Francais | English | Espanõl

Digital audio broadcasting

From Wikipedia, the free encyclopedia

(Redirected from Digital Audio Broadcasting)
Jump to: navigation, search

Digital Audio Broadcasting or DAB is a technology for broadcasting audio programming in digital form that was designed in the late 1980s but which is now being introduced in many countries. The original objectives of converting to digital systems were to enable higher fidelity, more stations, less inteference, mobile services and additional information such as text, although in practice the vast majority of radio stations on DAB sound worse than on FM.

The acronym DAB is used both to identify the generic technology of digital audio broadcasting, although it has become synonymous with the Eureka 147 standard. The Eureka 147 standard of DAB technology is the most commonly used and is coordinated by the World DMB Forum, which represents more than 30 countries. However other standards exist. The United States has opted for a proprietary system called HD Radio or IBOC). Digital television services also incorporate some digital audio channels on spare bandwidth using DVB-T and DVB-H standards.

Contents

[edit] Status

The first digital radio standard arose out of the Eureka 147 project which started in 1987. The choice of modulation was made soon after the inception of the Eureka 147 Project, and the audio codec and error correction coding schemes were chosen in 1990. 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.<ref> http://www.worlddab.org/benefits.php </ref> Japan is also broadcasting digital radio but using a different system called Integrated Services Digital Broadcasting.

[edit] DAB and FM/AM compared

Traditionally radio stations were broadcast on different frequencies via FM and AM, and the radio had to be tuned into each frequency. 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 single broadcast frequency called a DAB ensemble. Within an overall target bit rate for the DAB ensemble, individual stations can be allocated different bit rates. The number of channels within a DAB ensemble can be increased by lowering average bit rates, but at the expense of the quality of streams. Error correction under the DAB standard makes the signal more robust, but also reduces the total bit rate available for streams.

[edit] Claimed benefits of DAB

Image:Unbalanced scales.svg
The neutrality of this section is disputed.
Please see the discussion on the talk page.

Current AM and FM terrestrial broadcast technology is well established, compatible, and cheap to manufacture. Benefits claimed for DAB above conventional systems include the following:

  • DAB radios can automatically tune to all the available stations, offering a list of stations, from which favorites can be selected.
  • DAB can carry "radiotext" (in DAB terminology, Dynamic Label Segment, or DLS) from the station giving real-time information such as song titles, music type, news or traffic updates. Programme guides up to seven days in advance can also be transmitted. (This facility already exists on FM in the form of the RDS.)
  • Tags allow automotive radios to automatically change stations as they travel from city to city, to stay with a particular network or music style. (This facility already exists on FM in the form of the RDS.)
  • Some radios offer a pause facility on live broadcasts, caching the broadcast stream on local flash memory.
  • The DAB standard integrates features to reduce the negative consequences of multipath interference or fading, which sometimes afflict existing analog systems.
  • DAB is more bandwidth efficient than analogue for national radio stations due to the use of SFNs, enabling more stations to be placed into a smaller section of the spectrum, although it is no more efficient than FM for local radio stations.

[edit] Criticisms of DAB standard

  • The orginal DAB audio codec was MPEG-1_Audio_Layer_II - widely recognised as performing poorly at exactly the lower bit rates used in the DAB system.
  • The more stations that are added to the DAB ensamble, the lower the average bit rate per stream must be, reducing audio fidelity.
  • As transmission costs on DAB are far more expensive than on FM, in order to limit costs the broadcasters have put too many channels into a DAB ensamble, forcing bit rates to be used that deliver sound quality inferior to traditional FM (Digital_audio_broadcasting#Criticisms_of_DAB_in_the_UK).
  • In 2006 tests finally begun using the much improved HE-AAC codec for DAB. However, the new DAB standard is not backwards compatible, leaving early DAB adopters with incompatible hardware.
  • DAB chipsets have never been power efficient. Revised DAB 2 AAC+ chipsets are projected by manufacturers to be up to 7 times more power efficient, increasing battery life for portable radios by a factor of approximately three. [1].
  • If the signal reception becomes marginal the audio output for the whole multiplex simply mutes until the signal strength recovers again(dubious; discuss) . Sometimes it is easy to mistake this for a receiver fault(dubious; discuss) . Usually the same situation occurring with an FM broadcast receiver, assuming the muting is disabled, would progressively increase the audio noise(dubious; discuss) , tending to swamp the intended audio and identifying that the signal is becoming weak.

