Wide Area Augmentation System (WAAS): The WAAS, a satellite-based augmentation system operated by the U.S. Federal Aviation Administration (FAA), provides aircraft navigation for all phases of flight. Today, these capabilities are broadly used in other applications because their GPS-like signals can be processed by simple receivers without additional equipment. Using International Civil Aviation Organization (ICAO) standards, the FAA continues to work with other States to provide seamless services to all users in any region. Other ICAO standard space-based augmentation systems include: Europe's European Geostationary Navigation Overlay System (EGNOS), India's GPS and Geo-Augmented Navigation System (GAGAN), and Japan's Multifunction Transport Satellite (MTSAT) Satellite Augmentation System (MSAS). All of these international implementations are based on GPS. The FAA will improve the WAAS to take advantage of the future GPS safety-of-life signal and provide better performance and promote global adoption of these new capabilities.
?Taken from www.gps.gov