Calculation of SNR for a particular modulation scheme

Hi everyone

Could anyone hint me on how to find the SNR for a particular modulation
Basically i want to plot the BER v/s SNR curve for gmsk modulation
scheme on a particular link.
I have been successful enough to find BER but cant figure out a way to
find the SNR.
Should I use the FFT way…by calculating the Power spectral density in
matlab and then integrating?..
Or RMS value of the signal can be used (after subtracting the noise)?..

Kindly suggest something if anyone can,
thanks already…
Rashi Dixit

I have built a lower-bit quantization scheme in the rx_bufffer.v using
4-bit samples, storing one byte for each clock sample (for both I and Q)
and then filling up the 16-bit FIFO with another 8 bit value coming from
the next clock sample.

Whan I did some tests and plotted the results everything looked fine,
like frequency and sahpe of the waveform, I could see though some spikes
equal to a value of 1. This is coming from the rounding effect which I
have not removed. When I do remove that then the spikes become more (in
population not in amplitude) and then I had a look and I saw in the list
that there is a DC offset that causes that?

Can anyone advice me how to get rid of these spikes?

Thank you