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Re: [Discuss-gnuradio] OFDM demodulation problem / example video
From: |
Jens Elsner |
Subject: |
Re: [Discuss-gnuradio] OFDM demodulation problem / example video |
Date: |
Tue, 4 Apr 2006 19:04:17 +0200 |
User-agent: |
Mutt/1.3.28i |
I guess I was a little bit too quick with my answer...
In more detail:
> 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.
The fractional offset (0.35) was found manually by look at the
cross-correlation in the frequency domain and taking
df = (left_of_max - right_of_max) / (left_of_max+right_of_max).
Should be correct, shouldn't it?
> 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.
I didn't quite understand what you are saying until I though about it:
This should be equivalent to a small modulation in the frequency domain?
I just simulated that by:
% simulate fractional offset
d_resamp = d_resamp .* exp(j*linspace(0,2*pi*0.1,length(d_resamp)).');
No effect - after all I did resampling before.
Jens
- Re: [Discuss-gnuradio] OFDM demodulation problem / example video, (continued)
- Re: [Discuss-gnuradio] OFDM demodulation problem / example video, Achilleas Anastasopoulos, 2006/04/04
- Re: [Discuss-gnuradio] OFDM demodulation problem / example video, Jens Elsner, 2006/04/04
- Re: [Discuss-gnuradio] OFDM demodulation problem / example video, Robert McGwier, 2006/04/04
- Re: [Discuss-gnuradio] OFDM demodulation problem / example video, Prateek Dayal, 2006/04/05
- Re: [Discuss-gnuradio] OFDM demodulation problem / example video, Robert McGwier, 2006/04/05
- Re: [Discuss-gnuradio] OFDM demodulation problem / example video, Jens Elsner, 2006/04/05
- Re: [Discuss-gnuradio] OFDM demodulation problem / example video, Robert McGwier, 2006/04/05
- Re: [Discuss-gnuradio] OFDM demodulation problem / example video, Jens Elsner, 2006/04/06
- Re: [Discuss-gnuradio] OFDM demodulation problem / example video, Jens Elsner, 2006/04/05
- Re: [Discuss-gnuradio] OFDM demodulation problem / example video,
Jens Elsner <=
- Re: [Discuss-gnuradio] OFDM demodulation problem / example video, Achilleas Anastasopoulos, 2006/04/04
- Re: [Discuss-gnuradio] OFDM demodulation problem / example video, Achilleas Anastasopoulos, 2006/04/05