Accuracy enhancement for UWB indoor positioning using ray tracing

An ultra-wideband (UWB) system is known to be a viable solution for accurate positioning in dense multipath environments because of the exceptionally fine time resolution of the signal. However, the presence of a line-of-sight (LoS) blockage can degrade the positioning accuracy for two reasons. Firstly, it makes estimation of the time of arrival (ToA) of the direct path signal difficult by complicating the multipath structure of the propagation channel. Secondly, the higher dielectric constant of the LoS blocking material than that of free space introduces excess propagation delay which will bias the range estimation. In this paper, methods based on ray tracing to reduce the ranging error resulting from the second reason are posed. We take two different approaches; a statistical approach and a map-aided method. In the statistical approach, we establish a conditional distribution of the excess propagation delay caused by LoS blockages using a ray tracing technique. The lower bound of the ranging performance based on this model is estimated. The ray tracing method is also used for the map-aided ToA positioning approach. UWB propagation measurement data taken in an office environment is used to examine the performance of this method.