As physical layer security evolves to multi-user systems, multi-user interference (MUI) becomes an unavoidable issue. Recently, rate-splitting multiple access (RSMA) emerges as a powerful non-orthogonal transmission framework and interference management strategy with high spectral efficiency. Unlike most works fully treating MUI as noise, we take all users' secrecy rate requirements into consideration and propose an RSMA-based secure beamforming approach to maximize the weighted sum-rate (WSR), where MUI is partially decoded and partially treated as noise. User messages are split and encoded into common and private streams. Each user not only decodes the common stream and the intended private stream, but also tries to eavesdrop other users' private streams. A successive convex approximation (SCA)-based approach is proposed to maximize the instantaneous WSR under perfect channel state information at the transmitter (CSIT). We then propose a joint weighted minimum mean square error and SCA-based alternating optimization algorithm to maximize the weighted ergodic sum-rate under imperfect CSIT. Numerical results demonstrate RSMA achieves better WSR and is more robust to channel errors than conventional multi-user linear precoding technique while ensuring all users' security requirements. Besides, RSMA can satisfy all users' secrecy rate requirements without introducing WSR loss thanks to its powerful interference management capability.

翻译：随着物理层安全向多用户系统演进，多用户干扰成为不可回避的问题。近年来，速率分割多址接入（RSMA）作为一种高效的频谱利用率非正交传输框架与干扰管理策略逐渐兴起。与多数将多用户干扰完全视为噪声的研究不同，本文综合考虑所有用户的保密速率需求，提出一种基于RSMA的安全波束赋形方法以最大化加权和速率（WSR），其中多用户干扰被部分解码、部分视作噪声处理。用户消息被分割编码为公共流与私有流。每个用户不仅解码公共流及其自身私有流，还会尝试窃听其他用户的私有流。我们提出基于连续凸近似（SCA）的方法，在发射端完美信道状态信息（CSIT）条件下最大化瞬时WSR。进一步，针对非完美CSIT场景，提出联合加权最小均方误差与SCA的交替优化算法以最大化加权遍历和速率。数值结果表明，相较于传统多用户线性预编码技术，RSMA在保障所有用户安全需求的前提下能实现更优的WSR且对信道误差更具鲁棒性。此外，凭借其强大的干扰管理能力，RSMA可在不引入WSR损失的情况下满足所有用户的保密速率需求。