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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.
Jens