Robust time-based localization for asynchronous networks with clock offsets

Localization is indispensable for the successful deployment of wireless sensor networks (WSNs). Time-based localization approaches attract a lot of interest due to their high accuracy and potentially low cost. However, time-based localization is intensively coupled with clock synchronization. Thus, the reliability of timestamps in the time-based localization becomes an important yet challenging task to deal with. In this paper, we propose a robust time-based localization approach to locate a target node with the assistance of anchors (nodes with known positions) in an asynchronous network with clock offsets. We employ the asymmetric trip ranging (ATR) protocol to obtain time-of-arrival (TOA) measurements and facilitate clock offset cancellation. Regardless of the reliability of the timestamp report from the target node, closed-form least-squares (LS) and weighted LS estimators are derived to accurately estimate the target node position. As a result, we counter the uncertainties caused by the target node by ignoring the timestamps from this node. Furthermore, Cramér-Rao Bounds (CRBs) and simulation results corroborate the efficiency of our localization scheme.