Joint Cooperative Beamforming and Jamming for Physical-Layer Security of Decode-and-Forward Relay Networks

This paper proposes a new joint cooperative beamforming and jamming (JCBJ) scheme for improving the physical layer security of decode-and-forward wireless networks where a source node transmits to its destination with the aid of multiple intermediate nodes in the presence of an eavesdropper. In the proposed JCBJ scheme, we select the intermediate nodes succeeding in source decoding as the relays to forward the source transmission simultaneously by employing a beamforming weight vector, and meanwhile, use the remaining ones as the friendly jammers to disturb the eavesdropper by sending artificial noise. In order to achieve the secrecy rate maximum, we further study on the power allocation among the source, relays, and jammers under two assumptions of the wiretap link's channel state information. We derive the closed-form optimal solutions by first allocating the transmit power at the source within different ranges to consider all the possible relay selection schemes in which different numbers of relays are employed, and then transforming the multivariable power allocation problem to a set of single-variable optimization subproblems. Our numerical results show the superiority of the proposed JCBJ scheme and the proposed power allocation strategies.