Geometric-Projection-Based Rate Optimization for Multi-UAV Deployment and Power Allocation in Satellite-Assisted Cell-Free Massive MIMO

Abstract

Unmanned aerial vehicle (UAV)-assisted communications have emerged as a promising approach to enhance wireless network performance. However, a key challenge that remains insufficiently addressed in existing studies is the enforcement of minimum safety distance among UAVs, which is crucial for practical deployment in real-world scenarios. In this paper, we investigate the multi-UAV deployment problem for user rate optimization in a satellite-assisted cell-free massive MIMO (CF-mMIMO) downlink system subject to explicit inter-UAV safety-distance constraints. To address the resulting nonconvex deployment problem, we propose a geometric-projection-based deployment framework combined with a distance-constraint-decoupled penalty alternating optimization (DC-PAO) algorithm. The proposed approach decouples safety-distance constraints from rate optimization variables and iteratively updates the UAV positions through projection onto the feasible distance set in each iteration. Numerical results show that the proposed scheme explicitly maintains the prescribed inter-UAV safety-distance constraints and achieves a moderate but consistent improvement in the minimum user spectral efficiency over the considered SCA-based baseline.