Reliability and Threshold-Region Performance of TOA Estimators in Dense Multipath Channels

This paper investigates the reliability of time-of-arrival (TOA) based ranging using maximum-likelihood (ML) estimation in a dense multipath (DM) channel in terms of both the conventional mean squared error (MSE) as well as confidence bounds. We show that in the presence of DM the ML estimator distorts the signal mainlobe due to its whitening property, resulting in a bandwidth (BW) dependent bias, even before the outlier driven threshold region is reached. Low-complexity metrics for accurately determining the performance in terms of the probability density (PDF) of the estimation error of both ML estimation and joint ML estimation and detection are provided. These metrics are based on the well known method of interval estimation (MIE) combined with local error prediction using the normalized noise-free likelihood (NNLIKE) and consider the non-Gaussian effects of outliers as well as mainlobe distortion.