Physical Layer Security in Two-hop Cooperative Networks Based on Multi-node SWIPT

In this paper, we consider a multi-node-assisted two-hop cooperative network, where an energy constrained source (S) aims to establish secure communications with a legitimate user in the presence of an eavesdropper. The cooperative nodes simultaneously assist the transmission from base station to legitimate user. Each cooperative node applies power splitting protocol to coordinate the received signal energy for information decoding and energy harvesting. The power splitting ratios at multi-node are formulated based on decode-and-forward (DF) relaying protocols. Depending on the available channel state information (CSI) at the source, we propose two different jamming schemes for secrecy performance enhancement. An optimal node is selected as a jammer to interfere the eavesdropper or a relay to forward the information to legitimate user. we evaluate the network performance based on secrecy outage probability (SOP). In addition, simple and accurate approximations are obtained at different transmission speed thresholds. Furthermore, numerical results reveal that there exist unique splitting ratios and harvesting efficiency that minimize the SOP.