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In cognitive radio networks (CRNs), secondary users (SUs) transmission requests are fulfilled via the use of portions of the licensed bandwidth dedicated to primary users (PUs). Meanwhile, through spectrum sharing of dynamic spectrum access (DSA), the PUs gain either financial benefits or cooperative communications. Due to the fact that the spectrum bandwidth resources are restricted hence; the dynamic allocation requests have become the focus of attention in recent years. Therefore, the dynamic channel reservation (DCR) in CRNs has a significant influence on improving network performance via the adjustment of the optimal number of reserved channels. Also, the centralized control (central controller) with a software-defined network (SDN) can be employed effectively to manage configuration, simplify the complexities, and develop dynamic coordination between the users in the network. In this paper, two algorithms of DCR are investigated to determine the optimal number of reserved channels based on SU retainability or SU channel availability while taking into consideration PU's channel availability minimum limit in both cases. Performance metrics in both cases indicate the enhancement in system quality of service (QoS). Moreover, the results show a significant reduction in SU cost function and network unserviceable probability (Q<;span style="font-size: 14.5px;"><sub>s</sub><;/span>), while meeting the QoS requirements of PU through a minor inconsiderable impact on its channel availability and throughput compared to other previous models. In this paper, a proposed DCR algorithm is designed for selecting one of the two modes of operation depending on the incoming traffic requests to attain better performance characteristics.

Centralized Dynamic Channel Reservation Mechanism via SDN for CR Networks Spectrum Allocation