Fluid Antenna Array-Inspired Location-Posterior-Driven Subarray Sizing and Power Control for Two-Hop AF UAV Relaying

2026-08-17

AI Summary

This study addresses the imbalance between relay gain and pointing robustness, alongside high power consumption, in UAV relaying under location uncertainty. We propose an adaptive optimization framework leveraging fluid antenna arrays (FAAs). By exploiting posterior user location information, we derive a closed-form solution for subarray sizing and jointly optimize power control to minimize system energy consumption while satisfying rate constraints. This approach effectively balances array gain with beam robustness, significantly enhancing both energy efficiency and service reliability. Experimental results demonstrate that the proposed method achieves a 3.17 dB power saving compared to full-array schemes and attains a 60% service success rate under a 0.15 W power budget, validating its superiority in resource-constrained scenarios.

Abstract

This paper develops fluid antenna array (FAA)-inspired subarray sizing and transmit-power design for a two-hop amplify-and-forward (AF) unmanned aerial vehicle (UAV) relay using progressively contracting user-location posteriors. A contiguous reconfigurable subarray is shared by first-hop reception and second-hop forwarding, such that its active size jointly determines the receive gain, forwarding gain, and beamwidth. By adaptively controlling the effective aperture, the proposed design exploits geometric reconfigurability to balance array gain against pointing robustness under location uncertainty. Projecting the position covariance onto the array direction yields a closed-form direction-limited size inversely proportional to directional uncertainty. Posterior samples are propagated through the two-hop rate model, and the subarray size and transmit power are then selected to minimize UAV power subject to a worst-user lower-tail rate requirement and hardware power limits. The planned configuration is further audited over instantaneous two-hop Rician channels at the true user positions. At t = 8 s, the proposed design saves 3.17 dB over full-array narrow-beam transmission on paired feasible geometries and achieves 60.0% service success at a 0.15-W budget, compared with 43.2% for a fixed eight-element subarray.

Problem

• UAV relay
• fluid antenna array
• subarray sizing
• power control
• location uncertainty

Innovation

• Fluid Antenna Array
• Subarray Sizing
• Location Posterior
• UAV Relaying
• Power Control