clc
clear
Fs=500;
N=128;  %采樣點%
n=1:1/Fs:2;
F=0:Fs/N:1000;  %分辨率是Fs/N%
Xn=(200.^0.5)*sin(2*pi*60*n)+(2.^0.5)*sin(2*pi*200*n)+randn(size(n));
nfft=1024;
window=chebwin(256); %采用chebyshev窗%
noverlap=128;   %混疊分段點數(shù)128%
[Pw,f]=pwelch(Xn,window,noverlap,nfft,Fs);
plot(f,10*log10(Pw),'k');
ylabel('PSD'); 
xlabel('Freq Hz');