Maximum Likelihood Multipath Estimation in Comparison with Conventional Delay Lock Loops

The implementation of the maximum likelihood estimator for the time-delay estimation problem is practically intractable for navigation signals due to its complexity, especially when due to multipath reception several superimposed replica are taken into account. Recently it has been shown that signal compression techniques can overcome this problem, as the maximum likelihood estimator can be formulated efficiently upon a reduced data set of much smaller size compared to the original data, where the reduced data set forms a sufficient statistic for the estimated signal parameters. This paper focuses on the formulation of such a signal compression based estimator. Furthermore the integration of the estimator into navigation receivers is addressed, in particular by considering the delay lock loop architecture that is employed within conventional navigation receivers. A novel approach for integrating the efficient maximum likelihood estimator into a generic tracking loop is proposed. The performance of the proposed method is assessed by computer simulations. The results show that the conventional delay lock loop is outperformed with respect to noise performance as well as with respect to the multipath bias.