Constellation Design Based On LEO Satellite Navigation Augmentation

Over the past three decades,with the improvement of Global Navigation Satellite System(GNSS),the basic services of GNSS have been widely developed in different fields.However,GNSS has some inherent characteristics,like vulnerability,universality of error,uncertainty and the easily-obscured signal.Moreover,for the existing GNSS augmentation systems,the region where the monitoring stations can be built is usually limited.As a consequence,the navigation performance of GNSS is difficult to make further breakthroughs without the help of external augmentation.Fortunately,Low Earth Orbit(LEO)navigation augmentation technology is a potential solution to break through the bottleneck of navigation performance.In LEO-based navigation augmentation,the navigation performance metrics,e.g.,GDOP and NVS,are closely related to the LEO constellation.Therefore,the thesis discusses the design details of LEO constellation from three aspects: global navigation augmentation,regional navigation augmentation and integrity monitoring.The main contents are as follows:(1)From the perspective of global navigation augmentation,the key design factors of LEO constellation are detailedly discussed,such as orbital height,inclination and constellation configuration.By taking these factors as independent variables,the corresponding coverage performance is compared quantitatively.Based on the circularorbit-based Walker constellation,two constellations are designed.One is a single inclination constellation ensuring pole observation performance,the other is a mixedinclination constellation satisfying the condition of minimum GDOP.With Bei Dou-3Navigation Satellite System(BDS-3)being the navigation system to be augmented,the navigation augmentation performance of the aforementioned constellations is evaluated in terms of NVS and GDOP.It is demonstrated that the mixed constellation can achieve better coverage performance in middle and low latitudes.(2)From the perspective of regional navigation augmentation,the constellation design scheme based on elliptical orbit is presented.Owing to the large coverage region,and the long residence time of satellites in the apogee of elliptical orbit,the ellipticalorbit-based scheme is specifically suitable for regional navigation augmentation.Furthermore,the orbit parameter of each satellite is optimized under the Flower constellation framework to ensure that the trajectory of its subsatellite point can repeatedly pass through the center of the region.Specifically,a constellation instance is constructed to augment navigation performance in the region of Southwest China.By simulating NVS and GDOP of augmented BDS-3,it is validated that with the same number of LEO satellites,the proposed design achieves regional navigation augmentation performance.(3)Focusing on the requirement of integrity monitoring,the performance of Receiver Autonomous Integrity Monitoring(RAIM)is analyzed from two aspects.One is using LEO satellite as a “navigation information source”,the other is using it as a“satellite monitoring station”.By calculating the fault detection rate,it is validated that LEO satellites can effectively improve the performance of integrity monitoring.Additionally,the visibility from LEO satellites to BDS-3 is analyzed based on geometric model.The results can provide reference for constellation optimization in the case of integrity monitoring.(4)Based on B/S architecture,a visualization platform for LEO constellation design is implemented.On the platform,users can design satellite constellations,view the trajectories and get the navigation augmentation performance.The functional test shows that the platform possesses good interactivity and easily-understood information.