CharacteristicsofDataTransmissionCirsuitsNewwordsandphrases1sophisticatedadj.復雜的2repetitionn.重復,循環(huán)3intelligibilityn.可懂度，清晰度4attenuatevt.衰減attenuationn.衰減5dibitn.雙位6drawbackn.缺點,障礙7compromisevt.危害；損害（名譽）8Hartleyn.哈特萊ShannonHartleylaw香農(nóng)哈特萊定律9expectationn.期望(值)idealexpectation理想期望值10nonethelessadv.雖然如此,但是11minimumadj.最小的,最低的12precludevt.避免、阻止；使不可能

CharacteristicsofDataTransmissionCirsuits13impairmentn.損害,損傷14decibeln.分貝15crosstalkn.串話16pronouncedadj.顯著的,明顯的17interactionn.交互作用,交感

electromagneticinteraction電磁交感，電磁相互作用18braidedadj.編織的19foiln.箔,金屬薄片metalfoil金屬箔20shieldvt.屏蔽,保護；n.屏蔽,防護罩

shieldedcable屏蔽電纜21echon.回聲22suppressorn.抑制器echosuppressor回波抑制器23intactadj.原封不動的，完整的24bidirectionaladj.雙向的

CharacteristicsofDataTransmissionCirsuits25disablevt.禁止;使失效26reactivatev.復原，重激活，重新使用27abnormalityn.不正常，畸形28alterv.改變29commencev.開始30thereafteradv.此后；后來31presetadj.；vt.預置32leasevt.出租,租出33equalizationn.均衡adaptiveequalization自適應均衡34dedicatedadj.專用的dedicatedcircuit專用電路35understandablyadv.可理解地

CharacteristicsofDataTransmissionCirsuits1datastream數(shù)據(jù)流2squarewavesignal矩形波信號3HF(highfrequency)高頻4submarinecable海底電纜5audiblespectrum聲譜6datatransfer數(shù)據(jù)傳送7multilevelencoding多電平編碼8baudrate波特率9informationtransfer信息傳遞

CharacteristicsofDataTransmissionCirsuits10signalingpulse信號脈沖11signalingspeed通信速度,發(fā)碼速率12distortionlesstransmission無失真?zhèn)鬏?3bitrate比特率14transmissionefficiency傳輸效率15voicegradechannel話音級信道，電話線路16bps（bitspersecond）比特/秒17noisefreechannel無噪信道CharacteristicsofDataTransmissionCirsuits18signaltonoiseratio信噪比19envelopedelay包絡延遲，群時延

envelopedelaydistortion包絡線延遲失真(畸變)20transformerwinding變壓器繞組21electromagneticradiation電磁輻射22balancedcircuit平衡電路23twistedpair雙絞線24outofphase異相地,不協(xié)調(diào)地25inphase同相地,協(xié)調(diào)地26bidirectionaltransmission雙向傳輸

CharacteristicsofDataTransmissionCirsuits27frequencycomponent頻率成分28phasedelay相位延遲29timeslot時隙30intersymbolinterference碼間干擾,符號間干擾31reactto對……作出反應32drainoff漸漸枯竭33beconditionedto習慣于CharacteristicsofDataTransmissionCirsuits

Datacommunicationsbecameimportantwhentherapidtransferofdatabecamebothnecessaryandfeasible.Inotherwords,datacommunicationsemergedasanaturalresultofthedevelopmentofsophisticatedcomputersystems. Bandwidthrequirements—Datainmostinstancesconsistsofpulsetypeenergy.Thedatastreamissimilartoasquarewavesignalwithrapidtransitionsfromonevoltageleveltoanother,withtherepetitionratedependingonthebinaryrepresentationofthedataword.Forinstance,ifan8bitwordhasthevalue01010101,theresultingvoltagewouldappearasaseriesoffoursquarewaveswitheachnegativehalfcycleequaltoeachpositivehalfcycle.If,however,thedatawordhastheform00001111,thevoltagegraphwouldappearasasinglesquarewavewithnegativeandpositivehalfcyclesequalbutlongerthanthefirstexample.Noise—TheShannonHartleylawisrelatedtorandomnoise,butimpulsenoisecanalsobeharmfultosignals.Thesamplingtheorem

