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GPSCA码信号处理与分析的中期报告.docx

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GPSCA码信号处理与分析的中期报告 Introduction GPS(GlobalPositioningSystem)isaspace-basednavigationsystemthatallowsuserstodeterminetheirpreciselocationandvelocity.Itconsistsofanetworkofsatellitesinorbitaroundtheearth,groundcontrolstations,anduserequipment.Inordertodeterminetheirposition,GPSreceiverdevicesrelyonsignalsfromthesatellites,whicharetransmittedontwomainfrequencies:L1(1575.42MHz)andL2(1227.60MHz).ThesignalstransmittedbyGPSsatellitesaremodulatedwithcodeandphasecomponents,whichneedtobeaccuratelyprocessedbythereceiverinordertoobtainprecisepositionandtiminginformation.Inthisreport,wepresentanoverviewofthesignalprocessingandanalysistechniquesusedforGPSreceiverdevices. SignalStructureandComponents ThesignaltransmittedbyGPSsatellitesconsistsofseveralcomponents,includingthecarrierwave,thenavigationmessage,andthecodeandphasecomponents.Thecarrierwaveisahigh-frequencyelectromagneticwave,whichisusedtotransmittheGPSsignalsoverlongdistances.Thenavigationmessagecontainsinformationaboutthesatellite'sposition,velocity,andtime,aswellasotherdatasuchassatellitehealthandstatus.Thecodecomponentisadigitalsequencethatismodulatedontothecarrierwave,andisusedbythereceivertodeterminethetimeofarrivalofthesignal.Thephasecomponentisacontinuouswaveformthatisalsomodulatedontothecarrierwave,andisusedbythereceivertodeterminethephasedifferencebetweenthesignaltransmittedbythesatelliteandalocallygeneratedreferencesignal. SignalAcquisitionandTracking InordertoprocesstheGPSsignal,thereceivermustfirstacquireandtrackthesignalfromthesatellites.Theacquisitionprocessinvolvessearchingforthecodecomponentintheincomingsignal,andoncethecodecomponentisdetected,thereceivercandeterminethetimeofarrivalofthesignal.Thetrackingprocessinvolvesadjustingthelocalreferencesignalsothatitmatchesthephaseandfrequencyoftheincomingsignal,andcontinuouslymeasuringthephasedifferencebetweenthetwosignals.Thereceivercanthenusethisphasedifferencetodetermineitsposition. CodeandPhaseMeasurements ThecodeandphasemeasurementsusedbytheGPSreceivercanbe