Joint Relay Selection and Artificial Jamming Power Allocation for Secure DF Relay Networks

This paper studies cooperative transmission for securing a decode-and-forward (DF) two-hop network where massive cooperative nodes coexist with a potential single eavesdropper. With only the statistical channel state information (CSIs) of the eavesdroppers, we propose an opportunistic relaying with artificial jamming secrecy scheme, where a "best" cooperative node is chosen to forward the confidential signal and the others act as jammers to send the jamming signals to confuse the eavesdropper. Utilizing the limiting distribution technique of extreme order statistics, we optimize the power allocation between the confidential information and jamming signal based on the statistical CSIs of the legitimate nodes for ergodic secrecy rate (ESR) maximization. Although the optimization problems are non-convex, we propose a sequential parametric convex approximation (SPCA) algorithm to locate the KKT solutions. Then, we derive an analytical closed-form expression of the achievable ESR, which reduces the complexity of the system analysis and design.