Bob, thanks for the reply.
This is exactly what I am doing:
[...]
dem = data ./ data_l;
[...]
A point-wise division by the last OFDM symbol. This also restores
amplitude, but has the same effect on the phase.
I do not control the receiver, my data is from a radio station. I am
only trying to demodulate. I am synchronised in the
frequency domain. Time domain synch is also appropriate.
I guess I'll just have to get new data to verify this. It seems just too
odd.
Jens
On Mon, Apr 03, 2006 at 10:48:32AM -0400, Robert McGwier wrote:
> Jens:
>
> This pi/4-DQPSK. That means
>
> New-symbol * (complex conjugate (Old-symbol)) is pi/4 modulo pi/2.
> Are you taking this into account on both the transmitter and the
> receiver and it in all of the bins before your inverse fft provides the
> time domain signal to transmit would be my best best.
>
> I will look at it more carefully today if I have time but this question
> would be the first one I would ask the code to tell me.
>
> Bob
>
>
>
> Jens Elsner wrote:
> >Here is my little problem in animated frames.
> >
> >What you are seeing is already DQPSK. Displayed is the signal
> >constellation for one OFDM frame, 75 symbols. The code was posted earlier.
> >
> >The problem: The (differential!) signal constellation has a constant phase
> >offset for each OFDM symbol. Why? What to do about it?
> >
> >Jens
> >
>
> --
> AMSAT VP Engineering. Member: ARRL, AMSAT-DL, TAPR, Packrats,
> NJQRP/AMQRP, QRP ARCI, QCWA, FRC. ARRL SDR Wrk Grp Chairman
> Laziness is the number one inspiration for ingenuity. Guilty as charged!
>
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