21/05/2020
The WAAS is designed to improve the accuracy, integrity, and availability of signals. WAAS allows GPS to be used as the aviation navigation system from through Category I precision approaches. ICAO (International Civil Aviation Administration) has defined Standards for satellite-based augmentation systems (SBAS), and Japan and Europe are building similar systems that are planned to be interoperable with WAAS: EGNOS, the European Geostationary Navigation Overlay , and MSAS, the Japanese Multifunctional Transport (MTSAT) Satellite-based Augmentation System. .
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The result is a worldwide seamless navigation capability similar to GPS but with greater accuracy, availability, and integrity.
Unlike traditional ground-based navigation aids, WAAS will cover a more extensive area in which surveyed wide-area ground reference stations are linked to the WAAS network. Signals from the GPS satellites are monitored by these stations to determine satellite clock and ephemeris corrections. Each station in the relays the data to a wide-area master station where the correction information is computed. A correction message is prepared and uplinked to a geostationary satellite (GEO) via a ground uplink and then broadcast on the same frequency as GPS to WAAS receivers within the broadcast coverage area.
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In addition to providing the correction signal, WAAS provides an additional measurement to the aircraft receiver, improving the availability of GPS by providing, in effect, an additional GPS satellite in view. The integrity of GPS is improved through real-time monitoring, and the accuracy is improved by providing differential corrections to reduce errors. As a result, performance improvement is sufficient to enable approach procedures with GPS/WAAS glidepaths.
