Performance Evaluation of BDS-3 Satellite Clocks Based on Inter-Satellite Link and Satellite-Ground Observations

The onboard atomic clock is responsible for the generation and maintenance of the time and frequency reference signal on the satellite, and its performance directly affects the service performance of the navigation system. Accurate and reliable satellite clock offsets are the basic data source for the performance evaluation of onboard clocks. Based on the satellite clock offsets measured by the Ka-band inter-satellite links (ISL) and the L-band satellite-ground precise orbit determination and time synchronization (ODTS), the performance of BDS-3 onboard rubidium clocks and hydrogen clocks, including the frequency accuracy, the frequency drift rate and the frequency stability are compared and analyzed in this paper. The research results based on the experimental data show that the frequency accuracy and frequency drift rate of the BDS-3 satellite clocks evaluated by the Ka-band ISLs and the L-band ODTS are basically consistent, and the frequency accuracy and drift rate of the hydrogen clock are better than rubidium clock. For the evaluation of frequency stability, the stabilities of BDS-3 satellite clocks for the averaging time of 1000 s and one day reach 2.5 × 10–14 and 2.5 × 10–15, respectively. The results of hydrogen clocks are also better than those of rubidium clocks. In addition, the satellite clock stability evaluation using the L-band ODTS and Ka-band ISL have their respective advantages. The evaluation results based on the ODTS clock offsets show better short-term stability. When the averaging time of the Allen variance is greater than 5000 s, the ISL clock offsets show better medium and long-term stability. In addition, compared with the ODTS clock offsets, the ISL clock offsets are not affected by the orbit errors, and the frequency stability of IGSO/GEO satellites obtained based on the ISL is significantly better than the ODTS clock. Therefore, the ISL is more suitable for evaluating the frequency stability of the BDS-3 IGSO/GEO satellites.