说明：  基于Matlab对模拟调制系统及解调过程进行仿真，调制信号自定，调制信号频率为2kHz，载波c(t)=cos2πf_c t，f_c=20kHz，利用幅度调制AM进行调制和解调。
(The analog modulation system and demodulation process are simulated based on MATLAB. The modulation signal is self-determined. The frequency of the modulation signal is 2KHz,and the carrier C(T)=Cos2*pi* f_c(t),f_C = 20kHz,amplitude modulation AM is used for modulation and demodulation.)