电子科技大学：《无线系统中的微波与射频 Microwave and RF Design in Wireless Systems》课程教学资源（课件讲稿）ch09 Modulation Techniques 调制技术

●●● ●●●● 1.Signal-Sideband Modulation ●●●●● ●●●0 ●●●●● f(切 cosunt ●●●0 ●●●● MAAAAA ● PAv(1)=[A+f(t)]cos@t Ao+f(t) Modulation index: A0 调制指数 0 Am 中4w(o)=πA[δ(0+0）牛8(0-0)] 阝AM A ↓Fla +与F(oyF(0-o〗 USB LSB LSB USB 12

1. Signal-Sideband Modulation 0 0 ( ) [ ( )]cos AM  t A ft t    00 0 ( ) [ ( ) ( )] 1 [ ( ) ( )] 2 AM c c A F F                  USB LSB LSB USB Modulation index: 调制指数 0 m AM A A   12

●●● ●●●● 1.Signal-Sideband Modulation ●●●●● ●●●● DSB SSB ●0 m() vi(t) v(") v.(r) SoN。 Sideband F Baseband filter no/2 filter filter (AGWN) SSB modulator Channel receiver SSB demodulator m(t):bandlimited modulating waveform限制调制波形 f:the maximum frequency最高频率ofm() m(t)=cos2πfmt0≤fm≤fM n/2:two-sided power spectral density of Gaussian white noise. Contributed by the transmitter channel and noise generated by the input stages of the receiver.高斯白噪声的双边带功率谱密度， 它由发射通道和接收机输入级的噪声产生。 13

1. Signal-Sideband Modulation m(t): bandlimited modulating waveform限制调制波形 fM: the maximum frequency 最高频率of m(t) ( ) cos 2 0 m t m mM    f t f f n 0/2: two-sided power spectral density of Gaussian white noise. Contributed by the transmitter channel and noise generated by the input stages of the receiver.高斯白噪声的双边带功率谱密度， 它由发射通道和接收机输入级的噪声产生。 13

●●● The demodulator LO is identical in frequency and phase ●●●● ●●●● ●●0 with the modulator--synchronous or coherent demodulator) ●●●●0 ●●●0 解调器的本振与调制器同频同相，或者说相干。 ●●●色 ● v (1)=Acos(@+@)t+n(t) n(t)=x(t)cos@urt-y(t)sin@irt cosacosB=cos(a+B)+cos(a-B)/2 v (t)=v,(t)cos@t cos2a=(1+cos2a)/2 sin2a =2sinacosa A A ccos() +x(I+cos2@rt)-y(I)sin2@rl Out oftheLBF:()cos+x() 14

The demodulator LO is identical in frequency and phase with the modulator -- synchronous or coherent demodulator) 解调器的本振与调制器同频同相，或者说相干。 14 ( ) cos( ) ( ) ( ) ( )cos ( )sin i IF m IF IF v t A t nt nt xt t yt t                2 cos cos cos cos / 2 cos 1 cos2 / 2 sin 2 2sin cos                  1( ) ( )cos cos cos(2 ) 2 2 1 1 (1 cos2 ) ( )sin 2 2 2 i IF m IF m IF IF vt vt t A A t t x t yt t           0   1 ( ) cos 2 2 m A Out of the LBF: v t t xt   

●●●】 ●●●● ●●●● Input signal power:S,=42/2 ●●●● ()=4 ●●●● Output signal cos.1+2 ●●●● ● power: Input narrowband y-6nio=Foy+55rog noise power: =E{x2(t)}=E{y2(t)} Output noise power: The output SNR: So S, No Ni Conclusion:SSB demodulator does not degrade the input SNR 结论：单边带解调器并不恶化输入的信噪比。 15

Input signal power: Output signal power: Input narrowband noise power: Output noise power: The output SNR: Conclusion: SSB demodulator does not degrade the input SNR. 结论：单边带解调器并不恶化输入的信噪比。 15 2 / 2 i S A  2 2 0 1 ( ) 22 8 4i A A S S    0 1 ( ) cos 2 2 m A v t t xt    222 2 2 1 1 { ( )} { ( )} { ( )} 2 2 { ( )} { ( )} N En t Ex t Ey t i Ex t Ey t     2 2 0 1 1 {[ ( )] } { ( )} 24 4Ni N E xt E x t   0 0 i i S S N N 

●●● w=2x()=nof ●●●● ●●●●● ●●●0 ●●●●0 ●●●0 ●●●● ● fie fir -ftg-fM fie+fu (a) ASN N1 =4fu no noJM 8 2 客 -2f fufu 2fiF -2所e-M 2fF +fM (b) 5w。 =2(g）= noJM 8 -fM (c) N=2=w So S.14S.S. N。N,/4N, nofu 16

16 0 0 2 2 i MM n N f nf   0 0 0 / 4 / 4 i ii i iM SS S S N N N nf  