Back in the development days of DAB (digital audio broadcasting), the in-car listening market was held up as crucial to the success of the new technology. When digital radio was demonstrated in the UK during the late 1980s engineers and press were loaded on to a mini bus and driven round cities listening to DAB test transmissions.
But the take-up and profile of DAB were affected by the length of time it took manufacturers to get new - and affordable - radios on the market. By the time digital hi-fi tuners and transistor-style sets were widely available the in-car sector was still lagging behind.
That situation has changed in recent years. Receiver manufacturers are producing ranges of in-car radios and adaptor units for DAB on the road and (Pure Highway system pictured), more important, carmakers are now installing systems from scratch. Recent figures released by Digital Radio UK (DRUK) report that as of the fourth quarter of 2012 a third of all new cars (33.3 percent) have digital radio as standard.
As digital becomes available in more cars the crucial factor now is seamless reception as people drive from different parts of a country, with no annoying fiddling around with the radio's retuning buttons.
FM already has this through RDS (Radio Data System), which not only retunes to find the strongest signal but also automatically switches to local traffic reports. As countries contemplate switching off analogue radio transmissions, following the lead of Norway, a digital RDS equivalent will be a key part in establishing a fully connected network.
The UK government announced in 2010 that it was looking to move away from analogue radio. Under the proposals national, regional and urban services will be on DAB only, with FM retained for smaller local and community stations.
DRUK promotes digital radio in Britain and has been working with broadcasters and transmission specialist Arqiva to ensure that car drivers can carry on listening to their favourite station - or style of music - through the whole of their journey.
The basis of this is service following, as laid down in the 2012 ETSI (European Telecommunications Standards Institute) technical specifications paper TS 103, DAB: Rules of Implementation; Service Information Features (link will open pdf file). ETSI defines service following as "maintaining the same audio or data content that the user has selected in spite of the varying reception conditions that occur, for example, when travelling by car or train".
Speaking during last year's Radio Academy TechCon in Salford, Sam Bonham, technology development manager with DRUK, said this would be a major point influencing the government's decision on how any digital radio switch over would happen. "Consumers don't really care about technical issues like service following," he commented, "but they do care about continuity of services and being able to move about and listen to radio seamlessly."
Service following works with either hard linking - connecting to the same service as someone moves between multiplexes - or soft linking, finding a similar style of station if a hard link is not possible. Working with Arqiva, the BBC and commercial radio groups Bauer and Global, DRUK has carried out tests in different parts of the UK. In one trial people drove from London to Hastings on the south coast, a journey of only 62 miles but one that has many hills and valleys.
Mark Sutcliffe, a senior broadcast engineer at Arqiva, explained that while FM RDS involves a single data stream - the PI (programme information) code - DAB connectivity could need two, the SID (service identification) code and the EID (ensemble identification) code. He added that if the SIDs on two different multiplexes were the same then linking was straightforward. If not the EID was necessary as well.
Nick Piggott, head of creative technology for Global Radio, observed that the situation was sometimes more involved for the big media groups. "We have two networks - Heart and Capital - and each has local input like news, commercials and travel but they also act on a national level," he said. "So there are network programmes that are common to all stations but at other times we insert local information. With service following the aim is to have all the services effectively as one single frequency network but with inserts for specific areas."
Bonham commented that the key findings of the tests was that "a lot of receivers" did not have service following, while those that did feature it did not have it fully operational. "The future of service following is clear," he concluded. "We need broadcaster agreement and consistent implementation on receivers." With the UK government set to decide on the digital radio switchover towards the end of this year DRUK must be hoping all that comes soon.