Secrecy Outage Analysis for DF Buffer-Aided Multi-Antenna Underlay CRNs

Abstract

In this paper, we investigate the secrecy outage performance of decode-and-forward (DF) buffer-aided multi-antenna underlay cognitive relay networks (CRNs) in the presence of an eavesdropper. The secondary users (SUs) can concurrently access the same band as the primary users (PUs) using an underlay protocol provided that the transmit power of SUs keeps below the maximum tolerable interference threshold at PUs. On the other hand, we utilize maximal ratio combining (MRC) scheme at the secondary relays and maximal ratio transmission (MRT) scheme at the secondary destination to improve the secrecy performance due to the fact that the eavesdropper can intercept the secondary network communication. The max-link relay selection scheme is also adopted to enhance the secrecy performance by selecting the best link among all available source-to-relay and relay-to-destination links. Moreover, we derive a closed-form expression for secrecy outage probability by modeling the dynamic buffer state transitions as the Markov chain. The findings of this paper demonstrate that multi-antenna relaying networks yield to better secrecy performance than single antenna relaying networks. In addition, the system secrecy performance can also be enhanced by optimizing several parameters such as interference threshold, buffer size or the number of relays. Monte Carlo simulations validate the theoretical analysis.