Passive location estimation using TOA measurements

Ultra-wideband (UWB) radios offer highly accurate ranging, i.e., measurement of signal travel time. This is important for positioning (localization), in particular in indoor environments, where GPS is not available. This paper considers UWB-based positioning of passive objects, where one transmitter and multiple, distributed, receivers are employed. We consider the case where the transmitter and receivers can be synchronized, so that time-of-arrival (TOA) instead of time-difference-of-arrival (TDOA) information can be utilized. Assuming Gaussian errors for the range estimates, we propose a novel, Two-Step, Expectation Maximization (TSEM) based algorithm for the localization of the passive object. This algorithm achieves the Cramer-Rao Lower Bound (CRLB) of TOA algorithms. Simulation results show that the error variance of TSEM is much lower (often 30 dB) than that of the existing, TDOA-based, algorithms.