Availability Analysis of GNSS RAIM Based on Maximum Undetectable Position Bias

The combined use of multiple constellations of the Global Navigation Satellite System (GNSS) provides a great possibility to improve the integrity of the satellite navigation; however, with the increase of the number of satellites, the probability of multiple outliers increases. Although a number of studies analyzed the performance of the combined GNSS Receiver Autonomous Integrity Monitoring (RAIM), the analysis of the case of multiple outliers is still lacking. In this paper, a Maximum Undetectable Position Bias (MUPB) scheme, which is based on Bias Integrity Threat (BIT), is used to analyze the horizontal availability of RAIM with multiple outliers. We have analyzed the theoretical background for BIT and MUPB. Next, detailed simulations and analyses with single or combined GPS/BDS (BeiDou Satellite Navigation System)/GLONASS constellations were conducted to evaluate the performance of RAIM. In the simulated scenarios with three constellations (GPS  +  BDS  +  GLONASS) and 2 or 3 outliers occurring simultaneously, we compared the MUPB and the Horizontal Alert Level (HAL) of different aviation approach phases and analyzed the results.