- Digital radio
Digital radio has several meanings:
1. Today the most common meaning is digital radio broadcasting technologies, such as the digital audio broadcasting (DAB) system, also known as Eureka 147. In these systems, the analog audio signal is digitized into zeros and ones, compressed using formats such as mp2, and transmitted using a digital modulation scheme. The aim is to increase the number of radio programs in a given spectrum, to improve the audio quality, to eliminate fading problems in mobile environments, to allow additional datacasting services, and to decrease the transmission power or the number of transmitters required to cover a region. However, analog radio programs and equipment, especially for the FM broadcasting system, still dominate the market.
2. An older and more wide definition, that still is used in communication engineering literature, is wireless digital transmission technologies, i.e. microwave and radio frequency communication standards where analog information signals as well as digital data are carried by a digital signal, by means of a digital modulation method. This definition includes broadcasting systems such at digital TV and digital radio broadcasting, but also two-way digital radio standards such as the second generation (2G) cell-phones and later, short-range communication such as digital cordless phones, wireless computer networks, digital micro-wave radio links, deep space communication systems such as communications to and from the two Voyager space probes, etcetera.
3. A less common definition is radio receiver and transmitter implementations that are based on digital signal processing, but may transmit or receive analog radio transmission standards, for example FM radio. This may reduce noise and distortion induced in the electronics. It also allows software radio implementations, where the transmission technology is changed just by selecting another piece of software. In most cases, this would however increase the energy consumption of the receiver equipment.
- 1 One-way digital radio (digital broadcasting systems)
- 2 Two-way digital radio standards
- 3 References
- 4 External links
One-way digital radio (digital broadcasting systems)
One-way digital radio standards
One-way standards are those used for audio and video broadcasting, and sometimes also datacasting, as opposed to those used for two-way communication. Digital radio broadcasting standards may provide terrestrial or satellite radio service. Digital radio broadcasting systems are typically designed for handheld mobile devices, just like mobile-TV systems, but as opposed to other digital TV systems which typically require a fixed directional antenna. Some digital radio systems provide in-band on-channel (IBOC) solutions that may coexist with or simulcast with analog AM or FM transmissions, while others are designed for designated radio frequency bands. The latter allows one wideband radio signal to carry a multiplex consisting of several radio-channels of variable bitrate as well as data services and other forms of media. Some digital broadcasting systems allow single-frequency network (SFN), where all terrestrial transmitters in a region sending the same multiplex of radio programs may use the same frequency channel without self-interference problems, further improving the system spectral efficiency.
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:
Digital audio broadcasting systems
- Eureka 147 (branded as DAB)
- Digital Radio Oceane
- Internet radio
- FM band in-band on-channel (FM IBOC):
- AM band in-band on-channel (AM IBOC):
- Satellite radio:
- Systems also designed for digital TV:
- Low-bandwidth digital data broadcasting over existing FM radio:
- Radio Data System (branded as RDS)
- Radio pagers:
Digital television broadcasting (DTV) systems
- Digital Video Broadcasting (DVB)
- Integrated Services Digital Broadcasting (ISDB)
- Digital Multimedia Broadcasting (DMB)
- Digital Terrestrial Television (DTTV or DTT) to fixed mainly roof-top antennas:
- Mobile TV reception in handheld devices:
- Satellite TV:
See also software radio for a discussion of radios which use digital signal processing.
Status by country
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 began being released during 2007 with firmware updated available for some older receivers.
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.
The United States has opted for a proprietary system called HD Radio(TM) technology, 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 technology was developed and is licensed by iBiquity Digital Corporation. It is widely believed that a major reason for HD radio technology is to offer some limited digital radio services while preserving the relative "stick values" of the stations involved and to insure that new programming services will be controlled by existing licensees.
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.
Lucent Digital Radio, USA Digital Radio (USADR), and Digital Radio Express commenced tests in 1999 of their various schemes for digital broadcast, with the expectation that they would report their results to the National Radio Systems Committee (NRSC) 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. HD Radio technology has also made inroads in the automotive sector with factory-installed options announced by BMW, Ford, Hyundai, Jaguar, Lincoln, Mercedes, MINI, Mercury, Scion, and Volvo. Beyond the U.S., commercial implementation of HD Radio technology is gaining momentum around the world.
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.
On February 19, 2007, Sirius Satellite Radio and XM Satellite Radio merged, to form Sirius XM Radio.
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.
- It must be noted that "Digital Radio" has a limited listening distance from the tower site. FCC laws currently show that 10% maximum digital signal of any US analog signal ratio. "There are still some concerns that HD Radio on FM will increase interference between different stations even though HD Radio at the 10% power level fits within the FCC spectral mask." HD Radio HD Radio#cite note-14. "HD Radio" is only 2 channels in the USA, side by side with analog stations. HD channel 1 may be on 93.2 FM, Analog station on 93.3, and HD channel 2 is on 93.4 FM. Differing stations are multicasting on different frequencies, respectively.
