It is the sort of plan that might have been better presented to the WARC frequency planning conference in Geneva two years ago, but the team from the Digital TV Group has only just reported on its “blue sky” plan to deliver HD services to UK terrestrial homes. It is more of a work in progress than DTG policy, but provides a thoughtful insight in how to maintain the DTT network in the face of competition from the pay platforms.
Under the plan delivered by Dr Ian Childs to the DTG Summit held at BAFTA earlier this month, capacity for 40 HD channels could be created if the transmissions were made as part of a single frequency network (SFN), a proposal that had already been characteristically dismissed by Ofcom’s Greg Bensberg in his presentation earlier that morning.
Dr Childs said that his group welcomed Ofcom’s plan to reconfigure the present DTT line-up in such a way that a single HD multiplex might be created. However, he added that the proposal of four HD channels by 2012 might not be sufficiently attractive when compared with the rival offers of cable and satellite. There was also the question of how the entire platform could be migrated to the HD format.
“We would agree with Ofcom’s position that it doesn’t make sense to go out and renegotiate Geneva 2006, that would be two embarrassing two years after a major international settlement. These single frequency networks would have to go in some of the 14 channels that were released as part of the agreement.” He also said that other channels would have to be in addition to the Geneva plan and negotiated individually with the administrations concerned.
The spectrum efficiencies involved in a single frequency network are possible because the same frequency would be used throughout the country. It is also likely to have a regional single frequency network, where each region would have their own network, using different frequencies in different parts of the country. This would go some way towards addressing the problem of broadcasters not being able to run regional variations, when part of a national SFN, though regional networks are not a part of the proposal.
The proposal would take advantage of the increased guard interval found in the proposed DVB-T2 standard. This has the advantage of interference caused by distant signals.
“What we are proposing is not a complete shift towards single frequency networks, but a mixed portfolio. Some Multiple Frequency networks (MFNs) aimed at services where you want really good population coverage, supplemented with a national SFN networks, maybe with a reduced coverage but a better utilisation of the spectrum, “ said Dr Childs.
Two SFNs could be established after digital switchover containing eight HD channels, which Dr Childs says would be sufficient to compete with HD services on other platforms. Although admitting that he was relying on a “miracle to occur” and more spectrum was released, six SFNs and three MFNs would allow up to 40 HD channels. “This is roughly the amount of channels we have on Freeview at the moment and only using 22 frequencies, meaning we would be able to release back another 10 frequencies for other uses.”
Further frequencies could be used for the transmission of mobile services that would not need to rely on the existing aerial system.
