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White space debate comes to Blighty

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While the FCC is happy to let consumers in the USA make use of the space between TV channels, in the UK the debate is only just beginning.

Once analogue TV transmissions are switched off the digital network will still leave regional gaps, known as white spaces, where some believe low-powered devices should be allowed to hang out, as the FCC recently approved in the USA. But others point out that the UK is a small island and any use of white spaces is going to have to be strictly controlled to prevent interference with TV transmissions.

The problem was highlighted by Adrian Payne, a scientist presenting for NXP Semiconductors at a recent Institution of Engineering Technology seminar, PolicyTracker reports. Payne has calculated that a white-space system using channels directly adjacent to broadcast TV risks interferring if the device is within 27 metres of a TV aerial.

Even if there's a clear gap between the frequency used by TV channels and that being exploited by a white-space device interference is still possible if the device is less than four metres from the aerial.

In the USA using adjacent channels provides 114MHz of spectrum, while leaving a gap reduces that to 30MHz - still a useful amount of spectrum. But in the UK our transmitter density means that only 25MHz is available using adjacent channels, and nothing at all if a gap is left.

Ensuring that white-space devices remain more than 27 metres from any TV aerial is going to be a challenge, particularly in the UK where few people spend their time that far from an aerial. If Ofcom decides to adopt the no-licence-required approach agreed by the FCC it would seem impossible to use adjacent channels, but requiring a gap would limit white-space deployments to the Highlands and parts of Northern Ireland - perhaps useful for connecting rural communities, but that's not where the money is.

Ofcom is looking into the matter, as well as working with the PMSE (Programme Making & Special Events) industry about the continued use of wireless microphones after analogue switch-off. The PMSE crowd are still waiting to hear who's going to manage their spectrum - last month Ofcom admitted the business is worth just shy of a million quid a year (pdf) so that companies can bid sensibly, but they don't yet know where that spectrum will be so manufacturers can't make kit and production companies can't buy anything.

The concern is that PMSE will get pushed into white space, further squeezed between TV channels, and at risk from interference from unlicensed white-space devices that don't manage to sense and avoid legitimate users - something you don't want happening in the middle of a West End musical.

It's unlikely the UK debate will see animated evil telephones or endorsements from Dolly Parton - we don't tend to do things that way. But it is likely to be equally vehement, and no matter who loses you can be sure that Ofcom will get the blame. ®

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