More GPS or Smarter GPS?
The question is, how can the U.S. Government do more to help users overcome the limitations of GPS in their local environment? Adding more satellites (there are already 31) or improving their placement is always helpful, but the industry can do much on the user side with government help. If we are to extract maximum benefit from whatever resources exist, we must break some entrenched habits. Communicating with time-stamped measurements rather than rapidly perishable coordinates is an essential first step. Combining that information with algorithms already documented, with no proprietary rights claimed, affords enormous improvement in accuracy, integrity, availability, and continuity of service. Methods advocated herein are best matched with fast Fourier transform (FFT)-based receiver configurations, which eliminate the need for correlators and track loops. For a more detailed treatment on this see reference 6. Equipment could be certified by standardized blind tests derived from specified scenarios with degradations intentionally inserted into data streams. Testing is another whole issue requiring more space, but rest assured: only change – not any magic – is required.
High satellite availability over the past several years has led the navigation community to depend on full fixes and overdetermined solutions, deemphasizing the use of dynamics. Familiarity and preoccupation with instantaneous position have allowed robustness to become a casualty of convenience. The authors believe that marked improvements are entirely within reach, without a need for straining budgets or scientific breakthroughs, by exploiting a combination of well-known methods with other techniques which, due to relatively recent appearance, are largely unknown. The U.S. Government can take the lead by having its agencies actively explore and implement these options in helping their applications evolve to improve service using today’s available GPS resources.
The opinions expressed in this article are those of the authors and do not reflect those of the U.S. Government or any of its departments or agencies.
Robust Design for GNSS Integration, James L. Farrell, Proceedings of ION GNSS 2008, Savannah, Georgia link: http://jameslfarrell.com/wp-content/ uploads/2010/05/robust.pdf
Aging SV’s – We Have Solutions, James L. Farrell, Proceedings of ION GNSS 2009, Savannah, Georgia link: http://jameslfarrell.com/wp-content/ uploads/2010/05/gnss09.pdf
Aircraft surveillance based on GPS position broadcasts from Mode S beacon transponders, E. Bayliss, et al, Proceedings of ION GPS-94.
GNSS Aided Navigation and Tracking, James L. Farrell, Amer. Literary Press link: http://jameslfarrell.com/publishedbooks- gnss-aided-navigation-and-tracking/ gnss-aided-navigation-and-tracking
GPS for military surveillance, G.A. van Sickle, GPS World, Nov. 1996.
Comparison of two approaches for GNSS receiver algorithms: batch processing and sequential processing considerations, vanGraas, et. al., Proceedings of ION GNSS-2005
Copyright © 2010 John W. Lavrakas and James L. Farrell
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