Two years ago, Ofcom came up with a plan to raise a lot of cash by auctioning the former analogue UHF TV frequencies when the UK completes its switch to digital terrestrial TV in 2012 – the Digital Dividend – and What Sateliite magazine called its bluff.

Along with broadcasters and TV manufacturers, What Satellite thought there should be a space for high-definition TV and suggested that the regulator should do some better research into what the public wants from the Digital Dividend.

When Ofcom went back and showed people HD, hi-def was a lot more popular. It's fair to say that extra SD channels and more local TV were also popular, but Ofcom had ignored those, too.

So Ofcom came up with a plan to save face and appease its critics. The Digital Dividend will still provide a windfall before the next election but one of the six existing Freeview multiplexes will be cleared for high-definition TV channels.

The first three HD channels – from the BBC, ITV and Channel 4 – will launch in late 2009 in Granada, when the Winter Hill transmitter is switched to digital-only. The HD channels will be included in every DSO campaign from there on, and the regions that have already gone digital will have to go through an extra reorganisation to make room for HD.

The keys to this arrangement are some new broadcasting technology, and a rearrangement of the multiplexes which probably won't please anyone who's already been through digital switchover. DVB-T2 is a new version of the Freeview modulation standard which has been fast-tracked to meet Ofcom's schedule, and HD will need the same MPEG-4 compression used in Sky and Freesat HD.

Moving multiplexes

Freeview is divided into six multiplexes – three for the public service channels from the BBC, ITV, Channel 4 and Five (called PSB1-3), and three operated by commercial operators (called COM1-3).

They all work to the DVB-T standard but, owing to Freeview's erratic evolution, they operate on different 'modes'. Two are in 64QAM, which has a higher data rate of 24Mbit/s, the others are at 16QAM, which has a lower capacity of 16Mbit/s but is more resistant to interference, which is handy because they operate at a lower power to avoid interference with analogue TV.

All the multiplexes can be switched up to a higher power at Digital Switchover, so they can all go up to 64QAM, and makes enough for two or three new TV channels on those four multiplexes – maybe four at the compression levels used by some broadcasters.

Ofcom's plan first moves the non-PSB channels from PSB2 onto COM3 and COM4, such as ITV2 and E4. Then the BBC services on PSB3 move onto PSB1 and PSB2, but the BBC also has to give up 7Mbit on PSB2 for universal coverage of Five (or S4C or TeleG), so the BBC could lose some red button interactive services (left, centre column).

PSB3 is now an empty multiplex, ready for HD. Most Freeview receivers will retune automatically, but there will be old kit that doesn't, and Ofcom hasn't said who will pay for publicity in the Borders, West Country and some Welsh regions to make sure no one loses channels.

London, Birmingham, Tyne Tees and other urban areas on a later schedule might not have to wait too long, either. The BBC has asked Ofcom to release some 'interleaved spectrum' – empty frequencies between analogue TV channels – for low-power HD broadcasts in cities where it won't interfere with existing broadcasts.

A decision is expected soon.

HD-Day

DVB-T2 is a natural evolution of DVB-T, just as the DVB-S2 system used for HD on satellite evolved from DVB-S, but no one expected it to arrive this fast. Happily, DVB-T2 is very similar to DVB-S2, otherwise it's unlikely that the BBC and its partners would have gone from the DVB giving approval to the T2 specification in June 2008, to a live broadcast demo of three HD channels in August.