  Unmanned aerial vehicles (UAVs) have been successfully adopted to enhance the
flexibility and robustness of wireless communication networks. And recently,
the reconfigurable intelligent surface (RIS) technology has been paid
increasing attention to improve the throughput of the fifth-generation (5G)
millimeter-wave (mmWave) wireless communication. In this work, we propose an
RIS-outfitted UAV (RISoUAV) to secure an uninterrupted line-of-sight (LoS) link
with a ground moving target (MT). The MT can be an emergency ambulance and need
a secure wireless communication link for continuous monitoring and diagnosing
the health condition of a patient, which is vital for delivering critical
patient care. In this light, real-time communication is required for sending
various clinical multimedia data including videos, medical images, and vital
signs. This significant target is achievable thanks to the 5G wireless
communication assisted with RISoUAV. A two-stage optimization method is
proposed to optimize the RISoUAV trajectory limited to UAV motion and LoS
constraints. At the first stage, the optimal tube path of the RISoUAV is
determined by taking into account the energy consumption, instant LoS link, and
UAV speed/acceleration constraints. At the second stage, an accurate RISoUAV
trajectory is obtained by considering the communication channel performance and
passive beamforming. Simulation results show the accuracy and effectiveness of
the method.
