Ephemeris type a fault analysis and mitigation for LAAS

Abstract

The Local Area Augmentation System (LAAS) has been developed by the FAA to enable precision approach and landing operations using the Global Positioning System (GPS). Each LAAS installation provides services through a LAAS Ground Facility (LGF) which is located at the airport it serves. By monitoring the GPS signals, measurements, and navigation messages, the LGF is able to exclude unhealthy satellites and broadcast real-time range-correction messages for healthy satellites to users via a VHF data link. Airborne users apply these corrections to remove errors that are common between the LGF and the aircraft.The LGF is also responsible for warning the aircraft of any potential integrity threats that cannot easily be resolved by excluding unhealthy satellites. One source of potential errors is the satellite broadcast ephemeris message, which users decode and use to compute GPS satellite positions. In LAAS, potential GPS ephemeris faults are categorized into two types, A and B, based upon whether or not the fault is associated with a satellite maneuver. This work focuses on aviation navigation threats caused by Type A faults. To detect and mitigate these threats, we investigate two LGF monitors based on comparing expected ranges and range rates (based on broadcast ephemeris) with those measured by the LGF. The effectiveness of these monitors is analyzed and verified in this paper.

Targeted Parameter Inflation within Ground-Based Augmentation Systems to Minimize Anomalous Ionospheric Impact

“…The preinflation P value of 0.00014 is based on the maximum P value needed to protect against ephemeris faults. This P value is calculated by dividing the minimum detectable error of the ephemeris monitors of about 2700 m (in 3-D satellite orbit space) by the minimum range from GBAS ground facility to GPS satellite (about 2:018 10 7 m; note that using the minimum range maximizes the resulting P value) and rounding up [29,30].…”

Ephemeris Monitor for GBAS Using Multiple Baseline Antennas with Experimental Validation

“…There are three types of orbit ephemeris failures [1]. Type B failures occur when the broadcast ephemeris data is incorrect but no satellite maneuver is involved.…”

“…In contrast, previous ephemerides provide no benefit for the detection of type A1 and type A2 faults due to the presence of the satellite maneuver. In order to detect these faults, ground monitors based on the range and range rate of the satellite are utilized [1].…”

Optimal antenna topologies for spatial gradient detection in differential GNSS

“…Orbit ephemeris faults can also induce spatial gradient errors in differential GNSS systems, including GBAS [ Jing et al , ]. There are three types of orbit ephemeris faults [ Tang et al , ]. Type A1 faults occur when a satellite's broadcast ephemeris data has been updated incorrectly following a satellite maneuver; a type A2 fault exists if the broadcast ephemeris remains unchanged after the maneuver; and type B faults occur when the broadcast ephemeris data is incorrect but no satellite maneuver is involved.…”