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Re: [Discuss-gnuradio] Question about stream to complex and fft

From: rear1019
Subject: Re: [Discuss-gnuradio] Question about stream to complex and fft
Date: Fri, 14 Jun 2019 13:48:57 +0200

On Fri, 14 Jun 2019 at 09:08:55 +0000, S. L. wrote:
> Since I have vector-to-stream and fft to 1024 samples, I think or I
> guess it stores the first 1024 samples (from 0 ms to 32 ms) and the
> vector-to-stream module passes those samples to the FFT module that
> performs the FFT of those 1024 samples Then another 1024 samples (form
> 32 ms to 64 ms) would arrive and I would pass those samples to the FFT
> That is, the FFT block performs its function every 32 ms with 1024
> sample vectors
> Is this operating logic on the stream-to-vector and fft block correct?
> or I'm wrong

Your description of what happens is correct: The stream to vector block
waits for N samples and passes them to the FFT block (N being the vector
size). Strictly speaking the stream to vector blocks waits for n·N
samples where n is a positive integer, i.e. the delay can be bigger than
N samples. The value of n is determined by GNU Radio’s scheduler and is
not necessarily constant during the simulation.

The temporal aspect of your description is only correct if you refer to
the time passed “inside” the simulation. The time passed from the point
of view of a user watching the simulation (“real time”) may be
different. Your flowgraph does not restrict the processing speed, i.e.
generating and processing 32k samples will probably (depending on CPU)
take less than 1 second of real time. See also reply by Kyeong Su Shin.

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