Pinching-Antenna-Assisted Secure NOMA Systems Against Internal Eavesdropping

Abstract

This letter investigates a pinching-antenna (PA)-assisted downlink non-orthogonal multiple access (NOMA) system with an untrusted user acting as an internal eavesdropper. By exploiting the flexibility of PAs in reconfiguring wireless channel conditions, secure information transmission for the trusted user can be achieved in the considered system. Accordingly, we formulate an optimization problem aimed at maximizing the secrecy rate by jointly optimizing the power allocation coefficients and the positions of PAs. Given that the coupling between effective channel gains and power allocation coefficients makes the problem non-convex, we employ a joint optimization algorithm to solve it effectively. Specifically, we first derive a closed-form expression for optimal power allocation, and then, an element-wise algorithm is employed to optimize the PA positions. Simulation results demonstrate that, compared with fixed antenna systems, PAs can significantly enhance the secrecy performance of NOMA systems.