[Gallager] Principles of Digital Communication

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1、6.450:PrinciplesofDigitalCommunicationChapters1-3RobertG.Gallager,M.I.T.September7,2004iiPreface:IntroductionandObjectivesThedigitalcommunicationindustryisanenormousandrapidlygrowingindustry,roughlycom-parableinsizetothecomputerindustry.Theobjectiveofthiscourseistostudythoseaspectsofdig

2、italcommunicationsystemsthatareuniquetothesesystems.Thatis,ratherthanfocus-ingonhardwareandsoftwareforthesesystems,whichismuchlikehardwareandsoftwareformanyotherkindsofsystems,wefocusonthefundamentalsystemaspectsofmoderndigitalcommunication.Thisisthefirstsubjectinthetwo-termsequence,6.45

3、0and6.451.Ourintentionisthat6.450maybetakenonastand-alonebasisandbeaccessibletowell-preparedundergraduates.Itisalsoaprerequisitefor6.441(TransmissionofInformation),6.442(Opticalnetworks),andanalternateprerequisitefor6.432(Stochasticprocesses,detection,andestimation).Itshouldbetakenbyany

4、studentseriouslyinterestedinthedigitalcommunicationfield.Digitalcommunicationisafieldinwhichtheoreticalideashavehadanunusuallypowerfulimpactonactualsystemdesign.Thebasisofthetheorywasdeveloped55yearsagobyClaudeShannon,andiscalledinformationtheory.Forthefirst25yearsorsoofitsexistence,inform

5、ationtheoryservedasarichsourceofacademicresearchproblemsandasatantalizingsuggestionthatcommunicationsystemscouldbemademoreefficientandmorereliablebyusingtheseapproaches.Bythemid1970’s,mainstreamsystemsusinginformationtheoreticideasbegantobewidelyimplemented.Thefirstreasonforthiswastheincre

6、asingnumberofengineerswhounderstoodbothinformationtheoryandcommunicationsystemdevelopment.Thesecondreasonwasthatthelowcostandincreasingprocessingpowerofdigitalhardwaremadeitpossibletoimplementthesophisticatedalgorithmssuggestedbyinformationtheory.Asyoulearnaboutdigitalcommunicationsyste

7、msandtheirconceptualbasisininformationthe-ory,youwillcometoappreciatethattheseideasrequireafairlydeepunderstandingofsomewhatabstractconcepts.Doingtheproblemsetsisanimportantpartofdevelopingthisunderstanding,butitisnotsufficient.Inmanyundergraduateengineeringsubjects,theemphasis(r