Hybrid Relay-Reflecting Intelligent Surface-Assisted Wireless Communications

Reconfigurable intelligentsurface (RIS) has emerged as a cost- and energy-efficient solution to enhance the wireless communications capacity. However, recent studies show that very large surface is required for RIS-assisted system; otherwise, they may be outperformed by conventional relay. Furthermore, performance gain of RIS can considerably degraded hardware impairments such limited-resolution phase shifters. To overcome those challenges, we propose hybrid relay-reflecting intelligent (HR-RIS) architecture, in which single or few elements serve active relays, while remaining only reflect incident signals. We two HR-RIS architectures, namely, fixed dynamic HR-RIS. The joint transmit beamforming at base station are designed based on alternating optimization successive convex approximation methods. simulation results $4 \times 2$ multiple-input multiple-output system proposed with element achieve about 40% 25% improvement spectral efficiency energy efficiency, respectively, respect RIS-aided system. also outperform relaying scheme most considered scenarios.