Task-oriented secure communication in multiuser AF relaying networks

This paper studies the physical-layer security of a task-oriented multiuser amplify-and-forward (AF) relay network, operating in environments with multiple eavesdroppers. In the severe communication scenarios, such as urban areas with heavy shadowing or post-disaster zones, the direct communication paths are unavailable and the secure transmission depends solely on trusted relay nodes. To enhance the system secrecy performance, we introduce a relay–user pairing strategy aimed at minimizing the secrecy outage probability (SOP), taking into account the conditions of both legitimate and intercepting channels. Under Rayleigh fading, we derive closed-form SOP expressions and provide an asymptotic analysis that highlights the system’s diversity gain in the high main-to-eavesdropper ratio (MER) regime. Simulations confirm the validity of our theoretical and asymptotic results. Specifically, the analytical SOP exhibits excellent agreement with simulation ones across a wide MER range, confirming the correctness of the derived expressions. Moreover, the asymptotic expressions closely approximate the simulation results when MER exceeds 15 dB, highlighting their effectiveness for performance evaluation in high MER scenarios. Notably, the proposed relay–user selection strategy achieves a significant reduction in SOP compared to random or fixed pairing methods.