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Re: [Discuss-gnuradio] OFDM Updates

From: Shravan Rayanchu
Subject: Re: [Discuss-gnuradio] OFDM Updates
Date: Wed, 13 Feb 2008 16:56:30 -0600

Hi Tom,

I checked out the latest version of gnuradio from the trunk (svn co
http://gnuradio.org/svn/gnuradio/trunk gnuradio). I am running the
OFDM code on 2 USRP nodes over the air. The nodes are placed pretty
close to each other (a separation of ~1-1.5 meters) but this is what I
get as the output ::

ok: True        pktno: 100       n_rcvd: 60       n_right: 59
ok: True        pktno: 103       n_rcvd: 61       n_right: 60
ok: True        pktno: 105       n_rcvd: 62       n_right: 61

Basically, I seem to completely lose some of the packets in the air.
Of the packets I receive, almost all the packets are received
correctly. Initially, the error rate was too high (The packets were
getting lost and also among the packets received, lot of them were in
errors), so I increased tx-amplitude to ~3000.

Am I using the right version of the code ? Is the tarball release
better to use ? Can you please let me know if there are any parameters
which I need to change ?


On 2/7/08, Tom Rondeau <address@hidden> wrote:
> For anyone working with the OFDM code, my latest check-in to the trunk
> fixes some of the main issues of transmitting over the air. Using
> benchmark_ofdm_rx and benchmark_ofdm_tx on different machines, I am now
> able to successfully capture most packets with any modulation at the
> appropriate signal level.
> I say most packets because there is still an issue involved in the
> receiver where the regenerator signal pops up before the peak detector
> signal resets it and causes a problem in the packet sampler. To see what
> I mean, run
> "benchmark_ofdm.py --log"
> And look at the output of the regen and peak detector blocks:
> gr_plot_char.py ofdm_sync_pn-regen_b.dat ofdm_sync_pn-peaks_b.dat
> This will plot a series of 0's with a few 1's, where the peaks occur.
> The peak detector sends it out once, and then the regenerator takes
> over. For every packet, there is one output of the peak detector. If you
> look, sometimes the peak detector will hit just after a regenerated
> signal. By this point, it's too late and the ofdm_sampler has already
> triggered off of the regen signal and ignores the peak.
> It's a bit of a hassle, but I'll look into it soon. Any help is
> appreciated, though :)
> Tom
> _______________________________________________
> Discuss-gnuradio mailing list
> address@hidden
> http://lists.gnu.org/mailman/listinfo/discuss-gnuradio

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