Multi-Functional Reconfigurable Intelligent Surface: System Modeling and Performance Optimization

TL;DR

This paper introduces a multi-functional reconfigurable intelligent surface (MF-RIS) that supports reflection, refraction, amplification, and energy harvesting, significantly improving wireless signal coverage and system performance.

Contribution

It proposes a novel MF-RIS architecture with multiple functions, models its signal behavior, and develops an optimization framework for maximizing sum-rate in NOMA networks.

Findings

MF-RIS outperforms single-functional RIS in coverage and throughput.

There is a trade-off between sum-rate and energy harvesting.

Optimal deployment is near the transmitter for best performance.

Abstract

In this paper, we propose and study a multi-functional reconfigurable intelligent surface (MF-RIS) architecture. In contrast to conventional single-functional RIS (SF-RIS) that only reflects signals, the proposed MF-RIS simultaneously supports multiple functions with one surface, including reflection, refraction, amplification, and energy harvesting of wireless signals. As such, the proposed MF-RIS is capable of significantly enhancing RIS signal coverage by amplifying the signal reflected/refracted by the RIS with the energy harvested. We present the signal model of the proposed MF-RIS, and formulate an optimization problem to maximize the sum-rate of multiple users in an MF-RIS-aided non-orthogonal multiple access network. We jointly optimize the transmit beamforming, power allocations as well as the operating modes and parameters for different elements of the MF-RIS and its deployment location, via an efficient iterative algorithm. Simulation results are provided which show significant performance gains of the MF-RIS over SF-RISs with only some of its functions available. Moreover, we demonstrate that there exists a fundamental trade-off between sum-rate maximization and harvested energy maximization. In contrast to SF-RISs which can be deployed near either the transmitter or receiver, the proposed MF-RIS should be deployed closer to the transmitter for maximizing its communication throughput with more energy harvested.