Bridging GPS Outages in the Agricultural Environment using Virtualite Measurements.

Anthony Cole, Jinling Wang, Chris Rizos

Abstract:	This paper describes the design, analysis and testing of two methods that can be used to bridge GPS outages during an agricultural row cropping operation when using an integrated INS and code-based GPS system. The use of integrated systems in agricultural operations has become of increasing importance in recent years as farming operators are looking at combining different technologies to increase efficiency and to reduce the environmental 'footprint' of farming operations. Integrated GPS and INS systems are used to provide good long term stability through the GPS system, with higher data rates and reliability from the INS system. However these systems can still suffer from degradation during GPS blockages and increasing the availability of a position solution is one of the key challenges to improving the use of integrated systems in agricultural applications. The ""virtualite"" concept is a new method that involves the transformation of INS measurements into simulated GPS signals via the creation of virtual satellites (""virtualites"") that can be processed alongside real GPS measurements. In this paper two methods to bridge situations where operating tractors experience low GPS visibility by using virtualite measurements with the available GPS satellites were examined. The first method used virtualite measurements processed alongside real GPS measurements within a single receiver. The second method transformed the INS output into virtualite measurements and then constructed double-differenced code measurements for processing with double-differenced measurements formed from the visible GPS satellites. This method was used in order to obviate the need to simulate the receiver clock bias in the virtualite measurement simulation process. The effect on the position accuracy of placing the imaginary virtual satellites in different orbital positions was also examined. The two methods were compared in a real world test.
Published in:	Proceedings of IEEE/ION PLANS 2008 May 6 - 8, 2008 Hyatt Regency Hotel Monterey, CA
Pages:	497 - 504
Cite this article:	Cole, Anthony, Wang, Jinling, Rizos, Chris, "Bridging GPS Outages in the Agricultural Environment using Virtualite Measurements.," Proceedings of IEEE/ION PLANS 2008, Monterey, CA, May 2008, pp. 497-504. https://doi.org/10.1109/PLANS.2008.4570025
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