الفهرس 
Definition of Cognitive RadioOnly 14 pages are availabe for public view
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Abstract
In the last few decades, the great progress in wireless communications led to the spectrum scarcity problem. This is due to the fact that the allocated spectrum for wireless networks is characterized by a fixed assignment policy. The Federal Communication Commission (FCC) attributed the reason of spectrum scarcity to the heavy underutilization of the allocated spectrum. As a promising technology to overcome the problem of spectrum underutilization, Cognitive Radio (CR) was proposed. In CR, a secondary network (unlicensed network) is allowed to access the spectrum allocated to a primary network (licensed network) opportunistically and make use of the vacant bands in that spectrum.
The spectrum sensing in Cognitive Radio Networks (CRNs) are classified into three main categories according to the way in which a secondary network accesses the spectrum of a primary network. Firstly, the Single Spectrum Sensing, in which Secondary Users (SUs) sense the presence of Primary Users (PUs) and communicate only over the vacant bands. Secondly, Cooperative Spectrum Sensing, in which all SUs sense the vacant channels at the same time and share all the spectrum band with PUs. Finally, Cluster-Based Cooperative Spectrum Sensing, which is better than of the previous two categories.
In this thesis, Cooperative Sensing and Cluster Based Cooperative scheme are presented to improve spectrum sensing and reduce probability of error also, the problem of minimizing the total energy wasted in the CRN for spectrum sensing and improving the performance of CRN is considered.
Firstly, Cooperative Sensing is used in the spectrum to reduce channel problems, improve sensing performance and increase probability of detection.
Secondly, the proposed cluster based cooperative scheme is presented to improve spectrum sensing and reduce time delay in the CRN.
Finally, the proposed co-operative clustering in CRN using optimization scheme (Genetic Algorithm) constrains the total energy wasted by CRN