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, <address@hidden
<mailto:address@hidden>> 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,address@hidden <mailto:address@hidden> 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
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