Wireless Pers Commun (2010) 53:35–52 DOI 10.1007/s11277-009-9669-4 Ranking of TOA Measurements Based on the Estimate of the NLOS Propagation Contribution in a Wireless Location System Santiago Mazuelas · Francisco A. Lago · Patricia Fernandez · Alfonso Bahillo · Juan Blas · Ruben M. Lorenzo · Evaristo J. Abril Published online: 14 February 2009 © Springer Science+Business Media, LLC. 2009 Abstract The presence of non-line-of-sight (NLOS) propagation is a key issue that limits the accuracy of wireless location systems. The lack of direct sight causes the measurements obtained by location systems to be so unpredictable that they can produce high inaccuracies in the estimation of the mobile station location. In this paper we propose a novel technique to improve location reliability and accuracy in cases where NLOS propagation is present. For that, in registers of time of arrival (TOA) measurements taken from each base station (BS) in view, we detect the presence of NLOS propagation and estimate the ratio of the mea- surements coming from NLOS propagation. With this estimate we can assess how much is NLOS propagation affecting the measurements taken from each BS and then we can identify the best measurements and BSs to achieve the highest accuracies in location. Keywords Geolocation · NLOS · TOA 1 Introduction Satellite location systems such as GPS (Global positioning system) can provide poor and inac- curate performance in complex scenarios such as urban and indoor environments. The large deployment of cellular wireless networks for mobile communications and the widespread of those terminals within the population make those technologies optimal for developing a location system in such urban and indoor environments [1, 2]. In urban scenarios, each mobile user is under the coverage of several base stations (BSs) in a cellular wireless network; a mobile station (MS) can detect about half a dozen or more BSs. S. Mazuelas (B ) · A. Bahillo · J. Blas CEDETEL (Center for the Development of Telecommunications), Edificio Solar, Parque Tecnologico de Boecillo, 47151, Boecillo, Valladolid, Spain e-mail: smazuelas@cedetel.es F. A. Lago · P. Fernandez · R. M. Lorenzo · E. J. Abril Department of Signal Theory and Communications and Telematic Engineering, University of Valladolid, Camino del Cementerio s/n., Valladolid 47011, Spain 123