Ground monitor threshold models of BDS GBAS

The general method of evaluating the ground subsystem integrity risk consists of placing a series of monitors on the ground. However, only when the appropriate threshold is applied can the risk be accurately evaluated. For BDS GBAS, there is currently no developed method for threshold modeling. This paper proposes an improved method for threshold modeling of the BDS GBAS ground monitor based on real data collected at Dongying Airport. Compared with the original approach, this method results in certain improvements. The improvements are as follows: (1) Definition of the boundaries of the core and tails is proposed to verify satisfaction of the overbounding requirement in the inflation step to calculate thresholds. (2) This paper uses time instead of elevation for statistics that are independent of elevation in the normalization of test statistics. (3) The method of truncation is used in this paper to mitigate the heavy-tailed distribution that is encountered in the calculation of the data distribution. (4) The proposed method relies on the t distribution instead of the Gaussian distribution when dealing with the analysis of a small sample. Finally, combined with measured data and the proposed improved method mentioned, certain typical threshold models are developed and analyzed for different cases, including different constellations (GPS and BDS), frequencies and satellite orbits.