psd of any signal

How to find psd of any signal and I want the data as frequency(rad/sec) vs power

Answer 1

[Carlos]

Try something like this

N = length(x);
xfft = fft(x);
psdx = (1/(2*pi*N)).*abs(xfft).^2;
freq = 0:(2*pi)/N:2*pi-(2*pi)/N;
plot(freq./pi,10*log10(psdx)); grid on;

Answer 2

[Achintya Roy]

Is there any theory behind this

[Carlos]

http://www.mathworks.es/es/help/signal/ug/psd-estimate-using-fft.html