Enhancing Secrecy Rate in Cognitive Radio via Game Theory

This paper investigates the game theory based cooperation method to optimize the PHY security in both primary and secondary transmissions of a cognitive radio network (CRN) that include a primary transmitter (PT), a primary receiver (PR), a secondary transmitter (ST), a secondary receiver (SR) and an eavesdropper (ED). In CRNs, the primary terminals may decide to lease its own given bandwidth for a fraction of time to the secondary nodes in exchange for appropriate remuneration. We consider the ST as a trusted relay for primary transmission in the presence of the ED. The ST forwards the source message in a decode-and-forward (DF) fashion and, at the same time, allows part of its available power to be used to transmit an artificial noise (i.e., jamming signal) to enhance secrecy rates and avoid the employment of a separate jammer. In order to allocate power between message and jamming signals, we formulate and solve optimization problem of maximizing the primary secrecy rate (PSR) and secondary secrecy rate (SSR). We then analyse the cooperation between the primary and secondary transmitters from a game-theoretic perspective, where we model their interaction as a Stackelberg game. Finally, we apply numerical examples to illustrate the impact of the Stackelberg game on the achievable PSR and SSR. It shows that spectrum leasing based on trading secondary access for cooperation by means of relay and jammer is a promising framework for enhancing secrecy rate in cognitive radio.