A DISPUTE between rival British broadcasters is jeopardising Europe鈥檚 world lead in terrestrial digital TV technology. Europe鈥檚 Digital Video Broadcasting (DVB) group is now split over the best method for transmitting signals.
Terrestrial digital TV is expected to provide the opportunity for many more channels within existing frequencies. But the technical disagreement between the state-run BBC and independent National Transcommunications is delaying the development of standards. Until the matter is resolved, manufacturers dare not begin making microchips for digital TV sets.
NTL, formed when the Independent Broadcasting Authority was broken up in 1991, now says a key feature of the DVB鈥檚 draft standard is 鈥渄oomed to failure because it will take too long to implement and cost too much鈥�.
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The dispute hinges on the number of carrier waves used to bring the digital information to receivers. The BBC, which plans to be the first terrestrial TV broadcaster in Europe in 1997, believes that 8000 carrier waves are required to ensure that every home in the country will be able to receive pictures. But NTL says a cheaper 2000 carrier wave system will work adequately. The company is now lobbying for industry support and the DVB group cannot set a standard until the issue is settled.
The 150-member DVB group was formed in 1993 by major TV and electronics companies in Europe in order to avoid statutory interference from the European Commission. Its voluntary standards are merely rubber-stamped by the European Telecommunications Standards Institute.
Standards for digital TV transmission via satellites or cable networks were confirmed last year. But the provisional standard for terrestrial TV must be confirmed within a few months if broadcasters are to meet their schedules.
The core feature of the system is called COFDM (Coded Orthogonal Frequency Division Multiplexing). This splits the digital signal into many parallel data streams.
Each stream is broadcast on its own radio carrier wave, with all the waves bundled into the same UHF channel.
The more carrier waves there are, the greater the ability of the receiver to recognise and eliminate stray signals which might be arriving from distant transmitters. The proper functioning of this system is essential if all transmitters across the country are to use the same UHF channel a major advantage of digital TV. At present, transmitters in neighbouring regions must operate at different frequencies.
NTL initially agreed with others in the DVB about the 鈥�8K鈥� provisional standard. But now it argues that a 2K option will work adequately because viewers鈥� TV aerials are generally pointed towards their local transmitter and not distant ones. The 2K microchip is less complex than the 8K version by a factor of three, says NTL.
But the BBC argues that because some aerials must inevitably point in the direction of both near and distant transmitters, an 8K receiver is necessary to ensure these viewers will receive a picture.
The DVB group, including the BBC, has now agreed to consider the 2K system as a 鈥渇all-back option鈥�. But electronics manufacturers cannot afford to develop both the 2K and 8K chips, which are radically different. They must now await the results of further tests. 鈥淭he trouble is that no one has yet built a system, so no one knows what will work,鈥� admits a BBC engineer.
