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We’ve long been keen to see some high-definition material on Freeview, but we understand the issues surrounding available bandwidth — although we’re a little upset that our constant calls for shopping channels to be removed are being ignored. But it now appears that under new proposals announced today, Ofcom wants to do some spectrum jiggling to get HD on Freeview just in time for the Olympics.
Ofcom suggests the necessary space increases can be achieved in two ways. Firstly, there will be a switch to more efficient coding methods, including using MPEG-4 for certain services and the adoption of DVB-T2, which could (in theory) increase capacity by 30 per cent. It’s worth pointing out that both of these systems will require new set-top boxes. Secondly, there will be a reshuffling of the multiplexes, to enable multiplex B — currently used by the BBC for BBC Four, CBeebies and BBC Parliament — to be converted to MPEG-4 and DVB-T2.
Currently, because interference is a problem on DVB-T, both the BBC and National Grid Wireless are using a system called 16QAM. This has less bandwidth, 18Mbps, than the alternative 64QAM — 24Mbps. Once analogue goes dark, the multiplexes using 16QAM can convert to 64QAM, freeing up 6Mbps per multiplex — that’s a few extra channels.
No mention is made of using the BBC’s MIMO transmission system, which effectively doubles the number of channels you can broadcast on a multiplex, but we know Ofcom has been involved in the research the BBC has been conducting, and must be considering deploying it. This makes particular sense if a new set-top box is going to be needed anyway.
The caveat of this plan is almost certainly that a region won’t get any extra services until analogue broadcasts are switched off. That means London will be one of the last places to see HD channels via Freeview. Ofcom estimates all the technology will be ready by 2009, and should be in use by 2012.
We do have some reservations about this. Firstly, we really, really don’t want to see the existing Freeview picture quality degraded further by all this switching around — it’s bad enough as it is. We certainly don’t want to have low-bit rate HD channels, because that totally defeats the point. Secondly, we’re really hoping that Ofcom does allow HD channels to be carried using BBC R&D’s MIMO system — it makes a lot of sense, especially if people have to upgrade their set-top boxes anyway.
You can read the Ofcom proposal in full here. -Ian Morris
