부산대학교 도서관

This letter investigates the minimum number of reflecting elements to achieve secure and energy-efficient unmanned aerial vehicle (UAV)-reconfigurable intelligent surface (RIS) systems. Specifically, we consider a UAV equipped with a RIS as a passive relay to assist communication from a source to users while avoiding terrestrial eavesdroppers. Taking account into phase estimation errors caused by imperfect conditions such as UAV jitter, the minimum number of reflecting elements under secrecy and energy efficiency constraints is derived in closed form. Our simulation results verify the correctness of theoretical derivation and demonstrate that the UAV-RIS systems outperform terrestrial RIS systems. Our research provides theoretical guidance for configuring reflecting elements in practical UAV-RIS systems.