Re: OFDM packets

Scrive Eric B. [email protected]:

I use revision 6845 and RFX 2400.

anything else that might be relevant

Thanks,
Eric

Hi, thank you for your reply.
I use:

  • Linux K-Ubuntu 7.04
    *Gnuradio Trunk 6845
    The command are :
    –TX–
    sudo python benchmark_ofdm_tx.py -f 2.442e9 -T A --tx-amplitude 10000
    –RX–> sudo python benchmark_ofdm_rx.py -f 2.4419899e9 -T A
    (occuped tones, size packet and fft are default value)
    Important: If I don’t change Rx frequency it can’t receive!!
    I change the payload. I upload file to the code and I calculate its
    lenght.
    Number packets= (lenght file/ size packets)+1
    Before my modification I tested ofdm system and the result is similar
    then after
    modification.
    The trial simulation (without USRP and antennas) is perfect. I Receive
    all
    packets and they are correct.
    I tested with coax for estimate channel problem but the result is
    similar to
    real channel. I thought the problem was the channel but this experiment
    reject
    my theory.
    I don’t find the problem because my alteration code don’t change the
    core code.

This is my result. final packet

Trial simulation
ok: True pktno: 4609 n_rcvd: 4610 n_right: 4610

bit right 14750243
bit wrong 0.0

All correct

===================================================================================
Coax

ok: False pktno: 4000 n_rcvd: 1300 n_right: 830

bit right 2109817
bit wrong 2050183

Thank you a lot for your help.


Crespi F. wrote:

payload (binary file) and I receive check bit by bit.

which version of GNU Radio? trunk, tarball (which one), etc?

–RX–> sudo python benchmark_ofdm_rx.py -f 2.4419899e9 -T A
(occuped tones, size packet and fft are default value)

That’s a very high amplitude. The PAPR of OFDM will hit you at this
amplitude. Stay between 1000 and 4000.

Important: If I don’t change Rx frequency it can’t receive!!

OFDM is notoriously sensitive to frequency offset. With the RFX2400
boards, the frequency deviation is likely just outside the range we
allow.

Tom