Key system features
The DRM broadcasting 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 that assure mutual analogue and 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 DRM in AM 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 that are comparable to local FM services, whilst enhancing the listener experience with easier tuning and added data services. National and local LF and MF 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, increased coverage or additional services. DRM is unique in providing an extensive and extremely powerful ‘toolkit’ array 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 of modulation parameters (code-rates, constellation, guard-intervals etc.) to enable an optimum trade-off between capacity and signal robustness. DRM also supports both multi- and single-frequency network operation, (MFN/SFN), and hand-over to other frequencies and even other networks (AFS – Automatic Frequency Checking & Switching). 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, and Journaline – accompanying audio programmes with interactive textual information, like news, or graphics. DRM can alert the widest possible audiences in case of pending disasters through its built-in Emergency Warning Functionality (EWF), allowing to serve as a last resort when all local infrastructure is down by covering the affected area with radio signals from outside. In case of an emergency, DRM receivers are ordered to switch to and present the emergency programme, and may even be able to turn on automatically. The emergency programme combines on-screen signalling, audio content, DRM text messages, and may include Journaline text with detailed look-up information in multiple languages in parallel. DRM is being operated at power levels ranging from a few watts on 26 MHz through to several hundred kilowatts on long-wave. It is possible to utilise the one technical standard to provide coverage ranging from international, national (c.1000 km), and all the way down to local community radio (c.1 km radius)