Hybrid relaying and jamming for secure two-way relay networks with per-node power constraint

Cooperative relaying and jamming are two efficient schemes to improve the physical-layer security of a wireless transmission in the presence of an eavesdropper. In this paper, we propose a hybrid cooperative relaying and jamming mechanism to enhance the security of a two-way relay network, where some intermediate nodes adopt distributed beamforming to improve the channel quality to legitimate terminals and others jam the eavesdropper, simultaneously. Subjected to the more practical per-node power constraint of each cooperative node, we propose a secrecy scheme to maximize the secrecy sum rate of the two terminals. It is shown that the problem can be transformed into a semi-definite programming (SDP) problem with an additional rank-1 constraint. We then propose a penalty function method and an iterative algorithm to solve such a problem efficiently, instead of the popular semi-definite relaxation (SDR) and randomization technique in the previous literature. Simulations show that the proposed hybrid schemes greatly improve the security of the two-way relay networks.