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DVB-T

From Wikipedia, the free encyclopedia
Digital terrestrial television standard

The logo of DVB-T
List ofdigital television broadcast standards
DVB standards(countries)
ATSC standards(countries)
ISDB standards(countries)
DTMB standards(countries)
  • DTMB (terrestrial/mobile)
    • DTMB-A
  • CMMB (handheld)
  • ABS-S (satellite)
DMB standard(countries)
Codecs
TerrestrialFrequency bands
SatelliteFrequency bands

DVB-T, short forDigital Video Broadcasting – Terrestrial, is theDVB European-based consortium standard for the broadcast transmission ofdigital terrestrial television that was first published in 1997[1] and first broadcast inSingapore in February 1998.[2][3][4][5][6][7][8] This system transmitscompresseddigital audio,digital video and other data in anMPEG transport stream, using codedorthogonal frequency-division multiplexing (COFDM or OFDM) modulation. It is also the format widely used worldwide (including North America) forElectronic News Gathering for transmission of video and audio from a mobile newsgathering vehicle to a central receive point.It is also used in the US byamateur television operators.

Basics

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Rather than carrying one data carrier on a singleradio frequency (RF) channel,COFDM works by splitting the digital data stream into a large number of slower digital streams, each of which digitally modulates a set of closely spaced adjacent sub-carrier frequencies. In the case of DVB-T, there are two choices for the number of carriers known as 2K-mode or 8K-mode. These are actually 1,705 or 6,817 sub-carriers that are approximately 4 kHz or 1 kHz apart.

DVB-T offers three different modulation schemes (QPSK,16QAM,64QAM).

DVB-T has been adopted or proposed for digital television broadcasting by many countries (see map), using mainly VHF 7 MHz and UHF 8 MHz channels whereas Taiwan, Colombia, Panama, Trinidad, and Tobago use 6 MHz channels. Examples include the UK'sFreeview.

The DVB-T Standard is published as EN 300 744,Framing structure, channel coding and modulation for digital terrestrial television. This is available from theETSI website, as is ETSI TS 101 154,Specification for the use of Video and Audio Coding in Broadcasting Applications based on the MPEG-2 Transport Stream, which gives details of the DVB use of source coding methods forMPEG-2 and, more recently,H.264/MPEG-4 AVC as well as audio encoding systems. Many countries that have adopted DVB-T have published standards for their implementation. These include theD-book in the UK, the Italian DGTVi,[9] the ETSI E-Book and the Nordic countries and Ireland NorDig.

DVB-T has been further developed into newer standards such asDVB-H (Handheld), which was a commercial failure and is no longer in operation, andDVB-T2, which was initially finalised in August 2011.

DVB-T as a digital transmission delivers data in a series of discrete blocks at the symbol rate. DVB-T is aCOFDM transmission technique which includes the use of a Guard Interval. It allows the receiver to cope with strong multipath situations. Within a geographical area, DVB-T also allowssingle-frequency network (SFN) operation, where two or more transmitters carrying the same data operate on the same frequency. In such cases the signals from each transmitter in the SFN needs to be accurately time-aligned, which is done by sync information in the stream and timing at each transmitter referenced toGPS.

The length of the Guard Interval can be chosen. It is a trade-off between data rate andSFN capability. The longer the guard interval the larger is the potential SFN area without creatingintersymbol interference (ISI).It is possible to operate SFNs which do not fulfill the guard interval condition if the self-interference is properly planned and monitored.

Technical description of a DVB-T transmitter

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Scheme of a DVB-T transmission system

With reference to the figure, a short description of the signal processing blocks follows.

