Secrecy outage of dual-hop AF relay system with relay selection without eavesdropper's CSI

We evaluate the upper bound, lower bound and an approximate expression for secrecy outage probability of a dual hop Amplify-and-forward (AF) relay system when the single cooperating relay among the relays is selected without the knowledge of eavesdropper's instantaneous channel state information (CSI). This situation arises when eavesdropper is not a legitimate node, or being a trusted node, it acts maliciously and does not share its instantaneous CSI. We also obtain the tighter bounds in high signal-to-noise ratio (SNR) of the source to relay links and in high SNR of the relay to destination links.We show that when the SNR of the source to relay links tends to zero, it becomes the bottle neck for secure communication, and the secrecy outage tends to 1. We show that the approximate expression follows the simulated outage closely and the outage decreases with an increase in the number of relays and increases with an increase in the required secrecy rate.