The Role of Time and Frequency in the MTSAT Satellite-Based Augmentation System (MSAS)
NEC CORP TOKYO (JAPAN)
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The MTSAT Satellite-based Augmentation System MSAS is a satellite-based augmentation system SBAS for navigation. The MSAS is one of several applications that shares the use of the Multifunctional Transport Satellite MTSAT, a geostationary earth orbiting GEO satellite, which will be launched by the Japanese Ministry of Transport in August 1999. The MSAS design is based on the development of the US Wide Area Augmentation System WAAS and therefore may be familiar to those who are acquainted with the WAAS. Time and frequency play a critical role in four areas within MSAS, and these areas are the focus of this paper. Firstly, MSAS performs several functions. One - it collects data from the NA VSTAR Global Positioning System GPS two - it provides an independent ranging signal from MTSAT to supplement the navigation signals from the GPS constellotion three - it provides differential corrections to improve the navigation capability of the GPS four - it provides the offset of MSAS Network Time MNT from Coordinated Universal Time UTC andpve - it provides system integrity information to the user. With these functions, the MSAS can become the primary means of time distribution and synchronization within Japan and other areas under the footprint of the MTSAT. The accuracy and precision attainable by MSAS is critically dependent on the performance of the time and frequency subsystems in the four areas of discussion. The first area of discussion is the manner in which the data recording system tags its observations. Accurate recording of the time of observations is essential in order to measure the timeliness latency of all transmitted information. This information is based on algorithm that derive their input from data collected from a network of eight data collection sites,including four Ground Monitoring Stations GMS and four Monitor and Ranging Stations MRS. Each GMSMRS has three independent, free-running cesium-beam frequency standards.
- Navigation and Guidance