On the Secrecy Performance of Continuous-Aperture Arrays Over Fading Channels

2026-03-06

AI Summary

This study investigates the physical-layer security performance of continuous-aperture phased arrays (CAPAs) over fading channels in the presence of eavesdroppers. Focusing on three scenarios—single eavesdropper, multiple independent eavesdroppers, and multiple colluding eavesdroppers—the authors derive approximate probability density functions of the signal-to-noise ratios for both legitimate and eavesdropping links using Mercer’s theorem and Landau’s eigenvalue theorem, followed by high-SNR asymptotic analysis. The work establishes, for the first time, an equivalence among the high-SNR slope, diversity order, and spatial degrees of freedom inherent to CAPAs, and quantifies their array gain and power offset advantages. Both theoretical and simulation results demonstrate that CAPAs achieve higher secrecy rates and lower secrecy outage probabilities than conventional half-wavelength-spaced discrete arrays, while maintaining identical diversity order and high-SNR slope across all considered scenarios.

Technology Category

• Search and Optimization: Evaluation and Analysis
• Planning, Routing, and Scheduling: Optimization of Spatio-temporal Systems
• Application Domains: Security

Application Category

• Security and Privacy: Large-scale security measurements
• Systems and Infrastructure for Web, Mobile and WoT: Web performance, measurement, and characterization
• Graph Algorithms and Modeling for the Web: Efficient manipulation of static and dynamic Web-related graphs

Abstract

The secrecy performance of continuous-aperture array (CAPA)-based wiretap channels in terms of secrecy rate and secrecy outage probability (SOP) is analyzed. First, the system models of CAPA systems with maximum-ratio transmission under a Rayleigh fading channel are established, and approximate probability density functions for the legitimate user Bob's signal-to-noise ratio (SNR) and the eavesdropper Eve's SNR are derived using Mercer's theorem and Landau's eigenvalue theorem. Three scenarios are considered, including a single Eve, multiple independent Eves, and multiple collaborative Eves. Next, the expressions of the secrecy rate and SOP under these three scenarios are derived, and the high-SNR slope, high-SNR power offset, diversity order, and array gain in Bob's high-SNR region are obtained. It is then theoretically proven that, in all three scenarios, the CAPA system achieves the same high-SNR slope and the same diversity order, with the latter being equal to the spatial degrees of freedom. Moreover, the CAPA system with a single Eve has the smallest high-SNR offset and the highest array gain, whereas the CAPA system with multiple collaborative Eves exhibits the largest high-SNR offset and the lowest array gain. Finally, the theoretical analyses of secrecy rate, SOP, high-SNR performance are validated by the simulation results, and a higher secrecy rate and a lower SOP are achieved by the CAPA systems compared to the spatially-discrete array systems with half-wavelength antenna spacing.

Problem

• continuous-aperture array
• secrecy rate
• secrecy outage probability
• fading channels
• physical layer security

Innovation

• continuous-aperture array
• secrecy outage probability
• physical-layer security
• high-SNR analysis
• spatial degrees of freedom