9Cognitive Networks

9.1 Technology Background

9.1.1 Fundamentals

The concept of cognitive networks is motivated by the fact that a large portion of the assigned spectrum is used sporadically and geographical variations in the utilization of assigned spectrum ranges from 15 to 85% with a high variance in time. The limited available spectrum and the inefficiency in the spectrum usage have necessitated a new communication paradigm to exploit the existing wireless spectrum opportunistically. This new networking paradigm has been subject of extensive research and is referred to as cognitive radio networks (CRNs). In this section we present a brief overview of the cognitive radio technology and resulting network topologies. In the following chapters this technology will be revisited with emphasis on different details. The key enabling technology of CRNs is the cognitive radio. Cognitive radio techniques provide the capability to use or share the spectrum in an opportunistic manner. Dynamic spectrum access techniques allow the cognitive radio to operate in the best available channel. More specifically, the cognitive radio technology enables the secondary users (SUs) to: (i) determine which portions of the spectrum is available and detect the presence of licensed users when a user operates in a licensed band (spectrum sensing), (ii) select the best available channel (spectrum management), (iii) coordinate access to this channel with other users (spectrum sharing), and (iv) vacate ...

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