Constrained Least Squares Algorithm for TOA-Based Mobile Location under NLOS Environments

This paper presents a mobile station (MS) location method using constrained least-squares (CLS) estimation in the non-line-sight (NLOS) conditions. Three or more time-of-arrival (TOA) measurements of a signal traveling between a MS and base stations (BSs) are necessary for its localization. However, when some of the measurements are from NLOS paths, the location errors can be very large. We propose a method that mitigates possible large TOA error measurements caused by NLOS. This method does not depend on a particular distribution of the NLOS error. Simulation results show that the location accuracy is significantly improved over traditional algorithms, even under highly NLOS conditions.