Optimal SWIPT Transmission in RIS-Based Air-Ground Wireless Communication

With the rapidly increasing demands for wireless communication, unmanned aerial vehicles (UAVs) have been developed. However, the line-of-sight (LoS) links are susceptible to severe deterioration due to complex distribution environments. To confront this challenge, reconfigurable intelligent surface (RIS) technology is introduced to ameliorate the environment, as well as enhance communication performance. This article explores an RIS-assisted simultaneous wireless information and power transfer system to investigate the optimization problem involving UAV trajectory design, precoding, and RIS phase shift. The objective is to maximize the minimum information receivers' rate. Considering that the problem is nonconvex, we break it down into three subproblems and proceed to tackle it using an alternating optimization algorithm and the successive convex approximation technique. In addition, the article takes into account the phase dispersion of the UAV no-fly zone and RIS, based on the actual situation. To address these nonideal factors, we introduce an indicator function flag and employ the Dinkelbach method to attain the optimal solution for the nonideal optimization problem. The numerical outcomes clearly illustrate that the proposed algorithm significantly enhances the system's rate performance.