Secure Wireless Communication Using BD-RIS in UAV Networks

Non-terrestrial networks have recently gained significant attention as an effective solution for expanding wireless coverage using aerial platforms such as high-altitude platform stations (HAPS) and unmanned aerial vehicles (UAVs). Despite their advantages, the open nature of wireless transmission makes these networks vulnerable to security threats, particularly eavesdropping attacks. This paper investigates a secure communication framework for a UAV-based secondary network operating within a cognitive radio environment. To enhance communication security, a beyond-diagonal reconfigurable intelligent surface (BD-RIS) is integrated with the UAV to intelligently manipulate the wireless propagation environment. The BD-RIS improves the signal quality at the legitimate receiver while reducing information leakage toward a potential eavesdropper. In addition, an adaptive power control mechanism is employed to ensure that the interference introduced to the primary network remains within an acceptable threshold. The proposed framework is implemented using MATLAB and Simulink to evaluate the achievable secrecy rate under different system conditions. Simulation results indicate that the BD-RIS assisted system provides a notable improvement in secrecy performance compared to conventional communication schemes without intelligent surface support. Furthermore, increasing the UAV transmits power and the number of BD-RIS elements leads to further improvements in secure communication performance.