  • Source coding and MPEG-2multiplexing (MUX): Compressed video, compressed audio, and data streams are multiplexed intoMPEG program streams (MPEG-PSs). One or more MPEG-PSs are joined together into anMPEG transport stream (MPEG-TS); this is the basic digital stream which is being transmitted and received by TV sets or homeSet Top Boxes (STB). Allowedbit rates for the transported data depend on a number of coding and modulation parameters: it can range from about 5 to about 32Mbit/s (see the bottom figure for a complete listing).
  • Splitter: Two different MPEG-TSs can be transmitted at the same time, using a technique calledHierarchical Transmission. It may be used to transmit, for example a standard definitionSDTV signal and a high definitionHDTV signal on the samecarrier. Generally, the SDTV signal is more robust than the HDTV one. At the receiver, depending on the quality of the received signal, the STB may be able to decode the HDTV stream or, if signal strength lacks, it can switch to the SDTV one (in this way, all receivers that are in proximity of the transmission site can lock the HDTV signal, whereas all the other ones, even the farthest, may still be able to receive and decode an SDTV signal).
  • MUX adaptation and energy dispersal: The MPEG-TS is identified as a sequence ofdata packets, of fixed length (188 bytes). With a technique calledenergy dispersal, the byte sequence isdecorrelated.
  • External encoder: A first level of error correction is applied to the transmitted data, using a non-binaryblock code, aReed–Solomon RS (204, 188) code, allowing the correction of up to a maximum of 8 wrong bytes for each 188-byte packet.
  • Externalinterleaver:Convolutional interleaving is used to rearrange the transmitted data sequence, in such a way that it becomes more rugged to long sequences of errors.
  • Internal encoder: A second level of error correction is given by a puncturedconvolutional code, which is often denoted in STBs menus as FEC (Forward error correction). There are five valid coding rates: 1/2, 2/3, 3/4, 5/6, and 7/8.
  • Internal interleaver: Data sequence is rearranged again, aiming to reduce the influence of burst errors. This time, a block interleaving technique is adopted, with a pseudo-random assignment scheme (this is really done by two separate interleaving processes, one operating on bits and another one operating on groups of bits).
  • Mapper: The digital bit sequence is mapped into a base band modulated sequence of complex symbols. There are three validmodulation schemes:QPSK, 16-QAM, 64-QAM.
  • Frame adaptation: the complex symbols are grouped in blocks of constant length (1512, 3024, or 6048 symbols per block). Aframe is generated, 68 blocks long, and asuperframe is built by 4 frames.
  • Pilot and TPS signals: In order to simplify the reception of the signal being transmitted on the terrestrialradio channel, additional signals are inserted in each block. Pilot signals are used during the synchronization and equalization phase, while TPS signals (Transmission Parameters Signalling) send the parameters of the transmitted signal and to unequivocally identify the transmission cell. The receiver must be able to synchronize, equalize, and decode the signal to gain access to the information held by the TPS pilots. Thus, the receiver must know this information beforehand, and the TPS data is only used in special cases, such as changes in the parameters, resynchronizations, etc.
Spectrum of a DVB-T signal in 8k mode (note the flat-top characteristics)
  • OFDM modulation: The sequence of blocks is modulated according to theOFDM technique, using 1705 or 6817 carriers (2k or 8k mode, respectively). Increasing the number of carriers does not modify the payload bit rate, which remains constant.
  • Guard interval insertion: to decrease receiver complexity, every OFDM block is extended, copying in front of it its own end (cyclic prefix). The width of such guard interval can be 1/32, 1/16, 1/8, or 1/4 that of the original block length. Cyclic prefix is required to operate single frequency networks, where there may exist an ineliminable interference coming from several sites transmitting the same program on the samecarrier frequency.
  • DAC and front-end: The digital signal is transformed into an analogue signal, with adigital-to-analog converter (DAC), and then modulated to radio frequency (VHF,UHF) by theRF front end. The occupied bandwidth is designed to accommodate each single DVB-T signal into 5, 6, 7, or 8MHz wide channels. The base band sample rate provided at the DAC input depends on the channel bandwidth: it isfs=87B{\displaystyle f_{s}={\frac {8}{7}}B}samples/s, whereB{\displaystyle B} is the channel bandwidth expressed in Hz.
Available bit rates (Mbit/s) for a DVB-T system in 8 MHz channels
ModulationCoding rateGuard interval
1/41/81/161/32
QPSK1/24.9765.5295.8556.032
2/36.6357.3737.8068.043
3/47.4658.2948.7829.048
5/68.2949.2169.75810.053
7/88.7099.67610.24610.556
16-QAM1/29.95311.05911.70912.064
2/313.27114.74515.61216.086
3/414.92916.58817.56418.096
5/616.58818.43119.51620.107
7/817.41819.35320.49121.112
64-QAM1/214.92916.58817.56418.096
2/319.90622.11823.41924.128
3/422.39424.88226.34627.144
5/624.88227.64729.27330.160
7/826.12629.02930.73731.668

Technical description of the receiver

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The receiving STB adopts techniques which are dual to those ones used in the transmission.

