Multi-Frequency Pseudolites for Instantaneous Carrier Ambiguity Resolution

Kurt R. Zimmerman, Clark E. Cohen, David G. Lawrence, Paul Y. Montgomery, H. Stewart Cobb and Walter C. Melton

Abstract:	Satellite-based navigation has enabled significant efficiency gains in the open-pit mining industry. Some of the greatest gains have been achieved by using centimeter-level carrier phase positioning for drilling and shovel operations. Two leading architectures use GPS/GLONASS and L1/L2 receivers for carrier phase positioning. Both of these architectures degrade significantly as the mines get very deep because one or more steep walls will obscure enough satellites that the remaining satellites do not provide adequate geometry. The result can be a loss of availability that can significantly jeopardize mining operations. It has been recognized for quite a while that pseudolites placed around the rim of a mine should be able to compensate for blocked satellites and thus improve system availability. However, to date, pseudolites have not been added to mining operations for a number of reasons. One technical reason is that there is no straight- forward way to get carrier-phase accuracies in a mine using existing single-frequency pseudolite techniques. These techniques require that the vehicle move a significant distance until a large angle is subtended by the vehicle's vector to the pseudolite so that carrier cycle ambiguities can be resolved. In most mining situations, the distances that would need to be travelled to achieve the necessary geometry changes are impractical. There is much freedom to customize the signal when using pseudolites, and so a viable approach is to expand upon the principles employed by dual-frequency GPS receivers and apply them toward a multi-frequency system that can instantaneously resolve cycles with no motion whatsoever in the system. Importantly, such a multi-frequency system can be built upon existing GPS components, reducing design risk and cost. The four- frequency system discussed will produce superior performance over alternative techniques because instantaneous acquisition/reacquisition minimizes equipment down time. The cost of unnecessary idle time of mining equipment provides compelling justification for the development of a multi-frequency architecture. The multi-frequency system also features the ability to function as a pure pseudolite system with no satellites. Other anticipated benefits of the multi-frequency system include reduced multipath risk and more efficient communication of reference data.
Published in:	Proceedings of the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2000) September 19 - 22, 2000 Salt Palace Convention Center Salt Lake City, UT
Pages:	1024 - 1033
Cite this article:	Zimmerman, Kurt R., Cohen, Clark E., Lawrence, David G., Montgomery, Paul Y., Cobb, H. Stewart, Melton, Walter C., "Multi-Frequency Pseudolites for Instantaneous Carrier Ambiguity Resolution," Proceedings of the 13th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2000), Salt Lake City, UT, September 2000, pp. 1024-1033.
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