Physical layer security for cooperative NOMA networks via Nakagami-m fading channels

In this paper, we investigate the physical layer security in cooperative non-orthogonal multiple access (NOMA) networks over Nakagami-m fading channels. Both amplify-and-forward (AF) and decode-and-forward (DF) protocols are studied. More particularly, closed-form exact and asymptotic expressions for strictly positive secrecy capacity are provided considering NOMA-AF and NOMA-DF relaying systems. Numerical results are presented to justify the accuracy of the obtained theoretical analysis. These results show that NOMA-AF and NOMA-DF relaying networks have a similar secrecy performance. Furthermore, asymptotic results show that the strictly positive secrecy capacity goes to a constant for high signal-to-noise ratio regimes. Finally, our proposed NOMA systems provide a high secrecy performance especially for a great value of Nakagami-m parameter.