Secure Transmission for Multiuser Relay Networks

We investigate secure transmission for multiuser relay networks, where the undesired users who are not selected for data reception may overhear the source message as eavesdroppers. In this system, the secrecy performance may deteriorate as the number of users increases, since the number of eavesdroppers also increases. To address this issue, we consider a multiuser relay scheme with cooperative jamming (MUCJ). In this scheme, the desired user sends a jamming signal to the relay while the source sends its message to the relay, and then the relay amplifies and forwards the received signal to the desired user. Since the jamming can be subtracted only at the desired user, it acts as interference to prevent the eavesdroppers from intercepting the source message. We propose an optimal user selection scheme for the MUCJ, which is optimal in the sense of maximizing the secrecy rate. For the existing multiuser relay scheme (MURS) without cooperative jamming and the MUCJ, we derive the ergodic secrecy rates and analyze the asymptotic secrecy rate gains. We reveal that the ergodic secrecy rate can be increased as the number of users grows and much higher secrecy rate can be achieved by the MUCJ.