USRP1 cannot transmit/receive a OFDM packet discontinuously sometimes

Hi,

My problem is that I try to discontinuously send “a” OFDM packet by
using
time.sleep() on USRP1, but fail to successfully receive this OFDM packet
at
the receiver sometimes.

Brief Setting Description:
Code : gnuradio-example/python/ofdm/benchmark_ofdm_tx{rx}.py
Daughterboard : FLEX900
OS : Ubuntu 8.10
Tx :
send_pkt(data) -> time.sleep(1) -> send_pkt(data) -> time.sleep(1)
->

Rx :
ok = False , pktno = 65537, …
ok = True , pktno = 1 , …

I have surveyed about this discussion on the forum. Using discontinuous
transmission is to ensure the transmitter successly sending a packet and
receiver will receive this packet. And I try this scheme on single
carrier
case like benchmark_tx{rx}.py on digital file, every packet is
successful
receive at receiver. But when changing to OFDM, not every packet is
successful receive.

Is it that fft consumes lots of time and causes the transmitter doesn’t
send
this packet?
I think this is the main different between single carrier and OFDM.

If anyone have any idea about this problem, please let me know.
I am deeply appreciative.

Fisheep


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On Tue, Sep 14, 2010 at 12:52 AM, Fisheep [email protected] wrote:

OS : Ubuntu 8.10
receiver will receive this packet. And I try this scheme on single carrier

Fisheep

Fisheep,

I don’t think anyone has actually tried doing this. I know when Matt
and I put the system together, we were concerned only with the
continuous case. We have some improvements to the OFDM pieces that are
on my todo list, though, and once the continuous case is finished,
we’ll work on the discontinuous. Until then, though, I’m afraid the
only advice I could give would be completely speculative.

My first thought would be to see how the synchronization is behaving;
that’s almost certainly where the problem is. We have the
“gr_plot_ofdm.py” script that helps to visualize what’s happening with
the received symbols (you’ll need to turn logging on and have scipy
and matplotlib installed). Play with that in loopback mode to
understand what you’re seeing, then see what happens with your
over-the-air tests.

If you figure out ways to make it better, I’d love to hear it!

Tom

Hi Tom,

Thanks for your suggestion. I will take your advice and try it out.

But recently I connect two USRP1 with the cable not through the
antennas,
hoping to remove the channel effect in this experiment. At the receiver,
using the usrp_fft.py to observe the spectrum of received signal which
is
discontinuously transmitted from transmitter. The result shows that
sometimes the spectrum doesn’t get rise when transmitter send a
packet.Is it
possible that the transmitted packet doesn’t transmit from USRP1? If
possible, how do I examine this problem?

Sorry, I’m not very expert in hardware implementation, but I will do my
best
to get familiar with USRP.

Fisheep

Tom R. wrote:

Brief Setting Description:

this packet?

the received symbols (you’ll need to turn logging on and have scipy
[email protected]
http://lists.gnu.org/mailman/listinfo/discuss-gnuradio


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