说明：  用MATLAB产生一个频率为1Hz，功率为1的余弦信源，载波频率为10Hz，显示信号的波形及包络，求出调制信号的功率谱密度，以及相干解调后的信号波形
(A cosine source with 1 Hz frequency and 1 power is generated by using MATLAB. The carrier frequency is 10 Hz. The waveform and envelope of the signal are displayed. The power spectral density of the modulated signal and the waveform of the coherent demodulated signal are obtained.)