Active Reconfigurable Intelligent Surfaces for User Localization in mmWave MIMO Systems

This paper considers the user localization problem in a single-user and single-cell scenario with an active reconfigurable intelligent surface (RIS). Design perspectives on the RIS configuration and on the power split between the base station (BS) and the active RIS are illustrated, and a location estimator based on multiple signal transmissions and particle filtering (PF) is proposed. The said algorithm exploits additional features and degrees of freedom not available when a passive RIS is used. Theoretical performance bounds are derived and extensive numerical simulations show the effectiveness of the proposed approach with respect to a solution based on passive RIS and corroborate analytical findings.