Energy efficient air-to-ground communication networks with reconfigurable intelligent surface

Reconfigurable intelligent surface (RIS) assisted air-to-ground wireless powered communication networks (WPCNs) are constructed to promote the energy efficiency of system, in which unmanned aerial vehicles (UAV) reflects towards energy-constrained hybrid access points (HAP) through RIS. Subsequently, HAP uses collected communicate with users blind areas RIS-UAV. By optimizing parameters such as charging time ratio, transmit power and phase shifts matrix, for single multiuser scenarios maximized, respectively. The is modeled a non-convex quadratic programming problem inequality constraints single-user scenario. Then converted into an equivalent convex by using Taylor expansion approximation method. A joint optimization algorithm proposed obtain feasible solution. fractional multi-user scenario, solution obtained proposing alternating algorithm. Finally, both two compared system traditional amplify-and-forward (AF) relay, simulation results show that algorithms can provide up 150% 160% improvement scenarios, respectively, AF relay.