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Re: [Discuss-gnuradio] How to extract stable fine frequency offset based

From: somunsfool
Subject: Re: [Discuss-gnuradio] How to extract stable fine frequency offset based on the benchmark program?
Date: Fri, 20 May 2016 06:32:11 +0000 (UTC)
User-agent: Loom/3.14 (http://gmane.org/)

Marcus Müller <marcus.mueller <at> ettus.com> writes:

> Hi DingJing,
> I'm not sure what's going on here, but I think it could be likely that
> your estimate of the preamble-autocorrelation simply doesn't work all
> too well.
> Generally: ditch benchmark_rx and the blocks it uses. They are really
> superseeded by the OFDM blocks that were introduced in 2013 – they are
> far better, and also, will simply give you the estimates you want, I think.
> Make sure you have a recent version of GNU Radio, and look for the
> rx_ofdm.grc example (likely somewhere in
> /usr/share/gnuradio/examples/digital/ofdm). The "Schmidl & Cox OFDM
> synch." block /actually/ has an output "freq_offset", and the "OFDM
> Channel Estimation" block adds a stream tag containing the full
> subcarrier offset (if any). **
> Other than that:
> > I've been trying to figure out the frequency offset of USRP recently.
> Could you specify this a bit more?
> Best regards,
> Marcus

Dear Marcus Müller:
Thank you for you reply.
I just try out the benchmark in /usr/share/gnuradio/examples/digital/ofdm
with little modification. As you known,the benchmark use ofdm_sync_pn by
default for synchronisation.The "ofdm_sync_pn" block uses a block named
"sample_and_hold" which I think is the value of fine_offset,so I created a
block_file_sink and wrote
"self.connect(self.sample_and_hold,self.offset_file_sink) " to output the
offset value instead of set logging=Ture.Maybe I have some misunderstanding.
Best wishes~

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