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MODERNDIGITAL ANDANALOG COMMUNICATION SYSTEMS THEOXFORDSERIESINELECTRICALANDCOMPUTERENGINEERING
AdelS.Sedra,SeriesEditor AllenandHolberg, CMOSAnalogCircuitDesign,3rdedition
Boncelet, Probability,Statistics,andRandomSignals
Bobrow, ElementaryLinearCircuitAnalysis,2ndedition
Bobrow, FundamentalsofElectricalEngineering,2ndedition Campbell, FabricationEngineeringattheMicro-andNanoscale,4thedition Chen, DigitalSignalProcessing
Chen, LinearSystemTheoryandDesign,4thedition Chen, SignalsandSystems,3rdedition
Comer, DigitalLogicandStateMachineDesign,3rdedition Comer, Microprocessor-BasedSystemDesign
Cooper andMcGillem,ProbabilisticMethodsofSignalandSystemAnalysis,3rdedition
Dimitrijev, PrinciplesofSemiconductorDevice,2ndedition Dimitrijev, UnderstandingSemiconductorDevices
Fortney, PrinciplesofElectronics:Analog&Digital Franco, ElectricCircuitsFundamentals
Ghausi, ElectronicDevicesandCircuits:DiscreteandIntegrated GuruandHiziro ˘ glu, ElectricMachineryandTransformers,3rdedition Houts, SignalAnalysisinLinearSystems
Jones, IntroductiontoOpticalFiberCommunicationSystems
Krein, ElementsofPowerElectronics,2ndEdition Kuo, DigitalControlSystems,3rdedition LathiandGreen, LinearSystemsandSignals,3rdedition LathiandDing, ModernDigitalandAnalogCommunicationSystems,5thedition Lathi, SignalProcessingandLinearSystems
Martin, DigitalIntegratedCircuitDesign Miner, LinesandElectromagneticFieldsforEngineers
Mitra, SignalsandSystems
Parhami, ComputerArchitecture
Parhami, ComputerArithmetic,2ndedition RobertsandSedra, SPICE,2ndedition Roberts,Taenzler,andBurns, AnIntroductiontoMixed-SignalICTestandMeasurement,2ndedition Roulston, AnIntroductiontothePhysicsofSemiconductorDevices
Sadiku, ElementsofElectromagnetics,7thedition Santina,Stubberud,andHostetter, DigitalControlSystemDesign,2ndedition Sarma, IntroductiontoElectricalEngineering Schaumann,Xiao,andVanValkenburg, DesignofAnalogFilters,3rdedition SchwarzandOldham, ElectricalEngineering:AnIntroduction,2ndedition SedraandSmith, MicroelectronicCircuits,7thedition Stefani,Shahian,Savant,andHostetter, DesignofFeedbackControlSystems,4thedition Tsividis, OperationandModelingoftheMOSTransistor,3rdedition VanValkenburg, AnalogFilterDesign
WarnerandGrung, SemiconductorDeviceElectronics
Wolovich, AutomaticControlSystems
YarivandYeh, Photonics:OpticalElectronicsinModernCommunications,6thedition Zak, SystemsandControl
MODERNDIGITAL ANDANALOG COMMUNICATION SYSTEMS FifthEdition
B.P.Lathi ProfessorEmeritus
CaliforniaStateUniversity—Sacramento
ZhiDing Professor UniversityofCalifornia—Davis
OxfordUniversityPressisadepartmentoftheUniversityofOxford.Itfurthers theUniversity’sobjectiveofexcellenceinresearch,scholarship,andeducation bypublishingworldwide.OxfordisaregisteredtrademarkofOxfordUniversity PressintheUKandcertainothercountries.
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©2019byOxfordUniversityPress
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LibraryofCongressCataloging-in-PublicationData
Names:Lathi,B.P.(BhagwandasPannalal),author.|Ding,Zhi,1962-author. Title:Moderndigitalandanalogcommunicationsystems/B.P.Lathi, ProfessorEmeritus,CaliforniaStateUniversity—Sacramento,ZhiDing, Professor,UniversityofCalifornia—Davis.
Description:FifthEdition.|NewYork:OxfordUniversityPress,[2019]| Series:Oxfordseriesinelectricalandcomputerengineering Identifiers:LCCN2017034966|ISBN9780190686840(Hardcover)
Subjects:LCSH:Telecommunicationsystems.|Digitalcommunications.| Statisticalcommunicationtheory.
