This paper exploits a self-powered secondary relay to not only maintain but also secure communications between a secondary source and a secondary destination in cognitive radio networks when source-destination channel is unavailable. The relay scavenges energy from radio frequency (RF) signals of the primary transmitter and the secondary source and consumes the scavenged energy for its relaying activity. Under the maximum transmit power constraint, Rayleigh fading, the primary outage constraint, and the interference from the primary transmitter, this paper suggests an accurate closed-form expression of the secrecy outage probability to promptly assess the security performance of relaying communications in energy scavenging cognitive networks. The validity of the proposed expression is verified by computer simulations. Numerous results demonstrate the security performance saturation in the range of large maximum transmit power or high required outage probability of primary users. Moreover, the security performance is a function of several system parameters among which the relay’s position, the power splitting factor, and the time splitting factor can be optimized to achieve the minimum secrecy outage probability.
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