Apurva Mody finds the prospects thrilling, particularly because TV spectrum by its very nature is good for propagating over large distances, making it ideal for his aim of wide-area internet access.
“Five billion people across the world have no access to the internet. And the TV spectrum is ideally suited to connecting them.”
When he's not promoting the new wi-fi standard, Dr Mody chairs the Whitespaces Alliance, an international pressure group pressing governments to allow secondary users access to this unused spectrum.
TV spectrum is “the low hanging fruit” for cognitive radio, agrees Anant Sahai – and not only in the wide open spaces between cities. “Even in densely populated areas like city centres there is still a lot of white space - megahertz upon megahertz. What's more, the economics work out that you can deploy more infrastructure per square kilometre than you can in Wyoming.”
And because the spectrum is much more complicated in urban environment, cognitive radio will be essential as you go from street to street in finding which frequencies are free, and which you'll have to give up.
Companies are already gearing up to build the equipment that can hop into the white spaces. Among them is Neul, a UK company based in Cambridge, that has just announced what it says is the first integrated circuit capable of communicating over the TV white spaces.
True cognitive radio is still a long way off, says William Webb, Neul's Chief Technology Officer.
“Devices can't really detect transmissions with enough certainty to be sure what frequencies are free,” he explains. Instead, the system queries a geographic database indicating which frequencies are free where and when.
Designing the 4mm-wide chip was not easy, Webb admits. One of the key problems was to keep the signal from the chip phenomenally clean, ten times purer than that from 3G and 4G devices. This is because the devices will be operating in frequencies very close to commercial transmissions, and any corruption of the signal would result in interference with broadcasts that would be unacceptable.
That kind of consideration will be critical for any future implementation of full-blown cognitive radio. One compromise Neul had to make was to keep the data transmission rates low. High wave purity combined with high data rates would put an impossible demand on battery life, Webb says.
If cognitive radio can develop beyond those TV white spaces, then the available spectrum could grow enormously. But it would have knock on effects, not least for our smartphones.
“The first problem would be the antenna – one that could be reconfigured to operate across the whole wireless spectrum in an affordable and practical way for a small handheld – that would be impossible at the moment,” says Przemysław Pawełczak, software researcher at Delft University of Technology.
Then there would be the escalating complexity of the additional layers of programming the frequency-hopping protocols, and the battery-draining demands of the hardware.
“But the biggest problem is that people in the industry are sceptical, they are afraid of change. But I don't know of any idea that's more disruptive – I think it's the ultimate idea of what our radio devices should do. But we have a long way to go to implement it.”
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