Secure transmission for NOMA systems with imperfect SIC

This paper investigates secure transmission for non-orthogonal multiple access (NOMA) systems where the imperfect successive interference cancellation (SIC) is considered at both legitimate users and eavesdropper (Eve). A power allocation scheme is designed for the legitimate users to mitigate the effect of the SIC error caused by imperfect SIC. For characterizing the secrecy performance of the NOMA system, the closed-form expressions for connection outage probability (COP), secrecy outage probability (SOP), and effective secrecy throughput (EST) are derived over Nakagami-m fading channels in both NOMA and benchmark orthogonal multiple access (OMA) systems. We also provide security and reliability trade-off results (SRT) for the users in the NOMA and OMA systems. Simulation results verify our analysis and show that the strong users achieve better secrecy performance but worse reliability performance and NOMA outperforms OMA in terms of SRT.