智能窃听下协作NOMA网络的性能分析

针对下行双用户NOMA (Non-Orthogonal Multiple Access)系统模型中存在智能窃听者，该窃听者可以自适应地选择被动窃听或主动干扰工作模式，在不精确了解其干扰水平的情况下，部分NOMA用户很有可能遭遇传输质量下降乃至保密中断，这将对信息安全传输构成严重威胁。另外，由于信道衰落，用户的位置对系统整体性能有很大影响，难以保证距离源节点较远用户的传输质量。为解决上述问题，本文提出了一种新型的两阶段用户协作方案。第一阶段，远用户采用全双工(full-duplex，FD)干扰智能窃听者，第二阶段，近用户可作为一个中继协助源节点转发远用户信号信息，并在接收端采用串行干扰消除（Successive Interference Cancellation, SIC）技术进行解码。使用户间达成合作，提高通信链路安全性和用户服务质量。考虑到系统中不同用户的信息接收速率与通信需求不同之间的相关性，分别推导了遍历安全容量和遍历容量的解析表达式，同时分析了功率分配因子和用户间协作发射功率等因素对性能的影响，并通过Monte-Carlo仿真验证了其正确性。 

Performance analysis of cooperative NOMA Network with intelligent eavesdropping

In a downlink non-orthogonal multiple access (NOMA) system model, there exists an intelligent eavesdropper that performs either passive eavesdropping or active jamming adaptively. Without an accurate understanding of the interference level, some NOMA users are likely to experience degraded transmission quality or even confidential interruptions, which threaten the secure transmission severely. Besides, the user's location has a great influence on performance due to the open nature of wireless channel, so edge users far away from the source node cannot guarantee the user's information transmission rate. Thus, a new cooperative NOMA scheme is proposed, where the edge users employ the full-duplex jamming (FD) to send jamming signals to intelligent eavesdropper in the first stage, and close users can act as relays to assist edge users forwarding signals in the second stage. The successive interference cancellation technique is used to decode signals in the receiving terminal . This achieves the cooperation between the close users and edge users and improves the security of the communication link and the service quality of the users. Considering the correlation between different users of information receiving rates and communication demands in the system, the closed-form expressions of ergodic achievable secrecy rate (EASR)and ergodic capacity are derived respectively. Meanwhile, the influence of power allocation factor and the transmission power between users on performance are analyzed. At the same time, the influence of the power allocation factor and the transmission power between users on performance are analyzed. The correctness was verified by Monte-Carlo simulation.