CharacteristicsofDataTransmissionCirsuitsshowsthatallvaluesofasignalcanbedeterminedbysamplingthesignalatarateequaltoatleasttwicethebandwidth.Noiseaffectsthissamplingprocessbecausethenoisepulsewillbeinterpretedasadatabit(seeFig.10.1),ifthenoiseimpulseoccursatthetimeasampleistaken,andhasanamplitudeequaltoorexceedingtheminimumlevelrecognizedbythesystemasamark.Thepotentialforimpulsenoisetobecomeasourceoferrorsincreaseswiththenumberoflevelsofeach

CharacteristicsofDataTransmissionCirsuitscodeelement.Toachievethe30880bpsratementionedintheaboveexample,itmaybeshownthatfivelevelswouldberequiredforeachcodeelement.Anoisefreechannelwouldbenecessarytoprecludenoiseinduceddataerrors,butnoisefreechannelsdonotexistinpractice.Itisnoise,amongotherimpairments,whichtendstolimittheactual4kHzchanneldataspeedsto10800bpsorless.Itcanbeshownthatasystemusingathreelevelcodemusthaveasignaltonoiseratioof8.5dB,or3.7dBgreater,forequalperformanceinthesamechannel.Afourlevelcoderequiresasignaltonoiseperformanceof11.7dB.Improvementinthesignaltonoiseratiomakesuseofmultilevelencodingfeasible. Distortion—Communicationchannelstendtoreacttosignalsofdifferentspeedswithintheirpassbandindifferentways.CharacteristicsofDataTransmissionCirsuitsSpecifically,signalsofdifferentfrequenciescanbepassedbythechannelwithdifferentvaluesofamplitudeattenuationandatdifferentpropagationspeeds.Theresultisdistortion.Ofgreatimportancetosystemsusingphasemodulationisphasedelay(orenvelopedelay)distortion.Phasedelaydistortionoccursinachannelwhensignalsofonefrequencyarepassedthroughthecircuitatadifferentspeedthanothersignals.Theresultingdistortioncantaketheformofintersymbolinterference.Sincecharacterswhichhavelowerfrequencycomponentspassatadifferentspeedthandatacharacterswithhighfrequencycomponents,itispossibleinhigherspeedcircuitsforportionsofonecharactertoenterorremaininthetimeslotallocatedtoothercharacters

ExercisesⅠ.PleasetranslatethefollowingwordsandphrasesintoCersymbolinterference7.baudrate8.adaptiveequalization9.frequencycomponent10.echocanceller11.transformerwinding12.audiblespectrum

遠程終端數(shù)據(jù)傳輸信道帶寬信息傳遞國際標準符號間干擾，碼間干擾波特率自適應均衡頻率成分（分量）回波抵消器變壓器繞組聲譜ExercisesⅡ.PleasetranslatethefollowingwordsandphrasesintoEnglish.1.串話2.二進制表示法3.高頻4.期望值5.奈奎斯特速率6.方波信號7.屏蔽電纜8.相位延遲

crosstalkbinaryrepresentationHF(highfrequency)expectationNyquistratesquarewavesignalshieldedcablephasedelayExercises9.數(shù)據(jù)流10.均衡器11.傳輸效率12.雙絞電纜13.電磁交感14.包絡延遲15.海底電纜16.回波抑制器

datastreamequalizertransmissionefficiencytwistedpaircableelectromagneticinteractionenvelopedelaysubmarinecableechosuppressorExercisesⅢ.Fillintheblankswiththemissingword(s).1.Itispossibletoplotthedelaycharacteristicsofthechannelandinsertanequalizerwhichcanbeadjustedtocompensate

for

thedelayabnormalities.2.Theshieldsaregroundedtodrain

of

theinducedsignalsandnoise.3.Informationtransfercanoccuratarateequaltoordifferent

from

thebaudrate.4.Thedatastreamissimilar

to

asquarewavesignalwithrapidtransitionsfromonevoltagelevel

to

another,withtherepetitionratedependingonthebinaryrepresentationofthedataword.5.Thistypeofcrosstalkisreducedusing

by

twistedpaircablesandbalancedcircuitsalongwithshielding.6.However,itisquiteacceptable

for

dedicatedcircuitswithfixedterminations.

Exercises7.Theresultisachannelrelativelyfree

of

phasedelay.8.Thesignalswhichfalloutsidethechannelbandwidthareattenuatedbyfilterssothattheywillnotinterfere

with

othersignals.9.Torelatebaudrate

to

bandwidth,theobservationsofthetwentiethcenturyelectricalengineerNyquistareused.10.Therateofdatatransferdepends

on

severalaspectsofthetransmissionchannel,

of

whichsignalingspeedisveryimportant.11.Inas