WAAS Error Bounding During Ionospheric Storms

T.R. Schempp, L.J. Trautman

Abstract:	The Wide Area Augmentation System (WAAS) is a safety-critical, software-intensive system, augmenting the satellite-based Global Positioning System (GPS). The system provides airborne users with positions of adequate accuracy, availability, continuity, and integrity to support different phases of flight. WAAS has a top-level safety requirement to protect users against Hazardously Misleading Information (HMI) with seven 9’s of integrity (10-7 probability of HMI). An integral part of the proof that WAAS meets this strict safety requirement lies in analyzing how the system bounds errors during ionospheric storms. Many conservative features have been built into the WAAS algorithms to ensure that ionospheric storms can not cause HMI. This paper will show that the current release of WAAS has a great deal of integrity margin during ionospheric storms. Unfortunately, this margin comes at an availability cost. When the WAAS irregularity (storm) detector trips, the broadcast Grid Ionospheric Vertical Error (GIVE) bound is increased to a point where it is not useful for LNAV/VNAV operations. The paper will illustrate the importance of the irregularity detector in the current design and suggest an approach that may lessen its importance in the future and allow WAAS to maintain LNAV/VNAV operations during mild ionospheric storms while significantly improving availability on non-storm days.
Published in:	Proceedings of the 2003 National Technical Meeting of The Institute of Navigation January 22 - 24, 2003 Disneyland Paradise Pier Hotel Anaheim, CA
Pages:	175 - 182
Cite this article:	Schempp, T.R., Trautman, L.J., "WAAS Error Bounding During Ionospheric Storms," Proceedings of the 2003 National Technical Meeting of The Institute of Navigation, Anaheim, CA, January 2003, pp. 175-182.
Full Paper:	ION Members/Non-Members: 1 Download Credit Sign In