Future wireless connectivity is envisioned to accommodate functionalities far beyond broadband data transmission over point-to-point direct links, enabling novel scenarios, such as communication behind blockers and around corners, and innovative concepts, such as situational awareness, localization, and joint communications and sensing. In this landscape, beams that are able to propagate on bent paths are ideal candidates for dynamic blockage avoidance, interference management in selected regions, and user connectivity on curved trajectories. In this work, we study beam shaping for applications in near-field wireless connectivity. We explain the underlying mechanism of beam bending and we present the design principles for tailoring the curvature of the propagation trajectory. We discuss design aspects for the generation of such beams with large arrays and analyze the impact of several parameters on their performance, including the beam’s footprint shape, the aperture size, the inter-element spacing, the sub-array selection of active elements, the available phase levels of the array elements and the operating frequency. We introduce the concept of near-field virtual routing (NFVR) and we demonstrate that such beams are able to address challenges of high-frequency communications, such as dynamic routing, blockage avoidance, and energy-efficiency more efficiently than conventional beamforming.

The design of Reconfigurable Intelligent Surfaces (RISs) is typically based on treating the RIS as an infinitely large surface that steers incident plane waves toward the desired direction. In practical implementations, however, the RIS has finite size and the incident wave is a beam of finite k-content, rather than a plane wave of$\delta $-like k-content. To understand the implications of the finite extent of both the RIS and the incident beam, here we treat the RIS as a spatial filter, the transfer function of which is determined by both the prescribed RIS operation and the shape of the RIS boundary. Following this approach, we study how the RIS transforms the incident k-content and we demonstrate how, by engineering the RIS shape, size, and response, it is possible to shape beams with nontrivial k-content to suppress unwanted interference, while concentrating the reflected power to desired directions. We also demonstrate how our framework, when applied in the context of near-field communications, provides the necessary insights into how the wavefront of the beam is tailored to enable focusing, propagation with invariant profile, and bending, beyond conventional beamforming.

Future wireless networks are expected to be highly assisted by reconfigurable intelligent surfaces (RIS) in non-line-of-sight links. The role of the RIS is to redirect the incident beam from the transmitter to the receiver and possibly modify its characteristics, in order to maximize the signal power at the receiver and optimize the beamforming efficiency. 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 there is an interplay between the transmitter beamwidth and the RIS size that leads to a maximum power at the receiver. We demonstrate our findings with numerical examples that provide insight on the effect of the RIS size on the received signal power.

The primary role of a reconfigurable intelligent surface (RIS) is to restore the propagation path between the access point (AP) and the user equipment (UE) in a non-line-of-sight communication link. Depending on the RIS placement with respect to the AP and UE positions, different power levels can reach the UE, thus affecting the quality of the communication. Particularly when the UE moves freely, the RIS position that maximizes the received signal will depend strongly on the UE location. In this context, we use an analytical model to assess the decisions that have to be made concerning the positioning of the RIS, which are determined by the interplay of three crucial quantities, namely (a) the available AP gain, (b) the available positions for the AP and RIS placement, and (c) the minimum desired power levels at the UE. The impact of the AP antenna gain tunability on the RIS placement selection is assessed and illustrated in D-band indoor scenarios.

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 low-estimation 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.