What is Digital Audio Broadcasting ?

Digital Audio Broadcasting(DAB) is a digital radio technology for broadcasting radio stations, used in several countries, particularly in Europe.

DAB may offer more radio programmes over a specific spectrum than analogue FM radio. DAB is more robust with regard to noise and multipath fading for mobile listening, since DAB reception quality first degrades rapidly when the signal strength falls below a critical threshold, whereas FM reception quality degrades slowly with the decreasing signal.

DAB vs FM/AM

Traditionally radio programmes were broadcast on different frequencies via FM and AM, and the radio had to be tuned into each frequency, as needed. This used up a comparatively large amount of spectrum for a relatively small number of stations, limiting listening choice. DAB is a digital radio broadcasting system that through the application of multiplexing and compression combines multiple audio streams onto a relatively narrow band centered on a single broadcast frequency called a DAB ensemble.

Benefits

Benefits of DAB over analogue systems are:

· Improved features for user’s
· More stations
· Reception quality
· Less pirate interference
· Variable bandwidth

· Transmission costs

Technology

· Bands and modes – DAB uses a wide-bandwidth broadcast technology and typically spectra have been allocated for it in Band III (174–240 MHz) and L band (1452–1492 MHz), although the scheme allows for operation almost anywhere above 30 MHz

· Protocol stack – From an OSI model protocol stack viewpoint, the technologies used on DAB inhabit the following layers: the audio codec inhabits the presentation layer. Below that is the data link layer, in charge of packet mode statistical multiplexing and frame synchronization. Finally, the physical layer contains the error-correction coding, OFDM modulation, and dealing with the over-the-air transmission and reception of data.

· Services and ensembles – Various different services are embedded into one ensemble (which is also typically called a multiplex). These services can include:

Primary services, like main radio stations

Secondary services, like additional sports commentaries

Data services

· Electronic Programme Guide (EPG)

· Collections of HTML pages and digital images (Known as 'Broadcast Web Sites')

· Slideshows, which may be synchronized with audio broadcasts. For example, a police appeal could be broadcast with the e-fit of a suspect or CCTV footage.

· Video

· Java Platform Applications

· IP tunneling

· Other raw data

An upgraded version of this system is DAB+. DAB+ is approximately twice as efficient as DAB due to the adoption of the AAC+ audio codec, and DAB+ can provide high quality audio with as low as 64 Kbit/s. Reception qualities will also be more robust on DAB+ than on DAB due to the addition of Reed-Solomon error correction coding. More than 20 countries provide DAB transmissions, and several countries, such as Australia, Italy, Malta, Switzerland and Germany; have started transmitting DAB+ stations.

In spectrum management, the bands that are allocated for public DAB services, are abbreviated with T-DAB, where the "T" stands for terrestrial.