Non-orthogonal multiple access (NOMA) has come to the fore as a spectrally
efficient technique for fifth-generation networks and beyond. At the same time,
NOMA faces severe security issues in the presence of untrusted users due to
successive interference cancellation (SIC)-based decoding at receivers. In this
paper, to make the system model more realistic, we consider the impact of
imperfect SIC during the decoding process. Assuming the downlink mode, we focus
on designing a secure NOMA communication protocol for the considered system
model with two untrusted users. In this regard, we obtain the power allocation
bounds to achieve a positive secrecy rate for both near and far users.
Analytical expressions of secrecy outage probability (SOP) for both users are
derived to analyze secrecy performance. Closed-form approximations of SOPs are
also provided to gain analytical insights. Lastly, numerical results have been
presented, which validate the exactness of the analysis and reveal the effect
of various key parameters on achieved secrecy performance.Comment: 5 pages, 5 figures, and EUSIPCO 202