资源描述：
《通信专业外文翻译--基带信号解调与检测》由会员上传分享，免费在线阅读，更多相关内容在应用文档-天天文库。
1、毕业设计(专业外文翻译)BasebandDemodulation/DetectionInthecaseofbasebandsignaling,thereceivedwaveformsarealreadyinapulse-likeform.Onemightask,whythen,isademodulatorneededtorecoverthepulsewaveforms?Theansweristhatthearrivingbasebandpulsesarenotintheformofidealpulseshapes,eachoneoccupyi
2、ngitsownsymbolinterval.Thefilteringtosufferfrominter-symbolinterference(ISI)andthusappearasanamorphous“smeared”signal,notquitereadyforsamplinganddetection.Thegoalofthedemodulator(receivingfilter)istoreceiverabasebandpulsewiththebestpossiblesignal-to-noiseration(SNR),freeofa
3、nyISI.Equalization,coveredinthischapter,isatechniqueusedtohelpaccomplishthisgoal.Theequalizationprocessisnotrequiredforeverytypeofcommunicationchannel.However,sinceequalizationembodiesasophisticatedsetofsignal-processingtechniques,makingitpossibletocompensateforchannel-indu
4、cedinterference,itisanimportantareaformanysystems.Theband-passmodelofthefourthchapterdealswiththedetectionprocess,anddescribedinthischapteressentiallythesameasthebasebandmodel.Beforetesting,youmustfirstbandpassconversiontothebasebandsignal.Forsignaldetectioninlinearsystemsm
5、athematicalexpressionsdonotacceptthefrequencymove,andhavethefollowingequivalencetheorem(equivalencetheoremstates):thecurrentprocessingisfirstbandpasssignalisconvertedtothebase,andthenusingtheheterodynemethodbandsignal;theresultswiththefirstheterodynesignalisconvertedtotheba
6、sebandsignal,thecorrespondinglinearprocessingonthebasebandsignal."Heterodyne"(heterodying)referstoatechniquecalled"frequencyconverter(frequencyconversion),or"mixing"ofthefrequencyashamethatsoftwaremixingissignalprocessing,herealizedthespectrumofthesignalmove.Acorollaryofthe
7、equivalencetheorem,andlinearsimulationprocesstheChengDuijibandsignal(generally)theresultisthesameastheresultofbandpassrole,Thisindicatesthatmostofdigitalcommunicationsystemsasabasebandsystemtodescribeandanalyze.10毕业设计(专业外文翻译)1SIGNALSANDNOISE1.1Error-performanceDegradationin
8、CommunicationSystemsThepurposeofthedetectorisbasedonasfewerrorsaspossibletorestore
