导航星座自主导航的时间同步技术

Time Synchronization Techniques of the Autonomous Navigation of Navigation Constellation

导航星座自主导航能够有效地减少地面测控站的布设数量,减少地面站至卫星的信息注入次数,降低系统维持费用,实时监测导航信息的完好性,增强系统的生存能力。卫星时间同步是实现导航星座自主导航的关键技术之一,而星载原子时钟的频率稳定性能直接影响着卫星时间同步精度。本文基于星载原子时钟频率稳定性的Allan方差表达,建立系统状态方程,并以星间双向测量伪距差作为基本观测量,组成系统测量方程。从而,可以设计适用于导航星座卫星时间同步的Kalman滤波算法。系统仿真结果表明:通过滤波处理星间双向测距数据,不断地更新卫星时钟参数,能够实现星座卫星自主高精度时间同步。

By using the autonomous navigation techniques of navigation constellation, the number of the ground control stations, the injecting message frequency from the ground stations to satellites and system maintenance cost may be reduced significantly. Meanwhile, the integrity of navigation messages can be monitored real-time and the survivability of the navigation system also enhanced. The inter-satellite time synchronization is one of key techifiques to implement the autonomous navigation, while the stability of on-board atomic clocks＇ frequency would impact directly on the accuracy of the time synchronization. Generally, the stability of the atomic clocks＇ frequency was expressed quantificationally with Allan variance, and then the system state equations of the clocks established. Moreover, using the pseudorange differences between two satellites as the basic measurements, the measurement equations were gotten. Therefore, the Kalman filtering algorithm applied to inter-satellite time synchronization was designed easily. Finally, it is clearly shown from the simulated results that the autonomous time synchronization among the constellation satellites can be implemented highly-accurately by processing the inter-satellite measurement data with the on-board Kalman filters and updating continually the clock parameters of the satellites.