During the winter of 2012/13 an experimental DAB multiplex was set up in central Brighton (UK) using open source based technology. The work1 demonstrated that a standalone multiplex is feasible for delivering additional digital services to small areas, and identified several methods that could be used to reduce the costs. This work could potentially enable community and local commercial radio stations to gain a foothold on the UK’s digital radio platform in a cost effective manner.
Until recently, small scale radio stations were discouraged from considering DAB a relevant technology due to the high investment costs and the wide editorial coverage areas of the existing DAB single frequency networks.
The barriers to entry were lowered slightly by the publication of ‘Multi-Media Broadcasting Tools’ (mmbtools) by the Communication Research Centre of Canada under the General Public Licence.
The free software has been a catalyst – allowing engineers (who previously had no access to DAB equipment) to get ‘hands-on’ experience. This has culminated in test ensembles being operated in several countries including Switzerland, Ireland, Denmark, and the UK.
The tools were certainly the key to enabling the experimental DAB multiplex in Brighton. It was a great opportunity to test concepts including ARM source encoders, Wi-Fi transmitter links and ‘cloud’ multiplexing – a concept that could provide relief to those who might otherwise struggle to support such a system in-house.
In December the UK Government stated that it wanted to find ways to enable smaller stations to gain a foothold on DAB. It also supported plans by Ofcom (the UK communications regulator) to carry out work to refine the concept of small scale DAB, and to consider possible licensing options. This work will be carried out over the next two years.
Addressing the challenges
As part of the work, Ofcom is addressing the spectrum challenges and the early indications are that, for some areas at least, interleaved spectrum can be used. It is particularly efficient to re-use blocks that cannot be used for wide area coverage due to the presence of adjacent ‘county-wide’ networks. In more rural or less densely populated areas it should be possible to use frequency blocks that would otherwise lay fallow due to lower spectrum pressures. Although these early findings are encouraging, there is much work yet to be done!
DAB is well established in the UK and according to published statistics it currently delivers 22%2 of all radio listening hours. It is reasonable to expect that offering a broader range of services would benefit citizens and consumers and encourage further uptake, and increase the use of digital sets – to the benefit of all concerned.
Smaller broadcasters are also becoming attracted to DAB because of its established receiver base. There is also a compelling technical reason: the useful throughput of DAB is high relative to narrowband broadcasting. This could prove to be an ace card by providing capacity for innovation, and rich content for hybrid receivers. Capacity can also be shared with others to reduce costs. This is a compelling proposition for small stations seeking to keep distribution overheads to manageable levels in a multi-platform age.
Barriers to overcome
It isn’t all good news – the open source tools are reliable but they lack some important features. The software currently has no Graphical User Interface; no support for dynamic configuration; and no service linking functionality. Fortunately there are individuals and groups who are very active in developing these features. One key group is the Open Digital Radio non-profit association based in Switzerland. The group publishes a wiki at opendigitalradio.org, a crowd-sourced site where contributors can post links to their projects. The site collates information on open transmission software for various platforms. In time the tools will hopefully become full-featured.
The EBU’s Recommendation 1383 provides a clear road map for the journey ahead – DAB is to be Europe’s primary Digital Radio platform. It also illustrates a future of technology agnostic ‘hybrid’ receivers capable of displaying rich content while enabling the complimentary DRM standard to be used seamlessly where it is proven that DAB coverage is not possible.
(1) http://stakeholders.ofcom.org.uk/binaries/research/radio-research/Software-DAB-Research.pdf (2) Ofcom, Digital Radio Report 2013. Pg 15 Digital radio’s share of total radio listening hours, by platform. (3) EBU’s Recommendation 138
Senior Broadcast Specialist
Ofcom, United Kingdom