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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: |
Thu, 6 Apr 2006 11:25:40 +0200 |
User-agent: |
Mutt/1.3.28i |
(comments inlined)
On Wed, Apr 05, 2006 at 02:02:23PM -0400, Robert McGwier wrote:
> Yes. Here is what you are missing:
>
> Let us concentrate (as does your nice animated gif) on one channel in
> the OFDM.
Yes, what's depicted are all decoded symbols in one OFDM frame.
> Let us suppose you have a variable delay into the signal after its
> onset. This will happen with probability one because your clock and the
> transmitter clock will not be the same except in your computer simulation.
Agreed. But this delay will only be fractional, as I can determine the
exact start by correlation. The oscillators are pretty stable, so I can
exactly time one symbol. The offset will thus be fractional and constant.
I verified this by correlating every OFDM symbol with itself. This
shows that the cyclic prefix does not move.
> If you took the FFT beginning (say) 39 samples into the symbol at t,
> and then 52 samples after the beginning time for symbol at t+1,
> this will be an additional rotation due to the frequency offset of this
> channel from zero. Notice this means that every channel will have a
> different rotation which will be a multiple of the frequency offset from
> correct and the difference in time after symbol onset you go into the
> symbol to take the FFT.
I agree. But, as stated above, my time offset is fractional and
constant.
Jens
- Re: [Discuss-gnuradio] OFDM demodulation problem / example video, (continued)
- Re: [Discuss-gnuradio] OFDM demodulation problem / example video, Robert McGwier, 2006/04/03
- 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 <=
- Re: [Discuss-gnuradio] OFDM demodulation problem / example video, Jens Elsner, 2006/04/05
- Re: [Discuss-gnuradio] OFDM demodulation problem / example video, Jens Elsner, 2006/04/04
- 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