الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
The frequency spectrum is a precious resource of wireless communication. Apart from specific portions of the spectrum used for military purposes; governments assign some frequency bands to broadcasting and mobile communication companies for commercial use and other Industrial, Science, and Medical bands are available for the public free of charge. The emergence of dynamic spectrum access via cognitive radio is regarded as a solution for the increased demand and the inefficient spectrum utilization. The unlicensed secondary users are permitted to occupy temporarily the idle channels dedicated for licensed primary users without causing harmful interference to primary users. The two main goals in wireless networks are to provide channel allocation opportunities for incoming services and to assure the accomplishment of ongoing services. In this thesis, a channel reservation scheme in cooperative cognitive radio networks based on dynamic spectrum access is proposed. In cognitive radio networks, secondary users transmission requests are fulfilled via the use of portions of the licensed bandwidth dedicated to primary users. Meanwhile, through the spectrum sharing of dynamic spectrum access, the primary users gain either financial benefits or cooperative communications. The contributions of this thesis include two parts. The first part applies the static channel reservation concept with a variation of the number of the reserved channels to optimize the comprehensive network performance. The second part studies the dynamic channel reservation mechanism based on two different modes and coordinated by the software-defined network concept. In the proposed model, the spectrum is partitioned into two parts which are non-reserved channels and reserved channels where non-reserved channels can be accessed by higher privileged primary user and lower access priority secondary user. Further, the reserved channels are dedicated particularly for new secondary user transmission or preempted secondary user from non-reserved channels due to abrupt primary user arrival. Non-reserved channels can be exploited by licensed primary users and secondary users, while reserved channels are dedicated to active secondary users until the successful completion of their service. If secondary user session in non-reserved channels is interrupted by the sudden arrival of primary user, then a spectrum handover occurs to reserved channels to resume its session. The numerical results are analyzed and evaluated by applying a continuous-time Markov chain in schemes. In first part of the submitted work, static channel reservation is applied with a centralized cognitive manager to provide the dynamic coordination access for primary users and secondary users. Therefore, the reserved channel number is deduced upon the reduction of both forced termination and blocking probabilities for secondary users while satisfying primary users’ traffic demands. In addition to that, the system quality of service is enhanced by minimizing both the overall system cost and secondary user cost functions. Simulation results show a significant reduction in blocking and forced termination probabilities and improvement in utility function and ii service completion rate of secondary user while meeting primary users’ quality of service aims. Furthermore, blocking probability and service completion rate of PU are evaluated to demonstrate the effect of channel reservation variation on the system performance. Moreover, in the second part of the study, two modes of dynamic channel reservation are investigated to determine the optimal number of reserved channels based on secondary user retainability or channel availability while taking into consideration primary user’s channel availability minimum limit in both cases. Performance metrics in both cases indicate the enhancement in system quality of service based on the increase of secondary user retainability, channel availability, handover probability, and throughput. Since the spectrum bandwidth resources are restricted hence; the dynamic allocation requests have become the focus of attention in recent years. Thus, dynamic channel reservation 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 can be employed effectively to manage configuration, simplify the complexities, and develop dynamic coordination between the users in the network. Moreover, the results show a significant reduction in secondary users cost function and network unserviceable probability while meeting the quality of service requirements of primary user at the cost of a minor inconsiderable impact on its channel availability and throughput compared to other previous models. This proposed dynamic channel reservation concept is designed for selecting one of the two modes of operation depending on the system parameters to attain better performance characteristics. Initially, the software-defined network controller selects one of the two approaches to determine the optimal number of reserved channels in the network before the allocation of any new users. Subsequently, the number of reserved channels is readjusted and varied dynamically according to the network traffic load. A conclusion of this approach is to show the advantages and potentials of utilizing the software-defined network concept in CRN employing dynamic channel reservation.