Martin - I am thinking about doing beam forming around 900MHz. The number of antennas that I want to use is around 8x8. I am thinking about using USRP N210+SBX+OctoClock-G suggested by ettus. But not sure how much phase mis-alignment will I observe.
Marcus - Thanks for the tips. Maybe I should look at how other folks do phase calibration on USRP. Any recommendation of sample projects? Ideally, I hope that this process can be done automatically in software or in hardware. Pengyu On Tue, Mar 3, 2015 at 11:32 AM, <mle...@ripnet.com> wrote: > Indeed, I should have emphasized that despite having features like > "phase resynch", in any *practical* phased-array, you'll still need some > mechanism for calibrating the phase centers of all your antenna. > Differential environmental factors can, for example, affect the phasing of > the antenna feed paths, even with your LOs all agreeing quite-well on phase. > > In Radio Astronomy, they do this all the time--there's always a > phase-calibration process that is undertaken prior to observations, because > despite careful layout of common LOs, carefully-measured feedlines from the > same batch of cable, etc, differentials creep in. > > > > > > > On 2015-03-03 11:26, Martin Braun wrote: > > Can you give us some details (frequency, number of antennas) that you want to > have? > > A lot of people have done MIMO with USRPs, up to 100x100 antennas, so there > is some precedent. For beam forming, you'll need very good phase alignment, > depending on what you're planning to set up. This is always difficult, > because all sorts of things affect phase. You should, in any case, have a way > to test phase alignment. > > Cheers, > Martin > > On 03.03.2015 08:18, mle...@ripnet.com wrote: > > If you use the phase-resynch feature of the SBX card, and you have common > refclock and 1PPS across all your USRPs in the array, then you should be > OK. In *general*, synthesized downconverters use fractional-N synthesizers > where their starting phase after a re-tune is random with respect to any > other synthesizer using the same reference clock. That's just the way > fractional- N synthesis works. It happens that SBX uses an ADF4351 > synthesizer, which has a (rare!) hardware feature to allow phase-resynch > after tuning. In order to make this work, all SBXes in your "array" must be > tuned at exactly the same time, so the timed_commands feature must be used > to do the tuning. See: http://files.ettus.com/manual/page_sync.html On > 2015-03-03 11:05, Pengyu Zhang wrote: > > Hi Guys, I am planning to build a mimo system which supports beam forming. > Is USRP a good platform for my target? I do not want to use WARP because I > need to operate at frequencies lower than 2.4GHz. A potential problem of > USRP is phase alignment. As the following doc suggests, phase alignment can > be done by MANUALLY tuning the phase. This process can be labor intensive > when the number of antennas increases. I am also worried about the problem > that the manual phase calibration might need to be done each time you use > the mimo system. Is there any approach that can make this process much > easier? > http://www.ettus.com/content/files/kb/mimo_and_sync_with_usrp_updated.pdf > Would be great if you can give me some suggestions about what devices > should I use for building a mimo system for beam forming. Thanks. Pengyu > _______________________________________________ Discuss-gnuradio mailing > list Discuss-gnuradio@gnu.org <mailto:Discuss-gnuradio@gnu.org> > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > _______________________________________________ Discuss-gnuradio mailing > list Discuss-gnuradio@gnu.org > https://lists.gnu.org/mailman/listinfo/discuss-gnuradio > > _______________________________________________ > Discuss-gnuradio mailing > listDiscuss-gnuradio@gnu.orghttps://lists.gnu.org/mailman/listinfo/discuss-gnuradio > >
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