Joint null-space beamforming and jamming to secure af relay systems with individual power constraint

Cooperative beamforming and jamming are two efficient schemes to improve the physical-layer security of a wireless transmission in the presence of a passive eavesdropper. However, in most works they are discussed separately. In this paper, we propose a joint cooperative beamforming and jamming scheme to enhance the security of a cooperative relay network, where some intermediate nodes adopt distributed beamforming while the others jam the eavesdropper, simultaneously. Subjected to the more practical individual power constraint of each node, we propose a null-space beamforming based secrecy strategy. The beamformer design can be optimized by a bisection method and second-order convex cone programming (SOCP). Simulations show the joint scheme greatly improves the security.