Equilibrium Strategies for Interference Free Channel Access in Cognitive Radio based WRANs

Abstract—In this paper, we study how cognitive radio based wireless regional area networks (e.g., IEEE 802.22 networks) can adapt themselves so that they can co-exist with each other. These networks opportunistically accesses and uses under– utilized bands and relinquishes them when the primary user of that band initiates transmission. Such networks, deployed and operated by competing wireless service providers have to self-coexist among themselves by accessing different parts of the available spectrum. Since there is no coordination among the networks in accessing the spectrum bands, they have to adapt such that interference from neighboring networks is minimum. When interfered, a network can adopt either one of two choices – switch to a new band hoping to find a non-interfering band, or stay with its current band hoping that the interfering network(s) will move away to a new band. Using game theory, we model the spectrum band switching process as an ‘infinitely repeating ’ game where the aim of each network (player) is to minimize its cost of finding a clear channel. We first explore the pure strategy solution space for the game and show that a pure strategy equilibrium, though possible, is infeasible to implement in reality. Thus, we further explore the mixed strategy space and propose a mixed strategy Nash equilibrium among the networks. We analyze the game for the 2-player case, where a network is in interference with only one other network. We also provide hints on how to obtain the equilibrium for the n-player game. Keywords-IEEE 802.22 networks, self-coexistence, game the-ory, mixed strategy. I