Principles of Digital Communication by Gallager 2008.pdf

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1、PrinciplesofDigitalCommunicationRobertG.GallagerJanuary5,2008Citeas:RobertGallager,coursematerialsfor6.450PrinciplesofDigitalCommunicationsI,Fall2006.MITOpenCourseWare(http://ocw.mit.edu/),MassachusettsInstituteofTechnology.Downloadedon[DDMonthYYYY].iiPreface:introduc

2、tionandobjectivesThedigitalcommunicationindustryisanenormousandrapidlygrowingindustry,roughlycomparableinsizetothecomputerindustry.Theobjectiveofthistextistostudythoseaspectsofdigitalcommunicationsystemsthatareuniquetothosesystems.Thatis,ratherthanfocusingonhardwarean

3、dsoftwareforthesesystems,whichismuchlikehardwareandsoftwareformanyotherkindsofsystems,wefocusonthefundamentalsystemaspectsofmoderndigitalcommunication.Digitalcommunicationisafieldinwhichtheoreticalideashavehadanunusuallypowerfulimpactonsystemdesignandpractice.Thebasiso

4、fthetheorywasdevelopedin1948byClaudeShannon,andiscalledinformationtheory.Forthefirst25yearsorsoofitsexistence,informationtheoryservedasarichsourceofacademicresearchproblemsandasatantalizingsuggestionthatcommunicationsystemscouldbemademoreefficientandmorereliablebyusingth

5、eseapproaches.Otherthansmallexperimentsandafewhighlyspecializedmilitarysystems,thetheoryhadlittleinteractionwithpractice.Bythemid1970’s,however,mainstreamsystemsusinginformationtheoreticideasbegantobewidelyimplemented.Thefirstreasonforthiswastheincreasingnumberofengine

6、erswhounderstoodbothinformationtheoryandcommunicationsystempractice.Thesecondreasonwasthatthelowcostandincreasingprocessingpowerofdigitalhardwaremadeitpossibletoimplementthesophisticatedalgorithmssuggestedbyinformationtheory.Thethirdreasonwasthattheincreasingcomplexit

7、yofcommunicationsystemsrequiredthearchitecturalprinciplesofinformationtheory.Thetheoreticalprinciplesherefallroughlyintotwocategories-thefirstprovideanalyticaltoolsfordeterminingtheperformanceofparticularsystems,andthesecondputfundamentallimitsontheperformanceofanysyst

8、em.Muchofthefirstcategorycanbeunderstoodbyengineeringundergraduates,whilethesecondcategoryisdistinctlygraduateinnature.Itisno