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Digital radio

Digital radio describes radio technologies which carry information as a digital signal, by means of a digital modulation method. The most common meaning is digital audio broadcasting technologies, but the topic may also cover TV broadcasting as well as many two-way digital wireless communication technologies. The acronym DAB (Digital Audio Broadcasting) is synonymous with the Eureka 147 standard.

One-way digital radio

One-way digital radio standards

One-way standards are those used for broadcasting, as opposed to those used for two-way communication. While digital broadcasting offers many potential benefits, its introduction has been hindered by a lack of global agreement on standards. The Eureka 147 standard (DAB) for digital radio is the most commonly used and is coordinated by the World DMB Forum, which represents more than 30 countries. This standard of digital radio technology was defined in the late 1980s, and is now being introduced in many countries. Commercial DAB receivers began to be sold in 1999 and, by 2006, 500 million people were in the coverage area of DAB broadcasts, although by this time sales had only taken off in the UK and Denmark. In 2006 there are approximately 1,000 DAB stations in operation. There have been criticisms of the Eureka 147 standard and so a new 'DAB+' standard has been proposed.

To date the following standards have been defined for one-way digital radio:

See also software radio for a discussion of radios which use digital signal processing.

Status by country

DAB adopters

Digital Audio Broadcasting (DAB), also known as Eureka 147, has been under development since the early eighties, has been adopted by around 20 countries worldwide. It is based around the MPEG-1 Audio Layer II audio codec and this has been co-ordinated by the WorldDMB. DAB receivers are selling well in some markets.

WorldDMB announced in a press release in November 2006, that DAB would be adopting the HE-AACv2 audio codec, which is also known as eAAC+. Also being adopted are the MPEG Surround format, and stronger error correction coding called Reed-Solomon coding.. The update has been named DAB+. Receivers that support the new DAB standard will be released during 2007.

DAB and DAB+ cannot be used for mobile TV because they do not include any video codecs. DAB related standards Digital Multimedia Broadcasting (DMB) and DAB-IP are suitable for mobile radio and TV both because they have MPEG 4 AVC and WMV9 respectively as video codecs. However a DMB video sub-channel can easily be added to any DAB transmission - as DMB was designed from the outset to be carried on a DAB subchannel. DMB broadcasts in Korea carry conventional MPEG 1 Layer II DAB audio services alongside their DMB video services.

United States

The United States has opted for a proprietary system called HD Radio, a type of in-band on-channel (IBOC) technology. Transmissions use orthogonal frequency-division multiplexing, a technique which is also used for European terrestrial digital TV broadcast (DVB-T). HD Radio is owned and promoted by iBiquity Digital Corporation.

The FM digital schemes in the U.S. provide audio at rates from 96 to 128 kilobits per second (kbit/s), with auxiliary "subcarrier" transmissions at up to 64 kbit/s. The AM digital schemes have data rates of about 48 kbit/s, with auxiliary services provided at a much lower data rate. Both the FM and AM schemes use lossy compression techniques to make the best use of the limited bandwidth.

The National Radio Systems Committee (NRSC) and the three IBOC companies began tests in December 1999. Results of these tests remain unclear, which in general describes the status of the terrestrial digital radio broadcasting effort in North America. Some terrestrial analog broadcast stations are apprehensive about the impact of digital satellite radio on their business, while others plan to convert to digital broadcasting as soon as it is economically and technically feasible.

While traditional terrestrial radio broadcasters are trying to "go digital", most major US automobile manufacturers are promoting digital satellite radio. Satellite radio is distinguished by its freedom from FCC censorship in the United States, its relative lack of advertising, and its ability to allow people on the road to listen to the same stations at any location in the country. Listeners must currently pay an annual or monthly subscription fee in order to access the service, and must install a separate security card in each radio or receiver they use.

Ford and Daimler AG are working with Sirius Satellite Radio, previously CD Radio, of New York City, and General Motors and Honda are working with XM Satellite Radio of Washington, D.C. to build and promote satellite DAB radio systems for North America, each offering "CD quality" audio and about a hundred channels.

Sirius Satellite Radio launched a constellation of three Sirius satellites during the course of 2000. The satellites were built by Space Systems/Loral and were launched by Russian Proton boosters. As with XM Satellite Radio, Sirius implemented a series of terrestrial ground repeaters where satellite signal would otherwise be blocked by large structures including natural structures and high-rise buildings.

XM Satellite Radio has a constellation of three satellites, two of which were launched in the spring of 2001, with one following later in 2005. The satellites are Boeing (previously Hughes) 702 comsats, and were put into orbit by Sea Launch boosters. Back-up ground transmitters (repeaters) will be built in cities where satellite signals could be blocked by big buildings.

The FCC has auctioned bandwidth allocations for satellite broadcast in the S band range, around 2.3 GHz.

The perceived wisdom of the radio industry is that the terrestrial medium has two great strengths: it is free and it is local. Satellite radio is neither of these things; however, in recent years, it has grown to make a name for itself by providing uncensored content (most notably, the crossover of Howard Stern from terrestrial radio to satellite radio) and commercial-free, all-digital music channels that offer similar genres to local broadcast favorites.

Japan

Japan has started terrestrial sound broadcasting using ISDB-Tsb and MobaHO! 2.6 GHz Satellite Sound digital broadcasting

Korea

On 1 December 2005 South Korea launched its T-DMB service which includes both television and radio stations. T-DMB is a derivative of DAB with specifications published by ETSI. More than 110,000 receivers had been sold in one month only in 2005.

Developing nations

Digital radio is now being provided to the developing world. A satellite communications company named WorldSpace is setting up a network of three satellites, including "AfriStar", "AsiaStar", and "AmeriStar", to provide digital audio information services to Africa, Asia, and Latin America. AfriStar and AsiaStar are in orbit. AmeriStar cannot be launched from the United States as Worldspace transmits on the L-band and would interfere with USA military as mentioned above.

Each satellite provides three transmission beams that can support 50 channels each, carrying news, music, entertainment, and education, and including a computer multimedia service. Local, regional, and international broadcasters are working with WorldStar to provide services.

A consortium of broadcasters and equipment manufacturers are also working to bring the benefits of digital broadcasting to the radio spectrum currently used for terrestrial AM radio broadcasts, including international shortwave transmissions. Over seventy broadcasters are now transmitting programs using the new standard, known as Digital Radio Mondiale (DRM), and commercial DRM receivers are available. DRM's system uses the MPEG-4 based standard aacPlus to code the music and CELP or HVXC for speech programs. At present these are priced too high to be affordable by many in the third world, however.

Low-cost DAB radio receivers are now available from various Japanese manufacturers, and WorldSpace has worked with Thomson Broadcast to introduce a village communications center known as a Telekiosk to bring communications services to rural areas. The Telekiosks are self-contained and are available as fixed or mobile units.

Two-way digital radio standards

References

External links

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