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Re: [Discuss-gnuradio] UHD: Sink and source synchronization

From: Martin Braun
Subject: Re: [Discuss-gnuradio] UHD: Sink and source synchronization
Date: Thu, 21 May 2015 09:14:49 -0700
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.7.0


the tx_time tag is generated by the device, not by gr-uhd. So as a time
base, this should serve your purpose -- unless I misunderstood what
you're trying to do.


On 21.05.2015 07:14, Nicolas Cuervo Benavides wrote:
> Hi all,
> Right now I'm implementing tx and rx on the same device (USRP b210), and
> I'm trying to synchronize the two in order to determine the exact moment
> when a message is sent by the Tx. The purpose of this synchronization is
> to add an idle state for tx right after the "sending state", so the Rx
> part can "hear" the channel and determine if there are no active
> communications at the same time, that could lead to interference.
> I used first the gettimeofday function along with the uhd::time_spec_t,
> but I have been told that this is a kind of "system timer", and that
> could not be 100% reliable as a counter for the USRP's. The idea now is
> use the rx_time tag that comes at the start of every reception, but so
> far I havent been able to generate the idle state just before the
> sensing state, and I believe that I'm, so to say, interfering myself. 
> Now I was thinking on trying to extract a so-called tx_time tag not
> created beforehand but within the UHD block (as near to the usrp antenna
> as possible), that would tell me the time when the signal is going to be
> send. For that I would go into modifying the uhd blocks. Before doing
> that, I would like to hear some ideas of synchronization or some
> feedback from the mailing list. It would be really helpful if someone
> could lead into a more decent way than modifying the main blocks.
> Thank you in advance.
> Best Regards,
> Nicolas C. 
> -- 
> Nicolás Cuervo Benavides
> Handy: +49 157 70476855
> Electric and Electronic Engineering department.
> Electronic Engineering
> Universidad Nacional de Colombia
> --
> Student M.Sc. Information and Communication Technology
> Karlsruher Institut für Technologie
> Karlsruhe, Baden Würtemberg, Germany 
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