In this paper, a novel cooperation-aided localization and tracking approach, suitable for terahertz (THz) wireless systems is presented. It combines an angle of arrival (AoA) tracking algorithm with the two-way time of arrival method, in order to accurately track the user equipments (UE) position and reduce the deafness caused by the estimation errors of the tracking algorithms. This algorithm can be used by one base station (BS) to estimate the UEs position, or by multiple BSs, that cooperate with each other to increase the accuracy of the estimations, as well as the probability of successful estimations and guarantee lowestimation overhead. The efficiency of the algorithm is evaluated in terms of deafness and probability of successful AoA estimation and is compared with the corresponding performance of the fast channel tracking algorithm.

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Future wireless networks designed to operate in the millimeter-wave and terahertz bands are expected to be highly assisted by Reconfigurable Intelligent Surfaces (RIS). The role of the RIS will be to mediate possible non-line-of-sight link by redirecting the incident beam from the transmitter to the receiver and possibly modifying its characteristics, in order to optimize the beamforming efficiency and to maximize the signal power at the receiver. Therefore, it is crucial to understand what are the bounds imposed on the received power and how these bounds depend on the system design parameters. In this paper we show that, contrary to typical line-of-sight links, the increase of the transmitter gain does not always guarantee power increase at the receiver, even for an infinitely large RIS, and we explain how the RIS size can further affect the received power. We present an analytical model that captures the performance of the RIS-aided link in the limit of very large RIS, and we demonstrate numerical examples that provide insight on the interplay between the RIS size and the properties of the transmitter beam. INDEX TERMSBeamforming efficiency, beam steering, reconfigurable intelligent surface, THz communications.

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