Cooperative cognitive radio model for enhancing physical layer security in two-path amplify-and-forward relaying networks

In this paper, we investigate the secrecy performance achieved by a new cooperative cognitive radio (CR) model which employs the two- path amplify-and-forward (AF) relaying protocol. In this model, the secondary user (SU) network pairs (i.e., transmitter and receiver) serve as relaying nodes for the primary user (PU) network. The SU network employs the inter-relay- interference (IRI) between the two relay nodes to transmit its data while relays PU data. In this work, the improvement in PU network physical layer security against multiple passive eavesdroppers is studied in two different scenarios. Optimization problems are formulated to find the optimal power allocation approach that maximizes PU secrecy rate in terms of SU transmission power, amplifying factors. The Lagrangian multipliers method is used to obtain the optimal solutions. Numerical results and simulations are provided to prove that the new cooperative CR model can achieve a non-zero secrecy rate even if the wiretap channel is better than the main channel.