Joint wireless communication and radar sensing system1.docx

Joint wireless communication and radar sensing system1.docx

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Jointwirelesscommunicationandradarsensingsystem1

Jointwirelesscommunicationandradarsensingsystems–stateoftheartandfutureprospects

LiangHan,KeWu

Poly-GramesResearchCenter,CenterforRadiofrequencyElectronicsResearchofQuebec（CREER）,DepartmentofElectricalEngineering,EcolePolytechnique,UniversityofMontreal,Montreal,Quebec,CanadaH3T1J4E-mail:

liang.han@polymtl.ca

Abstract:

Thehistoricaldevelopmentandcurrentstate-of-the-artofvariousjointwirelesscommunicationandradarsensingsystemsarereviewedanddiscussedinthisstudy.Differentkindsofsystemsarecategorisedaccordingtotheirmodulationwaveformsandduplexschemes.Prosandconsofeachcategoryarehighlighted.Toshowcasethecurrentresearchadvances,severaldemonstrationsystemsareintroducedwithemphasisonproposedresearchcontributionsinthisemergingarea,andtheirperformancesarecomparedwithrespecttobothcommunicationandradarmodes.Also,anumberofchallengesareidentifiedforthenearfuturesystemdevelopmentsandapplications.

1Introduction

Theinventionofradiousheredthehistoryofmankindintoanewera.Amongvarioustypesofradioapplicationsknowntodate,themostubiquitousandprominenttwoofthemarewirelesscommunicationandradarsensing.Sincetheverybeginning,thesetwosortsofsystemshavebeendesignedanddevelopedinaquitedifferentmanner,eventhoughbothmakeuseofradiofrequencytransceiverfunctionalblocks.Ofcourse,theyhavegenerallybeenindependentlyandseparatelystudiedanddevelopedfromeachotherinmostscenariosexceptforsomeprimitiveapplicationexamplesofsystemfusionbetweenthemsuchastheso-calledsecondarysurveillanceradarsystemortheidentificationfriendorfoe（IFF）system[1].Althoughinformationexchangeisenabledinsuchkindofradarsystems,theresponderisingeneralnotabletotransmitdatatotheinterrogatorautonomously.Thereforedatafusionschemesbasedonthiskindofsystemoperation,thatis,radar-embeddedcommunications[2]andUWBRFID[3],willnotbefurtherdiscussedinthispaperbecausesuchsystemsdonotpresenta‘truly’blendedtransceiverarchitecturethatsimultaneouslypossessescommunicationandradarfunctions.

Ifsuccessfullyimplemented,thesystemfusionofwirelesscommunicationandradarsensingwoulddefinitelybringupmanybenefitsincludingarchitectureunificationandsimplification,functionalreconfigurationandfusionandespeciallyefficiencyenhancementandcostreduction.Naturally,thefusionoftwosystemsthroughonesingletransceiverallowsthereal-timeinterplayand‘dialogue’betweentwodifferentfunctions.AnearlyexampleofintegratedradarandcommunicationsubsystemcanbetracedbacktotheNASASpaceShuttleOrbiter[4].Recently,therehasbeenamultitudeofemergingneedsforintegratingwirelesscommunicationandradarsensingsystems.Theintelligenttransportationsystems[5],forexample,requireintelligentvehiclestohavethecapabilityofautonomouslysensingthedrivingenvironmentandcooperativelyexchanginginformationdatasuchasvelocityandbrakingbetweenvehiclesandalsoroad,trafficandweatherconditionsaswellasentertainmentcontentamongvehiclesandbeacons.Anotherexampleisthewirelesssensornetworks（WSN）[6]forpositioningandmonitoringpurposes,inwhicheachnodedetectstargetsandsharesitsinformationwithothernodesthroughwirelesscommunicationlinks,whichshouldbedesirablypartoftheWSNsystem.Furthermore,itshouldbementionedthatmultifunctionalin-situsystemswithactiveprotectionradar,widebandcommunicationsandcombatidentificationarealsohighlydemandedformodernmilitaryapplications[7].

Theunprecedentedsystemfusionhasgenerallypresentedmanystringentdesignrequirementssuchaslow-cost,simpleimplementation,flexiblefunctionalreconfigurationandhigh-powerefficiencyaswellasfastresponse.Thisisbecausethesystemfusionorintegrationshouldbemuchmoreadvantageousthanitspuremechanicallyassembledcounterpartoftwoseparatesystemarchitectures.Inthepasthalf-decade,anumberofsystemconceptswithrespecttowaveformdesignandtransceiverdevelopmenthavebeenproposedtointegratebothwirelesscommunicationandradarsensingfunctionswithinasingletransceiversystem.Thispaperbrieflyreviewsandsummarisesthestate-of-the-artsystems,describesanddiscussessomedemonstrationsystems,andpointsoutseveralchallengesforfuturesystemdevelopments.

