Media on the cheap

Electronics Times, Jan 8, 2001

Free-to-air digital audio broadcasting has got off to a slow start. Chris Edwards asks whether paid-for content is what it needs

If you look at the listening figures for radio, things have never looked so good for digital audio broadcasting (DAB). Consumers surfing the Web like to listen to something and, after years of decline in radio audience figures caused by the proliferation of TV, some have turned back to the wireless.

The question that faces the DAB radio builders is whether they take advantage of the increase or does DAB need a new beginning? Talking at Electronica late last year, Tony King-Smith, director of Panasonic System LSI Design Europe, reckoned that DAB could make it into the mass market on its own. But it could do with a helping hand.

Digital AM radio, recently approved by the International Telecommunications Union, threatens to bring a cheaper form of digital radio. DAB receivers are still expensive compared with other, often more sophisticated, consumer equipment. Competition from what could prove to be a cheaper technology, at least for receiver designs, is not competition that the current form of DAB needs.

DAB needs to find a profitable home or go the way of other technologies, such as digital audio tape (DAT), which never quite made it into the mass market and were forced to find new niches.

King-Smith argues that the free-to-air model has not helped DAB move into the mass market. Pointing to a mobile phone, he says the subsidies made possible by the decision by mobile network operators to charge more heavily for services proved critical to the success of the GSM digital phone system.

King-Smith said: "Broadcast is by far the cheapest way to get volume data to a wireless user. That is why we see DAB being integrated with other systems. It is also a lot cheaper to operate a DAB infrastructure than an FM infrastructure."

The only revenue that an existing DAB service provider with free-to-air services can expect to grab is advertising and sponsorship.

Panasonic's proposed approach is to use DAB for information delivery in the same way that satellite and terrestrial TV operators have decided to deliver Web pages to consumers. Use the high-speed broadcast channel to deliver the data; mobile terminals tell the server what needs to be delivered using a low-speed back channel.

The company is trying to set up a group, called Adept (Association for DAB-Enhanced Platform Technologies) that can bring together network operators, content providers and equipment manufacturers. The idea behind the group is to thrash out how DAB can be used to support subscription services.

When the Eureka-147 researchers developed DAB, they made sure that it could handle data as well as digital audio. Two of the European Union Information Societies Technologies research projects have focused on delivering data, such as traffic information, to in-car systems. The Diamond project, which completes at the end of the year, has looked at combining DAB delivery with GSM back-channels, together with GPS for location-based services, in transportation systems.

David Bowerman, Diamond project co-ordinator, who leaves the post early this year, said: "We see DAB as a complementary medium. There are some fairly simple applications that are just different ways of presenting information.

"You can use simple announcements. Another approach is to put information on to maps or deliver TMC [traffic message channel, as used by RDS] information. On top of that you can have tourist information, dynamic navigation and dynamic information. There are other features that are not part of ITS [intelligent transportation systems], such as infotainment."

For subscription services, King-Smith says GPRS would make an ideal way of sending information back to the server. But many services would not need that kind of datarate. Bowerman says the GSM short message service was often adequate for the applications in the Diamond project.

For DAB, the bandwidth of each multiplex is 1.536MHz, providing a useful bit-rate capacity of a little over 2Mbit/s. Each service in the multiplex can be error-protected independently. The coding overhead ranges from 25 to 300%, which brings the useful datarate down below 1.5Mbit/s.

Typically, a DAB multiplex can transmit five or six stereo radio channels using MPEG Audio Layer II encoding. Using MPEG Audio Layer III would improve the compression by a factor of two over Layer II and give DAB delivery services the ability to broadcast MP3 files.

Delivering MP3s and other medium-bandwidth data can be handled using existing DAB standards.

"There is no need to change the DAB standard. Different applications are constructed in different ways to use the protocols," said Bowerman.

The system is designed so that bandwidth can be reallocated dynamically to each of the channels as the type of data to be delivered changes. ETSI has defined a protocol called multimedia object transport (MOT) and the BBC has gone so far as to develop a source-level software library for it.