Enhancing the Physical Layer Security of Cooperative NOMA System

In the future wireless communication networks, the key technique such as NOMA of 5G becomes prevailing. This paper analyzes the physical layer security of cooperative NOMA system. In analysis, this system which adopts decode-and-forward (DF) consists of one base station (BS), M relays and two users. In particular, a two-stage relay scheme is proposed, and analytical results are developed to demonstrate that this two-stage relay scheme can achieve the lower outage probability among all possible relay schemes, and realize the full diversity gain. The closed-form expression on outage probability is derived, as well as the asymptotic expression on outage probability is derived in the high SNR. Meanwhile, Monte-Carlo simulations are provided to demonstrate that cooperative NOMA with this two-stage relay scheme outperforms that based on the conventional max-min approach.