Tertiary-Mode STAR-RIS for Secure NOMA: Integrating Transmission, Reflection, and Jamming

TL;DR

This paper explores the use of a tertiary-mode STAR-RIS to enhance physical layer security in NOMA systems by enabling transmission, reflection, and jamming simultaneously, with an optimization algorithm improving secrecy and sum rate.

Contribution

It introduces a novel tertiary-mode STAR-RIS-assisted NOMA system with an adaptive mode selection and beamforming optimization for improved security and performance.

Findings

Significant increase in achievable sum rate compared to benchmarks.

Enhanced secrecy performance with adaptive jamming mode.

Effective joint optimization of active and passive beamforming.

Abstract

This paper investigates the physical layer security of a non-orthogonal multiple access (NOMA) system assisted by a tertiary-mode simultaneously transmitting and reflecting reconfigurable intelligent surface (STAR-RIS), which can perform transmission, reflection, and jamming simultaneously. The system comprises a base station (BS) serving two users located on opposite sides of the STAR-RIS, assuming perfect channel state information (CSI) at the transmitter. To enhance secrecy performance, a subset of STAR-RIS elements is adaptively configured for jamming. A penalty-based alternating optimization algorithm is developed to jointly optimize the BS's active beamforming and the STAR-RIS's passive beamforming and mode selection. Simulation results demonstrate that the proposed design substantially improves the achievable sum rate and secrecy performance compared to conventional RIS-assisted and no-RIS benchmarks, highlighting the potential of tertiary-mode STAR-RIS for secure and efficient next-generation wireless communications.