Spectrum scarcity is an emerging issue in wireless communications systems due to the increasing demand of broadband services like mobile communications, wireless internet access, IoT applications, among others. The migration of analog TV to digital systems (a.k.a. TV digital switchover) has come with a release of significant spectrum that can be used to support those additional services. Likewise, TV white spaces emerge as spectrum opportunities to be explored too. Hence, cognitive radio (CR) looks like a feasible approach to exploit those gaps within the spectrum towards using these scarce resources efficiently. The goal of this paper is to show the state of the art around the TV white spaces usage, some of the most important approaches developed to exploit them, the upcoming opportunities and challenges for future research, and a suggestion to improve the current models. This paper starts by presenting an overview of the concepts involved in the subject, followed by a description of some actual applications and pilots developed on the field mostly focused in the USA, UK and Colombian cases, then an analysis of the challenges and opportunities are presented and it is closed with some final conclusions.
cognitive radio; digital switchover; DSA; spectrum sensing; TVWS