Problem of benchmark_ofdm_rx.py. Could not receive

GNU Radio
1

Hi,

I was doing a test using benchmark_ofdm_tx and rx to achieve the ofdm
communication between two USRPs. At first, both USRPs could transmit and
receive correctly. However, after swithing tx/rx part for a few times,
one
USRP suddenly failed in receiving (still can transmit), no matter which
host
PC it connected to. While, the other one still could work both in tx and
rx.
The one could not receive sometimes had “TIME OUT” after I stopped
transmitting on the other side, or sometimes it only displayed a
received
wrong package with a very big packge number, or sometimes it had nothing
to
display.

We tried to switched two daughter boards and the problem was the same,
still
that one could not receive. Here are our test information:

Ubuntu 9.04
gnuradio-3.2.2/gnuradio-examples/python/ofdm/benchmark_ofdm_tx & rx
USRP/RFX2400

run command:

sudo python benchmark_ofdm_tx.py -f 2.45G
sudo python benchmark_ofdm_rx.py -f 2.45G

Is there anyone who can help me with this problem? Thanks in advance!

Sincerely,

Yuan

2

Milo W. wrote:

or sometimes it had nothing to display.

We tried to switched two daughter boards and the problem was the same,
still that one could not receive. Here are our test information:

I’m not exactly sure what you mean by “switching tx/rx part.” Are you
switching which roles the USRPs play?

From what you say below, you’re running the RFX2400 board. This has
caused problems in the past if the oscillator frequency was too far off.
When you multiply this up to 2.4 GHz, it can cause two USRPs that are
nominally at 2.45 GHz to be off by a few kHz. This can be enough to
cause the USRPs to be out of frequency locking range. The oscillator
will also drift with temperature. Since they were working for you
originally, it might be that as they warmed up, they were pushed just
far enough outside the frequency range to become a problem.

Given the information you’ve provided, that’s the best answer I have
right now. Do you have any other daughterboards you can test with? Can
you run other examples that still work?

The “TIME OUT” message comes from the receiver when it correlates to the
access code but isn’t able to get the packets. So it’s seeming
something, just not well enough to fully receive.

Tom

3

Thank you, Tom.

What I mean by “switching tx/rx part” is just to switch the roles of two
USRPs from tx to rx(or inverse).

I only have RFX2400 at hand and I tried 2.45G and 2.5G freq later on. So
far, that one still could not receive the OFDM signal . But I tried
another
scheme (benchmark_tx & benchmark_rx) which performed well. So I could
exclude the possibility of USRP’s hardware problems. But after I
continued
to switched the tx&rx role of USRPs, there’s still one could not receive
unless I power ON and OFF to restart it. That means if I want to switch
the
tx/rx roles, I need to power on/off to get them restart. What’s the
problems
might be?

Thanks,

Yuan