通信原理(英文版)ppt課件

1、Figure 3.1.1 ModulatorModulatorModulatedsignal s(t)Modulating signal m(t)cos()(00tAtc1;.2;.(a) Frequency spectral density of input signalS (f)f0f-f00M(f)f0(b) Frequency spectral density of output signal( )( )m tM f)(cos)(0fStAtm)()(2)(00ffMffMAfS H(f)s (t)Modulated signals(t)Modulatingsignalm(t)Acos

2、 0t3;.m (t)101+m (t)101+m (t)4;.Figure 3.2.3 Waveform and spectrum of modulated signalm(t)s(t)M(f)C(f)c(t)A-Atfm-fmf0-f02 fmS (f)2 fm-f0f0ffftt5;.ttnttnAtmtysc00sin)(cos)()( 1)(ttnttnsc00sin)(cos)()()()( 1)(22tntnAtmtVscy)()( 1 )(tnAtmtVcyRectifierLow-pass filterFigure 3.2.4 Envelope detector6;.)()(

3、 )(tnAtmtvc)(/)(2220tnAtmErc)(/)( 121222tnAtmEri222222220)( 1 )(2)(/)( 121)(/)(tmtmEtnAtmtnAtmErrci7;.M(f)f0f00-f0fS(f)(a) Frequency spectral density of modulating signal Figure 3.2.5 Spectrum of double-sideband modulation signalU p p e r -sideband(b) Frequency spectral density of modulated signalU

4、p p e r -sidebandL o w e r -sideband8;.ttm0cos)()cos(0t)2cos()cos(21)cos(cos)()(000tttmtttmtr)cos()(21ttmFigure 3.2.6 Block diagram of DSB signal demodulatorBaseband signalm(t)Received signals(t)cos0tr (t) H(f)9;.Figure 3.2.7 Frequency spectrum of single-sideband signal(b)Upper-sideband filter chara

5、cteristic and signal frequency spectrumf00f-f00ff0-f0HH(f)HH(f)S(f)U p p e r -sidebandU p p e r -sideband(c)Lower-sideband filter characteristic and signal frequency spectrum-f0f0fHL(f)S(f)L o w e r-sideband(a)Signal frequency spectrum before filteringU p p e r -sidebandS(f)U p p e r -sidebandL o w

6、e r-sideband10;.Figure 3.2.7 Frequency spectrum of single-sideband signal(b) Upper-sideband filter characteristic and signal frequency spectrumf00f-f00ff0-f0HH(f)HH(f)S(f)U p p e r -sidebandU p p e r -sideband(c) Lower-sideband filter characteristic and signal frequency spectrum-f0f0fHL(f)S(f)L o w

7、e r -sideband(a) Signal frequency spectrum before filteringU p p e r -sidebandS(f)U p p e r -sidebandL o w e r -sideband11;.)()(2)(00ffMffMAfSs (t)A Acoscos 0 0t tH H( (f f) )DemoduDemodulated lated signalsignals s( (t t) )Modulating Modulating signalsignalm m( (t t) )()()(2)(00fHffMffMAfS12;.Baseba

8、nBaseband d signalsignalm m( (t t) )ReceivReceived ed signalsignals s( (t t) )coscos 0 0t tr (t) H H( (f f) )()(2100ffSffS)()()(2)(00fHffMffMAfS)()()2()()()2(40000ffHfMffMffHfMffMA)()()(400ffHffHfMA13;.)()()(400ffHffHfMACffHffH)()(00mfffM當(dāng), 0)(mffCffHffH,)()(0014;.H(f + f0)-(f0+fm)0000ffff0-f0f0+fm-

9、2f02f0-2f02f0fm-fmfmfH(f)H(f - f0)H(f + f0) + H(f f0)mffCffHffH,)()(0015;.)cos()(cos)(00tAtAtcdttdti)()(0)()(dttti16;.)cos()(cos)(00tAtAtc00( )( )pttk m t00( )cos( )pps tAtk m t)(t)0tmdtdkpi（17;.)()(0tmktfi000)()()(dttmktdtttfi)(cos)(00dttmktAtsff18;.19;. i20;.ttmmcos)(tktmktmfficos)()(00sin)/(coscoscos)(00ttAtdtktAtsmmmffmfmmfkffm21;.sin)/(coscoscos)(00ttAtdtktAtsmmmff)3cos()3)cos()2cos()2)cos()cos()cos(cos)()(00300200100ttmJttmJttmJtm