《电子信息专业英语》（第3版） 课件Chapter 6 Communication System 通信系统

活页式教材微课版电子信息专业英语行业PPT模板/hangye/Chapter6CommunicationSystem通信系统

教学目标6.1★调制与解调：掌握调制作用、信号与载波、模拟信号调制（调幅、调频、调相）、采样和编码、数字信号调制、解调。★通过调制与解调、通信信道和多路复用、移动电话三篇文章学习通信系统。6.2★通信信道和多路复用：掌握通信信道作用、有线传输介质（双绞线、同轴电缆、光纤）、无线传输介质（微波、通信卫星）、多路复用作用、频分复用、时分复用。6.3★移动电话：掌握移动电话功能和使用、移动电话组成、模数转化、数字信号处理、CPU、存储器、显示屏。

6.1

Lesson16ModulationandDemodulation

调制与解调NewWordsTechnicalTerms技术词汇modulationn.调制；调整telecommunicationn.电信；远程通信impressvt.施加于；给予印象carrierwave载波characteristicsn.特性，特征；特色inaccordancewith依照；与…一致altervt.改变，更改；vi.改变functionn.功能；函数；vi.运行sinusoidn.正弦曲线parametern.参数；系数magnituden.大小；量级；重要amplituden.振幅；丰富，充足termn.术语；学期；vt.叫做phasen.位相；阶段；vt.定相suitableadj.适当的；相配的amplitudemodulation调幅；波幅调制frequencymodulation调频；频率调制phasemodulation调相；相位调制TechnicalTerms技术词汇bandn.波段；乐队atanyinstant在任何时刻immunityn.免疫力；免除distortionn.变形；失真；扭曲attheexpenseof以…为代价；支付费用bandwidthn.带宽；频带宽度pulse-codemodulation脉冲编码调制samplevt.取样；抽样；n.样品compactdisc光碟，激光唱片quantizevt.量化；数字转换amplitude-shiftkeying幅移键控frequency-shiftkeying频移键控phase-shiftkeying相移键控finiteadj.有限的；限定的demodulationn.检波；反调制；解调extractvt.提取；取出detectorn.检测器；发现者；侦察器demodulatorn.解调器

6.1

Lesson16ModulationandDemodulation

调制与解调Inelectronicsandtelecommunications,modulationisatechniqueforimpressinginformation(

voice,music,picture,ordata

)onaradio-frequencycarrierwavebyvaryingoneormorecharacteristicsofthewaveinaccordancewiththesignal.Therearevariousformsofmodulation,eachdesignedtoalteraparticularcharacteristicofthecarrierwave.Ifwelookatageneralfunctionforasinusoid:f

(

t

)=Asin(

ωt+φ

).Wecanseethatthissinusoidhas3parametersthatcanbealtered,toaffecttheshapeofthegraph.Thefirstterm,A,iscalledthemagnitude,oramplitudeofthesinusoid.Thenextterm,ωisknownasthefrequency,andthelastterm,φisknownasthephaseangle.All3parameterscanbealteredtotransmitinformation.Thehighfrequencysinusoidalwavethatisusedinthemodulationisknownasthecarrier[4].Itisimportanttonoticethatasimplesinusoidalcarriercontainsnoinformationofitsown.Modulationisusedbecausethesomeinformationsignalsarenotsuitablefordirecttransmission,butthemodulatedsignalmaybemoresuitable.Text

6.1

Lesson16ModulationandDemodulation

调制与解调Inanalogmodulationsystems,varyingtheamplitude,frequency,orphaseofthecarrierresultsinamplitudemodulation(AM),frequencymodulation(FM),orphasemodulation(PM).Amplitudemodulation(AM)isthemodulationmethodusedintheAMradiobroadcastband.Inthissystem，theamplitudeofthecarrierwavevariesinaccordancewiththemodulatingsignal.Infrequencymodulation(FM),thefrequencyofthecarrierwaveisvariedinsuchawaythatthechangeinfrequencyatanyinstantisproportionaltothemodulatingsignal.Itsprincipalapplicationisalsoinradio,whereitoffersincreasednoiseimmunityanddecreaseddistortionovertheAMtransmissionsattheexpenseofgreatlyincreasedbandwidth.TheFMbandhasbecomethechoiceofmusiclistenersbecauseofitslow-noise,wide-bandwidthqualities;itisalsousedfortheaudioportionofatelevisionbroadcast.Phasemodulation,likefrequencymodulation,isaformofanglemodulation(socalledbecausetheangleofthesinewavecarrierischangedbythemodulatingwave).Text

