On Wed, Aug 27, 2014 at 9:33 AM, Jared Dulmage <[email protected]>
wrote:
> It appears that the MPSK m2m4 SNR estimator has an extra factor of 2.
>
> gnuradio/gr-digital/mpsk_snr_est.cc:169:175
> double
> mpsk_snr_est_m2m4::snr()
> {
> double y1_2 = d_y1*d_y1;
> return 10.0*log10(2.0*sqrt(2*y1_2 - d_y2) /
> (d_y1 - sqrt(2*y1_2 - d_y2)));
> }
>
> where d_y1 and d_y2 are the running 2nd and 4th moments of the input,
> respectively.
>
> The 2.0* is not present in the estimate expression from the reference
> (Pauluzzi and Beaulieu eq. 39).
>
> The 3 dB offset can also be seen by generating a signal (say random BPSK)
> with AWGN, measuring the signal and noise powers separately while
> estimating the SNR via the m2m4 on the sum.
>
> It's an easy fix, I just wanted to get verification and notify other users.
>
> Thanks,
> Jared.
>
Hi Jared,
I'd have to review the paper again, but I suspect you're right. I was using
this estimator just the other day and scratching my head about the results.
I was on a plane, though, and was really focused on something else.
Thanks!
Tom
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