3 Adaptive Switch

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DL OFDM Signal Generation

Page29

Antenna PortsCodewords

Scrambling

Scrambling

Modulation Mapper

Modulation Mapper

Layer Mapper

Precoding

Layers

Resource Element Mapper

Resource Element Mapper

OFDM Signal

Generation

OFDM Signal

Generation


1 Layer 2 Layers 3 Layers 4 Layers

1 1 2 1Rank 1 Rank 2 Rank 3 Rank 4

2 2 2 21 1

Codeword

1, 2 or 4 Antenna

Ports

2 or 4 Antenna

Ports

4 Antenna Ports

4 Antenna Ports

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Layer Mapping


Why Precoding

Page31

In ideal conditions, the layer data, after being precoded and passed through spatial channels, is equivalent to a group of independent parallel data without interfering with each other


Transmission Modes

Mode 1 - Single-Antenna transmission, port 0, no

MIMO

Mode 2 - Open-loop transmit diversity

Mode 3 - Open-loop spatial multiplexing

Mode 4 - Closed-loop spatial multiplexing

Mode 5 - Multi user MIMO (more than one UE is

assigned to the same resource block)

Mode 6 - Close-loop transmit diversity

Mode 7 - Single-antenna port, port 5 (beam forming)


Transmission Modes (Cont.)

Page33

Mode No. Name Description

Mode 2 OL-TD

In OL-TD mode, the diversity gain can be achieved. Space-frequency block coding (SFBC) is used in the case of two TX antennas. The combination of SFBC and frequency switched transmit diversity (FSTD) is used in the case of four TX antennas.

Mode 3 OL-SM

In OL-SM mode, the UE does not need to report precoding information. When the rank is equal to 1, OL-SM is equivalent to OL-TD. When the rank is equal to 2, 3, or 4, OL-SM maps data streams onto different layers and performs large-delay cyclic delay diversity (CDD) precoding.

Mode 4 CL-SM In CL-SM mode, the UE needs to report precoding information. It performs zero-delay CDD precoding.

Mode 6 CL-TD CL-TD is equivalent to CL-SM (rank = 1, precoding).


Contents

3 . DL MIMO

3.1 DL MIMO Implementation


3.3 Adaptive Switch

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Overview of Transmit Diversity

Page35

Transmit diversity is a diversity scheme in which

multiple antennas are used for signal transmission

and multiple versions of the same signal with

different fading degrees are combined at the RX end.

Transmit diversity is classified into OL-TD (mode 2)

and CL-TD (mode 6) based on whether the channel

information reported by the UE is used.


Transmit Diversity Layer Mapping

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Number of Layers

Number of Code words

Codeword to Layer Mapping 1,...,1,0 layersymb Mi

2 1

)12()(

)2()()0()1(

)0()0(

idix

idix

2)0(symb

layersymb MM

4 1

)34()(

)24()(

)14()(

)4()(

)0()3(

)0()2(

)0()1(

)0()0(

idix

idix

idix

idix

04mod if

04mod if

42

4)0(

symb

)0(symb

)0(symb

)0(symblayer

symb M

M

M

MM

If 04mod)0(symb M two null symbols are

appended to )1( )0(symb

)0( Md

Layer means the transmit antenna number in the

transmit diversity mode.

Rank must be one.


OL TD – SFBC (2 ANTs)

Open-loop transmit diversity uses the SFBC technique in

the case of two TX antennas.

Transmits signals x1 on subcarrier f1 of antenna TX1

Transmits signals x2 on subcarrier f2 of antenna TX1

Transmits signals –x2* on subcarrier f1 of antenna TX2

Transmits signals x1* on subcarrier f2 of antenna TX2

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OL TD – SFBC + FSTD (4 ANTs)

Open-loop transmit diversity uses SFBC+FSTD technique in the case of four TX

antennas.

Transmits signals x1 and x2 on subcarriers f1 and f2 of antenna TX1 respectively

Transmits signals x3 and x4 on subcarriers f3 and f4 of antenna TX2 respectively

Transmits signals –x2* and x1* on subcarriers f1 and f2 of antenna TX3

respectively

Transmits signals –x4* and x3* on subcarriers f3 and f4 of antenna TX4

respectively

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Close-Loop Transmit Diversity

Closed-loop transmit diversity (CL-TD) (mode 6) is

equivalent to CL-SM (rank = 1)

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Overview of Spatial Multiplexing

Spatial multiplexing is a technique in which multiple

antennas are used to transmit spatial data streams in

the same time domain and frequency domain.

