中文4350字外文原文HindawiPublishingCorporationInternationalJournalofNavigationandObservationVolume2021,ArticleID261384,8pagesdoi:10.1155/2021/261384ResearchArticleGPSCompositeClockAnalysisJamesR.WrightAnalyticalGraphics,Inc.,220ValleyCreekBlvd,Exton,PA19341,USACorrespondenceshouldbeaddressedtoJamesR.Wright,jwright@agiReceived30June2007;Accepted6November2007RecommendedbyDemetriosMatsakisCopyright©2021JamesR.Wright.ThisisanopenaccessarticledistributedundertheCreativeCommonsAttributionLicense,whichpermitsunrestricteduse,distribution,andreproductioninanymedium,providedtheoriginalworkisproperlycited.AbstractTheGPScompositeclockdefinesGPStime,thetimescaleusedtodayinGPSoperations.GPStimeisilluminatedbyexaminationofitsroleinthecompleteestimationandcontrolproblemrelativetoUTC/TAI.ThephaseofeachGPSclockisunobservablefromGPSpseudorangemeasurements,andthemeanphaseoftheGPSclockensemble(GPStime)isunobservable.Anewandusefulobservabilitydefinitionispresented,togetherwithnewobservabilitytheorems,todemonstrateexplicitlythatGPStimeisunobservable.SimulatedGPSclockphaseandfrequencydeviations,andsimulatedGPSpseudorangemeasurements,areusedtounderstandGPStimeintermsofKalmanfilterestimationerrors.1.INTRODUCTIONGPStimeiscreatedbyprocessingGPSpseudorangemeasurementswiththeoperationalGPSKalmanfilter.Brown[2]referstotheobjectcreatedbytheKalmanfilterastheGPScompositeclock,andtoGPStimeastheimplicitensemblemeanphaseoftheGPScompositeclock.ThefundamentalgoalbytheUSAFandtheUSNOistocontrolGPStimetowithinaspecifiedboundofUTC/TAI.(IrefertoTAI/UTCunderstandingthatUTChasanaccumulateddiscontinuity(asumofleapseconds)whencomparedtoTAI.Butuniquetwo-waytransformationsbetweenTAIandUTChavebeeninsuccessfuloperationalusesince1972.Ihavenone---本文来源于网络，仅供参考，勿照抄，如有侵权请联系删除---edhereintofurtherdistinguishbetweenTAIandUTC.)IpresenthereaquantitativeanalysisoftheGPScompositeclock,derivedfromdetailedsimulationsandassociatedgraphics.GPSclockdiffusioncoefficientvaluesusedherewerederivedfromAllandeviationgraphspresentedbyOaksetal.[12]in1998.Irefertothemas“realistic,〞andinthesequelIclaim“realistic〞resultsfromtheiruse.Figure1presentstheirdiffusioncoefficientvaluesandmyderivationofassociatedAllandeviationlines.MyinterestintheGPScompositeclockderivesfrommyinterestinperformingreal-timeorbitdeterminationforGPSNAVSTARspacecraftfromgroundreceiverpseudorangemeasurements.(JamesRWrightisthearchitectofODTK(OrbitDeterminationToolKit),acommercialsoft-wareproductofferedbyAnalyticalGraphics,Inc.(AGI).)TheestimationofNAVSTARorbitswouldbeincompletewithoutthesimultaneousestimationofGPSclockparameters.IusesimulatedGPSclockphaseandfrequencydeviations,andsimulatedGPSpseudorangemeasurements,tostudyKalmanfilterestimationerrors.ThispaperwasfirstpreparedforTimeNav’07[20].IamindebtedtoCharlesGreenhall(JPL)forencouragementandhelpinthiswork.2.THECOMPLETEESTIMATIONANDCONTROLPROBLEMTheUSNOoperatestwoUTC/TAImasterclocks,eachofwhichprovidesaccesstoanestimateofUTC/TAIinrealtime(1pps).OneoftheseclocksismaintainedattheUSNO,andtheotherismaintainedatSchrieverAirForceBaseinColoradoSprings.ThisenablestheUSNOtocompareUTC/TAItothephaseofeachGPSorbitalNAVSTARclockviaGPSpseudorangemeasurements,byusingaUTC/TAImasterclockinaUSNOGPSgroundreceiver.EachGPSclockisamemberof(internalto)theGPSensembleofclocks,buttheUSNOmasterclo...