Fluid Antenna Multiple Access for HF Skywave Communications

High Frequency (HF) communication, operating within the 3 to 30 MHz range, has been pivotal for long-distance wireless communication, especially in scenarios where infrastructure (such as satelittes or base stations) are limited or unavailable and beyond-line-of-sight. This paper investigates the potential of fluid antenna multiple access (FAMA) to enhance HF communication performance by leveraging the dynamic nature of fluid antenna systems to match the time-varying ionospheric channel. We first establish a comprehensive system model that incorporates both spatial block-correlation and ionospheric propagation characteristics. Based on this model, we derive closed-form expressions for outage probability under both high and low SNR scenarios. To address the challenges of user interference and frequency resource allocation, we propose an efficient user grouping algorithm based on K-means clustering, which considers users’ channel characteristics and spatial distribution. Furthermore, we develop a frequency selection strategy to optimize system performance while minimizing inter-group interference. Numerical simulations demonstrate that our proposed FAMA scheme significantly improves system reliability and resource utilization by reducing the outage probability under typical operating conditions.