38832294 0804C MIMO Techniques for Wireless Communications 2005

7/31/2019 38832294 0804C MIMO Techniques for Wireless Communications 2005

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MI MO Techniques for WirelessMI MO Techniques for Wireless

CommunicationsCommunications

TaTa-- Sung LeeSung Lee

Department of Communication Engineering

National Chiao Tung University

E-mail: [email protected]


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OutlineOutlinePart I: MIMO Background

MIMO Overview

MIMO Channel Capacity

Part II: Space-Time Coding Schemes

High Link Quality via Spatial DiversitySTBC/STTC

High Spectral Efficiency via Spatial MultiplexingLSTCPart III: MIMO for Future Wireless Communications

3GPP

IEEE 802.11nIEEE 802.16 (-2004: WiMAX)


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MIMO OverviewMIMO Overview[1][1] --[3][3]

Future trend for wireless communications

Future wireless applications create insatiability B

demand forhigh data rate and high link qualitywireless access

Spectrum has become a scarce and expensive resource

B bandwidth is very limited

Regulation, device and system capacity concerns B

transmit power is limited

Time and frequency domain processing are at limits, but

space is notB

MIMO


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Multi-input multi-output (MIMO) concept

Basic idea of MIMO: Improve quality (BER) and/or data

rate (bits/sec) by using multiple TX/RX antennas

Core scheme of MIMO: space-time coding (STC)Two main functions of STC: diversity & multiplexing

Maximum performance needs tradeoffs between diversity

and multiplexing

# #

1( )x k

2( )x k

( )Nx k

1

( )y k

2( )y k

( )My k

( )k

x ( )k

y


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Main history of MIMO techniques[1]-[3]

Spatial diversity

Delay diversity: Wittneben, 1991 (inspired); Seshadri &Winters, 1994 (first attempt to develop STC)

STTC: Tarokh et al., 1998 (key development of STC)

Alamouti scheme: Alamouti, 1998

STBC: Tarokh et al., 1998Spatial multiplexing

First results hint capacity gain of MIMO: Winters, 1987

Ground breaking results: Paulraj & Kailath, 1994

BLAST: Foschini, 1996MIMO capacity analysis: Telatar1995; Foschini1995 & 98

Spatio-temporal vector coding for channel with multipathdelay spread: Raleigh & Cioffi, 1998


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Four basic models*[1]

11 12 1

21 22 2

1 2

N

N

M M MN

h h h

h h h

h h h

=

H

"

"

# # % #

"

Note:

( ) ( ) ( )k k k= +y Hx v

( )ky( )kx

H

NTXs and MRXs

MRXs

NTXs

* Slow i.i.d. flat fading channel assumption


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Multipath v.s. capacity

Multipath propagation has long been regarded as an

impairment because it causes signal fadingTo mitigate this problem, diversity techniques were

developed

Antenna diversity is a widespread form of diversity

Recent research has shown that multipath propagation

can in fact contribute to capacity

I nformation theory has shown t hat w i th m ult ipath propagation, mult iple ant ennasat bot h t ransmit t er and receiver can est ablish essentially mult iple parallel channelsthat operat e simu lt aneously, on the same f requency band at t he same total radiatedpower

I nformation theory has shown t hat w i th mult ipat h propagat ion, mult iple ant ennasat bot h t ransmit t er and receiver can est ablish essentially mult iple paral lel channelsthat operat e simu lt aneously, on the same f requency band at t he same total radiatedpower

MIMO Channel CapacityMIMO Channel Capacity[1][1] --[4][4]


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Shannon bound forSISO

Information-theoretic capacity of a single antenna link is

limited by the links SNR according to Shannonsformula*

Each extra bps/Hz requires roughly a doubling of TX

power(To go from 1 bps/Hz to 11 bps/Hz, the TX power must beincreased by ~1000 times!)