  • Front-end and ADC: the analogue RF signal is converted to base-band and transformed into a digital signal, using ananalogue-to-digital converter (ADC).
  • Time and frequency synchronization: the digital base band signal is searched to identify the beginning of frames and blocks. Any problems with the frequency of the components of the signal are corrected, too. The property that the guard interval at the end of the symbol is placed also at the beginning is exploited to find the beginning of a newOFDM symbol. On the other hand, continual pilots (whose value and position is determined in the standard and thus known by the receiver) determine the frequency offset suffered by the signal. This frequency offset might have been caused byDoppler effect, inaccuracies in either the transmitter or receiver clock, and so on. Generally, synchronization is done in two steps, either before or after the FFT, in such way to resolve both coarse and fine frequency/timing errors. Pre-FFT steps involve the use of sliding correlation on the received time signal, whereas Post-FFT steps use correlation between the frequency signal and the pilot carriers sequence.
  • Guard interval disposal: the cyclic prefix is removed.
  • OFDM demodulation: this is achieved with an FFT.
  • Frequencyequalization: the pilot signals are used to estimate the Channel Transfer Function (CTF) every threesubcarriers. The CTF is derived in the remaining subcarriers via interpolation. The CTF is then used to equalize the received data in each subcarrier, generally using a Zero-Forcing method (multiplication by CTF inverse). The CTF is also used to weigh the reliability of the demapped data when they are provided to the Viterbi decoder.
  • Demapping: since there are Gray-encoded QAM constellations, demapping is done in a "soft" way using nonlinear laws that demap each bit in the received symbol to a more or less reliable fuzzy value between -1 and +1.
  • Internal deinterleaving
  • Internal decoding: uses theViterbi algorithm, with a traceback length larger than that generally used for the basic 1/2 rate code, due to the presence of punctured ("erased") bits.
  • External deinterleaving
  • External decoding
  • MUX adaptation
  • MPEG-2 demultiplexing and source decoding

Countries and territories using DVB-T or DVB-T2

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The following countries use the DVB-T or DVB-T2 broadcast standard: neighbouring countries may also pick up DVB signals due tosignal overspill.

Digital terrestrial television systems worldwide. Countries using DVB-T or DVB-T2 are shown in blue.[10]

Americas

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Europe

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Oceania

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Asia

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Africa

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DVB-T/T2 switch-off

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DVB-T/T2 is switched off in Switzerland and the Flemish part of Belgium:

  • Belgium: In Flanders,VRT free-to-air broadcasting ended on 1 December 2018. In Flanders region, the encrypted TV platformTV Vlaanderen's Antenne TV service has ended on 1 September 2024.[needs update]
  • Switzerland: Swiss public broadcasterSRG SSR terminated DTT network on 3 June 2019. A regional station from the Geneva area has kept broadcasting. A DVB-T2 antenna was later activated in the east of the country to relay Swiss TV to Austrian cable operators. A similar broadcast is planned to coverGrand Geneva.

