[Gallager] 数字通信原理 Principles of Digital Communication (英).pdf

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

2、dythoseaspectsofdigitalcommunicationsystemsthatareuniquetothesesystems.Thatis,ratherthanfocus-ingonhardwareandsoftwareforthesesystems,whichismuchlikehardwareandsoftwareformanyotherkindsofsystems,wefocusonthefundamentalsystemaspectsofmoderndigitalcommunication.Thisisth

3、efirstsubjectinthetwo-termsequence,6.450and6.451.Ourintentionisthat6.450maybetakenonastand-alonebasisandbeaccessibletowell-preparedundergraduates.Itisalsoaprerequisitefor6.441(TransmissionofInformation),6.442(Opticalnetworks),andanalternateprerequisitefor6.432(Stochast

4、icprocesses,detection,andestimation).Itshouldbetakenbyanystudentseriouslyinterestedinthedigitalcommunicationfield.Digitalcommunicationisafieldinwhichtheoreticalideashavehadanunusuallypowerfulimpactonactualsystemdesign.Thebasisofthetheorywasdeveloped55yearsagobyClaudeSha

5、nnon,andiscalledinformationtheory.Forthefirst25yearsorsoofitsexistence,informationtheoryservedasarichsourceofacademicresearchproblemsandasatantalizingsuggestionthatcommunicationsystemscouldbemademoreefficientandmorereliablebyusingtheseapproaches.Bythemid1970’s,mainstream

6、systemsusinginformationtheoreticideasbegantobewidelyimplemented.Thefirstreasonforthiswastheincreasingnumberofengineerswhounderstoodbothinformationtheoryandcommunicationsystemdevelopment.Thesecondreasonwasthatthelowcostandincreasingprocessingpowerofdigitalhardwaremadeit

7、possibletoimplementthesophisticatedalgorithmssuggestedbyinformationtheory.Asyoulearnaboutdigitalcommunicationsystemsandtheirconceptualbasisininformationthe-ory,youwillcometoappreciatethattheseideasrequireafairlydeepunderstandingofsomewhatabstractconcepts.Doingtheprobl

8、emsetsisanimportantpartofdevelopingthisunderstanding,butitisnotsufficient.Inmanyundergraduateengineeringsubjects,theemphasis(r