Introduction to Smart Antennas

184 Pages·2007·2.96 MB·English

by  Constantine Balanis

Introduction to Smart Antennas
Copyright© 2007byMorgan&Claypool
Allrightsreserved.Nopartofthispublicationmaybereproduced,storedinaretrievalsystem,ortransmittedin
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IntroductiontoSmartAntennas
ConstantineA.Balanis,PanayiotisI.Ioannides
www.morganclaypool.com
ISBN:1598291769 paperback
ISBN:9781598291766 paperback
ISBN:1598291777 ebook
ISBN:9781598291773 ebook
DOI:10.2200/S00079ED1V01Y200612ANT005
APublicationintheMorgan&ClaypoolPublishers’series
SYNTHESISLECTURESONANTENNAS#5
Lecture#5
SeriesEditor:ConstantineA.Balanis,ArizonaStateUniversity
FirstEdition
10987654321
Introduction to Smart Antennas
ConstantineA.Balanis
PanayiotisI.Ioannides
DepartmentofElectricalEngineering
ArizonaStateUniversity
SYNTHESISLECTURESONANTENNAS#5
M
&C &
M o r g a n C l a y p o o l P u b l i s h e r s
iv
ABSTRACT
Asthegrowingdemandformobilecommunicationsisconstantlyincreasing,theneedforbetter
coverage, improved capacity and higher transmission quality rises. Thus, a more efficient use
of the radio spectrum is required. Smartantennasystems are capable of efficiently utilizing the
radiospectrumand,thus,isapromiseforaneffectivesolutiontothepresentwirelesssystems’
problems while achieving reliable and robust high-speed high-data-rate transmission. The
purposeofthisbookistoprovidethereaderabroadviewofthesystemaspectsofsmartantennas.
In fact, smart antenna systems comprise several critical areas such as individual antenna array
design, signal processing algorithms, space-time processing, wireless channel modeling and
coding, and network performance. In this book we include an overview of smart antenna
concepts, introduce some of the areas that impact smart antennas, and examine the influence
of interaction and integration of these areas to Mobile Ad-Hoc Networks. In addition, the
generalprinciplesandmajorbenefitsofusingspace–timeprocessingareintroduced,especially
employingmultiple-inputmultiple-output(MIMO)techniques.
KEYWORDS
Adaptivearrays,Switched-beamantennas,Phasedarray,SDMA,Mutualcoupling,Direction
of arrival, Adaptive beamforming, Channel coding, MANET, Network throughput, Space–
timeprocessing.
v
Contents
1. Introduction..................................................................1
2. MobileCommunicationsOverview.............................................5
2.1 GeneralDescription......................................................5
2.2 CellularCommunicationsOverview........................................6
2.3 TheEvolutionofMobileTelephoneSystems...............................6
2.4 TheFramework..........................................................8
2.5 CellularRadioSystems:ConceptsandEvolution...........................10
2.5.1 OmnidirectionalSystemsandChannelReuse.......................10
2.5.2 CellSplitting....................................................12
2.5.3 SectorizedSystems...............................................12
2.6 PowerControl..........................................................14
2.6.1 SpectralEfficiency...............................................15
2.7 MultipleAccessSchemes................................................16
2.7.1 FDMA.........................................................16
2.7.2 TDMA.........................................................17
2.7.3 CDMA.........................................................17
2.7.4 OFDM.........................................................19
3. AntennaArraysandDiversityTechniques.....................................21
3.1 AntennaArrays.........................................................21
3.2 AntennaClassification...................................................22
3.2.1 IsotropicRadiators...............................................22
3.2.2 OmnidirectionalAntennas........................................22
3.2.3 DirectionalAntennas ............................................ 23
3.2.4 PhasedArrayAntennas .......................................... 23
3.2.5 AdaptiveArrays.................................................23
3.3 DiversityTechniques....................................................26
4. SmartAntennas..............................................................33
4.1 Introduction............................................................33
4.2 NeedforSmartAntennas................................................33
4.3 Overview...............................................................34
vi INTRODUCTIONTOSMARTANTENNAS
4.4 SmartAntennaConfigurations...........................................37
4.4.1 Switched-BeamAntennas........................................39
4.4.2 AdaptiveAntennaApproach......................................42
4.5 SpaceDivisionMultipleAccess(SDMA)..................................45
4.6 ArchitectureofaSmartAntennaSystem .................................. 48
4.6.1 Receiver ........................................................ 49
4.6.2 Transmitter.....................................................51
4.7 BenefitsandDrawbacks..................................................53
4.8 BasicPrinciples.........................................................55
4.9 MutualCouplingEffects.................................................64
