Differential-Differential GPS Navigation Concept

Wang Tang

Abstract:	For the conventional airborne application of differential GPS operation a data link is required to upload the pseudo-range correction information for each satellite in view to the airborne GPS receiver in real-time. The achievable accuracy in the differential mode is on the order of two to four meters. For certain missile applications this accuracy is highly desirable; however, the data link requirement is unacceptable. The concept of differential-differential GPS (DDGPS) introduced in this paper uses differential GPS to derive correction terms to be downloaded from the launch aircraft to the missile immediately prior to missile launch. For differential GPS operation, the accuracy improvement is due to the strong correlation of the GPS errors at two separate locations. This accuracy improvement is a function of the spatial correlation which, in turn, is a function of the distance between two receivers. GPS system errors are also strongly correlated in time, i.e., at any fixed location, the errors are slowly varying so that they can be estimated using the measurements collected a short while ago. By utilizing both temporal and spatial correlations, DDGPS can provide accuracies better than nominal GPS accuracy without the need of a real-time data link. Although DDGPS can be implemented with a number of specific filter and error estimation techniques, the implementations presented here are straightforward. A ground receiver similar to the one in the differential GPS operation is used to estimate the GPS system errors. The estimated errors are then uplinked to the carrier aircraft and transfered to the missile receiver prior to launch. During the missile mission, the estimated errors remain constant and are used as compensation terms in the GPS navigation computation.
Published in:	Proceedings of the 44th Annual Meeting of The Institute of Navigation (1988) June 21 - 23, 1988 U.S. Naval Academy Annapolis, Maryland
Pages:	88 - 92
Cite this article:	Tang, Wang, "Differential-Differential GPS Navigation Concept," Proceedings of the 44th Annual Meeting of The Institute of Navigation (1988), Annapolis, Maryland, June 1988, pp. 88-92.
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