Two-Step Time of Arrival Estimation for Pulse-Based Ultra-Wideband Systems

In cooperative localization systems, wireless nodes need to exchange accurate position-related information, such as time-of-arrival (TOA) and angle-of-arrival (AOA), in order to obtain accurate location information. One alternative for providing accurate position-related information is to use ultra-wideband (UWB) signals. High time resolution of UWB signals presents a potential for very accurate positioning based on TOA estimation. However, it is challenging to realize very accurate positioning systems in practical scenarios, due to both complexity/cost constraints and adverse channel conditions, such as multipath propagation. For example, although maximum likelihood estimators perform very closely to theoretical lower bounds for TOA estimation, they are impractical due to the need for extremely high sampling rates and the presence of large number of multipath components. On the other hand, the conventional correlation-based algorithm, which serially searches for possible signal delays, takes a very long time to estimate the TOA of a received UWB signal. Moreover, the first signal path does not always have the strongest correlation output, which can result in significant errors in TOA estimation. Therefore, first path detection algorithms are required for accurate TOA estimation. In this paper, a two-step TOA estimation algorithm is proposed in order to provide accurate TOA estimation in reasonable time intervals. In order to speed up the estimation process, the first step estimates a coarse TOA of the received signal based on received signal energy. Then, in the second step, the arrival time of the first signal path is estimated by considering a hypothesis testing approach. The proposed scheme uses low-rate correlation outputs, and is able to perform accurate TOA estimation in reasonable time intervals. The simulation results are presented to analyze the performance of the estimator.