Maximum likelihood estimation for geolocation in the presence of multipath

We consider the problem of estimating the location of an emitter in a multipath environment from measurements by multiple widely spaced sensors. We present a maximum likelihood approach for estimating the emitter position jointly with the positions of the reflectors, the unknown complex gains of the propagation paths, and the unknown transmitted signal. This approach provides unbiased emitter position estimates whether or not there is a direct line of sight. A variation of the Expectation-Maximization (EM) algorithm is used to provide an iterative, computationally feasible calculation of the maximum-likelihood location estimate. Closed form solutions are developed for the unknown gains and the signal.