A deterministic large-scale device-free passive localization system for wireless environments

The widespread usage of wireless local area networks and mobile devices has fostered the interest in localization systems for wireless environments. The majority of research in the context of wireless-based localization systems has focused on device-based active localization, in which a device is attached to tracked entities. Recently, device-free passive localization (DfP) has been proposed where the tracked entity is neither required to carry devices nor participate actively in the localization process. DfP systems are based on the fact that RF signals are affected by the presence of people and objects in the environment. Previous studies have focused on small areas with direct line of sight (LOS) and/or controlled environments. In this paper, we present the design, implementation and analysis of Nuzzer, a large-scale non-LOS DfP localization system, which tracks a single entity in real environments, rich in multipath. Without any additional hardware, Nuzzer makes use of the already-installed wireless data networks to monitor and process changes in the received signal strength (RSS) at one or more monitoring points transmitted from access points. The Nuzzer system enables many applications which support the elderly, including smart homes automation which can be used to assist the elderly, and intrusion detection which is used to protect the elderly's homes. We present deterministic techniques for DfP localization and evaluate their performance in a building, rich in multipath, with an area of 750 square meters. Our results show that the Nuzzer system gives device-free location estimates with less than 7 meters median distance error using only two monitoring laptops and three access points. This indicates the suitability of Nuzzer to a number of application domains.