EE‐RS and PA for untrusted relay network at high signal‐to‐noise ratio regime

In this study, the authors investigate the energy‐efficient (EE) relay selection (RS) and power allocation (PA) in a cooperative secured system. Their scenario includes a multiple‐antenna source, a multiple‐antenna destination and multiple amplify‐and‐forward untrusted relay nodes, where the relay nodes only have the channel‐amplitude information. To prevent the untrusted relays from intercepting the source message and to achieve positive secrecy rate, the destination‐based cooperative jamming technique is used. By maintaining a minimum required secrecy rate, three optimal joint RS and power minimisation schemes are studied. The first objective is minimising the total transmit power consumption, and therefore obtaining the corresponding EE‐RS and PA schemes. Second, they focus on relay power minimisation, and third sum power minimisation of the relay and one mobile node by considering a weighted factor are investigated. Closed‐form solutions are presented for three practical optimised networks. Finally, some numerical results are provided to show the merits of the proposed scheme. They also give some insights to system design.