Re: [Discuss-gnuradio] mimo beam forming on USRP

[Ralph A. Schmid, dk5ras]

When I read this, pCell comes in mind:
http://www.rearden.com/artemis/An-Introduction-to-pCell-White-Paper-150224.p
df 

Quite exciting stuff!

Ralph.

> -----Original Message-----
> From: address@hidden
> [mailto:address@hidden On Behalf Of
> Martin Braun
> Sent: Tuesday, March 3, 2015 5:26 PM
> To: Pengyu Zhang
> Cc: address@hidden
> Subject: Re: [Discuss-gnuradio] mimo beam forming on USRP
> 
> 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 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_updat
> ed
> >> .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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