6.1

Lesson16ModulationandDemodulation

调制与解调Inadigitalsignal,theinformationisencodedasasetofdiscretevalues.pulse-codemodulation(PCM)isamethodusedtodigitallyrepresentsampledanalogsignals.PCMhasbeenusedindigitaltelephonesystemsandisalsothestandardformfordigitalaudioincomputersandthecompactdiscformat.IntheFig.6-2diagram,asinewaveissampledandquantizedforpulse-codemodulation.Indigitalmodulation,acarrierwaveismodulatedbyadiscretesignal.Themostfundamentaldigitalmodulationtechniquesareamplitude-shiftkeying(ASK),frequency-shiftkeying(FSK),andphase-shiftkeying(PSK).Theparameterofthecarriersignalisshiftedbythediscreteamplitudesofthedigitalsignal(

Fig.6-3

).Demodulationistheactofextractingtheoriginalinformationsignalfromamodulatedcarrierwave.Eachtypeofmodulationisdifferentandrequiresdifferenttechniquestorecover(demodulate)theinformation.Forexample,forasignalmodulatedwithamplitudemodulation,wecanuseanenvelopedetector.Ontheotherhand,forasignalmodulatedwithanangularmodulation,wemustuseanFMdemodulatororaPMdemodulator.Differentkindsofcircuitsperformthesefunctions.Text

6.1

Lesson16ModulationandDemodulation

调制与解调Figures

Figure6-1Low-frequencyinformationsignal，AMradiowave，FMradiowaveFigure6-3Digitalsignal,ASK,FSK,PSKFigure6-2Samplingandquantizationofasignalfor4-bitPCM

6.1

Lesson16ModulationandDemodulation

调制与解调Ⅰ．Choosethebesttechnicaltermtocompletethefollowingstatements.ExercisesModulationisatechniqueforimpressinginformationonaradio-frequencycarrierwavebyvarying()ofthewaveinaccordancewiththesignal.A.amplitude B.frequency C.phase D.angleThesimplehighfrequencysinusoidalwavewhichcontainsnoinformationofitsownis().A.modulation B.generalfunction C.carrier D.transmission()isthemodulationmethodusedintheradiobroadcastsystem.A.AM B.FM C.PM D.PCMAttheexpenseofgreatlyincreasedbandwidth,()offersincreasednoiseimmunityanddecreaseddistortionintheradiobroadcast.A.amplitudemodulation

B.frequencymodulation C.phasemodulation D.musicmodulation

6.1

Lesson16ModulationandDemodulation

调制与解调Ⅰ．Choosethebesttechnicaltermtocompletethefollowingstatements.ExercisesPCMaudioisahighfidelity,uncompresseddigital()ofananalogaudiosignal.A.encoding B.sampling C.quantizing D.standardformIndigitalmodulation,()arefundamentaldigitalmodulationtechniques.A.PCM B.ASK C.FSK

D.PSK

6.1

Lesson16ModulationandDemodulation

调制与解调Ⅱ．TranslatethefollowingsentencesintoChinese.Exercises1．TheAmplitudeModulated(

AMradio

)carrierfrequenciesareinthefrequencyrange535-1605kHz.Carrierfrequenciesof540to1600kHzareassignedat10kHzintervals.2．TheFMradiobandisfrom88to108MHz.TheFMstationsareassignedcenterfrequenciesat200kHzseparationstartingat88.1MHz,foramaximumof100stations.3．ThesimplestandmostcommonformofASKoperatesasaswitch,usingthepresenceofacarrierwavetoindicateabinaryoneanditsabsencetoindicateabinaryzero.Thistypeofmodulationiscalledon-offkeying.4．Ifthecarrierfrequencybychangingthemethodtosendbinarysymbols,isthefrequencyshiftkeying(

