The ‘digital dividend’ describes the spectrum that will be released from its current use for broadcasting of analogue terrestrial TV, as a result of the switchover to digital transmission. The switchover is now underway across the UK, and is due for completion in 2012.
Although digital TV has been broadcast in the UK since the late 1990s, it has been operating using fewer transmitting stations and lower power than the fully installed digital network will, primarily because until analogue transmission is switched off, the digital signals are being broadcast simultaneously with analogue signals and so interference between the two has to be managed.
Once the UK has fully switched over to digital transmission, the digital networks will have better coverage and capacity as restrictions on the transmitter power will be lifted. For instance, the Public Service Broadcast multiplexes in the UK will reach 98.5% population coverage following digital switchover.
Since it is estimated that digital transmission is some six times more efficient than current analogue transmission, the switchover will result in spectrum currently used for analogue transmission being released from broadcasting use. The Government decided in 2003 that this released spectrum – totalling 112MHz in the UHF band – would be made available for new uses. A further 8MHz will be released from use by aeronautical radar from April 2009, bringing the total amount of cleared spectrum to 120MHz. Spare capacity available in the spectrum interleaved with the six digital-TV multiplexes will also be available for use.
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Figure 1: An overview of cleared spectrum in the UK (Source: Ofcom)
Ofcom has been considering how to make the digital dividend available since November 2005, and, in December 2007, published its decisions on how it will award this spectrum (see www.ofcom.org.uk/ consult/condocs/ddr/statement).
This statement set out three awards of the digital dividend:
- an auction of the cleared spectrum
- auctions of interleaved spectrum in defined locations of the UK, suitable (but not reserved) for local TV
- a beauty contest of the remaining interleaved spectrum with obligations toward users for programme making and special events (PMSE).
Ofcom’s statement builds on initial proposals, which were published for consultation in December 2006. These considered a wide range of issues including what new services might use the digital dividend, how new services might be planned alongside existing services, the impact of international spectrum coordination frameworks on new use and alternative options to award the available spectrum, both nationally and regionally.
From a market perspective, the cleared spectrum may be attractive for a range of uses due to the characteristics of these frequencies, which provide a cost efficient means of improving wireless network coverage (due to propagation characteristics).
Possible uses of the digital dividend range from highdefinition digital-terrestrial TV (DTT), local digital TV, mobile TV (possibly based on a range of networks including DVB-H and cellular), cellular radio and wireless broadband services. This spectrum could provide cheaper wireless coverage as much larger cell sizes could be used. The cleared spectrum may therefore be particularly attractive for operators wishing to extend coverage of existing networks in to more rural areas, as well as extending the reach of urban coverage (e.g. providing penetration of signals in to buildings from outdoor base stations).
A key issue for Ofcom in considering how to package the cleared and interleaved spectrum for auction, is how services with varying technical characteristics – such as mobile TV and wireless broadband – might co-exist, and also how these new services might co-exist alongside existing users of the spectrum. This includes DTT, PMSE and radioastronomy. Mason conducted a series of technical studies for Ofcom during 2007, which focused on use of the digital dividend for cellular mobile and broadband services. As part of these studies, we analysed the potential for adjacent channel interference between mobile use, DTT and mobile TV use and also assessed the implications of the ITU’s coordination requirements for this spectrum (as defined by the ITU planning conference in Geneva held in 2006 – GE-06) on use of the cleared spectrum for mobile applications.
Analysys Mason’s report concluded to Ofcom that, in the absence of interference constraints, using cleared spectrum can substantially reduce the cost of the infrastructure required to provide broadband mobile services to rural and urban areas, compared with the use of higher frequency bands such as 2100 MHz (which is the spectrum currently used by the UK’s 3G mobile operators). Ofcom has published the full details of Mason’s studies at www.ofcom.org.uk/ consult/condocs/ddr/statement/ddrannex.