Accurate positioning using a planar pseudolite array

When pseudolites are used, as in the wide area augmentation system (WAAS), or, when a Locata type array is used for accurately positioning of ground vehicles, a high vertical GDOP is invariably encountered. The latter translates into poor altitude estimates and potentially also poor position estimates, even in the case of a good planar geometry and where the user is near the center of the pseudolite array. Hence, the use of altitude measurements or terrain elevation information supplied by a GIS data base is investigated. In this paper concepts of operation are developed and algorithms are designed such that the best possible altitude and horizontal position estimates are obtained from the available measurements.