[edit] Digital radio standards

While DAB offers many potential benefits, its introduction has been hindered by a lack of global agreement on standards. Several DAB schemes are being promoted in the United States, none of which is compatible with the "Eureka 147" DAB standard now being implemented in Canada, Europe and parts of Asia.

[edit] DAB EUREKA 147

EUREKA was developed as a research project for the European Union. (Project number EU147.) It is based on orthogonal frequency division multiplexing for transmitting digital data over a radio channel. DAB broadcasts use the MP2 (MPEG-1 layer-2) audio coding technique created as part of the EU147 project. The system was designed in the late-1980s, with the choice of audio codec, modulation and error correction coding schemes being made in 1990. The project started in 1987 and ended in 2000.

The United Kingdom was the first country to receive a wide range of radio stations via DAB, with over 50 commercial and BBC services available in London in 2001 The UK has to date been the most successful market for DAB and is being projected to be in 40% of homes by 2009.<ref> [2] </ref>.

Eureka 147 DAB uses a wide-bandwidth broadcast technology and typically spectra have been allocated for it in Band III and L band, although the scheme allows for operation almost anywhere above 30 MHz. The US military has reserved L-Band in the USA only, blocking its use for other purposes in America, and the United States has reached an agreement with Canada that the latter will restrict L-Band DAB to terrestrial broadcast to avoid interference.

[edit] Bands and modes

DAB can use a number of different frequency bands for broadcasting. This includes:

  • Band III– Frequency band 174–240 MHz
  • L-Band– Frequency band 1452–1492 MHz

DAB has a number of country specific transmission modes (I, II, III and IV). For worldwide operation a receiver must support all 4 modes:

  • Mode I for Band III, Earth
  • Mode II for L-Band, Earth and satellite
  • Mode III for frequencies below 3 GHz, Earth and satellite
  • Mode IV for L-Band, Earth and satellite

[edit] Services and ensembles

Various different services are embedded into one ensemble (which is also typically called a multiplex). These can be a number of different things, including:

  • Primary services, like main radio stations
  • Secondary services, like additional sports commentaries
  • Data services

[edit] Bitrates

An ensemble has a maximum bitrate that can be carried, but this depends on which error protection level is used. However, all DAB multiplexes can carry a total of 864 "capacity units". The number of capacity units, or CU, that a certain bit rate level requires depend on the amount of error correction added to the transmission — the stronger the error protection is (which requires higher levels of redundant information to be added) the more robust the transmission will be, but this reduces the overall bit rate that can be transmitted. In the UK, most services transmit using 'protection level three', being an FEC of 0.5 which equates to a maximum bit rate per multiplex of 1152 kbit/s.

[edit] 'DAB version 2'

WorldDMB, the organisation in charge of the DAB standards, announced In a press release in November 2006<ref>http://www.worlddab.org/upload/uploaddocs/WorldDMBPress%20Release_November.pdf</ref> , that DAB would be adopting the HE-AAC audio codec<ref>http://www.worlddab.org/upload/uploaddocs/WorldDMBPress%20Release_November.pdf</ref>, which is also known as AAC+. Also being adopted are the MPEG Surround format, and stronger error correction coding called Reed-Solomon coding. WorldDMB are to unveil the name for the new DAB standard in January 2007<ref>http://www.worlddab.org/upload/uploaddocs/WorldDMBPress%20Release_November.pdf</ref>. The most likely names for the new standard are 'DAB+', 'DABv2', 'DAB-2', 'DAB 2.0' or 'DMB'.