C. ShannonBell Labs Technical Journal, 1948

TXTXTX RXRXRX( )2log 1 (bps/Hz)C = +

2SNR /T vP = =


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Single TX array: MISO

A single array provides transmit diversity against fading

Slow logarithmic growth of capacity with no. of antennas

Single RX array: SIMO

A single array provides receive diversity against fading


TXTXTX RXRXRX

#

RX M

RX 1

2log (1 )C = +

2log (1 )MC = +

TXTXTX

#

TX 1

TX N

2log (1 )C = +

RXRXRX

2log (1 )NC = + With channel info at TX

With channel info at RX


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Dual array: MIMO

Dual array provides diversity at both TX and RX ends


Dual array: MIMO

Dual array provides parallel spatial channels

Lineargrowth of capacity with no. of antennas

TXTXTX

#

TX 1

TX N

RXRXRX

#RX M

RX 1

2log (1 )C = +

2log (1 )NC M = +

With channel info atTX & RX

TXTXTX

#

TX 1

TX N

RXRXRX

#RX M

RX 1

2log (1 )C = +

2log (1 )C Q +

min{ , }Q M N=

With channel info at RX


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SpaceSpace--Time Coding SchemesTime Coding Schemes[6][6] --[11][11]

Types of space-time code

Spatial diversity perspective:

ST block code (STBC)[7], [8] Provides diversity gain but no coding gain

ST trellis code (STTC)[6]

Provides both diversity and coding gain

Originates from transmit diversity concept

Spatial multiplexing perspective:

Layered ST code (LSTC)[10], [11]

Provides some coding gain and diversity gain (depending on

code structure)

Provides bandwidth efficiency


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Two popular techniques in wireless MIMO systems

Receive and transmit diversity mitigates fading and

significantly improves link qualitySpatial multiplexing yields substantial increase in

spectral efficiency

TX RX

SpatialSpatial Diversity: Increased SNRDiversity: Increased SNR Spatial Multiplexing: Increased rateSpatial Multiplexing: Increased rate

TX RX


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High Link Quality via Spatial DiversityHigh Link Quality via Spatial Diversity

ST Block Code (STBC) / ST Trellis Code (STTC)ST Block Code (STBC) / ST Trellis Code (STTC)[6][6] --[8][8]

STC is a new coding / signal processing framework

having the potential of improving link quality for wireless

communications with multiple transmit and multiplereceive antennas

For an input symbol sequence, ST encoder chooses

constellation points to simultaneously transmit from all

antennas so that coding and diversity gains can be

maximized

InformationSource

InformationInformation

SourceSource ReceiverReceiver( )s k

1( )x k

Space-Time Encoder

( )Nx k

1( )y k

( )My k

( )s k


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High Spectral Efficiency via Spatial MultiplexingHigh Spectral Efficiency via Spatial Multiplexing

Layered STC (LSTC)Layered STC (LSTC)[9][9] --[11][11]

Horizontal layered ST (HLST) architecture[9], [10]

Diagonal LST (DLST) architecture[9], [10]

InformationSource S/PS/P

EncoderEncoder

EncoderEncoder

ModulatorModulator

ModulatorModulator

InterleaverInterleaver


####

1( )x k

( )N

x k

1 1 1 1

2 2 2 2

3 3 3 3

(1) (2) (3) (4)

(1) (2) (3) (4)

(1) (2) (3) (4)

x x x x

x x x x

x x x x

=

X

"

"

"

InformationSource S/PS/P

EncoderEncoder

EncoderEncoder

ModulatorModulator

ModulatorModulator



###

1( )x k

( )N

x kSpatial

Int.

SpatialInt.

