I finally got to this point that if one need to measure SNR, it means that he/she has to eliminate all the other channel effects as well as receiver uncertainties, (like fading, shadowing, Doppler shift, carrier frequency and phase offsets etc.) to have a correct estimate of SNR. Otherwise, he/she coudln't obtain signal-to-noise power ratio.
Remember the received signal formulation I mentioned before:
y(t) = h(t) * x(t) + n(t).
Thank you all. Any interesting ideas would be appreciated.