FSK

)method,‘1’whenthereisalowfrequency,‘0’whenthereisahighfrequency.6.2 Lesson17CommunicationChannelandMultiplexing

通信信道和多路复用NewWordsTechnicalTerms技术词汇communicationchannel通信信道transmissionn.播送；传递mediumn.介质；媒体median.介质；媒质wiredadj.有线的guidevt.引导；带领n.指南twistedpairn.双绞线coaxialcablen.同轴电缆opticalfibern.光纤，光导纤维electromagneticadj.电磁的propagatevt.传播；传送interferencen.干扰；干涉dielectricn.电介质metallicadj.金属的shieldn.防护物；vt.遮蔽electromagneticinterference电磁干扰coren.芯；核心；果心；要点TechnicalTerms技术词汇capacityn.容量；能力lineofsight视线repeatern.中继器；转发器atintervals相隔一定距离（或时间）relayn.中继；继电器；v.转播historicallyadv.历史上地；从历史观点intercontinentaladj.洲际的；大陆间的telephonyn.电话（学）hand-heldadj.手持的，便携式的terminaln.终端机uplinkn.上行链路downlinkn.下行链路multiplexingn.多路技术；v.多重发讯transmissionrate传输速度；传输率neighborhoodn.附近；邻居megahertzn.兆赫kilohertzn.千赫6.2 Lesson17CommunicationChannelandMultiplexing

通信信道和多路复用NewWordsTechnicalTerms技术词汇carrierfrequency载波频率adjacentstation邻站；相邻电台allowancen.容差；津贴；允许frequency-divisionmultiplexing频分多路复用allocatevt.分配；vi.指定TechnicalTerms技术词汇recurringadj.循环的；重现的segmentn.段；v.分割slotn.（时）隙；狭缝；投硬币口time-divisionmultiplexing时分多路复用hybridn.混合物；adj.混合的6.2 Lesson17CommunicationChannelandMultiplexing

通信信道和多路复用Acommunicationchannelisatransmissionmediumthatcarriesasignalbetweenthetransmitterandthereceiver.Transmissionmediaareclassifiedaswiredandwireless.Withwiredtransmissionmedia,thesignalsareguidedalongaphysicalpath,examplesofwiredmediaincludetelephonelines,twistedpaircables,coaxialcables,andopticalfibers.Withwirelesstransmissionmedia,electromagneticwavespropagatethroughtheair.Thetelephonelinesusedtocarrythevoiceanddatacommunicationsconsistofapairinsulatedcopperwires.Thewiresaretwistedaroundeachothertominimizeinterferencefromothertwistedpairsinthecable(Fig.6-4).Twistedpairsaretheleastexpensiveandmostwidelyusedtransmissionmediaforbothanaloganddigitalsignals.Acoaxialcablehasainnerconductorsurroundedbyanon-conductivedielectricinsulatingmaterial(Fig.6-5).Thedielectricissurroundedbymetallicshieldswhichformtheouterconductorandalsoshieldagainstelectromagneticinterference(EMI).Thetermcoaxialcomesfromtheinnerconductorandtheoutershieldsharingthesameaxis.Coaxialcableshavemorebandwidththantwistedpairs.Acoaxialcablecanhandle80timesasmanytelephonetransmissionsastwistedpairmedia.Andmanycomputersinlocalareanetworksarelinkedbycoaxialcables.Text6.2 Lesson17CommunicationChannelandMultiplexing

