摘要

In this study, the authors consider the physical-layer security problem in the relay networks. The relay nodes are employed not only to aid the information transmission but also to improve the network security in the physical layer by sending artificial noise to resist the potential malicious eavesdropper. By allowing shared randomness between the jamming nodes, it is shown that the maximum degrees of freedom (DoF) of the considered network is 1/2 almost surely. The necessary and sufficient conditions for the optimal DoF setup are established. Moreover, a simple DoF-optimal collaborative beamforming algorithm is proposed, and it works very well in the high signal-to-noise ratio regime, which is verified by computer simulations.