Accumulative Interference Modeling for Cognitive Radios with Distributed Channel Access

A cognitive radio (CR) network should be able to sense its environment and adapt its communication to utilize unused licensed spectrum without interfering with incumbents. Properly modeling the expected interference from the CR network is therefore very important in the definition of coexistence rules to efficiently protect the incumbents. In this paper we model the accumulative interference generated from a large-scale CR network and investigate how this affects the sensing requirements of the CRs to meet an interference constraint. More specifically, our model considers the impact of discrete topology and the impact of the distributed channel access scheme. As an instantiation of our model, we consider a CR network based on the IEEE 802.11 standard. We show that the interference generated is large, since collisions cannot be avoided.