Contents I. Introduction
In wireless communication networks, security and privacy, Energy Efficiency (EE), Spectral Efficiency (SE) and transmission reliability are the main metrics that researchers are focusing on to optimize. To implement a secure communication, a great deal of efforts has been made to develop the cryptographic protocols (i.e. RSA and AES) above the physical layer. But recent security in the physical layer is becoming an interesting research issue. It was first addressed by Shannon in his information-theoretic secrecy work [1] and later elaborated by Wyner [2], Csiszar and Korner [3], Leung and Hellman [4]. The physical layer security study concept is termed as the secrecy capacity (SC), which can be defined as the maximum communication rate achievable from the legitimate transmitter to the legitimate receiver, under the condition that the eavesdropper obtains no information. The potential idea of this information-theoretic security is to guarantee the transmitted messages not to be decoded by a third party malicious eavesdropping on the wireless medium. This is possible utilizing the combination of cryptographic schemes with channel coding techniques that exploit the randomness of the communication channels [5]
