基于协作NOMA系统的物理层安全性能研究

Research on Physical Layer Security Performance of Cooperative NOMA Systems

摘要: 针对协作非正交多址接入(Non-Orthogonal Multiple Access, NOMA)系统的物理层安全传输需求，本文提出一种基于解码转发(DF)与修改转发(MF)的自适应中继安全传输算法。首先构建包含发射端、中继节点、合法强弱用户及窃听者的协作NOMA系统模型，并推导信干噪比、保密容量及保密中断概率等关键性能指标的解析表达式。在此基础上，设计可根据实时信道状态动态切换转发模式的自适应策略，最终实现系统安全传输概率的最大化。仿真结果表明，相比传统正交多址接入系统与单一DF协议NOMA系统，所提自适应算法在全功率范围内实现了更低的保密中断概率；特别是在高发射功率(>25 dBm)阶段，该算法成功突破传统DF协议的安全容量瓶颈，使得安全传输概率持续攀升，有效提升了协作NOMA系统的物理层安全性能。

Abstract: To address the physical layer secure transmission requirements of cooperative non-orthogonal multiple access (NOMA) systems, this paper proposes an adaptive relay secure transmission algorithm based on decode-and-forward (DF) and modify-and-forward (MF) protocols. First, a cooperative NOMA system model comprising a transmitter, a relay node, legitimate strong and weak users, and an eavesdropper is established. Subsequently, analytical expressions for key performance metrics, including the signal-to-interference-plus-noise ratio, secrecy capacity, and secrecy outage probability, are derived. Building upon this, an adaptive strategy is designed to dynamically switch forwarding modes according to real-time channel state information, ultimately maximizing the secure transmission probability of the system. Simulation results demonstrate that, compared to traditional orthogonal multiple access systems and single DF-protocol NOMA systems, the proposed adaptive algorithm achieves a lower secrecy outage probability across the entire transmit power range. Particularly in the high transmit power regime (> 25 dBm), the algorithm successfully overcomes the secrecy capacity bottleneck inherent in traditional DF protocols, enabling a continuous increase in secure transmission probability and effectively enhancing the physical layer security performance of cooperative NOMA systems.