基于超高频rfid的实时定位系统研究

基于超高频rfid的实时定位系统研究

相关表1.4—Introductionuhf广播率的遗传因素（rfid）是生命和中期受体的特征。它以较高的速度和信息的速度命名。短程协议系统（rts）的基本信息是最好的。RTLSisawirelesssystemwiththeabilitytolocatethepositionofanitemorapersonanywhereinadefinedspaceatapointintimethatis,oriscloseto,realtime.RFID-basedRTLSwillgreatlyimpeltheapplicationofRFID.ManydifferentRFID-basedlocalizationsystemshavebeendevelopedandappliedtolotsofareasinrecentyears,likeemergencyrescuing,patienttracking,assetorlivestocktracking,andmanyotherareas.Thetechniquesofdistanceestimationcanbeclassifiedas:Timebased,Signalarrivalanglebased,andReceivedsignalstrengthindicatorbasedtechniques.ThispaperpresentsbehavioralmodelofRTLSbasedonUHFRFIDinMatlab/Simulink.Theorganizationofthepaperisasfollows.Inthefirstsection,theprincipleofRFID-basedRTLSispresented.ThesecondsectionproposedthearchitectureofRFID-basedRTLS.Keyproblemsandrelevantsolutionswerealsoproposed.Inthethirdsection,thewholelinkandsubsystemmodelofRTLSisillustrated.Inthefourthsection,simulationresultsaregivenanddiscussed.Andfinally,theconclusionwasdrawninthelastsection.1adrapte国际习惯法acpohening国际习惯法案例TheprincipleofUHFRFIDisbasedonbackscatteringaccordingtotheEPCGlobalGen2Standard,asshownisFig.1.Inthedownlink,RFIDreadertransmitsmodulatedcarrier.Themodulateddepthisfrom80%to100%.RFIDtagswithintheeffectiveoperationareacollectpowerfromtheelectromagneticwaveanddemodulatethesignal.Intheuplink,readertransmitscontinuouscarrierwithoutmodulation.Tagschangethereflectanceofantennatomodulateandbackscatterthecontinuouscarriertothereader.Inordertolocatethepositionofanitemorapersoninadefinedspace,atagisattachedtotheitemortheperson.ReaderinRFIDsystemcommunicateswiththetagineffectiveoperationareaanddetectsthedistanceLaswellasthedirectivityθofthetagtotracktheobjectinrealtime.ThedistanceLcanbecalculatedbythemeasuredtransfertimet,whichisknownasTOA(TimeofArrival),accordingtoEq.(1)Wherecisthepropagationspeedofelectromagneticwave.Thedirectivityθ,whichisknownasDOA(DirectionOfArrival),canbemeasuredbyadaptiveantennaorantennaarray.Distributedreadermethodcanalsobeusedtolocatetagsbasedontriangulation.Tocalculatethetransfertime,thetime-averageautocorrelationfunctionisintroduced.Beingameasureofthesimilaritybetweenapowersignalv(t)anditstimedisplacement,thetime-averageautocorrelationfunctionR(τ)isdefinedas:Ifv(t)isperiodicwithperiodT0,theintegrandofEq.(2)isperiodic,andthetimeaveragecanbetakenoverasingleperiod:R(τ)isafunctionofthedelayvariablerandgivesameasureofthesimilaritybetweenthesignalattimetandattimet+τ.τistheneededTOAwhenR(r)ismaximum.AlthoughR(τ)isperiodic,thecoherencebetweenasignalandadelayedversionofthesignalcanbemeasured.Thetransmittedsignalv(t)isarealbandpasssignal,whichcanbewrittenas:orWhereg(t)=x(t)+jy(t)isthecomplexenveloperepresentationofthebandpasssignal.x(t)andy(t)areknownastheinphaseandquadraturecomponents,respectively.Accordingtobandpasssamplingtheorem,thesamplingratecanbeminimumifabandpasssignalisrepresentedbyitscomplexenvelope.TheHilberttransformcanbeusedtodefinethecomplexenvelopeofarealbandpasssignal.AssumethepropagationchannelofRFIDsystemisfreespaceandthetransmittedsignalpowerisPT.Ifradiatedisotropically,thepowerdensityatadistanceLfromthereaderisgivenbyAndthefree-spacelossindecibelsisgivenbyWhereλcisthewavelengthofthewave.2sit确定rexiece安氏集的siphindTheproposedresolutionofRFID-basedRTLSisbasedonthePseudo-randomNumberRanging(PNR),andthearchitectureisshowninFig.2.Indownlink,justliketheabovementioned,readertransmitsmodulatedcarrierinTXblock.Intheuplink,readertransmitscarriermodulatedbyPNsequence.Themodulationdepthisonly10%andtagscannotdetecttheAMsignal.Sotagsmodulatetheantenna’sreflectanceandbackscatterthisAMsignalregularlytothereader.ReaderdemodulatesthereceivedPNsequenceinRXblockandcorrelatesitwiththetransmittedPNsequenceinDSPblock.Detailedstructureswillbeshowninthethirdsection.FromEq.(1)andEq.