As a natural scarcity in wireless networks, radio spectrum becomes a major investment in network deployment. How to improve the channel utilization (CU) of the spectrum is a challenging topic in recent research. In network environment, the utilization of a channel is measured by the effective CU (ECU), ie., the effective time in transmission or being sensed busy over its total operation time. However, the existing work does not provide a valid model for ECU. In this paper, we investigate the relationship between ECU and interference. First, we propose a new concept of co-transmission ratio to describe the overlap time of a channel usage. Second, we find the issues of the existing models. Third, we propose a new model that is based on the channel occupations of the nodes in a network. The new model has been proved mathematically, and verified by extensive simulation results in WLANs. It significantly improves the precision of ECU modeling and can be widely used in network planning, routing protocol design, and channel allocations. We present some possible applications for the model.
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