Classification:LCCTK5101.L3332018|DDC621.382–dc23LCrecord availableathttps://lccn.loc.gov/2017034966
Printingnumber:987654321
PrintedbyEdwardsBrothersMalloy,UnitedStatesofAmerica
CONTENTS PREFACE xv 1 INTRODUCTION 1 1.1COMMUNICATIONSYSTEMS 2
1.2DESIGNCHALLENGES:CHANNELDISTORTIONS ANDNOISES 3
1.3MESSAGESOURCES 4
1.4CHANNELEFFECT,SIGNAL-TO-NOISERATIO,ANDCAPACITY 8
1.5MODULATIONANDDETECTION 11
1.6DIGITALSOURCECODINGANDERROR CORRECTIONCODING 13
1.7ABRIEFHISTORICALREVIEWOFMODERN TELECOMMUNICATIONS 15
2 SIGNALSANDSIGNALSPACE 21 2.1SIZEOFASIGNAL 21
2.2CLASSIFICATIONOFSIGNALS 26
2.3SOMEUSEFULSIGNALOPERATIONS 29
2.4UNITIMPULSESIGNAL 33
2.5SIGNALSVERSUSVECTORS 36
2.6CORRELATIONOFSIGNALS 42
2.7ORTHOGONALSIGNALSETS 47
2.8TRIGONOMETRICFOURIERSERIES 51
2.9FREQUENCYDOMAINANDEXPONENTIALFOURIERSERIES 62
2.10MATLABEXERCISES 69
3 ANALYSISANDTRANSMISSION OFSIGNALS 93 3.1FOURIERTRANSFORMOFSIGNALS 93
3.2TRANSFORMSOFSOMEUSEFULFUNCTIONS 99
3.3SOMEFOURIERTRANSFORMPROPERTIES 107
3.4SIGNALTRANSMISSIONTHROUGHALINEARTIME-INVARIANT SYSTEM 124
3.5IDEALVERSUSPRACTICALFILTERS 129
3.6SIGNALDISTORTIONOVERACOMMUNICATION CHANNEL 134
3.7SIGNALENERGYANDENERGYSPECTRALDENSITY 139
3.8SIGNALPOWERANDPOWERSPECTRALDENSITY 148
3.9NUMERICALCOMPUTATIONOFFOURIERTRANSFORM: THEDFT 156
3.10MATLABEXERCISES 161
4 ANALOGMODULATIONSAND DEMODULATIONS 187
4.1BASEBANDVERSUSCARRIERCOMMUNICATIONS 187
4.2DOUBLE-SIDEBANDAMPLITUDEMODULATION 189
4.3AMPLITUDEMODULATION(AM) 198
4.4BANDWIDTH-EFFICIENTAMPLITUDEMODULATIONS 205
4.5FMANDPM:NONLINEARANGLEMODULATIONS 219
4.6BANDWIDTHANALYSISOFANGLEMODULATIONS 225
4.7DEMODULATIONOFFMSIGNALS 233
4.8FREQUENCYCONVERSIONANDSUPERHETERODYNE RECEIVERS 235
4.9GENERATINGFMSIGNALS 238
4.10FREQUENCYDIVISIONMULTIPLEXING(FDM) 244
4.11PHASE-LOCKEDLOOPANDAPPLICATIONS 245
4.12MATLABEXERCISES 253
5 DIGITIZATIONOFANALOG SOURCESIGNALS 284
5.1SAMPLINGTHEOREM 284
5.2PULSECODEMODULATION(PCM) 302
5.3DIGITALTELEPHONY:PCMINT1SYSTEMS 314
5.4DIGITALMULTIPLEXINGHIERARCHY 318
5.5DIFFERENTIALPULSECODEMODULATION(DPCM) 323
5.6DELTAMODULATION 328
5.7VOCODERSANDVIDEOCOMPRESSION 333
5.8MATLABEXERCISES 345
6 PRINCIPLESOFDIGITALDATA TRANSMISSION 365
6.1DIGITALCOMMUNICATIONSYSTEMS 365
6.2BASEBANDLINECODING 368
6.3PULSESHAPING 383
6.4SCRAMBLING 395
6.5DIGITALRECEIVERSANDREGENERATIVEREPEATERS 398
6.6EYEDIAGRAMS:ANIMPORTANTDIAGNOSTICTOOL 408
6.7PAM: M-ARYBASEBANDSIGNALING 411
6.8DIGITALCARRIERSYSTEMS 414
6.9 M-ARYDIGITALCARRIERMODULATION 422
6.10MATLABEXERCISES 428
FUNDAMENTALSOFPROBABILITY THEORY 445 7.1CONCEPTOFPROBABILITY 445
7.2RANDOMVARIABLES 461
7.3STATISTICALAVERAGES(MEANS) 480
7.4CORRELATION 489
7.5LINEARMEANSQUAREESTIMATION 493
7.6SUMOFRANDOMVARIABLES 496
7.7CENTRALLIMITTHEOREM 499
8 RANDOMPROCESSESANDSPECTRAL ANALYSIS 510 8.1FROMRANDOMVARIABLETORANDOMPROCESS 510
8.2CLASSIFICATIONOFRANDOMPROCESSES 515
8.3POWERSPECTRALDENSITY 519
8.4MULTIPLERANDOMPROCESSES 534
8.5TRANSMISSIONOFRANDOMPROCESSESTHROUGHLINEAR SYSTEMS 535
8.6BANDPASSRANDOMPROCESSES 556
9 PERFORMANCEANALYSISOFDIGITAL COMMUNICATIONSYSTEMS 580
9.1OPTIMUMLINEARDETECTORFORBINARY POLARSIGNALING 580
9.2GENERALBINARYSIGNALING 586
9.3COHERENTRECEIVERSFORDIGITALCARRIER MODULATIONS 594
9.4SIGNALSPACEANALYSISOFOPTIMUMDETECTION 599
9.5VECTORDECOMPOSITIONOFWHITENOISE RANDOMPROCESSES 604
9.6OPTIMUMRECEIVERFORWHITEGAUSSIAN NOISECHANNELS 610
9.7GENERALERRORPROBABILITYOFOPTIMUMRECEIVERS 635
9.8EQUIVALENTSIGNALSETS 644
9.9NONWHITE(COLORED)CHANNELNOISE 651
9.10OTHERUSEFULPERFORMANCECRITERIA 652
9.11NONCOHERENTDETECTION 655
9.12MATLABEXERCISES 663
10 SPREADSPECTRUM COMMUNICATIONS 691 10.1FREQUENCYHOPPINGSPREADSPECTRUM(FHSS) SYSTEMS 691
