In this paper, we investigate the physical layer security in the reconfigurable intelligent surface (RIS)-aided cell-free networks. A maximum weighted sum secrecy rate problem is formulated by jointly optimizing the active beamforming (BF) at the base stations and passive BF at the RISs. To handle this non-trivial problem, we adopt the alternating optimization to decouple the original problem into two sub-ones, which are solved using the semidefinite relaxation and continuous convex approximation theory. To decrease the complexity for obtaining overall channel state information (CSI), we extend the proposed framework to the case that only requires part of the RIS' CSI. This is achieved via deliberately discarding the RIS that has a small contribution to the user's secrecy rate. Based on this, we formulate a mixed integer non-linear programming problem, and the linear conic relaxation is used to obtained the solutions. Finally, the simulation results show that the proposed schemes can obtain a higher secrecy rate than the existing ones.
翻译:在本文中,我们调查了可重新配置智能表面辅助无细胞网络的物理层安全。 通过在基站联合优化主动波束成形(BF)和在RIS联合优化被动BF, 形成了最大加权和保密率问题。 为了处理这个非三重问题, 我们采用了交替优化, 将原始问题分解成两个子元素, 这些子元素使用半无限期放松和连续直线近似理论来解决。 为了降低获取整个频道状态信息的复杂性, 我们将拟议框架扩展至只需要部分RIS的CSI。 这是通过故意丢弃对用户保密率贡献很小的RIS来实现的。 基于这一点, 我们形成了一个混合的整数非线性编程问题, 并且用线性松动来获得解决方案。 最后, 模拟结果表明, 拟议的计划可以得到比现有计划更高的保密率。