Whitespace is radio spectrum (generally in the Digital Terrestrial Television [DTT] and Program Making and Special Events [PMSE] bands) in the UHF TV bands (470MHz to 790MHz) that isn't used in a particular area. This is because adjacent TV transmitters cant use the same radio frequencies, so there are geographic areas where certain spectrum is available, but those frequencies will be used elsewhere in the UK.
As certain frequencies are available in certain areas, these could be used (in lower power) by other devices such that they wont interfere with their use in neighbouring areas. In order for that to work, the devices (or central transmitter) will have to know where it is and how much power it can transmit and on what frequencies such that interference wont occur.
There are various uses for whitespace spectrum such as rural broadband or hotspot connectivity. Here the central transmitter would have to query the central database and CPE equipment would get transmit power and frequency use from the central transmitter.
Whitespace could also be used for in-home or M2M applications and in this case the central router (which would be connected to the Internet) would make the database queries and the rest of the in-home/M2M equipment would get the power/frequency information from the central router.
Ofcom is proposing making whitespace devices license except, though they will have to contact a central database and pass back their location and thus be given allowable frequencies and their power constraints.
As part of the consultation Ofcom has specified the types of queries and responses, but not how they're implemented as this would be down to the market to implement.