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Encyclopedia > Digital audio broadcasting
Countries with DAB, DAB+ or DMB broadcasts. (Source:WorldDMBForum country profile)
Countries with DAB, DAB+ or DMB broadcasts. (Source:WorldDMBForum country profile)

Digital Audio Broadcasting (DAB), also known as Eureka 147, is a digital radio technology for broadcasting radio stations, used in several countries, particularly in Europe. As of 2006, approximately 1,000 stations worldwide broadcast in the DAB format[1]. This article needs to be cleaned up to conform to a higher standard of quality. ... Broadcasting is the distribution of audio and/or video signals which transmit programs to an audience. ... A radio station is an audio (sound) broadcasting service, traditionally broadcast through the air as radio waves (a form of electromagnetic radiation) from a transmitter to an antenna and a thus to a receiving device. ...


The DAB standard was designed in the 1980s, and receivers have been available in many countries for several years. Proponents claim the standard offers several benefits over existing analogue FM radio, such as higher-fidelity audio, more stations in the same broadcast spectrum, and increased resistance to noise, multipath, fading, and co-channel interference. However, listening tests carried out by experts in the field of audio have shown that the audio quality on DAB is lower than on FM in the UK, which is the country that accounts for the vast majority of global DAB sales-to-date, due to 98% of stereo stations using a bit rate of 128 kbit/s with the MP2 audio codec, which is unable to match the audio quality provided by FM.[2][3][4] The word receiver has a number of different meanings: In communications and information processing, a receiver is the recipient (observer) of a message (information), which is sent from a source (object). ... An analog or analogue signal is any time continuous signal where some time varying feature of the signal is a representation of some other time varying quantity. ... The abbreviations FM, Fm, and fm may refer to: Electrical engineering Frequency modulation (FM) and its most common applications: FM broadcasting, used primarily to broadcast music and speech at VHF frequencies FM synthesis, a sound-generation technique popularized by early digital synthesizers Science Femtometre (fm), an SI measure of length... For the financial services company, see Fidelity Investments. ... Although some radiations are marked as N for no in the diagram, some waves do in fact penetrate the atmosphere, although extremely minimally compared to the other radiations The electromagnetic (EM) spectrum is the range of all possible electromagnetic radiation. ... This article is about noise as in sound. ... PRIMERGY MultiPath PRIMERGY MultiPath supports redundant Fiber Channel paths, the configured connections between server and subsystem that are such an important component of disaster-tolerant servers and clusters. ... Fading (or fading channels) are mathematical models for the distortion that a carrier-modulated telecommunication signal experiences over certain propagation media. ... In communications and especially in telecommunications, an interference is anything which alters, modifies, or disrupts a message as it travels along a channel between a source and a receiver. ... In telecommunications and computing, bit rate (sometimes written bitrate) is the frequency at which bits are passing a given (physical or metaphorical) point. It is quantified using the bit per second (bit/s) unit. ... MPEG-1 Audio Layer II (MP2, sometimes Musicam) is an audio codec defined by ISO/IEC 11172-3. ...


An upgraded version of the system was released in February 2007, which is called DAB+. DAB+ is not backward-compatible with DAB, which means that only receivers that support the new standard will be able to receive DAB+ broadcasts. DAB+ is 2 - 3 times more efficient than DAB due to the adoption of the AAC+ audio codec[5], which means that DAB+ can provide higher audio quality and more radio stations than DAB allows. Reception quality will also be more robust on DAB+ than on DAB due to the addition of Reed-Solomon error correction coding. In technology (especially computing), backward compatibility has several related but differing meanings: A system is backward compatible if it is compatible with earlier versions of itself, or sometimes other earlier systems, particularly systems it intends to supplant. ... MPEG-4 Part 3 (formally ISO/IEC 14496-3) is the third part of the ISO/IEC MPEG-4 international standard. ... Reed-Solomon error correction is a coding scheme which works by first constructing a polynomial from the data symbols to be transmitted and then sending an over-sampled plot of the polynomial instead of the original symbols themselves. ...


Italy has started transmitting DAB+ stations, Malta and Switzerland are due to launch DAB+ stations in 2008, and Australia and Germany planning on launching DAB+ in 2009. The radio industry in the UK is expecting DAB+ stations to launch between 2010 - 2013[6], and podcast services using the DAB+ format will be launched in the UK in 2009[7].

Contents

History

DAB has been under development since 1981 at the Institut für Rundfunktechnik (IRT). In 1985 the first DAB demonstrations were held at the WARC-ORB in Geneva and in 1988 the first DAB transmissions were made in Germany. Later DAB (or Eureka-147) was developed as a research project for the European Union (Eureka project number EU147), which started in 1987 on initiative by a consortium formed in 1986. The MPEG-1 Audio Layer II ("MP2") codec was created as part of the EU147 project. DAB was the first standard based on orthogonal frequency division multiplexing (OFDM) modulation technique, which since then has become one of the most popular transmission schemes for modern wideband digital communication systems. The Institut für Rundfunktechnik GmbH (IRT) is the research centre of the German broadcasters (ARD / ZDF / DLR), Austrias broadcaster (ORF) and the Swiss public broadcaster (SRG/SSR). ... MPEG-1 Audio Layer II (MP2, sometimes Musicam) is an audio codec defined by ISO/IEC 11172-3. ... Orthogonal frequency division multiplexing (OFDM) is a method of digital modulation causing a signal to be split into several narrowband channels at differing frequencies. ...


