# M2m4 SNR estimator off by 3 dB **URL:** \ **Category:** GNU Radio\ **Created:** [August 27, 2014, 6:34pm UTC](https://www.ruby-forum.com/t/m2m4-snr-estimator-off-by-3-db/234818 "2014-08-27T18:34:45Z")\ **Posts on this page:** 5\ **Page:** 1
**Author:** ![addis\_a](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/a/c4cdca/32.png) [@addis\_a](https://www.ruby-forum.com/u/addis_a)\ **Post date:** [August 27, 2014, 6:34pm UTC](https://www.ruby-forum.com/t/m2m4-snr-estimator-off-by-3-db/234818/1 "2014-08-27T18:34:45Z")
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**Author:** ![jared](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/848f3c/32.png) [@jared](https://www.ruby-forum.com/u/jared)\ **Post date:** [August 28, 2014, 4:05pm UTC](https://www.ruby-forum.com/t/m2m4-snr-estimator-off-by-3-db/234818/2 "2014-08-28T16:05:54Z")
On Wed, Aug 27, 2014 at 9:33 AM, Jared D. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > 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 ---
**Author:** ![jared](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/848f3c/32.png) [@jared](https://www.ruby-forum.com/u/jared)\ **Post date:** [August 28, 2014, 5:53pm UTC](https://www.ruby-forum.com/t/m2m4-snr-estimator-off-by-3-db/234818/3 "2014-08-28T17:53:41Z")
On Thu, Aug 28, 2014 at 7:04 AM, Tom R. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > ``` > > return 10.0*log10(2.0*sqrt(2*y1_2 - d_y2) / > > > > ``` > > > > with AWGN, measuring the signal and noise powers separately while > > 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 Just tested this and it looks fine the way it is. Are you doing real or complex signals? The estimators are designed to work with complex numbers, so that might be the difference you’re seeing. I just have a simple simulation that I can switch between BPSK and QPSK (both complex signals, though). I use the MPSK measurement block and calculate the power of the signal and noise separately and output that to a number sink. With the current method, I see the same SNRs on both paths. There is also the gr-digital/examples/snr\_estimators.py example you can explore to compare them. Tom ---
**Author:** ![jared](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/848f3c/32.png) [@jared](https://www.ruby-forum.com/u/jared)\ **Post date:** [August 28, 2014, 7:48pm UTC](https://www.ruby-forum.com/t/m2m4-snr-estimator-off-by-3-db/234818/4 "2014-08-28T19:48:09Z")
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**Author:** ![jared](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/j/848f3c/32.png) [@jared](https://www.ruby-forum.com/u/jared)\ **Post date:** [August 29, 2014, 12:11am UTC](https://www.ruby-forum.com/t/m2m4-snr-estimator-off-by-3-db/234818/5 "2014-08-29T00:11:13Z")
On Thu, Aug 28, 2014 at 10:46 AM, Jared D. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > get 10 dB SNR. This seems consistent with the extra 2 x factor in the > flowgraph so I could compare with mine? > > Thanks, > Jared. Ah, I’ve found the mistake in my tests. I was averaging the signals at the wrong place. Threw together the flowgraph too quickly this morning. (There’s actually a funny story here, but I don’t want to embarrass the person; so I’ll take on the embarrassment myself for not double checking things myself.) This identified that I was making similar mistakes with the other estimators – I would have forced them all to the same results and must have based it on a bogus starting target. I’ll check in corrections soon, tomorrow hopefully. The skewness estimator is giving me trouble for non-binary psk signals, though. Tom