To support this demand we need
even more pervasive WiFi deployments, which are, however,
limited by interference stemming from unlicensed operation.
Another possible solution to meet this demand is to increase
the cellular network’s density, which comes in the form of
small cells (e.g. femtocells) that operate in a licensed spectrum
underlay to macrocells. However, there is an alternative at
hand: whitespace spectrum and cognitive radio technologies