Synchronization for QPSK Transmission via Communications Satellites

Carrier phase and symbol timing synchronization performances are determined for QPSK transmission over the nonlinear communications satellite channel with several typical modem filtering configurations. A computer simulation is used that models conventional or offset QPSK transmission, the modem filters, the nonlinear satellite TWTA, and the receive modem synchronizers. These simulations are used to obtain errors in carrier phase and symbol timing estimates caused by both thermal noise and the modulation-pattern-induced jitter. The statistics of these errors are obtained for several channel filtering combinations and TWTA backoff levels. These experiments are extended to examine the overall effect of synchronization errors on bit-error probability for one particular implementation of the synchronizers.