Fluid Antenna System Enhancing Orthogonal and Non-Orthogonal Multiple Access

Fluid antenna system (FAS) has recently emerged as a promising candidate for the sixth generation (6G) wireless networks. Unlike traditional antenna systems (TASs), FAS is a new wireless communication system where the so-called 'fluid' antenna (FA) can finely change its position within a given area. This unique ability allows FAS to harness additional diversity and multiplexing gains. In this letter, we investigate the applications of FAS in orthogonal multiple access (OMA) and non-orthogonal multiple access (NOMA) networks for performance enhancement. Specifically, we maximize the sum-rate of these multiple access schemes via optimal port selection and power allocation subject to per-user rate requirement. We then obtain the optimal variables in closed-form expressions. Our results reveal that FAS significantly improves the sum-rate of OMA and NOMA when compared to TAS. More interestingly, we discover that it is possible for FAS without channel state information at the transmitter (CSIT) to outperform optimal TAS with CSIT.