《移动通信技术（英文）》课件-1.5.1 抗信道衰落技术-扩频

Anti-Channelfadingtechnology-spreadspectrumMobileCommunicationTechnologySpreadspectrumreferstothecommunicationofspreadspectrum,whichisakindofbroadbandcommunicationtechnology.Itismainlyusedinmilitarysecurecommunicationsandelectroniccountermeasuresystems.WiththechangeoftheworldwidepoliticalpatternandtheendoftheColdWar,thistechnologyhasgraduallyturnedto"commercialization."

ApplicationfieldInventorBackgroundHedyLamarr,BorninVienna,Austriain1914,filmandtelevisionactor,inventor,thefirstinventoroffrequencyhoppingtechnology,knownasthemotherofCDMA.HedyLamarr,themotherofCDMA01020304DefinitionofSpreadSpectrumTechnologyCharacteristicsofSpreadSpectrumTechnologyPrincipleofSpreadSpectrumTechnologyApplicationofSpreadSpectrumTechnologyCONTENT01DefinitionofSpreadSpectrumTechnologyPARTONESpreadspectrummodulationchannelSpreadspectrumdemodulationd(t)d(t)c(t)c(t)-Rb(t)-Rb(t)Rb(t)Rb(t)-Rc(t)Rc(t)干扰-Rc(t)Rc(t)AABBCCDDy(t)yr(t)干扰Itisawayofinformationtransmission,andthebandwidthofthesignalismuchgreaterthantheminimumbandwidthnecessaryforthetransmittedinformation(10-1000times).theexpansionofthefrequencybandisaccomplishedbyanindependentcodesequence,whichisrealizedbycodingandmodulation.

thereceiverusesthesamecodetoreceive,despreadandrecoverthetransmittedinformationdatasynchronously.EmphasizethreepointsDefinitionofSpreadSpectrumTechnology02CharacteristicsofSpreadSpectrumTechnologyPARTTWO①抗干扰能力强②隐蔽性好③可实现码分多址④抗衰落，抗多径干扰CharacteristicsofSpreadSpectrumTechnology03PrincipleofSpreadSpectrumTechnologyPARTTHEREsymbol

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+1spreadspectrummodulationspreadspectrumdemodulationchipdi（t）Ci（t）yi（t）

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+1yr（t）Ci（t）dr（t）接收的信号为：yr（t）=di（t）·Ci（t）解扩输出信号dr（t）=yr（t）·Ci（t）=di（t）·Ci（t）·Ci（t）=di（t）Narrowpulsesequenceiscalledspreadspectrumsignal,namelyspreadspectrumcodesequenceThereceiverusesthesamespreadspectrumcodesequenceasthetransmittertodespreadthereceivedspreadspectrumsignalandrecoverthetransmittedinformation.PrincipleofSpreadSpectrumTechnologyC=Bwlog2(1+S/N)=1.44Bwln

(1+S/N)whichCisthechannelcapacity,theunitisthebandwidthofthetransmittedsignal,theunitisHz;Sistheaveragepowerofthesignal,andNistheaveragepowerofthenoise.

Importantconclusions

UndertheconditionofkeepingCconstant,increasingthefrequencybandwidthofthesignalcantransmitinformationwitharbitrarilysmallerrorprobabilityundertheconditionoflowsignal-to-noiseratio,thatis,themethodofspreadspectrumcanbeusedinexchangeforthebenefitofsignal-to-noiseratio.Byexpandingthespectrum,theanti-jammingabilityofthesignalisimproved,thatis,thesecurecommunicationcanbeensuredundertheconditionofstronginterference.PrincipleofSpreadSpectrumTechnologyShannonformulaClaudeElwoodShannon(1916.04.30—2001.02.26）anAmericanmathematicianandfounderofinformationtheory.Hereceivedhismaster'sanddoctoratedegreesfromtheMassachusettsInstituteofTechnologyin1940andjoinedBellLaboratoriesin1941.

Shannonputforwardtheconceptofinformationentropy,whichlaidthefoundationforinformationtheoryanddigitalcommunication.

PrincipleofSpreadSpectrumTechnologyaccordingtothedifferentwaysofspreadingthesignalspectrum,thespreadspectrumcommunicationsystemismainlydividedinto:DS:spreadspectrumFH：FrequencyHoppingPrincipleofSpreadSpectrumTechnologyFrequencyHopping04ApplicationofSpreadSpectrumTechnologyPARTFOURhespectrumexpansionisusuallyrealizedbyanarrowpulsesequence,thatis,pseudorandom(PN)codemodulation.atpresent,therearethreecommoncodepatterns:MsequenceGLODsequenceWalshfunctioncodesThespreadspectrumtechnologyisadoptedinthetypicalsystemsof2Gand3Gmobilecommunications,andthechannelbandwidthfarexceedsthesinglechannelbandwidthoftheGSMsystem's200kHz.2G：IS-95CDMA（1.23MHz）3G：W