The study on centralized disposing mode timekeeping algorithm of autonomous running of navigation constellation

Abstract

The building algorithm of system time is one of the research focus of auto-navigation. This paper bases on centralized processing mode of auto-timekeeping, gives a kind of building algorithm of system time. On-board clock's weight are determined by the clock quantity which referring to the computation, change of clock velocity can reflect change of clock frequency, so it uses clock velocity instead of clock frequency for determining weight; this algorithm uses two kinds of method of predicting initial velocity: a. with the former two epochs each satellite of each day predict initial velocity, b. with the former two epochs each satellite of first day predict initial velocity. Choosing one clock as the main clock, according to defined sample interval, getting all the available clock error relative to the main clock. This paper gives the computation model of system time, testing the algorithm with IGS precise clock error(system time is IGST). The result shows: comparing to the equal weighted algorithm, the weighted algorithm has better stability. Adding prediction has a significant improvement on the system time's stability, method a: the difference between TA(weight) and TA(IGST) (International GNSS Service Time) is about 45ns, method b: the difference be-tween TA(weight) and TA(igst) (International GNSS Service Time) is about 65ns. The algorithm is in reason, it can be used for the building algorithm of system time of auto-navigation.