Minimum Indicator Approach for Use with Precise Differential GPS

This paper describes the design and testing of a high-speed, real-time kinematic, precise differential GPS positioning system for use in airborne applications such as automated aerial-refueling and close formation flying. Many of the current ambiguity resolution techniques use the residuals from the least squares position estimation to determine the true ambiguity set, this paper presents a novel approach to the ambiguity resolution problem, called the minimum indicator. Instead of assuming the ambiguity set with the lowest residuals is the true set, other special characteristics of the residuals are examined. The result was the first-ever successful six-degree of freedom, in-flight demonstration of close formation flight, culminating in over 11 hours of close formation flying with a mean radial spherical error of 3.3 centimeters. Other areas addressed include: the difference between "pre-fit" and "post-fit" residuals in the conditional probability calculation, and the impact of a simplified dynamics model on system performance.