Cooperative beamforming and jammer selection strategies for two-hop secure communication

In this paper, we propose a novel scheme to enhance the security of a single source-destination cooperative network with multiple helpers and one eavesdropper, where a helper operates as a jammer and the others use amplify-and-forward (AF) protocol to deliver a weighted version of the received signal. Since the instantaneous channel state information (CSI) of the eavesdropper is not available, we hope to achieve the maximum signal-to-noise ratio (SNR) and guarantee that the jamming signal is cancelled out at the destination. The weights of the relay can be obtained by just solving a semidefinite programming (SDP) without bisection search. We provide two jammer selection strategies for two cases, i.e., with or without knowledge of the eavesdropper´s position. Simulation results confirm a great improvement of the security in the considered network.