中文说明：
利用FFT估计正弦信号的频率,要估计一个叠加了高斯白噪声的正弦信号 的频率 ，可以通过对x(n)做傅里叶变换，得到频谱图，找出幅度的最大值对应的频率值 ，进行多次变换，求出均方误差 。改变信噪比SNR，通过仿真可以得出随着信噪比增加，均方误差减小。
English Description：
FFT is used to estimate the frequency of sinusoidal signal. In order to estimate the frequency of a sinusoidal signal superimposed with Gaussian white noise, we can do Fourier transform on X (n) to get the spectrum, find out the frequency value corresponding to the maximum amplitude, and carry out multiple transformations to get the mean square error. By changing SNR, the simulation results show that with the increase of SNR, the mean square error decreases.