Optimized secure and energy-efficient transmission in an untrusted relay network

In this paper, a near Optimum Power Allocation (OPA) for a cooperative jamming relay network is proposed, by using physical layer security to protect the user's messages from relay's interception. The network uses Amplify and Forward (AF) relay to enlarge the coverage area, however the relay is untrusted. By defining secure Energy Efficiency (EE) as the ratio of the instantaneous secrecy rate to the total power consumption to measure the performance of the network. To simplify such optimization problem, an approximated OPA on the basis of Taylor expansion is derived. The numerical results show that the approximated OPA error does not exceed 1% even in the worst case, which verifies the correctness and lower complexity of the proposed algorithm.