Odd behavior on new ofdm_benchmark_* code

Hello all,

Running the new ofdm benchmark code doesn’t seem to be working quite
right. I only receive packets when I start the rx side while the tx side
is already running, and even then I receive:

on one:
$ python benchmark_ofdm_tx.py -f 907M

on the other:
$ python benchmark_ofdm_rx.py -f 907M

ok: False pktno: 69 n_rcvd: 1 n_right: 0
ok: False pktno: 79 n_rcvd: 2 n_right: 0
ok: False pktno: 83 n_rcvd: 3 n_right: 0
ok: False pktno: 97 n_rcvd: 4 n_right: 0
ok: False pktno: 111 n_rcvd: 5 n_right: 0
etc…

Restarting the tx side yields more received packets. However if the rx
side is ever started when the tx side is not running, nothing ever gets
received. Benchmark_loopback, the old benchmark_ofdm_* code and the new
and old digital benchmark_* programs all run perfectly with these two
computers/usrps. Any suggestions?

Thanks,
Dev R.

Dev R. wrote:

$ python benchmark_ofdm_rx.py -f 907M
gets received. Benchmark_loopback, the old benchmark_ofdm_* code and
the new and old digital benchmark_* programs all run perfectly with
these two computers/usrps. Any suggestions?

Thanks,
Dev R.
Dev,

We’re still working on this code. I don’t have much time to work with
two USRPs where I am right now, so I’ve only been working in the
loopback case and not over the air. In loopback mode, things look good
under various SNRs, frequency offsets, and multipath conditions. There
is a problem with the reciever locking up under certain conditions
because of the peak detector. In loopback, this is with a low SNR, so no
signal would probably trigger this pretty quickly. We have a possible
solution for this, but I don’t know when I’ll have time to work on it.

The other things to look at is the transmit power, decimation rate, and
interpolation rates. Scale the power so you have enough signal strength
at the receiver but not so much that you start clipping (remember the
high peak to average power ratio in an OFDM signal). I think we found
~2000 for --tx-amp was ok.

Tom

Tom,

Ok, thanks for the note and the ofdm code in general. I’ll continue
using the old version in my research for now and will see if I can help
debug the new version.

Dev