Optimal SWIPT transmission in RIS-based air-ground wireless communication

With the rapidly increasing demands for wireless communication networks, 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 tackle this issue, Reconfigurable Intelligent Surface (RIS) technology has been introduced to ameliorate the propagation environment and enhance communication performance. This paper explores a RIS-assisted simultaneous wireless information and power transfer (SWIPT) system to investigate the optimization problem involving UAV trajectory design, precoding, and RIS phase shift. The objective is to maximize the minimum information receivers' (IRs) rate. Considering that the problem is nonconvex, we decompose it into three subproblems and then solve it using an alternating optimization algorithm and the successive convex approximation (SCA) technique. Additionally, the paper takes into account the phase dispersion of the UAV no-fly zone and RIS, based on the actual situation. To address these non-ideal factors, we introduce an indicator function flag and employ the Dinkelbach method to obtain the optimal solution for the non-ideal optimization problem. The numerical results demonstrate that the proposed algorithm considerably improves the rate performance of the system.