The goal of this paper is to model heterogeneous channel Access in Cognitive Radio Networks (CRNs). In CRNs, when licensed users, known as Primary Users (PUs), are idle, unlicensed users, known as Secondary Users (SUs) can use their assigned channels. In the model we consider in this paper, there are two types of licensed channels, where one type has a larger bandwidth, and hence a higher service rate for SUs. Therefore, SUs prefer to use such channels, if available, over channels in the second

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... type which have a lower service rate. SUs may also switch from the second to the first type of channels when they become available, even if their current channels are still available. Moreover in our performance model, we model the SUs' sensing process, and its dependence on the system load, and number of sensing users. We use a Continuous Time Markov Chain (CT M C) modeling approach, and derive SUs' performance metrics, which include SUs admission and blocking probabilities, and their average waiting time in the system. We also develop a baseline model in which SUs do not switch channels between the two types, unless they are interrupted by PUs, and compare its performance to our proposed model. Our numerical analysis shows that our proposed model outperforms the baseline model. We also, found that if sensing time is very small (≤ 1 ms), its effect on SUs performance is insignificant.