Secure transmission of cognitive untrusted relay networks with selection diversity

In this paper, we investigate the secrecy performance of a cognitive untrusted relay network with a direct link using selection combining (SC) scheme, where a secondary source communicates with a secondary destination through an untrusted relay. We first examine the connection outage probability (COP) and secrecy outage probability (SOP) to investigate the reliability and security performance of the considered system. Notably, the reliability level can be improved by loosing the interference temperature constraint, which unfortunately increases the risk that the untrusted relay succeeds in eavesdropping the source information. Then, we characterize the reliability and security in a unified manner by effective secrecy throughput (EST). In order to gain additional insights on the performance evaluation, we provide the asymptotic expressions for the COP, SOP, and EST in high signal-to-noise ratio (SNR) region. Finally, Monte Carlo simulation results validate our numerical analysis.