Relay Selection for Improved Security in Cognitive Relay Networks With Jamming

In this letter, we consider an underlay cognitive radio network in which a secondary transmitter (ST) communicates with a secondary destination (SD) with the aid of multiple cognitive relays, and multiple colluding eavesdroppers attempt to intercept the secondary transmission. Assuming that there is no ST-SD link, one of the cognitive relays is selected to convey the confidential information, while the others cooperate in jamming the eavesdroppers by transmitting artificial noise. Since the eavesdroppers' channel information state is considered to be absent, two opportunistic relay selection schemes are proposed to enhance the security of the system. We derive novel closed-form expressions for the secrecy outage probability. Simulation results are presented to validate our analysis.