Amirkabir University of Technology AUT Journal of Electrical Engineering 2588-2910 48 2 2016 11 21 Performance Study of Untrusted Relay Network Utilizing Cooperative Jammer Performance Study of Untrusted Relay Network Utilizing Cooperative Jammer 93 100 820 10.22060/eej.2016.820 EN Ali Kuhestani Ph.D. Student, Electrical Engineering Department, Amirkabir University of Technology Abbas Mohammadi Professor, Electrical Engineering Department, Amirkabir University of Technology 0000-0002-5505-1660 Mohammad Javad Emadi Assistant Professor, Electrical Engineering Department, Amirkabir University of Technology Journal Article 2015 09 30 Abstract—In this paper, the problem of secure transmission in two-hop amplify-and-forward (AF) systems with an untrusted relay is investigated. To prevent the untrusted relay from intercepting the source message and to achieve positive secrecy rate, the destination-based cooperative jamming (DBCJ) technique is used. In this method the destination sends an intended jamming signal to the relay. This jamming signal helps protecting the source message from being captured reliably at the untrusted relay, while the destination cancels itself intended jamming signal. The optimal power allocation (OPA) technique is considered for the presented system. It is observed that the objective function is a quasiconcave function at high signal-to-noise-ratio (SNR) regimes. Based on this OPA technique, we study the ergodic secrecy rate (ESR) and the secrecy outage probability (SOP) of the system when the source and relay are equipped with a single antenna while the destination is equipped with largescale antenna arrays (LSA). Using the achieved closed-form expressions, one can evaluate the performance of the secure system easily and fast and also, they provide significant insight for system design. Finally, simulation results indicate the accuracy of the derived expressions. https://eej.aut.ac.ir/article_820_e2a2dcc36a08a345332c751b2f2e476c.pdf