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单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,8,Communication systems,8.1,Complex Exponential and Sinusoidal,Amplitude Modulation,Modulating system model:,8.,Communication Systems,x(t),c(t),y(t)=x(t)c(t),x(t)-modulating signal,c(t)-Carrier signal,8,Communication systems,8.1.1,Amplitude Modulation with Complex,Exponential Carrier,Exponential carrier:,For convenience,let,c,=0,so,Output signal,(modulated signal),:,(1)Modulation Theory,8,Communication systems,8,Communication systems,(1)Implementation,8,Communication systems,8.1.2,Amplitude Modulation with Sinusoidal signal,For convenience,choose,c,=0,so,8,Communication systems,D,ouble,S,ide,B,and,S,ingle,S,ide,B,and in Problem 8.28.,8,Communication systems,8,Communication systems,8.2,Demodulation for Sinusoidal AM,8.2.1,Synchronous demodulation,(1),Demodulation process,8,Communication systems,In frequency domain:,In time domain:,Expected signal:,8,Communication systems,8,Communication systems,(2),Synchronous problem,8,Communication systems,Time domain:,The output of,lowpass,filter:,Ideal output:x(t),When,it is referred to as synchronous,demodulation.,8,Communication systems,8.2.2,Asynchronous demodulation,Amplitude-modulated signal:,8,Communication systems,Asynchronous demodulator,
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