Hey Emmanuela,
As I understand you want to calculate the and plot the power spectral density of complex envelop. I would suggest you to go through the following reasoning.
- Power spectral density of a signal in general can be evaluated by "absolute value squared of the DFT of the signal".
- Complex envelop conceptually is the baseband representation of the passband signal.
With above reasoning taking the absolute value squared of the DFT of the complex would give the PSD of complex envelop without any change with respect to how it is done for any other signal.
I would also suggest you to make use of periodogram from signal processing toolbox from the following link https://www.mathworks.com/help/signal/ref/periodogram.html for easy estimation of PSD.
