What is DRM?

The DRM Broadcasting system has been designed by broadcasters, for broadcasters, but with the active assistance and participation of both transmitter & receiver manufacturers and other interested parties (such as regulatory bodies). It has been designed specifically as a high quality digital replacement for current analogue radio broadcasting in the AM and FM/VHF bands, and as such it can be operated with the same channelling and spectrum allocations as currently employed. An overview of the frequency-bands where DRM operates is shown in Fig. 1 below.

Operational frequency-bands

The DRM standard describes a number of different operating modes, which may be broadly split into two groups as follows:

  • 'DRM30' modes, which are specifically designed to utilise the AM broadcast bands below 30MHz, and
  • 'DRM+' modes, which utilize the spectrum from 30MHz to VHF Band III, centred on the FM broadcast band II

DRM has received the necessary recommendations from the ITU, hence providing the international regulatory support for transmissions to take place. The main DRM standard has been published by both the IEC and ETSI, but ETSI publishes and is the main repository of the entire range of current DRM technical standards.

Apart from the ability to fit in with existing spectrum requirements, the DRM system also benefits from being an open system. All manufacturers have free access to the complete technical standards, and are able to design and manufacture equipment on an equitable basis. This has proved to be an important mechanism for ensuring the timely introduction of new systems to the market and for accelerating the rate at which equipment prices reduce. This is a significant consideration for broadcasters and even more for the listeners who will need to invest in new DRM-capable receivers.

Key system features

The system is specifically designed to allow the new digital transmissions to co-exist with the current analogue broadcasts, and a significant amount of work has been undertaken to quantify the operating parameters which assure mutual analogue/digital compatibility. Hence the changeover from analogue to digital broadcasting can be phased over a period of time, which in turn allows existing broadcasters to spread the required investment to meet any budgetary constraints. Furthermore, unlike some other digital systems, the DRM system has been designed to allow suitable analogue transmitters to be modified to switch easily between digital and analogue broadcasts. This can significantly reduce the initial investment cost for a broadcaster. An additional budgetary benefit is the reduction of transmission energy costs.

  • DRM exploits the unique propagation properties of the AM bands. The introduction of DRM30 services allows a broadcaster to provide listeners with significantly improved audio quality and service reliability. As a result, international broadcasters can provide services on SW and MW which are comparable to local FM services, whilst enhancing the listener experience with easier tuning and added data services. National and local LW and MW broadcasters will derive similar benefits.
  • In the VHF bands, DRM+ can be configured to use less spectrum than current stereo FM broadcasts, whilst additionally deriving the potential benefits of increased robustness, reduced transmission power and/or increased coverage.

DRM is unique in providing an extensive and extremely powerful “toolkit” of operating modes and techniques, which allow a broadcaster to tailor the system to best meet the needs of his or her particular market. For instance, DRM allows the independent selection modulation parameters (code-rates, constellation, guard-intervals etc). DRM also supports both multi- and single-frequency network operation, (MFN/SFN), and hand-over to other networks (AF). This latter feature allows a broadcaster operating on several different platforms to hand a listener from DRM to AM, FM or DAB and back again. The appropriate signalling is intrinsically supported by DRM and DAB, and by data carriers on AM and FM (AMSS and RDS respectively). Of particular note amongst the various data services is the DRM Electronic Programme Guide (EPG), which allows listeners with appropriate receivers to access the broadcast schedule and set recording times accordingly.

DRM has been successfully operated at power levels ranging from a few watts on 26MHz through to several hundred kilowatts on long-wave. It is possible to utilise the one technical standard to provide coverage ranging from national (c.1000 km) right down to local community (c.1 km radius).

Finally, there are three MPEG4 audio codecs included within the standard, catering for a wide range of bit-rates and catering for both speech and music content.

Background: The DRM Consortium

The DRM Consortium (Digital Radio Mondiale) is an international not-for-profit organisation composed of broadcasters, network providers, transmitter and receiver manufacturers, universities, broadcasting unions and research Institutes. Its aim is to support and spread a digital broadcasting system suitable for use in all the frequency bands up to and including VHF Band III. There are currently 93 members and 90 Supporters from 39 countries active within the Consortium.

DRM was formed in Guangzhou, China in 1997, initially with the objective of “digitising” the AM broadcast bands up to 30MHz (long, medium and short-wave). The DRM System Specification for broadcasting below 30MHz (”DRM30”) was first published by ETSI in 2001.

Subsequently, a number of ancillary supporting standards were issued, including a Distribution and Communication Protocol. In 2005 a decision was taken to extend the DRM system to incorporate modes designed to operate in the VHF broadcasting bands. This required the addition of high-frequency modes, which, following refinement through laboratory testing and field-trials, resulted in the publication of the current (extended) DRM specification ES 201 980 v3.1.1.