OFDM-based cognitive radios for dynamic spectrum access networks

Abstract

With the advent of new wireless applications, as well as growth of existing wireless services, demand for additional bandwidth is rapidly increasing. As a result, the possibility of spectrum scarcity becomes more of a reality. Existing "command-andcontrol" spectrum allocations defined by government regulatory agencies prohibit unlicensed access to licensed spectrum, constraining them instead to several heavily populated, interference-prone frequency bands. This spectrum scarcity is apparent since it has been shown that the spectrum is not utilized efficiently. For instance, measurement studies have shown that many licensed bands are relatively unused across time and frequency [1]. To make better use of radio spectrum resources, government regulatory agencies such as the Federal Communications Commission (FCC) are currently working on the concept of unlicensed users "borrowing" spectrum from incumbent license holders. This concept is called dynamic spectrum access (DSA) [2, 3]. Wireless communication technology needs to be sufficiently agile in order to perform DSA such that spectrum utilization is improved while not interfering with incumbent user transmissions. The development of software-defined radio (SDR) technology has made modern wireless transceivers more versatile, powerful, and portable, by performing baseband processing, such as modulation/demodulation and equalization, entirely in software and digital logic.With the ease and speed of programming baseband operations, SDR technology is a prime candidate for DSA networks. In addition to the agility of the SDR technology, the radio needs to be spectrally aware as well as autonomous in order to dynamically utilize spectrum. A radio that can adapt its transmitter parameters based on interaction with the environment1 in which it operates is known as cognitive radios [4]. With recent developments in cognitive radio technology, it is now possible for these systems to simultaneously respect the rights of incumbent license holders while providing additional flexibility and access to spectrum. © 2007 Springer Science+Business Media, LLC.