Joint cooperative jamming and beamforming for secure transmission in two-cell networks

In this paper, we consider secure downlink transmission in two-cell networks where the one base station (Alice) provides secure wireless services to its legitimate receiver (Bob) in the presence of a passive eavesdropper (Eve). For multi-cell networks, the inter-cell interference to Bob and Eve has a great impact on the security performance. In order to improve the confidentiality of information transfer from Alice to Bob, it is crucial to properly design the transmit strategies. With the results of conventional cooperative jamming (CJ) scheme, we propose a modified CJ scheme for cooperative base station (CBS) to further degrade the quality of signal reception at Eve, and therefore the secrecy rate can be increased. Both theoretical analysis and numerical results show that the modified CJ scheme outperforms the conventional CJ scheme by achieving a higher secrecy rate. Additionally, by taking the energy efficiency into account, we formulate an adaptive cooperation, in which the CBS is allowed to provide services to its desired receiver. We design a cooperative beamforming for CBS to satisfy the rate requirement while maximizing the secrecy rate of legitimate channel. Numerical results validate the effectiveness of the proposed cooperation scheme.