5. DOAEstimationFundamentals .............................................. 69
5.1 Introduction............................................................70
5.2 TheArrayResponseVector..............................................71
5.3 ReceivedSignalModel .................................................. 73
5.4 TheSubspace-BasedDataModel.........................................75
5.5 SignalAutocovarianceMatrices...........................................77
5.6 ConventionalDOAEstimationMethods..................................78
5.6.1 ConventionalBeamformingMethod .............................. 78
5.6.2 Capon’sMinimumVarianceMethod..............................79
5.7 SubspaceApproachtoDOAEstimation .................................. 79
5.7.1 TheMUSICAlgorithm..........................................80
5.7.2 TheESPRITAlgorithm ......................................... 82
5.8 UniquenessofDOAEstimates...........................................85
6. BeamformingFundamentals..................................................87
6.1 TheClassicalBeamformer...............................................88
6.2 StatisticallyOptimumBeamformingWeightVectors.......................89
6.2.1 TheMaximumSNRBeamformer.................................90
6.2.2 TheMultipleSidelobeCancellerandtheMaximum
SINRBeamformer...............................................91
6.2.3 MinimumMeanSquareError(MMSE)...........................92
6.2.4 DirectMatrixInversion(DMI)................................... 94
6.2.5 LinearlyConstrainedMinimumVariance(LCMV).................95
6.3 AdaptiveAlgorithmsforBeamforming....................................96
6.3.1 TheLeastMean-Square(LMS)Algorithm ........................ 97
6.3.2 TheRecursiveLeast-Squares(RLS)Algorithm.....................99
CONTENTS vii
6.3.3 TheConstant-Modulus(CM)Algorithm.........................101
6.3.4 TheAffine-Projection(AP)Algorithm...........................102
6.3.5 TheQuasi-Newton(QN)Algorithm.............................104
7. IntegrationandSimulationofSmartAntennas................................107
7.1 Overview..............................................................107
7.2 AntennaDesign ....................................................... 108
7.3 MutualCoupling ...................................................... 110
7.4 AdaptiveSignalProcessingAlgorithms...................................111
7.4.1 DOA..........................................................111
7.4.2 AdaptiveBeamforming..........................................112
7.4.3 BeamformingandDiversityCombiningforRayleigh-Fading
Channel.......................................................114
7.5 Trellis-CodedModulation(TCM)forAdaptiveArrays....................114
7.6 SmartAntennaSystemsforMobileAdHocNETworks
(MANETs)...........................................................117
7.6.1 TheProtocol...................................................118
7.6.2 Simulations....................................................118
7.7 Discussion.............................................................122
8. Space–TimeProcessing......................................................125
8.1 Introduction...........................................................125
8.2 DiscreteSpace–TimeChannelandSignalModels.........................129
8.3 Space–TimeBeamforming..............................................134
8.4 IntersymbolandCo-ChannelSuppression................................135
8.4.1 ISISuppression ................................................ 136
8.4.2 CCISuppression...............................................137
8.4.3 JointISIandCCISuppression...................................137
8.5 Space–TimeProcessingforDS-CDMA..................................137
8.6 CapacityandDataRatesinMIMOSystems..............................138
8.6.1 Single-UserDataRatecLimits...................................139
8.6.2 Multiple-UsersDataRateLimits ................................ 140
8.6.3 DataRateLimitsWithinaCellularSystem.......................143
8.6.4 MIMOinWirelessLocalAreaNetworks.........................145
8.7 Discussion.............................................................148
9. CommercialAvailabilityofSmartAntennas...................................149
viii INTRODUCTIONTOSMARTANTENNAS
10. Summary...................................................................155
Acknowledgments...........................................................157
References..................................................................159
1
C H A P T E R 1
Introduction
Inrecentyearsasubstantialincreaseinthedevelopmentofbroadbandwirelessaccesstechnolo-
giesforevolvingwirelessInternetservicesandimprovedcellularsystemshasbeenobserved[1].
Becauseofthem,itiswidelyforeseenthatinthefutureanenormousriseintrafficwillbeexpe-
riencedformobileandpersonalcommunicationssystems[2].Thisisduetobothanincreased
numberofusersandintroductionofnewhighbitratedataservices.Thistrendisobservedfor
second-generation systems, and it will most certainly continue for third-generation systems.
Theriseintrafficwillputademandonbothmanufacturersandoperatorstoprovidesufficient
capacityinthenetworks[3].Thisbecomesamajorchallengingproblemfortheserviceproviders
tosolve,sincethereexistcertainnegativefactorsintheradiationenvironmentcontributingto
thelimitincapacity[4].
