View source for Digital radio

{{about|digitally-encoded radio transmission systems|the use of digital signal processing technology in the reception of analog AM and FM transmissions|Software-defined radio|and|DSP radio}}
{{Short description|Use of digital technology to transmit or receive across the radio spectrum}}
{{Digital radio broadcast standards}}
'''Digital radio''' is the use of digital technology to transmit or receive across the [[radio spectrum]]. [[Digital transmission]] by [[radio wave]]s includes [[digital broadcasting]], and especially [[digital audio radio service]]s. This should not be confused with [[Internet radio]] which also is digital but not transmitted by radio waves in the radio spectrum.

[[File:DAB Digital Radio.jpg|thumb|Example of a digital radio]]

== Types ==
In [[digital broadcasting]] systems, the analog audio signal is [[digital audio|digitized]], [[Audio compression (data)|compressed]] using an [[audio coding format]] such as [[AAC+]] ([[MDCT]])<ref>{{cite book |last1=Britanak |first1=Vladimir |last2=Rao |first2=K. R. |title=Cosine-/Sine-Modulated Filter Banks: General Properties, Fast Algorithms and Integer Approximations |date=2017 |publisher=Springer |isbn=978-3-319-61080-1 |page=478 |url=https://books.google.com/books?id=cZ4vDwAAQBAJ&pg=PA478 |access-date=2019-10-24 |archive-date=2023-07-01 |archive-url=https://web.archive.org/web/20230701082239/https://books.google.com/books?id=cZ4vDwAAQBAJ&pg=PA478 |url-status=live }}</ref> or [[MPEG-1 Audio Layer II|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 (AM and FM) is still more popular and listening to radio over IP ([[Internet Protocol]]) is growing in popularity.

In 2012, four digital wireless radio systems are recognized by the [[International Telecommunication Union]]: the two European systems [[Digital Audio Broadcasting]] (DAB) and [[Digital Radio Mondiale]] (DRM), the Japanese [[ISDB-T]] and the [[in-band on-channel]] technique used in the US and [[Arab world]] and branded as [[HD Radio]]. - [[5G Broadcast]] is a joint digital terrestrial broadcasting platform for radio and television under development in the UHF band being tested in 20 countries (2025) for more than five years. 

An older definition, still used in communication engineering literature, is [[wireless]] [[digital transmission]] technologies, i.e. [[microwave]]  and [[radio communications|radio frequency communication]] standards where analog [[information]] signals as well as digital data are carried by a [[Digital signal (electronics)|digital signal]], by means of a digital modulation method. This definition includes broadcasting systems such as [[digital TV]] and digital radio broadcasting, but also [[#Two-way digital radio standards|two-way digital radio standards]] such as the second generation ([[2G]]) cell-phones and later, [[Dedicated short-range communications|short-range communication]] such as [[DECT|digital cordless phones]], [[wireless computer network]]s, digital micro-wave radio links, [[Deep Space Network|deep space communication systems]] such as communications to and from the two [[Voyager program|Voyager space probes]], etc.


==One-way (broadcasting) systems==

===Broadcast standards===
[[Digital audio radio service]] standards may provide [[terrestrial radio|terrestrial]] or [[satellite radio]] service. Digital radio broadcasting systems are typically designed for handheld mobile devices, like [[Mobile television|mobile-TV]] systems and unlike 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 [[statistical multiplexing|multiplex]] of several radio-channels of various bitrates 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 (communication)|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 and many disadvantages. The DAB [[Eureka 147]] standard for digital radio is coordinated by the [[World DMB Forum]]. This standard of digital radio technology was defined in the late 1980s, and is now being introduced in some European countries. Commercial DAB receivers began to be sold in 1998 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.<ref>{{cite web|url=http://www.worlddab.org/benefits.php|title=Digital Broadcast - bringing the future to you<!-- Bot generated title -->|archive-url=https://web.archive.org/web/20071017232328/http://worlddab.org/benefits.php|archive-date=2007-10-17}}</ref> There have been criticisms of the Eureka 147 standard and so a new '[[Digital Audio Broadcasting#DAB+|DAB+]]' standard has been introduced.

