基于星间链路体制的北斗卫星时间同步可行性分析

BD-3试验星上搭载了Ka频段星间链路（ISL）设备，可进行Ka波段对地观测。推导了星间链路时分观测体制双向时间同步的数学模型；以ISL星地观测数据为样本分析ISL体制时间同步的可行性，并与L波段观测结果比对。结果表明，ISL体制钟速拟合参数与L波段结果一致性较好，7 d和3 d弧段拟合精度在1 ns以内，1 d和1 h弧段拟合精度均在0.2 ns以内，较L波段拟合精度有所提高,其中1 d为最优拟合时长；利用7 d的实测星地钟差进行向后1 d的钟差预报，结果显示，ISL星地钟差1 d预报误差为2 ns，较L波段预报精度略有提高；最后采用星地星间联合钟差观测，2 d内观测残差为0.52 ns，验证了ISL钟差观测的可行性。

Feasibility Analysis of Time Synchronization of Beidou Satellite Using Inter-Satellite Observation Data

Beidou-3 experimental satellites are equipped with Ka band inter-satellite link(ISL) equipment, which provides satellite-ground orbit determination and time synchronization observation means of ISL mode. The mathematical model of synchronous observation of time-division satellite-ground two-way ISL mode is derived. Taking the satellite-ground data of ISL as a sample, the feasibility of time synchronization in ISL system is analyzed and compared with L band observations. The results show that the fitting parameters of clock offset in ISL system are consistent with those of L band. The fitting accuracies within 7 days, 3 days, 1 day and 1 hour are respectively 1 ns, 0.85 ns, 0.2 ns and 0.2 ns, which, especially for 1 day fitting, are better than those of L band. At the same time, the clock offset prediction accuracy of the next day is analyzed by using seven-day measurements of the satellite ground clock offset. The prediction error of ISL satellite clock offset is within 2 ns. Finally, the satellite-ground and inter-satellites combined observation is carried out. The error in 2 days observation is 0.52 ns. The feasibility of ISL observation is verified.