Physical Layer Security Performance Analysis of MIMOME Systems Over Keyhole Channels

Abstract

The inherent openness of wireless networks exposes them to eavesdropping threats. In dense urban environments, signal propagation is frequently characterized by the keyhole effect, which causes channel rank deficiency and cascaded fading, challenging the assumptions of conventional multiple-input multiple-output (MIMO) physical layer security. This paper investigates the secrecy performance of MIMO multiple-antenna-eavesdropper (MIMOME) systems over keyhole channels with independent legitimate and eavesdropper links. We analyze the secrecy performance under three progressive scenarios: perfect CSI without artificial noise (AN), perfect CSI with AN-aided transmission, and practical imperfect CSI with AN. Specifically, we derive closed-form asymptotic expressions for the secrecy outage probability (SOP) and average secrecy rate (ASR) in the high signal-to-noise ratio (SNR) regime using Meijer G-functions and Gauss hypergeometric functions, from which the secrecy diversity order and secrecy array gain are explicitly extracted. The analytical results reveal that AN injection successfully restores the secrecy diversity order from zero to one, while imperfect CSI causes AN leakage that leads to ASR saturation and an SOP floor. The derived asymptotic expressions are verified by Monte Carlo simulations. Our findings provide theoretical guidelines by quantifying the trade-off between AN suppression capabilities and self-interference in cascaded fading environments.