الفهرس 
Introduction and Thesis LayoutOnly 14 pages are availabe for public view
 |  | from | 16 |  |  |
| | | from | 16 | | |
Abstract
It is an important issue these days to find out approaches to face and overcome the spectrum
scarcity arising recently due to the dependent on fixed spectrum allocation methodology in
wireless services. On the other hand, the spectrum usage is concentrated on certain portions of
the spectrum while a significant amount of the spectrum remains unutilized (white spaces). To
solve this problem and exploit the existing wireless spectrum opportunistically, we need to use
the concept of spectrum reuse by using cognitive radios (CR).
First chapter gives an introduction showing the motivation of this thesis and also introduce an
outline of the thesis.
Second chapter discusses seven points which can be considered as a brief introduction to the
concept of cognitive radio. These points are as follows: first point discusses the need to new
technology that makes spectrum utilization efficient. Second point presents an overview of
some standardization activities on cognitive radio. Third and fourth points are concerned with
definition of cognitive radio including the main characteristics and the architectures of CR
networks. The aim of the thesis which is the spectrum sensing is reported in the fifth point
showing the different methods of spectrum sensing and states the advantages and
disadvantages of each one. Sixth point demonstrates the types of spectrum sharing. And in the
seventh point we present the concept of spectrum pooling and the use of OFDM techniques in
wideband based cognitive radio.
Third chapter discusses the sensing in individual cognitive radio through nine points. First
point demonstrates why we use the energy detector, while in the second point a brief historical
background on signal processing is presented. Third point discusses the two hypotheses in
sensing the primary users and, the model derived for each one. In the fourth and fifth points,
expressions for the probability of detection and probability of false alarm will be derived. The
sixth point discussed the optimization of threshold in order to minimize the overall error
probability. The seventh point presents an approximate model for both probability of detection
and false alarm for the purpose of simplicity in analysis. In the eighth point that approximated
model is used in determining the optimal sensing duration to maximize the achievable
throughput. The ninth point discusses the concept of splitting the sensing slot in each frame to
multiple discontiguous mini-slots.
Fourth chapter discusses the spectrum sensing through cognitive radio users collaboration.
This chapter consists of five points which are considered as follows: The first point presents a
brief discussion showing the need for cooperative spectrum sensing. The second point
demonstrates the various fusion rules used in making the final decision. Third point discusses
the impact of realistic reporting channels, while the fourth point introduces two techniques
used to overcome the performance degradation resulting from the imperfect reporting
channels. The fifth point focuses on the impact of user collaboration on the performance of
opportunistic spectrum access.