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Re: [Discuss-gnuradio] Sample alignment between two USRPs

From: Eric Blossom
Subject: Re: [Discuss-gnuradio] Sample alignment between two USRPs
Date: Fri, 8 Sep 2006 08:37:01 -0700
User-agent: Mutt/1.5.9i

On Thu, Sep 07, 2006 at 04:42:37PM -0700, R and D wrote:
> Has anyone done any work on getting sample alignment between multiple USRPs?
> We have multiple USRPs clock-synchronized, but we haven't found a way
> to set things up so that the different sample streams hit the D/A
> converters at the same clock.
> Any suggestions appreciated. :-)

Welcome mystery person ;)

Martin Dvh has gotten multiple USRPs synchronized for receive.  That
FPGA code and host code is in the subversion.  Searching the archives
will provide serious clues on how to use it.

For transmit, the problem could be a bit more difficult, depending on
whether you can deal with a constant phase difference between the
transmitting USRPs or not (MIMO vs beam forming).  

If you need the phases to be identical between the USRPs then you will
have to change the verilog such that you are no longer using the
digital upconverters in the AD9862 and instead implement the DUC in
the FPGA.  This is because there's no way to directly control the
phase accumulator in the AD9862.

If you can deal with a constant phase offset, then a strategy similar
to what Marin used for Rx should work for Tx.


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