I figured out what was causing my numbers to be incorrect using M2M4. I was overlooking the fact that I was injecting noise at sample rate, but estimating noise power and a decimated rate. Once I took this into account, the estimate was in line with what I expect.
I have not reconciled the difference between the paper algorithm and implemented gnuradio algorithm, but that will have to wait for another day, since it seems to work for now. Rich On Tue, Oct 13, 2015 at 6:10 PM, Richard Bell <[email protected]> wrote: > 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? > > Thanks, > Rich >
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