GEOSTAR: navigation location system

The author describes the Radiodetermination Satellite Service (RDSS). The initial phase of the RDSS provides for a unique service enabling central offices and headquarters to obtain position-location information and receive short digital messages from mobile user terminals throughout the contiguous United States, southern Canada, and northern Mexico. The system employs a spread-spectrum, code division multiple access (CDMA) modulation technique allowing multiple customers to use the system simultaneously, without preassigned coordination with fellow users. Position location is currently determined by employing an existing radio determination receiver, such as loran-C, GPS, or Transit, in the mobile user terminal. In the early 1990s position location will be determined at a central Earth station by time-differential ranging of the user terminals via two or more geostationary satellites. A brief overview of the RDSS system architecture is presented with emphasis on the user terminal and its diverse applications