Localization is one of the fundamental tasks in wireless sensor network. Measuring time of arrival (TOA) and time difference of arrival of a signal (TDOA) are two widely used criteria for localization. In TOA based schemes target must be synchronous with anchors while target can be asynchronous with anchors in TDOA schemes. In this paper, we propose a target localization scheme based on measuring TDOA for inhomogeneous underwater environment. One of the properties of inhomogeneous underwater is that waves travel over curved path due to the inhomogeneity of the underwater. This phenomenon makes TDOA based localization in underwater a different problem from localization in terrestrial wireless sensor network. Our proposed TDOA based localization is developed by iterative algorithm. Simulation results shows that while our proposed underwater-TDOA algorithm converges to the Cramer Rao Lower Bound (CRLB), it outperforms the line-of-sight- TDOA algorithm in accuracy sense and also underwater- TOA algorithm for localizing an asynchronous target.

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