Digital radio with the coverage of AM
Project from - present
What we're doing
Not to be confused with Digital Rights Management, Digital Radio Mondiale is a digital broadcasting system developed originally for the Long- Medium- and Short-wave bands - the bands traditionally used for AM (Amplitude Modulation) broadcasting.
Why it matters
Radio waves in these bands can travel very long distances and cover large areas, making them very useful both for international broadcasting and for domestic coverage of large and sparsely populated countries.
The BBC World Service uses shortwave extensively to broadcast around the world, and in the UK the BBC broadcasts on both long- and medium-wave. However, audio quality on AM is poor compared to FM and digital radio, and the international DRM consortium was set up in 1997 to develop a new system capable of bringing digital quality to the AM bands.
How it works
DRM uses Coded Orthogonal Frequency Division Multiplexing (COFDM), the same core technology used in DAB, DVB-T and DVB-T2 as well as in telecommunications standards such as LTE (the "4G" standard). COFDM, combined with a Multi-level Coding (MLC) scheme for error correction, allows the system to handle the time-varying, multi-path channels encountered in the AM bands, particularly shortwave. This is coupled with MPEG4 HE-AAC audio coding to provide clear and bright audio over the limited bandwidth of an AM channel.
The DRM standard was first published by ETSI as ES 201 980 in September 2001, and in March 2012 version 3.2.1 was published, extending the system to the VHF bands, and hundreds of hours of transmissions are on air every day from transmitters around the world.
BBC R&D has been a key member of the consortium: we made contributions to standardisation, played a leading role in field trials, long-term reception measurements and compliance testing, and developed our own modulator and receiver implementations. Our receiver design was licensed by a number of manufacturers and our modulators were used on-air at the Rampisham and Bonaire transmitting stations. We investigated innovative developments including diversity reception and large-scale Single Frequency Networks (SFNs). We also contributed significantly to the open-source Dream receiver, which is available from Sourceforge.
Although DRM has largely moved beyond the research phase, we still carry out DRM work within Lindsay Cornell's Future of Radio project: in addition to providing general expertise and technical leadership, we have facilities in our South Lab for measuring true receiver sensitivities by generating controlled electromagnetic fields. Lindsay is also the chair of the DRM Consortium's Technical Committee.