Receivers that support the new DAB standard will be released in the UK in 2007, and Ofcom has said that services using the old MPEG-1_Audio_Layer_II audio format used on the old DAB system can be switched off once the vast majority of receivers can support the new HE-AAC audio format. The new HE-AAC audio format is around 3 - 4 times as efficient as the old MPEG-1_Audio_Layer_II audio format, so this will allow 3 - 4 times as many stations to transmit as is currently possible, or the audio quality can be increased, or a combination of both these things can occur.

DAB and DAB-2 can't be used for mobile TV because they don't 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 subchannel 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.

[edit] USA

The three US IBOC schemes are being promoted by iBiquity Digital. All three schemes are based on "Orthogonal Frequency Division Multiplexing (OFDM)" modulation, which is also used for European terrestrial digital TV broadcast (DVB-T). All three companies have now entered into a joint venture to form iBiquity.

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 the US.

[edit] Japan and Korea

Japan has started terrestrial sound broadcasting using ISDB-Tsb and 2.6 GHz Satellite Sound digital broadcasting, with Korea using the latter as well.

[edit] Single frequency networks

Image:Merge-arrow.gif
It has been suggested that this article or section be merged into Single-frequency_network. (Discuss)

A major advantage of DAB over FM is the provision of single frequency networks (SFNs). Provided the transmitters are synchronised, the multiplex licence holder may operate several in a relatively small geographic area at the same multiplex frequency without any destructive interference occurring at the receiver. SFNs allow substantial service areas to be built up steadily and efficiently as the network develops, funding allows and frequency spectra becomes available. Compared to FM where service areas operating at the same carrier frequency cannot overlap, a typical DAB network will comprise several relatively low powered closely spaced transmitters operating at the same multiplex frequency. This saves frequency spectrum, reduces the complexity and cost of the transmitter hardware and avoids the need for frequent re-tuning of mobile receivers as they move about within the network. It also means that each transmitter has a smaller audience, thus mitigating the service loss should a transmitter fail. Because of this synchronisation, receivers which are located in places where the service areas of two or more transmitters overlap will interpret one of the signals as a slightly delayed version of the other, effectively an apparent deliberate multipath interference. The actual delays will depend on the radio path geometry and any extra delays that may be added artificially when the network is commissioned. Within the receiver then a relatively simple form of delay filtering may be applied to extract the desired data.

[edit] Regional implementations of DAB

[edit] Australia

In October 2005, Helen Coonan, the Australian Minister for Communications, Information Technology and the Arts, announced Australia's plans for digital radio. Helen Coonan announced the adoption of a Eureka 147 system but added that the Australian radio industry should investigate the use of newer audio compression technology that would allow more services to be broadcast in the available spectrum, which has been reserved in Band III and L-Band <ref>Minister Helen Coonan's speech to the Australian radio industry 14 October 2005</ref>.

The Australian Government has set a launch date for digital radio in the country with 1 January 2009 being the set date.

[edit] Austria

In Austria so far there is just a test operation of DAB. The national broadcasting company ORF tests Digital Audio Broadcasting in the capital Vienna and in the province Tirol.

[edit] Belgium

DAB was launched in Belgium in 1997. The transmitter network is rather dense, resulting in an excellent mobile coverage. The ensembles include audio services (four new "DAB only" programmes and simulcasts from FM),<ref>http://www.digitaleradio.be/dab/home/home.html</ref> programme related data (program type, announcements and dynamic label) and data services. The receiver situation is improving the last year. Tuners, kitchen radios and handheld devices are on the market and sales are growing fast as a result of a marketing campaign. Investments in new DAB services and more networks are expected, especially for the commercial and regional networks. An upgrade of the transmitter network for excellent indoor coverage is planned.