The DRM standard has been used for several years to broadcast digitally on frequencies below 30&nbsp;MHz (shortwave, mediumwave and longwave). Also there is now the extended standard DRM+, which is designed for VHF bands.<ref>{{cite web|url=http://www.drm.org/technical-info/|title=Digital Radio Mondiale - Technical Info|website=www.drm.org|access-date=29 April 2018|url-status=live|archive-url=https://web.archive.org/web/20171023020536/http://www.drm.org/technical-info/|archive-date=23 October 2017}}</ref> Tests of DRM+ has been made in countries such as in Brazil, Germany, France, India, Sri Lanka, the UK, Slovakia, Italy (incl. the Vatican), as well as Sweden.<ref>{{cite web|url=http://www.drm.org/drm-testing-gets-underway-today-in-stockholm-sweden/|title=Digital Radio Mondiale - DRM+ Testing gets underway today in Stockholm, Sweden|website=www.drm.org|access-date=29 April 2018|url-status=live|archive-url=https://web.archive.org/web/20180202190244/http://www.drm.org/drm-testing-gets-underway-today-in-stockholm-sweden/|archive-date=2 February 2018}}</ref>

The two pan-European associations for community radio ''Community Media Forum Europe (CMFE)'' and ''AMARC Europe'' have stated to the European Commission that FM radio should be retained for local radio. In case of a future digital transition DRM+ would be the choice.
<ref>{{cite web|url=https://digitalradioinsider.blogspot.com/2013/10/community-radio-makes-its-stand-for-fm.html|title=Community Radio Makes Its Stand for FM Radio in Brussels |access-date=8 April 2025}}</ref>
<ref>{{cite web|url=http://www.public-service.net/docu/digiradio2014open.pdf|title=Community Radio: FM and Digitalization. Future Distribution Platforms for Community Radio in Europe (Green paper for CMFE (2014)|website=Public servicerådet |access-date=8 April 2025}}</ref>

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

====Digital audio broadcasting systems====
* [[Eureka 147]] (branded as [[Digital Audio Broadcasting|DAB]])
* [[Digital Audio Broadcasting#DAB+|DAB+]]
* [[5G Broadcast]]
* [[ISDB-TSB]]
* [[Internet radio]] (Technically not a true broadcast system)
* T-DMB V-Radio
* '''AM band [[in-band on-channel]] (AM IBOC):'''
** [[HD Radio]] (AM IBOC [[sideband]])
** [[Digital Radio Mondiale]] (branded as DRM) for the short-, medium- and long-wave bands
* '''FM band [[in-band on-channel]] (FM IBOC):'''
** [[HD Radio]] (OFDM modulation over AM and FM band [[IBOC]] [[sideband]]s)
** [[FMeXtra]] (FM band [[IBOC]] [[subcarrier]]s)
** [[Digital Radio Mondiale]] extension (DRM+) (OFDM modulation over AM band [[IBOC]] [[sideband]]s)
** Convergent Digital Radio (CDR) (OFDM modulation over FM band [[IBOC]] [[sideband]]s)
* '''[[Satellite radio]]:'''
** [[WorldSpace]] in Asia and Africa
** [[Sirius XM Radio]] in North America
** [[MobaHo!]] in Japan and the Republic of (South) Korea
* '''Systems also designed for digital TV:'''
** [[Digital Multimedia Broadcasting|DMB]]
** [[DVB-H]]
** [[ISDB-T]]
** [[Digital Terrestrial Multimedia Broadcast|DTMB]]
* '''Low-bandwidth digital data broadcasting over existing FM radio:'''
** [[Radio Data System]] (branded as RDS)
* '''Radio [[pager]]s:'''
** [[FLEX (protocol)|FLEX]]
** [[ReFLEX]]
** [[POCSAG]]
** [[Nippon Telegraph and Telephone|NTT]]