10.2MULTIPLEFHSSUSERSYSTEMSANDPERFORMANCE 695
10.3APPLICATIONSOFFHSS 698
10.4DIRECTSEQUENCESPREADSPECTRUM 702
10.5RESILIENTFEATURESOFDSSS 705
10.6CODEDIVISIONMULTIPLE-ACCESS(CDMA)OFDSSS 707
10.7MULTIUSERDETECTION(MUD) 715
10.8MODERNPRACTICALDSSSCDMASYSTEMS 721
10.9MATLABEXERCISES 730
11 DIGITALCOMMUNICATIONSOVER LINEARLYDISTORTIVECHANNELS 747
11.1LINEARDISTORTIONSOFWIRELESSMULTIPATHCHANNELS 747
11.2RECEIVERCHANNELEQUALIZATION 751
11.3LINEAR T -SPACEDEQUALIZATION(TSE) 757
11.4LINEARFRACTIONALLYSPACEDEQUALIZERS(FSE) 767
11.5CHANNELESTIMATION 772
11.6DECISIONFEEDBACKEQUALIZER 773
11.7OFDM(MULTICARRIER)COMMUNICATIONS 776
11.8DISCRETEMULTITONE(DMT)MODULATIONS 788
11.9REAL-LIFEAPPLICATIONSOFOFDMANDDMT 793
11.10BLINDEQUALIZATIONANDIDENTIFICATION 798
11.11TIME-VARYINGCHANNELDISTORTIONSDUETOMOBILITY 799
11.12MATLABEXERCISES 803
12 INTRODUCTIONTOINFORMATION THEORY 825 12.1MEASUREOFINFORMATION 825
12.2SOURCEENCODING 829
12.3ERROR-FREECOMMUNICATIONOVERANOISYCHANNEL 835
12.4CHANNELCAPACITYOFADISCRETEMEMORYLESS CHANNEL 838
12.5CHANNELCAPACITYOFACONTINUOUSMEMORYLESS CHANNEL 845
12.6FREQUENCY-SELECTIVECHANNELCAPACITY 862
12.7MULTIPLE-INPUT–MULTIPLE-OUTPUTCOMMUNICATION SYSTEMS 867
12.8MATLABEXERCISES 875
13 ERRORCORRECTINGCODES 891 13.1OVERVIEW 891
13.2REDUNDANCYFORERRORCORRECTION 892
13.3LINEARBLOCKCODES 895
13.4CYCLICCODES 902
13.5THEBENEFITOFERRORCORRECTION 912
13.6CONVOLUTIONALCODES 916
13.7TRELLISDIAGRAMOFBLOCKCODES 926
13.8CODECOMBININGANDINTERLEAVING 927
13.9SOFTDECODING 930
13.10SOFT-OUTPUTVITERBIALGORITHM(SOVA) 932
13.11TURBOCODES 934
13.12LOW-DENSITYPARITYCHECK(LDPC)CODES 943
13.13MATLABEXERCISES 949
APPENDICES A ORTHOGONALITYOFSOMESIGNALSETS 964
A.1TRIGONOMETRICSINUSOIDSIGNALSET 964
A.2ORTHOGONALITYOFTHEEXPONENTIALSINUSOID SIGNALSET 965
B CAUCHY-SCHWARZINEQUALITY 966
C GRAM-SCHMIDTORTHOGONALIZATIONOFA VECTORSET 967
D BASICMATRIXPROPERTIES ANDOPERATIONS 970
D.1NOTATIONS 970
D.2MATRIXPRODUCTANDPROPERTIES 971
D.3IDENTITYANDDIAGONALMATRICES 971
D.4DETERMINANTOFSQUAREMATRICES 972
D.5TRACE 973
D.6EIGENDECOMPOSITION 973
D.7SPECIALHERMITIANSQUAREMATRICES 974
E MISCELLANEOUS 975
E.1L’HÔPITAL’SRULE 975
E.2TAYLORANDMACLAURINSERIES 975
E.3POWERSERIES 975
E.4SUMS 976
E.5COMPLEXNUMBERS 976
E.6TRIGONOMETRICIDENTITIES 976
E.7INDEFINITEINTEGRALS 977
INDEX 979
PREFACE Sincethepublicationofthefourthedition,wehavecontinuedtobeastoundedbythe remarkableprogressofdigitalrevolutionmadepossiblebyadvancedtelecommunication technologies.Withinonedecade,smartphonesandsmartphoneapplicationshavechangedthe livesofbillionsofpeople.Furthermore,thereislittledoubtthatthenextwaveofdigital revolution,likelycenteredaroundtransformativetechnologiesinmachinelearning,data mining,Internetofthings,andartificialintelligence,shallcontinuetodrivethedevelopment ofnovelcommunicationsystemsandapplications.Itisthereforeagoodtimeforusto deliveraneweditionofthistextbookbyintegratingmajornewtechnologicaladvances incommunicationsystems.Thisfiftheditioncontainsmajorupdatestoincorporaterecent technologicaladvancesoftelecommunications.
Asengineeringstudentsbecomemoreandmoreawareoftheimportantrolethat communicationsystemsplayinthemodernsociety,theyareincreasinglymotivatedtolearn throughexperimentingwithsolid,illustrativeexamples.Tocaptivatestudents’attention andstimulatetheirimaginations,thisneweditionplacesstrongemphasisonconnecting fundamentalconceptsofcommunicationtheorytotheirdailyexperiencesofcommunication technologies.Weprovidehighlyrelevantinformationontheoperationandfeaturesofwireless cellularsystems,Wi-Finetworkaccess,andbroadbandInternetservices,amongothers.
