With the deployment of the global BeiDou navigation satellite system (BDS-3) constellation completed, the positioning service performance is significantly improved relative to the regional system (BDS-2). As one of the key prerequisite products for precise point positioning (PPP), the combined BDS-2/BDS-3 real-time satellite clock estimation method is investigated in this study. Since the code hardware delays of BDS-2/BDS-3 satellites might be inconsistent for some receiver types, the inter-system bias (ISB) is considered in the combination although the overlapping B1I/B3I signal is employed. The combination processing is comprehensively evaluated in terms of satellite tracking coverage, clock precision, and convergence time. The experiment results indicate that the standard deviation (STD) precision of the estimated clocks for BDS-2 medium Earth orbit (MEO) satellites is improved by 52.0% from 0.150 ns to 0.072 ns due to the improvement of satellite tracking coverage. Introducing the ISB parameter as piece-wise constants improves the STD of all clocks from 0.076 ns to 0.067 ns and BDS-3 clocks achieve a significant improvement from 0.065 ns to 0.053 ns. The real-time clock estimation is demonstrated to be robust for the clock datum transformation, and it converges after one hour to a stable precision but needs a long time to achieve the best performance. The BDS real-time clocks are estimated with the proposed strategy to support real-time PPP based on the predicted satellite orbits. Results show that the clock STD is about 0.1 ns for most BDS satellites and the positioning accuracy of about 10 cm is achieved after the convergence time of about half an hour. The clock precision for BDS-2 geostationary Earth orbit (GEO) satellites is degraded to 0.303 ns due to the impact of poor orbit prediction errors. The exclusion of GEO satellites improves the positioning accuracy by about 15% and reduces the convergence time by 22–34%.

随着全球北斗卫星导航系统（BDS-3）星座的部署完成，定位服务性能相对区域系统（BDS-2）有了显着提升。作为精确点定位（PPP）的关键前提产品之一，本研究研究了组合的BDS-2/BDS-3实时卫星时钟估计方法。由于某些接收机类型的 BDS-2/BDS-3 卫星的代码硬件延迟可能不一致，尽管采用了重叠的 B1I/B3I 信号，但在组合中考虑了系统间偏差 (ISB)。组合处理从卫星跟踪覆盖范围、时钟精度、收敛时间等方面综合评价。实验结果表明，由于卫星跟踪覆盖范围的提高，北斗二号中地球轨道（MEO）卫星估计时钟的标准偏差（STD）精度从0.150 ns提高到0.072 ns，提高了52.0%。引入 ISB 参数作为分段常数将所有时钟的 STD 从 0.076 ns 提高到 0.067 ns，BDS-3 时钟实现了从 0.065 ns 到 0.053 ns 的显着改进。实时时钟估计被证明对时钟基准转换具有鲁棒性，并且在一小时后收敛到稳定的精度，但需要很长时间才能达到最佳性能。BDS 实时时钟是根据所建议的策略估计的，以支持基于预测的卫星轨道的实时 PPP。结果显示时钟 STD 约为 0。大多数北斗卫星为1 ns，经过半小时左右的收敛时间后，定位精度达到10 cm左右。BDS-2地球静止轨道（GEO）卫星的时钟精度由于轨道预测误差不佳的影响而下降到0.303 ns。排除 GEO 卫星后，定位精度提高了约 15%，收敛时间缩短了 22-34%。