In this correspondence, we investigate the physical layer security for cooperative non-orthogonal multiple access (NOMA) systems, where both amplify-and-forward (AF) and decode-and-forward (DF) protocols are considered. More specifically, some analytical expressions are derived for secrecy outage probability (SOP) and strictly positive secrecy capacity (SPSC). Results show that AF and DF almost achieve the same secrecy performance. Moreover, asymptotic results demonstrate that the SOP tends to a constant at high signal-to-noise ratio (SNR). Finally, our results show that the secrecy performance of considered NOMA systems is independent of the channel conditions between the relay and the poor user.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: This work was in part supported by the National Natural Science Foundation of China (NSFC) under Grant 61372096 and 61671160, the Department of Education of Guangdong Province (No. 2016KZDXM050), and the open research fund of National Mobile Communications Research Laboratory, Southeast University (No. 2018D01). The review of this paper was coordinated by Dr Richard Souza.