Secrecy Capacity in CRN With Malicious Energy Harvester Using Game Theoretic Techniques

In this paper, an underlay-based cognitive radio network (CRN) consisting of a secondary transmitter (ST), a secondary receiver (SR), an energy harvesting node (EHN), and a primary transmitter-receiver pair, is considered. The EHN is an energy constrained node and is thereby, assumed to have a power splitter at its receiver to decode information and harvest energy simultaneously from the received RF signal. The EHN behaves maliciously and decodes ST's messages when it is granted with a permission to (only) harvest energy from the received RF signal, thereby reducing the secrecy capacity of the ST-SR link. Since both ST and EHN are selfish with conflicting interests, we model the interaction between them as a Stackelberg game (SG). Further, we analyze the behavior of the nodes in a non-cooperative game (NCG) theoretic framework and prove the existence of a unique Nash equilibrium (NE) strategy. Simulation results show that the SG framework performs better than the NCG framework, in terms of the achievable secrecy capacity of the ST-SR link. Thereby the proposed SG model is applied to the considered CRN with multiple STs and a unique equilibrium is found. In case the STs possess limited channel state information (CSI), we model the competition among the STs as a Bayesian game and found its equilibrium solution, known as Bayesian NE (BNE). Simulation results demonstrate that BNE performs better than the NE when the STs possess limited CSI.