- Also note that "HD Radio" is digital radio, but is not "high definition" as most of the US population thinks. "HD" stands for "Hybrid Digital."
In the United Kingdom, 35.8% of the population owns a DAB digital radio set and 25% of listening is to digital platforms. 40.5% of all adults, or 20.9 million people, listen to digital radio each week, according to RAJAR, which equates to 45% of all radio listeners.
The UK currently has the world's biggest digital radio network, with 103 transmitters, two nation-wide DAB ensembles and 48 local and regional DAB ensembles, broadcasting over 250 commercial and 34 BBC radio stations; 51 of these stations are broadcast in London. On DAB digital radio most listeners can receive around 20 additional stations, in addition to the analogue stations available on digital.
Some areas of the country are not yet covered by DAB but the BBC has announced plans to build out national coverage to 92% by the end of 2011 with 40 new transmitters being launched in 2011. The Government will make a decision on a radio switchover subject to listening and coverage criteria being met. A digital radio switchover would maintain FM as a platform, while moving some services to DAB-only distribution. Digital radio stations are also broadcast on digital television platforms such as Sky, Virgin Media and Freeview, as well as internet radio.
Australia commenced regular digital audio broadcasting using the DAB+ standard in May 2009, after many years of trialling alternative systems. Normal radio services operate on the AM and FM bands, as well as four stations (ABC and SBS) on digital TV channels. The services are currently operating in five state capital cities, namely, Adelaide, Brisbane, Melbourne, Perth and Sydney, and is being trialled in Canberra and Darwin.
Japan has started terrestrial sound broadcasting using ISDB-Tsb and MobaHO! 2.6 GHz Satellite Sound digital broadcasting
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.
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
The key breakthrough or key feature in digital radio transmission systems is that they allow lower transmission power, they can provide robustness to noise and cross-talk and other forms of interference, and thus allow the same radio frequency to be reused at shorter distance. Consequently the spectral efficiency (the number of phonecalls per MHz and base station, or the number of bit/s per Hz and transmitter, etc.) may be sufficiently increased. Digital radio transmission can also carry any kind of information whatsoever - just as long at it has been expressed as a sequence of ones and zeroes. Earlier radio communication systems had to be made expressly for a given form of communications: telephone, telegraph, or television, for example. All kinds of digital communications can be multiplexed or encrypted at will.
- Digital cellular telephony (2G systems and later generations):
- Digital Mobile Radio:
- Wireless networking:
- Military radio systems for Network-centric warfare
- JTRS (Joint Tactical Radio System- a flexible software-defined radio)
- SINCGARS (Single channel ground to air radio system)
- Amateur packet radio:
- Digital modems for HF:
- Satellite radio:
- Wireless local loop:
- Broadband wireless access:
- ^ Digital Broadcast - bringing the future to you
- ^ http://www.worlddab.org/upload/uploaddocs/WorldDMBPress%20Release_November.pdf
- ^ Behrens, Steve. "Field testing resumes for radio’s digital best hope." Current, Aug. 16, 1999. Available at http://www.current.org/tech/tech915r.html
- ^ http://www.ibiquity.com/automotive
- ^ Plunkett, John (3 February 2011). "Rajars, Digital radio, Radio industry (Media), Media". The Guardian (London). http://www.guardian.co.uk/media/2011/feb/03/rajars-digital-radio-listening.
- ^ "Listening to radio as popular as ever with over 90% of the population tuning in each week". http://www.rajar.co.uk/docs/news/data_release_2010_Q4.pdf.
- ^ "Castaways found online and on Radio 4 Extra in BBC plans for digital radio". http://www.bbc.co.uk/pressoffice/pressreleases/stories/2011/03_march/01/did.shtml.
- ^ Digital Radio Plus (accessed 26 July 2011)
- "Digital, DTV, Internet, Mobile phone and MP3 Listening" - Dec 2006, RAJAR organisation.
- Online Terrestrial Radio - Search & and Listen to Live Radio Digitally
- Online Digital Radio - Select Station and Listen Live
Analog and digital audio broadcastingTerrestrial Radio modulation Frequency allocations Digital systemsSatellite Frequency allocations Digital systems Commercial radio providersSubcarrier signalsRelated topics
Technical (Audio): Audio processing · Audio data compression
Technical (AM Stereo formats): Belar · C-QUAM · Harris · Magnavox · Kahn-Hazeltine
Technical (Emission): Digital radio · Error correction · Multipath propagation · SW Relay Station · AM radio · AM broadcasting · Extended AM broadcast band · FM radio · FM broadcasting · FM broadcast band · Cable radio
Cultural: History of radio · International broadcasting
Comparison of radio systems
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