Real Time UWB Error Estimation in a Tightly- Coupled GPS/UWB Positioning System

This paper presents a tightly-coupled integration of GPS observations and ultra-wideband ranges that accounts for systematic UWB errors in real-time using additional error states to augment an extended Kalman filter. Results of range measurements obtained using commercially available UWB radios in optimal line-of-sight conditions are compared to surveyed ranges using conventional methods to assess UWB error characteristics. UWB range measurements from multiple UWB reference stations as well as differential GPS measurements (i.e. pseudorange, Doppler, and carrier phase) are collected during a kinematic field test to assess the ability to estimate UWB bias and scale factor states and then assess the ability to perform UWB augmented RTK surveying in a degraded GPS signal environment. The collected measurements are post-processed with a simulated realtime approach with an extended Kalman filter that utilizes differential GPS pseudorange and carrier phase measurements as well as UWB ranges The accuracy of the ‘real-time’ bias and scale factor estimation is compared to post-processed best line fit analysis. The positioning output of the estimation filter is compared to surveyed reference points and the accuracy and geometry (i.e. DOP) improvement is quantified with and without the addition of UWB.