Performance Study of Untrusted Relay Network Utilizing Cooperative Jammer

In this paper, the problem of secure transmissionin twohop amplifyandforward (AF) systems with an untrustedrelay is investigated. To prevent the untrusted relay from interceptingthe source message and to achieve positive secrecy rate,the destinationbased cooperative jamming (DBCJ) technique isused. In this method the destination sends an intended jammingsignal to the relay. This jamming signal helps protecting thesource message from being captured reliably at the untrustedrelay, while the destination cancels itself intended jamming signal.The optimal power allocation (OPA) technique is considered forthe presented system. It is observed that the objective functionis a quasiconcave function at high signaltonoiseratio (SNR)regimes. Based on this OPA technique, we study the ergodicsecrecy rate (ESR) and the secrecy outage probability (SOP)of the system when the source and relay are equipped witha single antenna while the destination is equipped with largescaleantenna arrays (LSA). Using the achieved closedformexpressions, one can evaluate the performance of the securesystem easily and fast and also, they provide significant insight forsystem design. Finally, simulation results indicate the accuracyof the derived expressions.