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Digital Audio Broadcasting

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Digital audio broadcasting or DAB is a fairly new technology for broadcasting audio programming in digital form that was designed in the late 1980s. The original objectives of converting to digital systems were to enable higher fidelity, greater noise immunity, mobile services, and new services, although in practice the audio quality is invariably worse than on FM.

The acronym DAB is used both to identify the generic technology of digital audio broadcasting, and specific technical standards, particularly the Eureka 147 standard described below. Standardization of DAB technology is promoted by the World DAB Forum, which represents more than 30 countries but excluding the United States, which has opted instead for a proprietary system called HD Radio or IBOC.

DAB should not be confused with other types of audio broadcasting 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. Other cases are DVB-T and DVB-H services which, although designed for digital video broadcasts, often incorporate some digital audio channels to utilise spare bandwidth.

In addition to regular-style receivers, one can use a radio card to hear DAB through a personal computer and various models are on the market. The Psion Wavefinder was the original DAB radio for the personal computer, with a unique design and colourful screen; however this device is no longer available.

Terrestrial digital audio broadcast

Digital audio broadcasting is now being introduced in many countries. Whilst 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. This standard was developed by EUREKA as a research project for the European Union. (Project number EU147.) It is based on orthogonal frequency division modulation for transmitting digital data over a radio channel. DAB broadcasts use the MP2 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. The service (if existent at all) is still considered experimental in most other countries and in some countries expiremental services have been abandoned or put on hold with the result that some sceptics are branding the technology "Dead And Buried"

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. Also, it can carry "radiotext" (in DAB terminology, Dynamic Label Segment, or DLS) from the station giving real-time information such as song titles or traffic updates. In principle, this could even be extended to full screen static pictures, provided that they were only updated occasionally, which could provide an enhanced experience to those users with a suitable screen.

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, 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.

The three US IBOC schemes are being promoted by USA Digital Radio (USADR), Lucent Technologies, and Digital Radio Express. 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.

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

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.

The standards issue is one obstacle to the adoption of digital radio. The other problem is a lack of consumer demand. Current AM and FM terrestrial broadcast technology is cheap, reliable, and works well, and unless digital systems offer significant new benefits, there will be no strong consumer interest in the new technology.

Other digital information may be sent along with the audio as well, such as text indicating artist and title, news headlines, and so on. Broadcasts can provide digital "tags" to identify themselves, allowing a digital radio receiver to scan for channels by type of music, such as JAZZ or CLASSICAL. Tags can also allow automotive radios to automatically change stations as they travel from city to city, to stay with a particular network or music style.

Technical Description

The Effective Elimination of Multipath Interference

Provided a sufficiently strong signal is available for it to operate correctly, DAB was designed with special features to practically eliminate multipath interference or fading, a serious affliction of most of the existing analog systems of frequency modulated (FM) broadcast services which DAB is intended to eventually replace. The standards were targeted at the largest potential audience sector for DAB: those in moving vehicles for which FM multipath fading is the most troublesome. Multipath fading also often degrades the quality of reception on portable radios which rely on an integral (telescopic rod-type) antenna when they are used in domestic environments.

Perception of a Service 'Threshold'

The advantages of DAB can only be experienced if sufficient signal is available at the receiver, and that is dependent on many factors such as the closeness of its antenna to the transmitter, radio propagation conditions, the local geography, and the influence of hills, large buildings and metallic reflective structures such as bridges, warehouses etc. One criticism of DAB is that, if the received signal becomes marginal, with most consumer receivers there is no apparent 'threshold' warning, the audio output for the whole multiplex simply mutes until the signal strength recovers again. Sometimes it is easy to mistake this for a receiver fault. Usually the same situation occurring with an FM broadcast receiver, assuming the muting is disabled, would progressively increase the audio noise, tending to swamp the intended audio and identifying that the signal is becoming weak.

The Difference Between DAB and FM

In terms of technology, DAB and FM are almost completely different, because DAB is a digital radio system whereas FM is an analogue radio system.