A choice of audio codec, modulation and error-correction coding schemes and first trial broadcasts were made in 1990. Public demonstrations were made in 1993 in the United Kingdom. The protocol specification was finalized in 1993 and adopted by the ITU-R standardization body in 1994, the European community in 1995 and by ETSI in 1997. Pilot broadcasts were launched in several countries in 1995. The ITU Radiocommunication Sector (ITU-R) is a standards body subcommittee of the International Telecommunication Union (ITU) relating to radio communication. ... The European Telecommunications Standards Institute (ETSI) is a standardization organization of the telecommunications industry (equipment makers and network operators) in Europe, with worldwide projection. ...


The UK was the first country to receive a wide range of radio stations via DAB. Commercial DAB receivers began to be sold in 1999 and over 50 commercial and BBC services were available in London by 2001. A radio station is an audio (sound) broadcasting service, traditionally broadcast through the air as radio waves (a form of electromagnetic radiation) from a transmitter to an antenna and a thus to a receiving device. ... For other uses, see BBC (disambiguation). ...


By 2006, 500 million people worldwide 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 world wide.[8] The United Kingdom of Great Britain and Northern Ireland is a country in western Europe, and member of the Commonwealth of Nations, the G8, the European Union, and NATO. Usually known simply as the United Kingdom, the UK, or (inaccurately) as Great Britain or Britain, the UK has four constituent...


The standard was coordinated by the European DAB forum, formed in 1995 and reconstituted to the World DAB Forum in 1997, which represents more than 30 countries. In 2006 the World DAB Forum became the World DMB Forum which now presides over both the DAB and DMB standard. The World DAB Forum is an international non-governmental organisation which defines the standards for Digital audio broadcasting. ... The World DAB Forum is an international non-governmental organisation which defines the standards for Digital audio broadcasting. ... The WorldDMB (formerly World DAB Forum) is an international non-governmental organisation which defines the standards for Digital audio broadcasting. ...


In October 2005, the World DMB Forum instructed its Technical Committee to carry out the work needed to adopt the AAC+ audio codec and stronger error correction coding. This work led to the launch of the new DAB+ system. The WorldDMB (formerly World DAB Forum) is an international non-governmental organisation which defines the standards for Digital audio broadcasting. ... MPEG-4 Part 3 (formally ISO/IEC 14496-3) is the third part of the ISO/IEC MPEG-4 international standard. ... In mathematics, computer science, information theory, the issue of error correction and detection has great practical importance in maintaining data (information) integrety accross noisy channels and less than relyable storage mediums. ...


DAB and FM/AM compared

Traditionally radio programmes 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. The abbreviations FM, Fm, and fm may refer to: Electrical engineering Frequency modulation (FM) and its most common applications: FM broadcasting, used primarily to broadcast music and speech at VHF frequencies FM synthesis, a sound-generation technique popularized by early digital synthesizers Science Femtometre (fm), an SI measure of length... AM broadcasting is radio broadcasting using Amplitude Modulation. ... In telecommunications, multiplexing (also muxing or MUXing) is the combining of two or more information channels onto a common transmission medium using hardware called a multiplexer or (MUX). ... DAB ensembles are groups of Digital audio broadcasting broadcasters transmitting multiple digital radio channels on a single radio transmission. ...


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 reduces the total bit rate available for streams. DAB ensembles are groups of Digital audio broadcasting broadcasters transmitting multiple digital radio channels on a single radio transmission. ... DAB ensembles are groups of Digital audio broadcasting broadcasters transmitting multiple digital radio channels on a single radio transmission. ...


Use of frequency spectrum and transmitter sites

DAB gives substantially higher spectral efficiency, measured in programmes per MHz and per transmitter site, than analogue communication. However, since there are no plans yet to cease analogue FM transmissions, and most radio channels are transmitted both over FM and digitally, this advantage is not exploited to a high degree. Spectral efficiency or spectrum efficiency refers to the amount of information that can be transmitted over a given bandwidth in a specific digital communication system. ...

Numerical example: FM requires 0.3 MHz per programme. The frequency reuse factor is approximately 15, meaning that only one out of 15 transmitters can use the same channel frequency without problems with co-channel interference, i.e. cross-talk. This results in 1 / 15 / (0.3 MHz) = 0.22 programmes/transmitter/MHz. DAB with 192 kbit/s codec requires 1.536 MHz * 192 kbit/s / 1136 kbit/s = 0.26 MHz per audio programme. The frequency reuse factor for local programmes and multi-frequency broadcasting networks (MFS) is typically 4, resulting in 1 / 4 / (0.26 MHz) = 0.96 programmes/transmitter/MHz. This is 4.3 times as efficient. For single frequency networks (SFN), for example of national programmes, the channel re-use factor is 1, resulting in 1/1/0.25 MHz = 3.85 programmes/transmitter/MHz, which is 17.3 times as efficient as FM. This article or section is not written in the formal tone expected of an encyclopedia article. ... Co-channel interference is interference from 2 different radio stations on the same frequency. ... Metropolitan Fiber Systems was a telecommunications service provider aquired by Worldcom in 1997. ...

Note the above capacity improvement may not always be achieved at the L-band frequencies, since these are more sensitive to obstacles than the FM band frequencies, and may cause shadow fading for hilly terrain and for indoor communication. The number of transmitter sites or the transmission power required for full coverage of a country may be rather high at these frequencies, to avoid that the system becomes noise limited rather than limited by co-channel interference.


