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Re: [Discuss-gnuradio] OFDM Updates

Subject: Re: [Discuss-gnuradio] OFDM Updates
Date: Wed, 26 Mar 2008 09:26:11 -0500

Hello Tom,

Based on your information below I know the problem will be receiver. However, 
if I want to solve the receiver's problem. Where is the starting point you 
suggestion? From the gnu-radio core part?


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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