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[Discuss-gnuradio] UHD: Sink and source synchronization

From: Nicolas Cuervo Benavides
Subject: [Discuss-gnuradio] UHD: Sink and source synchronization
Date: Thu, 21 May 2015 16:14:47 +0200

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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