人工噪声在速率分拆多址保密通信中的作用

The Role of Artificial Noise in RSMA-based Secure Communications

本文研究速率分拆多址接入(Rate Splitting Multiple Access,RSMA)多输入单输出安全通信中,人工噪声(Artificial Noise,AN)对提升系统保密速率性能的作用以及不同方案下公共流和私有流的功率分配情况。用户消息被分拆并编码为公共流和私有流。与传统将多用户干扰视为性能瓶颈的想法不同,通过对MUI部分解码并将其余部分视为噪声,RSMA中的公共流既是合法用户的有用数据,又充当干扰外部窃听者的AN。基于此,本文研究是否需要额外的AN来增强保密性能。考虑用户公平性,提出了有或无AN的发射预编码优化方案最大化最小保密速率,采用基于逐次凸逼近的方法得到最优解。仿真结果表明,完美CSI条件下,单纯依赖RSMA中的公共流充当AN与AN辅助的RSMA安全预编码方案的可达保密速率几乎一致,额外的人工噪声并不能提高系统保密速率性能。

This work focuses on investigating the role of artificial noise(AN)and the corresponding power allocation of dif⁃ferent streams in enhancing the secrecy rate performance for the rate-splitting multiple access(RSMA)based wireless net⁃works.In RSMA,user messages are split and encoded into common and private streams.Contrary to the conventional idea that regarding the multi-user interference(MUI)as performance bottleneck and fully treating it as noise,by partially de⁃coding the MUI and partially treat it as noise,the common stream in RSMA is able to serve not only as useful data for in⁃tended legitimate users,but also AN to confuse the external eavesdroppers.Considering this,whether an additional AN is needed to enhance secrecy is worth investigating.Aiming to ensuring user fairness,the transmit beamforming design with or without additional AN is formulated to maximize the minimum achievable secrecy rate.To deal with the non-convexity of the formulated problem,a successive convex approximation-based optimization solution is proposed.Numerical results showed that under perfect CSI condition,whether in overloaded(including strictly overloaded)or underloaded scenarios,the achievable secrecy rate achieved by relying solely on the common stream in RSMA as the noise to interfere with external single-antenna eavesdroppers is almost the same as the secrecy rate of AN-assisted RSMA secure precoding scheme,and the additional AN cannot further improve the secrecy rate performance of the system.