Effect of Feedback Delay on Secure Cooperative Networks with Joint Relay and Jammer Selection

Physical layer security is a promising technique to realize secure wireless communications without relying on conventional cryptographic methods. In cooperative networks with secrecy constraints, joint relay and jammer selection (JRJS) is an efficient approach to improving the security performance. However, due to feedback delay, the channel state information (CSI) used in the selection process may become outdated and differ from the CSI during the actual transmission of data and jamming. In this work, we study the effect of feedback delay on the JRJS scheme with decode-and-forward relaying strategy. We provide a lower bound for the ergodic secrecy capacity (ESC) and approximate closed-form expressions for the secrecy outage probability (SOP). Monte Carlo simulations are performed to verify the analytical results. The simulation results show that feedback delay decreases the ESC and increases the SOP floor of JRJS. However, in spite of the performance degradation, JRJS outperforms the conventional relay selection scheme without jamming.