====Digital television (DTV) broadcasting systems====
* [[Digital Video Broadcasting]] (DVB)
* [[5G Broadcast]]
* [[Integrated Services Digital Broadcasting]] (ISDB)
* [[Digital Multimedia Broadcasting]] (DMB)
* '''[[Digital terrestrial television|Digital Terrestrial Television]] (DTTV or DTT) to fixed mainly roof-top antennas:'''
** [[DVB-T]] (based on [[OFDM]] modulation)
** [[Integrated Services Digital Broadcasting|ISDB-T]] (based on [[OFDM]] modulation)
** [[ATSC Standards|ATSC]] (based on [[8VSB]] modulation)
** [[T-DMB]] (based on [[OFDM]] modulation)
** [[Digital Terrestrial Multimedia Broadcast]] (DTMB) (based on [[OFDM]] modulation)
* '''[[Mobile TV]] reception in handheld devices:'''
** [[DVB-H]] (based on [[OFDM]] modulation)
** [[MediaFLO]] (based on [[OFDM]] modulation)
** [[Digital Multimedia Broadcasting|DMB]] (based on [[OFDM]] modulation)
** [[Multimedia Broadcast Multicast Service]] (MBMS) via the [[GSM]] [[Enhanced Data Rates for GSM Evolution|EDGE]] and [[UMTS]] cellular networks
** [[DVB-SH]] (based on [[OFDM]] modulation)
** [[China Multimedia Mobile Broadcasting]] (CMMB) (based on [[OFDM]] modulation)
* '''[[Satellite TV]]:'''
** [[DVB-S]] (for [[Satellite TV]])
** [[Integrated Services Digital Broadcasting|ISDB-S]]
** [[4DTV]]
** [[S-DMB]]
** [[MobaHo!]]
** Advanced Broadcasting System-Satellite (ABS-S)

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

===Status by country===

====DAB adopters====
{{Further|Countries using DAB/DMB}}
[[Digital Audio Broadcasting]] (DAB), also known as Eureka 147, has been adopted by around 20 countries worldwide. It is based on the [[MPEG-1 Audio Layer II]] [[audio coding format]] and this has been co-ordinated by the [[World DAB Forum|WorldDMB]].

WorldDMB announced in November 2006 that DAB would be adopting the [[HE-AAC]]v2 audio coding format, also known as [[eAAC+]]. Also being adopted are the [[MPEG Surround]] format, and stronger [[error correction coding]] called [[Reed–Solomon error correction|Reed–Solomon]] coding.<ref name="autogenerated1">{{cite web |url=http://www.worlddab.org/upload/uploaddocs/WorldDMBPress%20Release_November.pdf |title=New High Efficiency Audio Option Added for DAB Digital Radio |access-date=2016-02-06 |archive-url=https://web.archive.org/web/20080308204329/http://www.worlddab.org/upload/uploaddocs/WorldDMBPress%20Release_November.pdf |archive-date=2008-03-08 }}</ref> 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 coding format]]s. 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.

==== Australia ====

Australia commenced regular digital audio broadcasting using the DAB+ standard on 4 May 2009,<ref>{{Cite web|url=https://www.radioinfo.com.au/news/8-million-people-hear-about-digital-radio-industry-unites-launch|title=Digital Radio Launch|date=August 2009|website=Radioinfo|access-date=2019-05-28|archive-date=2019-05-28|archive-url=https://web.archive.org/web/20190528080917/https://www.radioinfo.com.au/news/8-million-people-hear-about-digital-radio-industry-unites-launch|url-status=live}}</ref> 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: [[Adelaide]], [[Brisbane]], [[Melbourne]], [[Perth, Western Australia|Perth]] and [[Sydney]], and is being trialled in [[Canberra]] and [[Darwin, Northern Territory|Darwin]].<ref>[http://www.digitalradioplus.com.au/index.cfm Digital Radio Plus] {{webarchive|url=https://web.archive.org/web/20110729002542/http://www.digitalradioplus.com.au/index.cfm |date=2011-07-29 }} (accessed 26 July 2011)</ref>

====Canada====
Canada has begun allowing experimental HD Radio broadcasts in December 2012 and digital audio subchannels on a case-by-case basis, with the first stations in the country being [[CFRM-FM]] in [[Little Current, Ontario|Little Current]], [[CING-FM]] in [[Hamilton, Ontario|Hamilton]], and [[CJSA-FM]] in [[Toronto]] (with a fourth, [[CFMS-FM]] in the Toronto suburb of [[Markham, Ontario|Markham]] applying to operate HD Radio technology), all within the province of Ontario.<ref>{{cite web|url=http://www.crtc.gc.ca/eng/archive/2006/pb2006-160.htm|title=Digital radio policy - In this public notice, the Commission sets out its revised policy for digital radio broadcasting |website=Canadian Radio-television and Telecommunications Commission | date=15 December 2006 |url-status=live|archive-url=https://web.archive.org/web/20140918234506/http://www.crtc.gc.ca/eng/archive/2006/pb2006-160.htm|archive-date=2014-09-18}}</ref><ref>{{cite web|url=http://blog.fagstein.com/2014/01/16/crtc-hd-radio/|title=CRTC looking at bringing HD Radio to Canada|work=Fagstein|date=16 January 2014 |url-status=live|archive-url=http://archive.wikiwix.com/cache/20140429010411/http://blog.fagstein.com/2014/01/16/crtc-hd-radio/|archive-date=2014-04-29}}</ref>

