Improving DGPS Accuracy With Clock Aiding Over Communication Links

Patrick Y. Hwang, Gary A. McGraw, Bernard A. Schnaufer and David A. Anderson

Abstract:	With few exceptions, GPS (and DGPS) vertical accuracy is generally poorer than its horizontal accuracy. This is particularly acute for raised masked angles that restrict the visible sky and lead to clustering of the available satellites. A similar effect on horizontal accuracy is also found to be caused by clustering of satellites in a directional sense. For airborne applications that require vertical accuracy for guidance and control, but are saddled with operational environments of restricted satellite visibility, previous efforts have been focused primarily on lowering the range error or raising the number of ranging sources, both of which give only limited possibilities for performance improvement. This paper describes a method to significantly improve vertical accuracy for differential GPS operation using high precision time transfer across a two-way communication link, which in addition to serving as the differential data link, is being used as a sensor to augment GPS. An accuracy analysis of various operational scenarios having varying degrees of satellite signal obscuration is provided along with discussion on the extent to which the proposed method will improve on the navigation accuracy performance. The paper includes simulation analysis results that support the error reduction and provide a realistic error budget for the total system performance that represents the operational environment. Real-life performance measurements made from a lab bench breadboard system of the auxiliary sensor assembled at Rockwell Collins will also be presented to validate some of the error models used in the analysis and simulation.
Published in:	Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005) September 13 - 16, 2005 Long Beach Convention Center Long Beach, CA
Pages:	1961 - 1970
Cite this article:	Hwang, Patrick Y., McGraw, Gary A., Schnaufer, Bernard A., Anderson, David A., "Improving DGPS Accuracy With Clock Aiding Over Communication Links," Proceedings of the 18th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2005), Long Beach, CA, September 2005, pp. 1961-1970.
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