Beyond the digital TV switchover

However, for every hi-def channel there are a dozen barely watchable ultra-compressed standard-definition channels. Bandwidth on Freeview becomes so expensive that even major broadcasters transmit at surprisingly low quality.

Digital TV 4.0: screens everywhere
2011 and beyond
Compression: MPEG-2 HD & SD; MPEG-4 HD & SD
Broadcast: DVB-S2; DVB-T2; DVB-H2
Platforms: Satellite, terrestrial, cable, broadband, mobile

The ups: By digital switchover, there should be a national Freeview multiplex using DVB-T2 and MPEG-4 to carry four hi-def channels to most of the UK, plus free HD on Freesat, and maybe 50 HD channels on Sky. Even cable and broadband should have some hi-def – probably via on-demand.

The years after switch-off will see a set of mature digital TV technologies designed to last into the 2020s and approaching the Shannon Limit, a mathematical ceiling on signal compression. Some countries will also add MIMO, where you use both horizontal and negative polarity signals on the same frequency to double the capacity.

In particular, DVB-T2 is designed to allow Single Frequency Networks (SFNs), which use a single frequency to cover the whole country. Today, Freeview uses Multi-Frequency Networks, which use around five frequencies across different parts of the country, but moving to SFNs would release even more space for Ofcom to auction.

The question is, what do we do with the opportunity?

Britain's TV and spectrum regulator, Ofcom, doesn't have any official plans beyond the digital switchover in 2012, other than auctioning the Digital Dividend. Fortunately, a group of leading broadcast engineers – The Independent Expert Industry Group – have turned their eyes to the future and come up with a few ideas.

IEIG member Ian Childs, who also sits on the British Digital TV Group's Technical Council, told the DTG's 2008 summit: "The debate was HDTV or mobile. We don't want to pick winners ahead of things happening, we'd like a way of allowing both to establish a toe-hold, and defer the decision until we've got a bit more input from the marketplace.

"The Ofcom HD proposal makes quite a simple prospect for the consumers that want to upgrade, but how do we look at being able to migrate the whole platform to HDTV? We came up with a possible way ahead, to use single frequency networks to improve the spectrum efficiency and the number of HD services on offer. That would probably give us up to about 40 HDTV programmes."

To start with, the IEIG's plan would hold back some Digital Dividend frequencies to launch two national frequency networks after 2012, covering roughly 70 per cent of the UK and carrying eight hi-def channels in DVB-T2/MPEG-4. Gradually, the UK would switch to a more efficient Freeview network entirely based on DVB-T2 and MPEG-4, with perhaps three conventional multi-frequency networks and single-frequency networks. These would be so efficient that Freeview would be using less capacity than it now occupies, so the government could run another spectrum auction.

The group is also proposing a national pilot project for portable TV in 2012, so the London Olympics could be broadcast to anyone over a new single frequency network.

"If that proved successful, mobile TV could be one contender for some of the spectrum we'll be releasing at the time we make the transition to HDTV," adds Childs.

The downs: With Freesat now offering hi-def channels and several HD pay-TV options, it's easy to think there's no need to advance Freeview beyond a token set of HD channels.

Childs said: "If you look at the richness of the offerings from satellite and cable by the time we get to 2012, will four HD programmes be a sufficiently compelling prospect for the consumer to buy into terrestrial and keep it competitive?"

Perhaps more succinctly, as Professor David Youlton, DTG chairman, said: "DSO isn't digital switchover, it's Digital Spectrum Optimisation. Leave government out of it because they tend to screw it up big-time and 'short-term' the issues."