Physical layer security is an important and timely topic in the research of future wireless systems and it constitutes a part of the Internet of Things (IoT) notion. IoT oriented systems are largely characterized by a stringent quality of service and enhanced security requirements, which comes at a cost of increased computational complexity that needs to be maintained within sustainable levels. In the present contribution, we investigate the physical-layer security of a dual-hop energy RF-Powered cognitive radio network over realistic multipath fading conditions. Assuming a spectrum sharing scenario, our analysis assumes that a source S communicates with a destination D with the aid of a multi-antenna relay R and in the presence of an eavesdropper E who is attempting to overhear the communication of both S-R and R-D links. The involved relay is powered by the renewable energy harvested from the signal sent by the source based on the power-splitting energy harvesting strategy. Furthermore, the relay uses a maximum ratio combining technique to process effectively the received signals. In addition, owing to the underlying strategy, both S and R adjust their respective transmit powers in order to avoid causing interference to the primary network. By considering both the independent identically distributed and the independent but not necessarily identically distributed flat Rayleigh fading channels, closed-form expressions for the secrecy outage probability are derived, based on which an asymptotic analysis is carried out. Our results quantify the impact of the main key system parameters and point out the optimal values ensuring a high-security performance of such a communication system. The validity of the derived results is verified extensively through comparisons with respective Monte Carlo simulation results and useful theoretical and technical insights are developed which are expected to be useful in the design of future cooperative CRNs.
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