Coordinated Reconfigurable Intelligent Surface for Cellular-Connected UAV

Inter-cell interference (ICI) and limited sky coverage are major challenges to the development of cellular-connected unmanned aerial vehicle (UAV). To address these challenges, we consider the applications of reconfigurable intelligent surface (RIS). RIS is a promising solution capable of reconfiguring the phase of a reflected radio signal so as to enhance the desired signal strength or mitigate the ICI. In this paper, we propose a coordinated RIS-aided cellular-connected UAV scheme to provide ubiquitous coverage in the sky and mitigate the ICI of aerial users (AUs) while improving the performance of existing terrestrial users (TUs). We further develop an optimization algorithm to obtain the optimal coordinated beamforming and phase shift that maximize the weighted sum-rate (WSR) of the TUs subject to the AUs' rate requirement. Our simulation results show that the proposed coordinated RIS-aided cellular-connected UAV scheme is a promising solution where the WSR of the TUs increases with respect to the number of reflecting elements while satisfying the AUs' rate requirement. Compared to the baseline scheme without RIS, the proposed scheme also provides a WSR gain up to 48%.