This letter exploits multiuser diversity to enhance the physical layer security in transmit antenna selection systems. Since fading channels among different users are nonidentically distributed, new expressions of the exact and asymptotic secrecy outage probability are derived in an accumulate way. Also, an efficient closed-form derivation rather than a numerical root-finding is presented to evaluate the ε-outage secrecy capacity.
Simulations are provided to verify our analysis and show that 1) the number of users has a great impact on secrecy performance; 2) the multiuser diversity should be exploited appropriately considering the statistics of the legitimate users and the eavesdropper.