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1、AnIntroductiontoSpread-SpectrumCommunicationsAbstract:Thisapplicationnoteisatutorialoverviewofspread-spectrumprinciples.Thediscussioncoversbothdirect-sequenceandfast-hoppingmethods.Theoreticalequationsaregiventoallowperformanceestimates.Thefollowingdiscussionofdirect-sequencespr
2、ead-spectrum(DSSS)andfrequency-hoppingspread-spectrum(FHSS)methods.Asspread-spectrumtechmiquesbecomeincreasinglypopular,electricalengineersoutsidethefieldareeagerforunderstandableexplanationsofthetechnology.Therearebooksandwebsitesonthesubject,butmanyarehardtounderstandordescrib
3、esomeaspectswhileignoringothers(e.g.,theDSSStechniquewithextensivefocusonPRN-codegeneration).Thefollowingdiscussioncoversthefullspectrum.1.AShortHistorySpread-spectrumcommunicationstechnologywasfirstdescribedonpaperbyanactressandamusician!In1941HollywoodactressHedyLamarrandpiani
4、stGeorgeAntheildescribedasecureradiolinktocontroltorpedos.TheyreceivedU.S.Patent#2.292.387.ThetechnologywasnottakenseriouslyatthattimebytheU.S.Armyandwasforgottenuntilthe1980s,whenitbecameactive.Sincethenthetechnologyhasbecomeincreasinglypopularforapplicationthatinvolveradiolink
5、sinhostileenvironments.Typicalapplicationsfortheresultingshort-rangedatatransceiversincludesatellite-positioningsystemsGPS，3Gmobiletelecommunications,W-LAN(IEEE®802.11a,IEEE802.11b,IEEE802.11g),andBluetooth®.Spread-spectrumtechniquesalsoaidintheendlessracebetweencommunicationnee
6、dsandradio-frequencyavailability-situationswheretheradiospectrumislimitedandis,therefore,anexpensiveresource.2.TheoreticalJustificationforSpreadSpectrumSpread-spectrumisapparentintheShannonandHartleychannel-capacitytheorem:C=B×log2(1+S/N)(Eq.1)Inthisequation,Cisthechannelcapacit
7、yinbitspersecond(bps),whichisthemaximumdatarateforatheoreticalbit-errorrate(BER).BistherequiredchannelbandwidthinHz,andS/Nisthesignal-to-nosiepowerratio.Tobemoreexplicit,oneassumesthatC,whichrepresentstheamountofinformationallowedbythecommunicationchannel,alsorepresentsthedesire
8、dperformance.Bandwidth(B)isthepricetobepaid,bac
