I. Introduction
The huge demand to access information wirelessly and ubiquitously in the past decade in conjunction with the scarcity of radio resources [1] has resulted in intensive research towards the concept cognitive radio networks (CRNs) [2]. Nonetheless, only a small subset of published works have found their way into implementation and standardization. This is due to many factors; among them are the ambiguity of the cognitive radio concept for which many definitions exist, and the lack of complete implementable solutions.