[edit] Canada

Promotion of digital radio is mostly taking place by the Canadian Association of Broadcasters, which represents private broadcasters in Canada, though an organization called Digital Radio Rollout, Inc. [3]

Currently, CBC operates DAB stations in Ottawa, Toronto, Vancouver, Montreal, and Windsor, Ontario. All these markets also contain commercial stations that operate secondary DAB frequencies. All together, according to the 2005 edition of WRTH, 11 million potential listeners will be covered by this service. There are stations in Halifax, Nova Scotia that are currently field-testing DAB and a DAB-only station is schduled to operate soon. Altogether, DAB has been well-received in Canada and coverage, whilst still using the L-band, is excellent. Compared to CHUM's subscription digital radio service using the L-band, the stations currently operating in DAB right now are free-to-air.

On 16 June 2005 the CRTC approved two subscription satellite digital services, which are partnerred with the Sirius (Sirius Canada Inc.) and XM services (Canadian Satellite Radio Inc.) in the United States, and a third subscription service to be provided by the CHUM radio group using terrestrial transmitters that will only cover mainly urban areas in the south. This system intends to use a derivative of the DAB system for transmission. Among the services planned to be offered on the channels includes urban music, rock, oldies, dance, Motown, francophone, classical, opera, Christian, Aboriginal, and radio theatre. With Bell Globemedia's purchase of CHUM, however, there is currently no indication regarding how this will affect the service.

Channels used in the Canadian implementation of DAB (L-Band):

  1. 1452.816 MHz
  2. 1454.560 MHz
  3. 1456.304 MHz
  4. 1458.048 MHz
  5. 1459.792 MHz
  6. 1461.536 MHz
  7. 1463.280 MHz
  8. 1465.024 MHz
  9. 1466.768 MHz
  10. 1468.512 MHz
  11. 1470.256 MHz
  12. 1472.000 MHz
  13. 1473.744 MHz
  14. 1475.488 MHz
  15. 1477.232 MHz
  16. 1478.976 MHz
  17. 1480.720 MHz
  18. 1482.464 MHz
  19. 1484.208 MHz
  20. 1485.952 MHz
  21. 1487.696 MHz
  22. 1489.440 MHz
  23. 1491.184 MHz

[edit] China

China decided to use DAB and T-DMB for broadcasting radio and televisions. China placed early in 2006 an order of 500 000 receivers. They already broadcast some programs at Beijing and Guangdong.

[edit] Czech Republic

There is currently no DAB coverage in the Czech Republic. However the infrastructure is in place to provide coverage to 20% of the population around Prague.<ref>http://tdab.cz/</ref> In April 2006 the Czech Parliament adopted a version of the media law focused on digital broadcasting. Public Czech Radio has applied for permission to broadcast DAB. The new digital radio stations CRo 4 - Radio WAVE, Radio Cesko, Radio Leonardo and Radio D-dur are provided by Czech radio. These programs are currently transmitting via DVB-T and the Internet. The three current radio stations from Plzen applied for new DAB frequencies in L-band. The Czech Council for Radio and TV broadcasting announced that the DAB licence procedure will start on autumn 2006.

[edit] Denmark

In Denmark an extensive rollout of DAB has been made by Danmarks Radio. The goal is that the entire country should be covered in 2007. More info can be obtained from http://www.dabradio.dk/ including a current coverage map. 700,000 Danes (13%) had access to a DAB radio in 2006<ref>http://politiken.dk/erhverv/article168837.ece</ref> and DAB radio is increasing in popularity.

[edit] Finland

Finland switched off their DAB transmitters in 2005. Finland is now investigating providing digital radio via other digital broadcasting systems, such as DVB-H.

[edit] France

In a public consultation on digital radio, the four largest French radio broadcasters objected to using the current DAB system; new stakeholders were in favour of keeping compatibility with the UK version. The French communications regulator CSA decided to launch a technical forum about the right choice for digital radio. Some broadcasters asked the regulator to strictly adopt the digital radio system in order to preserve transborder roaming (car radio) and some suggested to design technical variants of the European standard. Implementation of Band III has been strongly suggested by most contributors. The five largest French radio broadcasters are currently participating in a trial of the DVB-H and T-DMB digital broadcasting system in Paris.