====Germany====
In 2020, DAB+ signals cover more than 90% of Germany. A national multiplex contains three public stations by [[Deutschlandfunk]] and 12 commercial stations. In most areas, additional multiplexes with public broadcasters and regional commercial stations are available.

The first DAB station network was deployed in Bavaria since 17 October 1995 until full coverage in 1999. Other states had funded a station network but the lack of success led them to scrap the funding - the MDR switched off in 1998 already and Brandenburg declared a failure in 2004. Instead Berlin/Brandenburg began to switch to digital radio based on an audio-only DVB-T mode given the success of the DVB-T standard in the region when earlier analogue television was switched off in August 2003 (being the first region to switch in Germany). During that time the DVB-H variant of the DVB family was released for transmission to mobile receivers in 2004. During 2005 most radio stations left the DAB network with only one public service broadcaster ensemble to remain in the now fully state-funded station network. At last the {{ill|lt=KEF|Kommission zur Ermittlung des Finanzbedarfs der Rundfunkanstalten|de|vertical-align=sup}} (''commission to determine the financial needs of broadcasters'') blocked federal funding on 15. July 2009 until economic viability of DAB broadcasting would be proven - and pointing to DVB-T as a viable alternative.

Digital radio deployment was rebooted during 2011 - a joint commission of public and private radio broadcasters decided upon "DAB+" as the new national standard in December 2010. The new station network started as planned on 1. August 2011 with 27 stations with 10&nbsp;kW each giving a coverage of 70% across the nation. A single "Bundesmux" ("fed-mux": short for "federal multiplex") was created on band 5C as a single-frequency network on channel 5C (see [http://digitalradio.de/index.php/de/empfangneu]). With the initial market success of DAB+ the contractors decided on an expansion of the digital radio station network in November 2012.

====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.

====Hong Kong====
Hong Kong replaced DAB with DVB-T2 Lite.

====Norway====
Norway was the first country where analog FM radio was switched off in 2017 being replaced by nationwide DAB+ distribution.

Local stations can continue broadcasting in FM at least until 2031.

====Other European Countries====
With DAB being available across Belgium, Netherlands, Switzerland, Denmark, Norway and Northern Italy there is good coverage across the [[European backbone|European Backbone]] area (see [[countries using DAB/DMB]]) indicating a sufficient momentum on the market. France, Spain, Sweden and Poland use DAB+ only in the big cities.

Portugal and Finland abandoned DAB. Finland is requesting the EU to mandate that automakers support FM similarly to DAB.

====Japan====

Japan has started terrestrial sound broadcasting using [[Integrated Services Digital Broadcasting#ISDB-Tsb|ISDB-Tsb]] and MobaHO! [[Integrated Services Digital Broadcasting#2.6 GHz Satellite Sound digital broadcasting|2.6 GHz Satellite Sound digital broadcasting]]

====United Kingdom====
{{main|Digital radio in the United Kingdom}}

In the [[United Kingdom]], 44.3% of the population now has a DAB digital radio set and 34.4% of listening is to different digital platforms. Because of the early success of the old DAB standard, the transition to the more efficient DAB+ takes more time. If DAB was switched off, older receivers would become worthless. In 2020, about half of the stations in the UK use DAB+.

