Here's a google drive link with images of the phase drift between rx4 and tx 1&2, and tx 3&4
https://drive.google.com/open?id=1Bg6F0WHzzwVhpFBlrlfqJgpGg9JtTczH On Thu, Nov 8, 2018 at 11:32 AM Mark Wagner <m2wag...@eng.ucsd.edu> wrote: > Hi guys, > > Maybe I could jump in and share some related results. My group has been > developing a MIMO system with N310 units. We did a test sounding recently > where we sent 4, length 4096, orthogonal multitone signals from the > transmitters to the receivers and processed the data by finding the channel > response between each transmitter and receiver pair (16 in total) and > recording the magnitude and phase of the arrival spikes between each pair. > > We took several seconds of data and processed it in length 4096 chunks > (around 1500 chunks in total) and looked at the phase difference between > transmitter pairs as time progressed. Since transmitters 1 and 2 are > sharing an LO and our setup was not moved during the sounding we expected > to see a constant phase difference between transmitters 1 and 2 and a > single receiver (same with tx 3 and 4), but we saw some drift. Worse yet, > not all LO sharing pairs drifted in the same way, some didn't drift much at > all while some drifted in linear or non-linear patterns. > > If you're all fine with me breaking the rules I can attach some png images > of what we recorded so you can see what it looks like. Later this week > we'll repeat the experiment but leave the machines running longer to see if > the drift diminishes as the machines run longer. > > Cheers, > -Mark > > > > > > On Thu, Nov 8, 2018 at 9:03 AM Daniel Jepson via USRP-users < > usrp-users@lists.ettus.com> wrote: > >> Hi Serge, >> >> Are you measuring the phase offset between the TX0 and TX2 signals in a >> steady-state case, or the time difference in the start of those signals? >> >> In the former case, your results could be impacted by the lack of >> internal LO sharing between daughterboards. I would fully expect an unknown >> phase offset between channels 0 and 2 every time you reconfigure the >> device. In the latter case, it sounds like a start trigger mismatch like >> Marcus mentioned. >> >> Can you share more details as to how you're measuring the phase offset? >> >> Thanks, >> -Daniel >> >> >> >> On Thu, Nov 8, 2018 at 5:30 AM Serge Malo via USRP-users < >> usrp-users@lists.ettus.com> wrote: >> >>> Yes: we are using UHD 3.13.1.0 RC1, with the latest file system image >>> >>> I can try to use lower tx start times to see if the time offset changes >>> with that. >>> >>> Thanks, >>> Serge >>> >>> On Wed, 7 Nov 2018 at 21:44, Marcus D. Leech <patchvonbr...@gmail.com> >>> wrote: >>> >>>> On 11/07/2018 09:31 PM, Serge Malo wrote: >>>> >>>> Yes: >>>> We only use one streamer for all RF outputs, and send time_spec with >>>> each call to the streamer's send method. >>>> We reset the internal time with set_time_unkown_pps(0), and program the >>>> first samples to be streamed at a time of 0.800s. >>>> It is basically the same code we used on the X300/X310. >>>> >>>> Thanks, >>>> Serge >>>> >>>> Well, that is quite strange--the magnitude of the time offsets is >>>> larger than I would expect. >>>> >>>> Perhaps someone from the N310 team can comment? >>>> >>>> Serge, are you using the latest UHD and system image versions for the >>>> N310? >>>> >>>> >>>> >>>> On Wed, 7 Nov 2018 at 21:03, Marcus D. Leech via USRP-users < >>>> usrp-users@lists.ettus.com> wrote: >>>> >>>>> On 11/07/2018 08:53 PM, Serge Malo via USRP-users wrote: >>>>> >>>>> Hi all, >>>>> >>>>> We are trying to send 4 synchronous signals from the 4 Tx ports of the >>>>> N310. >>>>> We are using UHD 3.13.1.0 RC1 under Ubuntu. >>>>> Central Freq = 1575.42 GHz and 1227.6 MHz >>>>> Master Clock rate = 153.6 MHz >>>>> >>>>> We would expect to have less than 3ns offset between all TX ports of >>>>> the N310, like we do with the X300/X310. However, we have measured 4700ns >>>>> between TX RF ports 0 and port 2. >>>>> We have tried the next things with no more success: >>>>> - Sampling rates of 25.6MSps, 38.4Msps, 76.8Msps >>>>> - Init with the device options "init_cals=ALL" and "force_reinit=1" >>>>> - Use the internal GPSDO >>>>> - Use clock_source=external and time_source=external (from an >>>>> Octoclock). >>>>> >>>>> Can you tell us: >>>>> -What time offset between TX RF ports we should expect to achieve? >>>>> -Is there anything else we can try to reduce this offset to less than >>>>> 3ns? >>>>> >>>>> Best regards, >>>>> Serge >>>>> >>>>> >>>>> How are you setting up your TX streamer? Is it time-tagged to start >>>>> at a particular device time? >>>>> >>>>> >>>>> >>>>> _______________________________________________ >>>>> 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 >>> >> >> >> -- >> >> Daniel Jepson >> >> Digital Hardware Engineer >> >> National Instruments >> >> >> >> O: +1.512.683.6163 >> >> daniel.jep...@ni.com >> _______________________________________________ >> USRP-users mailing list >> USRP-users@lists.ettus.com >> http://lists.ettus.com/mailman/listinfo/usrp-users_lists.ettus.com >> > > > -- > Mark Wagner > University of California San Diego > Electrical and Computer Engineering > > -- Mark Wagner University of California San Diego Electrical and Computer Engineering
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