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Re: [Discuss-gnuradio] Re: benchmark_ofdm_rx not working


From: Tom Rondeau
Subject: Re: [Discuss-gnuradio] Re: benchmark_ofdm_rx not working
Date: Tue, 30 Oct 2007 10:50:34 +0000
User-agent: Thunderbird 2.0.0.6 (Windows/20070728)

Archana Ragothaman wrote:


    Archana Ragothaman wrote:
    > Hello,
    >
    > I am using two USRPs rev 4 and two RFX2400. I am basically
    trying to
    > make the USRPs communicate with each other using the
    > benchmark_ofdm_tx.py and benchmark_ofdm_rx.py scripts. The
    commands I
    > am executing are
    >
    > ./benchmark_ofdm_tx.py -f2.4e9 -T A (at one USRP connected to
    laptop)
    >
    > ./benchmark_ofdm_rx.py -f2.4e9 -R A (at the other USRP connected to
    > another laptop)
    >
    > The benchmark_ofdm_tx.py script is working as I can see the packet
    > number displayed(I wrote a print pktno in the script)
    >
    > However the benchmark_ofdm_rx.py script does not give any output. I
    > don't think the rx_callback function is being executed(as the
    packets
    > are printed in that function).
    >
    > Can anyone please help me out and give suggestions as to what the
    > problem could be?
    >
    > Thank you.

    First, try running the benchmark_ofdm_tx on one side and tht
    usrp_fft to
    display the received power at the receiver. What does this look like?

    The problem is likely that you are not transmitting enough power.
    There
    is a --tx-amplitude flag to adjust this. Set it to 2000 - 4000.

    Tom


Hello,

I increased the amplitude to around 3000 on the tx usrp. I also ran the usrp_fft.py on the rx side. I could observe the spectrum of the rx signal which was around 30 dB. So I know that the rx side usrp is able to receive the packets trasnmitted. However, now when I run the benchmark_ofdm_rx.py script on the rx side, I do not see any output. The output that I get is

After rx_callback( ) definition
>>> gr_fir_ccf: using SSE
>>> gr_fir_fff: using SSE
INIT Completed Successfully!!!!
fg=usrp_graph(....) called (comment added for debugging)
gr_buffer::allocate_buffer: warning: tried to allocate
   20 items of size 1600. Due to alignment requirements
   64 were allocated.  If this isn't OK, consider padding
   your structure to a power-of-two bytes.
   On this platform, our allocation granularity is 4096 bytes.
fg.start() (comment added for debugging)
Inside RX _Callback pktno (comment added for debugging)
ok: False        pktno: 58626    n_rcvd: 1       n_right: 0

Only one packet is received after a long time. Could you suggest as to why the output is not displayed?

Try decreasing the bandwidth by increasing the interpolation and decimation rates (and make sure the decimation is half the interpolation value you use). The OFDM system takes quite a lot of resources right now to run, so slowing things down may help.

Unfortunately, the output you've displayed there isn't really showing anything wrong except you're not getting any packets. There's little to go on to help you debug it. Try to run in verbose mode (-v), which will output all of the settings of the (de)modulator.

Tom





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