Development of the LAAS Accuracy Models

Abstract

This paper provides details underlying the pseudorange accuracy models originally developed for the GPS LAAS MASPS. During the development of the MASPS, WG-4 of RTCA SC-159 realized that it needed standardized error models for LAAS availability assessments. To meet this need, various Ground and Airborne Accuracy Designators were defined based upon performance that could be achieved using currently available GPS receiver technology. In addition Signal-In-Space error models were developed for such effects as tropospheric and ionospheric temporal and spatial decorrelation. Pseudorange errors are modeled as a function of predictable parameters such as satellite elevation angle. When combined with assumptions about the differential correction methodology, airborne positioning algorithm, and integrity limit computations, these pseudorange error models permit a determination of the availability of a desired level of service from the LAAS. Refinements of the models have also been made since their original publication in the LAAS MASPS, notably in the development and validation of the ICAO GNSS SARPs.