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Re: [Discuss-gnuradio] OFDM / DAB demodulation

From: Jens Elsner
Subject: Re: [Discuss-gnuradio] OFDM / DAB demodulation
Date: Sun, 2 Apr 2006 09:28:54 +0200
User-agent: Mutt/1.3.28i

On Sat, Apr 01, 2006 at 01:59:09PM -0800, Matt Ettus wrote:
> Jens Elsner wrote:
> > I resampled all the data to do a proof-of-concept. The frames are
> > only a small part of the "chunk" variable. What I am getting is a
> > fairly nice pi/4 DPSK. Only that in between OFDM Symbols (there are
> > 76 in a frame) there is some sort of random phase jitter. And I am
> > clueless what it could be. Frequency offset is compensated, the
> > channel doesnt vary that fast.
> I'm confused.  Are you seeing:
> good symbol -- jitter -- good symbol -- jitter -- good symbol
> or
> good symbol 76 times and then jitter
> ?
> Are you accounting for the cyclic prefix?  I assume that COFDM has one.

I am seeing only good symbols, but with a random phase offset (up to pi/8). 
The prefix is accounted for. If I do not account for it correctly this
results in ISI. Looks like added noise, not like the effect I'm seeing.


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