DS-CDMA for uplink low data rate transmission in multibeam satellite communications: radio capacity perfromance

This paper presents a performance evaluation of various spreading codes applied to DS-CDMA for uplink low data rate transmission in multibeam, variable-rate, and quasisynchronous satellite communication over a LOS channel. The simulation results indicate that both PP-Gold/Long and Walsh/Long codes provide the best performance. If the timing offset for the two-level spreading scheme is smaller than a determined limit, there is no capacity loss as compared to the perfect synchronous case. Furthermore, a code reuse scheme is also given to improve the radio capacity of the system, but it requires more precise synchronization. In general, the performance of a CDMA-based satellite system is mainly limited by the interbeam interference.