Performance Analysis of Pinching Antenna-Assisted NOMA Systems with Untrusted Users

Abstract

Pinching-Antenna System (PASS) has emerged as a promising paradigm for next-generation wireless networks, leveraging dielectric particles attached to clips to radiate power from the waveguide and establish strong line-of-sight (LoS) links. PASS enables a large-scale spatial deployment to fundamentally eliminate small-scale fading. However, a single waveguide radiates identical signals at any given time, posing a challenge for multiuser spectral efficiency. Integrating non-orthogonal multiple access (NOMA) with PASS offers a win-win solution to enhance spectral efficiency and user rates, yet the successive interference cancellation (SIC) decoding process introduces severe security risks in the presence of untrusted users. In this paper, we investigate the physical layer security of PA-assisted NOMA systems with an untrusted user. We analyze the system performance, and derive a closed-form expression for the secrecy outage probability (SOP). Theoretical analysis and numerical results reveal that equal power model and proportional power model exhibit limitations in power regulation for physical layer security. To address this issue, we propose a flexible power strategy to improve the security by adjusting the radiated power of PA. The results validate the correctness of theoretical analysis and demonstrate that the proposed strategy effectively enhances the secrecy performance of proposed system.