Only one VHF T-DAB assignment is implemented. In France T-DAB is implemented in L-band. The percentage of households that can already, or are expected in the near future to receive the quoted number of VHF multiplexes is not significant. However, for the future digital Plan, France has decided to implement T-DAB in Band III. For the time being, CSA has authorised for 6 months an experiment over Paris for T-DMB on channel 11B. The experiment is established by TF1, Europe 1, Europe 2 and VDL, and for duration of six months, beginning on 15 October 2005. It is authorised to broadcast a set of programmes of radio or television having been already the object of agreements with the Council.

[edit] Germany

After some years of test operation, regular T-DAB service was launched in April 1999. Licences have been granted to 8 different network operators. They use the T-DAB frequency blocks of the WI95 Plan. The cumulative area of all allotment areas corresponds to seamless coverage of Germany. All network operators are obliged to implement the networks within a time frame of 5 to 8 years in order to provide coverage of more than 80% of the total population. At present about 85% of the German households are located within the service area of T-DAB transmitter networks. However, the market penetration of receiver equipment is still low. In order to improve the situation, several activities are underway. The platform of the "Initiative for Digital Broadcasting" chaired by the Federal Ministry of Economics and Labour investigates T-DAB issues and aspects of improving the market development. An "Initiative for Marketing Digital Radio" has been founded by the German network operators and is an open forum for equipment manufacturers, program providers, network operators and marketing experts. An associated "Initiative for Marketing Digital Radio" plays its role as marketing enterprise and is equipped with a budget which is adequate to organize and perform PR- and marketing activities on a larger scale.<ref>http://www.digitalradio.de/</ref>

[edit] Indonesia

Indonesia will begin DAB trial transmission on August 2006. There will be four DAB radio stations: Prambors, Ramako, Sonora and I-Radio. On the trial period, DAB radios will use 10 D FHV frequency.

[edit] Ireland

On 20 December 2005, Ireland's national broadcaster and owner of the sole national transmission network, RTÉ, announced that DAB trials would begin along the east coast on 1 January 2006. This date is 80 years after Radio Éireann (RTÉ's predecessor) began. By 5 January, two transmitters, Clermont Carn and Three Rock Mountain, were transmitting a single multiplex on channel 12C, carrying 6 channels - RTÉ Radio 1, RTÉ 2fm, RTÉ Lyric FM, Raidió na Gaeltachta, Today FM and the World Radio Network, all at 192 kbit/s. In May, this was reduced to just RTÉ Radio 1 and RTÉ 2FM at 160 kbit/s. The test DAB transmissions ceased on 13 July and there have not been any DAB transmissions since then, although a further trial is expected in late 2006.

DAB development is limited, at least in the short term, by the lack of Band III frequencies - only 12C is allocated to RTÉ for the entire country, with 12A allocated to commercial broadcasting. 11B, 11C, 11D and 12D are also allocated to regional services, but collision with Band III television and Northern Irish DAB allocations make these mostly unusable for the time being.

Local radio franchise areas have been allocated an L band DAB channel, as well as any counties which do not match radio franchises. L band capable receivers are relatively rare in Europe, although are the standard in Canada and other countries.

[edit] 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.

[edit] Malta

T-DAB spectrum licenses have been awarded in March 2006. In August 2005, the Malta Communications Authority (MCA) together with the Ministry for Competitiveness and Communications published Malta's policy and implementation strategy on T-DAB. It is expected that the 3 T-DAB band III frequency blocks allotted to Malta under the WI-95 allotment plan be made available to those interested to provide T-DAB services in Malta.

[edit] The Netherlands

In March 2005, following criticism from politicians from all parties, the Dutch Minister of Economic Affairs Laurens Jan Brinkhorst announced that The Netherlands has postponed plans to push ahead with rolling out DAB, and will instead wait for new technologies to arrive so that they can be assessed. The new technologies, which include the new version of DAB, DRM+ and DVB-H, are much more efficient than the current version of DAB, so an announcement to assess the new technologies makes it very unlikely that The Netherlands will end up using the current version of DAB.

Dutch public radio has been transmitting in block 12C since 2004. Nine radio channels are available, including a non-stop Top 2000 channel and a continuous repetition of the last news bulletin. Territorial coverage of the Netherlands is currently limited.

