COMPARISON OF MASTER STATION AND USER ALGORITHMS FOR WIDE-AREA AUGMENTATION SYSTEM

The global positioning system will be used for a wide variety of appli cations, However, aircraft use of any satellite-based navigation syste m raises significant concern with respect to accuracy and integrity. T he wide-area augmentation system (WAAS) is a navigation system that ad ds an independent ground network and increases navigation accuracy and integrity. The WAAS will be a supplemental navigation aid for all pha ses of Right down to category I precision approach in 1997, Eventually , it will be a primary navigation aid, Stanford University installed t hree wide-area reference stations in the Western United States and has been conducting independent flight tests of WAAS since 1994, The comp arison of the two different WAAS algorithms and the results from the S tanford University WAAS static and flight tests are presented. The res ults showed that 3.5 m of WAAS user vertical positioning accuracy, com pared to 80 m for stand-alone, can be achieved using both WAAS algorit hms. That accuracy is within the +/- 4.1-m 95% error limits for a cate gory I instrument landing system. An improvement on the existing grid ionosphere estimation algorithm is also included as well as the introd uction of a weighted least-square solution in WAAS user position compu tation.