One of the key challenges to meet the growing demand for spectrum is to find innovative ways of increasing the spectral efficiency of the emerging broadband systems. Cognitive Radio (CR) is an emerging technology that addresses the specific aspects of exploiting under-utilized radio spectrum to increase spectral efficiency and capacity. CR opens up a rich set of technical issues which is attracting the attention of a growing number of researchers. An overview of these technical aspects is the focus of this tutorial.

In the physical layer (PHY), one of the main challenges in CR - spectrum sensing and analysis, will be discussed. The different methods available and their relative merits will be presented. The uncertainties in spectrum sensing combined with the effects of fading and shadowing pose significant challenges in CR systems. The use of cooperative sensing is an attractive approach to improve the reliability of spectrum sensing. Some of the aspects of cooperative sensing will be covered. The research and design issues in the PHY layer including various aspects of multicarrier / OFDM transmission, use of non-contiguous carriers, dynamic power and bit loading will be presented. Some technical considerations of ultra wideband (UWB)-OFDM will be discussed. CR also opens up interesting information-theoretic aspects such as capacity considerations in a multiple user CR network. The key technical elements of IEEE 802.22 standard, which is a Cognitive Radio based Wireless Regional Area Network (WRAN), will be presented. The use of cognitive radio principles in other wireless applications such as interference mitigation will be mentioned.

This tutorial is targeted towards a broad audience of researchers and practicing engineers in the areas of wireless communications and signal processing, and will aim to provide an up-to-date technical summary of the key aspects of the emerging inter-disciplinary field of cognitive radio and its enabling technologies.