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