Sound quality

The original objectives of converting to digital transmission were to enable higher fidelity, more stations and more resistance to noise, co-channel interference and multipath than in analogue FM radio. However, in the UK, Denmark, Norway and Switzerland, which are the leading countries with regard to implementing DAB, 98% of stereo radio stations on DAB have a lower sound quality than FM due to the bit rate levels they use being too low for the inefficient MPEG Layer 2 audio codec to provide good audio quality.[3] For the financial services company, see Fidelity Investments. ... PRIMERGY MultiPath PRIMERGY MultiPath supports redundant Fiber Channel paths, the configured connections between server and subsystem that are such an important component of disaster-tolerant servers and clusters. ... The abbreviations FM, Fm, and fm may refer to: Electrical engineering Frequency modulation (FM) and its most common applications: FM broadcasting, used primarily to broadcast music and speech at VHF frequencies FM synthesis, a sound-generation technique popularized by early digital synthesizers Science Femtometre (fm), an SI measure of length... MPEG-1 Audio Layer II (MP2, sometimes Musicam) is an audio codec defined by ISO/IEC 11172-3. ...


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: For other uses, see BBC (disambiguation). ...

A value of 256 kbit/s has been judged to provide a high quality stereo broadcast signal. 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.
 
— BBC R&D White Paper WHP 061 June 2003[9]

On 6 July 2006 the BBC reduced the bit-rate of transmission of Radio 3 from 192 kbit/s to 160 kbit/s. The resulting degradation of audio quality prompted a number of complaints to the Corporation.[10] 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.[11] is the 187th day of the year (188th in leap years) in the Gregorian calendar. ... Year 2006 (MMVI) was a common year starting on Sunday of the Gregorian calendar. ...


The UK Government seeks to maximize license-revenue from the available spectrum.[citation needed] Therefore it ‘squeezes in’ as many stations as possible.


‘Squeezing in’ techniques include:

  • Minimizing the bit-rate, to the lowest level of sound-quality that listeners are willing to tolerate. (This is generally 128 kbit/s for stereo. BBC Radio 3 is exceptional in using 192 kbit/s. There was an outcry when BBC Radio 3 reduced the bit-rate to 160 kbit/s, so 192 kbit/s was restored.)
  • Heavy compression - compressing the dynamic range of a signal (reducing sound-quality).
  • Having few digital channels broadcasting in stereo.

These factors reduce sound-quality to the point where it is technically inferior to FM.


Maximizing Government license-revenue is not such an issue with TV, so BBC TV audio streams use a bit-rate of 256 kbit/s MP2.


Despite some criticism of sound quality (see the criticism section), a recent survey among radio listeners in the UK, a territory where the low bit-rates are often criticised, revealed that 94% experience a sound quality that is "much better", "better" or "the same" as FM.[12]


Benefits of DAB

Current AM and FM terrestrial broadcast technology is well established, compatible, and cheap to manufacture. Benefits of DAB over analogue systems are explained below. Terrestrial radio is a term which encompasses the AM and FM ground-based radio technologies, the term was coined around Howard Sterns move to Sirius Satellite Radio. ...


Improved end-user features

DAB radios automatically tune to all the available stations, offering a list of all stations.


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 and news or traffic updates. Advance programme guides can also be transmitted. A similar feature also exists on FM in the form of the RDS. (However, not all FM receivers allow radio stations to be stored by name.) The abbreviations FM, Fm, and fm may refer to: Electrical engineering Frequency modulation (FM) and its most common applications: FM broadcasting, used primarily to broadcast music and speech at VHF frequencies FM synthesis, a sound-generation technique popularized by early digital synthesizers Science Femtometre (fm), an SI measure of length... Radio Data System, or RDS, is a standard from the European Broadcasting Union for sending small amounts of digital information using conventional FM radio broadcasts. ...


Some radios offer a pause facility on live broadcasts, caching the broadcast stream on local flash memory, although this function is limited.


More stations

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 only marginally more efficient than FM for local radio stations. For other uses, see SFN (disambiguation). ...


In certain areas — particularly rural areas — the introduction of DAB gives radio listeners a greater choice of radio stations. For instance, in South Norway, radio listeners overnight experienced an increase in available stations from 6 to 21 when DAB was introduced in November 2006. Sørlandet is the geographical region (landsdel) of the Skagerrak coast of southern Norway. ...


Total cost of ownership

DAB transmits several channels per multiplex, meaning ownership and maintenance can be outsourced and provided by one organisation instead of each radio station, lowering the maintenance cost over time. [13]


Reception quality

The DAB standard integrates features to reduce the negative consequences of multipath fading and signal noise, which afflict existing analogue systems. PRIMERGY MultiPath PRIMERGY MultiPath supports redundant Fiber Channel paths, the configured connections between server and subsystem that are such an important component of disaster-tolerant servers and clusters. ... An analog or analogue signal is any time continuous signal where some time varying feature of the signal is a representation of some other time varying quantity. ...


Also, as DAB transmits digital audio, there is no hiss with a weak signal, which can happen on FM. However, radios in the fringe of a DAB signal, can experience a "bubbling mud" sound interrupting the audio and/or the audio cutting out altogether.


Less pirate interference

The specialised nature and cost of DAB broadcasting equipment provide barriers to pirate radio stations broadcasting on DAB. In cities such as London with large numbers of pirate radio stations broadcasting on FM, this means that some stations can be reliably received via DAB in areas where they are regularly difficult or impossible to receive on FM due to pirate radio interference. The term Pirate Radio usually refers to illegal or unregulated radio transmission. ...


Variable bandwidth

Mono talk radio, news and weather channels and other non-music programs need significantly less bandwidth than a typical music radio station, which allows DAB to carry these programmes at lower bit rates, leaving more bandwidth to be used for other programs. However, this had led to the situation where numerous music radio stations are being broadcast in mono, see the section on music radio stations broadcasting in mono for more details. Countries with DAB, DAB+ or DMB broadcasts. ...


