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

Mansi Nema, Kuntal Deka, Sanjeev Sharma, Tharmalingam Ratnarajah

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.

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

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.

Paper Structure

This paper contains 12 sections, 30 equations, 5 figures, 1 table, 1 algorithm.

Table of Contents

  1. Introduction
  2. System Model and Problem Formulation
  3. Channel Model
  4. Signal Model
  5. STAR-RIS Operation Modes
  6. SINR and Achievable Rates
  7. Problem Formulation
  8. Proposed Solution
  9. Active Beamforming Optimization
  10. Passive Beamforming Optimization
  11. Results and Discussion
  12. Conclusion

Figures (5)

  • Figure 1: STAR-RIS assisted MISO NOMA communication system.
  • Figure 2: Sum-rate versus transmit power for different schemes ($K=30$).
  • Figure 3: Impact of STAR-RIS elements $K$ on the sum-rate versus transmit power performance.
  • Figure 4: Distribution of STAR-RIS modes (reflection, transmission, jamming) versus transmit power.
  • Figure 5: Convergence rate of the proposed algorithm for the STAR-RIS system at 40 dBm.