Secrecy Outage Probability Analysis for Downlink Untrusted NOMA Under Practical SIC Error

TL;DR

This paper analyzes the secrecy outage probability of downlink untrusted NOMA systems considering practical SIC errors, proposing a new residual interference model and deriving analytical expressions to evaluate security performance.

Contribution

It introduces a novel residual interference model for imperfect SIC in NOMA and derives new SOP expressions for untrusted users, enhancing realistic security analysis.

Findings

Residual interference significantly affects secrecy outage probability.

The derived SOP expressions match simulation results closely.

System parameters influence the secrecy performance notably.

Abstract

Non-orthogonal multiple access (NOMA) serves multiple users simultaneously via the same resource block by exploiting superposition coding at the transmitter and successive interference cancellation (SIC) at the receivers. Under practical considerations, perfect SIC may not be achieved. Thus, residual interference (RI) occurs inevitably due to imperfect SIC. In this work, we first propose a novel model for characterizing RI to provide a more realistic secrecy performance analysis of a downlink NOMA system under imperfect SIC at receivers. In the presence of untrusted users, NOMA has an inherent security flaw. Therefore, for this untrusted users' scenario, we derive new analytical expressions of secrecy outage probability (SOP) for each user in a two-user untrusted NOMA system by using the proposed RI model. To further shed light on the obtained results and obtain a deeper understanding, a high signal-to-noise ratio approximation of the SOPs is also obtained. Lastly, numerical investigations are provided to validate the accuracy of the desired analytical results and present valuable insights into the impact of various system parameters on the secrecy rate performance of the secure NOMA communication system.