The traditional approach of dealing with spectrum management in wireless communications has been the definition of a licensed user granted with exclusive exploitation rights for a specific frequency. While it is relatively easy in this case to ensure that excessive interference does not occur, this approach is unlikely to achieve the objective to maximize the value of spectrum, and in fact recent spectrum measurements carried out worldwide have revealed a significant spectrum underutilization, in spite of the fact that spectrum scarcity is claimed when trying to find bands where new systems can be allocated. Just to mention some examples of measurements, different studies can be found in [1-6], revealing that overall occupation in some studies for frequencies up to 7GHz could be in the order of only 18%.