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.