1 2 3 1 2 3

1 2 3 1 2

1 2 3 1

(1) (1) (1) (4) (4) (4)

0 (2) (2) (2) (5) (5)

0 0 (3) (3) (3) (6)

x x x x x x

x x x x x

x x x x

=

X

"

"

"

HLST DLST


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Potential MIMO ApplicationsPotential MIMO ApplicationsMIMO applications in future wireless standards

3GPP[12]-[17]: MIMO-CDMA

Spatial diversitySpatial multiplexing

IEEE 802.11n[18]-[19]: MIMO-OFDM

Beamforming

Spatial diversity

Spatial multiplexing

IEEE 802.16 (-2004: WMAX)[20]-[21]: MIMO-OFDM

BeamformingSpatial diversity

Spatial multiplexing


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MIMO Techniques in 3G CDMA Systems

Open loop

Time-switched transmit diversity (TSTD)[12]: adopted in3GPP

Orthogonal transmit diversity (OTD)[13]: adopted in 3GPP

Space-time transmit diversity (STTD)[7]: adopted in 3GPP

Space-time spreading (STS)[14]: adopted in 3GPP2

IST-METRA (HSDPA)[15]: adopted in 3GPP

CDMA-BLAST (HSDPA)[16]: adopted in 3GPP

Closed loop

Switched transmit diversity (STD): adopted in 3GPP[17]

Transmit adaptive array (TXAA): adopted in 3GPP[17]

3GPP3GPP[12][12]--[17][17]


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IEEE 802.11 Task Group n (TGn) is defining next

generation standard for high speed WLANs

Existing IEEE 802.11 standards are typically designatedby their peak physical data rates

IEEE 802.11n seeks to improve peak throughput to at

least 100 Mbps, measured at MAC data service access

point (SAP)

Improvement of at least fourtimes the throughput

obtainable using existing IEEE 802.11 systems

100 Mbps200+ MbpsIEEE 802.11n

25 Mbps (when 11b is not present)54 MbpsIEEE 802.11g

25 Mbps54 MbpsIEEE 802.11a

5 Mbps11 MbpsIEEE 802.11b

MAC SAP EstimatesOver-the-Air EstimatesIEEE WLAN Standard

[Source: Intel Labs]

Wireless LAN Throughput by IEEE Standard

IEEE 802.11nIEEE 802.11n[18][18]


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Key Features in IEEE 802.11n

Enhancements to OFDM PHY

Enables 2 x 2 MIMO operation in 20 MHz to achieve100 Mbps throughput

Up to 4 x 4 MIMO to achieve 500+ Mbps

Package of enhancements carries over to all antenna

configurations and bandwidths

Bandwidth extension option

Employees channel doubling (40 MHz) to further

increase data rate


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IEEE 802.16 (IEEE 802.16 (--2004: WMAX)2004: WMAX)[20][20]--[21][21]

WiMAX: Worldwide Interoperability for Microwave

Access based on IEEE 802.16 (-2004) standard

IEEE 802.16: an emerging suite of air interfacestandards for combined fixed, portable and mobile

broadband wireless access

[Source: Reference [20]]

FullMobility

Vehicular SpeedMobility,

> 3G Bandwidth,Any IP Service

Nomadicity

Portabilitywith

SimpleMobility

Stationary BroadbandAccess:

Laptops, PDAWherever you are

Pedestrian SpeedMobility

Boot for latencyTolerant services

FixedAccess

Residential/SMBBroadband Access

Usage Evolution


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MIMO-OFDM Techniques in WiMAX[20], [21]

Main features of IEEE 802.16-2004

Carrier: 2-11 GHz (licensed and license-exempt)For NLOS environments (more multipath propagation)

Use advanced antenna systems (AAS): MIMO techniques

Three PHY layers defined:

Single carrier access (SCa)OFDM with TDMA (256 sub-carriers)

OFDMA (2048 sub-carriers)

OFDM

TDD, FDD

TDD, FDD

TDD, FDD

Duplexing

Alternative

High-speed Mobile

AccessAAS, ARQ, STC

2-11 GHz

Licensed BandsWMAN-OFDMA

Fixed AccessAAS, ARQ, Mesh,

STC

2-11 GHz

Licensed BandsWMAN-OFDM

Backhaul LinksAAS, ARQ, STC2-11 GHz

Licensed BandsWMAN-SCa

Application

ScenarioOptionsApplicabilityDesignation

[Source: Reference [20]]


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ReferencesReferences[1] A. J. Paulraj, R. Nabar and D. Gore, Introduction to space-time wireless

communications, Cambridge University Press, 2003.

