Ofcom decides on white-space parameters

Location, location, location and a bit of sensing

By Bill Ray, 2nd July 2009

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UK regulator Ofcom has been considering what restrictions to place on white-space-exploiting cognitive radios, and has concluded that a location-based database is the only way to be sure.

The conclusion comes in a statement following up on the consultation Ofcom launched back in February, and concludes that detection mechanisms might one day work, but for the foreseeable future any device intending to operate in white-space spectrum will need to check its location against an online database to make sure no one else is around before it starts transmitting.

Advocates of utilising white space - bits of radio spectrum used to broadcast TV in one part of the country which lie unused in other places - have been arguing that devices can detect and avoid transmissions, though tests have demonstrated the difficulty of that approach.

The easiest approach is to have an online database of available frequencies and require devices to check before they start transmitting. That means white-space-using devices either have to be fitted with GPS, or be set up by an engineer - with the latter option being most likely as the restrictions mean that white space is only really going to be used for fixed point-to-point connections.

Assuming it gets used at all, that is: Ofcom's statement makes no reference to the calculations of Adrian Payne, who argued last December that even if transmissions are allowed in white space the density of TVs in the UK makes any commercial deployment impractical.

Ofcom's almost religious dedication to the capabilities of cognitive radio makes such calculations irrelevant, as well as making it impossible to reject detect and avoid entirely, as the FCC has done in the US. So in the UK, it will be possible to deploy a cognitive radio without checking the database - though at very low power levels and only if you continue checking for other users at least once a second.

Ofcom also isn't saying what criteria it's going to use to judge usable detect and avoid devices, noting that "detection-only devices [are] likely many years away and hence there is little advantage in rapidly making the necessary regulations to licence-exempt such devices". The regulator is, however, planning to publish proposals for location-based white space systems later this year, which should prove interesting. ®

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