Fluid Antennas: Pioneering a New Era in Next-Generation Wireless Communications

The evolution towards sixth-generation (6G) wireless communication demands antenna technologies that are highly flexible, energy efficient, and scalable to satisfy the demands of massive connectivity, ultra-low latency, and dynamic propagation environments. Fluid antenna systems (FAS) have emerged as a promising solution, offering superior spatial reconfigurability through utilization of a single radio frequency (RF) chain. By dynamically adapting to channel conditions, FAS supports simplified hardware architectures, efficient interference suppression, and enhanced user separation, thereby eliminating the need for complex signal processing methods such as precoding or Successive Interference Cancellation (SIC). This survey presents a comprehensive review of FAS, starting with a tutorial-style introduction to its structural fundamentals, core multiple access mechanisms, and synergy with key 6G enablers including Non-Orthogonal Multiple Access (NOMA), Reconfigurable Intelligent Surfaces (RIS), Simultaneous Wireless Information and Power Transfer (SWIPT), Artificial Intelligence (AI) and Terahertz (THz) communication. In addition, it explores fluid material selection, port selection strategies, and recent advances in Channel State Information (CSI) acquisition, while providing a cross-layer perspective that links fluid material properties to communication performance. The transformative potential of FAS is further explored in the context of Multiple-Input Multiple-Output (MIMO) integration, AI-driven enhancements, and compatibility with other emerging wireless communication paradigms. The paper concludes by highlighting critical open challenges and proposing future research directions essential for fully realizing the capabilities of FAS in next-generation wireless systems.