Optimal full-duplex jamming for safeguarding two-hop relay networks

The relay networks face with such a circumstance that an eavesdropper overhears every hop of the relay networks. To solve the issue, we propose a full-duplex friendly-jamming relaying (FDFJR) scheme to secure the information transmissions for a two hop relay network, where a malicious eavesdropper attempts to overhear the private messages transferred by the transmitter and the relay. In the scheme, we take advantage of the capacity of simultaneous reception and transmission of fullduplex (FD) relay. Specifically, in the first hop, the full-duplex jamming relay (FDJR) receives the private information from the transmitter while transmitting the jamming signals to the malicious eavesdropper. And in the second hop, FDJR continues transferring the jamming signals to the eavesdropper, rather than merely amplifying and forwarding the information signals previously received. Furthermore, the ergodic secrecy capacity (ESC) of the networks is characterized and its asymptotical expression is derived. To maximize ESC, we formulate a novel power scheduling problem satisfying several key power and rate requirements. By solving the problem, an exact analytic solution regarding power allocation factor is acquired. Finally, numerical results are provided to validate the accuracy of analytical results and the superiority of our proposed scheme.