导航星座激光/微波星间链路协同时间同步方法研究

Cooperative time synchronization via laser/radio inter-satellite links in navigation constellations

时间同步是卫星导航系统提供定位、导航以及授时服务的关键.星座自主运行模式下需要通过星间链路组网进行星座整网时间同步,以支持正常的导航定位服务.相比于微波链路,连续建链的激光链路可以提供时标统一的、更高精度的钟差测量结果.本文提出一种星座自主运行模式下激光/微波星间链路协同时间同步方法.通过连续观测的激光星间链路建立时间比对网络,基于加权平均算法生成星间时间基准;激光比对网络外卫星通过时分体制微波链路,利用分布式卡尔曼滤波算法溯源至星间时间基准,实现星座整网时间同步.基于新一代北斗星座进行整网时间同步性能仿真,激光/微波协同时间同步方法生成的时间基准相比微波星间链路生成的时间基准,短期、中期稳定度均有明显提高,整网时间同步误差标准差优于0.05 ns.

Time synchronization is vital in positioning,navigation,and time services in satellite navigation systems.Under the autonomous operation mode,time synchronization of the entire constellation is realized via inter-satellite links to support normal navigation and positioning services.Compared with radio inter-satellite links,continuous laser links are able to provide clock deviation measurements with the same time tag and higher accuracy.In this paper,cooperative time synchronization via laser/radio inter-satellite links is proposed.First,a time comparison network based on the continuous laser inter-satellite link is established,and an inter-satellite time reference is generated using the weighted average algorithm.Then,through radio inter-satellite links,clocks of satellites outside the laser inter-satellite link network are traced to the time reference by using the distributed Kalman filter algorithm,thereby realizing time synchronization of the entire constellation.Finally,a simulation based on the new generation of BeiDou constellation is performed.Results show that the stability in the short and medium terms of the time reference generated via the cooperative time synchronization method is significantly improved compared with that generated via radio inter-satellite links.The standard deviation of the time synchronization error in the constellation is better than 0.05 ns.