低轨卫星星座监测BDS空间信号完好性新方案的关键算法研究

BeiDou navigation system (BDS) is one of the Global Navigation Satellite Systems (GNSS). Its Signal In Space (SIS) integrity should be monitored to improve the service capability. However, building optimal global-wide Ground Monitoring Network (GMN) is very difficult for China. This will undoubtedly impact the safe operation of BDS. We proposed a novel conception of employing Low Earth Orbiters (LEO) constellation as the monitoring network. An example of Iridium Constellation validated this new scheme primarily. Campared with the traditional methods using GMN, the proposed one could advance the monitoring capability. Several key problems that must be solved were condensed after the initial study, which are the main research topics for this program: optimal selection of LEO constellation parameters; the impact of LEO position and time synchronization error on the monitoring performance; quick detection of the failed BDS satellite etc. Proposed technical solutions to the above problems are as follows, correspondingly. (1)Theoretical analysis and simulation calculation are combined to choose the optimal LEO constellation parameter set under the two-body gravitation condition and the perturbed condition, respectively. (2)The worst user location algorithm and the maximum slope algorithm, which are usually used in Galileo SISA and Reciever Autonomous Integrity Monitoring researches, are introduced to analyze the impact of LEO related errors on BDS SIS integrity monitoring performance. (3) Taking the fact that LEO moves very fast into account during the algorithm design, we will use Quasi-Accurate Detection and Kalman filtering to quickly and efficiently detect the abrupt-type and slope-type fault of BDS satellite. This will obviously improve the ingtegrity monitoring function, since the observation geometry of LEO to the observable BDS satellites changes much faster than that of GMN. These crucial problems will be overcomed through comprehensive researches. Thus, this paves the way for the new conception to become reality. This program is the extension of high-mediam-low earth orbiter data processing theory. So it is an important research topic and deserves much attention.

北斗系统(BDS)作为全球卫星导航系统之一，应监测卫星的空间信号完好性以提升服务性能。因客观条件限制，我国难以在全球优化布设地面监测网。为解决这一难题，并作为地面监测网的拓展，我们在预研阶段提出了低轨卫星（LEO）星座作为监测网的新思路，以铱星星座为例初步验证了该方案的可行性。与以地面监测为主的传统方案相比，新监测方案可提升监测能力。凝练出新方案须解决的关键算法，并作为本项目的主要研究内容：LEO星座参数的优化选取；LEO卫星轨道误差及时间同步误差对监测性能的影响；快速探测BDS卫星观测异常的算法等。提出如下解决方案：理论分析与仿真计算相结合优化星座参数；采用最差点算法与特征斜率算法分析LEO相关误差对监测性能的影响；结合新方案特点，采用拟准检定法与滤波算法快速探测BDS卫星观测异常。突破这些技术难点，可为新监测方案的论证奠定基础。本项目是高中低轨卫星数据处理理论的拓展，有重要理论意义。

目前GNSS空间信号完好性监测主要依赖地面监测站或导航卫星星间链路，这对于我国BDS空间信号完好性监测不一定适用：⑴无法在全球范围内均匀布设监测站；⑵IGSO/GEO星间链路的信号衰减较大，且监测几何结构改善不明显。本项目提出了采用低轨卫星（Low Earth Orbit-LEO）星座作为监测站网的BDS空间信号完好性监测方案。与布设地面监测站网的传统方案相比，该方案具有以下优势：⑴合理的LEO轨道设计可使监测站分布尽量均匀；⑵星站观测几何结构变换较快，利于提升异常监测敏感性；⑶观测数据质量更高；⑷若采用合理的LEO星上监测模式可降低地面监测站网通讯及数据处理的复杂程度；⑸服务范围更广。 本项目主要研究内容有：⑴不同LEO星座参数配置对BDS卫星空间信号完好性监测覆盖性能影响的研究；⑵LEO星座监测站网覆盖性能及监测性能分析研究；⑶仿真验证方案设计。通过深入研究，完成了相关研究内容，攻克了关键问题：⑴以铱星星座为参考，采用分布在6个圆轨道面的24颗卫星的Walker星座，研究了轨道高度和倾角对监测覆盖特性的影响；⑵通过研究发现，利用LEO星座的监测覆盖深度具有条带特征，由低纬向高纬地球逐渐增大，对传统地面监测网在海洋区域的监测覆盖增益较为明显；⑶结合STK软件与编写的数仿程序仿真了星载BDS观测数据，并对基于LEO星载的BDS空间信号异常监测方法进行了验证。此外，项目组利用实测低轨卫星数据对GPS空间信号异常进行了检测，实验证明可以准确探测到引起完好性风险的超限误差，利用LEO星座卫星检测导航系统空间信号完好性是可行的。本项目结合现有技术条件，开展基于LEO星座卫星监测BDS空间信号完好性的关键问题研究工作，不仅为对提升BDS系统性能提供新的思路，且可拓展高中低轨卫星的数据处理理论。因此具有重要的理论意义及实用价值，具有前瞻性与创新特色。