User-Centric Cell-Free Massive MIMO with Access Points Empowered by Fluid Antennas

Fluid antennas have recently emerged as a new antenna technology to boost the capacity of wireless networks. Thanks to the capability of tuning the position of the antenna within a given variability interval, it is possible to "tune" the channel coefficients so that the system performance can be properly optimized. This paper considers a cell-free massive MIMO system where access points (APs) are equipped with fluid antennas. The problem of maximizing the minimum uplink rate across users w.r.t. the uplink transmitted power and the antenna positions at the APs is considered. The problem is solved through an alternating optimization approach that provably converges to a steady solution. Numerical results show that the use of fluid antennas may grant improvements to the system performance w.r.t. the case of fixed antenna position, paving the way to further investigations on the use of such devices in cell-free massive MIMO systems.