Dear Rob and Marcus: Thank you for the prompt response. Based on my limited knowledge of digital circuit, the 180 degree phase ambiguity may occur at the PLL circuit initiation (power on) stage. After PLL is powered on, there is no phase ambiguity. Is it right? My question actually comes to: When I switch N310 from RX mode (in time slot 1) to TX mode (in time slot 2) and then back to RX mode (in time slot 3), would there be a phase ambiguity in those two RX modes (in time slots 1 & 3)?
When I used USRP N210 with SBX, I did not observe such a phase ambiguity in this case. But when I used USRP N210 with WBX, the phase ambiguity does exist (based on my understanding). Thank you! Hua On Wed, Oct 7, 2020 at 10:03 AM Rob Kossler via USRP-users < [email protected]> wrote: > > On Tue, Oct 6, 2020 at 11:50 PM Marcus D. Leech via USRP-users < > [email protected]> wrote: > > > > On 10/06/2020 10:29 PM, Zeng, Huacheng via USRP-users wrote: > > > Hello: > > > > > > I am using N310 for 4x4 MIMO transmission. Are N310's 4 TX/RX channels > > > internally synchronized for MIMO applications? Does it need an > > > external device (e.g., OctoClock-G CDA-2990) to synchronize those 4 > > > channels for MIMO applications? > > > > > > I am also exploring channel reciprocity using N310. I have successful > > > experience with SBX in the implementation of channel calibration. But > > > it seems WBX does not fit for this purpose because of some phase > > > ambiguity issue (if I remember correctly). Would the daughterboards in > > > N310 have the phase ambiguity issue? > > > > > > Many thanks in advance! > > > > > > Hua > > > > > The N310 has a pair of AD9371 RFFE chips. Those chips have two channels > > each, and those channels are coherent with respect to each other. > > There will be an unknown phase offset due to the nature of > > (particularly Frac-N) synthesizers between the channels of the two > halves. > > > > Unless the N310 channels implement phase-resynch via timed commands (I > > don't think that they do), you'd need some external method for > > phase-aligning those channels. > > > > Now because they're using a common reference clock, once the phase > > offset has been factored out they should be in perfect synchronization > > both in time and phase from that point forward. > > In addition to the common reference clock that Marcus mentioned, the N310 > also has capability > <https://files.ettus.com/manual/page_usrp_n3xx.html#n3xx_mg_external_lo> > to use an external LO for all channels. But, there will still be a 180 deg > phase ambiguity. > Rob > _______________________________________________ > USRP-users mailing list > [email protected] > http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >
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