Measurement of Relative Position and Orientation using UWB

This paper introduces a new approach to measure relative positioning and orientation (RPO), by instrumenting mobile equipment with ultra-wideband (UWB) distance measurements. In this experiment RPO is tested without a surrounding stationary UWB anchor network; all necessary UWB devices are directly mounted on the machinery. This results in a simplified implementation in the industry, but also challenges the RPO determination. Due to this, the precision and uncertainty of the UWB measurements were characterized in a real application environment, i.e., on a quay to determine if a large body of water would influence the high frequency signals. It was determined that the UWB distance measurements had an uncertainty of approximately 20mm when measuring orthogonal to the antenna and 35mm at large angles; both results for 95% confidence. Based on these results a new approach to calculating the RPO was implemented and tested. The goal was to minimize the effects of horizontal dilution of precision. Three new algorithms were implemented and tested, the best results were obtained with a non-linear covariance weighted least squares computation with self calibration. With this approach the standard deviation of the x and y positions were 64mm and 13mm respectively. This is a very significant improvement in performance with respect to trilateration, which is currently the standard approach.