الفهرس 
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Abstract
Cognitive Radio (CR) network is an adjustable, smart radio that
can be programmed and configured effectively. CR technology is
used to automatically distinguish wireless channels in
definite spectrum and change transmission parameters to allow
more concurrent communications in order to restrict user
interfering, overcrowding and furthermore boost radio operating
performance. Therefore, high Quality of Service (QoS) is demanded
in Cognitive radio system. The Opportunistic Spectrum Access
(OSA) is considered one of the most promising methodologies in
CR. In OSA, unlicensed users are enabled to access licensed
frequency bands which are detected to be idle. Therefore, the
achievable throughput of the secondary user network must be
maximized to increase the spectrum efficiency. Recently, several
studies have been accomplished to enhance the spectrum sensing
methods. To distinguish between the spectrums of various selective
bands, different approaches are proposed. It can be claimed that,
spectrum sensing is one of the most significant issues for CR. This
thesis proposes a new technology such as Multi-Taper, MultiII
Taper-Diversity and Multiple Input Multiple Output (MIMO)
spectrum sensing techniques that have been compared with the
traditional systems. A number of important factors affecting this
system and operating efficiency have been studied with the
suggestion of some assumptions and modifications that may
improve system efficiency and increase safety factors for the
licensed user.