Sigma Overbounding using a Position Domain Method for the Local Area Augmentaion of GPS

The local area augmentation system (LAAS) is a differential GPS navigation system being developed to support aircraft precision approach and landing navigation with guaranteed integrity and availability. While the system promises to support Category I operations, significant technical challenges are encountered in supporting Category II and III operations. The primary concern has been the need to guarantee compliance with stringent requirements for navigation availability. This paper describes how a position domain method (PDM) may be used to improve system availability by reducing the inflation factor for standard deviations of pseudo-range correction errors. Used in combination with the current range domain method (RDM), a 30% reduction in the inflation factor is achieved with the same safety standard. LAAS prototype testing verifies the utility of the PDM to enhance Category II/III user availability.