الفهرس 
History and Definition of Cognitive RadioOnly 14 pages are availabe for public view
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Abstract
Cognitive Radio Network (CRN) is a future promising technology that is used to solve the spectrum scarcity problem. In fact this is due to 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. The allocated spectrum in CRN is used in dynamic manner to be capable of sensing and adapting to the environments. There are two types of users: unlicensed user referred to as Secondary User (SU) which can access the unused spectrum of the licensed user that referred to as Primary User (PU) without disturbing the communication of the primary user.
This thesis addresses the problem of the high error rate in cognitive radio network and proposed some techniques that used to minimize it such as using relay, multi-hopping techniques and multi-antennas techniques.
Wireless networks are exposed to different channel problems such as fading and path loss. To overcome these problems, relay will be used. Wireless cooperative relay system using multi-hopping (multi relays) multi-antennas at the relay will achieve the advantages of spatial diversity which is a powerful communication receiver technique that provides wireless link improvement over a fading radio channel at a relatively low cost.
Firstly, Single and multi-antennas multi-hop techniques will be introduced with Amplify and Forward (AF) relay protocol. AF relaying technique offers a simpler hardware circuitry for its implementation compared to decode and forward relaying but suffers from the noise amplification problem which can degrade the signal quality.
Secondly, Decode and Forward (DF) protocol will be applied on the multi-antennas multi-hoping system to overcome the problem of using AF technique. DF technique removes the noise by decoding the received signal sent from the source node and then re-encoding the decoded signal and forwards it to the destination.