Connectivity Maximization in UAV Networks using RIS Placement and SDP Optimization

In this paper, we study the problem of placing a reconfigurable intelligent surface (RIS) and tuning its reflected links to improve the resiliency and connectivity of uncrewed aerial vehicle (UAV) networks. We formulate an optimization problem of maximizing network connectivity that jointly optimizes RIS position, its phase shift, and UE-RIS-UAV link scheduling. Such problem is computationally expensive combinatorial optimization. To tackle this problem, we first design the phase control strategy at the RIS for the UE-RIS-UAV link scheduling. With such design, we propose an optimal linear search method, which has high computational complexity for large networks. Then, leveraging the convex relaxation method and the designed phase strategy, we propose another solution using semi-definite programming (SDP) optimization, which solves the problem in polynomial time. Simulation results show that our proposed solutions outperform other benchmark schemes.