Potential DoD Worldwide Differential/Kinematic GPS Positioning

Alan G. Evans, James P. Cunningham, Andrew W. Sutter, Bruce R. Hermann and S. Roger Horman

Abstract:	Near real-time, highly accurate positioning of Department of Defense (DoD) assets using a worldwide network of Global Positioning System (GPS) reference tracking stations is proposed. World Geodetic System (WGS 84) coordinates for dynamic platforms can be delivered with high GPS accuracy for long baselines, which many DoD applications require. Centimeter-level positioning accuracy of GPS reference sites has allowed their use in both differential and kinematic positioning solutions over such baselines. The application of multiple, distant (over 1000 km baseline), reference sites has already been demonstrated with meter-level accuracy for differential positioning and decimeter-level accuracy for kinematic positioning. Further, since the reference site positions are known to centimeter- level accuracy, the differential/kinematic positions are essentially absolute positions in WGS 84. This paper evaluates the extension of regional reference- aided positioning to worldwide DoD applications. A number of issues are addressed, such as the number of reference tracking sites required. The National Image and Mapping Agency (NIMA) GPS tracking network potentially provides reference stations applicable to worldwide differential/kinematic positioning for DoD customers. Each GPS satellite is in view to at least two of the NIMA tracking sites at all times. This means that a user anywhere in the world has satellites in common with at least two NIMA reference sites, a core requirement for worldwide differential positioning. Another issue addressed is the amount of data to be transferred to the user and the update rate of the data. Both corrector-based and measurement- based techniques are evaluated. Compression techniques are expected to reduce the dual-frequency reference station data to fewer than 500 bytes per epoch. Further, the Precise Positioning Service (PPS), not affected by Selective Availability (SA) variation, is expected to require a slow update rate; an update rate of over a minute has been demonstrated for regional differential positioning. A communications link to the user needs to be defined. At these very low data rates, a number of possibilities are available; these are reviewed with respect to ease of implementation. The paper addresses these issues and presents test results demonstrating potential positioning accuracy.
Published in:	Proceedings of the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2000) September 19 - 22, 2000 Salt Palace Convention Center Salt Lake City, UT
Pages:	1148 - 1156
Cite this article:	Evans, Alan G., Cunningham, James P., Sutter, Andrew W., Hermann, Bruce R., Horman, S. Roger, "Potential DoD Worldwide Differential/Kinematic GPS Positioning," Proceedings of the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2000), Salt Lake City, UT, September 2000, pp. 1148-1156.
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