[2] H. Bocskei and A. J. Paulraj, Multiple-input multiple-output (MIMO) wirelesssystems, Cambridge University Press, 2003.

[3] D. Gesbert, M. Shafi, D. Shiu, P. J. Smith and A. Naguib, From theory to

practice: An overview of MIMO space-time coded wireless systems, IEEE

J. Select. Areas Commun., vol. 21, no. 3, pp. 281-302, April 2003.

[4] G. J. Foschini and M. J. Gans, On limits of wireless communications in a

fading environment using multiple antennas, Wireless Personal Commun.,

vol. 6, no. 3, pp. 311-355, 1998.

[5] A. F. Naguib and A. R. Calderbank, Space-time coding and signal

processing for high data rate wireless communications, Wireless Commun.

and Mob. Comput., vol. 1, pp. 13-43, 2001.


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[6] V. Tarokh, N. Seshadri and A. R. Calderbank, Space-time codes for high

data rate wireless communication: Performance analysis and code

construction, IEEE Trans. Inform. Theory, vol. 44, no. 2, pp. 744-765,March 1998.

[7] S. M. Alamouti, A simple transmit diversity technique for wireless

communications, IEEE JSAC, vol. 16, no. 8, pp. 1451-1458, Oct. 1998.

[8] V. Tarokh, H. Jafarkhani and A. R. Calderband, Space-time block codesfrom orthogonal designs, IEEE Trans. Inform. Theory, vol. 45, no. 5, pp.

1456-1467, July 1999.

[9] B. Vucetic and J. Yuan, Space Time Coding, W. Sussex, England: John

Wiley & Sons, 2003.

[10] G. J. Foschini, Layered space-time architecture for wireless

communication in a fading environment when using multiple antennas,

Bell Labs Syst. Tech. J., vol. 1, pp. 41-59, Autumn 1996.


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[11] P. W. Wolniansky, G. J. Foschini, G. D. Golden, and R. A. Valenzuela,V-BLAST: An architecture for realizing very high data rates over the rich-scattering wireless channel, Proc. ISSSE VTC91, pp. 259-300, Apr.

1998.[12] A. Hiroike, F. Adachi, and N. Nakajima, Combined effects of phase

sweeping transmitter diversity and channel coding, IEEE Trans. Veh.Tehnol., vol. 41, no. 2, pp. 170-176, May 1992.

[13] TIA/EIA IS-2000 Physical layer specification of CDMA spread spectrumcommunication system, June 2000.

[14] B. Hochwald, T. L. Marzetta and C. B. Papadias, A transmitter diversityscheme for wideband CDMA systems based on space-time spreading,

IEEE JSAC, vol. 19, no. 1, pp. 48-60, Jun. 2001.[15] IST METRA, METRA public Deliverables http://kom.auc.dk/~schum/

MIMO/index.html, 2002.


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[16] H. Huang, H. Viswanathan and G. J. Foschini, Achieve high data rates

in CDMA systems using BLAST techniques, Proc. Glovecom99, pp.2316-2320, 1999.

[17] High speed downlink packet access (HSDPA), 3GPP TR 25.855, V5.0.0

(Release 5), Sept. 2001.

[18] Airgo Networks, Bermai, Broadcom,Conexant, ST Microelectronics,

Texas Instruments, WWiSE IEEE 802.11n Proposal WWiSE IEEE802.11n Proposal Technical Technical Summary ,, WWiSE group, Aug.2004.

[19] F. Petr, B. V. Poucke, A. Bourdoux, and L. V. Perre, MIMO-OFDM for

High-Speed WLANs, IMEC, Jan. 2004.[20] Intel Corp. WiMAX, Intel technology journal, vol. 8, no. 3, pp. 173-258,

Aug. 2004.

[21] IEEE Std. 802.16-2004.

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38832294 0804C MIMO Techniques for Wireless Communications 2005