Criticisms of DAB

Music radio stations broadcasting in mono

A large and increasing number of music radio stations and stations that carry drama on DAB in the UK are being broadcast in mono when they should be in stereo [1]. These stations are virtually all available in stereo on other digital platforms and on FM where applicable.


Reception quality

The reception quality on DAB can be poor even for people that live well within the coverage area. The reason for this is that the old version of DAB uses weak error correction coding so that when there are a lot of errors with the received data not enough of the errors can be corrected and a "bubbling mud" sound occurs. In some cases a complete loss of signal can happen. This situation will be improved upon in the new DAB standard (DAB+, discussed below) that uses stronger error correction coding and as signal powers are increased. In mathematics, computer science, information theory, the issue of error correction and detection has great practical importance in maintaining data (information) integrety accross noisy channels and less than relyable storage mediums. ... In mathematics, computer science, information theory, the issue of error correction and detection has great practical importance in maintaining data (information) integrety accross noisy channels and less than relyable storage mediums. ...


Poor Marketing

The advantages of DAB have been promoted without mentioning limitations and has led to some consumer disappointment.


Signal Delay

The signal processing required in the receiver (FFT) takes time to perform. This delays the signal to the listener by about 2 seconds (depending on the decoding circuitry used). This has two disadvantages: (i) DAB radios are out of step with live events so time signals are not accurate and the experience of listening to live commentaries on events being watched is impaired, and (ii) listeners using a combination of FM and DAB radios (e.g. in different rooms of a house) will not hear an intelligible signal when both receivers are within earshot. The second problem could have been overcome by defining a delay for all DAB receivers and delaying the FM broadcast signal by the same amount, but that would extend the first problem to all radios. Solving the first problem would require delaying signals from all media by the same amount, and still would not work for someone carrying a radio to a sports event.


Coverage

As DAB is at a relatively early stage of deployment, DAB coverage is poor in nearly all countries in comparison to the high population coverage provided by FM. The abbreviations FM, Fm, and fm may refer to: Electrical engineering Frequency modulation (FM) and its most common applications: FM broadcasting, used primarily to broadcast music and speech at VHF frequencies FM synthesis, a sound-generation technique popularized by early digital synthesizers Science Femtometre (fm), an SI measure of length...


Transmissions cost

Transmission on DAB is far more expensive than on FM, and measures taken by broadcasters to limit their costs have resulted in some DAB ensembles having to carry too many channels, forcing bit rates to be reduced to levels that deliver sound quality inferior to traditional FM (see Criticisms of DAB in the UK). A typical DAB digital radio receiver with the Digital Radio Development Bureau DAB digital radio marketing logo In the United Kingdom, the roll-out of digital radio is proceeding since test transmissions were started by the BBC in 1990. ...


Compatibility

In 2006 tests finally began using the much improved HE-AAC codec for DAB+. Virtually none of the current receivers in the field support the new codec, however, thus making them partially obsolete once DAB+ broadcasts begin and completely obsolete once the old MPEG-1 Layer 2 stations are switched off. High Efficiency AAC (HE-AAC) is a lossy data compression scheme for digital audio. ...


Power requirements

As DAB requires digital signal processing techniques to convert from the received digitally encoded signal to the analogue audio content, the complexity of the electronic circuitry required to do this is high. This translates into needing more power to effect this conversion than compared to an analogue FM to audio conversion, meaning that portable receiving equipment will tend to have a shorter battery life, or require higher power (and hence more bulk).


As an indicator of this increased power consumption, dual FM/DAB radios quote the length of time they can play on a single charge. For DAB, this is often between one-sixth and one-twelfth of the time they can play when in FM mode. [14]


Other criticism

If the signal reception becomes marginal the audio will first start to burble or cut out rapidly and if the signal continues to degrade the audio will cut out more often. There is also less chance of long distance reception that hobbyists enjoy because each frequency/multiplex is used more often.


Technology

Bands and modes

Eureka 147 DAB uses a wide-bandwidth broadcast technology and typically spectra have been allocated for it in Band III (174–240 MHz) and L band (1452–1492 MHz), 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. Band III is the name of a radio frequency range within the very high frequency part of the electromagnetic spectrum. ... L band (20-cm radar long-band) is a portion of the microwave band of the electromagnetic spectrum ranging roughly from 0. ... MegaHertz (MHz) is the name given to one million (106) Hertz, a measure of frequency. ...


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

This article is about artificial satellites. ...

Protocol stack

From a protocol stack viewpoint, the technologies used on DAB inhabit the following layers: the audio codec inhabits the application layer. Below that is the physical layer, which contains the error-correction coding and OFDM modulation, dealing with the over-the-air transmission and reception of data. Some aspects of these are described below. A protocol stack (sometimes communications stack) is a particular software implementation of a computer networking protocol suite. ... The application layer is the seventh level of the seven-layer OSI model. ... This article does not cite any references or sources. ...


Audio codec

The older version of DAB that is being used in the UK, Ireland, Denmark, Norway and Switzerland, uses the MPEG-1 Audio Layer 2 audio codec, which is also known as MP2 due to computer files using those characters for their file extension. MPEG-1 Audio Layer II (MP2, sometimes Musicam) is an audio codec. ... A filename extension or filename suffix is an extra set of (usually) alphanumeric characters that is appended to the end of a filename to allow computer users (as well as various pieces of software on the computer system) to quickly determine the type of data stored in the file. ...


