Abstract
In this paper, the benefit of distinguishable diversity order within a co-operative relay system is exploited to overcome the problem of secure communication in an underlay wiretap cognitive radio network. This network is in a coexistence with a primary transceiver network and it is subjected to multiple eavesdropping attacks which employ a specific interception strategy. To improve the physical layer security, simple relay selection schemes will be proposed that aims at maximizing the minimum of the dual hop communication secrecy rates under primary network constraints. For Rayleigh fading channels, exact and asymptotic closed form expressions will be derived for the secondary system outage and secrecy rate. Furthermore, based on the network topology, tight inner and outer bounds will subsequently be derived on the system secrecy outage probability. By employing analytical and simulation results, the gain of the system diversity order is obviously investigated and emphasized.