Relay power allocation for security enhancement in three-phase AF two-way relaying systems

Abstract

In this work, information security of a cooperative wireless communication system over three-phase amplify-and-forward (AF) two-way relaying channels is investigated. A relay power allocation scheme is proposed to improve secrecy capacity of the system. We first derive the secrecy rate expression for the basic scenario which consists of one source, one destination, one single relay, and an eavesdropper. A relay power allocation scheme which maximizes the overall secrecy rate of the single-relay system is studied accordingly. Then the power allocation coefficients are calculated under the assumption of perfect channel state information (CSI). This design framework is then extended to a cooperative wireless system having multiple relays. In the numerical example, secrecy rate performance of the proposed scheme is compared with the classic three-phase two-way AF scheme and it is concluded that conducting power allocation at the relay can achieve the goal of improving the secrecy capacity. It is also observed that the best performing scenario of the relay power allocation scheme is when the relay locates right in the middle of the two legitimate communicants.