DESCRIPTION AND ASSESSMENT OF REAL-TIME ALGORITHMS TO ESTIMATE THE IONOSPHERIC ERROR BOUNDS FOR WAAS

The Federal Aviation Administration (FAA) is developing a Wide-Area Augmentation System (WAAS) to augment GPS for use during en route through Category I (CAT I) precision approach flight operations. WAAS has three components : (1) extra ranging sources using geostationary earth orbiting (GEO) communications satellites ; (2) a vector of corrections to the GPS signal-in-space, including components for ionospheric delay estimations and clock and ephemeris errors ; and (3) integrity monitoring to alert users of out-of-tolerance conditions. This paper describes real-time ionospheric algorithms that are part of the accuracy and integrity monitoring functions. A performance assessment is made with respect to the requirements specified in the WAAS procurement.