通信信道和多路复用Opticalfiberconsistsofacenterglasscoresurroundedbyseverallayersofprotectivematerials(Fig.6-6).Ittransmitslightratherthanelectronicsignalseliminatingtheproblemofelectricalinterference.Opticalfiberhastheabilitytotransmitsignalsovermuchlongerdistancesthancoaxialandtwistedpair.Ithas26,000timesthetransmissioncapacityoftwistedpairmedia.Italsohasthecapabilitytocarryinformationatvastlygreaterspeeds.Microwavetransmissiondiffersfromthepreviouslymentionedcommunicationschannelsinthatsignalistransmittedthroughtheairinsteadofthroughwiresorcables.Microwavetransmissionsoperateathighoperatingfrequenciesof3to10GHz.Thisallowsthemtocarrylargequantitiesofinformationduetothelargebandwidth.Microwavetransmissionislineofsighttransmission.Inordertoovercometheproblemoflineofsightandpoweramplificationofweaksignal,repeatersareusedatintervalsof25to30kilometersbetweenthetransmittingandreceivingend(Fig.6-7).Acommunicationsatelliteisamicrowaverelaystationplacedinouterspace.Insatellitecommunication,microwavesignalistransmittedfromatransmitteronearthtothesatelliteinspace.Thesatelliteamplifiestheweaksignalandtransmitsitbacktothereceiveronearth(Fig.6-8).ThemainadvantageofsatelliteText6.2 Lesson17CommunicationChannelandMultiplexing

通信信道和多路复用communicationisthatitisasinglemicrowaverelaystationvisiblefromanypointofaverylargearea.Thefirstandhistoricallymostimportantapplicationforcommunicationsatelliteswasinintercontinentallongdistancetelephony.Theyarealsousedformobileapplicationssuchascommunicationstoships,vehicles,planesandhand-heldterminals,andforTVandradiobroadcasting.Multiplexingisaformofsignaltransmissioninwhichonecommunicationchannelcarriesseveraltransmissionsatthesametime.Thetelephonelinesthatcarryourdailyconversationscancarrythousandsorevenmoreofconversationsatatimeusingmultiplexing.Theexactnumberofsimultaneoustransmissiondependsonthetypeofcommunicationchannelandthedatatransmissionrate.Forexample,oneradiostationcanbroadcastradiowavesintofreespaceatfrequenciesintheneighborhoodof94.5MHz(megahertz)whileanotherradiostationcansimultaneouslybroadcastradiowavesatfrequenciesintheneighborhoodof96.1MHz.Eachradiostationwouldtransmitradiowavesoverafrequencybandwidthofabout180kHz(kilohertz),centeredatfrequenciessuchastheabove,whicharecalledthe‘carrierfrequencies’.Eachstationinthisexampleisseparatedfromitsadjacentstationsby200kHz,andthedifferencebetween200kHzand180kHz(20kHz)isanengineeringallowanceinthecommunicationsystem.Text6.2 Lesson17CommunicationChannelandMultiplexing

通信信道和多路复用Intheexampleabove,the‘freespacechannel’hasbeendividedintocommunicationschannelsaccordingtofrequencies,andeachchannelisassignedaseparatefrequencybandwidthinwhichtobroadcastradiowaves.Thissystemofdividingthemediumintochannelsaccordingtofrequencyiscalled‘frequency-divisionmultiplexing’(FDM)(Fig.6-9).Anotherwayofdividingacommunicationsmediumintochannelsistoallocateeachsenderarecurringsegmentoftime(a‘timeslot’,forexample,20millisecondsoutofeachsecond),andtoalloweachsendertosendmessagesonlywithinitsowntimeslot.Thismethodofdividingthemediumintocommunicationchannelsiscalled‘time-divisionmultiplexing’(TDM)(Fig.6-10),andisusedinopticalfibercommunication.SomeradiocommunicationsystemsuseTDMwithinanallocatedFDMchannel.Hence,thesesystemsuseahybridofTDMandFDM.Text6.2 Lesson17CommunicationChannelandMultiplexing

通信信道和多路复用Figures

Figure6-4TwistedpairwiringFigure6-7Microwavetransmission

Figure6-5CoaxialcableFigure6-6Opticalfiber6.2 Lesson17CommunicationChannelandMultiplexing

通信信道和多路复用Figures

Figure6-8SatellitecommunicationFigure6-9FDMFigure6-10TDM6.2 Lesson17CommunicationChannelandMultiplexing

