I've been comparing the m2m4 algorithm from the Norman Beaulieu paper "A Comparison of SNR Estimation Techniques" to what is implemented in the mpsk_snr_est.cc file. I see two implementations of the algorithm in that file, one of which looks perfectly in-line with the paper and the other does not. I am having issues producing proper noise power estimates using the MPSK SNR Estimator Probe block, so it forced me to dig into this stuff.
The algorithm that does not match the paper, is what is actually used in gnuradio, so I'd like to discuss this. The two different implementations are in the mpsk_snr_est.cc file and are defined in two different functions
1) mpsk_snr_est_m2m4::snr()
2) snr_est_m2m4::snr()
The algorithm in 1) is what is instantiated and used referring to the set_type() function defined in probe_mpsk_snr_est_c_impl.cc.
The problem with 1) is that it uses equation 39 from the paper, which represents SNR and concluded the Signal power must be the numerator and the noise power must be the denominator. This is not necessarily true, because much simplification has occurred to produce that SNR equation. The algorithm in 2) does not make this mistake and is what I believe should be used.
As far as I can tell, 2) snr_est_m2m4::snr never gets used. This happens to be the algorithm that agrees with the paper perfectly. What is going on here, is this a place holder or can this be used without re-compiling GNU Radio?