DAB itself is not nowadays regarded as the optimum solution to the requirement for a digital broadcast radio standard. DAB was state-of-the-art in the late 1980s but it is certainly not now, and several European countries have already decided not to adopt it. Variants on the original specification, notably DAB+ and DMB (Digital Multimedia Broadcasting) have emerged as alternatives.
In 2009, the WorldDMB Forum and the European Broadcasting Union jointly issued a press release in which they set out how they wished to achieve a "unified digital radio market" in Europe. This involved the publication of a set of minimum features and functions for all digital radio receivers, known as the WorldDMB Digital Radio Receiver Profiles. These specified a set of minimum requirements and features to be built in to different classes of digital radio receivers, ensuring the "…interoperability of all new digital radio receivers across European countries whose broadcasters are using either DAB, DAB+ or DMB. Together these are known as the Eureka 147 Family of Standards."
The features and functions appropriate to in-car systems were also defined. They included automatic retuning between digital and analogue services and "…advanced travel and traffic services for real-time satellite navigation. These Profiles will enable drivers travelling across borders to receive all Eureka 147 digital radio broadcasts on their car radios." Amongst other things, the obvious implication is that a digital radio which can cater for all three modes, rather than just DAB, is likely to be required in the foreseeable future by those who travel widely in Europe.
DRM: A Digital Alternative for AM, FM Too… maybe
Another complicating factor is a system known as DRM. The DAB standard was intended as a replacement for FM services but a complementary digital system is required to replace conventional AM broadcasting on LW and MW, and indeed on short-wave (HF) as well. What has come to be called DRM (Digital Radio Mondiale) emerged from an informal meeting between some large international broadcasters and equipment manufacturers in September 1996. The consensus of the meeting was that the days of international broadcasting below 30MHz were limited unless a suitable digital standard could be developed. A formal proposal for the system was approved by the ITU in April 2000.
DRM employs a technique known as AAC (Advanced Audio Coding) supplemented by SBR (Spectral Band Replication). In essence SBR relies on the fact that the brain is not very discerning at high audio frequencies and is quite content if they are reconstructed from harmonically related frequencies which are present lower in the audible range. This allows a considerable reduction in bandwidth. SBR is also used in DAB+ and the SiriusXM system (see below) and is a constituent part of the MP4 specification.
The DRM channel coding and modulation system has some similarities to DAB in that it uses a variety of orthogonal frequency-division modulation (OFDM) with very comprehensive error correction and multi-level coding. The result is capable of fitting within the same channel or 'pipe' (see earlier analogy) as that currently used for analogue AM. Under good conditions DRM can produce audio quality which is rather like monophonic FM, with slightly less high-frequency content. Under severe conditions the results are still very good, reminiscent of a strong transmission from a local medium-wave outlet. Fading and distortion simply do not take place, although the audio can occasionally disappear completely. As with DAB, various forms of programme associated data can be transmitted at the same time as the programme material.
A variant known as DRM+ has been proposed to replace FM transmissions and tests in Germany in 2010 suggested that it performed very well under mobile conditions.
DRM's proponents in the broadcast industry have been very bullish about the mode but neither DRM nor DRM+ are included in the Eureka standards family, and by 2011 the future for both was looking unclear. There is some international DRM broadcasting on HF and several trials have taken place on medium-wave frequencies in the UK. A few DRM receivers are commercially available but low-cost integrated-circuit decoders are not yet manufactured. Nevertheless it is possible that DRM+ could have a future in some European countries, and DRM itself may replace analogue domestic AM broadcasting in some areas of the world, notably South America and parts of Asia.
The Final Twist From Above: Satellite Radio
And finally there is the prospect of broadcast radio via satellite. In the USA, Sirius and XM (originally separate companies when the services began in 1997 but now merged as SiriusXM) currently offer something over 200 channels of radio programming to about 19 million subscribers. Reception in vehicles is generally very good, as is the audio quality. Several proposals for similar pan-European satellite radio services have been made but have not yet been realised, chiefly for geographical and financial reasons. But who knows what the future may bring?
PART 1: Why, how and when DAB Digital Radio developed in the UK
Report on DAB and the future of digital radio commissioned in April 2011 by the MMSA from
Crew Green Consulting Ltd. ©2011 Mobile Media Specialist Association Ltd. No reproduction allowed, in part or in full, without written consent.
In the second part of our report commissioned by the MMSA into Digital Audio Broadcasting in the UK, we look at the future for DAB - a system considered state-of-the-art in the late 1980s but no longer quite as shiny and impressive today. DAB variants or an alternative digital radio format could take the lead.