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
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 B. wrote:
Can you give us some details (frequency, number of antennas) that you want to
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.
On 03.03.2015 08:18, [email protected] 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 Z.
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?
 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 [email protected]
_______________________________________________ Discuss-gnuradio mailing
list [email protected]
Discuss-gnuradio mailing list