RIS-Assisted UAV-Enabled Wireless Powered Communication Network

This paper examines a Reconfigurable Intelligent Surface (RIS)-assisted unmanned aerial vehicle (UAV)-supported wireless powered communication network (WPCN). In the system, the UAV is used as a hybrid access point (HAP) for charging a subscriber in the downlink (DL) and receiving data in the uplink (UL). The RIS helps to improve the efficiency of the DL and UL. Our goal is to maximize the minimum throughput for all terrestrial users by jointly optimizing the horizontal position of UAVs, the transmit power of the users, the transmission time allocation, and the reflection beamforming vectors at the RIS. We present a low-complexity optimization algorithm, decompose four sub-problems, and solve their problems. Specifically, the lower bound of composite channel gain constraint is established, and the two-dimensional suspension stop position of UAV is optimized based on the successive convex approximation (SCA). The transmit power closed-form optimum solutions are then obtained, and the transmission time allocation problems reformulated as a linear programming problem. Finally, the reflection beamforming vector is optimized by semidefinite relaxation (SDR) algorithm. The numerical results support this algorithm effectively, and it is proved that the WPCN supported by RIS-assisted UAV is better than the traditional WPCN.