Secrecy Analysis of Relay-User Selection in AS-AF Systems Over Nakagami Fading Channels

This paper presents the secrecy outage probability of relay and user (RU) selection in the antenna selection (AS)-amplify and forward (AF) system over integer-valued $m$ Nakagami fading channels for the physical layer security. This work derives the lower bound (LB) and asymptotic cumulative density functions (CDFs) of the signal to noise ratio (SNR) for the RU selection in the AS-AF system. This study also considers the impact of the two types of receivers, i.e., maximal ratio combining (MRC), selection combining (SC) for the authorized system and eavesdropper. Using the lower bound CDFs, the LB expressions of the secrecy outage probability are derived for various scenarios. Applying the asymptotic CDFs, the diversity order of the secrecy performance is also quantified for each case. From analysis results, we show that the diversity order of the secrecy outage probability in the proposed system is only affected by authorized system's parameters, not by eavesdropper's parameters. Further, the relay and user nodes with the MRC receiver provide the SNR gain compared to the SC receiver regardless of eavesdropper's receiver type. Finally, the secrecy outage probability of the proposed RU system with the SC eavesdropper has the SNR gain compared to the MRC eavesdropper, while the diversity order is identical to each other.