Reconfigurable Intelligent Surface Assisted mmWave UAV Wireless Cellular Networks

In this paper, we consider a RIS-assisted mmWave UAV wireless cellular network, where a UAV is serving several users with the help of multiple RIS. We jointly optimize the deployment, user scheduling, beamforming vector and RIS phases to maximize the sum-rate, with the constraints of the minimum rate, the UAV movement, the analog beamforming and the RIS phases. To solve this complex problem, we use an iterative method, in which when we optimize one variable, we fix the other three variables. When optimizing the deployment, we find the optimal position for the UAV by a sphere search. Then, we formulate an integer linear programming to find the best scheduling. We also design the analog beamforming vector by compensating the phases of the channel which combines the direct path and the RIS paths. When optimizing the RIS phases, we formulate a semi-definite programming to find the best phases. The proposed joint optimization outperforms the system without RIS assistance and the system without deployment optimization.