Low Complexity TOA Estimation for Impulse Radio UW

MITSUBISHIELECTRICRESEARCHLABORATORIES(UWB)channelsmakestimeofarrival(TOA)estimationextremelychallenging,wheretheleading-edgepathisnotnecessar-ilythestrongestpath.SincethebandwidthofareceivedUWBsignalisverylarge,theNyquistratesamplingbecomesimpractical,hencemotivatinglowercomplexityandyetaccuraterangingtechniquesatfeasiblesamplingrates.Inthispaper,weconsiderTOAestimationbasedonsymbolratesamplesthatareobtainedafterasquare-lawdevice.Signalconditioningtechniquesbasedonwaveletsandabankofcascadedmulti-scaleenergycollectionfiltersareintroduced,wherecorrelationsacrossscalesareexploitedforedgeandpeakenhancementstowardsamoreaccu-ratedetection.Anadaptivethresholdselectionapproachbasedontheminimumandmaximumvaluesoftheenergysamplesisintroduced,andoptimalvaluesofthethresholdsfordifferentsignaltonoiseratios(SNRs)areinvestigatedviasimulations.Theoreticalclosedformexpres-sionsarederivedformeanabsoluteTOAestimationerror,andcomparedwithsimulations.TheperformancesofthediscussedalgorithmsaretestedonIEEE802.15.4aresidentialline-of-sight(LOS)andnon-LOSchannels.Simulationresultsshowthattheintroducedmulti-scaleenergyproducttechniquesupportedwithasearch-backsteptodetecttheleadingedgeperformsbetterthanalltheothertechniques,excludingthepurethresholdcomparisonalgorithmatverylargeSNRvalues.IEEEJournalonSelectAreasinCommunicaitonsThisworkmaynotbecopiedorreproducedinwholeorinpartforanycommercialpurpose.Permissiontocopyinwholeorinpartwithoutpaymentoffeeisgrantedfornonprofiteducationalandresearchpurposesprovidedthatallsuchwholeorpartialcopiesincludethefollowing:anoticethatsuchcopyingisbypermissionofMitsubishiElectricResearchLaboratories,Inc.;anacknowledgmentoftheauthorsandindividualcontributionstothework;andallapplicableportionsofthecopyrightnotice.Copying,reproduction,orrepublishingforanyotherpurposeshallrequirealicensewithpaymentoffeetoMitsubishiElectricResearchLaboratories,Inc.Allrightsreserved.CopyrightcMitsubishiElectricResearchLaboratories,Inc.,2005201Broadway,Cambridge,Massachusetts02139MERLCoverPageSide2LowComplexityTOAEstimationforImpulseRadioUWBSystemsI.Guvenc1,2,Z.Sahinoglu11MitsubishiElectricResearchLabs,201BroadwayAve.,Cambridge,MA,021392DepartmentofElectricalEngineering,UniversityofSouthFlorida,Tampa,FL,33620E-mail:{guvenc,zafer}@merl.comAbstractDuetoextremelynarrowpulses,animpulseradiosignalinghasastrongpotentialforhigh-precisionpositioning.Highlydispersivenatureofultra-wideband(UWB)channelsmakestimeofarrival(TOA)estimationextremelychallenging,wheretheleading-edgepathisnotnecessarilythestrongestpath.SincethebandwidthofareceivedUWBsignalisverylarge,theNyquistratesamplingbecomesimpractical,hencemotivatinglowercomplexityandyetaccuraterangingtechniquesatfeasiblesamplingrates.Inthispaper,weconsiderTOAestimationbasedonsymbolratesamplesthatareobtainedafterasquare-lawdevice.Signalconditioningtechniquesbasedonwaveletsandabankofcascadedmulti-scaleenergycollectionfiltersareintroduced,wherecorrelationsacrossmultiplescalesareexploitedforedgeandpeakenhancementstowardsamoreaccuratedetection.Anadaptivethresholdselectionapproachbasedontheminimumandmaximumvaluesoftheenergysamplesisintroduced,andoptimalvaluesofthethresholdsfordifferentsignaltonoiseratios(SNRs)areinvestigatedviasimulations.TheoreticalclosedformexpressionsarederivedformeanabsoluteTOAestimationerror,andcomparedwithsimulations.TheperformancesofthediscussedalgorithmsaretestedonIEEE802.15.4aresidentialline-of-sight(LOS)andnon-LOSchannels.Simulationresultsshowthattheintroducedmulti-scaleenergyproducttechniquesupportedwithasearch-backsteptodetecttheleadingedgeperformsbetterthanalltheothertechniques,excludingthepurethresholdcomparisonalgorithmatverylargeSNRvalues.1I.INTRODUCTIONThisdecadewillseeariseinlocationawareapplicationsindiversefieldsfromassetmanagementandhome/buildingautomationtoenvironmentalmonitoringanddisastermanagement.ThiswidemarketneedrecentlyurgedemergingIEEE802.15.4astandardsworkgroup(WG)toinviteproposalsforanalternativePHYtotheexistingIEEE802.15.4standards,requiringasub-meterprecisionrangingcapability.Thecontentofthisarticleonmulti-scalenon-coherentTOAestimation,hasbeenoneoftherangingproposalsunderconsiderationinIEEE802.15.4a.Hightimeresolutionisoneofthekeybenefitsofultra-wideband(UWB)signalsforprecisionranging.DuetoextremelyshortdurationoftransmittedUWBpulses,UWBreceivers,asopposedtotypicalnarrow-bandwirelessreceivers,enjoybeingabletoobserveindividualmultipathcomponents;andtheaccuracyofTOAestimationischaracterizedbyhowfinelythefirstarrivingsignalpathisidentified,whichmaynotbethestrongest.UWBreceiverstypicallyhavetooperateatverylowsamplingrates.ThismakesitdifficulttoeffectivelycapturetheenergyateachindividualmultipathcomponentusingRakereceivers,asitisextremelydifficulttosynchronizetoeachtap.Achip-spacedsamplingofthechannelcan