Energy-Efficient UAV-Mounted RIS Assisted Communication with Tilting Effect

The combination of ummanned aerial vehicle (UAV) and reconfigurable intelligent surface (RIS) is beneficial for improving the data transmission environment. However, for the UAV-mounted RIS (U-RIS), the tilting effect of the UAV plays a detrimental role in the transmission efficiency, which is usually neglected by the existing works. In this paper, we study a U-RIS assisted communication system considering the tilting effect. Based on geometric and force analysis, we obtain a relation between the power consumption and the tilt angle, and derive a power radiation pattern of the RIS. To counter-act the influence of the tilting effect on the communication performance and the UAV power consumption, a joint design of the UAV trajectory, user scheduling and RIS passive beamforming is proposed to maximize the energy efficiency (EE) of the UAV. To tackle this problem, we develop an efficient algorithm to solve it by applying the successive convex approximation technique. Simulation results show that the proposed algorithm improves the EE performance significantly and the negative impact of the tilting effect can be mitigated efficiently.