Collaborative Relay Beamforming for Secure Broadcasting

In this paper, collaborative use of relays to form a beamforming system with the aid of perfect Channel State Information (CSI) and to provide communication in physical layer security between a transmitter and two receivers is investigated. In particular, the authors describe decode-and-forward based null space beamforming schemes and optimize the relay weights jointly to obtain the largest secrecy rate region. Furthermore, the optimality of the proposed schemes is investigated by comparing them with the outer bound secrecy rate region. The open nature of wireless communications allows for the signals to be received by all users within the communication range.