[Discuss-gnuradio] transmitting with 4 antennas

[Ketan Mandke]

I am part of the Hydra group at UT Austin
(http://hydra.ece.utexas.edu). We have developed a MIMO prototype
utilizing GNU Radio & the USRP board. The physical layer for our
design is based on the draft standard for IEEE 802.11n. Our current
system is designed to support 2 antennas (i.e. utilizing one USRP
board per node), however, we would like to extend this to 4 antennas.

We are currently following the directions on the 'USRPClockingNotes'
page for synchronizing the local oscillators of two USRP boards. The
only problem that remains is aligning the samples. I have been looking
through the GNU Radio codebase for some insight on how to do this. I
found 'usrp_multi.py' which describes how to do this for the receive
chain. However, I also have to be able to align samples for the
transmit chain.

Does anyone have any experience with transmitting waveforms using
multiple USRP boards? Specifically, do you have to go through any
special process to ensure that transmitted samples are properly
aligned?

-- 
Ketan Mandke
http://www.ece.utexas.edu/~mandke