Imagine surfing the web or playing multiplayer online games in your local park, a couple of hundred metres beyond the point where your Wi-Fi router signal dies.
Impossible? Right now, yes. But not if white space radio gets off the ground.
White spaces pop up wherever broadcasters fear a conflict with their neighbours. To prevent interference, each TV channel is broadcast at a different frequency within a chunk of the ultra-high frequency (UHF) region of the spectrum. Where two neighbouring cities – A and B – are broadcasting distinct channels, each must leave a gap – a white space – on its frequency plan corresponding to the other city's frequency chunk, again to minimise interference.
But city A could use city B's frequencies at very low power for short-range use, say both the US Federal Communications Commission and the UK's broadcasting regulator Ofcom. That would open the way for a new generation of UHF Wi-Fi routers which would extend the range of home networks, or let cities run their CCTV networks wirelessly (PDF), say proponents running tests in the US and UK.
Walls no obstacle
Most routers now transmit only a short distance, using radiation at a frequency of 2.4 gigahertz – because that's close to the frequency used in microwave ovens, boosting the signal strength to increase the range could pose a health risk. A white space router working at 400 to 800 megahertz would pose less of a risk even with a stronger signal, while the longer waves produced at these frequencies – 75 centimetres rather than 12 centimetres – are better able to pass through walls and other obstacles.
However, although white-space technology has been gaining credence since early 2008, its development has hit a barrier: no one can yet guarantee that white-space devices won't interfere with TV signals – or with the signals from other white-space devices.
The solution is to identify the usable white-space channels. But an early suggestion – "cognitive radios" built into white-space devices that "sniff" the airwaves for free space – simply doesn't work, says William Webb, technology director at Ofcom. The FCC has arrived at a similar conclusion, following tests it undertook on devices made by Intel, Motorola, Microsoft and Philips.
"The power level they had to detect with 99.9 per cent accuracy to prevent interference was one-thousandth the power a mobile phone receives at the edge of a mast's coverage area," says Webb.
They know where you live
Some technology firms think it's too early to give up on the idea. Luke D'Arcy, an engineer at Cambridge Consultants in the UK, says the company is developing smart technology it claims can detect ultra-weak signals. But Ofcom and the FCC are now pressing ahead with another solution: a white space "geolocation database" run by the private sector.
In this scenario, every white-space device can connect to GPS to find where it is, and contacts an online database of free frequencies available in its area every time it is switched on. This database will allocate frequencies and power levels so devices do not interfere.
Running such a database could be a politically charged affair, however. In the US, for instance, Google is among the six firms that have applied to run the FCC's white spaces geolocation database – but as the firm delivering YouTube, Gmail and other services to white-space devices, that may be deemed a conflict of interest.
The system could also infringe users' privacy. "We don't know yet what information your white-space device should supply to the database, for instance," says Webb. "Or what information it will send back." Such issues are now being thrashed out at Ofcom, he told a conference in Reading, UK, in late April: a legal framework has to be established that will allow underperforming database operators to be taken off the job but will keep private data safe.
With these problems to be overcome, it looks like we won't be logging on to our home networks from the park any time soon. "Establishing the database and approving the white-space consumer devices is going to take until at least 2012," Webb predicts.