Maximum likelihood estimation of time-varying delays in the presence of directional interference

The structure and performance of the maximum likelihood (ML) estimator of slowly varying time delays when the received signals are contaminated by additive noise containing a strongly directional component, due to the presence of a fixed, localized source of interference in the acoustic environment is investigated. The ML estimator is obtained by maximizing the output of the log-likelihood processor. The latter is shown to consist of a slowly varying noise canceler followed by a minimum mean square error estimator of the source signal and a correlator. Closed-form expressions are obtained for the Cramer-Rao lower bound (CRLB) on the error covariance matrix of time-varying delay estimators. The effects of directional interference on the CRLB are investigated numerically for a simplified configuration consisting of two sensors and linearly varying time delays