Fundamental limits of cognitive radio networks
Cognitive radios have the potential to greatly improve spectral effi- ciency in wireless networks. In this chapter we explore the fundamental limits of communication in channels employing cognitive radios. We take an informationtheoretic approach, making use of information theory's wide variety of tools and ability to characterize communication limits independent of actual implementations. The chapter first surveys information theoretic results on a simple wireless channel where a primary link and a secondary (or cognitive) link share the same spectrum: the cognitive radio channel. Our survey includes recent capacity and achievable rate region calculations for the case when the channel is known to all transmitters and receivers. We compare the rates achieved through new non-orthogonal schemes where the cognitive and primary user simultaneously use the channel to more traditional spectral gap filling solutions. In the second part of the chapter we outline new results on the limits of cognitive radio channels where the fading coefficients are known to different degrees at the nodes. © 2007 Springer Science+Business Media B.V.
