Future mobile applications are expected to demand high accuracy positioning from cellular networks. However, most time-delay estimators used for cellular trilateration ignore the multipath channel, resulting in a poor positioning performance. This paper investigates the use of advanced joint time-delay and channel estimation techniques for Long Term Evolution (LTE) mobile localization, as a predecessor of fifth generation (5G) technologies. This is especially relevant for sub-6 GHz bands, where the bandwidth and the dedicated positioning resources are limited. Thus, joint maximum likelihood (JML) estimators are presented in order to reach the achievable ranging accuracy, which is first assessed with the derivation of their Cramér-Rao bound (CRB). Simulation and laboratory experiments are then used to obtain an estimation of their achievable positioning performance. Periodic-tap JML estimators are shown to achieve the best position accuracy with respect to state-of-the-art threshold-based and super-resolution techniques, due to their robustness against multipath overlapping and noise effects for reduced bandwidths. A robust position accuracy of around 10 meters for a 10-MHz system bandwidth can be achieved with periodic-tap JML estimators in challenging urban environments.
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