From a radio listener's perspective the difference between DAB and FM really boils down to things like the number of stations and the audio quality available.

DAB's main advantage compared to FM is that it offers more radio stations. This is possible because DAB multiplexes use single-frequency networks (SFNs), which, as the name suggests, the multiplex is transmitted on the same frequency from all transmitters. This means that national DAB multiplexes use spectrum much more efficiently than FM national stations, because FM stations must be transmitted on different frequencies in different locations to avoid interfering with one another, which consumes a lot of spectrum for national FM stations.

Local DAB multiplexes, however, are no more spectrum-efficient than local FM stations, because local FM stations are only transmitted on one frequency, so the benefit from using SFNs is lost.

In the UK the broadcasters have also decided to squeeze a large number of radio stations into each DAB multiplex. This also increases the number of radio stations available, but the drawback to this is that the bit rates that the stations use has had to be reduced, which in turn reduces the audio quality.

The main technology that is causing a problem for DAB is that it uses the MP2 audio codec, which needs to be used at high bit rates of 192 kbit/s or higher to provide good audio quality for a stereo radio station. Unfortunately, at 192 kbit/s only six radio stations can be carried on one DAB multiplex.

In the UK, however, instead of using the accepted bit rate levels such as 192 kbit/s that are sufficient to provide good audio quality, the broadcasters have reduced the bit rates to squeeze in more radio stations. Now, 98% of all stereo radio stations on DAB in the UK use a bit rate level of 128 kbit/s, which unfortunately results in radio stations on DAB sounding worse -- usually much worse -- than the same stations sound on FM. Many are broadcast in mono to increase the amount of stations that can be carried, seen by many as step backwards as stereo transmisisons have been available on FM since the 1960s.

However, Ofcom, the UK's communications regulator, announced in late 2005 that it hopes the UK broadcasters will work with manufacturers to release dual-standard DAB receivers so that in a number of years' time, once the vast majority of all DAB receivers can receive both DAB standards, it will be possible for the UK to change to the new standard, thus allowing the audio quality of existing stations to be hugely increased and to allow more radio stations to transmit on DAB.

Coded Orthogonal Frequency Division Multiplexing

The modulation used in DAB is Coded Orthogonal Frequency Division Multiplexing (COFDM). According to this acronym the three properties of COFDM are: 'C' for coding; 'O' for orthogonal modulation and 'FDM' for frequency division multiplexing. These are described here.

Coding

Coding refers to convolutional coding and means that the original data carried over the multiplex is deliberately manipulated by splitting it into small blocks and adding some intelligently designed redundant information to each, thus generating a data 'overhead'. The overhead bits added to each block are determined according to rules applied to the true data content of the block. After demodulation at the receiver the digital signal processor examines both the actually received data and overhead bits and regenerates what it believes to be the original data based on a set of statistical rules known as an algorithm. The regenerated data may include a number of data bit corrections. The algorithm used in DAB is known as a Viterbi algorithm, and is an example of a maximum likelihood algorithm. This works by maintaining a history of demodulated bit sequences, building up a view of their probabilities and then using these to finally select either a 0 or 1 for the bit under consideration. This type of coding is also known as an example of forward error correction (FEC).

To some extent the types of errors most likely to be present with DAB can be mathematically predicted and therefore corrected for. The addition of FEC requires extra information to be transmitted at the same time as the original traffic data and therefore requires an increased channel capacity, needing extra bandwidth, compared to if it had been uncoded. DAB carries different 'strengths' of FEC, a stronger one being used for the control of critical features in the receiver.

