Stacked intelligent metasurface (SIM) extends the concept of single-layer reconfigurable holographic surfaces (RHS) by incorporating a multi-layered structure, thereby providing enhanced control over electromagnetic wave propagation and improved signal processing capabilities. This study investigates the potential of SIM in enhancing the rate fairness in multiuser downlink systems by addressing two key optimization problems: maximizing the minimum rate (MR) and maximizing the geometric mean of rates (GMR). {The former strives to enhance the minimum user rate, thereby ensuring fairness among users, while the latter relaxes fairness requirements to strike a better trade-off between user fairness and system sum-rate (SR).} For the MR maximization, we adopt a consensus alternating direction method of multipliers (ADMM)-based approach, which decomposes the approximated problem into sub-problems with closed-form solutions. {For GMR maximization, we develop an alternating optimization (AO)-based algorithm that also yields closed-form solutions and can be seamlessly adapted for SR maximization. Numerical results validate the effectiveness and convergence of the proposed algorithms.} Comparative evaluations show that MR maximization ensures near-perfect fairness, while GMR maximization balances fairness and system SR. Furthermore, the two proposed algorithms respectively outperform existing related works in terms of MR and SR performance. Lastly, SIM with lower power consumption achieves performance comparable to that of multi-antenna digital beamforming.
Randomized Space-Time Stacked Intelligent Metasurfaces for Massive Multiuser Downlink Connectivity
University Federico II（那不勒斯费德里科二世大学）；Italian Aerospace Research Centre (CIRA)（意大利航空航天研究中心）；University of Sannio（桑尼奥大学）；University of Campania Luigi Vanvitelli（坎帕尼亚路易吉范维特利大学）
Reconfigurable intelligent surface has recently emerged as a promising technology for shaping the wireless environment by leveraging massive low-cost reconfigurable elements. Prior works mainly focus on a single-layer metasurface that lacks the capability of suppressing multiuser interference. By contrast, we propose a stacked intelligent metasurface (SIM)-enabled transceiver design for multiuser multiple-input single-output downlink communications. Specifically, the SIM is endowed with a multilayer structure and is deployed at the base station to perform transmit beamforming directly in the e…
Beijing University of Posts and Telecommunications（北京邮电大学）；University of Science and Technology Beijing（北京科技大学）；Tsinghua University（清华大学）；Fudan University（复旦大学）；Nanyang Technological University（南洋理工大学）
A Survey on Stacked Intelligent Metasurfaces: Fundamentals, Recent Advances, and Challenges
University of Luxembourg（卢森堡大学）；National Institute of Technology Warangal（瓦朗加尔国立技术学院）；National and Kapodistrian University of Athens（雅典国家与卡波迪斯特里阿斯大学）；University of Illinois Chicago（伊利诺伊大学芝加哥分校）
Over-the-Air Semantic Alignment with Stacked Intelligent Metasurfaces
DIAG Department, Sapienza University of Rome（罗马大学信息与通信系）；National Inter-University Consortium for Telecommunications (CNIT)（电信国家大学联合体）；Informatics and Telecommunications Department, National and Kapodistrian University of Athens（雅典国家与卡波迪斯特里亚大学信息与通信系）；DIET Department, Sapienza University of Rome（罗马大学电子工程系）
