Performance analysis of advanced RAIM with the inclusion of BeiDou

The BeiDou Navigation Satellite System, also named BDS for short, is China's second-generation satellite navigation system that will be capable of providing all-weather and seamless positioning, navigation and timing services to users on a continuous worldwide basis. As a GNSS constellation, BDS is being developed and operated by China and will be compatible with other navigation satellite systems worldwide once completed. However, to satisfy the rigorous requirement of civil aviation navigation, more augmentation methods are necessary to improve the performance of BDS. As a method of aircraft based augmented system (ABAS), Receiver Autonomous Integrity Monitoring (RAIM) is still the most prevalent use of satellite navigation system in aircraft today. Airborne GNSS RAIM can monitor the real-time navigation performance using redundant navigation information and it is the last vital key link related to life safety when applying in civil aviation. As the development and implement of BDS, we can use multi-constellation for advanced Receiver Autonomous Integrity Monitoring (ARAIM) on the basis of interoperability between BDS and GPS. Advanced RAIM with multi-constellation has greatly improved the number and geometry of satellites in view which will lead to an improvement of the integrity and availability of the system. However, the BDS system is still under construction which has very different performance on satellite fault characteristics as well as the broadcast User Range Accuracy (URA) values from GPS so we can't treat BDS satellites exactly as the same as GPS satellites. Therefore it is critical to understand these differences and we feel it is very essential to have the capability to model this parameter differently for GPS and BDS constellation. This paper first summarizes main characteristics and performance of BDS constellation based on information that has been published by administration and researchers of BDS up to now. As follows, we compared the global visibility of GNSS satellites as well as the Geometric Dilution of Precision (GDOP) when BDS is incorporated to that of the GPS only case. Then a detailed introduction is made to Multiple Hypothesis Solution Separation (MHSS) algorithm which can account for different fault modes, different URA values and different probabilities of satellite faults. Among this algorithm a model for GPS-BDS combined constellation fault modes is established and then RAIM integrity on a fixed location and global availability based on the algorithm is simulated with real-time data. Finally, the result shows how RAIM performance is affected with the inclusion of BDS.