USRP baseband board problems


I’ve been having some trouble with the USRP (version 1) boards. We are
using the two transmit antennas in a 2x2 MIMO systems, but we have
noticed the side B antenna has a significantly lower transmit power
(~10dB) than the side A antenna. We have tried swapping the
daughterboards (flex2400) and using different ones but the symptom
remains. The only way I have been able to reproduce the loss in power
of side B on side A is to decrease the PGA setting on side A. We
haven’t quantitatively analyzed the exact power loss; instead we’ve
been using observations from the constellation and channel
measurements from our system to gauge the loss. After all of our
testing, we have come to the conclusion that this might be a problem
in either the baseband board or the fpga. Also, we’ve been able to
reproduce this error using combinations of different USRP baseband
boards & RF daughterboards. Any idea what might be going on here?

Also, this is not a problem with our physical layer implementation as
I’ve tested that code over simulated channels, and everything is
working fine. I thought that the problem might have been caused by
some problem in the way that I set up the USRP, but I haven’t found
anything yet that could be causing this. I will continue to try and
diagnose the problem, and keep you abreast of any developments.

FYI, here’s a list of the different hardware I’ve tried:
USRP (v1) - rev 4.1 and 4.5
RFX2400 RF - rev 30 12-26-2006

Ketan M.

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