This paper investigates the performance of physical (PHY) layer secrecy in a cooperative relaying with opportunistic relay selection, where an eavesdropper intercepts the transmit signals between the authorized users. At first, theoretical expressions are derived for three performance criteria for evaluating the PHY security, namely: the secrecy outage probability, the average of secrecy capacity, and the probability of non-zero secrecy capacity. Then the secrecy performance in information transmissions is investigated. Moreover, using the computer simulations, the validity of the derived expressions and the carried out analyses are examined and verified. To show the enhancement on the secrecy performance in the presented system that employs opportunistic relay selection, the secrecy outage probabilities of the opportunistic relay selection system, one relay cooperation system, and direct transmission system are also compared.

本文研究了带有机会中继选择的协作中继中物理（PHY）层保密性的性能，其中窃听者拦截了授权用户之间的传输信号。首先，推导了用于评估PHY安全性的三个性能标准的理论表达式，即：保密中断概率，保密容量的平均值和非零保密容量的概率。然后研究了信息传输中的保密性能。此外，使用计算机模拟，对导出的表达式和进行的分析的有效性进行了检查和验证。为了显示在采用机会中继选择的系统中保密性能的增强，机会中继选择系统的保密中断概率，