Active Dual STAR-RISs for Full-Duplex MIMO Communications: An Energy-Efficient Optimization Framework

Abstract

Simultaneously transmitting and reflecting reconfigurable intelligent surfaces (STAR-RISs) can dynamically adjust wireless channels through joint controls. The recent development of dual STAR-RISs (D-STAR) architecture provides capacity improvement by utilizing signals impinging from 360-degree for full-plane service coverage. In this paper, we consider an active D-STAR (AD-STAR) architecture in a full-duplex (FD) multi-input-multi-output (MIMO) system. Each AD-STAR element comprises a power amplifier and an on-off controller. We aim to maximize energy efficiency (EE) by optimizing transmit beamforming of the base station (BS) and uplink users as well as the AD-STAR configurations, while ensuring quality-of-service (QoS) for both downlink/uplink. We design a joint optimization of transmit beamforming and AD-STAR configurations (JOTA) algorithm. By adopting Dinkelbach’s and Lagrangian dual transformation, we partition the problem into three sub-problems and utilize successive convex approximation, convex upper bound, abstract Lagrangian duality, difference of two concave functions approximation, and penalty convex-concave programming methods to solve these sub-problems. Our numerical results verify the effectiveness of the proposed AD-STAR architecture in FD systems. The proposed JOTA scheme achieves at least 50.27% higher EE than the considered algorithmic benchmarks under the same AD-STAR architecture and adopted simulation settings.