###### Abstract  
Global navigation satellite system (GNSS) plays a crucial role in many fields, such as aerospace and transportation. Integrity is the measure of trust used in GNSS positioning especially in safety-critical applications. Advanced receiver autonomous integrity monitoring (ARAIM), taking full advantage of multi-constellation GNSS, shows huge potential to provide vertical navigation in civil aviation en route navigation and terminal approaches. However, the multi-constellation ARAIM also greatly exposes computational complexity and potential performance hazards in fault modes determination and fault-tolerant positioning. From the perspective of integrity risk control, rather than the pursuit of better positioning accuracy blindly for safety-critical applications, the concept of constellation dynamic selection is proposed and implemented in ARAIM and the performance analysis is discussed in this paper. Only the best two constellations which have the best vertical geometry performance are involved in ARAIM calculation anytime anywhere. The proposed method shows superiority in both integrity availability and computational complexity in both simulations and actual GNSS signal experiments. While the computational complexity is less than 10% of that using four constellations, 100% availability under LPV-200 criteria can be achieved in worldwide coverage experiment. The proposed method also overcomes the shortcomings of ARAIM with two fixed constellations and shows good robustness under depleted scenarios. Furthermore, the statistics results from observation stations proved the applicability and generality of the proposed method under current developing GNSS constellations. GNSS; navigation; positioning; ARAIM; multi-constellation; integrity +
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proposed to provide integrity solution for civil aviation vertical guidance using airborne monitors. Different from the traditional RAIM, ARAIM can monitor multiple simultaneous fault modes like two satellite fault and constellation fault [10; 11]. The recent Galileo constellation outage further reminds us that it definitely happened even though its probability is extremely low [12; 13]. It is irresponsible to take such chances under safety-critical applications. ARAIM can effectively detect and exclude such faults and provide a higher-level integrity for GNSS availability. The ARAIM user algorithm is implemented based on multi-constellation and dual-frequency GNSS, where the spatial geometry will be improved greatly and the ionosphere error can be corrected easily through dual-frequency observations combination [14; 15]. ARAIM is outlined by the GPS Evolutionary Architecture Study (GEAS) and has been further developed within the EU-US Cooperation on Satellite Navigation Working Group C ARAIM Technical subgroup (ARAIM TSG) [16]. The research of ARAIM TSG focuses on GPS/Galileo dual-constellation. It is believed that the four global constellations, GPS/GLONASS/Galileo/BDS, will provide more solutions and tap more potentials for the ARAIM development. As a navigation integrity solution, ARAIM has also shown wide-ranging applicability and potentiality in other GNSS safety-critical applications like connected car network and anti-spoofing [17; 18]. ARAIM uses multi-constellation observations to improve the satellite geometry and increase redundant measurements. However, a core question is that whether more constellations are better for receiver integrity monitoring. On the one hand, the recent simulation research has shown that based on two constellations, ARAIM can cover about 90% of the world with a 99.5% availability, where the 99.5% availability herein means that the ARAIM is available during 99.5% of the time at the test point [19]. The fact is the regions cannot meet the above requirements are mainly concentrated in the polar regions where the civil aviation demand is not strong in the foreseeable future.