The new DAB+ standard has adopted the HE-AAC version 2 audio codec, commonly known as AAC+ or aacPlus. AAC+ is approximately three-times more efficient than MP2[15], which means that broadcasters using DAB+ will be able to provide far higher audio quality or far more stations than they can on DAB, or, as is most likely, a combination of both higher audio quality and more stations will be provided. High Efficiency AAC (HE-AAC) is a lossy data compression scheme for digital audio. ...


One of the most important decisions regarding the design of a digital radio system is the choice of which audio codec to use, because the efficiency of the audio codec determines how many radio stations can be carried on a multiplex at a given level of audio quality. The capacity of a DAB multiplex is fixed, so the more efficient the audio codec is, the more stations can be carried, and vice versa. Similarly, for a fixed bit-rate level, the more efficient the audio codec is the higher the audio quality will be.


Error-correction coding

Error-correction coding (ECC) is an important technology for a digital communication system because it determines how robust the reception will be for a given signal strength - stronger ECC will provide more robust reception than a weaker form.


The old version of DAB uses punctured convolutional coding for its ECC. The coding scheme uses unequal error protection (UEP), which means that parts of the audio bit-stream that are more susceptible to errors causing audible disturbances are provided with more protection (i.e. a lower code rate) and vice versa. However, the UEP scheme used on DAB results in there being a grey area in between the user experiencing good reception quality and no reception at all, as opposed to the situation with most other wireless digital communication systems that have a sharp "digital cliff", where the signal rapidly becomes unusable if the signal strength drops below a certain threshold. When DAB listeners receive a signal in this intermediate strength area they experience a "burbling" sound which interrupts the playback of the audio, and listeners find this to be more unpleasant to listen to than hiss on FM.[citation needed] In telecommunication, a convolutional code is a type of error-correcting code in which (a) each m-bit information symbol (each m-bit string) to be encoded is transformed into an n-bit symbol, where m/n is the code rate (n ≥ m) and (b) the transformation is a function... The code rate or information rate of a forward error correction (FEC) code, for example a convolutional code, states what portion of the total amount of information that is useful (non redundant). ...


The new DAB+ standard has incorporated Reed-Solomon ECC as an "outer layer" of coding that is placed around the "inner layer" of convolutional coding used by the older DAB system, although on DAB+ the convolutional coding uses equal error protection (EEP) rather than UEP. This combination of convolutional coding as the inner layer of coding, followed by a byte interleaver then an outer layer of Reed-Solomon coding - so-called "concatenated coding" - became a popular ECC scheme in the 1990s, and NASA adopted it for its deep-space missions. One slight difference between the concatenated coding used by the DAB+ system and that used on most other systems is that it uses a rectangular byte interleaver rather than Forney interleaving in order to provide a greater interleaver depth, which increases the distance over which error bursts will be spread out in the bit-stream, which in turn will allow the Reed-Solomon error decoder to correct a higher proportion of errors. Reed-Solomon error correction is a coding scheme which works by first constructing a polynomial from the data symbols to be transmitted and then sending an over-sampled plot of the polynomial instead of the original symbols themselves. ... Reed-Solomon error correction is a coding scheme which works by first constructing a polynomial from the data symbols to be transmitted and then sending an over-sampled plot of the polynomial instead of the original symbols themselves. ... For other uses, see NASA (disambiguation). ... Reed-Solomon error correction is a coding scheme which works by first constructing a polynomial from the data symbols to be transmitted and then sending an over-sampled plot of the polynomial instead of the original symbols themselves. ...


The ECC used on DAB+ is far stronger than is used on DAB, which, with all else being equal (i.e. if the transmission powers remained the same), would translate into people who currently experience reception difficulties on DAB receiving a much more robust signal with DAB+ transmissions. It also has a far steeper "digital cliff", and listening tests have shown that people prefer this when the signal strength is low compared to the shallower digital cliff on DAB[16].


Modulation

Immunity to fading and inter-symbol interference (caused by multipath propagation) is achieved without equalization by means of the OFDM and DQPSK modulation techniques. Orthogonal frequency division modulation (OFDM, also called orthogonal frequency division multiplexing) is a technique for the modulation of digital information onto an analog carrier electromagnetic (e. ... Phase-shift keying (PSK) is a digital modulation scheme that conveys data by changing, or modulating, the phase of a reference signal (the carrier wave). ...


Using values for the most commonly used transmission mode on DAB, Transmission Mode I (TM I), the OFDM modulation consists of 1,536 subcarriers that are transmitted in parallel. The useful part of the OFDM symbol period is 1 millisecond, which results in the OFDM subcarriers each having a bandwidth of 1 kHz due to the inverse relationship between these two parameters, and the overall OFDM channel bandwidth is 1,537 kHz. The OFDM guard interval for TM I is 246 microseconds, which means that the overall OFDM symbol duration is 1.246 milliseconds. The guard interval duration also determines the maximum separation between transmitters that are part of the same single-frequency network (SFN), which is approximately 74 km for TM I. Orthogonal frequency division modulation (OFDM, also called orthogonal frequency division multiplexing) is a technique for the modulation of digital information onto an analog carrier electromagnetic (e. ...


Single-frequency networks

OFDM allows the use of single-frequency networks (SFN), which means that a network of transmitters can provide coverage to a large area - up to the size of a country - where all transmitters use the same transmission frequency. Transmitters that are part of an SFN need to be very accurately synchronised with other transmitters in the network, which requires the transmitters to use very accurate clocks. Orthogonal frequency division modulation (OFDM, also called orthogonal frequency division multiplexing) is a technique for the modulation of digital information onto an analog carrier electromagnetic (e. ...