Spatial multiplexing increases the system capacity

and provides the spatial multiplexing gain.

Spatial multiplexing is classified into OL-SM (mode 3)

and CL-SM (mode 4) based on whether precoding

information is reported by the UE.

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Spatial Multiplexing Layer Mapping

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One layer means an independent data steams. Through layer

mapping data streams are divided into many different parallel

data steams.

Number of Layers

Number of Codewords

Codeword to Layer Mapping 1,...,1,0 layersymb Mi

1 1 )()( )0()0( idix )0(symb

layersymb MM

2 2 )()( )0()0( idix

)()( )1()1( idix

)1(symb

)0(symb

layersymb MMM

2 1

)12()(

)2()()0()1(

)0()0(

idix

idix layer (0)symb symb 2M M

3 2 )()( )0()0( idix

)12()(

)2()()1()2(

)1()1(

idix

idix

2)1(symb

)0(symb

layersymb MMM

4 2

)12()(

)2()()0()1(

)0()0(

idix

idix

)12()(

)2()()1()3(

)1()2(

idix

idix

22 )1(symb

)0(symb

layersymb MMM


Precoding for CL- SM

CL-SM uses zero-delay CDD precoding, according to

3GPP specifications

The precoding matrix is reported by UE

Precoding provides the spatial multiplexing gain if the

interval between UE reports on the precoding

information (for example, precoding matrix indication

(PMI) is not too long. CL-SM is applicable to slowly

moving UEs.

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Codebook for Zero-Delay CDD

Page43Page 43

For open-loop use

For closed-loop use

Codebook for 4 ANTs, Codebook for 2 ANTs


OL-SM Precoding – Large Delay CDD OL-SM provides the diversity gain in addition to the spatial multiplexing

gain because it uses large-delay CDD precoding, according to 3GPP

specifications.

The purpose of large delay CDD precoding and unitary matrix is to

make radio condition of each layer to be equal which can reduce

uplink feedback signaling. It is applicable for high movement

scenarios that which can overcome the feeding caused by the

delay. Both multiplexing gain and diversity gain can be achieved.

It is only valid in case of rank= 2, 3 or 4

When the rank is equal to 1, OL-SM is same as of OL-TD

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( ) ( ) ( ) ( )y i W i D i Ux i


Large-Delay Cyclic Delay Diversity

j denotes the sub-carrier index. Different sub-carrier uses different phase shift. In the time domain, the time delay will be different.

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Contents

3 . DL MIMO

3.1 DL MIMO Realization


3.5 Adaptive Switch

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Application Scenarios of MIMO Modes

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Moving Speed

SINR

OL-SM (mode 3)

CL-TD (mode 6)

OL-TD (mode 2)

CL-SM (mode 4)


Selection & Switch of MIMO Scheme The eNodeB can select the most appropriate MIMO

mode based on actual conditions and switch one

mode to another. There are four selection and

switching schemes:

Open-loop and closed-loop adaptive scheme

Open-loop SM/TD adaptive scheme

Closed-loop SM/TD adaptive scheme

Fixed scheme

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Open-Loop and Closed-Loop Adaptive Scheme

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Maximum Rank Configuration (eRAN6.0 Enhancement)

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MIMO Adaptive Switch Configuration

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Open loop and closed loop adaptive switch, rank adaptive among rank 1,2,3 or 4

Closed loop adaptive switch, rank adaptive among rank 1,2,3 or 4


Related Command (Cont.)

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Open loop adaptive switch, rank adaptive among rank 1, 2, 3 or 4

Fixed MIMO scheme


The benefit of MIMO

UL MIMO receiver technologies

DL transmission mode

MIMO adaptive switching principle

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Summary


Abbreviation

IRC: Interference Rejection Combing

MMSE: Minimum Mean Square Error

MIMO: Multiple Input Multiple Output

MRC: Maximum Ratio Combining

PSIC: Parallel Soft Interference Cancellation

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6 Lte Eran6.0 Mimo Feature Issue 1.00