Characterization and Comparison of Galileo and GPS Anomalies

Abstract

Receiver autonomous integrity monitoring (RAIM) has long relied on GPS to achieve lateral navigation by different aerospace and aviation systems. However, an advanced form of RAIM, called ARAIM, would achieve the additional function of vertical navigation. However, because vertical operations require tighter integrity capabilities than what is currently achievable by RAIM, more stringent evaluations of GNSS performance has become a greater focus, especially as new satellite service constellations such as Galileo become more operationally mature. There are two categories of satellite faults that ARAIM requires knowledge of: satellite fault, which affects each satellite independently, and constellation fault, which affects multiple satellites simultaneously due to a common cause. By analyzing GNSS performance, estimates for the likelihood of each type of fault can be obtained and its impact on ARAIM performance can be assessed. Different fault likelihoods result in different safety comparisons, thus, it is important to evaluate the fault types and their probabilities of occurrence. This paper examines the last 3 years of Galileo clock and ephemeris errors to obtain appropriate estimates for the probability of independent satellite failures, P sat , and the probability of simultaneous satellite failures, P const . This paper also examines the two most recent GPS faults in 2022 and 2023 and near-faults from 2017 to 2021 given that there have been no GPS faults between 2012 and early 2022, but still some anomalous events worthy of analysis.