Today's wireless networks are characterized by fixed spectrum assignment policy. The spectral scarcity and the inefficiency in the spectrum usage necessitate new communication paradigms to exploit the existing wireless spectrum, opportunistically. Software Defined Radio (SDR) and Cognitive Radio (CR) are the very paradigms 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 chapter is focused on software defined radio, its architecture, its limitations, evolution to cognitive radio network, architecture of the CR, and its relevance in wireless and mobile ad-hoc networks.
Optimal Power Allocation for a Relaying-Based Cognitive Radio Network in a Smart Grid