As with DVB-T, DVB-T2 uses OFDM, but allows for more carriers (the individual information streams) and higher-capacity modulation constellations. It also introduces improved error protection in the form of low-density parity check (LDPC) and BCH coding.
T2 had been expected to achieve a 30 per cent improvement over DVB-T, but the demo had a 36Mbit/s multiplex at 256QAM – 50 per cent more than a 64QAM mux in the same bandwidth. The partners – BBC Research & Innovation, Arqiva, Pace and NXP – told Wotsat at the IBC2008 technology show that they think the final result could be even better.
The prototype set-top box from NXP and Pace may have looked more like Blake 7's Orac than something you'd stick under your TV, but they were confident there will be receivers – probably PVRs – in production by mid-2009, ready for the Winter Hill switch.
Fortunately, the compression side of Freeview HD needs little work. The 2008 trials used MPEG-4, which is now well-established as the standard compression format for high definition. BBC HD on Freesat broadcasts at 18Mbit/s, but the IBC demo had three HD channels at 11Mbit/s that looked flawless on large monitors (even after seeing Ultra HD).
MPEG-4 is moving on fast, and engineers talk confidently of acceptable HD images going under 10Mbit in the next few years. Ofcom wants to add a fourth HD channel for Five HD by 2012, and it looks very possible.
New box, or not new box?
All of the HD launches so far have needed a new receiver, and Freeview will be no different – but IDTV owners might get a reprieve.
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Most IDTVs these days are HD Ready and, thanks to European standards, they all carry a common interface slot. A few Freeview PVRs also have one of these, and an HDMI output, but the EC didn't insist on it.
The CI is typically used to add a conditional access module for pay-TV, but French firm Neotion has already produced a CI module that enables a receiver or IDTV to decode MPEG-4 in SD or HD (the HD unit demo'd at IBC 2008). Experts at this year's Digital TV Group Summit floated the idea of a similar module for adding DVB-T2, but so far it's just an engineer's dream.
At least you won't need a new aerial; the DVB-T2 signal will be just as powerful and even more robust than standard Freeview.
Unfortunately, Ofcom's current plans mean there will only be one multiplex using DVB-T2 for the foreseeable future. It could be used to double the number of channels on Freeview, but that will take a government with its eye on more than the next election.
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First published in What Satellite, Issue 270
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