I. Introduction
As the demand for high data rates in mobile communication networks rapidly increases, the exploitation of underutilized frequency bands becomes more and more important. An example of such frequency resources are the TV white spaces (TVWS), which are locally unused portions of the spectrum allocated to terrestrial TV broadcasting. White space devices (WSDs) may access TVWS on a license exempt basis, as long as TV receivers are not negatively affected by interference. Due to the importance of new frequency resources for wireless services, regulators are promoting the use of TVWS in many regions of the world [1].