On Mon, Jan 30, 2012 at 11:12 AM, Martin Braun
<address@hidden> wrote:
On Mon, Jan 30, 2012 at 04:11:05PM +0100, Florian Schlembach wrote:
> We have now extended our tests to the tests with two USRP2s with
> daughterboards: Neither the benchmark_tx.py example nor the tunnel.py is
> receiving any packets. We checked the spectrum and tuned the gains as well.
> (OFDM)
>
> Now, we played with the benchmark files and tunnel.py located in the narrowband
> folder and therefore changed the modulation scheme from BPSK to GMSK and
> ultimately receiving all the packets!! That's strange.
>
> Does anybody knows what code be the problem that we can't establish any
> connection using higher order modulation schemes? Could it possibly be our
> slightly outdated UHD version?
>
> We are totally clueless, so we appreciate any idea/help!
This won't really help, but I remember we had exactly the same troubles here.
This was before UHD was even released, so I doubt that's the reason.
Unfortunately, I can't remember how (or: if) we fixed it :( but I'll
keep you updated if my memory comes up with something.
But fiddling with gain values is often useful; even if you've already
done that I recommend trying again, by reducing tx-amplitude and the
actual gain values, shifting the terminals around (perhaps they're too
close?).
MB
The benchmark OFDM scripts were made as simple examples of OFDM and were not made very robust. I can get them working within an office space fairly easily, but I seem to be the only one. When I moved everything over the using the UHD interface, I tested everything OTA successfully, so they do still work.
One thing that I noticed was that the --tx-amp=0.8. That's very high for OFDM with it's large PAPR. Try backing off on that (to around 0.2 - 0.3) and try again. You won't get much range from this signal, though.
Tom