(3),wecanseethattheoverallaccuracyisdeterminedbyTOA,butthetimedelaydetectedbyreadermakesupofmanyparts:readertransceiver’sdelay,freespacetransmissiondelay,anddigitalclockdelay,etc.OnlythefreespacetransmissiondelayisvalidTOA.Othersareinvalid,butinherentinagivenRFIDsystems.Asaresult,calibrationneedstoaddinbeforethecorrelation,asdepictedinFig.2,inordertogettherealTOA.Multi-patheffectisanotherkeyproblemwhichshouldbecarefullyconsidered.Thetransmittedsignalisreflectedbyenvironmentthroughmultiplepaths,asshowninFig.3.Typically,therearetagswhichweareinterestedin(Tag-A),theWall,theGround,andothersilenttags(Tag-B).Fig.3showsthatonlysignalmodulatedbyTag-AcontainstheneededTOA.Othersignalsaremerelyreflected,notmodulatedbythereflectors.IftheperiodofPNsequenceTPNisequaltothatofthetag’sbackscatteredsignalTTAG,wecanseparatesignal-AbydelayingthereceivedsignalbyTPNandsubtractingitfromthereceivedone,asshowninFig.3.TheresultsignalcontainstheneededPNsequenceandwecangetTOAafterDSPandcorrelation.LeakagefromreadertransmittertoreceiverisalsoacriticalprobleminRFIDsystemduetolowisolationbetweenthem.Theleakageblocksthesignalandevendesensitizesthefrontendifthe1-dBcompressionpointisnothighenough.Measuresshouldbetakentoavoidthedesensitization.3fig.4arespityingmortgageBeforethemodel,wehavesomerationalconsiderations:Firstly,thecarrierfrequencyofUHFRFIDrangesfrom860MHzto960MHz.Herewechoose920MHz.Secondly,thedataratefromtagtoreaderrangesfrom40kHzto640kHz,andhere160kHzischosen.Thirdly,onlyFreeSpacePathLossismodeledaschannelloss.Fourthly,theisolationbetweenTXBlockandRXBlockis-40dB,whichisfeasibleindualantennatransceiver.ThewholesystemofRFID-basedRTLSismodeledinMatlab/Simulinkandcomprisedofreader,channelandtags,asdiscussedabove.Inaddition,non-idealfactorslikeGaussiannoise,phasenoiseofLocalOscillator(LO),andquantizationnoiseofADCandDACareconsideredinthemodel.NonlineardistortionsofPA,Up-mixer,Down-mixerandVGAarealsomodeledinthesystem.Fig.4(a)isthebehavioralmodelofthewholelinkwhileFig.4(b)toFig.4(f)arethesubsystemmodels,respectively.Fig.4indicatesthatthesystemmodelofRFID-basedRTLShasthefollowingparts:(1)TXBlock,includingPNSequenceGenerator,raise-cosinefilter(RCF),Hilberttransform,DAC,andUp-mixer.(2)ChannelBlock,includingfreespaceattenuationandGaussiannoisegenerator.(3)RXBlock,includingDown-mixer,VGA,andADC.(4)Tag-A,Tag-BandWall.(5)DSPBlock,includingIntegerDelay,Gainblock,digitalfilterandcorrelation.Theparametersofeachblockareshownasfollows:DAC:14bit;ADC:12bit;Up-mixer:gain=10dB,NF=15dB,IIP3=10dBm;Freespacepathloss:-25dB～-55dB;ThesystemarchitectureofRFID-basedRTLSisatypicaldirect-conversiontransmitterandhomodynereceiver.ThetransmittedbasebandsignalistransformedbyHilbertandrepresentedbythecomplexenvelopethroughinphaseandquadraturechannels.Sothesystemsamplingfrequencyisdeterminedbytheover-samplingrate(OSR=32)ofPNsequence.Thecomplexenvelopeisup-convertedbyup-mixerandamplifiedbypoweramplifierandradiatedinfreespace.Tag-Amodulatesthecomplexenvelopeandbackscattersittofront-endreceiver.Down-mixerinsteadofLNAisusedasthefirststageofRFIDreceiverduetoitshighcompressionpoint.Thisisaneffectivewaytoeasetheabovementioneddesensitization.TherealandimaginarypartsofthecomplexenvelopearefilteredbyLPF,amplifiedbyVGAandquantizedbyADCsininphaseandquadraturechannels,respectively.AccordingtoFriisequation,thetotalnoisefigureofthefrontendreceiverinourarchitectureisinevitablylargerthanthenormal.Byadjustingthegain,noisefigureandIIP3ofeachblock,thesensitivityandtotalnoisefigurearekeptinareasonablerange.Thenthecomplexenvelopeisprocessedbydigitalpart.CalibrationisaddedintogettherealTOA,asdescribedbelow.First,setthecalibrationdistance(8meters,forexample)andsimulatethetimedelayunderthissetting.Second,calculatethecoherenttimedelayinthesystemandrecordit.Practically,thecalibrationsettingswillbesavedontheEPROMinthereaderandtheyarevalidforallfurthermeasurementsuntilthereisachangeincablingorantennas.4规训correlationthichmotivationRFID-basedRealTimeLocatingSystemshouldrangeallthetagswithintheoperatingarea.Herearesimulationresultsbasedonthemodelwhenthetargettagisput10maway.Fig.5(a)showsauto-correlationofthetransmittedPNsequenceandcrosscorrelationoftransmittedPNsequenceandreceivedPNsequence.Fig.5(a)indicatesthateveryTPN,orevery1984samplingpoints,thereisacorrelationpeak.TovisuallyrevealTOA,amplifiedcorrelationresultsarealsopresentedinFig.5(b).ThedifferenceinX-axisbetweentwopeaksis10samplingpoints,whichmeansTOAis63nsandthedistanceis9.45m.5细胞pack注重表面活性剂的使用,引发排汗行为BehavioralmodelofUHFRFID-basedRealTimeLocatingSystemispresentedinMatlab/Simulink.Non-idealfactorsofUHFRFIDtransceiverandpropagationchannelwerestrictlymodeledtosimulaterealoperatingcondition.TheproposedresolutionisbasedonthePseudo-randomNumbe