On the secrecy performance of aerial IRS-assisted wireless communications

The high mobility and aerial nature of unmanned aerial vehicles (UAVs) enable flexible deployment and low-cost infrastructure, which makes UAV-based aerial communication an important part of the 6G system. Combining Intelligent reflecting surface (IRS) with UAV provides new degrees of freedom for improved secrecy performance and deployment flexibility. This paper investigates the secrecy performance of an IRS-assisted wireless communication system, where an IRS is mounted on a UAV to secure the communication between a base station (BS) and a receiver in the presence of a passive eavesdropper. By exploiting the flexibility of the UAV, the orientation and location of the IRS are skillfully controlled to secure the multiple-input single-output communication system. With the assumption of the spatially correlated Rayleigh fading channel model, the closed-form expression of secrecy outage probability and average secrecy rate is derived. The soundness of theoretical analysis is verified through Monte Carlo simulations. Extensive simulation results reveal the impact of the BS antenna number, UAV location, and IRS normal vector on secrecy performance. Finally, recommendations are given for the deployment of aerial IRS to secure and assist terrestrial communications. The secrecy performance can significantly improve by making the eavesdropper in the IRS coverage blind zone.