Secure Cooperative Untrusted-Relay Network With Outdated CSI

This paper studies the secrecy performance of an untrusted amplify-and-forward relaying network where both the relaying and the direct links are used to convey the source's information. Since relays act as eavesdroppers, a source-based jamming technique is proposed to keep the source's message secret from these helper nodes. We analyze the secrecy capacity of partial relay selection based on outdated channel state information. The study is conducted analytically by deriving the lower-bound expression for the ergodic secrecy capacity (ESC). We demonstrate through the simulation results the tightness of the derived bound. The use of the direct link is shown to improve the secrecy performance of the proposed scheme. In this case, we found that ESC performance with maximum ratio combining at the destination is better than that with selection combining. The system performance worsens as the correlation coefficient decreases. Furthermore, the maximum of ESC is achieved when relays are in the middle between the source and the destination with equal power allocation between the information and the jamming signals at the source.