When a receiver receives a signal that has been transmitted from the different transmitters that are part of an SFN, the signals from the different transmitters will typically have different delays, but to OFDM they will appear to simply be different multipaths of the same signal. Reception difficulties can arise, however, when the relative delay of multipaths exceeds the OFDM guard interval duration, and there are frequent reports of reception difficulties due to this issue when there is a lift, such as when there's high pressure, due to signals travelling farther than usual, and thus the signals are likely to arrive with a relative delay that is greater than the OFDM guard interval.


Low power gap-filler transmitters can be added to an SFN as and when desired in order to improve reception quality, although the way SFNs have been implemented in the UK up to now they have tended to consist of higher power transmitters being installed at main transmitter sites in order to keep costs down.


Bit rates

An ensemble has a maximum bit rate 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 depends on the amount of error correction added to the transmission, as described above. In the UK, most services transmit using 'protection level three', which provides an average ECC code rate of approximately ½, equating to a maximum bit rate per multiplex of 1184 kbit/s. In telecommunications and computing, bit rate (sometimes written bitrate) is the frequency at which bits are passing a given (physical or metaphorical) point. It is quantified using the bit per second (bit/s) unit. ... In computer science and information theory, error correction consists of using methods to detect and/or correct errors in the transmission or storage of data by the use of some amount of redundant data and (in the case of transmission) the selective retransmission of incorrect segments of the data. ...


Services and ensembles

Various different services are embedded into one ensemble (which is also typically called a multiplex). These services can include: In telecommunications, multiplexing (also muxing or MUXing) is the combining of two or more information channels onto a common transmission medium using hardware called a multiplexer or (MUX). ...

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

The Sky Digital EPG in the United Kingdom and Republic of Ireland. ... HTML, an initialism of HyperText Markup Language, is the predominant markup language for web pages. ... A digital image is a representation of a two-dimensional image as a finite set of digital values, called picture elements or pixels. ... A website, Web site or WWW site (often shortened to just site) is a collection of webpages, that is, HTML/XHTML documents accessible via HTTP on the Internet; all publicly accessible websites in existence comprise the World Wide Web. ... Slideshow is a modern concatenation of Slide Show. A slideshow is a display of a series of chosen images, which is done for artistic or instructional purposes. ... For other uses, see Video (disambiguation). ... The Java platform is the name for a bundle of related programs, or platform, from Sun Microsystems which allow for developing and running programs written in the Java programming language. ... A tunneling protocol is a network protocol which encapsulates one protocol or session inside another. ...

DAB+ and DMB

Eureka 147 provides the infrastructure for several DAB versions.


DAB+

WorldDMB, the organisation in charge of the DAB standards, announced a major non-backwardly compatible upgrade to the Eureka 147 system in 2006 when the HE-AAC v2 audio codec[17] (also known as AAC+) was adopted. The new standard, which is called DAB+, has also adopted the MPEG Surround audio format and stronger error correction coding in the form of Reed-Solomon coding. DAB+ has been standardised as ETSI TS 102 563. The WorldDMB (formerly World DAB Forum) is an international non-governmental organisation which defines the standards for Digital audio broadcasting. ... High Efficiency AAC (HE-AAC) is a lossy data compression scheme for digital audio. ... MPEG-4 Part 3 (formally ISO/IEC 14496-3) is the third part of the ISO/IEC MPEG-4 international standard. ... MPEG Surround (ISO/IEC 23003-1 or MPEG-D) is a lossy compression format for multi-channel audio that provides a method for extending mono or stereo audio services to multi-channel audio in a backwards compatible fashion. ... In mathematics, computer science, information theory, the issue of error correction and detection has great practical importance in maintaining data (information) integrety accross noisy channels and less than relyable storage mediums. ... Reed-Solomon error correction is a coding scheme which works by first constructing a polynomial from the data symbols to be transmitted and then sending an over-sampled plot of the polynomial instead of the original symbols themselves. ... The European Telecommunications Standards Institute (ETSI) is a standardization organization of the telecommunications industry (equipment makers and network operators) in Europe, with worldwide projection. ...


As DAB+ is not backwards-compatible ordinary DAB receivers cannot receive DAB+ broadcasts, however DAB receivers that will be able to receive the new DAB+ standard via a firmware upgrade went on sale in July 2007. If a receiver is DAB+-upgradeable there will be a sign on the product itself or in the literature for the product, but the vast majority of receivers on sale don't support DAB+ yet. A microcontroller, like this PIC18F8720 is controlled by firmware stored inside on FLASH memory In computing, firmware is a computer program that is embedded in a hardware device, for example a microcontroller. ...


DAB+ broadcasts have already launched in Italy, and several other countries are also expected to launch DAB+ broadcasts over the next few years, such as Switzerland in 2008, Malta in 2008, Australia on 1st January 2009,Israel in 2009, Germany in 2009. When DAB+ stations launch in the UK, Norway and Denmark, they will transmit alongside existing DAB stations that use the old MPEG-1 Audio Layer II audio format, and most existing DAB stations are expected to continue broadcasting until the vast majority of receivers support DAB+[18], at which point stations using the old DAB format will be switched off. There is also a great deal of interest in using DAB+ in Asian countries, such as China. Read Regional implementations of DAB for details. MPEG-1 Audio Layer II (MP2, sometimes Musicam) is an audio codec defined by ISO/IEC 11172-3. ...