MajorRevisionsandAdditions Anumberofmajorchangesaremotivatedbytheneedtoemphasizethefundamentalsof digitalcommunicationsystemsthathavepermeatedourdailylives.Insteadoftraditional approachesthatdisproportionallydrillonthebasicsofanalogmodulationanddemodulation, thisneweditionshiftsthemajorfocusontothetheoryandpracticeofthebroadlydeployed digitalcommunicationsystems.Specifically,afterintroducingtheimportanttoolsofFourier analysisinChapter2andChapter3,onlyasinglechapter(Chapter4)isdevotedtothe analogamplitudeandanglemodulations.Theauthorsexpectmoststudentstobefarmore interestedindigitalsystemsthattheyusedailyandtobehighlymotivatedtomasterthe state-of-the-artdigitalcommunicationtechnologiesinordertocontributetofuturewavesof thedigitalrevolution.
Oneofthemajorgoalsinwritingthisneweditionistomakelearningagratifying oratleastalessintimidatingexperienceforstudentsbypresentingthesubjectinaclear, understandable,andlogicallyorganizedmanner.Toenhanceinteractivelearning,thisnew editionhasupdatedanumberofcomputer-basedexperimentalpracticesthatarecloselytied tothefundamentalconceptsandexamplesinthemaintext.Studentscanfurtherstrengthen theirunderstandingandtesttheirowndesignsthroughnumericalexperimentationbasedon thenewlyincludedcomputerassignmentproblemsfollowingeachmajorchapter.
Everyefforthasbeenmadetodeliverinsights—ratherthanjustderivations—aswellas heuristicexplanationsoftheoreticalresultswhereverpossible.Manyexamplesareprovided
forfurtherclarificationofabstractresults.Evenapartialsuccessinachievingthisstatedgoal wouldmakealloureffortsworthwhile.
Reorganization Atorrentoftechnologicaladvanceshasnurturedanewgenerationofstudentsextremely interestedinlearningaboutthenewtechnologiesandtheirimplementations.Thesestudents areeagertounderstandhowandwheretheymaybeabletomakecontributionsasfuture innovators.Suchstrongmotivationmustbeencouragedandleveraged.Thisneweditionwill enableinstructorseithertocoverthetopicsthemselvesortoassignreadingmaterialsthat willallowstudentstoacquirerelevantinformation.Theneweditionachievesthesegoals bystressingthedigitalaspectsofthetextandbyincorporatingthemostcommonlyknown wirelessandwirelinedigitaltechnologies.
Withrespecttoorganization,thefiftheditionbeginswithatraditionalreviewofsignal andlinearsystemfundamentalsbeforeproceedingtothecorecommunicationtopicsofanalog anddigitalmodulations.Wethenpresentthefundamentaltoolsofprobabilitytheoryand randomprocessestobeusedinthedesignandanalysisofdigitalcommunicationsinthe secondpartofthetext.Aftercoveringthefundamentalsofdigitalcommunicationsystems, thefinaltwochaptersprovideanoverviewofinformationtheoryandthefundamentalsof forwarderrorcorrectioncodes.
Ideally,tocoverthemajorsubjectsinthistextwithsufficienttechnicaldepthwould requireasequenceoftwocourses:oneonthebasicoperationsofcommunicationsystems andoneontheanalysisofmoderncommunicationsystemsundernoiseandotherdistortions. TheformerreliesheavilyondeterministicanalyticaltoolssuchasFourierseries,Fourier transform,andthesamplingtheorem,whilethelatterreliesontoolsfromprobabilityand randomprocessestotackletheunpredictableaspectsofmessagesignalsandnoises.Intoday’s academicenvironment,however,withsomanycompetingcoursesandtopics,itmaybe difficulttofittwobasiccoursesoncommunicationsintoatypicalelectricalorcomputer engineeringcurriculum.Someuniversitiesdorequireacourseinprobabilityandrandom processesasaprerequisite.Inthatcase,itispossibletocoverbothareasreasonablywell inaone-semestercourse.Thisbookisdesignedforadoptioninbothcasesregardlessof whetheraprobabilityprerequisiteisavailable.Itcanbeusedasaone-semestercourse inwhichthedeterministicaspectsofcommunicationsystemsareemphasizedwithmild considerationoftheeffectsofnoiseandinterference.Itcanalsobeusedforacoursethat dealswithboththedeterministicandtheprobabilisticaspectsofcommunicationsystems. Thebookisself-contained,byprovidingallthenecessarybackgroundinprobabilitiesand randomprocesses.Itisimportanttonotethatifbothdeterministicandprobabilisticaspectsof communicationsaretobecoveredinonesemester,itishighlydesirableforstudentstohave asolidbackgroundinprobabilities.
Chapter1presentsapanoramicviewofcommunicationsystemsbyexplaining importantconceptsofcommunicationtheoryqualitativelyandheuristically.Buildingonthis momentum,studentsaremotivatedtostudythesignalanalysistoolsinChapters2and3, whichdescribeasignalasavector,andviewtheFourierspectrumasawayofrepresentinga signalinawell-knownsignalspace.Chapter4discussesthetraditionalanalogmodulationand demodulationsystems.Someinstructorsmayfeelthatinthisdigitalage,analogmodulation shouldberemovedaltogether.Weholdtheviewthatmodulationisnotsomuchamethod ofcommunicationasabasictoolofsignalprocessingandtransformation;itwillalwaysbe needed,notonlyintheareaofcommunication(digitaloranalog),butalsoinmanyotherareas ofengineering.Hence,fullyneglectingmodulationcouldprovetobeshortsighted.