26 million people, or 39.6% of the population of 65.64 million, now tune into digital radio each week, up 2.6 million year on year, according to RAJAR in Q1 2013. But FM listening has increased to 61% and DAB decreased to 21% DAB listeners may also use AM  & FM too.<ref name="Vaizey kicks analogue switchoff can">
{{cite web
 |title       = Analogue radio will CONTINUE in Blighty as Minister of Fun dodges D-Day death sentence
 |website = [[The Register]]
 |url         = https://www.theregister.co.uk/2013/12/16/minister_kicks_dab_can_miles_down_the_road/
 |url-status     = live
 |archive-url  = https://web.archive.org/web/20161110043935/http://www.theregister.co.uk/2013/12/16/minister_kicks_dab_can_miles_down_the_road/
 |archive-date = 2016-11-10
}}</ref>

The UK currently has the world's biggest digital radio network, with about 500 transmitters, two nationwide [[DAB ensemble]]s and 48 local and regional DAB ensembles, broadcasting over 250&nbsp;commercial and 34&nbsp;BBC [[radio station]]s; about 100 stations can be received in [[London]]. On DAB digital radio most listeners can receive around 30 additional stations.

Digital radio stations are also distributed on [[digital television]] platforms such as Sky, Virgin Media and Freeview, as well as [[internet radio]].

The [[Her Majesty's Government|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.

DAB+ devices in the UK have been available to the public since 2010.

====United States====
The [[United States]] has opted for the proprietary [[HD Radio]] technology, a type of [[in-band on-channel]] (IBOC) technology. According to [[iBiquity]], "HD Radio" is the company's trade name for its proprietary digital radio system, but the name does not imply either high definition or "hybrid digital" as it is commonly incorrectly referenced.

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{{by whom|date=August 2021}} 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 ensure 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&nbsp;kbit/s. The AM digital schemes have data rates of about 48&nbsp;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 (signal processing)|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.<ref name="currentSiteRef">Behrens, Steve. "Field testing resumes for radio's digital best hope." ''Current'', Aug. 16, 1999. Available at {{cite web |url=http://www.current.org/tech/tech915r.html |title=Current.org &#124; Testing digital radio systems, 1999 |access-date=2009-06-15 |archive-url=https://web.archive.org/web/20090720071416/http://www.current.org/tech/tech915r.html |archive-date=2009-07-20 }}</ref> Results of these tests remain unclear, which in general describes the status of the terrestrial digital radio broadcasting effort in [[North America]].

While traditional terrestrial radio broadcasters are trying to "go digital", most major US [[automobile manufacturer]]s 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, and Volvo.<ref>{{cite web|url=http://www.ibiquity.com/automotive|title=iBiquity Digital Corporation - Automotive|url-status=live|archive-url=https://web.archive.org/web/20081117191606/http://www.ibiquity.com./automotive|archive-date=2008-11-17}}</ref>

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.

Sirius Satellite Radio launched a [[satellite constellation|constellation]] of three Sirius satellites during the course of 2000. The satellites were built by [[Space Systems/Loral]] and were launched by [[Russia]]n [[Proton (rocket)|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 702]] comsats, and were put into orbit by [[Sea Launch]] boosters. Back-up ground [[transmitter]]s ([[repeater]]s) 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 [[Federal Communications Commission|FCC]] has auctioned bandwidth allocations for satellite broadcast in the [[S band]] range, around 2.3&nbsp;GHz.

Terrestrial broadcasting has advantages in being free and local. Satellite radio is neither of these things; however, in the early 21st century it has grown 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 [[radio format]]s to local stations.

The "HD Radio" signal of an FM broadcast station in the US has a limited listening distance from the broadcast tower site. FCC regulations currently limit the power of the digital part of the station's transmission to 10% of the existing analog power permitted the station. Even at this power level, the presence of the digital signal right next to the station's analog signal can result in older radios picking up noise due to trouble rejecting the adjacent digital signal. "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" allows each existing broadcast station to add additional "channels" in the US by transmitting a digital signal on both sides of its channel, just beyond their existing analog Frequency Modulation signal. The HD Radio signal occupies the 0.1&nbsp;MHz that begins 0.1&nbsp;MHz above and below the carrier frequency station. For instance, if a station's analog signal's carrier frequency is 93.3&nbsp;MHz, the digital signal will fill 93.1–93.2&nbsp;MHz and 93.4–93.5&nbsp;MHz within the FM Broadcast Band. Several digital audio streams, or "subchannels", can be carried within this single digital data stream, with the number of audio of subchannels and bandwidth allocations at the choice of the station. On the radio tuner, these will appear as (in the above case) "93.3-2", "93.3-3", and so on. The frequencies that are used do not change as more channels are added to the one radio station (93.3&nbsp;MHz in the example above). Instead, a fixed total amount of bandwidth is simply reallocated across the audio streams such that each now receives less bandwidth, and therefore lower audio quality, than before.

