Secrecy Diversity Analysis with Multi-user Scheduling for Overlay Cognitive Radio Systems

In this paper, we consider a cognitive radio (CR) network which is made up of multiple secondary users (SUs), a secondary destination (SD) and an eavesdropper (E) which may overhear the legitimate communication between SUs and SD. In order to ensure the secure communication from SUs to SD, we investigate round-robin scheduling and optimal user scheduling to prohibit eavesdropper attacking. In optimal user scheduling, the channel state information (CSI) of all links including SUs-D, SUs-E, primary user (PU)-D and PU-E are available. Because of intercept probability is an important metric of security for wireless communications, we discuss the intercept probability of both scheduling. To further present the impact of number of users on secrecy performance, we also analyze the secrecy diversity of round robin scheduling and optimal user scheduling. Final results indicate that round robin scheduling obtains only one diversity order, however optimal user scheduling achieves full diversity order. Additionally, optimal user scheduling performs better than round robin scheduling in terms of intercept probability and the secrecy performance will significantly improve as the number of users increases.