Proactive Eavesdropping via Jamming in NOMA Network

Recently, non-orthogonal multiple access (NOMA) has been considered as a promising technique in 5G network, and many investigations have addressed on the physical layer security to improve the security performance. In this paper, an alternative problem, where the eavesdropping process is considered as a legal activity, will be analyzed to track suspicious communications. More specifically, we study a wireless surveillance system in which the legitimate monitor is equipped with multi-antenna to overhear the messages between the suspicious receiver and the suspicious transmitter. Suspicious users are grouped into pairs and use the NOMA technique to transmit signals to a suspicious base station. Meanwhile, the legitimate monitor (LM) simultaneously transmits jamming signals, listens to suspicious links, decode-and-forward (DF) the eavesdropped information to the legitimate eavesdropper (LE). Based on the proposed mechanism, we investigate the power allocation policies for jamming signals of the legitimate monitor under deterministic and non-deterministic interference channel. Accordingly, we derive the closed-form expression of the successful eavesdropping probability for the best and the worst user to evaluate the system performance. Monte Carlo simulations are provided to verify our analytical results.