Comparison of GPS-based autonomous vehicle following using global and relative positioning

Abstract

Differential GPS methods are developed for use in automated vehicle convoy positioning. The GPS pseudo-range and carrier phase measurements are used to compute relative position vectors between two vehicles with sub-meter errors. The carrier phase measurement makes this level of accuracy attainable, but carrier phase ambiguity must be resolved prior to the relative position estimation. An algorithm, referred to as the Dynamic base Real Time Kinematic (DRTK) algorithm, is described to estimate carrier phase ambiguity and the relative position vector between two GPS receivers. A comparative study of the performance of the algorithm using either single or dual frequency measurements is presented. The use of relative positioning to autonomously follow a human-driven lead vehicle is presented. Time Difference Carrier Phase (TDCP) measurements are used to estimate the change in the position of the following vehicle between measurement epochs. The TDCP algorithm is combined with the DRTK algorithm to estimate the position of the following vehicle relative to a virtual lead vehicle position. Analysis of the accuracy of the TDCP algorithm at individual measurement epochs and over varying time intervals is presented. The DRTK/TDCP following method (using relative positioning information) is compared to a GPS waypoint following method (using global positioning information) using an all-terrain vehicle which is automated to follow a human-driven lead vehicle.