Reflection and Relay Dual-Functional RIS Assisted MU-MISO Systems

TL;DR

This paper introduces a dual-functional RIS architecture that combines reflection and relay capabilities to improve coverage and system performance in MU-MISO wireless systems, addressing limitations of passive RISs.

Contribution

The paper proposes a novel dual-functional RIS design and an efficient algorithm for joint beamforming and RIS configuration to maximize sum-rate in MU-MISO systems.

Findings

Dual-functional RIS enhances coverage and signal strength.

Proposed algorithm outperforms existing methods.

Simulation confirms improved system sum-rate.

Abstract

Reconfigurable intelligent surfaces (RISs) have been deemed as one of potential components of future wireless communication systems because they can adaptively manipulate the wireless propagation environment with low-cost passive devices. However, due to double fading effect, the passive RIS can offer sufficient signal strength only when receivers are nearby and located at the same side as the incident signals. Moreover, RIS cannot provide service coverage for the users at the back side of it. In this paper we introduce a novel reflection and relay dual-functional RIS architecture, which can simultaneously realize passive reflection and active relay functionalities to enhance the coverage. The problem of joint transmit beamforming and dual-functional RIS design is investigated to maximize the achievable sum-rate of a multiuser multiple-input single-output (MU-MISO) system. Based on fractional programming (FP) theory and majorization-minimization (MM) technique, we propose an efficient iterative transmit beamforming and RIS design algorithm. Simulation results demonstrate the superiority of the introduced dual-functional RIS architecture and the effectiveness of the proposed algorithm.