Sensing RISs: Enabling Dimension-Independent CSI Acquisition for Beamforming

Abstract

Reconfigurable intelligent surfaces (RISs) are envisioned as a potentially transformative technology for future wireless communications. However, RIS's inability to process signals and their attendant increased channel dimension have brought new challenges to RIS-assisted systems, which greatly increases the pilot overhead required for channel estimation. To address these problems, several prior contributions that enhance the hardware architecture of RISs or develop algorithms to exploit the channels' mathematical properties have been made, where the required pilot overhead is reduced to be proportional to the number of RIS elements. In this paper, we propose a dimension-independent channel state information (CSI) acquisition approach in which the required pilot overhead is independent of the number of RIS elements. Specifically, in contrast to traditional signal transmission methods, where signals from the base station (BS) and the users are transmitted in different time slots, we propose a novel method in which signals are transmitted from the BS and the user simultaneously during CSI acquisition. Under this method, an electromagnetic interference random field (IRF) will be induced on the RIS, and we employ a sensing RIS to capture its features. Moreover, we develop three algorithms for parameter estimation in this system, and also derive the Cramér-Rao lower bound (CRLB) and an asymptotic expression for it. Simulation results verify that our proposed signal transmission method and the corresponding algorithms can achieve dimension-independent CSI acquisition for beamforming.

Reconfigurable Intelligent Surfaces for 6G: Applications, Challenges and Solutions

“…Recently, to overcome the complexity of control information interaction between RIS and the network, literature [28] [29] proposed that RIS self-control mode can be adopted. Literature [29] proposed that RIS can adopt a blind beamforming mechanism to achieve self-regulation and beamforming.…”

“…The blind beamforming is only suitable for single-user scenarios. Literature [28] proposed that RIS can self-implement channel estimation and beamforming based on interference phenomena. Again, this mechanism can only be used in single-user scenarios.…”

Reconfigurable Intelligent Surfaces for 6G: Applications, Challenges and Solutions

“…Recently, to overcome the complexity of control information interaction between RIS and the network, literature [33] [34] proposed that RIS self-control mode can be adopted. Literature [34] proposed that RIS can adopt a blind beamforming mechanism to achieve self-regulation and beamforming.…”

“…The blind beamforming is only suitable for single-user scenarios. Literature [33] proposed that RIS can self-implement channel estimation and beamforming based on interference phenomena. Again, this mechanism can only be used in singleuser scenarios.…”