DMB

DAB-related standards Digital Multimedia Broadcasting (DMB) and DAB-IP are suitable for mobile radio and TV both because they support 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. Digital Multimedia Broadcasting (DMB) is a digital radio transmission system for sending multimedia (radio, TV, and datacasting) to mobile devices such as mobile phones. ... Digital Multimedia Broadcasting (DMB) is a digital radio transmission system for sending multimedia (radio, TV, and datacasting) to mobile devices such as mobile phones. ... H.264, MPEG-4 Part 10, or AVC, for Advanced Video Coding, is a digital video codec standard which is noted for achieving very high data compression. ...


Regional implementations of DAB

More than 20 countries provide DAB broadcasts, either as a permanent technology or as test transmissions. The UK, along with Denmark, Norway, Belgium, Switzerland and South-Korea maintain a growing base of DAB listeners.

See also

ATSC redirects here. ... Digital Audio Radio Satellite or DARS (also as SDARS, for Satellite Digital Audio Radio Service, among many variations) is the FCC term for satellite radio, currently being made popular in the U.S. by XM Radio and Sirius. ... This article needs to be cleaned up to conform to a higher standard of quality. ... Digital Multimedia Broadcasting (DMB) is a digital radio transmission system for sending multimedia (radio, TV, and datacasting) to mobile devices such as mobile phones. ... Digital Radio Mondiale (DRM) is a set of digital audio broadcasting technologies designed to work over the bands currently used for AM broadcast, particularly shortwave. ... Digital television (DTV) refers to the sending and receiving of moving images and sound by means of discrete (digital) signals, in contrast to the analog signals used by analog TV. Introduced in the late 1990s, this technology appealed to the television broadcasting business and consumer electronics industries as offering new... Satellite Digital Radio (SDR) is an activity of the standardisation organisation ETSI. It addresses broadcast systems where a satellite transmits directly to mobile and handheld receivers and is complemented by terrestrial transmitters. ... The European Multimedia Associations Convention (EMMAC) is a European network of multimedia associations. ... FMeXtra is an in-band on-channel digital radio broadcasting technology created by Digital Radio Express. ... HD Radio is an in-band on-channel (IBOC) digital radio system created by iBiquity for broadcasting via existing FM and AM radio stations. ... Integrated Services Digital Broadcasting (ISDB) is the digital television (DTV) and digital radio format that Japan has created to allow radio and television stations there to convert to digital. ... OpenCable is a set of specifications created by CableLabs to Define the next-generation of advanced digital cable-ready devices. OpenCable uses SCTE standards for the video, transport and various interface requirements, but also adds a requirement for a Java based interpreter and an encryption system employing CableCARDs. ... Orthogonal Frequency-Division Multiplexing (OFDM) — essentially identical to Coded OFDM (COFDM) — is a digital multi-carrier modulation scheme, which uses a large number of closely-spaced orthogonal sub-carriers. ... Orthogonal Frequency-Division Multiplexing (OFDM) — essentially identical to Coded OFDM (COFDM) — is a digital multi-carrier modulation scheme, which uses a large number of closely-spaced orthogonal sub-carriers. ... Sirius Satellite Radio NASDAQ: SIRI is one of two satellite radio (SDARS) services operating in the United States and Canada, along with XM Satellite Radio. ... Spectral efficiency or spectrum efficiency refers to the amount of information that can be transmitted over a given bandwidth in a specific digital communication system. ... ... “XM” redirects here. ...

References

  1. ^ World DMB forums list of benefits
  2. ^ DUO - Digital utgivelse ved Universitetet i Oslo - Lydkvalitetet i DAB digitalradio
  3. ^ a b OFCOM: Regulation in digital broadcasting: DAB digital radio bitrates and audio quality; Dynamic range compression and loudness
  4. ^ DAB Around the World
  5. ^ http://worlddab.org/pdf/DAB+brochure.pdf
  6. ^ http://www.digitalradiotech.co.uk/documents/DRDB_UK_DAB+_policy.pdf
  7. ^ http://www.ofcom.org.uk/radio/ifi/rbl/dcr/applications/app_national/4digital.pdf
  8. ^ World DMB forums list of benefits
  9. ^ BBC R&D White Paper WHP 061 June 2003, DAB:An introduction to the EUREKA DAB System and a guide to how it works. Retrieved on 2007-05-08.
  10. ^ Friends of Radio 3 (FoR3) BBC & R3 News
  11. ^ Friends of Radio 3 (FoR3) Campaign Update
  12. ^ Broadcasting - News - Ofcom reveals DAB sound quality opinions - Digital Spy
  13. ^ BBC has chosen DAB by Factum
  14. ^ Freeplay Energy Plc
  15. ^ http://worlddab.org/pdf/DAB+brochure.pdf
  16. ^ http://worlddab.org/pdf/DAB+brochure.pdf
  17. ^ http://www.worlddab.org/upload/uploaddocs/WorldDMBPress%20Release_November.pdf
  18. ^ release: New High Efficiency Audio Option Added for DAB Digital Radio
  • ETSI Specifications available at ETSI Publications Download Area (this will open ETSI document search engine, to find the latest version of the document enter a search string; free registration is required to download PDF)
  • Stott, J. H.; The How and Why of COFDM, BBC Research Development

Year 2007 (MMVII) was a common year starting on Monday of the Gregorian calendar in the 21st century. ... is the 128th day of the year (129th in leap years) in the Gregorian calendar. ...

