Automated determination of fault detection thresholds for integrity monitoring algorithms of GNSS augmentation systems

The reference stations of GNSS augmentation systems including GBAS (Ground Based Augmentation System) and SBAS (Space Based Augmentation System) are designed to provide correction and integrity information for airborne users so that they can estimate the positions accurately and reliably using GNSS signal measurements. Therefore the integrity monitoring algorithms of the reference stations should detect and exclude GNSS signals with faults or anomalies which could cause user position errors. Normally, the detection thresholds are determined based on the nominal data collected during the site assessment and installation process assuming that there will be no critical environmental changes that impact on the test statistics of integrity monitoring algorithms. However, the characteristics of the test statistics could change in case of new constructions or RF interference nearby, which could induce higher continuity and integrity risk than allocated to the monitor. In order to prevent it and establish updated thresholds, this paper proposes an automated fault detection threshold determination procedure and environment change indicators. Examples with real GPS data show that the proposed procedure detects the environment change and determines new thresholds successfully.