产生一个高斯白噪声
利用MATLAB自带的fir1函数产生一个低通滤波器，限制高斯白噪声的带宽，由此产生了视频噪声。
利用产生的视频噪声，分别代入噪声调幅干扰的时域表达式，并且进行100次的积累后求平均值，对其进行快速傅里叶变换后，由此画出噪声调幅干扰的频域波形。
重复上述步骤，分别代入噪声调频干扰与噪声调相干扰的时域表达式，分别画出其频域波形与时域波形。(Generate a Gauss white noise
The fir1 function of MATLAB is used to generate a low-pass filter, which limits the bandwidth of Gauss white noise, and thus produces video noise.
Using the generated video noise, the time domain expressions of noise amplitude modulation interference are substituted, and the average value is calculated after 100 times accumulation. After fast Fourier transform, the frequency domain waveform of noise amplitude modulation interference is drawn.
Repeat the steps mentioned above, and substitute the time-domain expressions of noise FM interference and noise coherent interference, and draw the frequency-domain waveform and time-domain waveform respectively.)