13.1 Introduction

Technology is futile without its application. One of the major driving forces of a new technology is the combination of man s endless thirst for knowledge, unequal intuitive mind, and limitless ambition to better his life. The other important factor consists of user demand, user necessity, and increasing user desire to have it all in one single device.

Wireless communication involves accessing and utilizing air spectrum for communication purpose. More and more devices may fall under the umbrella of wireless communication technology in the near and distant future. For example, every personal computer may soon be connected to its keyboard and mouse via the radio medium. This in turn can eliminate hardware manufacturing cost, manual labor for connection, and hardware pollution of the discarded parts. Wireless technology thus opens up an endless market of wireless communication applications.

Cognitive Radio (CR) in the wireless world is relatively new and comprises of two magical words that encompass everything! It is the radio with intelligence [1]; capable of using its radio ability in the most optimum manner by interacting with surrounding environment, learning about the environment, and using the learned knowledge to improve communication. The traditional radio on the other hand lacks cognitive intelligence; uses fixed spectrum, special purpose hardware dedicated to that spectrum, and its ability is confined to manufacturer driven specifications.

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