数据通信与网络编码信息ppt课件.ppt

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1、Chapter5ENCODING第五章编码5.1Digital-to-DigitalEncoding5.2Analog-to-DigitalEncoding5.3Digital-to-AnalogEncoding5.4Analog-to-AnalogEncoding5.5SummaryContentsIntroductionofEncodingTheinformationordatamustbeencodedintosignalsbeforeitcanbetransportedacrossthecommunicationmedia.Thesigna

2、lmustbemanipulatedsothatitcontainsidentifiablechangesthatarerecognizabletothesenderandreceiverasrepresentingtheinformationintended.DifferentencodingschemesEncodingDigital/digitalAnalog/digitalDigital/analogAnalog/analogIntroductionofEncodingHowinformationisencodedependsonitsor

3、iginalformatandontheformatusedbycommunicationhardware.5.1Digital-to-digitalencodingDigital-to-digitalencodingistherepresentationofdigitalinformationbyadigitalsignal.Boththeoriginaldataandtransmitteddataaredigital.Thebinary1sand0saretranslatedintoasequenceofvoltagepulsethatcanb

4、epropagatedoverwire.Typesofdigital-to-digitalencodingDigital/digitalencodingUnipolarPolarBipolar5.1Digital-to-digitalencoding单极性编码极化编码双极性编码5.1.1Unipolar(单极性编码)Digitaltransmissionsystemsworkbysendingvoltagepulsesalongamedialink(wireorcable).Inmosttypesofencoding,onevoltagelevel

5、standsforbinary0andanotherlevelstandsforbinary1.Thepolarityofpulse(脉冲极性)refertowhetheritispositiveornegative.Unipolarencodingissonamedbecauseitusesonlyonepolarity.5.1.1Unipolar(单极性编码)The1sareencodedaspositivevalue;The0sareencodedaszero,oridle.振幅时间01000111Theideaofunipolarenco

6、ding.Advantage:VerySimpleandStraightforward;inexpensivetoimplementDisadvantages:1、同步(synchronization)whenasignalisunvarying,thereceivercannotdeterminethebeginningandendingofeachbits.Therefore,asynchronizationprobleminunipolarencodingcanoccurwheneverthedatastreamincludesalongun

7、interruptedseriesof1sor0s.5.1.1Unipolar(单极性编码)synchronizationTocorrectlyinterpretthesignalsreceivedfromthesender,thereceiver'sbitintervalsmustcorrespondexactlytothesender'sbitintervals.Ifthereceiverclockisfasterorslower,thebitintervalsarenotmatchedandthereceivermightmisinterpr

8、etthesignals.Thesolutionofsynchronizationparallellinecarrying