System-Level Gains of Dual-Band RIS: From Wireless Communication to SWIPT

Abstract

This paper introduces the integration of dual-band reconfigurable intelligent surfaces (DBRIS) in wireless system design, and investigates the ensuing performance gains in different application scenarios. This type of metasurfaces offers a compelling technology due to their reduced material usage, compact design, and multi-functional operation across multiple frequency bands compared to single-band RISs. Two representative use cases are considered to assess the achievable performance gains with the said integration, namely, DBRIS-assisted wireless communication, and DBRIS-assisted simultaneous wireless information and power transfer (SWIPT). For the first design, where the DBRIS is deployed as a relay, we focus on the energy efficiency (EE) maximization of the communication system. An alternating manifold method is proposed for the joint optimization of the source transmit power and the DBRIS phase shifting. For the second design, we investigate a DBRIS-assisted SWIPT system using a novel power splitting approach. An EE metric is defined, and an alternating optimization algorithm is developed to maximize it. Numerical results validate the advantages of the proposed design architectures as well as the proposed optimization framework. In particular, we highlight the energy efficiency gains enabled by the DBRIS as compared to operations with conventional single-frequency surfaces, in both application scenarios.