NDGPS Network Enhancments in FY01

L. W. Allen, D. B. Wolfe, C. L. Judy, E. J. Haukkala and R. W. James

Abstract:	While implementing the world’s largest ground-based GPS augmentation service, Nationwide DGPS (NDGPS), the US Coast Guard (USCG) has explored numerous enhancements. Designed to operate in concert to create a more accurate, robust and appealing system; enhancements are wide ranging in design and function. NDGPS is the descendant of Maritime DGPS designed to fulfill the USCG’s original responsibility, i.e. provide DGPS coverage to all harbors and harbor approaches of the United States. The Maritime DGPS Broadcast Site network continues to provide differential corrections along the Atlantic, Pacific and Gulf Coasts, the Great Lakes and the coastal waterways of Hawaii, Puerto Rico and southern Alaska. As the number of users and uses of DGPS increased, the need to expand the DGPS coverage area has also increased. An agreement with the US Army Corps of Engineers expanded the USCG’s DGPS coverage to the inland rivers of the US. The NDGPS expansion effort now includes over 70 Broadcast Sites with 56 more scheduled for construction. When completed, the system will provide double DGPS coverage across the continental United States and along the transportation corridor in Alaska and single coverage over the rest of Alaska, Hawaii and Puerto Rico. In 1997, the Department of Transportation (DOT) assembled an Executive Steering Group and a Policy and Implementation Team (PIT) composed of Federal agencies to determine a cost effective way to provide DGPS corrections to terrestrial users throughout the United States. The system had to meet a high level of accuracy, integrity and availability and be flexible enough to be easily improved to meet future user needs. The Executive Steering Group and PIT looked at several existing systems including commercial FM subcarrier and satellite provided systems, the Federal Aviation Administration’s Wide Area Augmentation System and Local Area Augmentation System and the Coast Guard’s DGPS service. This Executive Steering Group decided the most efficient and cost effective way to create a nationwide system was to expand the USCG’s Maritime DGPS network. Based upon their experience with providing DGPS coverage, USCG was designated as lead agency responsible for the design, construction and implementation of the Broadcast Sites and Control Stations in the NDGPS expansion. Integrity, availability and accuracy continue to drive enhancements to the NDGPS network. This paper details several projects that work in concert to propel NDGPS into a versatile network that only a high degree of accuracy can bring. Topics include: specific aspects of the High Accuracy NDGPS project sponsored by the USCG Navigation Center (NAVCEN) and TASC; the Federal Highway’s (FHWA) high accuracy project technologies; current high accuracy engineering implementations including Long-Range Aids to Navigation (LORAN) diplexing; RF studies; and future NDGPS system upgrades like the Nationwide Control Station (NCS) and RSIM Transmitter Control Interface (RTCI). From software and hardware enhancements to engineering ground stations, NDGPS is continuously improving to meet the needs of all maritime and terrestrial users.
Published in:	Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001) September 11 - 14, 2001 Salt Palace Convention Center Salt Lake City, UT
Pages:	2722 - 2734
Cite this article:	Allen, L. W., Wolfe, D. B., Judy, C. L., Haukkala, E. J., James, R. W., "NDGPS Network Enhancments in FY01," Proceedings of the 14th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2001), Salt Lake City, UT, September 2001, pp. 2722-2734.
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