HARQ for Slow Fluid Antenna Multiple Access

2026-07-20

AI Summary

Existing research on slow fluid antenna multiple access (sFAMA) has focused solely on physical-layer performance under single transmission scenarios, overlooking the impact of retransmission mechanisms on overall network performance. This work proposes HARQ-sFAMA, a novel framework that integrates hybrid automatic repeat request (HARQ) with sFAMA for the first time. In the downlink, it leverages the spatial reconfigurability of fluid antennas, enabling users to select distinct antenna ports in each HARQ round and coherently combine received signals across rounds to enhance decoding reliability. An analytical model based on queueing theory and stochastic processes is developed to evaluate outage probability, average packet waiting time, and energy efficiency. Both theoretical analysis and simulations demonstrate that HARQ-sFAMA significantly outperforms conventional sFAMA in reliability, latency, and energy efficiency, offering a standards-compliant and efficient solution for massive wireless access.

Abstract

Slow fluid antenna multiple access (sFAMA), enabled by the fluid antenna system (FAS), has recently emerged as a practical and low-complexity paradigm for supporting massive wireless connectivity. While existing studies have characterized its physical-layer performance under one-shot transmission, its interaction with retransmission protocols and the resulting networking performance remain largely unexplored. In this paper, we study a downlink hybrid automatic repeat request (HARQ)-assisted sFAMA framework, termed HARQ-sFAMA, in which each user performs distinguished port selection in every HARQ round and combines the received signals across multiple rounds to improve decoding reliability. We develop a comprehensive analytical framework to characterize the outage probability, average packet waiting time, and energy efficiency of the proposed system. The analysis reveals how HARQ exploits the spatial reconfigurability of FAS to simultaneously enhance reliability and improve queueing performance. Numerical results corroborate the theoretical analysis and demonstrate that the HARQ-sFAMA system significantly outperforms conventional one-shot sFAMA in terms of reliability, delay, and energy efficiency. These findings suggest that the integration of HARQ and sFAMA provides a promising pathway toward a practical and standards-compatible massive access solution for future wireless networks.

Problem

• slow fluid antenna multiple access
• HARQ
• retransmission protocols
• networking performance
• massive wireless connectivity

Innovation

• HARQ
• fluid antenna system
• sFAMA
• spatial reconfigurability
• massive access