UREAL: Underwater Reflection-Enabled Acoustic-Based Localization

Abstract

The underwater medium is an extreme environment for achieving accurate localization due to its many challenges, some of which includes propagation delay, multipath, rough surfaces, and more. Localization relies on accurate ranging information such as time of arrival, time difference of arrival, and angle of arrival (AOA). In the underwater environment, these ranging measurements will be prone to errors especially when the algorithm relies on the stability of the line-of-sight (LOS) link. This error is mainly attributed to the multipath nature of the underwater medium, most notably in shallow water setups. To circumvent these issues, we propose a novel underwater signal reflection-enabled acoustic-based localization scheme (UREAL) that employs both LOS and surface-reflected nonline-of-sight (NLOS) ranging information to locate a node that has drifted away. We classify both the LOS and surface-reflected NLOS links by leveraging our previous work, which uses homomorphic deconvolution to recover the channel IR containing the link information. Our UREAL scheme uses both azimuthal and elevation AOA measurements to provide the 3-D ranging required for the position estimation process. We then present a closed-form least squares method that is used to locate the lost node with either LOS AOA measurements and/or with surface-reflected AOA ranging information. The approach is validated using a 3-D underwater setup and is shown to outperform competing schemes.