EBU Technical Review : No. 274 (Winter 1997)
Safeguarding our future DAB multiplexes
One of the fundamental reasons for the enduring success of radio is that it is suitable for different modes of use. In the early days of radio, listeners gave their undivided attention to the programmes by gathering around their radios in their living rooms. The arrival of TV and the invention of the transistor have dramatically changed this environment. Some radio listeners still tune in to listen attentively to specific programmes but, for many people, a radio in every room now provides audible wallpaper. Nowadays, most radio listeners are "multi-tasking" – as well as listening to the radio, they might also be driving a car, doing household chores or reading a newspaper. On the other hand, TV viewing requires that you can see the screen – which may be impossible, inconvenient or, even worse, unsafe.
When FM broadcasting started in the 1950s, the requirements for portability and mobility were not foreseen. Indeed, the FM transmitter networks were planned on the basis that each listener would erect an external aerial at 10 metres above ground level. Despite the invention of the transistor in 1947, portable radios did not become successful until the early 1960s. Even then, early transistor radios were AM – only because transistors capable of operating at VHF were not widely available until the late 1960s.
Recognizing that reception on portable and mobile FM radios was often poor, broadcasters attempted to mitigate this problem by adding vertically-polarized signals. Although this helped, multipath propagation remains the dominant problem with FM reception - resulting in variable reception quality, especially on portable and mobile radios. DAB can solve such problems, since the Eureka DAB system has been designed to provide flawless reception on portable and mobile radios in the presence of multipath propagation.
The introduction of DAB also allows radio broadcasters to offer sophisticated multimedia services, instead of being limited to straightforward audio services. Many broadcasters have ambitious plans for DAB multimedia services, such as "super-teletext", still pictures to illustrate a news bulletin or maps showing current traffic congestion.
Network operators will also be keen to exploit commercial opportunities for the transmission of data via DAB. Whilst such interest is welcome, broadcasters must ensure that adequate capacity is reserved for their future multimedia broadcasting applications. A key feature of DAB is that it allows broadcasters to "flex" the multiplex: the bit-rate allocated to the individual services in the multiplex can be changed on a dynamic basis to meet the needs of the broadcasters and the public. If control of the multiplex is given to network operators, safeguards will be needed to ensure that their decisions are not unduly influenced by the needs of commercial data services.
Radio broadcasting has a long and proud history. DAB will assure
its continued success in an increasingly competitive environment.
.
Philip Laven
Director
EBU Technical Department
European Broadcasting Union