[edit] New Zealand

New Zealand is trailing DAB since November 2006 in Wellington and west Auckland

[edit] Norway

More than 15 stations are available on DAB, including all of NRKs broadcast channels and commercial P4 as well as their DAB-only transmisson P4 Bandit. There is also a private DAB broadcaster with a music channel, Moox Radio. An audio book channel, Bokradioen, was taken off air because of royalty issues. In addition NRK has several niche DAB channels, some of which also are available via the FM net in parts of the country. A national commercial broadcaster Kanal 24 recently received a DAB licence. As the DAB network is expanded, some local radio stations are licenced to broadcast via DAB.

NRK Alltid klassisk started broadcasting in June 1995 and was the world's first all-digital around-the-clock radio, with non-stop classical music. NRK Alltid nyheter (news radio) started broadcasting in 1997, at a time when there were only about 25 DAB receivers in Norway. These stations are available on FM in some major locations.

DAB radio in Norway is divided into a national multiplex on channel 12D, and several regional multiplexes. The regional multiplexes broadcast versions of NRK P1 with regional programming and several other NRK channels which do not fit on the national band.

The first test transmissions were started in the middle of the 1990s. As of December 2005 about 70% of the population is potentially covered by DAB. However, FM is by far the most common method of radio distribution. In Norway the DAB market was very small until the close of 2004, with few available receivers and little demand. Since Christmas 2004, the market has been rapidly growing; more than 50,000 units were sold in 2005, and more than 20,000 units sold so far in 2006<ref>50 000 DAB-radioer solgt</ref>, and DAB radio is increasing in popularity.

As of the 26th of november 2006, the norwegian goverment decided to let DAB coverage expand to 80% of the population, with two multiplexes available in all areas in May 2007. Norway aims at reaching full national DAB coverage before 2014.

A government working group appointed by Medietilsynet released a report on 19 December 2005 where it proposes that all FM distribution should be switched off by 2014, to be replaced by DAB, and DRM for smaller local radio channels.<ref>http://medieforvaltning-no.inforce.dk/graphics/SMF/Rapporter/Kringkasting/DABDelrapport_03.pdf</ref>

[edit] Poland

"Polskie Radio S.A.", the Polish public sound broadcaster, had to stop broadcast its 4 audio services in Band II DAB Block (105,008 MHz), which covered 8% of the Polish population, due to the lack of electromagnetic compatibility with the existing VHF FM services. In October 2001 the test transmission was resumed in Warsaw on the DAB Block 10B. It is foreseen that this transmission will form the first part of the SFN covering Central Poland.

In January 2004 Poland's Office of Telecommunications and Post Regulation (URTiP) has presented a new concept of a frequency planning in Band III. This idea is based on full exploitation of the spectrum by digital sound and television broadcasting after analogue switch off and changing channel spacing from 8 to 7 MHz. This allows to accommodate three national T-DAB layers and one national DVB-T multiplex at the same time.

The official governmental document concerning the digital radio is still being prepared. Unlike in the case of DTT it will not be a possible strategy but rather an analysis of implementation of the system available: T-DAB/DMB or DVB-T/DVB-H. One of the document's recommendations is to plan digital radio networks as flexible as possible in order to be able to implement a chosen system.

Polskie Radio (the public broadcaster) intends to locate its own audio services within the DVB-T multiplex.

[edit] Romania

As of summer 2005, in Bucharest there is a single emitter that broadcasts five radio stations multiplexed on channel 12A (223,936 MHz - Band III). The five digital radio stations (three public service and two commercial) are: Radio România Actualitati, Radio România Muzical, Antena Bucurestilor, Radio Romantic and ProFM.<ref>http://www.investromania.ro/news/news.php?aid=2606</ref>

[edit] Russian Federation

There are no T-DAB transmitters working at present time, but two licences for commercial T-DAB broadcasting services supposed to be granted now, because of existing interest and demands. [citation needed]

[edit] Singapore

In Singapore, MediaCorp's SmartRadio was launched on 19 November 1999. Using the Eureka 147 DAB system, SmartRadio provides six digital-only stations and eight simulcast FM services, along with images and text to supplement the audio. Singapore was the firs country to reach full DAB coverage <ref>http://www.smartradio.sg/aboutsr.htm</ref>.

