Ray-Tracing Correction For Through-The-Wall Propagation: Application To Uwb Indoor Positioning

Ultra Wide Band (UWB) is known to be a viable technology for accurate ranging, localization and positioning in dense multipath environments because of the fine time resolution of the signal. In UWB context, the authors have already presented a deterministic channel modeling tool [1] using a ray-tracing technique [2] for paths determination and Geometrical Optics (GO) and/or Uniform Theory of Diffraction (UTD) for computation of the total electromagnetic field and/or UWB received pulses [3]. But this deterministic modeling is not suitable for UWB positioning. Indeed, the used ray-tracing considers that rays are not deflected by building materials, in order to reduce computation time. However, in indoor environments and Non Line-of-Sight (NLoS) scenarios, building materials imply, most of the time, that the first signals coming to the receiver are refracted and consequently deflected by materials. These received signals can then be used to determine the position of the "target". Therefore, if a through-the-wall transmission appears during the ray propagation, the estimation of times of arrival and range will be biased if deflection is not considered. In this paper, we present a novel method for correcting the ray transmitted through walls that takes into account the thickness and the dielectric constant of the building materials. With the extreme points positions of the transmitted path obtained by the ray-tracing, the algorithm can find the deflected ray and also reflections inside the building material if needed. Knowing the exact path of the double refracted ray, the method is able to compute the excess delay of the deflected ray compared to the non-deflected ray and can, consequently, evaluate the potential range error in a transmission scenario.