TV White Space database was first brought as a way to overcome the technical hurdles faced by spectrum sensing techniques to precisely detect very weak primary signals.
Spectrum is deemed available, or unavailable, to unlicensed usage depending on criteria that are regulator specific and thus the database operation can significantly vary between countries.
Currently, spectrum regulators from several countries have determined the set of rules to access white space in a secondary manner and which database operators must follow in order to be authorized for service provision.
TV White Space was available to secondary devices provided that these kept a safe distance from the broadcaster contour, depending only on the antenna's altitude and not transmit power.
How to process topography and the adopted radio propagation model, both being determined by regulations, have been recently shown to play a key role on the degree of white space availability of a country.