Re: [Discuss-gnuradio] OFDM demodulation problem / example video

[Achilleas Anastasopoulos]

Jens,

I got interested in this discussion and looked at the
standard briefly and at your matlab code.
I have a couple of initial points; I will spend more time sometime this 
week on your code:

1) where in the standard it says that this is pi/4 DQPSK ?
I only saw that the modulation used is DQPSK.

2) You have done frequency correction manually: did you do this by 
looking at the DC subcarrier (no power transmitted here) in the
received signal prior to OFDM demod?
Frequency synchronization in OFDM is very crucial, because the OFDM 
symbol rate is small! To see why, try to understand the effect of a 
small frequency error at the output of the FFT demodulator.

3) You have found the beginning of the frame manually. In your matlab 
code you posted there is a variable  "start_resamp" that indicates this.
How do you know that the begining of frame is not BETWEEN two samples?
in other words there is no fine timing synchronization. I wonder what 
the effect of a small timing error is at the output of the FFT demodulator.

Achilleas