USRP2 for WCDMA carrier phase tracking

Hi All,

I used a USRP2 locked to a GPSDO to collect some complex data in a
WCDMA downlink band. My objective is to carry out carrier phase tracking
using an FPLL (based on modified Costas loop )similar to that seen in
GPS. Since the USRP2 is locked to GPSDO, phase noise and drift are
limited from USRP2 itself. This set up is to understand the drift in the
base station oscillator.

Currently I am processing the data in Matlab. My idea is to use CPICH
for estimating the carrier phase. Since the I and Q channels in the
downlink chain are expected to contain the same despreaded symbols (all
1s ) for CPICH, I am using an error detector based on (I-Q) in place of
arctan(Q/I) used for GPS. I have had some success in getting the symbols
to be positive values but am not sure if this is exactly how it usually
done. Can any one please chip in with some ideas of their own?