[edit] Sweden

On 14 December 2005 the Swedish Culture minister, Leif Pagrotsky, announced that the Swedish government was freezing investment in DAB, citing that DAB was very expensive to transmit and that cheaper digital radio systems should be investigated, and digital radio should also be transmitted via the Internet and via the digital terrestrial TV system. The government decision has been criticised by Swedish broadcasters. DAB transmissions continue, however, with coverage of Stockholm and other cities.

On 27 November 2006 the Swedish Culture minister, Lena Adelsohn Liljeroth signed a bill ending the pursuit of DAB by the Swedish government.

[edit] Switzerland

The extension map shows the order in which the various regions will be added to the DAB network. In 2005, the North-Eastern parts of Switzerland and the main traffic artery in the Ticino will be fitted out for DAB reception. The year after, Central Switzerland will be added to the DAB reception area and by the end of 2007, the whole German speaking population should be within reach of one of the DAB stations. The tunnels along the main traffic arteries should be covered by DAB by the end of 2007. The remaining regions will be fitted out for DAB reception during the years 2007 to 2010. By 2010, DAB will be available in all of Switzerland.<ref>http://www.dab-digitalradio.ch/</ref>

[edit] United Kingdom

In the United Kingdom, the rollout of digital radio is proceeding. Experimental transmissions by the BBC started in 1990 with permanent transmissions covering London in September 1995. In September 1997 the BBC announced its national DAB rollout plans and soon reached 65% coverage. In 2006 the majority of national broadcasters all broadcast on DAB (as well as traditional AM/FM). As well as being available on DAB, many radio stations are also available via Freeview, digital satellite, cable and the Internet.

The public service broadcaster, the BBC, has been promoting its DAB Digital Radio stations since September 1995 and at present (2006) covers about 85% of the population, including the major motorway network. Progress beyond this figure seems to be slow, leaving some 9,000,000 of the UK population who still do not know when they will be able to receive DAB. The switch from analogue TV to digital TV (DSO) is imminent, possibly relegating DAB to a lower order of priority. FM will not be switched off when analogue TV is switched off, however, which is a growing misconception.

Receivers are growing in availability, and the £30 barrier was broken in 2006.

UK broadcasters and Ofcom have used lower bit rates to increase the choice & variety of radio stations in each multiplex, leading to critisms of reduced audio fidelity (see the Criticism of DAB in the UK section below).

As of August 2005, the BBC national DAB multiplex contains a number of different services, including Radios 1-5, and digital-only services such as Radio Five Live Sports Extra, 6 Music, 1Xtra and BBC7, as well as an EPG.

The Digital One national commercial multiplex contains eight audio stations, an EPG and an experimental video service for mobile phones which was launched in October 2006. Coverage of commercial national DAB Digital Radio is at 88% of the population. It currently operates the world's biggest digital radio network, with 103 transmitters. Digital One began broadcasts on 15 November 1999 with 69% coverage and since then its DAB network has always been more extensive than the BBC's. Digital One also developed along with Frontier Silicon a low cost silicon chip used in the majority of receivers and is directly responsible for DAB receiver prices falling below £100 in 2002, and as little as £30 in 2006. As a result of this, DAB portable radios are now outselling their analogue counterparts at the highstreet chain Currys.Digital (formerly Dixons).

