Energy efficiency (EE) is one of the most important metrics for the beyond fifth generation (B5G) and the future sixth generation (6G) wireless networks. Reconfigurable intelligent surface (RIS) has been widely focused on EE enhancement for wireless networks because it is power-saving, programmable, and easy to be deployed. However, RIS is generally passive and thus difficult to obtain corresponding full channel state information (CSI), which severely impacts the EE enhancement of RIS-assisted wireless communications. To solve this problem, in this paper we propose the new single-active-antenna combined RIS transmitter structure, which can replace traditional multiple antennas to reduce hardware cost and power consumption. Based on the single-active-antenna combined RIS structure, we develop the Dumb RIS-Assisted Random Beamforming (Darb)-based Joint RIS-Elements and Transmit-power optimizAtion (Jeta) scheme, where dumb RIS randomly changes its phase shift according to isotropic distribution only depending on the CSI feedback from users to RIS-assisted transmitter. Then, we jointly design the number of RIS elements and optimize the transmit power to maximize the EE of RIS-assisted wireless communications. Simulation results show that compared with the traditional multi-antenna system, our developed Darb-based-Jeta scheme can significantly increase the EE without the full CSI.

翻译：能量效率（EE）是超第五代（B5G）及未来第六代（6G）无线网络最重要的性能指标之一。可重构智能表面（RIS）因其节能、可编程和易于部署的特性，被广泛关注用于提升无线网络的能量效率。然而，RIS通常为无源器件，难以获取相应的完整信道状态信息（CSI），这严重影响了RIS辅助无线通信的EE提升。为解决这一问题，本文提出新型单有源天线结合RIS的发射机结构，可替代传统多天线系统以降低硬件成本和功耗。基于该单有源天线结合RIS结构，我们开发了基于Dumb RIS辅助随机波束成形（Darb）的RIS单元数与发射功率联合优化（Jeta）方案，其中dumb RIS仅根据用户向RIS辅助发射机反馈的CSI，依据各向同性分布随机改变其相移。随后，我们联合设计RIS单元数量并优化发射功率，以最大化RIS辅助无线通信的EE。仿真结果表明，与传统多天线系统相比，我们提出的基于Darb的Jeta方案能够在无需完整CSI的情况下显著提升EE。