Physical Layer Security Optimization in IRS-assisted Cooperative RSMA Networks

Cooperative rate-splitting multiple access (C-RSMA) has garnered significant attention for its advantages in physical layer security (PLS). However, the process of relay users' forwarding decoded common messages can compensate for performance losses due to user channel disparities, but it is also vulnerable to eavesdropping. To address these issues mentioned above, this paper proposes an intelligent reflecting surface (IRS)-assisted C-RSMA secure transmission model aimed at maximizing the secrecy sum rate (SSR). Due to the high coupling between optimization variables, directly solving the problem is challenging. Therefore, an alternating iterative algorithm is proposed to decompose the optimization problem into two sub-problems, namely beamforming and time slot optimization, as well as phase shift optimization. We solve both sub-problems in an iterative way using successive convex approximation (SCA). Numerical results show that compared with C-RSMA, W/O IRS, C-NOMA, W/IRS and C-NOMA, W/O IRS, the proposed scheme can achieve a significant gain in SSR, which verified the effectiveness of the proposed scheme.