Re: [Discuss-gnuradio] Fourier Transform on multiple OFDM symbols

[Aditya Virmani]

Hello

Yes, I think this is the same thing I am trying to do, but I am not getting the results I expected. Can you please share the GRC file for this. In my execution, I was getting null signals.

You can see my setup in the attached file. It's a rather simple version just for illustration. I don't understand why that is not working.

On Sun, Jan 3, 2016 at 7:45 PM, Ron Economos <address@hidden> wrote:

If you want to see individual carriers, you have to use a high resolution FFT. Here's a 262144 point FFT on a DVB-T2 OFDM signal with a 1K FFT (853 active carriers). The carriers are spaced about 9 kHz. Stronger tones are pilots.

https://twitter.com/drmpeg/status/670769195160858624

Ron

On 01/03/2016 04:34 PM, Aditya Virmani wrote:

Hello sir

Thank you for your reply. Well, I am trying to do some additional operation to the receiver side of the OFDM transceiver (rx_OFDM).

I am intending to detect a doppler shift in the received signal, for which I am trying to do an FFT over symbols collected in 1 second.

To test the case, I tried to do a large FFT over 4 same OFDM symbols, which means a 4 x 64 FFT, which should give me 48 (corresponding to occupied tones) peaks instead of a band.

The theory of peaks can be illustrated simply by the FFT theory. I can share the reference for that if needed.

I hope I am clear here.

On Sun, Jan 3, 2016 at 7:06 PM, Martin Braun <address@hidden> wrote:

Typically, you'd do 1 (I)FFT per OFDM symbol. I recommend having a look
at the tx_ofdm.grc and rx_ofdm.grc examples, which show a full flow graph.

M

On 01/03/2016 01:22 PM, Aditya Virmani wrote:
> Hello everyone
>
> Iam trying to do run-time FFT over multiple OFDM symbols.
> For this, I feed in the same sequence of bytes for each OFDM symbol.
> As per my understanding, as I am feeding in the same sequence of bytes,
> it should be generating same set of symbols, and then further if we do
> FFT over multiple symbols which are same, we should get a sequence of
> peak-and-zeros, instead of continuous FFT graph.
> This works fine if I do just with two symbols (screenshot of that
> attached), but when I feed in more than two, it results in error ( I
> think that the data doesn't reach the FFT block concurrently, because
> the graph I get is same when I feed Null source and a Symbol source to
> FFT).
>
> It would be great if someone can guide me with it.
>
>
> Regards
> Aditya Virmani
>
>
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> Discuss-gnuradio mailing list
> address@hidden
> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
>


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sampled.grc
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