This system used a 1PPS to sync the radios - for the sake of getting it up and running quickly. A GPSDO would work just as well, with ~50 ns of accuracy, which is pretty good.
Alternatively, as Josh said, you could synchronize the radios with other methods, like over-the air broadcast of a "system time". The beauty of this solution is that you could potentially implement this functionality on high protocol layers(i.e. link management) and use the ctrl ports of the blocks to make adjustments to the USRPs time. I should have better documentation up next week so you can mold this to your application. -John On Wed, Sep 26, 2012 at 12:43 PM, Josh Blum <j...@ettus.com> wrote: > > > On 09/26/2012 03:20 PM, Alex Zhang wrote: > > Hi Josh, > > > > A quick question, what is the time reference you are using for the TDMA > > engine? Is it GPS or something else? How accurate about the time > > synchronization? > > In this case we tested in the LAB with shared reference and PPS. GPSDO > per USRP should be great too. Both of these options will be highly > accurate. > > Now, it should be possible for a more advanced TDMA engine to try and > determine the transmit windows without explicit synchronization. I hope > we get this into the example as well. > > The guard interval parameter could be modified depending upon the accuracy. > > -josh > > > > > On Wed, Sep 26, 2012 at 1:31 PM, Josh Blum <j...@ettus.com> wrote: > > > >> Hey list, > >> > >> For those who were not at the GR Conference 2012: I presented some work > >> demonstrating a simple ARQ MAC over TDMA; using GNU Radio and USRPs in > >> GRC. Its very cool work, I encourage anyone to take a peek at the > >> slides, and checkout the repo and run the examples. > >> > >> The MAC layer work is actually the work of John Malsbury (I'm just the > >> messenger). He will be continually polishing and debugging the code over > >> the next week or so. There should be a wiki page soon... > >> > >> So, I promised at the presentation that I would email the slides and the > >> relevant information to checkout the repository. > >> > >> -------------------------------------------------------------------- > >> -- Here is the presentation (pdf format): > >> -------------------------------------------------------------------- > >> > >> > https://github.com/guruofquality/grextras/blob/pre_cog/pre_cog_pres.pdf?raw=true > >> > >> -------------------------------------------------------------------- > >> -- Here are some teaser screenshots from the slides: > >> -------------------------------------------------------------------- > >> http://i.imgur.com/HYgeb.png > >> http://i.imgur.com/EvDof.png > >> > >> -------------------------------------------------------------------- > >> -- The code is available on the pre_cog branch of grextras: > >> -------------------------------------------------------------------- > >> GRExtras main wiki page: > >> https://github.com/guruofquality/grextras/wiki > >> GitHub URL > >> $ git clone https://github.com/guruofquality/grextras.git > >> Check out this branch: > >> $ git checkout pre_cog > >> GRC flowgraphs are here: > >> <src dir>/examples/*.grc > >> Contact > >> j...@ettus.com > >> j...@ettus.com > >> > >> *Note*: Users will have to generate the tdma hier block first, and then > >> reload GRC to use the top level simple MAC block. > >> > >> -------------------------------------------------------------------- > >> Feedback is always welcome! > >> -Josh > >> > >> _______________________________________________ > >> Discuss-gnuradio mailing list > >> Discuss-gnuradio@gnu.org > >> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > >> > > > > > > > > _______________________________________________ > Discuss-gnuradio mailing list > Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio >
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