Abstract: An indirect time synchronization method is proposed to be applied in forward link for time synchronization requirements of satellite spread spectrum communication system. Based on GNSS timing, an indirect clock correction loop consisting of ground-satellite round-trip link and phase lock loop is designed to correct the transmitter clock. The initial code phase of forward link spread spectrum signal is synchronized with GNSS 1 PPS at the receiving end. The spread spectrum signal timing receiving without bit synchronization is realized. A formula for time synchronization error and relationship of the error with loop bandwidth of the indirect clock correction loop are derived. The optimal loop bandwidth to minimize the synchronization error is also proposed. The satellite-ground link experiments show that variation of the synchronization error with the loop bandwidth is in agreemeent with theoretical analysis, and the minimum 1σ error of 20 ns is reached. It is concluded that the proposed method is efficient and qualified for satellite spread spectrum communication system. Under the condition of 20 ns synchronization error, the receiver has successfully finished the synchronization of the spread spectrum pseudo code and the message demodulation. The auxiliary of satellite navigation timing for communication is realized.

Key words: satellite communication, indirect time synchronization, 1 PPS, loop bandwidth