الفهرس 
History of Cognitive RadioOnly 14 pages are availabe for public view
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Abstract
Recent years, Wireless communication has become an essential procedure for the modern and advanced communication society. Over these years, rabidly increased demands on new wireless communication systems, applications and services have witnessed. In accordance with that the traditional approaches to spectrum managements become more crowded by licensed systems, in the sense that more frequency bands are needed to be acclimated with the rapidly communication demands requirements. Based on the report of the Federal Communication Commission (FCC) indicated that the available radio spectrums are allocated by the licensed (primary) systems and these systems have utilization to their spectrum bands from 15 % reached to 85% under maximum usage.
from this perspective, cognitive radio is a new hopeful and promising technique which is suggested to improve the spectrum utilization and efficiency. With Cognitive Radio Networks (CRNs), a secondary network (unlicensed network) is allowed to access the spectrum allocated to a primary network (licensed network) sensing the vacant bands in that spectrum to communicate concurrent with the licensed systems without affecting on their Quality of Service (QoS). There are three modes of operation in this network. Firstly, Opportunistic Spectrum Access (Overlay), in which Secondary Users (SUs) are allowed to sense the presence of Primary Users (PUs) and communicate only over the vacant bands while ensuring QoS of PUs. Secondly, the Spectrum Sharing (Underlay), in which SUs are allowed to access the licensed spectrum and share this band with PUs to achieve QoS requirements of PUs with acceptable QoS for secondary systems. It will be done by making interference on each PU in the primary network below a specified threshold level. Finally, Sensing-Based Spectrum Sharing, which is a combination of overlay and underlay modes.
In this thesis, the problem of maximizing the secondary throughput in downlink CRNs based on power optimization strategies, handoff and channel selection and Multicarrier Modulation (MCM) techniques in CRNs were considered. Also, Capacity gain over different fading channel conditions will be considered. This maximization problem will occurred under some constraints like maximum transmit power for secondary network and interference power level at each PU receiver.