On the cascading spectrum contention problem in self-coexistence of cognitive radio networks

In cognitive radio (CR) networks, the coexistence between neighboring secondary networks is referred to as self coexistence. As prescribed in IEEE 802.22, a self-coexistence protocol enables a CR network in need of more spectrum resources to acquire spectrum (channels) from neighboring CR networks via a distributed inter-network spectrum contention process. A network that forfeits part of its spectrum in a spectrum contention process may later become short of spectrum, and in turn, it initiates a cascading spectrum contention process to acquire more spectrum resources. As a result, a local spectrum contention may trigger a series of successive contention instances that proliferate over the whole network, which may waste the network resources. In this paper, we systematically study the cascading spectrum contention problem using a percolation-based model in the context of CR networks. We show that cascading spectrum contentions under existing spectrum contention resolution rules is equivalent to a site percolation process that can readily lead to a network-wide cascade. To address such a problem, we identify the critical conditions for determining the occurrence of cascading spectrum contentions, and propose a biased spectrum contention protocol that intentionally lowers the probability that a starving network can trigger successive spectrum contentions. We show that the proposed solution can effectively restrict the spatial cascading impact of contentions.