Secrecy Outage Probability Analysis for Downlink NOMA with Imperfect SIC at Untrusted Users

TL;DR

This paper analyzes the secrecy outage probability in downlink NOMA systems with imperfect SIC at untrusted users, deriving analytical expressions and bounds to enhance understanding of security performance under realistic decoding conditions.

Contribution

It introduces a realistic system model considering imperfect SIC and derives analytical SOP expressions for secure NOMA communication with untrusted users.

Findings

Derived closed-form SOP expressions for both users.

Identified power allocation bounds for positive secrecy rates.

Numerical results validate analysis and show parameter effects.

Abstract

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.