Ofcom's Digital Dividend review has given a clear endorsement to the unlicensed use of cognitive radio - devices able to seek out unused spectrum - ahead of EU approval and indeed the existence of any such devices. Meanwhile, the FCC has today received a letter signed by five senators promoting the same technology.

The statement from Ofcom follows the US (FCC) lead in testing cognitive radio technology, with the expectation that use of the technology will be unrestricted once it becomes practical. In the US the issue has become highly controversial, and the endorsement by five senators is significant.

Cognitive radio is wonderful in theory, but much harder to put into practice. The idea is that an intelligent device listens on a range of frequencies until it finds one which is unoccupied, and then transmits on that frequency. The problem is that detecting use isn't always easy, and a user expecting an empty band might be surprised to find cognitive devices camping in their space: you certainly wouldn't want a cognitive radio identifying an emergency frequency as unoccupied just before your emergency.

Even if the listening, and use, is restricted to specific bands - such as the so-called "white space" between TV channels - it's not easy to detect usage. A transmitter located behind a hill might be invisible to the cognitive radio, but visible to the nearby houses who are about to lose their TV reception.

Both Ofcom and the FCC, in the UK and USA respectively, expect to see cognitive radios dancing around, and between, the digital terrestrial television (DTT) channels being expanded thanks to the switch-off of analogue TV. In the USA, the companies running DTT are fighting the technology as they believe it will generate unwelcome interference: they even have a website with animated interference for the hard of thinking.

Policy Tracker spoke to Ofcom Chief Executive Ed Richards, who assured them that any equipment deployed in the UK would have to pass stringent testing to ensure that there's no chance of interference with digital TV, though such reassurances haven't gone down well in the USA.

The European Regulators Organisation CEPT is carrying out its own testing of cognitive radios, to see if they can happily coexist with DTT systems, but their report isn't expected until April. ®

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