الفهرس 
3Multiband Spectrum SensingOnly 14 pages are availabe for public view
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Abstract
Cognitive radio network technology is an emerging wireless mobile technology that received much attention from researchers and research entities in the last few years. It is a very prominent candidate as a part of the fifth generation mobile technology.
Cognitive radio exploits the underutilization state of the already allocated frequency bands to different applications and services which will lead to a higher overall spectrum utilization efficiency.
In addition to this intelligent idea, cognitive radio offers many advantages including easy and soft establishment, it will cause no harm to the already working systems. It will be a solution for very difficult unmanageable situation like crisis relief, military actions at the international level; unknown battle fields also a new branch of satellite assisted communication system.
The cognition cycle consists of multitude of activities or functionalities, (each of them is a deep branch of research) like spectrum sensing, feature extraction, channel state estimation, decision making regarding the utilized and non-utilized frequency bands, awareness of the wireless transmission environment current state, for either primary or secondary users. A big entity which has a major function is the fusions centre, which collects sensing data from secondary devices and uses this data to decide which band is empty and broadcast this decision to all users. It also, coordinates the operation of the network transmission.
In this research cognitive radio network features are studied as a complete system, stress is made on two important functionalities. The first is the spectrum sensing, the second is the fusion centre control of the way of transmission of the secondary users. Our main objective is to enhance and improve the quality of service of these cognitive radio networks. To suggest the required solutions it was imperative to study the performance of cognitive radio networks under different operational situations and different types of channels.
Spectrum sensing is an important activity in the operation of cognitive radio network. It provides the data required for deciding whether certain band is busy or idle. There are many types spectrum sensing like energy, cyclostationary, compressive and cooperative spectrum sensing. The most recent type of spectrum sensing is the compressed type, specially the cooperative wide band multi rate sub-Nyquist spectrum sensing MS3.
For this type (MS3) the thesis presents its way of operation, its construction (block diagram), the effect of the state of the sensing channel and the type of fading that it encounters. Stress is made on two types of fading namely; Rician fading and Nakagami-m fading.
Results for the performance of this system under these two types of fading are analyzed and results were found to be consistent with results of other researches published recently.
Also, the way of operation of the fusion centre and the share of time of the length of the frame allocated for sensing operation are studied with the main objective of improving the quality of service of the network. An optimization problem is designed with the objective of determining an optimum value of the sensing time (To) that will maximize the total throughput of the SUs. Consequently, it will provide maximum protection for the primary users.