Chapter5servesasthefundamentalbridgethatconnectsanaloganddigitalcommunicationsystemsbycoveringtheprocessofanalog-to-digital(A/D)conversionforavarietyof applicationsthatincludespeechandvideosignals.Chapter6utilizesdeterministicsignal analysistoolstopresenttheprinciplesandtechniquesofdigitalmodulations.Itfurther introducestheconceptofchanneldistortionandpresentsequalizationasaneffectivemeans ofdistortioncompensation.
Chapters7and8providetheessentialbackgroundontheoriesofprobabilityandrandom processes,toolsthatareessentialtotheperformanceanalysisofdigitalcommunication systems.Everyeffortwasmadetomotivatestudentsandtoguidethemthroughthesechapters byprovidingapplicationstocommunicationsproblemswhereverpossible.Chapter9teaches theanalysisandthedesignofdigitalcommunicationsystemsinthepresenceofadditive channelnoise.Itderivestheoptimumreceiverstructurebasedontheprincipleofminimizing errorprobabilityinsignaldetection.Chapter10focusesontheinterferenceresilientspread spectrumcommunicationsystems.Chapter11presentsvariouspracticaltechniquesthat canbeusedtocombattypicalchanneldistortions.Onemajoremphasisisonthepopular OFDM(orthogonalfrequencydivisionmodulation)thathasfoundbroadapplicationsin state-of-the-artsystemsrangingfrom4G-LTEcellularsystems,IEEE802.11a/g/nWi-Fi networks,toDSLbroadbandservices.Chapter12providesmanyfundamentalconceptsof informationtheory,includingthebasicprinciplesofmultiple-input–multiple-output(MIMO) technologythatcontinuestogainpracticalacceptanceandpopularity.Finally,theprincipal andkeypracticalaspectsoferrorcontrolcodingaregiveninChapter13.
CourseAdoption Withacombinedteachingexperienceofover60years,wehavetaughtcommunicationclasses underbothquarterandsemestersystemsinseveralmajoruniversities.Ontheotherhand,the students’personalexperienceswithcommunicationsystemshavecontinuedtomultiply,from asimpleradiosetinthe1960s,totheturnofthetwenty-firstcentury,withitseasyaccess toWi-Fi,cellulardevices,satelliteradio,andhomeInternetservices.Hence,moreandmore studentsareinterestedinlearninghowfamiliarelectronicgadgetswork.Withthisimportant needandourpastexperiencesinmind,werevisedthefiftheditionofthistexttofitwellwithin severaldifferentcurriculumconfigurations.Inallcases,basiccoverageshouldalwaysteach thefundamentalsofanaloganddigitalcommunications(Chapters1–6).
OptionA:One-SemesterCourse(withoutstrongprobability background) Inmanyexistingcurricula,undergraduatestudentsareonlyexposedtoverysimpleprobability toolsbeforetheystudycommunications.Thisoccursoftenbecausethestudentswererequired totakeanintroductorystatisticalcoursedisconnectedfromengineeringscience.Thistextis wellsuitedtostudentsofsuchabackground.Chapters1–6deliveracomprehensivecoverage ofmoderndigitalandanalogcommunicationsystemsforaverageundergraduateengineering students.Suchacoursecanbetaughtwithinonesemester(inapproximately45instructional hours).UnderthepremisethateachstudenthasbuiltasolidbackgroundinFourieranalysis viaaprerequisiteclasson signalsandsystems,mostofthefirstthreechapterscanbetreated asareviewinasingleweek.Therestofthesemestercanbefullydevotedtoteaching Chapters4—6,withselectivecoverageonthepracticalsystemsofChapters10and11to broadenstudents’communicationbackground.
OptionB:One-SemesterCourse(withastrongprobabilitybackground)
Forstudentswhohavebuiltastrongbackgroundonprobabilitytheory,amuchmore extensivecoverageofdigitalcommunicationscanbeachievedwithinonesemester.Arigorous probabilityclasscanbetaughtwithinthecontextofsignalandsystemanalysis(cf.Cooperand McGillem, ProbabilisticMethodsofSignalandSystemAnalysis,3rded.,OxfordUniversity Press,1998).Underthisscenario,inadditiontoChapters1–6,Chapter9andpartofChapters 10–11canalsobetaughtinonesemester,providedthatthestudentshaveasolidprobability backgroundthatpermitscoveringChapter7andChapter8inahandfulofhours.Students completingsuchacoursewouldbewellpreparedtoenterthetelecommunicationsindustryor tocontinuegraduatestudies.
OptionC:Two-SemesterSeries(withoutaseparateprobabilitycourse)
Theentiretextcanbethoroughlycoveredintwosemestersforacurriculumthatdoesnot haveanypriorprobabilitycourse.Inotherwords,foratwo-courseseries,thegoalistoteach bothcommunicationsystemsandfundamentalsofprobabilities.Inaneraofmanycompeting coursesinatypicalengineeringcurriculum,itishardtosetasidetwo-semestercoursesfor communicationsalone.Inthiscase,itwouldbedesirabletofoldprobabilitytheoryintothe twocommunicationcourses.Thus,fortwo-semestercourses,thecoveragecanbeasfollows:
• 1stsemester:Chapters1–6(SignalsandCommunicationSystems)
• 2ndsemester:Chapters7–12(ModernDigitalCommunicationSystems)
OptionD:One-QuarterCourse(withastrongprobabilitybackground)
Inaquartersystem,studentsmusthavepriorexposuretoprobabilityandstatisticsatarigorous level(cf.CooperandMcGillem, ProbabilisticMethodsofSignalandSystemAnalysis,3rd ed.,OxfordUniversityPress,1998).TheymustalsohavesolidknowledgeofFourieranalysis (coveredinChapters2and3).Withinaquarter,theclasscanteachthebasicsofanalogand digitalcommunicationsystems(Chapters3–6),analysisofdigitalcommunicationsystems (Chapter9),andspreadspectrumcommunications(Chapter10).
