A Tractable Approximation for Evaluating the Performance of Slow Fluid Antenna Multiple Access

A fluid antenna system (FAS) promises outstanding flexibility that can lead to enhanced connectivity by enabling each user’s equipment in the network to exploit the interference null created naturally by multipath propagation. Consequently, in fluid antenna multiple access (FAMA), each user finds the best port in space that maximizes the signal-to-noise-interference over all the ports, allowing many more users to share the same radio channel without demanding involved signal processing. This paper concentrates on the practical version of FAMA, called slow FAMA (s-FAMA), where the fluid antenna of each user updates its best port only if the fading channel changes. Unlike previous works, where the performance metrics are derived in single/double fold integral, we provide a tractable analysis of the system performance of the s-FAMA scheme. Although s-FAMA schemes require complex analysis, we provide simple yet accurate closed-form approximate expressions for calculing the outage probability (OP) and the multiplexing gain metrics, thus facilitating their numerical evaluation in any computer software. Finally, useful insights on determining the number of ports at the FAS to attain a predefined multiplexing gain in the s-FAMA network are also provided.