To secure amplify-and-forward relay systems via joint cooperative beamforming and jamming

Securing the wireless transmissions in the physical layer is a new perspective of security. In a wireless relay system, cooperative beamforming and jamming are two efficient schemes to improve the physical-layer security in the presence of passive eavesdroppers. However, in most works these two techniques are used in phase II of the cooperative transmission, which leaves the phase I out of protection. In this paper, we propose a joint cooperative beamforming and jamming scheme to enhance the security of a cooperative relay network, where a part of intermediate nodes adopt distributed beamforming while others jam the eavesdropper, simultaneously, such that both phases are secured. Since the instantaneous channel state information (CSI) of the eavesdropper may not be known, we propose a cooperative artificial noise transmission based secrecy strategy, subjected to the individual power constraint of each node. The beamformer weights and power allocation can be obtained by solving a second-order convex cone programming (SOCP) together with a linear programming problem. Simulations show the joint scheme greatly improves the security.