北斗广播电文钟差模型精度评估及改善策略

Abstract

星载原子钟是北斗卫星导航系统（BDS）的核心设备，其钟差模型是北斗广播电文的重要组成部分，模型精度直接影响BDS的服务性能。本文采用星地双向时频传递（TWSTF）钟差测量为参考，评估了BDS广播电文钟差模型精度，结果表明BDS广播电文钟差模型精度优于2 ns（数据龄期小于12 h）。针对BDS广播电文钟差参数解算问题，结合BDS地面段的钟差模型解算策略，本文提出进一步提升精度的多种策略。对于1 h时长的短期预报，本文提出加权线性模型与混合区间线性模型的钟差拟合预报方法，短期预报精度可提高20%以上；对于预报时长大于6 h的中长期预报，本文采用谱分析钟差时间序列，并根据谱分析结果构造预报模型，与简单的二次多项式模型预报相比，预报6 h精度提高13%，预报12 h平均提高了21%；对于IGSO/MEO卫星，本文提出将TWSTF的设备时延值作为参数估算，使钟差模型在设备切换后精度提高18%。最后，利用本文提出的改进策略对2017年1月-6月的钟差数据重新处理，获得了新的广播电文钟差模型时间序列。利用新的广播电文钟差模型进行北斗监测接收机定位，结果表明，N、E、U 3个方向精度分别提高14.22%、29.39%、14.91%，显著提升了BDS广播电文钟差服务性能。

Alternate abstract:

The spaceborne atomic clock is the core equipment of Beidou Satellite Navigation System (BDS). Clock error model is an important part of BDS broadcast messages, and its accuracy directly affects the service performance of BDS. In this paper, the accuracy of the BDS clock model is evaluated using the TWSTF clock error measurement as a reference. The results show that the accuracy of the BDS clock model is better than 2 ns (data age less than 12 h). Aiming at the problem of calculating the clock error parameters of BDS, combined with the clock error model solution strategy of the BDS ground segment, this paper proposes a variety of strategies to further improve the accuracy. For the short-term forecast of 1 h duration, this paper proposes a clock error forecast method of weighted linear model and mixed interval linear model. The accuracy of short-term forecast can be increased by more than 20%. For medium and long-term (>6 h), clock error time series is analyzed by spectral method and prediction model is constructed according to the spectral analysis results. Compared with simple quadratic polynomial model, the prediction accuracy of the clock error model is improved by 13% in 6 h and 21% in 12 h on average. For IGSO/MEO satellite, this paper proposes a strategy of using TWSTF equipment delay as parameters to estimate, which improves the accuracy of clock error model by 18% after equipment switching. Finally, using the improvement strategy proposed in this paper, the clock error data from January to June 2017 is reprocessed to obtain a new broadcast clock error model time series. Using the new broadcast clock error model to locate the BDS monitoring receiver, the results show that, the direction accuracy of N, E and U is increased by 14.22%, 29.39% and 14.91% respectively, which significantly improves the service performance of BDS broadcast clock error model.