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Cognitive Radio (CR) is a comparatively new technology which is based on the revolutionary idea that provides solution to the underutilization of spectrum and spectrum scarcity problem. CR allows a group of users to identify and access to available spectrum resources for their optimum use. In this paper we describe the CR starting from the traditional Radio and Software Defined Radio (SDR). We also introduce the concept of reconfigurability. CR can be implemented using reconfigurable hardware. Therefore, it needs a platform that offers higher performance and reconfigurability. In this paper we describe different existing implementation of CR in reconfigurable platform and make a comparative study of them. General TermsCognitive radio: its implementation techniques on reconfigurable hardware and complexity analysis.

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Today’s wireless networks are characterized by fixed spectrum assignment policy. The spectral scarcity and the inefficiency in the spectrum usage necessitate a new communication paradigm to exploit the existing wireless spectrum, opportunistically. Cognitive Radio (CR) is that very paradigm for wireless communication, in which either a network or a wireless node reconfigures its transmission or reception parameters to communicate efficiently avoiding interference with licensed or unlicensed users. CR adapts itself to the newer environment on the basis of its intelligent sensing and captures the best available spectrum to meet user communication requirements. When the radio link features are extended to the network layer, the cognitive radios form the cognitive radio network. This book chapter is focused on cognitive radio network, architecture of the CR, and its relevance in the wireless and mobile Ad Hoc networks.