Towards secure communication via a wireless-powered full-duplex jammer

This paper explores the use of a full-duplex (FD) friendly jammer to secure the communication between a transmitter and a receiver in the presence of a passive eavesdropper. The friendly jammer is considered as a wireless-powered node without embedded power supply but can harvest energy from radio frequency (RF) signals, accumulate it in the storage, and use the harvested energy to perform the cooperative jamming (CJ). A novel CJ protocol termed accumulate-and-jam (AnJ) is proposed to improve the jammer efficiency, which splits the transmission blocks into dedicated energy harvesting (DEH) blocks and opportunistic energy harvesting (OEH) blocks. In DEH blocks, the transmitter transfers wireless power to replenish the jammer. In OEH blocks, the transmitter sends information to the receiver. Using the accumulated energy, the jammer transmits jamming signals to confound the eavesdropper. Mean-while, thanks to the FD capability, the jammer can continue to harvest energy from the signals overheard from the transmitter. Compared with the existing protocols using a wireless powered half-duplex (HD) jammer, the proposed design possesses the advantage of uninterrupted energy harvesting at the jammer. A closed-form expression for the secrecy outage probability of the considered system is derived. Numerical results show that our proposed AnJ protocol can significantly outperform its HD counterpart in terms of secrecy outage probability.