Orthogonal

Orthogonal is the mathematical term applied to two RF sinusoidal signals when their phase relationship is precisely 90 degrees. Alternatively they may be said to be in 'quadrature'. In DAB the sub-carrier frequency spacing is chosen to be the reciprocal of the active symbol period. Under this condition the DAB modulation results in successive sub-carriers having a quadrature relationship with each other. The frequency spectra components of one modulated sub-carrier will therefore integrate to zero at the corresponding components from both of the adjacent sub-carriers. This has two advantages: (a) the modulated sub-carrier spectra will efficiently occupy the allocated bandwidth with a degree of controlled overlapping and (b) simple I-Q demodulation to zero intermediate frequency (zero-IF) can be used in the receiver without needing the costly hardware overhead of many bandpass filters to extract the sub-carriers.

Frequency Division Multiplexing

Frequency division multiplexing (FDM) is the process where two or more basic information channel bandwidths or basebands are shifted in frequency and added to others to form an aggregate wider bandwidth containing the information from all of the constituent basebands. To avoid mutual interference, their bandwidths would normally require shifting (translating) in frequency and no two translated basebands would occupy any part of the same frequency spectrum. In the context of DAB, FDM refers to the manner in which the modulated sub-carriers are assembled across the allocated frequency range.

Modulation Type

DAB uses a digital modulation type known as differential quadrature phase shift keying (DQPSK), which is an incoherent modulation scheme. DQPSK differs from the more common quadrature phase shift keying (QPSK) in that the modulated carrier phase for the current symbol being detected depends on its phase relative to that phase detected for the previous one. In QPSK it is just the absolute phase of the modulated carrier that determines the associated symbol. A differential modulation scheme can be more resillient to the typical fading scenarios of DAB. The modulation scheme also incorporates a form of Gray coding in that only one bit changes on moving from one symbol state to an adjacent one. For a constant phase progression, the consecutive set of symbols are represented by the bit pairs 00, 01, 11 and 10.

Time Interleaving

DAB uses data buffering which enables the data symbols to be transmitted over the RF path in a different time-order from which they were generated the audio source (studio). At the receiver they are re-assembled and returned to the original time-order before conversion back to analog signals to feed the receiver audio output. This process is called time interleaving. Typical multipath interference experienced in a moving vehicle is regular over time so an intelligent choice of time interleaving to some degree 'averages' out the resulting error bursts over time. This data buffering and other processing contributes to a delay, typically of a few seconds, between the studio source and the receiver. This is much longer than the equivalent delay for am FM broadcast channel which would typically be a fraction of a second. For most broadcasts such a delay would be unimportant but it does mean that, for example, real-time reference signals for setting clocks such as those re-broadcast by the BBC on DAB from their national FM service are actually quite inaccurate.

Frequency Interleaving

DAB also uses frequency interleaving, a similar technique to time interleaving but applied to the sub-carriers centre frequencies in the RF spectrum instead. The data stream from the studio is deliberately not modulated serially onto sub-carriers across the frequency range, but instead in a more random way. Multipath and other forms of selective fading generally affect a relatively narrow part of the RF multiplex bandwidth at any one time so frequency interleaving would tend to average out 'bursts' of errors resulting from these.

Single Frequency Networks

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.

