Performance Analysis of MIMO Wireless Communications over Fading Channels - A Review
38832294 0804C MIMO Techniques for Wireless Communications 2005
Transcript of 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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8* Channel coefficient is normalized with unit-variance
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
Slow logarithmic growth of capacity with no. of antennas
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
Slow logarithmic growth of capacity with no. of antennas
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
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
InterleaverInterleaver
InterleaverInterleaver
###
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.