how to calculate signal power spectrum density(PSD) in dB in frequency domain ?

Hi Everyone ,

I have signal in time domain as data with two columns t(ns)=data(:,1) and signal=data(:,2). my signal period is from 0.6 (ns) to 2.4 (ns). I have used FFT to convert it to frequency domain in order to get PSD (dB). Please help me to get power of signal . One more Question , If my signal has period of 2.4 ns -0.6 ns = 1.8 ns and as Fc=1/t then Fc=1/1.8 ns = 555.5 MHz . is this frequency similar to center frequency in FFT plot ?

Fs = 8e9; (chose for testing but my Fc is 4.0GHz)

time=data(:,1);

x=data(:,2);

E=abs(x.^2); a=0.6e-9; b=2.4e-9; N=0.5e-9:2.4e-9; delta=b-a/N;

pow=sum(E)*delta/1.8e-9; power=sum(E);

%pow_db=mag2db(pow); Fs = 8e9; %t = 0:1/Fs:1-1/Fs; Power = (1/20)*sum(x(1:20).^2) xdft = fft(x); xdft = xdft(1:length(x)/2+1); xdft(2:end-1) = 2*xdft(2:end-1); psdest = 1/(length(x)*Fs)*abs(xdft).^2;<<<<<<<<http://mathworks.com/matlabcentral/images/surf.gif>>>>>>>> freq = 0:Fs/length(x):Fs/2;

figure(1) plot(time,x); xlabel('Time(ns)'); ylabel('Amplitude'); grid on;

figure(2) plot(freq,10*log10(psdest)); xlabel('Frequency (GHz)'); ylabel('Magnitude'); grid on;

*******Plot links of signal in Time Domain **********************

<file:////lsbu.ac.uk/EagleDFS-UsersG/g/gh/ghafarim/My%20Pictures/Output_signal.JPG>

*******Plot link of FFT of time Domain signal ********************** <file:////lsbu.ac.uk/EagleDFS-UsersG/g/gh/ghafarim/My%20Pictures/FFT%20_%20freqency%20Domain.JPG>