A spectrum access game in bidirectional cognitive relay networks

We consider a cognitive relay network where two secondary users can access the unutilized spectrum and conduct bidirectional communication via the help of primary users. The primary users are regarded as relay nodes of the secondary users and adopt amplify-and-forward relaying strategy. Physical-layer network coding is used when both secondary users select the same relay. The spectrum access problem in the considered system model is defined as joint relay selection and discrete power control. We formulate the problem as a noncooperative game where the players are the secondary users and the common payoff function takes both transmission rate and power consumption into account. The proposed game falls into the framework of potential games where at least one pure strategy Nash equilibrium (NE) exists. Furthermore, the social optimal solution is also a pure strategy NE of the proposed game. We then propose a distributed algorithm based on learning automata to achieve the pure strategy NE. Numerical results show that the proposed algorithm has good convergence and near optimal performance.