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Re: [Discuss-gnuradio] Re: questions on SNR estimation from digital-bert

From: Alexandru Csete
Subject: Re: [Discuss-gnuradio] Re: questions on SNR estimation from digital-bert examples
Date: Fri, 1 Apr 2011 20:52:05 +0200

On Fri, Apr 1, 2011 at 7:07 PM, William Cox <address@hidden> wrote:
> Here's an image of the BER vs. SNR plot plotted along with the theoretical
> BPSK line.
> http://www.flickr.com/photos/gallamine/5580109538/
> You can see that the experimental data is 3-4 dB greater than the
> theoretical BPSK values.
> My setup looks like:
> GNURadio -> USRP -> LED -> water -> photodiode -> USRP -> GNURadio.
> I'm using the "benchmark_tx.py" and "benchmark_rx.py" code with default
> settings. Carrier is 5e6 hz and rate is 1e6 symbol/sec. Decimation at the
> receiver is 32.
> Above 12 dB the BER values saturate down at 1.85e-11.
> Any ideas why the experimental results are so far off theoretical?

Hi William,

What would you consider to be a reasonable deviation from the theoretical value?
In my limited experience, 3-4 dB "implementation loss" is not that bad
when using hardware and software that haven't been tuned and optimized
for the specific purpose.
Also note that you compare your results with the theoretical values
for transmission over an AWGN channel
http://en.wikipedia.org/wiki/AWGN - does water qualify as such?


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