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In this paper, two dynamic spectrum sharing models are proposed, namely a Markov-chain model and a queue-based model in order, to evaluate the performance of CRAHNs, where the shared Primary Channels (PCs) are complemented by unshared Secondary Channels (SCs). The new contribution of this paper is as follows. Firstly, our Markov-chain model is extendable to any practical number of PCs and SCs and remains accurate for any practical Primary User (PU) and Secondary User (SU) tele-traffic intensity. As a benefit, our technique accurately estimates the maximum number of Secondary Users Per Second (NSUPS) supported by a system, both by queuing analysis and by the Markov-chain model. In addition to our Markov-chain model, we also conceive queue-based models, which generally impose a lower modeling complexity than that of Markov-chain models, although at the cost of being more inaccurate. Our numerical results confirm the reduced evaluation complexity and improved accuracy of the proposed models and analysis.