Joint Beamforming and Deployment Optimization for UAV-Assisted Maritime Monitoring Networks

With the wide application of Internet of Things (IoT) systems in the smart ocean, many unmanned surface vehicles (USVs) have been deployed jointly with unmanned aerial vehicles (UAVs) to monitor the maritime environment. However, conventional means of maritime communications fail to provide high-rate services due to the complex maritime channel conditions and large transmission distance, which will affect the environmental monitoring performance. In this paper, we propose a USV-UAV collaborative patrol scheme for maritime environment monitoring networks. Considering the characteristic of energy concentration in beamforming, we investigate the joint beamforming and location deployment optimization problem (BLDO) for UAV relay. Specifically, we decompose the BLDO problem into two subproblems. In the first sub-problem, the location deployment of UAV and beam gain allocation is optimized via an iterative algorithm based on the approximated beam patterns. The algorithm can effectively reduce the computational complexity of the grid-search method. In the second sub-problem, beamforming optimization is conducted with a high-dimensional constant-modulus (CM) constraint. A micro-particle swarm optimization-based algorithm with boundary relaxation (BR- mu PSO) is proposed to obtain an optimal solution. Finally, the simulation results demonstrate that the proposed algorithms can improve the performance in terms of the achievable sum rate and the beam gain.