Here's an image of the BER vs. SNR plot plotted along with the theoretical BPSK line. http://www.flickr.com/photos/gallamine/5580109538/
<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? Thanks. -William On Tue, Mar 29, 2011 at 7:52 PM, William Cox <wc...@ncsu.edu> wrote: > Newbie here. I have some questions regarding the example programs under > gnuradio-examples/python/digital-bert. I just ran a link and swept my signal > power. I recorded the estimated snr and ber and I'm trying to plot them and > verify things are working properly. Is the SNR estimation done at baseband > or passband? When I plot the theoretical BPSK snr vs. ber curve, there's a > significant offset between my experimental data and theoretical plot (and > yes, I'm ignoring SNR values below 7 dB). Also, a more basic question is > what is the best method to find documentation for the code? The class > documentation under the wiki seems rather overwhelming and I have a hard > time finding what I need. > > My second question is how the BER is calculated? I'm seeing values < 1e-11. > But this is entirely unreasonable, as I'd have to be sending > 100 gb of > data to be getting a BER close to that value. Looking at the code, its not > clear to me over what packet size the BER is calculated and what the actual > BER confidence value should be. > > Thanks for any help that can be offered. > -William > >
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