联合星地与星间Ka伪距的北斗三号卫星一体化定轨和时间同步

北斗三号卫星之间及卫星与锚固站之间在Ka频段的伪距测量为其提供了一种不依赖于地面监测站的独立定轨和时间同步能力。本文针对星间链路分时测量的特点,采用分段一次多项式对卫星钟差进行建模,直接利用原始的星地和星间单程Ka伪距实现一体化定轨和时间同步并同时解算锚固站设备硬件时延。利用北斗三号8颗卫星和2个锚固站的实测Ka伪距数据进行验证,结果表明:在利用导航电文的预报钟速信息进行修正的情况下,星间Ka伪距残差RMS为0.052 m;R方向卫星轨道确定和预报精度(RMS)分别为0.016、0.033 m;卫星钟差估计和预报精度(95%)分别为0.038、0.992 ns;解算得到的锚固站收发设备时延之和的稳定性优于0.5 ns。试验还展示了该方法的适应能力:在没有预报钟速信息的极端情况下,虽然星间Ka伪距残差RMS增大了242%,但R方向轨道确定和预报精度仍分别达到0.021、0.041 m,钟差估计和预报精度分别达到0.040、1.092 ns。

Integrated orbit determination and time synchronization for BDS-3 satellites with satellite-ground and inter-satellite one-way Ka-pseudoranges

The Ka-band pseudoranges measured between satellites and between satellites and anchor stations provide the third-generation BeiDou navigation satellite system (BDS-3) an alternate approach to achieve orbit determination (OD) and time synchronization (TS) which is completely independent of monitoring stations. In this paper, by modeling the clock offsets with piece-wise linear polynomials, we directly process the inter-satellite (IS) and satellite-ground Ka-pseudoranges to conduct integrated OD and TS with simultaneously estimation for the hardware delay of anchor stations. Experiments with real Ka-pseudorange data observed at 8 BDS-3 satellites and 2 anchor stations are carried out. It is demonstrated that, with the broadcast clock drift corrections, the RMS of IS Ka-pseudorange residuals is 0.052 m; the accuracy (RMS) in radial direction of the estimated and predicted orbits are 0.016 and 0.033 m, respectively; the accuracy (95%) of the estimated and predicted clocks are 0.038 and 0.992 ns, respectively. The standard deviations of estimated hardware delays of anchor stations are smaller than 0.5 ns. The proposed method is adaptable as it also works even if no predicted clock drift is available. In this extreme case, the RMS of the IS pseudorange residuals is dramatically increased by 242%; However, the accuracies are 0.021 m and 0.041 m for the estimated and predicted orbits, respectively, while 0.040 ns and 1.092 ns for the estimated and predicted clocks, respectively.