DAB Eureka 147

Bands and Modes

  • Band III: DAB – frequency band 174–240 MHz
    • 5A 174.928 MHz
    • 5B 176.640 MHz
    • 5C 178.352 MHz
    • 5D 180.064 MHz
    • 6A 181.936 MHz
    • 6B 183.648 MHz
    • 6C 185.360 MHz
    • 6D 187.072 MHz
    • 7A 188.928 MHz
    • 7B 190.640 MHz
    • 7C 192.352 MHz
    • 7D 194.064 MHz
    • 8A 195.936 MHz
    • 8B 197.648 MHz
    • 8C 199.360 MHz
    • 8D 201.072 MHz
    • 9A 202.928 MHz
    • 9B 204.640 MHz
    • 9C 206.352 MHz
    • 9D 208.064 MHz
    • 10N 210.096 MHz
    • 10A 209.936 MHz
    • 10B 211.648 MHz
    • 10C 213.360 MHz
    • 10D 215.072 MHz
    • 11A 216.928 MHz
    • 11N 217.088 MHz
    • 11B 218.640 MHz
    • 11C 220.352 MHz
    • 11D 222.064 MHz
    • 12A 223.936 MHz
    • 12N 224.096 MHz
    • 12B 225.648 MHz
    • 12C 227.360 MHz
    • 12D 229.072 MHz
    • 13A 230.784 MHz
    • 13B 232.496 MHz
    • 13C 234.208 MHz
    • 13D 235.776 MHz
    • 13E 237.488 MHz
    • 13F 239.200 MHz
  • L-Band: DAB – frequency band 1452–1492 MHz
    • T-DAB (terrestrial)
      • LA 1452.960 MHz
      • LB 1454.672 MHz
      • LC 1456.384 MHz
      • LD 1458.096 MHz
      • LE 1459.808 MHz
      • LF 1461.520 MHz
      • LG 1463.232 MHz
      • LH 1464.944 MHz
      • LI 1466.656 MHz
      • LJ 1468.368 MHz
      • LK 1470.080 MHz
      • LL 1471.792 MHz
      • LM 1473.504 MHz
      • LN 1475.216 MHz
      • LO 1476.928 MHz
      • LP 1478.640 MHz
    • S-DAB (satellite)
      • LQ 1480.352 MHz
      • LR 1482.064 MHz
      • LS 1483.776 MHz
      • LT 1485.488 MHz
      • LU 1487.200 MHz
      • LV 1488.912 MHz
      • LW 1490.624 MHz
  • DAB-Mode I, II, III and IV: country specific transmission mode. 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

Note: Canada use slightly different central frequencies for L-band DAB while in many European countries DAB is limited part of Band III due to television and mobile two way radio using the rest.

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

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.


DAB-2

New DAB standards — dubbed DAB version 2, DAB-2 or DABv2 — are expected to be released in 2006. It is expected that DAB-2 will incorporate the AAC, AAC+ and probably WindowsMedia audio codecs together with Convolutional coding + RS coding. By incorporating these relatively new technologies the quality of audio on digital radio will be significantly increased overall when compared on a bit for bit system with the current MPEG1 layer 2 system. I.e. the quality of audio at say 128kbit/s using the AAC/+ codec will be significantly superior to the same audio encoded at the same bitrate using the MPEG1 layer 2 codec. DAB and DAB-2 can't be used for mobile TV because they don't include any video codecs. DAB related standards DMB and DAB-IP are suitable for mobile radio and TV both because they have H.264 and WMV9 respectively as video codecs.

DAB in Europe

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), 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.

Denmark

The Danish national radio has made an extensive rollout of DAB. 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.

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.

France

In a public consultation on digital radio, the four largest French radio broadcasters objected to using the current DAB system. The French Radio Authority decided to launch a technical forum about the right choice for digital radio. Some broadcasters asked the communications regulator, CSA, to adopt a digital radio system that uses the MPEG-4 AAC and HE AAC audio codecs. 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 October 15th, 2005. It is authorized to broadcast a set of programs of radio or television having been already the object of agreements with the council.

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.

Ireland

On December 20 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 January 1 2006. This date is 80 years after Radio Éireann (RTÉ's predecessor) began. By January 5, 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.

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.

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.

The Netherlands

In March 2005, following criticism from politicians from all parties, the Dutch Minister of Economic Affairs Laurens Jan Brinkhorst announced that Holland 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 Holland 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.

Norway

Several channels are available on DAB, including all of NRKs broadcast channels and P4. There is also a private DAB broadcaster with two channels (a music channel, Radio 2 Digital, and an audio book channel, Bokradioen). In addition NRK has several niche DAB channels, some of which also are available via the FM net in parts of the country. The national commercial broadcaster Kanal 24 has yet to receive a DAB license. No local radio stations are licensed 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 existed only about 25 DAB receivers in Norway.

DAB radio in Norway is divided into a nation band and several regional bands. The regional bands broadcast versions of NRK P1 with regional programming and several other national 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 and approximately 25,000 units have been sold in Norway as of November 2005.

