Radio Resource Allocation Techniques for Efficient Spectrum Access in Cognitive Radio Networks

This paper provides an overview of cognitive radio (CR) networks, with focus on the recent advances in resource allocation techniques and the CR networks architectural design. The contribution of this work is threefold. First, a systematic way to study the resource allocation problem is presented; various design approaches are introduced, such as signal-to-interference-and-noise ratio (SINR) or transmission power-based, and centralized or distributed methods. Second, CR optimization methods are presented, accompanied by a comprehensive study of the resource allocation problem formulations. Furthermore, quality of service criteria of the physical or/and the medium access control layers are investigated. Third, challenges in spectrum assignment are discussed, focusing on dynamic spectrum allocation, spectrum aggregation and frequency mobility. Such approaches constitute an emerging trend in efficient spectrum sharing and affect the performance of resource allocation techniques. The open issues for future research in this area are finally discussed, including adaptability-reconfigurability, dual accessibility, and energy efficiency.

I. Introduction

DURING the last decade, significant research efforts have been undertaken to investigate and design efficient resource allocation schemes aiming at serving a continuously increasing number of users through the fixed spectrum range. As wireless devices become ubiquitous and offer new services with increased quality of service (QoS) characteristics and data rate demands, resource allocation becomes an even more difficult and challenging problem. The constantly growing request for advanced multimedia services, combined with the resource constraints of wireless networks, places increased stress on the fixed radio spectrum used by the current access technologies. The need for improved resource allocation techniques becomes even more essential as some spectrum usage measurements indicate that a significant amount of spectrum is used sporadically, leading to its underutilization [1]. Therefore, spectrum scarcity can be considered as a result of poor spectrum management policies rather than a physical shortage of frequencies [2]– [5].