Amajorlimitationincapacityisco-channelinterferencecausedbytheincreasingnumber
ofusers.Theotherimpairmentscontributingtothereductionofsystemperformanceandcapac-
ityaremultipathfadinganddelayspreadcausedbysignalsbeingreflectedfromstructures(e.g.,
buildingsandmountains)anduserstravelingonvehicles.Toaggravatefurtherthecapacityprob-
lem,in1990stheInternetgavethepeoplethetooltogetdataon-demand(e.g.,stockquotes,
news, weather reports, e-mails, etc.) and share information in real-time. This resulted in an
increaseinairtimeusageandinthenumberofsubscribers,thussaturatingthesystems’capacity.
Wireless carriers have begun to explore new ways to maximize the spectral efficiency
of their networks and improve their return on investment [5]. Research efforts investigating
methodsofimprovingwirelesssystemsperformancearecurrentlybeingconductedworldwide.
The deployment of smartantennas (SAs) for wireless communications has emerged as one of
the leading technologies for achieving high efficiency networks that maximize capacity and
improvequalityandcoverage[6].SmartAntennasystemshavereceivedmuchattentioninthe
last few years [6–11] because they can increase system capacity (very important in urban and
denselypopulatedareas)bydynamicallytuningoutinterferencewhilefocusingontheintended
user[12,13]alongwithimpressiveadvancesinthefieldofdigitalsignalprocessing.
Selectedcontrolalgorithms,withpredefinedcriteria,provideadaptivearraystheunique
ability to alter the radiation pattern characteristics (nulls, sidelobe level, main beam direction,
2 INTRODUCTIONTOSMARTANTENNAS
andbeamwidth).Thesecontrolalgorithmsoriginatefromseveraldisciplinesandtargetspecific
applications (e.g., in the field of seismic, underwater, aerospace, and more recently cellular
communications)[14].ThecommercialintroductionofSAsisagreatpromiseforbigincrease
in system performance in terms of capacity, coverage, and signal quality, all of which will
ultimatelyleadtoincreasedspectralefficiency[14].
As the necessity of exchanging and sharing data increases, users demand ubiquitous,
easy connectivity, and fast networks whether they are at work, at home, or on the move.
Moreover, these users are interested in interconnecting all their personal electronic devices
(PEDs)inanadhoc fashion.ThistypeofnetworkisreferredtoasMobileAdhocNETwork
(MANET), and it is beginning to emerge using BluetoothTM technology. BluetoothTM is a
short-range, low-power radio link (10–100 m) that allows two or more BluetoothTM devices
to form a communication channel and exchange data [15, 16]. Because BluetoothTM uses
.
an omnidirectional antenna (operating in the unlicensed 24 GHz industrial, scientific, and
medical(ISM)band),itlackstheabilitytosteertheradiationbeamtowardtheintendedusers
andformnullstocanceljammers.Thislimitstheoverallsystemcapacityornetworkthroughput
of MANETs. Furthermore, because of the omnidirectional antenna, battery life in PEDs is
reducedsinceenergyisradiatedeverywhereandnotjusttowardthedesireduser.Consequently,
thebenefitsprovidedbysmartantennaswouldenhancetheoverallperformanceofMANETs
[17].
Current trends concentrate on space–time processing and coding, a technique that
promises to greatly improve the performance in wireless networks by using multiple antennas
at the transmitter and the receiver [18]. Space–time processing can be viewed as an evolution
of the traditional array signal processing techniques such as antenna array and beamforming.
Operatingsimultaneouslyonmultiplesensors,space–timereceiversprocesssignalsamplesboth
in time and space, thereby improving resolution, interference suppression, and service qual-
ity. Sophisticated space–time processing methods applied to multiple-input multiple-output
(MIMO) systems are expected to provide great capacity and data rate increases in cellular
systemsandwirelesslocalareanetworks.
This book is organized as follows: in Chapter 2 an overview of wireless communication
systems is presented, a requisite to analyze smart antenna systems. Following this, a chapter
on antenna arrays and diversity techniques is included that describes antenna properties and
classifiesthemaccordingtotheirradiationcharacteristics.InChapter4,thefunctionalprinciples
of smart antennas are analyzed, different smart antenna configurations are exhibited and the
benefits and drawbacks concerning their commercial introduction are highlighted. Chapter 5
deals with different methods of estimating the direction of arrival. The more accurate this
estimate is, the better the performance of a smart antenna system. Chapter 6 is devoted to
beamformingtechniquesthroughwhichthedesiredradiationpatternsoftheadaptivearraysare