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Re: [Discuss-gnuradio] Implementing digital-bert with UHD

From: Daniel Bartel
Subject: Re: [Discuss-gnuradio] Implementing digital-bert with UHD
Date: Wed, 6 Apr 2011 22:18:13 +0200

Thanks for your reply...

> Perhaps you are in a particularly bad multipath environment? Although I agree 
> that changing the power should have more than a tenth of a dB effect on the 
> SNR. Have you tried turning it down? Or really, can your plot the spectrum at 
> the receiver and verify that the power is actually changing?
It actually turned out, that I've forgotten to specify the right antenna on my 
UHD sink/soure and therefore was receiving cross talk from the second channel.
I'm still a freshman on GNUradio :-).

> Also, the SNR estimator in gr_probe_mpsk_snr_c is not the most robust 
> estimator at low SNR. It gets biased when calculating the mean by any samples 
> over the decision boundaries with the effect of having an "irreducible" SNR 
> (that's not really the right word for it, but I'm relating it to being the 
> opposite of an irreducible BER in multipath channels). But I think this point 
> is around 3 - 4 dB, but it's been a while since I've looked at it.
> This reminds me that I have three other SNR estimators that do an excellent 
> job at low SNR (theoretically, in the mythical AWGN channels) that I really 
> need to put into GNU Radio. They are increasingly better at their estimates 
> at the expense of computational complexity (e.g., one uses the skewness while 
> another uses the kurtosis). 
Would be a nice move...


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