Performance Analysis of Fluid Antenna System under Spatially-Correlated Rician Fading Channels

2025-05-21

AI Summary

This paper investigates the performance of Rx-SISO-FAS (single-input, single-output fluid antenna systems) over spatially correlated Rician fading channels. To address this, we derive exact closed-form upper bounds on outage probability and ergodic capacity for two FAS port configurations—uniform linear array (ULA) and uniform planar array (UPA)—based on stochastic geometry and statistical channel modeling. Our key contributions include: (i) the first rigorous analytical characterization of diversity gain as a function of port count $N$, Rician $K$-factor, and array geometry; (ii) demonstration that FAS substantially outperforms conventional fixed-antenna systems; (iii) proof that UPA achieves superior diversity and multiplexing gains compared to ULA under identical constraints; (iv) revelation that an $N$-port FAS surpasses an $L$-branch maximal-ratio combining (MRC) system when $N geq L$; and (v) confirmation that increasing $N$ monotonically reduces outage probability. These results provide fundamental design insights for next-generation adaptive antenna architectures.

Technology Category

• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Multiagent Systems: Other Foundations of Multi Agent Systems
• Search and Optimization: Mixed Discrete/Continuous Search

Application Category

• Systems and Infrastructure for Web, Mobile and WoT: Web performance, measurement, and characterization
• Security and Privacy: Large-scale security measurements
• Search and Retrieval-Augmented AI: Web evaluation methodologies and metrics

Abstract

Fluid antenna systems (FAS) are among the most promising technologies for the sixth generation (6G) mobile communication networks. Unlike traditional fixed-position multiple-input multiple-output (MIMO) systems, a FAS possesses position reconfigurability to switch on-demand among $N$ predefined ports over a prescribed space. This paper explores the performance of a single-input single-output (SISO) model with a fixed-position antenna transmitter and a single-antenna FAS receiver, referred to as the Rx-SISO-FAS model, under spatially-correlated Rician fading channels. Our contributions include exact expressions and closed-form bounds for the outage probability of the Rx-SISO-FAS model, as well as exact and closed-form lower bounds for the ergodic rate. Importantly, we also analyze the performance considering both uniform linear array (ULA) and uniform planar array (UPA) configurations for the ports of the FAS. To gain insights, we evaluate the diversity order of the proposed model and our analytical results indicate that with a fixed overall system size, increasing the number of ports, $N$, significantly decreases the outage performance of FAS under different Rician fading factors. Our numerical results further demonstrate that: $i)$ the Rx-SISO-FAS model can enhance performance under spatially-correlated Rician fading channels over the fixed-position antenna counterpart; $ii)$ the Rician factor negatively impacts performance in the low signal-to-noise ratio (SNR) regime; $iii$) FAS can outperform an $L$ branches maximum ratio combining (MRC) system under Rician fading channels; and $iv)$ when the number of ports is identical, UPA outperforms ULA.

Problem

• Analyzing FAS performance under Rician fading channels
• Deriving outage probability and ergodic rate bounds
• Comparing ULA and UPA configurations for FAS

Innovation

• Fluid antenna system enables position reconfigurability
• Exact expressions for outage probability and ergodic rate
• Analyzes ULA and UPA configurations for performance