In addition to the national services, by the end of 2004 there were 48 local and regional radio multiplexes, providing over 250 commercial and 34 BBC stations. For example, in London there are already more than 51 different digital stations available. Further regional and local multiplexes are being planned by Ofcom, the UK regulator. The UK leads the world in having the largest number of DAB stations broadcasting in the world, and the highest numbers of listeners to these services.[4]

[edit] Criticisms of DAB in the UK

Although DAB offers a vastly greater choice & variety of radio stations than FM, the audio quality is poorer than perfect reception on FM as 98% of all stereo stations on DAB in the UK use a bit rate of 128 kbit/s with the MP2 audio codec<ref>http://www.david.robinson.org/commsbill/#1_2_3 </ref>, which is a bit rate at which the MP2 audio codec has been officially classified as providing 'Annoying' audio quality in blind listening tests <ref> http://www.telos-systems.com/techtalk/00222.pdf (page 17) - the curve for MP2 is labelled 'LII' </ref>. In order to increase the choice of stations in each multiplex, broadcasters have utilised lower bit rates. A bit rate of 128 kbit/s would result in satisfactory sound quality if the audio codec were MP3 or AAC, however DAB uses the MP2 audio codec, which is meant to be used at bit rate levels of 192 kbit/s or higher to provide good audio quality.

The following paragraph about bit rate levels to be used on DAB was written by an engineer in the BBC Research & Development department and highlights why bit rates as low as 128 kbit/s should not be used on DAB:

   
Digital audio broadcasting
 A value of 256 kbit/s has been judged to provide a high quality stereo broadcast signal [4]. However, a small reduction, to 224 kbit/s is often adequate, and in some cases it may be possible to accept a further reduction to 192 kbit/s, especially if redundancy in the stereo signal is exploited by a process of 'joint stereo' encoding (i.e. some sounds appearing at the centre of the stereo image need not be sent twice). At 192 kbit/s, it is relatively easy to hear imperfections in critical audio material.
   
Digital audio broadcasting
 
— [5]

On 6 July 2006 the BBC reduced the bitrate transmission of Radio 3 from 192 kbit/s to 160 kbit/s. The resulting degradation of audio quality prompted a number of complaints being made to the Corporation.<ref>http://www.for3.org/second/BBC_R3_news.html#poorDAB</ref> The BBC later announced that following this testing of new equipment, it would resume the previous practice of transmitting Radio 3 at 192 kbit/s whenever there were no other demands on bandwidth.<ref>http://www.for3.org/second/campaign_update.html#dab_rethink</ref>

As well as the problem with the audio quality, about 90 UK local radio stations are either unable to transmit on DAB because there is no space for them on a local DAB multiplex or because they are unable to pay the high transmission costs of DAB that the multiplex operators (that are mostly owned by the large commercial radio groups) are being charged by transmission companies and passing on.

Ofcom announced in 2005 that it regarded DRM (Digital Radio Mondiale) as an option for the local stations unable to secure carriage or unable to pay the high transmission costs of DAB.

[edit] United States

While traditional radio broadcasters are trying to "go digital", major US automobile manufacturers are exploring DAB satellite radio from orbit on a subscription basis.

Ford and DaimlerChrysler 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. Satellite DAB would allow people on the road to listen to the same stations in any location in the country.

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 Boeing Sea Launch boosters. Back-up ground transmitters (repeaters) will be built in cities where satellite signals could be blocked by big buildings.

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.

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

While terrestrial DAB may be a non-starter (in North America), satellite DAB has some clear advantages. People who lead mobile existences would find it convenient to access familiar stations while on the road, for example. Terrestrial analog broadcast stations are apprehensive about what satellite DAB may do to their business.

The perceived wisdom of the radio industry is that the medium has two great strengths: it is free and it is local. Since satellite radio is neither of these things, it is seen as a niche market at best. However, in recent years, satellite radio 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.

[edit] Third World

Digital radio is now being provided to the third (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.

[edit] See also

[edit] References

<references/>
  • Stott, J. H.; The How and Why of COFDM, BBC Research Development

[edit] External links

de:Digital Audio Broadcasting es:Radiodifusión de audio digital fr:Digital Audio Broadcasting nl:Digital Audio Broadcasting ja:DAB no:DAB nn:DAB ru:Цифровое радио fi:DAB sv:DAB

Retrieved from "http://en.wikivisual.com/index.php/Digital_audio_broadcasting"
Personal tools