An Experimental Analysis of Cyclic and Reference Signals of 4G LTE for TOA Estimation and Positioning in Mobile Fading Environments

By design, the 4G LTE signals contain a few patterns that repeat in time and frequency (e.g., various reference signals and the cyclic prefix) to facilitate timing synchronization, frequency error estimation, and channel equalization. For communications, these signal components are considered "overhead" serving the purpose of extracting information-carrying symbols for data decoding. When used as signals of opportunity for navigation, they provide times of arrival (TOA), and changes in TOA estimates can be related to the receiver displacement. Indeed, successful use of LTE signals has been reported for ground vehicles, airborne platforms, and indoor positioning in the literature. Even though LTE signals are well specified in the 3GPP standards, some aspects are left to operators as implementation options that depend on the actual deployment environment and local traffic conditions. To better understand the practical aspects of in-the-air LTE signals, experiments were carried out and an initial study of the cyclic and reference patterns in LTE signals for TOA estimation is presented in this article and in particular the effect of antenna ports on TOA estimation. This article aims at providing essential and insightful information directly useable for developing TOA estimation algorithms and ultimately for navigation with LTE signals.