Securing FC-RIS and UAV Empowered Multiuser Communications Against a Randomly Flying Eavesdropper

This letter investigates a wireless network consisting of an unmanned aerial vehicle (UAV), a fully-connected reconfigurable intelligent surface (FC-RIS), and multiple users, where the downlink signal can simultaneously be captured by the users as well as an aerial eavesdropper at a random location. To improve the physical-layer security (PLS) of the considered multiuser communications, we propose the FC-RIS aided round-robin scheduling (FCR-RS) and the FC-RIS and ground channel state information (CSI) aided proportional fair scheduling (FCR-GCSI-PFS) schemes. Thereafter, we derive closed-form expressions of the zero secrecy rate probability (ZSRP). Numerical results not only validate the closed-form ZSRP analysis, but also verify that the proposed GCSI-PFS scheme obtains the same performance gain as the full-CSI-aided PFS in FC-RIS-aided communications. Furthermore, optimizing the hovering altitude remarkably enhances the PLS of the FC-RIS and UAV empowered multiuser communications.