Matlab power spectrum density(PSD) implement equation

Question

Folks, I am learning how to calculate PSD of a signal with matlab. I know function Periodogram() works good, but I want to use fft method directly. When I want to learn in detail, I find this website is very helpful:

https://www.mathworks.com/help/signal/ug/power-spectral-density-estimates-using-fft.html

However, I have a problem in the first example. I am a little confused about this statement

psdx = (1/(Fs*N)) * abs(xdft).^2;

I don't know why using Fs and N as parameter.

Answer 1

The (1/(Fs*N)) is a normalization factor to ensure that the numerical algorithm complies with Parseval's Theorem.