Research on transmission method of CDMA satellite communication system based on time division duplexing

A noval signal transmission method of asynchronous code division multiple access (CDMA) is proposed to improve the utilization of uplink timeslots for the time division duplexing (TDD) satellite communication systems. The terminals at different positions within a beam of the satellite antenna transmit their data blocks at different moments in the uplink timeslot window according to a certain rule. The uplink guard time can be reduced to one time the maximum propagation delay difference in this beam, while the uplink guard time of two times the maximum propagation delay difference was needed for the synchronous reception case in Reference. Furthermore, two specific schemes are introduced to instantiate the proposed signal transmission method: transmission at discrete moments and transmission at continuous moments, and their multiple access interference (MAI) performances are analyzed and compared via simulation. It is shown that the performance of discrete transmission scheme is slightly better than the other one.