Adaptive Transmission for Secure AN-Aided Cooperative Networks with RF-EH Untrusted Relaying using Outdated CSI

In this paper, we investigate a trade-off between energy consumption and physical layer security in a dual-hop untrusted multiple amplify-and-forward relaying network. Considering the presence of the direct link, we propose an adaptive switching scheme between the direct and the relaying modes. Since relay nodes are energy-constrained, the direct link is prioritized. With outdated channel state information (CSI), to save energy while forwarding the source information, we adopt a greedy relay selection scheme and derive a tight upper bound on the secrecy outage probability. We quantify the impact of outdated CSI on the secrecy performance and the secrecy gains of our proposed mode switching scheme over its fixed transmission counterparts.