Secrecy Outage Performance of Buffer-Aided Underlay Cognitive Relay Networks with Outdated CSI

This work investigates the secrecy outage performance of decode-and-forward (DF) buffer-aided underlay cognitive relay networks (CRNs) with outdated channel state information (CSI) in the presence of an eavesdropper. The transmit power of the secondary users (SUs) is limited by the predefined interference threshold to guarantee the quality of service (QoS) requirement of the primary users (PUs). We adopt the max-link relay selection scheme, which can improve the secrecy performance by selecting the best link among all available source-to-relay and relay-to-destination links. Moreover, a closed-form expression of the secrecy outage probability is derived by modeling the state transition of the buffer as a Markov chain. Monte Carlo simulations validate the theoretical analysis. The findings of this paper demonstrate that the outdated CSI degrades the secrecy outage performance, but optimizing several parameters can improve the system secrecy performance significantly.