OptionE:One-QuarterCourse(withoutastrongprobability background)
Intherarecaseofstudentswhocomeinwithoutmuchprobabilityknowledge,itisimportant toimpartbasicknowledgeofcommunicationsystems.Itiswisenottoattempttoanalyze digitalcommunicationsystems.Instead,thebasiccoveragewithoutpriorknowledgeof probabilitycanbeachievedbyteachingtheoperationsofanaloganddigitalsystems(Chapters 1–6)andahigh-leveldiscussionofspreadspectrumwirelesssystems(Chapter10).
OptionF:Two-QuarterSeries(withbasicprobabilitybackground)
Unlikeaone-quartercourse,atwo-quarterseriescanbewelldesignedtoteachmostof theimportantmaterialsoncommunicationsystemsandtheiranalysis.Theentiretextcan beextensivelytaughtintwoquartersforacurriculumthathassomepreliminarycoverage ofFourieranalysisandprobabilities.EssentiallytreatingChapters2,3,and7partlyas informationreview,thecoveragecanbeasfollows:
• 1stquarter:Chapters1–8(CommunicationSystemsandAnalysis)
• 2ndquarter:Chapters9–12(DigitalCommunicationSystems)
MATLABandExperiments Sincemanyinstitutionsnolongerhavehardwarecommunicationlaboratories,weprovide MATLAB-basedcommunicationtestsanddesignexercisestoenhancetheinteractivelearning experience.Studentswillbeabletodesignsystemsandmodifytheirparameterstoevaluate theoveralleffectsontheperformanceofcommunicationsystemsthroughsignaldisplaysand biterrorratemeasurement.Thestudentswillacquirefirst-handknowledgeofhowtodesign andtestcommunicationsystems.Toassisttheinstructors,computerassignmentproblemsare suggestedformostchaptersinthisedition.
Acknowledgments First,theauthorswouldliketothankallthestudentsandteachingassistantstheyhaveworked withoverthemanyyearsofteaching.Thiseditionwouldnothavebeenpossiblewithoutmuch feedbackfrom,andmanydiscussionswith,ourstudents.Theauthorsthankallthereviewers forprovidinginvaluableinputstoimprovethetext.Finally,theauthorsalsowishtothank manyfellowinstructorsfortheirhelpfulcommentsregardingthelastedition.
B.P.Lathi,Carmichael,California,USA
ZhiDing,Davis,California,USA
1 INTRODUCTION Let’sfaceit.Ourworldhasbeentotallytransformedbyrecentadvancesin communicationandinformationtechnologies.Specificallyinthepast20years, wehavewitnessedanexplosivegrowthofcommunicationapplicationsranging fromInternettoBluetoothhand-freedevices.Inparticular,smartphonesandsmartphone applicationshavemadeinformationtechnologiesandInternetfullyaccessibletopeopleof everyagegrouponeverycontinentalmostubiquitously.Inlessthanadecade,wireless communicationtechnologieshavecompletelytransformedtheworldeconomyandpeople’s livesinmorewaysthanimaginableatthebeginningofthismillennium.Globally,itisquite difficulttofindanindividualinanypartoftheworldtodaythathasnotbeentouchedbynew communicationtechnologiesrangingfrome-commercetoonlinesocialmedia.Thisbook teachesthebasicprinciplesofcommunicationsystemsbasedonelectricalsignals.
Beforemoderntimes,messageswerecarriedbyrunners,homingpigeons,lights,and smokesignals.Theseschemeswereadequateforthedistancesand“datarates”oftheage.In mostpartsoftheworld,thesemodesofcommunicationhavebeensupersededbyelectrical communicationsystems,∗ whichcantransmitsignalsovervastdistances(eventodistant planetsandgalaxies)andatthespeedoflight.
Modernelectroniccommunicationsystemsaremoredependableandmoreeconomical, oftenplayingkeyrolesinimprovingproductivityandenergyefficiency.Increasingly, businessesareconductedelectronically,savingbothtimeandenergyovertraditionalmeans. Ubiquitouscommunicationallowsreal-timemanagementandcoordinationofproject participantsfromaroundtheglobe.E-mailisrapidlyreplacingthemorecostlyandslower “snailmail.”E-commercehasalsodrasticallyreducedcostsanddelaysassociatedwith marketingandtransactions,allowingcustomerstobemuchbetterinformedaboutnew productsandtocompleteonlinetransactionswithaclick.Traditionalmediaoutletssuch astelevision,radio,andnewspapershavealsobeenrapidlyevolvinginrecentyearsto copewithandbetterutilizenewcommunicationandnetworkingtechnologies.Furthermore, communicationtechnologieshavebeen,andwillalwaysbe,playinganimportantrolein currentandfuturewavesofremarkabletechnologicaladvancesinartificialintelligence,data mining,andmachinelearning.
Thegoalofthistextbookistoprovidethefundamentaltechnicalknowledgeneededby future-generationcommunicationengineersandtechnologistsfordesigningevenmoreefficientandmorepowerfulcommunicationsystemsoftomorrow.Critically,onemajorobjective ofthisbookistoanswerthequestion:Howdocommunicationsystemswork?Thatis,how canweaccessinformationremotelyusingsmalldevicessuchasasmartphone?Beingableto answerthisquestionisessentialtodesigningbettercommunicationsystemsforthefuture.
