In a downlink non-orthogonal multiple access (NOMA) system, the reliable transmission of cell-edge users cannot be guaranteed due to severe channel fading. On the other hand, the presence of eavesdroppers can severely threaten the secure transmission due to the open nature of wireless channel. Thus, a two-user NOMA system assisted by a multi-antenna decode-and-forward relay is considered in this paper, and a two-stage jamming scheme, full-duplex-jamming (FDJam), is proposed to ensure the secure transmission of NOMA users. In the FDJam scheme, using full-duplex, the relay transmits the jamming signal to the eavesdropper while receiving confidential messages in the first stage, and the base station generates the jamming signal in the second stage. Furthermore, we eliminate the self-interference and the jamming signal at the relay and the legitimate node, respectively, through relay beamforming. To measure the secrecy performance, analytical expressions for secrecy outage probability (SOP) are derived for both the cellcenter and cell-edge users, and the asymptotic SOP analysis at high transmit power is presented as well. Moreover, two benchmark schemes, half-duplex-jamming and full-duplex-nojamming, are also considered. Simulation results are presented to show the accuracy of the analytical expressions and the effectiveness of the proposed scheme.
|Original language||English (US)|
|Number of pages||14|
|Journal||IEEE Transactions on Communications|
|State||Published - 2019|
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: The work of N. Zhao was supported by the National Natural Science Foundation of China (NSFC) under Grant 61871065 and 61871139,
the open research fund of State Key Laboratory of Integrated Services Networks under Grant ISN19-02, and the Xinghai Scholars Program. This paper will be presented in part at the Proceedings of IEEE/CIC ICCC 2019. The associate editor coordinating the review of this paper and approving it for publication was D. B. da Costa.