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1、DOPPLERSHIFTEDSPREADSPECTRUMCARRIERRECOVERYUSINGREAL-TIMEDSPTECHNIQUESBradleyJ.ScaifeandPhillipL.DeLeonNewMexicoStateUniversityManuelLujanCenterforSpaceTelemetryandTelecommunicationsABSTRACTInanysatellitecommunication,theDopplershiftassociatedwiththesatel
2、litespositionandvelocitymustbecalculatedinordertodeterminethecarrierfrequency.IfthesatellitestatevectorisunknownthensomeestimatemustbeformedoftheDoppler-shiftedcarrierfrequency.Oneelementarytechniqueistoexaminethesignalspectrumandbasetheestimateonthedomin
3、antspectralcomponent.If,however,thecarrierisspread(asinmostsatellitecommunications)thistechniquemayfailunlessthechiprate-to-datarateratio(processinggain)associatedwiththecarrierissmall.Inthiscase,theremaybeenoughspectralenergytoallowpeakdetectionagainstan
4、oisebackground.Inthispaper,wepresentamethodtoestimatethefrequency(withoutknowledgeoftheDopplershift)ofaspread-spectrumcarrierassumingasmallprocessinggainandbinary-phaseshiftkeying(BPSK)modulation.Ourmethodreliesonasimple,averageddiscreteFouriertransformal
5、ongwithpeakdetection.Weprovidesimulationresultsindicatingtheaccuracyofthismethod.Inaddition,wewilldescribeanall-digitalhardwaredesignbasedaroundaMotorolaDSP56303andhigh-speedA/Dwhichimplementsthistechniqueinreal-time.ThehardwaredesignistobeusedinNMSUsimpl
6、ementationofNASAsdemandassignment,multipleaccess(DAMA)service.KEYWORDSFrequencyestimation,Dopplershiftedcarrierrecovery,fastfouriertransform,spreadspectrum.1.INTRODUCTIONThepurposeofthisworkistoprovideameansbywhichaspread-spectrum,binary-phaseshiftkeying(
7、BPSK)carrier,havingundergoneanunknownDopplershift,canbequicklyandaccuratelyestimated.ThesystemdescribedhereinistobeutilizedtoimplementNewMexicoStateUniversitys(NMSU)proposeddemandassignment,multipleaccess(DAMA)serviceontheexistingTrackingandDataRelaySatel
8、liteSystem(TDRSS)[1].Currently,thegroundstationreceiver(GSR)canperformdemodulationgiventheDopplershifttowithin±3kHz.AstheproposedDAMAcarrierhasbeenshowntohaveatheoreticalshiftof±64kHzandthestatevectorofthesatellitei