1.1COMMUNICATIONSYSTEMS Figure1.1presentsthreefamiliarcommunicationscenarios:awirelinetelephone-to-cellular phoneconnection,aTVbroadcastingsystem,andacomputernetwork.Becauseofthe numerousexamplesofcommunicationsystemsinexistence,itwouldbeunwisetoattempt tostudythedetailsofallkindsofcommunicationsystemsinthisbook.Instead,themost efficientandeffectivewaytolearnisbystudyingthemajorfunctionalblockscommonto practicallyallcommunicationsystems.Thisway,wearenotmerelylearningthemechanics ofthoseexistingsystemsunderstudy.Moreimportantly,wecanacquirethebasicknowledge neededtodesignandanalyzenewsystemsneverencounteredinatextbook.Tobegin,itis essentialtoestablishatypicalcommunicationsystemmodelasshowninFig.1.2.Thekey componentsofacommunicationsystemareasfollows.
wireline network
wireless laptops and smartphones
wireless access point
Figure1.1 Someexamplesofcommunicationsystems.
The source originatesamessage,suchasahumanvoice,atelevisionpicture,ane-mail message,ordata.Ifthedataisnonelectric(e.g.,humanvoice,e-mailtext,ascene),itmustbe convertedbyan inputtransducer intoanelectricwaveformreferredtoasthe messagesignal throughphysicaldevicessuchasamicrophone,acomputerkeyboard,oracharge-coupled device(CCD)camera.
The transmitter transformstheinput(message)signalintoanappropriateform forefficienttransmission.Thetransmittermayconsistofoneormoresubsystems:an analog-to-digital(A/D)converter,anencoder,andamodulator.Similarly,thereceivermay consistofademodulator,adecoder,andadigital-to-analog(D/A)converter.
The channel isamediumofchoicethatcanconveytheelectricsignalsatthetransmitter outputoveradistance.Atypicalchannelcanbeapairoftwistedcopperwires(e.g.,in telephoneandDSL),coaxialcable(e.g.intelevisionandInternet),anopticalfiber,oraradio cellularlink.Additionally,achannelcanalsobeapoint-to-pointconnectioninameshof interconnectedchannelsthatformacommunicationnetwork.
The receiver reprocessesthesignalreceivedfromthechannelbyreversingthesignal transformationmadeatthetransmitterandremovingthedistortionscausedbythechannel. Thereceiveroutputispassedtothe outputtransducer,whichconvertstheelectricsignalto itsoriginalform—themessage.
The destination istheunitwherethemessagetransmissionterminates.
1.2DESIGNCHALLENGES:CHANNEL DISTORTIONSANDNOISES Achannelisaphysicalmediumthatbehavespracticallylikeanimperfectfilterthatgenerally attenuatesthesignalanddistortsthetransmittedwaveforms.Thechannelattenuationdepends onthedistancethesignalsmusttravelbetweenthetransmitterandthereceiver,varying frommildtosevere.Signalwaveformsarefurtherdistortedbecauseofphysicalphenomena suchasfrequency-dependentelectronics,multipatheffects,andDopplershift.Forexample, a frequency-selective channelcausesdifferentamountsofattenuationandphaseshiftto differentfrequencycomponentswithintheinputsignal.Ashortrectangularpulsecan beroundedor“spreadout”duringtransmissionoveralowpasschannel.Thesetypesof distortion,called lineardistortion,canbepartlycorrectedatthereceiverbyanequalizer withgainandphasecharacteristicscomplementarytothoseofthechannel.Channelsmayalso cause nonlineardistortion throughattenuationthatvarieswiththesignalamplitude.Such distortionscanalsobepartlymitigatedbyacomplementaryequalizeratthereceiver.Channel distortions,ifknown,canalsobeprecompensatedbytransmittersusingchannel-dependent predistortions.
Inapracticalenvironment,signalspassingthroughcommunicationchannelsnotonly experiencechanneldistortionsbutalsoarecorruptedalongthepathbyinterferingsignals anddisturbanceslumpedunderthebroadterm noise.Theseinterferingsignalsareoften randomandunpredictablefromsourcesbothexternalandinternal.Externalnoiseincludes interferencesignalstransmittedonnearbychannels,human-madenoisegeneratedbyfaulty switchcontactsofelectricequipment,automobileignitionradiation,fluorescentlightsor naturalnoisefromlightning,microwaveovens,andcellphoneemissions,aswellaselectric stormsandsolarorintergalacticradiation.Withpropercareinsystemdesigns,externalnoise canbeminimizedoreveneliminatedinsomecases.Internalnoiseresultsfromthermal motionofchargedparticlesinconductors,randomemission,anddiffusionorrecombination ofchargedcarriersinelectronicdevices.Propercarecanmitigatetheeffectofinternalnoise butcanneverfullyeliminateit.Noiseisoneoftheunderlyingfactorsthatlimittherateof telecommunications.
Thusinpracticalcommunicationsystems,thechanneldistortsthesignal,andnoise accumulatesalongthepath.Worseyet,thesignalstrengthattenuateswhilethenoiselevel remainssteadyregardlessofthedistancefromthetransmitter.Thus,thesignalqualitywould continuouslydegradealongthelengthofthechannel.Amplificationofthereceivedsignal tomakeupfortheattenuationisineffectivebecausethenoisewillbeamplifiedbythesame proportion,andthequalityremains,atbest,unchanged.∗ Thesearethekeychallengesthatwe mustfaceindesigningmoderncommunicationsystems.
