Cooperation for Secure Communication: The Relay Wiretap Channel

It is well known that a non-zero secrecy capacity of the wiretap channel is only possible when the legitimate receiver is less noisy than the wiretapper. This work shows that user cooperation is an efficient solution to this limitation. In particular, the four-terminal wiretap relay channel is considered in our work where several cooperation strategies, that enable secure communication, are constructed and the corresponding rate-equivocation regions are characterized. Of particular interest is the novel noise forwarding strategy which establishes the deaf helper phenomenon. Here, the relay is able to facilitate secure communication over the main channel while being totally ignorant of the transmitted message. The gain offered by the proposed strategies is proved theoretically and validated numerically in the additive white Gaussian noise (AWGN) channel. Overall, our work establishes the utility of user cooperation in facilitating secure communication over wireless channels.