In view of many problems associated with the availability of global navigation satellite system (GNSS) signals in high-altitude space, this paper presents a comprehensive and systematic analysis. First, the coverage and strength characteristics of GNSS signals in high-altitude space (i.e., space above the GNSS constellation) are presented, and the visibility of GNSS signals is evaluated by combining these two factors. Second, the geometric configuration and geometric dilution of precision (GDOP) of visible GNSS satellites are analysed. Then, the Doppler shift range of the GNSS signals is deduced based on the dynamic performance of high-altitude spacecraft. Finally, taking GaoFen-4 (GF-4) as the application object, the availability of GNSS signals is simulated and evaluated. GNSS signals in high-altitude space are generally weak, and the visible GNSS satellites are concentrated in the high-elevation range. The combination of main and side lobe signals and compatibility of multiple constellations can increase the number of visible satellites, improve the geometry configuration, reduce GDOP, and thus improve the availability of GNSS signals. The results of this research can provide technical support for the design and development of GNSS receivers suitable for high-altitude space.

中文翻译：

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GNSS 星座上方 GNSS 信号的可用性分析

鉴于全球导航卫星系统（GNSS）信号在高空空间的可用性存在诸多问题，本文进行了全面系统的分析。首先，给出了GNSS信号在高空空间（即GNSS星座上方的空间）的覆盖范围和强度特性，并结合这两个因素评估了GNSS信号的可见性。其次，分析了可见GNSS卫星的几何构型和几何精度稀释（GDOP）。然后，根据高空航天器的动态性能推导出GNSS信号的多普勒频移范围。最后，以高分四号（GF-4）为应用对象，对GNSS信号的可用性进行了仿真评估。高空空间的 GNSS 信号一般较弱，可见的GNSS卫星集中在高海拔范围内。主瓣和旁瓣信号的结合以及多星座的兼容可以增加可见卫星的数量，改善几何配置，降低GDOP，从而提高GNSS信号的可用性。该研究成果可为适用于高空空间的GNSS接收机的设计和开发提供技术支持。