Frequency Performance Evaluation of BeiDou-3 Satellite Clocks

The satellite navigation system is a positioning, navigation and timing system based on time measurement. The performance of its satellite clocks determines its service accuracy. With the BeiDou-3 satellite clock operating successfully in orbit, it is providing a stable time-frequency reference for the space segment. In this work, the frequency performance evaluation system of BeiDou-3 satellite clocks is established. Frequency accuracy is evaluated by the average frequency deviation through hourly fitting. Considering that any clock product will introduce method errors which will affect the accurate evaluation of clock performance, the Combined Overlapping Hadamard deviation (COHDEV) is proposed as the frequency stability index based on the error characteristics of different products. The evaluation results show that the frequency accuracy of the BeiDou-3 satellite clock is better than 10^–11, the frequency drift of the passive hydrogen maser (PHM) is better than 10^–15/day, and the stability reaches 10^–15/day. In contrast, the rubidium clock has obvious frequency drift, and the long-term frequency stability is worse than that of PHMs.