Understanding Dynamic Spectrum Access: Models,Taxonomy and Challenges

In last few years, especially after release of the FCC Spectrum Policy Task Force (SPTF)´s seminal report in 2002, we have witnessed growing interest in the field of Dynamic Spectrum Access (DSA) networks. Terms such as reconfigurable networks, Software Defined Radios (SDRs), Cognitive Radios and Cognitive Radio Networks (CRNs) have gained common use. Radio spectrum is a multidimensional entity; space, time, polarization, frequency, power of signal transmission and interference are some of the key dimensions. The static, command- and-control management of spectrum has led to barriers to accessing the spectrum in various dimensions. The notion of dynamic spectrum access can break these barriers in one or more of the dimensions. A review of published research in the technology, policy and legal facets of this broad area indicates that the community is addressing this problem from multitude of angles. In fact, we believe the situation is analogous to story of seven blind men attempting to describe an elephant based on what they perceive when they touch various parts of the elephant. As such, we contend that unless a clear taxonomy of various ways of dynamic access is developed, significant confusion can prevail within the community dealing with these new ways. This paper tries to rectify this situation. It aims to develop a clear taxonomy of various forms of DSA networks, describe in detail various models and identify required technology capabilities, architectural innovations and policy changes.