due to the characteristics of wireless channels, it is particularly vulnerable for wireless networks to be attacked by an eavesdropper, which puts forward great challenges to secure communications. Traditional security approaches apply different cryptographic algorithm to achieving confidentiality and authentication in communications. Meanwhile, physical layer security (PLS) is applied by Shannon theory to exploring secrecy communication by coding. The basic idea of PLS is to explore the random nature of physical layer media to enhance the quality of legitimate channel while attenuating the quality of eavesdropping channel. Compared with traditional cryptographic technologies mainly at upper layers, PLS shows more security in some degree with its advantages, for example, applying proper coding and signal processing to guarantee message confidentiality, while traditional cryptographic methods can be broken by advanced computing technologies; PLS can be easily and conveniently achieved rather than massive resources and infrastructure exploited by sharing cryptographic materials among legitimate users; and the authentication of PLS for legitimate nodes is quick. Hence, as an important and promising technique to prevent eavesdropping, it has attracted more attention in both industry and academic fields [1-5]. Related works in physical layer security were pioneered by Shannon’s information theoretic secrecy analysis [1] and Wyner’s discrete memory-less wiretap channel secrecy analysis [2]. Wyner proved that if it is a degraded version of the main channel for the eavesdropper’s channel, the source and destination can achieve a positive perfect information rate, which is defined as the secrecy rate. And secrecy capacity is defined as the maximum secrecy rate from the source to the destination. In order to enhance physical layer security, there are numerous studies focused on node cooperation approaches, especially three-point cooperation mode with one source, one destination and one relay (or multiple relays) [3-5].