There is no federally mandated transition to HD Radio for both FM and AM stations. However, on October 27, 2020, the FCC approved voluntary all-digital AM operation nationwide.<ref name=october2020>{{cite web |url=https://docs.fcc.gov/public/attachments/DOC-367780A1.pdf |title=FCC AUTHORIZES ALL-DIGITAL AM RADIO |author=<!--Not stated--> |date=October 27, 2020 |website=fcc.gov |publisher=[[Federal Communications Commission]] |access-date=2020-10-27 |archive-date=2020-10-29 |archive-url=https://web.archive.org/web/20201029192036/https://docs.fcc.gov/public/attachments/DOC-367780A1.pdf |url-status=live }}</ref>

====Developing nations====

Digital radio is now being provided to the developing world. A now defunct satellite communications company named [[WorldSpace]] was 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 could not be launched from the [[United States]] as Worldspace transmitted on the L-band and would interfere with USA military as mentioned above.{{Citation needed|date=December 2008}}. in its heyday provided service to over 170,000 subscribers in eastern and southern Africa, the Middle East, and much of Asia with 96% coming from India. [[Timbre Media]] along with Saregama India plan to relaunch the company. As of 2013 Worldspace is defunct, but two satellites are in orbit which still have a few channels. See main [[WorldSpace]] article.

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 were 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 [http://www.drm.org/index.php?p=products / commercial DRM receivers] are available (though there are few models on the DRM website and some are discontinued). 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. Take-up of DRM has been minuscule and many traditional Shortwave broadcasters now only stream on Internet, use fixed satellite (TV set-boxes) or Local Analogue FM relays to save on costs. Very few (expensive) DRM radio sets are available and some Broadcasters (RTE in Ireland on 252&nbsp;kHz) have ceased trials without launching a service.

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 [[Interactive kiosk#Telekiosk|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 [[frequency reuse|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 [[Digital data|digitally]]. 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 [[encryption|encrypted]] at will.
* '''Digital [[cellular telephony]]''' ([[2G]] systems and later generations):
** [[GSM]]
** [[UMTS]] (sometimes called W-CDMA)
** [[TETRA]]
** [[IS-95]] (cdmaOne)
** [[IS-136]] (D-AMPS, sometimes called TDMA)
** [[IS-2000]] (CDMA2000)
** [[iDEN]]
* '''Digital Mobile Radio''':
** [[Multi-Band Excitation]]
** [[TETRA]]
** [[TETRAPOL]]
** [[NXDN]]/[[dPMR]]
** [[Digital Mobile Radio|DMR]]
** [[D-STAR]]
* '''[[Wireless network]]ing''':
** [[Wi-Fi]]
** [[HIPERLAN]]
** [[Bluetooth]]
** [[DASH7]]
** [[Zigbee]]
** [[6LoWPAN]]
* '''[[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)
* '''[[Packet radio|Amateur packet radio]]''':
** [[AX.25]]
* '''Digital modems for HF''':
** [[PACTOR]]
* '''[[Satellite radio]]''':
** [[Satmodem]]s
* '''[[Wireless local loop]]''':
** [[Basic Exchange Telephone Radio Service]]
* '''Broadband wireless access''':
** [[IEEE 802.16]]

==See also==
{{Portal|Radio}}
* [[Satellite television]]

==References==
{{reflist}}

==External links==
* [http://www.rajar.co.uk/quarterlysummary/qstsvfiles/138/Q42006_Digital_DTV_Internet_Mobile.pdf "Digital, DTV, Internet, Mobile phone and MP3 Listening"] - December 2006, [[RAJAR]] organisation.
* [https://web.archive.org/web/20101120063759/http://www.durocast.com/ Online Terrestrial Radio] - Search & and Listen to Live Radio Digitally

{{Audio broadcasting}}
{{Wireless video}}
{{Broadcasting}}
{{Digital electronics}}
{{Authority control}}

{{DEFAULTSORT:Digital Radio}}
[[Category:Digital radio| ]]