Determination of Monitor Thresholds for a GBAS ground station

Abstract

The Ground Based Augmentation System (GBAS) is designed to provide sufficient availability of accuracy, continuity, and integrity to satisfy the demanding requirements of aircraft precision approach, landing, and surface navigation under poor visibility conditions. The use of the GPS constellation alone is not practical because the satellites do not provide enough ranging accuracy on their own and there are too few of them to provide 99.9% availability. To enhance GPS positioning accuracy, the GBAS ground facility (GGF) generates differential corrections, based on the surveyed location of reference receivers, and broadcasts the correction message to an approaching airplane using a VHF data link. To ensure navigation integrity, the GGF is also responsible for detection and removal of anomalies such as ground-based or space-based system failures. Thus, the broadcast data also contain alerts on system failures and integrity parameters which reflect the quality of the correction. Based on the GBAS messages, the users determine which satellites can be used safely and correct their ranging measurements. GBAS ground facility runs different monitor to detect and isolate failures on measurements and satellite orbits. Once a failure is detected, the associated measurement, satellite and/or receiver is excluded to guarantee the integrity of the differential corrections. The target of this project is to develop and implement a methodology to estimate the integrity thresholds for the following monitors: Code carrier Divergence, Carrier smoothed Code (Innovation), Carrier Acceleration ramp and B-values Test. Objectives: - Background literature review to know the state of the Art. - To study the main GBAS Ground Facility monitors. - To develop algorithms estimate the integrity thresholds for the monitors: o Code carrier Divergence, o Carrier smoothed Code (Innovation), o Carrier Acceleration ramp - To write a report summarising the work done and with a critical review of methodology and results.