一种应用于卫星通信的间接时间同步方法

An indirect time synchronization method for satellite communication

针对卫星扩频通信系统的时间同步需求,提出一种基于GNSS授时的卫星通信前向链路间接时间同步方法。通过由星地自发自收链路与锁相环构成的钟差间接修正环路,对发送端码时钟进行闭环修正。这将使前向链路信号起始扩频码相位在到达接收端的时刻与卫星导航授时模块输出的1 PPS保持精确稳定的同步。实现了不需要位同步的扩频信号定时接收。分析并得到间接时间同步误差表达式及其与环路带宽的变化关系,给出使同步误差最小的最优环路带宽值。星地链路试验结果表明时间同步误差随环路带宽的变化关系与理论分析一致,最佳环路带宽对应的钟差间接修正环路秒脉冲1σ同步误差约为20 ns,验证了本方法的有效性。在此同步误差条件下,接收端成功地进行扩频伪码的同步和电文解调,实现了卫星导航授时对通信的辅助。

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.