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Re: [Discuss-gnuradio] OFDM and SNR EST

From: Tom Rondeau
Subject: Re: [Discuss-gnuradio] OFDM and SNR EST
Date: Sun, 12 Aug 2012 13:10:25 -0400

On Fri, Aug 3, 2012 at 10:36 AM, Vanessa Gardellin
<address@hidden> wrote:
> Dear all,
> we are trying to use the block digital_mpsk_snr_est in an OFDM flowgraph.
> We think that the right place for the snr_est is after the ofdm_frame_sink
> however we have the following error:
> itemsize mismatch: ofdm_frame_sink(27):0 using 1600, mpsk_snr_est_cc(28):0
> using 8
> (consider that we have 200 occupied tones and hence 1600 is 200*8)
> Do you have any idea?
> Thank you
> Vanessa


I don't think that the mpsk_snr_est is really appropriate for OFDM.
It'd probably work if you applied it directly to one subcarrier, but
definitely not the entire symbol. It really is designed for MPSK
signals, after all.

There are other methods for measuring OFDM SNR that I've seen in
papers; of course, I can't recall what they are off the top of my
head, but they definitely exist. So I'd spend my time looking at
algorithms that are specific to OFDM instead of trying to cram the
MPSK SNR ests into it.


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