Outage performance for amplify-and-forward channels with an unauthenticated relay

We investigate a relay network where the source can potentially utilize an unauthenticated amplify-and-forward (AF) relay to augment its direct transmission of a confidential message to the destination. Since the relay is unauthenticated, it is desirable to protect the confidential data from it while simultaneously making use of it to increase the reliability of the transmission. We study the likelihood of achieving simultaneously secure and reliable message transmission via the secrecy outage probability (SOP) of the relay network. We first characterize the SOP for three different schemes: direct transmission, conventional AF relaying, and cooperative jamming. Subsequently, an asymptotic analysis is conducted to determine the optimal policies for different power budgets and channel gains. Numerical results are presented to verify the theoretical predictions of the preferred transmission policies from a secrecy outage perspective.