%0 Electronic Article %A Khuong Ho-Van %A Thiem Do-Dac %K unlicenced/secondary users %K asymptotic intercept outage probability expressions %K information transmission %K licenced/primary users %K secondary relay %K fading channels %K relay selection %K eavesdroppers %K Monte Carlo simulations %K information wire-tapping %K maximum transmit power constraint %K underlay cognitive networks %X Underlay cognitive networks allow unlicenced/secondary users (SUs) to opportunistically access licenced frequency bands, and hence information transmission is undoubtedly wire-tapped by eavesdroppers. This study analyses security performance of a relay selection scheme, which selects a secondary relay to minimise information wire-tapping of eavesdroppers, in underlay cognitive networks. Toward this end, the authors propose approximate and asymptotic intercept outage probability expressions which account for interference power constraint for licenced/primary users, maximum transmit power constraint for SUs, independent non-identical fading channels, and direct channel between secondary source and eavesdropper. Moreover, they determine diversity order and coding gain of this relay selection based on the proposed asymptotic expression. Monte Carlo simulations validate these expressions and numerous results demonstrate that the investigated relay selection prevents the eavesdropper from obtaining full diversity order offered by all relays and source, induces the intercept outage probability saturated at either large maximum transmit power or large maximum interference power, and improves information security performance with respect to the increase in the number of relays. %@ 1751-8628 %T Analysis of security performance of relay selection in underlay cognitive networks %B IET Communications %D January 2018 %V 12 %N 1 %P 102-108 %I Institution of Engineering and Technology %U https://digital-library.theiet.org/;jsessionid=5fgt739bvo2cd.x-iet-live-01content/journals/10.1049/iet-com.2017.0445 %G EN