On Tue, Feb 02, 2010 at 10:12:02AM -0800, dougekim wrote: > > I recently purchased two new USRP2 boards each with a XCVR2450 transceiver > board. In testing the two boards, I began by conducting a simple tx/rx test > in which both boards share a COMMON 10MHz reference clock, as opposed to two > independent references. This test was conducted to determine if the > measured channel would remain relatively unchanged (time invariant) in a > static channel environemnt. > > A single 2MHz tone was used as my baseband test signal (no BPSK or QAM). In > comparing the baseband tx signal to the baseband rx signal, I noticed that > although both signals were 2MHz in frequency, they were out of phase as > expected. However, the phase difference was not constant over time. Rather > the phase difference was changing over time quite a bit. > > This occurrence may limit the MIMO capabilities of these boards since the > residual carrier offsets must be corrected for individually for each > transceiver. Take a 2x2 MIMO system fore example. Four different carrier > offsets may need to be corrected rather than one as in the case of a fully > coherent system. > > I'm curious as to whether other users have encountered similar problems with > their systems as well, and if so, would be able to explain this occurrence.
Doug, Did you call u.config_mimo(WE_LOCK_TO_SMA) in your host code? If you didn't, the USRPs are still using their internal free running oscillators. Eric _______________________________________________ Discuss-gnuradio mailing list Discuss-gnuradio@gnu.org http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
