Software Defined Radio—Guest Editorial

Abstract

Cognitive Radio (CR) is under intensive investigation since Joseph Mitola III published his doctoral dissertation in 2000. It is common understanding that Software Defined Radio (SDR) is the enabling technology for CR. A CR is an SDR that additionally senses its environment, tracks changes, and reacts upon its findings. A CR is an autonomous unit in a communications environment that frequently exchanges information with the networks it is able to access as well as with other CR. The main focus of CR publications since 2005 is on Dynamic Spectrum Access (DSA). Here CR is described as a means for the enhancement of efficiency in spectrum utilization, i.e. a means to combat under-utilization of spectrum. Exactly this subject is discussed by William Webb in his invited paper Dynamic Spectrum Access is the Solution: What’s the Problem? to this special issue. First of all, he argues that spectrum sensing is not viable by hand held low-cost consumer terminals, “DSA devices will not be able to rely on sensing alone”. He shows that geolocation is a promising alternative approach. Moreover, the change from sensing to geolocation tends to favor networked applications. In answering the question what the problem is to which DSA is the solution, Webb underlines the importance “to divorce DSA from cognitive radio and SDR”. His conclusion is that DSA is useful for narrow bandwidth network-based applications and he offers machine-to-machine communication as the most obvious example. We have arranged the ten regular papers that are introduced below into four categories. The first category contains four contributions.