How to add awgn noise to a signal in Fourier domain for given SNR I want to know the equations required to add awgn noise to a signal in Fourier domain for different SNR values. I know the procedure in time domain but not able to do the same in  frequency domain for the signal $x(t) = e^{2 \pi j f t}$ .

Thank you
Since the Fourier transform (and its discrete version) is linear, there is literally no difference in the way you do this in time and frequency domain: 

You observe the energy in your signal, set the Gaussian's variance according to the desired SNR, and add the noise. Not a single flop was given about in which domain you were that day!