Joint Beamforming Design for Sub-Connected Active Reconfigurable Intelligent Surface

Active reconfigurable intelligent surface (RIS) has recently emerged as a promising solution to combat the severe “double fading” effect, which is deemed as a major obstacle in passive RIS-assisted systems. However, the existing fully-connected active RIS equips each element with an integrated power amplifier, which leads to the enormous cost and power consumption due to many active components. In this paper, we introduce a novel economical and energy-efficient sub-connected active RIS structure, in which multiple adjacent phase-shifter elements are driven by only one amplifier. Aiming at maximizing the sum-rate of this active RIS-assisted multiuser multi-input single-output (MU-MISO) system, we also propose a joint design of transmit precoding and reflection beamforming under the power constraints. Simulation results verify the superiority of the proposed sub-connected structure over the fully-connected scheme as well as the effectiveness of proposed algorithm.