Re: [Discuss-gnuradio] OFDM packets

[Crespi Floriana]

Scrive Eric Blossom <address@hidden>:

> On Thu, Feb 28, 2008 at 12:51:18PM +0100, Crespi Floriana wrote:
> > Hi,
> > I have a problem with OFDM system.
> > I transmit OFDM signal at 2.4 GHz, but I receive half of the total packets.
> > Moreover, only half of the packets received are correct.
> > CRC controller is perfect but i want a ber estimate, so I change the
> > payload (binary file) and I  receive check bit by bit.
> > The result of my alteration test is similar than CRC test.
> > I have a lot of frequency offset, therefore I change manually the frequency
> > receiver.
> > I use revision 6845 and RFX 2400.
> > Example with crc:
> > The final packet I receive:
> > ok: False      pktno 4602   n_rcvd 1300       n_right 83
> >
> > Why can't i get all the packets?
> > Could you help me??
> >
> > I'm testing OFDM system without USRP and none of the packets are lost.
> >
> > Thanks a lot.
> >
>
> Hi Crespi,
>
> You have neglected to tell us virtually anything about your problem.
> Could you please tell us:
>
>   which version of GNU Radio?  trunk, tarball (which one), etc?
>   what operating system, distribution and architecture?
>   the command line you issued
>   any modifications you may have made to distributed code?
>   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.
_________________________________________________________________