Over the past decades, multiple antenna technologies have appeared in many different forms, most notably as multiple-input multiple-output (MIMO), to transform wireless communications for extraordinary diversity and multiplexing gains. The variety of technologies has been based on placing a number of antennas at fixed locations which dictates the fundamental limit on the achievable performance. By contrast, this paper envisages the scenario where the physical position of an antenna can be switched freely to one of the N positions over a fixed-length line space to pick up the strongest signal in the manner of traditional selection combining. We refer to this system as a fluid antenna system (FAS) for tremendous flexibility in its possible shape and position. The aim of this paper is to study the achievable performance of a single-antenna FAS system with a fixed length and N in arbitrarily correlated Rayleigh fading channels. Our contributions include exact and approximate closed-form expressions for the outage probability of FAS. We also derive an upper bound for the outage probability, from which it is shown that a single-antenna FAS given any arbitrarily small space can outperform an L-antenna maximum ratio combining (MRC) system if N is large enough. Our analysis also reveals the minimum required size of the FAS, and how large N is considered enough for the FAS to surpass MRC.
Fluid antenna represents a concept where a mechanically flexible antenna can switch its location freely within a given space. Recently, it has been reported that even with a tiny space, a single-antenna fluid antenna system (FAS) can outperform an L-antenna maximum ratio combining (MRC) system in terms of outage probability if the number of locations (or ports) the fluid antenna can be switched to, is large enough. This letter aims to study if extraordinary capacity can also be achieved by FAS with a small space. We do this by deriving the ergodic capacity, and a capacity lower bound. This let…
Fluid antenna is a novel technology that can make an antenna appear instantly at one of N preset locations in a predefined space. An important application is to adopt fluid antenna in a small space of mobile device for obtaining the tremendous diversity hidden in the small space. Previous results have revealed that a single-antenna fluid antenna system, even with a very small space, can outperform a multiple antenna maximum ratio combining (MRC) system if $N$ is large enough. This paper explores the potential of using fluid antenna for multiple access through performance analysis. Fluid antenn…
Multiple-input multiple-output (MIMO) technology has significantly impacted wireless communication, by providing extraordinary performance gains. However, a minimum inter-antenna space constraint in MIMO systems does not allow its integration in devices with limited space. In this context, the concept of fluid antenna systems (FASs) appears to be a potent solution, where there is no such restriction. In this paper, we investigate the average level crossing rate (LCR) of such FASs. Specifically, we derive closed-form analytical expressions of the LCR of such systems and extensive Monte-Carlo si…
UAV-Enabled Fluid Antenna Systems for Multi-Target Wireless Sensing over LAWCNs
Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences（中国科学院深圳先进技术研究院）；Shenzhen Future Network of Intelligence Institute（深圳未来网络智能研究所）；University of Chinese Academy of Sciences（中国科学院大学）；School of Automation and Intelligent Manufacturing, Southern University of Science and Technology（南方科技大学自动化与智能制造学院）；Department of Electrical and Electronic Engineering, Imperial College London（帝国理工学院电气电子工程系）
OFDM Enabled Over-the-Air Computation Systems with Two-Dimensional Fluid Antennas
School of Electronics and Information Technology, Sun Yat-sen University（中山大学电子与信息工程学院）；School of Computer Science and Engineering, Sun Yat-sen University（中山大学计算机科学与工程学院）
Fluid-Antenna-Assisted Distributed Joint Decoding for Cell-Free Massive MIMO Unsourced Random Access
Southeast University（东南大学）；National Mobile Communications Research Laboratory, Frontiers Science Center for Mobile Information Communication and Security, Southeast University（国家移动通信重点实验室，移动信息与安全前沿科学中心，东南大学）；Purple Mountain Laboratories（紫金山实验室）
Group Relative Policy Optimization for Robust Blind Interference Alignment with Fluid Antennas
Harbin Institute of Technology, Shenzhen（哈尔滨工业大学（深圳））；Guangdong Provincial Key Laboratory of Aerospace Communication and Networking Technology, Harbin Institute of Technology, Shenzhen（广东省航天通信与网络技术重点实验室，哈尔滨工业大学（深圳））；Shenzhen Institute of Advanced Technology, Chinese Academy of Sciences（中国科学院深圳先进技术研究院）；KeyLaboratory of Systems and Control, Institute of Systems Science, Academy of Mathematics and Systems Science (AMSS), Chinese Academy of Sciences (CAS)（中国科学院数学与系统科学研究院系统与控制重点实验室）；School of Information Science and Engineering, Southeast University（东南大学信息科学与工程学院）；Southern University of Science and Technology（南方科技大学）
Electrical Engineering Department, University of Brasília (UnB)（巴西布拉斯维利亚大学电子工程系）；Department of Electrical Engineering, German Jordanian University（约旦杰拉森大学电子工程系）；Communications Engineering Department, Princess Sumaya University for Technology（技术 princess sumaya 大学通讯工程系）；National Institute of Telecommunications (Inatel)（电信国家研究所（Inatel））
Off-Grid Position Optimization under Mutual Coupling in Fluid Antenna Arrays
National Mobile Communications Research Laboratory, Frontiers Science Center for Mobile Information Communication and Security, Southeast University（东南大学国家移动通信重点实验室、移动通信与信息安全前沿科学中心）；Purple Mountain Laboratories（紫金山实验室）；Key Laboratory of Intelligent Support Technology for Complex Environments, Ministry of Education, Nanjing University of Information Science and Technology（南京信息工程大学教育部复杂环境智能支撑技术重点实验室）
Fluid Antennas Assisted RIS-NOMA Communication Networks
Beihang University（北京航空航天大学）；North China University of Water Resources and Electric Power（华北水利水电大学）；Manchester Metropolitan University（曼彻斯特城市大学）；Queen Mary University of London（伦敦玛丽女王大学）
Specific Absorption Rate-Aware Multiuser MIMO Assisted by Fluid Antenna System
National Mobile Communications Research Laboratory, Southeast University（东南大学国家移动通信实验室）；Purple Mountain Laboratories（紫金山实验室）；University College London（伦敦大学学院）；Yonsei Frontier Lab, Yonsei University（延世大学延世前沿实验室）；Institute for Communication Systems (ICS), University of Surrey（萨里大学通信系统研究所）
Finite-blocklength Fluid Antenna Systems With Spatial Block-Correlation Channel Model
National Mobile Communications Research Laboratory, Southeast University（东南大学国家移动通信重点实验室）；School of Artificial Intelligence, Nanjing University of Information Science and Technology（南京信息工程大学人工智能学院）；Department of Electronic and Electrical Engineering, University College London（伦敦大学学院电子电气工程系）；Yonsei Frontier Lab., Yonsei University（延世大学延世前沿实验室）；Department of Signal Theory, Networking and Communications, University of Granada（格拉纳达大学信号理论与网络通信系）；Telecommunications Research Institute (TELMA), University of Malaga（马拉加大学电信研究所（TELMA））；School of Integrated Technology, Yonsei University（延世大学综合技术学院）
Geometry-Structured Channel Reconstruction for Conventional and Fluid Antenna Systems: Bayesian Inference and Fundamental Limits
National Mobile Communications Research Laboratory, Frontiers Science Center for Mobile Information Communication and Security, Southeast University（东南大学移动通信国家重点实验室、移动信息与安全前沿科学中心）；Purple Mountain Laboratories（紫金山实验室）；University of Granada（格拉纳达大学）；Southeast University（东南大学）；University of Manchester（曼彻斯特大学）；University College London（伦敦大学学院）；Kyung Hee University（庆熙大学）
