WIDE AREA AUGMENTATION OF THE GLOBAL POSITIONING SYSTEM

The Wide Area Augmentation System (WAAS) is being deployed by the Fede ral Aviation Administration (FAA) to augment the Global Positioning Sy stem (GPS). The WAAS will aid GPS with the following three services. F irst, it will broadcast spread-spectrum ranging signals from communica tion satellites. The airborne WAAS receiver will add these new ranging signals to the GPS constellation of measurements. By so doing, the au gmented position fix will be less sensitive to the failure of individu al system components, thus improving time availability and continuity of service. Second, the WAAS will use a nationwide ground network to m onitor the health of all satellites over our airspace and flag situati ons which threaten flight safety. This data will be modulated on to th e WAAS ranging signals and broadcast to the users, thereby guaranteein g the integrity of the airborne position fix. Third, the WAAS will use the ground network to develop corrections for the errors which curren tly limit the accuracy of unaugmented GPS. This data will also be incl uded on the WAAS broadcast and will improve position accuracy from app roximately 100 m to 8 m. When complete, the augmented system will prov ide an accurate position fix from satellites to an unlimited number of aircraft across the nation. It will be the primary navigation system for aircraft in oceanic routes, enroute over our domestic airspace, in crowded metropolitan airspaces, and on airport approach.