无线通信原理与应用-第二章传输技术基础ppt课件.ppt

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1、TransmissionFundamentalsChapter2ElectromagneticSignalFunctionoftimeCanalsobeexpressedasafunctionoffrequencySignalconsistsofcomponentsofdifferentfrequenciesTime-DomainConceptsAnalogsignal-signalintensityvariesinasmoothfashionovertimeNobreaksordiscontinuitiesint

2、hesignalDigitalsignal-signalintensitymaintainsaconstantlevelforsomeperiodoftimeandthenchangestoanotherconstantlevelPeriodicsignal-analogordigitalsignalpatternthatrepeatsovertimes(t+T)=s(t)-¥

3、alogordigitalsignalpatternthatdoesn'trepeatovertimePeakamplitude(A)-maximumvalueorstrengthofthesignalovertime;typicallymeasuredinvoltsFrequency(f)Rate,incyclespersecond,orHertz(Hz)atwhichthesignalrepeatsTime-DomainConceptsPeriod(T)-amountoftimeittakesforonerep

4、etitionofthesignalT=1/fPhase()-measureoftherelativepositionintimewithinasingleperiodofasignalWavelength()-distanceoccupiedbyasinglecycleofthesignalOr,thedistancebetweentwopointsofcorrespondingphaseoftwoconsecutivecyclesSineWaveParametersGeneralsinewaves(t)=A

5、sin(2ft+)Figure2.3showstheeffectofvaryingeachofthethreeparameters(a)A=1,f=1Hz,=0;thusT=1s(b)Reducedpeakamplitude;A=0.5(c)Increasedfrequency;f=2,thusT=½(d)Phaseshift;=/4radians(45degrees)note:2radians=360°=1periodSineWaveParametersTimevs.DistanceWhentheho

6、rizontalaxisistime,asinFigure2.3,graphsdisplaythevalueofasignalatagivenpointinspaceasafunctionoftimeWiththehorizontalaxisinspace,graphsdisplaythevalueofasignalatagivenpointintimeasafunctionofdistanceAtaparticularinstantoftime,theintensityofthesignalvariesasafu

7、nctionofdistancefromthesourceFrequency-DomainConceptsFundamentalfrequency-whenallfrequencycomponentsofasignalareintegermultiplesofonefrequency,it’sreferredtoasthefundamentalfrequencySpectrum-rangeoffrequenciesthatasignalcontainsAbsolutebandwidth-widthofthespec

8、trumofasignalEffectivebandwidth(orjustbandwidth)-narrowbandoffrequenciesthatmostofthesignal’senergyiscontainedinFrequency-DomainConceptsAnyelectromagneticsignalcanbeshowntoconsisto