Expectation maximization-based passive localization in asynchronous wireless networks

This paper studies TOA-based localization of a passive target with one transmitter and multiple distributed receivers. Different from the existing studies which assume synchronous or quasi-synchronous network, we consider a more practical case in which all the receivers have different time offsets to the transmitter. To tackle the multi-dimensional optimization problem in the maximum likelihood estimation, an expectation maximization (EM) algorithm is proposed. Taylor expansion to the result obtained in the expectation step is applied, which enables us to give a closed-form solution of localization in the maximization step. The Cramér-Rao bound of the target's position estimation with asynchronous receivers is derived. Simulation results show that the proposed EM-based algorithm outperforms the traditional methods and can perfectly attach the derived Cramér-Rao bound.