Objectives The advanced receiver autonomous integrity monitoring (ARAIM) algorithm equally allocates the integrity and continuity risk, which leads to a conservative protection level calculation.
Methods We systematically analyze the factors affecting the protection level calculation, and propose an optimal risk allocation method for ARAIM considering the dilution of precision (DOP), and verifie the effectiveness of the method using three kinds of data from the multi-GNSS experiment (MGEX) station, vehicle and airborne experiments.
Results The results show that the proposed method can realize a tighter envelope of the protection level to the position error, and its performance is better than that of the half-interval search method. Compared to the risk-averaged method, the protection level improvement rates of BeiDou satellite navigation system（BDS） in the three types of experiments are 7.5%, 11.6% and 8.8%, respectively. In addition, the protection level optimization effect is closely related to the satellite observation geometry, and the improvement effect varies in different systems and regions.
Conclusions For BDS, the improvement in the non-Asia-Pacific region is better than that in the Asia-Pacific region, with 3.6 m and 1.0 m respectively in the two regions. In the Asia-Pacific region, the optimization effects in BDS and BDS/GPS are 1.0 m and 0.6 m, respectively, with the single BDS enhancement being more significant.
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