GPS Augmentation With Pseudolites for Navigation in Constricted Waterways

T. Morley and G. Lachapelle

Abstract:	This paper investigates the use of a portable ground-based transmitter, or pseudolite (pseudo-satellite), to augment the existing space-borne GPS satellite constellation. As the emphasis is on shipbome navigation, the use of a height constraint is also exploited. A simulation analysis is conducted to investigate the effect of increasing mask angle on GPS availability, accuracy and reliability measures. Up to three pseudolites at various locations are then introduced in the simulation to illustrate the improvements in the above measures. Finally, results from a field test conducted at Lake Okanagan, in British Columbia, Canada are presented. It was found that, even with a relatively modest elevation mask angle of lo”, there are periods when the horizontal accuracy measures (HDOP) are satisfactory, although the possible maximum horizontal error (MHE) due to an undetectable blunder is unacceptable. By augmenting the standard GPS satellite constellation with one or more pseudolites (PL), the accuracy and reliability measures can be improved significantly. For an unaugmented constellation and a 20” mask angle the average 24-hour HDOP was 1.7 1, and the average value for the maximum (worst-case) horizontal error possible was 37.8 m. The use of just one pseudolite reduced these values to 1.39 and 12.6 m, respectively.
Published in:	Proceedings of the 1997 National Technical Meeting of The Institute of Navigation January 14 - 16, 1997 Loews Santa Monica Hotel Santa Monica, CA
Pages:	595 - 605
Cite this article:	Updated citation: Published in NAVIGATION: Journal of the Institute of Navigation
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