通信專業(yè)外文翻譯--基帶信號(hào)解調(diào)與檢測(cè)_第1頁
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1、畢業(yè)設(shè)計(jì)(專業(yè)外文翻譯)1BasebDemodulationDetectionInthecaseofbasebsignalingthereceivedwavefmsarealreadyinapulselikefm.OnemightaskwhythenisademodulatneededtorecoverthepulsewavefmsTheansweristhatthearrivingbasebpulsesarenotinthefmofi

2、dealpulseshapeseachoneoccupyingitsownsymbolinterval.Thefilteringtosufferfromintersymbolinterference(ISI)thusappearasanamphous“smeared”signalnotquitereadyfsamplingdetection.Thegoalofthedemodulat(receivingfilter)istoreceiv

3、erabasebpulsewiththebestpossiblesignaltonoiseration(SNR)freeofanyISI.Equalizationcoveredinthischapterisatechniqueusedtohelpaccomplishthisgoal.Theequalizationprocessisnotrequiredfeverytypeofcommunicationchannel.Howeversin

4、ceequalizationembodiesasophisticatedsetofsignalprocessingtechniquesmakingitpossibletocompensatefchannelinducedinterferenceitisanimptantareafmanysystems.Thebpassmodelofthefourthchapterdealswiththedetectionprocessdescribed

5、inthischapteressentiallythesameasthebasebmodel.Befetestingyoumustfirstbpassconversiontothebasebsignal.Fsignaldetectioninlinearsystemsmathematicalexpressionsdonotacceptthefrequencymovehavethefollowingequivalencetheem(equi

6、valencetheemstates):thecurrentprocessingisfirstbpasssignalisconvertedtothebasethenusingtheheterodynemethodbsignaltheresultswiththefirstheterodynesignalisconvertedtothebasebsignalthecrespondinglinearprocessingonthebasebsi

7、gnal.“Heterodyne“(heterodying)referstoatechniquecalled“frequencyconverter(frequencyconversion)“mixing“ofthefrequencyashamethatsoftwaremixingissignalprocessingherealizedthespectrumofthesignalmove.Acollaryoftheequivalencet

8、heemlinearsimulationprocesstheChengDuijibsignal(generally)theresultisthesameastheresultofbpassroleThisindicatesthatmostofdigitalcommunicationsystemsasabasebsystemtodescribeanalyze.畢業(yè)設(shè)計(jì)(專業(yè)外文翻譯)3Tounderlinethenmalizedbwidt

9、hbitratefmofequation(1.1)0NEbNSinto(1.2)???????RWNSNEb0Digitalcommunicationsystemsthemostimptantperfmancemeasureisoneofthebiterrratecurve(seeFigure1.1)theof.BP0NEb00xNEb?0PPB?Dimensionlessratioisastarddigitalcommunicatio

10、nssystemperfmance0NEbindicatsthatcanbeasameasureofcomparativeperfmanceadvantages0NEbdisadvantagesofthetwocommunicationsystems:theconditionsfagivenerrprobabilitytherequiredissmallerthehigheraccuracyofdetection.0NEbENbox0P

11、0BP???????RWNSNEb0F00xNEb?0PPB?Figure1.1GeneralshapeofthePversusENcurveBbo1.3WhyENisaNaturalFigureofMeritboBeginnerdigitalcommunicationthereadermaydoubttheusefulnessoftheparameter.Inanalogcommunicationisaveryusefulindica

12、tofthe0NEbNSmolecularexpecttomaintainthetransmissionofpowerthedenominatrepresentsthesizeofthenoise.Butwhyyouwanttouseindigitalcommunicationwiththedifferentindicats(perbitenergytonoisepowerspectraldensityratio)Theexplanat

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