IRS-assisted security transmission scheme based on user cooperative interference

For the information security issue of highly open wireless channels in cooperative communication networks，a downlink physical-layer security transmission scheme based on IRS-assisted communication and user cooperative interference was proposed，and an algorithm for maximizing security capacity based on alternative iteration was given． In this scheme， phase shifts of IRS were adjusted to assist confidential communication for legitimate user，and full-duplex user was assigned to send the artificial noise while receiving useful signals to enhance information security of the system． The optimization problem of maximizing system secrecy capacity is non-convex and thus is decomposed into three subproblems in an alternative manner． To be specific， the beamforming vectors at the base station， and the power allocation coefficient of the system and the phase shift matrix at the IRS were optimized alternatively． In the process of optimization， the closed-form expression of the beamforming vectors and power allocation coefficient were derived， while successive convex approximation (SCA) and Riemannian manifold (RM) optimization algorithms were adopted to obtain the optimal phase shifts of the IRS． Analysis and simulation results show that the alternative iteration can converge quickly and the optimization algorithm based on RM has lower complexity than that based on SCA．Furthermore， compared with benchmarks of random phase and fixed power coefficient， the proposed scheme can significantly improve the system security performance. © 2023 Huazhong University of Science and Technology. All rights reserved.