الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
The frequency spectrum is an essential resource of wireless communication. Specialsections of the spectrum are used for military purposes, governments sell some frequencybands to broadcasting and mobile communications companies for commercial use, otherssuch as ISM (Industrial, Science and Medical) bands are available for the public free ofcharge. As the spectrum becomes overcrowded, there seem to be two possible solutions:pushing the frequency limits higher to frequencies of 60 GHz and above, or reaggregating thedensely used licensed frequency bands. The new Cognitive Radio (CR) approach comes withthe feasible solution to spectrum scarcity. Secondary utilization of a licensed spectrum bandcan enhance the spectrum usage and introduce a reliable solution to its dearth. In such acognitive radio network, secondary users can access the spectrum under the constraint that aminimum quality of service is guaranteed for the licensed primary users.In this thesis, we focus on spectrum sharing techniques in cognitive radio network wherethere is number of secondary users sharing unoccupied spectrum holes. More specifically, weintroduce two collaborative cognitive radio networks in which the secondary user cooperatewith the primary user to deliver the primary’s data.Firstly, we point out cognitive radio system with energy constraint imposed on the primaryand secondary users. In this model, we study the cooperative cognitive radio network withenergy harvesting primary and secondary users. The stable throughput region of the system ischaracterized for different Primary User (PU) and Secondary User (SU) energy harvestingrates. Moreover, the energy constrained cooperative system is compared with the cooperativesystem without energy constraints, and the non-cooperative energy constrained system.Additionally, we formulated mathematically the conditions at which the energy constrainedsystem acts identically as the system with reliable power supply. Finally, we characterize theconditions for the system to switch between cooperative and non-cooperative modes.Secondly, we propose a new method for cooperation and underlay mode selection incognitive radio networks. We assume another system in which we study thespectrum sharing in the hybrid mode. In this model, we assume that the cognitiveuser could occupy the channel either in the overlay mode with cooperation, or witha small power in the underlay mode. The secondary user cooperates with thehIprimary user in order to exploit the feedback message from the primary destinationabout the channel quality and getting more opportunities to access the channel. The acceptance of PU packets at the secondary user is regulated via admission control.This admission is function of the channel quality of the direct link between primarysource and destination. To illustrate, the SU decision to cooperate with PU or not isdepending on the PU channel quality. We formulate the problem as a belief/rewardfunction and mathematically express these, belief and reward functions, seekingbest performance of the system. Performance analysis displays that our proposedalgorithm is better than conventional non-cooperative and cooperative systems interms of secondary user throughput.