Whitespace is the spectrum that is unused in certain areas due to geographic transmission systems that can not overlap and in this case relates to the UHF TV channels (470 MHz to 790 MHz). As there are multiple transmitters across the UK, adjacent transmitters can not operate in the same frequency bands (especially for digital TV) or the transmitters would interfere with each other.
This leads to large chunks of the UHF spectrum not being used in a particular geographic zone, which could be used for other purposes (as long as it was low power and didn't reach neighbouring areas).
Current plans are that whitespace devices will monitor what bands are in use (by listening to those frequencies) and thus not use them, in the UK they must also contact a central database, report their location and the database will specify what frequencies are available and what power they can transmit at.
There are other services that can also be interfered with such as program making and special events (PMSE) - things like outside broadcast units which can use some of the spectrum for remote TV cameras and such like, which also have to be catered for.
Ofcom have already said they will allow whitespace use on a license exempt basis, but they also must ensure that there will be no harmful interference to digital terrestrial television (DTT) and PMSE.
Whitespace technology is new and thus there is some uncertainty on how whitespace devices may interfere with DTT or PMSE services. However Ofcom doesn't want to overly constrain whitespace use such that large amounts of spectrum go unused, or that power levels/etc are so restrictive that reaching any sizeable population is unrealistic.
Ofcom will currently err on the side of caution and setting parameters that can be relaxed in future. Later this year there will be a set of pilot trials across the UK with a number of service providers where the increased power levels can be used for limited periods of time to ensure interference doesn't occur. The trials (and stakeholder consultations) will continue until Summer 2014 and will help Ofcom set the parameters for future national whitespace roll-outs starting in Q3 2014.
Ofcom has set the parameters and algorithms for use in trials to minimise the effects on
- Digital Terrestrial Television services
- licensed users of equipment for Programme Making and Special Events
- services above and below the UHF TV band.
Though it is yet early days, whitespace spectrum should allow high bandwidth services with good propagation characteristics (coverage) which could be used to provide mobile network operator capacity off-loading, broadband and machine-to-machine (M2M) services.