Novel FAS Positioning Strategies for Ultra-Dense B5G Network Scenarios

Fluid Antenna Systems (FAS) promise significant gains by repositioning antenna ports, but network-level deployment is critically constrained by the often-neglected costs of switching latency, pilot overhead, and control signaling. Link-level studies that maximize ergodic rate often assume these costs are negligible, leading to non-viable solutions. To bridge this gap, we propose a novel, cost-aware two-timescale framework that optimizes for net utility, balancing network-wide Area Spectral Efficiency (ASE) against the practical reconfiguration costs. We formulate a scalable optimization problem based on statistical CSI and a probabilistic port-selection surrogate, which is solved efficiently via projected-gradient methods. We then propose three specialized strategies-Interference-Aware (IADP), Load-Balanced (LBSD), and Multi-Objective (MOPO)-that optimize this new utility. System-level simulations in ultra-dense B5G scenarios show our framework achieves substantial gains in net ASE and user throughput, while the explicit cost penalties provably control switching activity and pilot burden, unlike cost-ignorant baselines. Our results provide the first actionable guidelines for the practical, cost-effective deployment of FAS in 6G networks.