Hi all, Thanks for the extra comments Mark.
Just to be clear: I'm not talking about phase offset between RF Outputs, but only time offset. (Once time offset is fixed, we will try to have phase-coherent RF outputs). I have made other measurements today, here are the results. I'm transmitting a signal at 1.57542GHz, and a second signal at 1.2276GHz. Sample Rate on N310: 25.6Msps (MCR of 153.6Mhz) Sample Rate on X300: 25.0Msps (MCR of 200Mhz) Using External Clock and External PPS from Octoclock 1) Using X300 (RF A and RF B) and UHD 3.10.3.0, we see les than 3ns time offset (See image here: link <https://drive.google.com/file/d/1FBC3CHOhGO4xLdJU3LhjB0pTjexNpJik/view?usp=sharing> ) 2) Using X300 (RF A and RF B) and UHD 3.13.1.0 RC1, we see 7300us time offset (See image here: link <https://drive.google.com/file/d/1mV2XrUVz1PC4boi0BzUmxFcWo2b8zj3Y/view?usp=sharing> ) 3) Using N310 (RF 0 and RF 2) and UHD 3.13.1.0 RC1, we also see 7300us time offset. Important: the "timed commands" seem to be broken in UHD 3.13.1.0, either for X300 or N310. When we change the time_spec of the first "send" call, the time at which the samples are transmitted does not change. For example, I tried to set tie_spec to 10s, but the Tx starts right away. This was working correctly with UHD 3.10.3.0 Let me know if you have ideas I could try. Best regards, Serge On Thu, 8 Nov 2018 at 14:44, Mark Wagner <m2wag...@eng.ucsd.edu> wrote: > 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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