Time Distribution Capabilities of the Wide Area Augmentation System (WAAS)

Because of the role of time as a secondary mission of the Wide Area Augmentation System WAAS, the FAA has been interested in developing the use of the WAAS for time distribution. An economical, evolutionary approach to the development of the WAAS for time distribution has been pursued. Several groups have been participating in a program to develop a Time Distribution System TDS. Data presented to date indicate that the WAAS is probably not at the same level as GPS for time distribution. Recent WAAS data indicate that the daily average values of the differences between UTC USNO and WAAS Network Time WNT range between 20 ns and -25 ns. Recent GPS data from USNO obtained with a single frequency GPS Time Transfer Unit indicate that 2-day average values of the differences between UTC USNO and GPS Time range between 6 ns and -15 ns. Because of foreseeable improvements in the not-too-distant future, it seems reasonable to expect that the WAAS will soon exceed the performance of GPS for time distribution. Among these improvements are operational improvements within the WAAS as it matures, and improved orbits for the geostationary satellites as more stations inaugurate satellite-based augmentation system SBAS observations for time.