Each B210 will have a GPSDO, they'll be separated by a few kilometers. My understanding is as follows:
1) When each B210 syncs, the 1PPS pulse between each USRP would be aligned to +-50 nsec. Since they're only separated by a few km, I suspect the alignment might be better because of common errors (Ionosphere, orbits, clocks, etc) in the GPS solution 2) The initial sync to 1PPS aligns the internal FPGA real time clock to, say, 50 nsec 3) From here on, time will be aligned to 50 nsec +- the 10 MHz frequency stability integrated over your observation time. 4) With the Ettus GPSDO allan deviation spec of 1e-11 @ 1 second, this means for any 1 second interval the relative clock offset between two B210s should be around sqrt(2)*1e-11 seconds. My specific applications doesn't necessarily need the LOs to have the same phase, just the time of each sample be know. As a backup, since the B210 has 2 RX chains, I can do my application with RX1 and record GPS L1 signals on RX2, then post-process the GPS data to solve for clock offset. Regards Stephan On Wed, Oct 10, 2018 at 1:26 AM Marcus D. Leech via USRP-users < usrp-users@lists.ettus.com> wrote: > On 10/09/2018 01:24 PM, Marcus Müller via USRP-users wrote: > > Works! > > > > Don't forget that PPS accuracy of a GPS receiver is theoretical best- > > case some 50 ns; in reality, things can get a little worse than that. > > > > Best regards, > > Marcus > It wasn't clear to me whether that was a *single* GPSDO whose outputs > were being distributed, or whether this > was individual B210s with on-board GPSDOs distributed over several > kilometers. > > So, Stephan, which case is it? > > > > > > On Tue, 2018-10-09 at 09:32 +0200, Stephan Esterhuizen via USRP-users > > wrote: > >> Hi All, > >> > >> I'm looking at using multiple B210s synchronized with GPSDO > >> distributed over a few kilometers. The idea is to measure time-of- > >> arrival of a signal source. I understand the limitations of the GPSDO > >> 1pps & 10 MHz reference frequency/time stability. > >> > >> What I'm curious about is whether anybody has done this, and whether > >> it worked without too much trouble. The only references I see of > >> distributed MIMO, is where NI recommends using the N210: > >> > >> http://www.ni.com/tutorial/14705/en/ > >> > >> Any advice would be greatly appreciated. > >> > >> Stephan > >> _______________________________________________ > >> USRP-users mailing list > >> USRP-users@lists.ettus.com > >> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com > > > > _______________________________________________ > > USRP-users mailing list > > USRP-users@lists.ettus.com > > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com > > > _______________________________________________ > USRP-users mailing list > USRP-users@lists.ettus.com > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >
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