通信信道和多路复用Ⅰ．Decidewhetherthefollowingstatementistrueorfalse,andexplainyouranswers.Exercises1．Transmissionmediaincludetelephonelines,twistedpaircables,coaxialcables,opticalfibers,microwavetransmissions,satellitetransmissions,andcellularradiosystems.2．Twistedpairshavefewerbandwidththancoaxialcableoropticalfiber.3．Coaxialcablesareusedtotransmitbothanaloganddigitalsignal.Theyhavesuperiorfrequencycharacteristicscomparedtotwistedpair,andtheycansupporthigherfrequenciesanddatarates.4．Amajoradvantageofopticalfibermediaisnotsusceptibletoelectronicinterference.Therefore,theyareamorereliableformofdatatransmission.5．OpticalFibercablesaresignificantlylessexpensivethancoaxialcable.Adisadvantageofopticalfiberchannelsisthattheycannotcarryinformationovergreatdistances.6．Microwavesarehigh-frequencyradiowavesthatcanonlybedirectedinstraightlines.Consequently,formicrowavetransmissionstobeabletooccuroverlargerdistances,datamessagesmustberelayedfromonelocationtoanotherusingantennasplacedathighaltitudes.6.2 Lesson17CommunicationChannelandMultiplexing

通信信道和多路复用Ⅰ．Decidewhetherthefollowingstatementistrueorfalse,andexplainyouranswers.Exercises7．Acommunicationsatelliteisusedtolinktwoormoreground-basedmicrowavetransmitters/receivers.Thesatellitereceivestransmissionsononefrequencyband(uplink),amplifiesorrepeatsthesignal,andtransmitsitonanotherfrequency(downlink).8．FDM(

FrequencyDivisionMultiplexing

)andTDM(

TimeDivisionMultiplexing

)aretwomethodsofmultiplexingmultiplesignalsintoasingletransmissionchannel.6.2 Lesson17CommunicationChannelandMultiplexing

通信信道和多路复用Ⅱ．TranslatethefollowingsentencesintoChinese.Exercises1．Thesetwisted-pairinstallationsaregenerallydesignedtosupportvoicetrafficusinganalogsignaling.However,byusingamodem,theycanalsohandledigitaldata.2．Coaxialcableisusedasatransmissionlineforradiofrequencysignals.Itsapplicationsincludefeedlinesconnectingradiotransmittersandreceiverswiththeirantennas,anddistributingcabletelevisionsignals.3．Infiber-opticcommunication,thelightformsanelectromagneticcarrierwavethatismodulatedtocarryinformation.Becauseofitsadvantagesoverelectricaltransmission,opticalfibershavelargelyreplacedcopperwirecommunicationsincorenetworks.4．Communicationssatellitesareofteningeostationaryorbit.Atthehighorbitalaltitudeof35,800kilometers,ageostationarysatelliteorbitstheEarthinthesameamountoftimeittakestheEarthtorevolveonce.5．Inanalogtransmission,signalsarecommonlymultiplexedusingfrequency-divisionmultiplexing(

FDM

),inwhichthecarrierbandwidthisdividedintosubchannelsofdifferentfrequencywidths,eachcarryingasignalatthesametimeinparallel.6．Indigitaltransmission,signalsarecommonlymultiplexedusingtime-divisionmultiplexing(

TDM

),inwhichthemultiplesignalsarecarriedoverthesamechannelinalternatingtimeslots.

6.3

Lesson18MobilePhone

移动电话NewWordsTechnicalTerms技术词汇mobileadj.移动的；n.移动物体cellphone手机duplexn.双工basestation基站publictelephone公用电话网networkfixedline固定线路antennan.天线outgoingadj.外出的incomingadj.引入的DSP数字信号处理器signal-manipulation信号处理choren.家庭杂务；日常零星事务commandv.命令，指挥；n.命令operatingsystem操作系统commitvt.致力于，承诺，从事customizableadj.可定制的TechnicalTerms技术词汇directoryn.目录；姓名地址录rechargevt.再充电；再控告internaladj.内部的；内在的flashmemory闪速存储器SIMcard用户识别卡；智能卡service-subscribern.服务订户；服务用户keyn.钥匙；密钥；关键slidevt.滑动；使滑动featuren.特色，特征；v.特写built-inadj.嵌入的；n.内置incorporatevt.包含，吸收；合并webbrowser

