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 [2]
>
> 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
> https://lists.gnu.org/mailman/listinfo/discuss-gnuradio [1]
Links:
------
[1] https://lists.gnu.org/mailman/listinfo/discuss-gnuradio
[2]
http://www.ettus.com/content/files/kb/mimo_and_sync_with_usrp_updated.pdf
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