Secrecy Performance of Finite-Sized Cooperative Full-Duplex Relay Systems with Unreliable Backhauls

This paper investigates secrecy performance of finite-sized cooperative full-duplex relay (FDR) systems with unreliable wireless backhaul connections across multiple transmitters under Nakagami- $m$ fading. Closed-form expressions for the secrecy outage probability and probability of nonzero achievable secrecy rate are derived in terms of self-interference (SI), transmitter cooperation, and backhaul reliability. It is shown that transmitter cooperation can effectively enhance the secrecy performance, while the asymptotic limits on the secrecy outage probability and probability of nonzero achievable secrecy rate are exclusively determined by backhaul reliability. With the aid of transmitter cooperation, the burden of SI cancelation can be alleviated for the FDR system in achieving the smallest allowed secrecy outage probability. Compared to that of a half-duplex relay (HDR) system, the FDR system achieves a lower secrecy outage probability with well suppressed SI. The analysis shows that the secrecy outage probability achieved by the FDR system converges to that of the HDR system under perfect backhaul as the target secrecy rate becomes small. The secrecy performance metrics of the considered system are verified by simulations for various backhaul scenarios.