Wireless Communications

15Cognitive Radio

Abstract

Cognitive radio (CR) emerges to address the challenge of inefficient use of the precious electromagnetic spectrum resource, which stems from the widely adopted policy of fixed spectrum allocation. This chapter is focused on the enabling technology of CR, that is, spectrum sensing, although a brief summary of its current status in standardization and commercialization is also included.

15.1 Introduction

The ever-increasing demand for high-data-rate wireless transmission poses a challenge of efficiently utilizing the precious electromagnetic spectrum. The current practice in many countries is a static spectrum allocation policy, whereby governmental agencies allocate wireless spectra to licensed users on a long-term basis for large geographical regions. Licensed users are also known as primary users (PU) in the literature . A careful study released by the U.S. Federal Communications Commission (FCC) [1], however, reveals that most of the allocated spectra are underutilized, at less than 25% [2]. A possible solution is the use of dynamic spectrum access (DSA). Cognitive radio (CR) [3, 4] is one such emerging technique that provides unlicensed users, usually referred to as CR users or secondary users (SU), with the capability to share the licensed spectrum in an opportunistic manner. The secondary users usually do not operate individually, but rather work jointly to form a CR network coexisting with the primary network over the same geographical area. ...