1.3MESSAGESOURCES Messagesincommunicationsystemscanbeeitherdigitaloranalog.Digitalmessagesare orderedcombinationsoffinitesymbolsorcodewords.Forexample,printedEnglishconsists of26letters,10numbers,aspace,andseveralpunctuationmarks.Thus,atextdocument writteninEnglishisadigitalmessageconstructedfromtheASCIIkeyboardof128symbols. Analogmessages,ontheotherhand,arecharacterizedbysignalswhosevaluesvaryovera continuousrangeandaredefinedforacontinuousrangeoftime.Forexample,thetemperature ortheatmosphericpressureofacertainlocationovertimecanvaryoveracontinuousrange andcanassumean(uncountably)infinitenumberofpossiblevalues.Ananalogmessage typicallyhasalimitedrangeofamplitudeandpower.Adigitalmessagetypicallycontains M symbolsandiscalledan M -ary message.
Thedifferencebetweendigitalandanalogmessagescanbesubtle.Forexample,thetext inaspeechisadigitalmessage,sinceitismadeupfromafinitevocabularyinalanguage. However,theactualrecordedvoicefromahumanspeakerreadingthetextisananalog waveformwhoseamplitudevariesoveracontinuousrange.Similarly,amusicalnoteisa digitalmessage,consistingofafinitenumberofmusicalsymbols.Thesamemusicalnote, whenplayedbyamusician,becomesanaudiowaveformthatisananalogsignal.
1.3.1TheDigitalRevolutioninCommunications Itisnosecrettoevenacasualobserverthateverytimeonelooksatthelatestelectroniccommunicationproducts,anothernewerandbetter“digitaltechnology”isdisplacingtheoldanalog technology.Between1990and2015,cellularnetworkscompletedtheirtransformationfrom
∗ Actually,amplificationmayfurtherdeterioratethesignalbecauseofadditionalamplifiernoise.
Figure1.3
(a)Transmitted signal.
(b)Received distortedsignal (withoutnoise).
(c)Received distortedsignal (withnoise).
(d)Regenerated signal(delayed).
thefirst-generationanalogAMPStothecurrentthird-generation(UMTS,CDMA2000)and fourth-generation(i.e.,4G-LTE)digitaloffsprings.Mostvisiblyineveryhousehold,digital videotechnology(DVD)andBlu-rayhavemadetheanalogVHScassettesystemsobsolete. DigitaliPodandMP3playershavetotallyvanquishedtheoncepopularaudio-cassetteplayers inconsumerelectronics.Theglobalconversiontodigitaltelevisionisnownearlycomplete indrivingoutthelastanalogholdoutofcolortelevision.Thisbegsthequestion:Whyare digitaltechnologiessuperior?Theanswerhastodowithbotheconomicsandquality.The caseforeconomicsismadebytheeaseofadoptingversatile,powerful,andinexpensive high-speeddigitalmicroprocessors.Butmoreimportantlyatthequalitylevel,oneprominent featureofdigitalcommunicationsistheenhancedimmunityofdigitalsignalstonoiseand interferences.
Digitalmessagesaretransmittedasafinitesetofelectricalwaveforms.Inotherwords, adigitalmessageisgeneratedfromafinitealphabet,whileeachcharacterinthealphabet canberepresentedbyonewaveformorasequentialcombinationofsuchwaveforms.For example,insendingmessagesviaMorsecode,adashcanbetransmittedbyanelectrical pulseofamplitude A andadotcanbetransmittedbyapulseofnegativeamplitude A (Fig.1.3a).Inan M -arycase, M distinctelectricalpulses(orwaveforms)areused;each ofthe M pulsesrepresentsoneofthe M possiblesymbols.Oncetransmitted,thereceiver mustextractthemessagefromadistortedandnoisysignalatthechanneloutput.Message extractionisofteneasierfromdigitalsignalsthanfromanalogsignalsbecausethedigital decisionmustbelongtothefinite-sizedalphabet.Considerabinarycase:twosymbolsare encodedasrectangularpulsesofamplitudes A and A.Theonlydecisionatthereceiveris toselectbetweentwopossiblepulsesreceived;thefinedetailsofthepulseshapearenotan issue.Afinitealphabetleadstonoiseandinterferenceimmunity.Thereceiver’sdecisioncan bemadewithreasonablecertaintyevenifthepulseshavesufferedfrommodestdistortion andnoise(Fig.1.3).ThedigitalmessageinFig.1.3aisdistortedbythechannel,asshownin Fig.1.3b.Yet,ifthedistortionisnottoolarge,wecanrecoverthedatawithouterrorbecause weonlyneedtomakeasimplebinarydecision:Isthereceivedpulsepositiveornegative? Figure1.3cshowsthesamedatawithchanneldistortionandnoise.Hereagain,thedatacan berecoveredcorrectlyaslongasthedistortionandthenoisearewithinlimits.Incontrast, thewaveformshapeitselfinananalogmessagecarriestheneededinformation,andevena slightdistortionorinterferenceinthewaveformwillshowupinthereceivedsignal.Clearly, adigitalcommunicationsystemismoreruggedthanananalogcommunicationsysteminthe sensethatitcanbetterwithstandnoiseanddistortion(aslongastheyarewithinalimit).
Atypicaldistortedbinarysignalwithnoiseacquiredoverthechannelisshownin Fig.1.3c.If A issufficientlylargeincomparisontotypicalnoiseamplitudes,thereceiver
