Original URL: http://www.theregister.co.uk/2008/11/05/white_space_risks/

Will 'wi-fi on steroids' give you spots, baldness and liver damage?

Playing nicely in the white spaces

By Bill Ray

Posted in Broadband, 5th November 2008 15:27 GMT

The FCC has voted to allow unlicensed use of White Space spectrum between the TV stations. Meanwhile UK-regulator Ofcom today published a statement on cooperative common spectrum, but both proposals are based on technically unproven concepts of radio agility that hardly stack up.

The concept of a radio that happily hops around other spectrum users filling all the gaps caused by other, less efficient, radio systems is compelling - but like most promises of "something-for-nothing" the reality is rather more complicated. Regulators and manufacturers both promise that equipment will play nicely, but manufacturers have little incentive to make it so, and regulators may lack the ability to enforce any kind of politeness protocols once the devices hit the streets.

The debate about US exploitation of White Space, now concluded with yesterday's FCC vote, has enabled a mass of ill-informed, soundbite-driven comment. Terms such as "wi-fi on steroids" are calculated to engender public sympathy. After all, wi-fi doesn't interfere with TV, and this is like wi-fi only better! But white space has no relation to wi-fi, technically or architecturally, to compare the two is like arguing that we should build more roads because I like my boat.

Not that the anti-white-space lobby was any less manipulative. Calling on Dolly Parton and assorted church ministers to condemn the plan, not to mention creating the most menacing cartoon telephone we've ever seen along with animations predicting the end of TV as we know it.

Detecting, and avoiding, other users of radio spectrum is really, really hard. The only currently-deployed system that manages it is DECT - the phone system that scans the 10 available frequencies in Europe (or 5 elsewhere) and allocates one to each handset. But DECT only works because all radios operating between 1880-1900MHz in Europe (1920-1930 in the USA and elsewhere) are using the same technical standard, so are transmitting within those 10 clearly-defined slots. But white-space devices, and those proposed by Ofcom, will be technology-neutral - so closer to the chaos of the 2.4GHz band.

Up at 2.4GHz things are a mess. Wi-fi sits in 5MHz-wide slots and is quite easy to detect, but Bluetooth changes frequency a thousand times a second, so even noticing it is a challenge unless you know the protocol you're trying to detect. White-space devices could well operate with different slots, different sizes of slot, and different frequency-hopping algorithms, making them invisible to each other but able to interfere at a moment's notice.

Even detecting the TV transmissions between which white-space devices are supposed to fit may prove impractical. Consider a TV channel that can be received using a roof-top aerial, but is impossible to get using rabbit-ears on a portable TV - a white-space device inside the house will find that spectrum empty, and happily start transmitting a signal that the sensitive roof-top antenna will pick up and confuse with the broadcast.

The FCC has sensibly mandated that all white-space devices use a location-sensing technology (realistically that will be GPS), combined with a database of known transmitters. This combination mandates that white-space devices be mostly outdoors, and connecting to a server for updates every few days - which will also allow firmware updates and the shutting down of errant devices. But the FCC and the industry are confident that technology will eventually solve those problems, and allow unrestricted use of white space.

Similarly Ofcom states that devices should "implement a method to become aware of other users of the same resources", and "not monopolize the resources so that other users cannot access them", but stops short of explaining how to go about that. Indeed, Ofcom points out that to mandate any particular technology would be against EU regulations as well as contravening the Ofcom policy of being technology-neutral.

At least Ofcom isn't letting these devices loose in the UK's white spaces - in Blighty the unused TV spectrum will be licensed, allowing Ofcom to revoke licences if devices or users start trying to make too much use of the spectrum.

The FCC decision to go unlicensed will let the genie out of the bottle, and it won't go back in. It's not hard to conceive of devices that spend less time enforcing equitable spectrum use in order to provide greater bandwidth to their users, or hacks for legitimate devices that pervert them in that way. After all - would you be prepared to interfere with your neighbour's TV reception for the sake of a decent network for your BitTorrent downloads, and would your neighbour do the same?

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