Enhancing the Physical Layer Security of Non-orthogonal Multiple Access in Large-Scale Networks (1612.03901v2)

Abstract: This paper investigates the physical layer security of non-orthogonal multiple access (NOMA) in large-scale networks with invoking stochastic geometry. Both single-antenna and multiple-antenna aided transmission scenarios are considered, where the base station (BS) communicates with randomly distributed NOMA users. In the single-antenna scenario, we adopt a protected zone around the BS to establish an eavesdropper-exclusion area with the aid of careful channel-ordering of the NOMA users. In the multiple-antenna scenario, artificial noise is generated at the BS for further improving the security of a beamforming-aided system. In order to characterize the secrecy performance, we derive new exact expressions of the security outage probability for both single-antenna and multiple-antenna aided scenarios. To obtain further insights, 1) for the single antenna scenario, we perform secrecy diversity order analysis of the selected user pair. The analytical results derived demonstrate that the secrecy diversity order is determined by the specific user having the worse channel condition among the selected user pair; and 2) for the multiple-antenna scenario, we derive the asymptotic secrecy outage probability, when the number of transmit antennas tends to infinity. Monte Carlo simulations are provided for verifying the analytical results derived and to show that: i)~The security performance of the NOMA networks can be improved by invoking the protected zone and by generating artificial noise at the BS; and ii)~The asymptotic secrecy outage probability is close to the exact secrecy outage probability.

• The paper demonstrates that protected zones and artificial noise significantly enhance NOMA security in both single- and multiple-antenna systems.
• The study employs stochastic geometry and channel ordering to derive exact expressions for secrecy outage probabilities and diversity orders.
• Monte Carlo simulations validate the analysis, highlighting the optimal power balance between signal and noise to bolster security.

Enhancing the Physical Layer Security of Non-orthogonal Multiple Access in Large-Scale Networks

This paper presents an exploration into the physical layer security of Non-orthogonal Multiple Access (NOMA) within large-scale network environments. The approach leverages stochastic geometry to analyze both single-antenna and multiple-antenna transmission scenarios. Key strategies include the implementation of a protected zone surrounding the base station (BS) and the introduction of artificial noise in beamforming-aided systems.

In the single-antenna context, the paper investigates the use of protected zones to establish eavesdropper-exclusion areas and applies channel-ordering techniques among NOMA users. For multiple-antenna systems, artificial noise is generated at the BS to bolster security. The paper derives exact expressions for the security outage probability in both scenarios and extends this through secrecy diversity order analysis, providing expressions for asymptotic secrecy outage probabilities when the number of transmit antennas approaches infinity.

The analytical results demonstrate that secrecy diversity is determined by the user with the worse channel condition among a selected pair. For systems with multiple antennas, increasing antenna numbers has minimal impact on eavesdropper SNR due to the vast array’s properties. The findings suggest that the security performance of NOMA networks is significantly improved with protected zones and artificial noise application.

The Monte Carlo simulations corroborate the analytical outcomes, evidencing that the asymptotic results are closely aligned with the computed security outage probability. Notably, the presence of an optimal balance between signal-power and artificial noise power is indicated, impacting secrecy outage probabilities.

Implications and Speculation on Future Developments

The paper's implications are manifold. Practically, this work provides a clear pathway to enhance the security of future 5G and beyond networks deploying NOMA, especially useful in environments heavily congested by interconnected devices. Theoretically, it extends the understanding of physical layer security within stochastic network frameworks, contributing to the literature on NOMA’s feasibility in complex settings.

Moving forward, further developments could explore dynamic power allocation strategies among users to optimize security performance further. Real-world implementations might align this research with machine learning techniques to dynamically adjust protected zones and artificial noise parameters in response to changing network topologies and traffic conditions, enhancing adaptive security measures in real-time environments. Additionally, addressing challenges related to imperfect successive interference cancellation might further consolidate NOMA's applicability in diverse communication scenarios.

This paper lays important groundwork in the continual advancement of secure communications, highlighting the potential of NOMA in navigating the burgeoning needs of modern and future wireless networks.