UAV-Enabled Cell-Free Networks: Joint Optimization for User Fairness

This paper aims to enhance user fairness in unmanned aerial vehicles (UAVs) enabled cell-free wireless networks. We consider a scenario where multiple UAVs serve as access points for ground users (UEs). We jointly design the UAV deployment, power allocation, UAV-UE association, and pilot assignment to maximize the minimum downlink user rate, while taking account the impact of pilot contamination. The design is formulated as a mixed-integer non-convex optimization problem. To circumvent the problem non-convexity and facilitate the design of a computationally efficient suboptimal solution, a series of transformations and approximations are proposed based on the particle swarm optimization and successive convex approximation techniques. Simulation results are presented to demonstrate the effectiveness and advantages brought by the joint design for enhancing user fairness. Furthermore, our study provides new insights into the feasibility of using sparse association to reduce costs while maintaining performance, especially in scenarios with a large number of users.