Re: [Discuss-gnuradio] OFDM / DAB demodulation

[Jens Elsner]

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