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[Discuss-gnuradio] OFDM Updates

From: Tom Rondeau
Subject: [Discuss-gnuradio] OFDM Updates
Date: Thu, 07 Feb 2008 14:09:58 +0000
User-agent: Thunderbird (Windows/20071031)

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 :)


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