  The paper describes an NLOS (Non-Line-of-Sight) mitigation method intended
for use in a UWB positioning system. In the proposed method propagation
conditions between the localized objects and the anchors forming system
infrastructure are classified into one of three categories: LOS
(Line-of-Sight), NLOS and severe NLOS. Non-Line-of-Sight detection is conducted
based on first path signal component power measurements. For each of the
categories, average NLOS inducted time of arrival bias and bias standard
deviation have been estimated based on results gathered during a measurement
campaign conducted in a fully furnished apartment. To locate a tag, an EKF
(Extended Kalman Filter) based algorithm is used. The proposed method of NLOS
mitigation consists in correcting measurement results obtained in NLOS
conditions and lowering their significance in a tag position estimation
process. The paper includes the description of the method and the results of
the conducted experiments.
