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.
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
>
>
> _______________________________________________
> Discuss-gnuradio mailing list
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>
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