2Waveformdesign

Differentunderlyingoperationprinciplesofwirelesscommunicationandradarsensingsystemssuggestdifferentrequirementswithregardtocertainsystemandtransceiverdesignconsiderations,suchasduplexmode,modulationschemeandbandwidthaswellassignalprocessingalgorithms.Forinstance,frequencydivisionduplexmodecommonlyusedinwirelesscommunicationisnotsuitableforradarapplicationssincethespectraoftransmittedandreceivedradarsignalsarealmostco-locatedinthesamefrequencychannel.Inmostcases,thedesignrequirementsforcommunicationandradarfunctionsmaybeinconflict,whichposeagreatchallengeinthedevelopmentofsuchsystemarchitecturefusions.Withrapidprogressofdigitalcircuits,therehasbeenatrendtosimplifythedesignofradio-frequency（RF）front-endcircuitsbyimplementingmostofthesystemfunctionsbaseduponsoftware-reconfigurablesignalprocessingalgorithms.Thesesoftware-definedradioplatformsprovideuswithagoodopportunitytoachievejointcommunicationandradaroperationswithinthesameRFfront-endcircuit.

Table1summarisestheprosandconsoftypicalcommunication–radarfusionschemesthathaverecentlybeenproposedandstudiedin[8–24].Thejointwaveformschemecanbefurthercategorisedintosingle-carrierandmulti-carriersystems.Inthesingle-carriersystems,thefrequency-domainschemeisfoundmuchlesspopularthanitscode-domain（spreadspectrum）counterpartsbecauseofthemutualorcross-channelinterferencecausedbythespectrumoverlapping[8].Thespreadspectrumtechniquewasfirstlyimplementedinaboomerangtransmissionsystemforvehicularcommunicationandrangingapplications[9].Essentially,theproposedsystemissimilartoanIFFsystemexceptthatitadoptsthedirect-sequencespreadspectrum（DSSS）techniquetoimprovethesystemperformance.Followingthatdevelopment,thespreadspectrumtechniquehaswidelybeenexploitedforfusingcommunicationandradarfunctions,suchasDSSS[9–13],THSS[14]andCSS[15].Thecode-domainschemesallowforsecurecommunicationandhigh-resolutionrangingattheexpenseofutilisingexcessivespectrumresourcesfordatacommunication.Moreover,differentuserscansharethesamefrequencybandsimultaneouslybyusingdifferentspreadingcodes,whichisverybeneficialformultiuserapplicationscenarios.RegardingtheradarrangingandDopplerestimationbasedonthespreadspectrumtechnique,therearetwomaindrawbacks.Oneisthatthepeak-to-sideloberatioislimitedbytheimperfectauto-correlationcharacteristicsofthepseudorandomcodes,anditisalsoimpactedbythespreadingfactorandtheDopplershift.TheotheristhatforDopplerprocessing,thespreadspectrumtechniquerequiresahugeamountofcomputations.Ingeneral,theconcernofusingaspreadspectrumtechniqueisrelatedtoitshighcomplexityandcostandlowefficiencyintermsofsystemimplementation.

Multi-carrier,especiallytheorthogonalfrequency-divisionmultiplexing（OFDM）technique,whichhaswidelybeenusedinwirelesscommunications,wasalsointroducedinthedesignofradarwaveform[25].TheuseofOFDMradarwaveformswasdemonstratedinmultiple-inputandmultipleoutput（MIMO）radarsystems[16]andradarnetworks[26,27]aswellassyntheticapertureradar（SAR）systems[17,28–30].OneattractivefeatureoftheOFDMradarsignalsisthatthereisnorange–DopplercouplingissueandthereforeindependentrangeandDopplerprocessingbecomespossible[31,32].Inthepastfewyears,differentsignalprocessingtechniqueshavebeenproposedandimplemented.Inthebeginning,matchedfilterswereusedtoperformrangeandDopplerestimationin[18,33–37].However,correlation-basedprocessingmethodstillsuffersfromsuchproblemsaslowdynamicrange（orpeak-to-sideloberatio）andambiguities.Inordertoincreasethedynamicrangeandpreservethetransmittedcommunicationdata,anovel‘modulationsymboldomain’OFDMprocessingalgorithmwasproposed[38–41]andvalidatedthroughexperimentalsystemprototypes[19,42].Althoughpreservingtheresolutionandtheprocessinggainofthecorrelation-basedprocessingmethod,thisadvancedjointrangeandDopplerestimationalgorithmfortheOFDM-basedjointwaveformhasmuchhigherdynamicrangethanthesingle-carrierspreadspectrumapproachbymanyordersofmagnitude,especiallyforhighSNRlevels.Moreover,theDopplerfrequency（ortargetrelativevelocity）canbeeasilyestimatedindependentlyfromthetargetrange.Acomprehensivereviewoftheproposedsignalprocessingtechniqueandrelatedsystemdemonstrationcanbefoundin[43].Thistechniquehasbeenrecentlyextendedtotackleamultipathandmultiuserscenarioin[44].AlthoughtheOFDMtechniqueshavepresentedanumberofadvantageslistedinTable1,thehighimplementationcostofOFDMsystemsbecauseofthecomplexsignalprocessingandhighpeak-to-averagepowerratioofOFDMsignalsstillimpedetheirwidespreadapplications.

Almostinparallelwiththejointwaveformscheme,thetime-domainduplexschemehasalsostimulatedresearchinterestbecauseofitshighspectralefficiencyandeasysystemimplementationaswellaslowcost[20–24].Inthetime-domainplatforms,comm