A government working group appointed by Medietilsynet released a report on December 19, 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.[1]

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.

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.[2]

Russian Federation

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

Sweden

On December 14, 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.

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.

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. The timing of this was presumably to pre-empt the advertisement of the national commercial DAB multiplex licence by the Radio Authority a few months later. In 2006 the majority of national broadcasters all broadcast in DAB (as well as traditional AM/FM), including Radio 1, BBC Radio 2, BBC Radio 4 and BBC Radio 5 Live. There are now also digital-only stations such as 6 Music, and Radio 7, available on DAB, Freeview or Satellite TV only.

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 and includes the major motorway network. The BBC coverage was expected to rise to about over 85% in 2005. 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.

Criticisms

Although DAB offers more radio stations than FM, the audio quality is poorer than on FM due to 98% of all stereo stations using a bit rate of 128 kbit/s with the MP2 audio codec. In order to squeeze more stations onto their multiplexes, broadcasters have lowered their audio 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. Also, numerous stations are broadcasting in mono only, where their FM counterparts are in stereo. Also, many of the additional stations on DAB are little more than automated "jukebox" stations, and are derided by many for sounding virtually the same, some of these have bitrates as low as 64kbit/s.

As a result of the problem with the audio quality, WorldDAB, the organisation in charge of overseeing the DAB standards, has begun working on new DAB standards that incorporate the modern AAC and HE AAC (otherwise known as AAC+) audio codecs, and it now looks like nearly all of the other countries that are considering DAB will adopt the new version of DAB, dubbed DABv2 or DAB+. Unfortunately, too many DAB radios have been sold in the UK (and Denmark) for them to change to the new DAB standards, because if such a change were made that would render all DAB radios sold to date obsolete.

Coverage of commercial national DAB Digital Radio is at 88% of the population. Digital One, the national commercial operator, announced further transmitters to be switched on, five for 2005 and a further five for 2006. It currently operates the world's biggest digital radio network, with 103 transmitters. Digital One began broadcasts on 15th November 1999 with 69% coverage and since then its DAB network has always been more extensive than the BBC's (which is unusual for a commercial broadcaster). Digital One is generally regarded as one the driving force behind digital radio in the UK, having also developed 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 £34 in 2006. However, when Digital One invested in the low cost silicon chip they continued to use the original 1980s technology of which DAB is comprised, and therefore the opportunity to avoid the problem with the audio quality was missed.

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.

Receivers are growing in availability, and the £50 barrier was broken in 2004. DAB radios are sometimes given away as competition prizes by BBC and commercial radio stations as part of their commitment to promoting and increasing public awareness of the platform.

As of August 2005, the BBC national multiplex contains a number of different services: channels like BBC Radio 4 that are also available on analogue radio, digital-only services such as BBC Radio Five Live Sports Extra, BBC 6 Music, 1Xtra and BBC 7, and an EPG. The multiplex may change configuration, sometimes adding extra temporary extra services.

Digital One contains eight audio stations, and EPG and an experimental video service for mobile phones which is due to be launched in Summer 2006.

However, 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 unwilling to pay the high transmission charges that the multiplex operators (that are all owned by the large commercial radio groups) are charging. The problem with high transmission costs are, like the problem with the poor audio quality, a result of DAB being a very inefficient system because it uses 1980s technology. Modern and far more efficient digital broadcasting systems include DRM, DVB-H, DMB and MediaFLO.

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

DAB around the world

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. [3]

Canada

On June 16 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.
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

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 brodacast some programs at Beijing and Guangdong.

Korea

On the 1st 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.

Singapore

In Singapore, MediaCorp's SmartRadio was launched on the 19th of 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. [4]

Digital radio for the US automotive market

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 two satellites, both of which were launched in the spring of 2001. 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 nonstarter (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.

Digital radio for the 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 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.


References

Stott, J. H.; The How and Why of COFDM, BBC Research Development

See also

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