The amount of white space that can be reclaimed for broadband access is directly related to regulations governing white space access in a country. 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. Particularly, in the US, the FCC had originally limited secondary access to white space spectrum based on a fixed transmit power rule. 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. This has been shown to significantly affect the amount of white space available in a country. Several other factors also directly impact white spaces. 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. ==References==