Improving physical layer security via multiple-level relay network

Cooperative relay is considered as an efficient scheme to improve the physical layer security of a wireless relay system in the presence of eavesdroppers. In this paper, multiple-level relay scheme is proposed. We consider relay weight design for secrecy rate maximization subject to a power constraint. The results show that a higher achievable secrecy rate is achieved in the two-level relay channel than that of the one-level relay channel when the destination node is far away from the source node. Therefore, the performance of the two-level relays channel is generally better under the circumstances of the long distance transmission.