浏览器smartphonen.智能手机resolution

n.[物]分辨率；决议；解决；决心touchscreenn.触摸屏optimizedadj.最佳化的6.3

Lesson18MobilePhone

移动电话Amobilephone(alsocalledmobileorcellphone)isanelectronicdeviceusedforfullduplextwo-wayradiotelecommunicationsoveracellularnetworkofbasestations(Fig.5-3).Amobilephoneallowsitsusertomakeandreceivetelephonecallstoandfromthepublictelephonenetworkwhichincludesothermobilesandfixedlinephonesacrosstheworld.Cellphonecontainsafewindividualparts:Anamazingcircuitboardcontainingthebrainsofthephone,antenna,aLiquidCrystalDisplay(LCD),akeyboard,amicrophone,aspeakerandabattery(Fig.5-4).Thecircuitboardistheheartofthesystem.HereisonefromatypicalNokiadigitalphone(Fig.5-5,Fig.5-6).Inthephotos,thereareseveralchips.Theanalog-to-digitalanddigital-to-analogconversionchipstranslatetheoutgoingaudiosignalfromanalogtodigitalandtheincomingsignalfromdigitalbacktoanalog.Thedigitalsignalprocessor(DSP)isahighlycustomizedprocessordesignedtoperformsignal-manipulationcalculationsathighspeed.Themicroprocessorhandlesallofthechoresforthekeyboardanddisplay,dealswithcommandandcontrolsignalingwiththebasestationandalsocoordinatestherestofthefunctionsontheboard.Text6.3

Lesson18MobilePhone

移动电话TheROMandFlashmemorychipsprovidestorageforthephone’soperatingsystemandcustomizablefeatures,suchasthephonedirectory.Thepowersectionhandlespowermanagementandrecharging.Finally,theRFamplifiershandlesignalstravelingtoandfromtheantenna.Somephonesstorecertaininformation,ininternalFlashmemory,whileothersuseexternalcardssuchasSIMcard(Fig.5-7).TheSIMstorestheservice-subscriberkeyusedtoidentifyasubscriberonmobiledevice.TheSIMcardmakesiteasytoswitchtoanewphonebysimplyslidingtheSIMoutoftheoldphoneandintothenewone.Thedisplay(Fig.5-8)hasgrownconsiderablyinsizeasthenumberoffeaturesincellphoneshaveincreased.Mostcurrentphonesofferbuilt-inphonedirectories,calculatorsandgames.Andmanyofthephonesincorporatewebbrowser.Asmartphoneisamobilephonebuiltonamobileoperatingsystem.Smartphonestypicallyaddedthefunctionsofpersonaldigitalassistant(PDA)，portablemediaplayers,digitalcameras,andGPSnavigationunitstoformonemulti-usedevice.Modernsmartphonesalsoincludehigh-resolutiontouchscreensandwebbrowsersthatdisplaystandardwebpagesaswellasmobile-optimizedsites.High-speeddataaccessisprovidedbyWi-FiandMobileBroadband.Text6.3

Lesson18MobilePhone

移动电话Figures

Figure5-3Cellularnetwork6.3

Lesson18MobilePhone

移动电话Figures

Figure5-5PCBFront

Figure5-4PartsofacellphoneFigure5-8Display&keypadFigure5-7SIMcardFigure5-6PCBBack6.3

Lesson18MobilePhone

移动电话Ⅰ．Decidewhetherthefollowingstatementistrueorfalse,andexplainyouranswers.Exercises1．Amobilephoneusercanonlymakecallstoothermobilesandonlyreceivetelephonecallsfromthefixedlinephones.2．Mobilephonecontainsabrain,aheart,acircuitboard,anantenna,aLCD,akeyboard,amicrophone,aspeakerandabattery.3．Thereareanalog-to-digitalanddigital-to-analogconversionchips,DSPchip,microprocessorchip,ROMandFlashmemorychips,andotherchipsonthecircuitboa