Joint beamforming for secure communication in RIS-assisted cognitive radio networks

This paper studies the security and communication efficiency problem of a reconfigurable intelligent surface (RIS) assisted cognitive radio network, in which we proposed a scheme where secrecy rate (SR) and transmission rate are jointly considered. In specific, with the help of RIS, we exploit the green interference caused by the secondary network to ensure the physical layer security of the primary network. By taking the mutual interference between these two networks into account, we establish a problem to minimize the total transmit power subject to the quality-of-service requirement of secondary user (SU), SR requirement of the primary users (PUs) and limited interference temperature of PUs. In our proposed iterative algorithm, the transmit and reflect beamforming are alternatively optimized by transforming PUs' SR constraint into a second order cone (SOC) form, and the optimal transmit and reflect beamforming are achieved based on the iterative penalty function. Simulation results show the superiority of our proposed algorithm in terms of the total transmit power requirement compared with other benchmarks, and the total transmit power of our proposed algorithm is not very susceptible to the number of eavesdroppers and PUs, which is conducive to serving multiple users in the wireless communication system.