北斗三频数据的两个无电离层组合轨道钟差估计及其应用

本文针对全球连续监测评估系统（iGMAS）和国际多系统GNSS试验计划（MGEX）两个观测网接收到不同频率北斗卫星数据的情况，提出了一种北斗卫星（BDS）3个频率（B1I、B2I、B3I）的两种无电离层组合（B1/B3和B1/B2）数据精密定轨（POD）和钟差估计（CE）方法。该方法可以统一处理上述两个观测网收到的北斗二代（BDS-2），北斗三代试验系统（BDS-3e）和北斗三代全球系统（BDS-3g）3个频率的观测数据，并在一次程序运行中对所有北斗卫星进行联合处理，可有效提高一次运行的数据使用率，从而提高参数估计精度。采集了多天iGMAS、MGEX的GPS和BDS数据进行试验。结果表明，对BDS-3e+BDS-2+GPS联合定轨时，采用三频两组合方法后由于增强了观测几何，BDS轨道重叠RMS为15.9 cm，比传统双频法定轨精度提高11.3%。新方法引入了与卫星端3个频率相关的码偏差，该量多天估计结果稳定，证明了模型和方法可靠。将新方法用于BDS-3g+BDS-3e+BDS-2+GPS联合定轨，6颗BDS-3g的MEO卫星轨道重叠RMS为14.5 cm，钟差重叠RMS为0.43 ns，与BDS-3e的15.1 cm和0.49 ns相当。开展了北斗卫星精密单点定位（PPP）试验，结果显示增加了BDS-3g的6颗MEO的精密轨道和钟差后，测站定位精度水平为39.6 mm，天顶为37.8 mm，比仅用BDS-2和BDS-3e卫星定位精度提高了11.1%。

Orbit determination and clock estimation via two ionosphere-free combinations of observation from BDS triple-frequency data and its application

The international GNSS monitoring and assessment system (iGMAS) and the multi-GNSS experiments (MGEX) receive BeiDou navigation signals on different frequencies. In this paper, orbit determination and clock estimation based on two ionosphere-free combinations of observation (B1/B3 and B1/B2) from BDS triple-frequency data is proposed. In this method, data of both networks from BeiDou 2nd generation (BDS-2), BeiDou 3rd generation test system (BDS-3e) and BeiDou 3rd generation global system (BDS-3g) can be processed uniformly in one program run, which can effectively improve data usage at one run, thereby improving parameter estimation accuracy. The GPS and BDS data of iGMAS and MGEX were collected for several days for testing. The results show that for the BDS-3e+BDS-2+GPS joint orbit determination, the orbit overlap RMS of the BDS MEO is 9.5 cm after using the triple-frequency two-combination method, which is 29% higher than the accuracy of traditional dual-frequency processing. The new method introduces a code bias parameter related to three frequencies of each involving BDS-2 satellite. The result shows values of the parameter are quite stable for continuous one-day solutions, which proves that the model is reliable. The new method is used for BDS-3g+BDS-3e+BDS-2+GPS joint orbit determination. The 6 BDS-3g MEO satellite orbit overlap RMS is 14.5 cm, and the clock error overlap RMS is 0.43 ns, which is equivalent to 15.1 cm and 0.49 ns of BDS-3e. The BDS precise point positioning (PPP) test was carried out. The results show that after adding the precise orbit and clock difference of the six MEOs of BDS-3g, the horizontal positioning accuracy of the station is 39.6 mm, and the zenith accuracy is 37.8 mm, which increases positioning accuracy by 11.1% than BDS-2 and BDS-3e satellites only.