Preface

The subject of cognitive radio is a relatively new area of research. It was introduced in 1998 by Joseph Mitola III and has since then attracted many researches around the word. Cognitive radio stems from the concept of software-defined radio and is an intelligent adaptive radio that moni‐ tors its own performance continuously. It determines the radio environment and adjusts its set‐ tings to provide the required quality of service. Most importantly, the cognitive radio is able to find the spectrum necessary for its work by itself. In this book, we present several new research papers about cognitive radio written by people of around the word.

In the chapter 'Reliable Broadcast over Cognitive Radio Networks: A Bipartite Graph-Based Al‐ gorithm', Y. A. Al-Mathehaji, S. Boussakta and M. Johnston address the problem of reliable broadcast in cognitive radio networks. The focus is on developing a cognitive system that does not use a common control channel to enable control message exchange. They use graph theory, more precisely bipartite graphs, to map the problem at hand to the problem of set cover. Then, they develop an algorithm, which guarantees a distributed reliable selection of the broadcast channel with a facilitative channel switching facility where primary user activity is detected without the need for frequent reselection.

The chapter by M. Namdar and A. Basgumus 'Outage Performance Analysis of Underlay Cogni‐ tive Radio Networks with Decode-and-Forward Relaying' evaluates outage performance of re‐ laying over Rayleigh fading channels subject to the relay location for a secondary user. The authors provide optimal location of the relay terminals in cognitive networks. The analysis pro‐ vides maximum transmission rates of the secondary user and the outage probabilities.

The chapter by J. R. G. Oya, M. Chavero and R. M. Clemente 'Analog-to-Digital Conversion for Cognitive Radio: Subsampling, Interleaving, and Compressive Sensing' focuses on analog-todigital conversion techniques. The conversion is necessary if the source signal is in analog form like speech or music. The chapter gives an overview of promising techniques like subsampling, interleaving and compressive sensing and discusses solutions of integrating these techniques into a unique analog-to-digital conversion process.

The chapter 'Reconfigurable Antennas for UWB Cognitive Radio Communication Applications' by Y. Li and Y. Wang concentrates on antennas for ultrawideband cognitive radio communica‐ tion applications. The chapter discusses the defected microstrip structure and uses the structure to form antennas that can filter out interfering narrowband signals. After that, the authors focus on creating notches in the antenna response.

It is hoped that the book is useful for researchers and engineers in both academia and industry working on problems related to radio communications in general and cognitive radio in particular.

> **Tõnu Trump** Virgostell OÜ, Tallinn, Estonia

**Section 1**
