Abstract: To solve the problems of large channel fading damage, low resource utilization and loss of security in high-spectrum short packet communications, a hybrid Intelligent Reflecting Surface (IRS) and relay assisted secure transmission scheme based on cooperative interference was proposed, which used artificial noise to interfere with the channel quality of eavesdroppers in the Multi-Input Single-Output (MISO) system to improve physical layer security. First, the closed-form solution of the base station beamforming vector at the transmitter was derived to optimize the multi-antenna beamforming problem of the base station. Then, the continuous convex approximation method was used to obtain the optimal allocation of noise power, and then the gradient descent Riemannian manifold optimization method was used to obtain the optimal phase shift matrix to solve the respective local optimal solutions respectively. Finally, an alternating optimization algorithm was used to iterate the global optimal solution. The simulation results show that the proposed algorithm has good convergence performance. When the number of IRS elements are 128, the secrecy rate of the proposed scheme is doubled compared to the IRS-only scheme and about twice as much as the relay-only scheme. In addition, when the location of the IRS in the system is not fixed, the optimal power allocation scheme of the hybrid network has higher security performance.

Key words: physical layer security, decode-and-forward (DF), intelligent reflecting surface (IRS), artificial noise, secrecy rate

摘要： 针对高频谱短包通信中信道衰落损伤大、资源利用率较低和保密性丢失等问题，提出一种基于协作干扰的混合智 能反射面(IRS)和中继辅助的安全传输方案，该方案利用人工噪声干扰多输入单输出(MISO)系统中窃听者的信道质量以提升物 理层安全。首先，推导出基站发射端波束成形矢量的闭式解，优化多天线波束成形。其次，使用连续凸逼近方法求得噪声功 率的最佳分配比，再使用梯度下降的黎曼流形优化方法获得最优相移矩阵，分别求解出各自的局部最优解。最后，使用交替 优化算法迭代出全局最优解。仿真结果表明，所提算法具有良好的收敛性能，且当 IRS 单元数为 128 时，所提方案的安全速 率比仅 IRS 方案提升了一倍，比仅中继的方案提升了约两倍。此外，当 IRS 在系统的位置不固定时，混合网络的最优功率分 配方案具有更高的安全性能。

关键词: 物理层安全, 协作转发, 智能反射面, 人工噪声, 保密速率