Energy Efficiency Maximization for Active RIS Switcher Assisted MISO Systems

Reconfigurable intelligent surface (RIS) is treated as a promising technology for future wireless communications. In this letter, we investigate the active RIS-assisted MISO systems, which can overcome the multiplicative fading effect introduced by the passive RIS. In particular, the active sub-connection architecture of RIS is used to overcome the high power consumption of the existing fully-connected architecture, where each component independently controls its phase shift but shares the same power amplifier. In order to reduce the power loss of each component, we propose to add a switcher device in the power amplifier to select the most appropriate component. As the component is selected, the active number of components is significantly reduced along with less power consumption. Our analysis shows that the introduced switcher brings less performance loss, indicating that higher energy efficiency (EE) can be achieved. Furthermore, EE maximization problems with power constraints are considered in the active RIS assisted system for the architecture with switcher, and the corresponding joint beamforming design is derived. Simulation results show that the proposed structure and method with switcher can effectively improve EE compared with the schemes without switcher.