A method of time synchronization of uplink signal on LEO satellite

Reducing multiple access interference to enhance system capacity is a problem that urgent to be solved in LEO satellite communication system. Spreading codes with zero correlation window are applied in Quasi-synchronous CDMA System so that the system could have a similar performance of anting multiple access interference with Synchronous System. Meanwhile, the system would have a lower requirement of the time synchronization of uplink signal. However, the high relative velocity between user and satellite would influence the performance of synchronization in LEO satellite communication system. This paper proposes a method that using non-coherent pseudo code ranging and the tracking of pilot signal to estimate the distance between user and the satellite to deal with this problem. The simulation results show that the method proposed in this paper could have a high accuracy of time synchronization of uplink signal. Besides, this method could greatly reduce the frequency of ranging, which could result in a low consume of resource onboard. So this method can satisfy the requirements of Satellite Quasi-synchronous CDMA System.