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Can white-space Wi-Fi really work for cities?

A number of stumbling blocks are still to be overcome before white-space spectrum can be used to deliver a viable Wi-Fi service.
Written by Ben Woods, Contributor

Research into the use of white space - the unused gaps between certain wireless spectrum frequencies - is continuing apace, with suggestions that white-space Wi-Fi could prove a viable conduit for town or city-wide broadband.

While the most appropriate use case for white-space spectrum is typically considered to be machine-to-machine (M2M), where the spectrum could be used to transmit a high volume of very small messages across a network, some companies are also considering using it to provide Wi-Fi services because it has very wide reach and works well inside buildings.

One of the appeals of white-space spectrum for a communications company looking to use it for a network is that it is likely to be unlicensed, meaning there are no fees for using it - much like the 2.4Ghz band used for Wi-Fi. The absence of licence fees means any company or small start-up looking at the possibility of providing new services is spared a significant set-up cost.

Variable bandwidth

However, questions remain over white space's coverage, and whether it's sufficient to cope with the high network demands Wi-Fi would put on it.

"The amount of bandwidth in white space is hugely variable - it depends on the number of transmissions in [a given] region, which vary hugely as you move across the country. On average there's a lot of white space, about 100MHz, which is about the same as the existing 2.4GHz used for the Wi-Fi band," William Webb, chief executive of the Weightless SIG, said.

"But there are some places where there is much less than that, say around 8MHz or so, being transmitted, so it's a hugely variable picture," he added.

Superior reach

Supporters of white-space Wi-Fi argue that with its superior reach - it has good in-building penetration, too - Wi-Fi hotspots in towns could be placed in white-space spectrum to create urban broadband services.

"You'd have to actually plan a town knowing how much white space was available" — William Webb, Weightless SIG

Even so, Webb said that while that using white-space spectrum would extend the reach of a Wi-Fi hotspot from around 20m to up to 200m, broadband services using such spectrum would likely provide a lower data rate than even 4G (although he did note that the service could also be cheaper than 4G as the spectrum is unlicensed).

"If you don't have much white-space spectrum available then a white-space router [...] can probably only provide 5-10Mbps and that's divided among the number of users," Webb said.

"If you start making these densely overlapping cells, then that will create interference, and further reduce the spectrum requirement - it all gets horribly complicated. You'd have to actually plan a town knowing how much white space was available," Webb added.

Will hardware makers help or hinder?

While planning a town around the availability is certainly a challenge, it's not an impossibility. The bigger challenge however would likely be in persuading manufacturers to put the white-space Wi-Fi chips into their hardware.

"It's always a struggle to get manufacturers to put yet another radio into devices," Webb said.

The use of white space by mobile devices is still an issue being mulled over by the UK telecoms regulator Ofcom.

On 22 November, the watchdog announced a framework and consultation on the issue in a bid to hopefully have mobile white-space services up and running before the end of 2013.

Whether or not white space will be able to provide enough bandwidth to enough users for a viable Wi-Fi service is a problem that still needs to be solved, but with enough advanced planning, it is at least possible, in theory.

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