Joint Optimization for RIS-Assisted Wireless Communications: From Physical and Electromagnetic Perspectives

TL;DR

This paper presents a comprehensive optimization framework for RIS-assisted MISO wireless systems, deriving closed-form solutions for beamforming and phase shifts, and demonstrating significant performance improvements in mmWave/THz communications.

Contribution

It introduces a joint optimization approach considering physical and electromagnetic factors, including RIS positioning, with closed-form solutions and a dimensional-reducing theory for 3D placement.

Findings

Closed-form solutions closely approach the upper bound of received power.

RIS significantly enhances mmWave/THz communication performance.

Proposed solutions are robust to perturbations.

Abstract

Reconfigurable intelligent surfaces (RISs) are envisioned to be a disruptive wireless communication technique that is capable of reconfiguring the wireless propagation environment. In this paper, we study a free-space RIS-assisted multiple-input single-output (MISO) communication system in far-field operation. To maximize the received power from the physical and electromagnetic nature point of view, a comprehensive optimization, including beamforming of the transmitter, phase shifts of the RIS, orientation and position of the RIS is formulated and addressed. After exploiting the property of line-of-sight (LoS) links, we derive closed-form solutions of beamforming and phase shifts. For the non-trivial RIS position optimization problem in arbitrary three-dimensional space, a dimensional-reducing theory is proved. The simulation results show that the proposed closed-form beamforming and phase shifts approach the upper bound of the received power. The robustness of our proposed solutions in terms of the perturbation is also verified. Moreover, the RIS significantly enhances the performance of the mmWave/THz communication system.