Digital radio describes radio technologies, which carry information as a digital signal (Free Dictionary). The launch of AM radio during the 1920s signaled the first generation and was followed in the 1970s by FM (Thomson, 1997). Radio is being digitalized in many ways, from webcasting through to subscription DAB. Although the different digital radio systems have different strengths and weaknesses, the CRA have decided to introduce the Eureka system to Australia.
DRM is a narrowband digital transmission system that utilises a High Frequency channel only 9kHz wide to deliver 25kbs of data, enough for a single service [Tanner, Giles 2002]. Because DRM operates on lower bit rates it provides lower audio quality compared to most other digital radio systems. However DRM could allow international services such as Radio Australia to go digital without the cost of high power satellites, or it could be used to replace AM services in regional areas [Tanner, Giles 2002]. At the last ABA Conference, the BBC's Lindsay Cornell suggested a hybrid DRM/Eureka receiver might provide Australian broadcasters with an ability to boost coverage in the bush where it is difficult for Eureka to broadcast because of lack of VHF spectrum. Implementation of DRM trials at the BBC and Deutsche Telecom has been helped through using existing infrastructure (Rohde & Schwarz, 2004). A DRM signal can be broadcast from an upgraded AM transmitters. Also the DRM coding and decoding is simpler than most digital systems. This means no expensive computers or software but at the same time simple coding impacts audio compression.
Eureka 147 is commonly known as Digital Audio Broadcast (DAB) and has been introduced to most of Europe and parts of Asia and South Africa. This transmission system has set the global standard in digital broadcasting. The system allows several radio stations to share a single radio signal by compiling their digital audio signals together. Each Eureka DAB transmitter can deliver five CD quality audio channels or a larger number of lower quality channels. Eureka 147 is mostly transmitted in the L band but can also operate in VHF and UHF bands. This transmission is not just able to carry a radio service but around a million bits of information (1 mbs). In terms of bandwidth, this falls somewhere between your home Internet fax modem, which probably carries 56,000 bits per second (56 kbs), and a digital television channel, which carries 20 million bits (20 mbs). Under the Digital Radio Advisory Committee's findings Eureka 147 is currently being trialed in Sydney and Melbourne, Australia.
IBOC is a method of transmitting both digital and analog radio signals through the same frequency. It is a hybrid transmission system, which utilises the spare signal space adjacent to analogue signals. These side bands complement both AM and FM broadcasts. IBOC is designed to implement digital radio in two phases. The first is a Hybrid phase, which supplements an existing AM or FM analog radio signal with a digital signal carried alongside the transmission of the analog signal. During this phase the analog signal is used as a backup when the digital signal drops out. The second is an All-Digital phase in which the analog signal is removed and the digital signal reconfigured Digital Radio Study Group. Although the IBOC transmission is not as clean as Eureka, IBOC technology removes the need for extra transmission frequencies. The IBOC system also enables broadcasters to use of existing infrastructure and minimise upgrade costs. Its receiver design avoids abrupt reception failures common in digital systems at the edge of the coverage area. iBiquity is currently developing the system for introduction to the United States.
ISDB-t is a flexible digital transmission system very similar to the ISDB systems which deliver television and radio services in Japan. The system is similar to ISDB because of its ability to allow multiple channels of data to be transmitted. ISDB-TSB has the capacity to provide one to about seven “CD� quality services in channels of 429 kHz or 1.286 MHz depending on the broadcaster Digital Radio Study Group. ISDB-t has been designed to operate in VHF Bands II and III and UHF Bands IV and V. ISDB-t can also deliver low bit rate video programs. Commercial trials of this system are not yet available in Australia.
Finally, Australia might be able to supplement Eureka with DVB or satellite systems. DVB has developed a number of related digital broadcasting systems for cable, satellite and terrestrial television. Remote areas of Australia are already provided with free-to-air TV, Pay-TV and digital radio services through DVB-S satellite services. Worldspace digital radio operates in L-band at approximately 1.5 GHz, via satellite. This satellite system provides digital radio to Asia, Africa and the Middle East. The US operates two similar satellite digital radio subscription services. Both services offer about 100 audio channels. They operate in S-Band (2.3 GHz)
Free Dictionary http://encyclopedia.thefreedictionary.com/digital%20radio accessed 15/10/04
Tanner, Giles 2002, "Has radio a digital future?" last accessed 12/10/04.
Digital Radio Mondiale last accessed 12/10/04.
ISDB-t last accessed 12/10/04.
Eureka 147 last accessed 12/10/04.
iBiquity last accessed 12/10/04.
Rohde & Schwarz (2004) DAB audio broadcasting - background [on-line] Available at: http://www.rohde-schwarz.com/www/dev_center.nsf/html/114212 Accessed: October 12, 2004.
