Power Density Spectrum (PDS)

The power density spectrum is given by ${\Gamma }_{xx}(f)$, which is defined by

$${\Gamma }_{xx}(f)=\sum _{l=-\infty }^{\infty }{\gamma }_{xx}[l]e^{-j2\pi fl}$$

A measure of a signal’s power content versus frequency. ${\gamma }_{xx}$ is the Autocorrelation. It is also possible with Crosscorrelation power density spectrum.

It is the z transform of the Autocorrelation evaluated in $z=j2\pi f$ (unit circle).