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
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