Hybrid active and passive localization for small targets

Ultra-Wideband (UWB) is an emerging technology for short-range wireless communications. Due to the high bandwidth of UWB signals, accurate ranging is possible, which is one of many reasons why UWB is a candidate physical layer for wireless sensor networks (WSNs). Reliable position information, obtained with a reasonable complexity overhead and possibly low energy consumption, is often paramount for a successful operation of these networks. The paper concerns a novel approach for improving the trade-off between energy consumption and performance in a localization tracking process. The scenario of application is common: a set of fixed beacons is used for tracking the position of a target that is moving in a limited indoor environment. The principle behind the proposed approach is relatively simple: tracking a small target device is realized by mixing active signal transmissions, which allow using standard techniques for deriving distances and locations, as well as passive signal receptions, which exploit scattering caused by small targets during signal propagation. The entire tracking process exploits the combination of these two types of transmissions with the advantage of possibly saving energy in the target device. The algorithm performance is highlighted by computer simulations using channel models adopted by the IEEE 802.15.4a working group.