External links

Digital audio comprises audio signals stored in a digital format. ... Broadcasting is the distribution of audio and/or video signals which transmit programs to an audience. ... In telecommunications, modulation is the process of varying a periodic waveform, i. ... Amplitude modulation (AM) is a technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. ... In telecommunications, frequency modulation (FM) conveys information over a carrier wave by varying its frequency. ... Orthogonal Frequency-Division Multiplexing (OFDM) — essentially identical to Coded OFDM (COFDM) — is a digital multi-carrier modulation scheme, which uses a large number of closely-spaced orthogonal sub-carriers. ... This article does not cite any references or sources. ... Mediumwave radio transmissions (sometimes called Medium frequency or MF) are those between the frequencies of 300 kHz and 3000 kHz. ... Medium frequency (MF) refers to radio frequencies (RF) in the range of 300 kHz to 3000 kHz. ... A solid-state, analog shortwave receiver Shortwave radio operates between the frequencies of 3 MHz (3,000 kHz) and 30 MHz (30,000 kHz) [1] and came to be referred to as such in the early days of radio because the wavelengths associated with this frequency range were shorter than... High frequency (HF) radio frequencies are between 3 and 30 MHz. ... Very high frequency (VHF) is the radio frequency range from 30 MHz (wavelength 10 m) to 300 MHz (wavelength 1 m). ... L band (20-cm radar long-band) is a portion of the microwave band of the electromagnetic spectrum ranging roughly from 0. ... Digital Radio Mondiale (DRM) is a set of digital audio broadcasting technologies designed to work over the bands currently used for AM broadcast, particularly shortwave. ... HD Radio is an in-band on-channel (IBOC) digital radio system created by iBiquity for broadcasting via existing FM and AM radio stations. ... FMeXtra is an in-band on-channel digital radio broadcasting technology created by Digital Radio Express. ... Compatible Amplitude Modulation - Digital or CAM-D is a proposed hybrid digital radio format for AM broadcasting, put forth by respected broadcast engineer Leonard Kahn. ... L band (20-cm radar long-band) is a portion of the microwave band of the electromagnetic spectrum ranging roughly from 0. ... The S band ranges from 2 to 4 GHz. ... The Ku band (kay-yoo kurz-under band) is a portion of the electromagnetic spectrum in the microwave range of frequencies ranging from 11 to 18 GHz. ... Satellite Digital Radio (SDR) is an activity of the standardisation organisation ETSI. It addresses broadcast systems where a satellite transmits directly to mobile and handheld receivers and is complemented by terrestrial transmitters. ... DVB-H (Digital Video Broadcasting - Handheld) is one of three prevalent mobile TV formats. ... Astra Digital Radio (ADR) is a system used by SES Astra for digital radio transmissions on their Astra 1 satellites, using the audio subcarrier frequencies of analogue television channels. ... Commercial broadcasting - Wikipedia /**/ @import /skins-1. ... Sirius Satellite Radio NASDAQ: SIRI is one of two satellite radio (SDARS) services operating in the United States and Canada, along with XM Satellite Radio. ... WorldSpaces AfriStar control center in Washington, D.C. WorldSpace is the worlds first digital satellite radio network. ... “XM” redirects here. ... A codec is a device or program capable of encoding and/or decoding a digital data stream or signal. ... Advanced Audio Coding (AAC) is a standardized, lossy compression and encoding scheme for digital audio. ... MPEG-1 Audio Layer II (MP2, sometimes Musicam) is an audio codec defined by ISO/IEC 11172-3. ... AMR-WB+ is an extension of AMR-WB. It adds support for stereo signals and higher sampling rates. ... The amplitude modulation signalling system (AMSS or the AM signalling system) is a digital system for adding low bit rate information to an analogue amplitude modulated broadcast signal in the same manner as the Radio Data System (RDS) for frequency modulated (FM) broadcast signals. ... DirectBandâ„¢ is a North American wireless datacast network owned and operated by Microsoft. ... Metadata (Greek: meta-+data information) means While this definition is commonly offered, it is also commonly not helpful. ... Radio Data System, or RDS, is a standard from the European Broadcasting Union for sending small amounts of digital information using conventional FM radio broadcasts. ... Subsidiary Communications Authority (SCA), is the FCCs official designation for subcarrier channels transmitted by a broadcast FM radio station along with its main carrier. ... This article needs to be cleaned up to conform to a higher standard of quality. ... This article or section does not cite its references or sources. ... For the controversy about who invented radio, see Invention of radio. ... The purpose of this article is to explain the process and means of international broadcasting in a non-technical manner. ...

  Results from FactBites:
 
What is digital audio broadcasting? - a definition from Whatis.com - see also: DAB, digital radio, high-definition ... (463 words)
- Digital audio broadcasting (DAB), also known as digital radio and high-definition radio, is audio broadcasting in which analog audio is converted into a digital signal and transmitted on an assigned channel in the AM or (more usually) FM frequency range.
DAB is said to offer compact disc (CD)- quality audio on the FM (frequency modulation) broadcast band and to offer FM-quality audio on the AM (amplitude modulation) broadcast band.
A DAB receiver includes a small display that provides information about the audio content in much the same way that the menu screen provides an overview of programs in digital television (DTV).
Digital audio broadcasting - encyclopedia article about Digital audio broadcasting. (7377 words)
DAB receivers should not be confused with other types of radio receivers generically referred to as digital, but which are in fact primarily based on analog technology with a few complementary digital features such as synthesized tuning and LCD frequency displays - e.g.
DAB has the advantage that stations do not have to be re-tuned as you move from area to area, such as in a car.
Digital One, the national commercial operator, announced further transmitters to be switched on, five for 2005 and a further five for 2006.
  More results at FactBites »

 
 

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