Code tracking loop performance for an orthogonal CDMA uplink SATCOM system

The use of orthogonal CDMA for uplink satellite communication requires that all user codes arrive at the satellite despreader at a common time. To this end schemes for network synchronization among all users are necessary; these involve two stages: code acquisition and code tracking. We propose a code tracking loop that extends between the satellite and the ground terminal. The traditional code tracking loop is broken into two segments: the satellite segment of the loop conducts the phase difference extraction; while the ground segment of the loop at the Earth station performs the filtering and phase adjustment. The major difference of this tracking system and the traditional loops is the long propagation delay entering the loop delay and secondarily the satellite motion. The optimization of the tracking loop filter is undertaken with respect to the steady state error and the variance of the timing error. The performance of the code tracking loop scheme is evaluated for a single-beam fully-loaded SATCOM system