See also

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Notes

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  1. ^"ETSI EN 300 744 – Digital Video Broadcasting (DVB); Framing structure, channel coding and modulation for digital terrestrial television"(PDF).European Telecommunications Standards Institute. October 2015. p. 66.Archived(PDF) from the original on 26 March 2016.
  2. ^"DATAONE LIMITED RESPONSE TO CONSULTATION PAPER ON DATACASTING"(PDF).Infocomm Media Development Authority, Singapore.Archived(PDF) from the original on 5 February 2020.
  3. ^"TELEVISION BROADCAST FOR SINGAPORE – March 3, 1998"(PDF). 8 October 1999.Archived(PDF) from the original on 8 October 1999. Retrieved5 February 2020.
  4. ^"Advent Television launches the world's first digital terrestrial service in Singapore"(PDF). 8 October 1999.Archived(PDF) from the original on 8 October 1999. Retrieved5 February 2020.
  5. ^"The Future is in Digital Broadcasting and that future is with Advent Television". 11 April 2001.Archived from the original on 11 April 2001. Retrieved5 February 2020.
  6. ^"Press Release – April 27, 1998"(PDF). 4 June 2000.Archived(PDF) from the original on 4 June 2000. Retrieved5 February 2020.
  7. ^"S'pore testing digital TV format".The Business Times. 5 March 1998. p. 4.
  8. ^"SBA plans to launch digital TV after trying out systems".The Straits Times. 9 March 1998. p. 30.
  9. ^"DGTVi – Per la Televisione Digitale Terrestre" (in Italian). Archived from the original on 2008-04-19. Retrieved2008-07-30.
  10. ^DVB.orgArchived 20 March 2011 at theWayback Machine, Official information taken from the DVB website
  11. ^"Colombia adopta el estándar europeo para la tv digital terrestre".El Espectador (in Spanish). 28 August 2008. Archived fromthe original on 13 April 2019. Retrieved28 August 2008.
  12. ^"TV Digital no ha llegado a toda Colombia y la CNTV ya piensa en modificar la norma".Evaluamos (in Spanish). 21 July 2011.
  13. ^"Panama adopts DVB-T".DVB.org. 19 May 2009. Archived fromthe original on 3 September 2013. Retrieved26 June 2016.
  14. ^"KTV Ltd". Retrieved26 June 2016.
  15. ^"Plan for the introduction of terrestrial digital television broadcasting (DVB-T) in the Republic of Bulgaria" (in Bulgarian).Ministry of Transport, Information Technology and Communications of Bulgaria. Retrieved17 December 2012.
  16. ^"Digital Television". NURTS (TV tower operator). Archived fromthe original on 1 December 2012. Retrieved17 December 2012.
  17. ^"Digital Ísland" (in Icelandic). fjarskiptahandbokin.is. Archived fromthe original on 31 August 2009. Retrieved27 October 2009.
  18. ^"Russia adopts DVB-T2".Advanced-Television.com. 29 September 2011.
  19. ^"ETV: trial DVB-T2 network" (in Serbian). Archived fromthe original on 16 April 2012. Retrieved22 March 2012.
  20. ^"Switzerland to switch off DTT on June 3, 2019". 6 December 2018.
  21. ^"TRT Kurumsal Profil - TRT Kurumsal".
  22. ^"RTÜK | Sayısal Yayıncılık Nedir?".
  23. ^"Freeview technical upgrade could make older screens go blank".
  24. ^"BBCB-PSB3 content of DTT UK London / National".
  25. ^"DTT channel and multiplex listings for industry professionals".
  26. ^"100,000 likes – Oqaab reaches over 1 Mio TV Households".Oqaab.af. 31 March 2015. Archived fromthe original on 23 March 2016. Retrieved26 June 2016.
  27. ^abcdefghHawkes, Rebecca (19 May 2014)."Samart eyes Middle East market for digital TV-enabled smartphone".Rapid TV News. Archived fromthe original on 20 May 2016. Retrieved26 June 2016.
  28. ^"Digital TV services to be introduced in Bangladesh by 2014".Asia-Pacific Broadcasting Union. 5 June 2012.
  29. ^"PERSYARATAN TEKNIS ALAT DAN PERANGKAT PENERIMA TELEVISI SIARAN DIGITAL BERBASIS STANDAR DIGITAL VIDEO BROADCASTING TERRESTRIAL – SECOND GENERATION"(PDF).KomInfo.go.id.Ministry of Communication and Information Technology (Indonesia).Archived(PDF) from the original on 31 March 2014. Retrieved1 April 2017.
  30. ^"Standar Penyiaran Televisi Digital"(PDF).KomInfo.go.id.Ministry of Communication and Information Technology (Indonesia). Archived fromthe original(PDF) on 27 June 2017. Retrieved19 February 2012.
  31. ^Hawkes, Rebecca (26 February 2014)."Kuwait TV opts for Harris DVB-T2 technology".Rapid TV News. Retrieved11 April 2014.
  32. ^"Kyrgyztelecom launches DVB-T2 & DVB-S2".DVB.org. 7 November 2014. Archived fromthe original on 19 April 2016. Retrieved7 April 2016.
  33. ^"北朝鮮で4局が地上デジタル放送を実施中、ASUS ZenFone Go TVで確認".blogofmobile.com (in Japanese). 8 September 2019. Retrieved24 June 2020.
  34. ^Williams, Martyn (17 March 2013)."Report: DPRK testing digital TV".North Korea Tech – 노스코리아테크.Archived from the original on 23 September 2019. Retrieved25 September 2019.
  35. ^"Qatar Goes DVB-T2".DVB.org. 11 December 2013. Archived fromthe original on 26 September 2019. Retrieved12 April 2014.
  36. ^"Tajikistan Confirms DVB-T2 Adoption".DVB.org. 4 February 2014. Archived fromthe original on 29 December 2016. Retrieved7 April 2016.
  37. ^Mochiko, Thabiso (26 November 2010)."BusinessDay – State U-turn on Nyanda's digital-TV signal plan".BusinessDay.co.za. BDFM Publishers.Archived from the original on 30 November 2010. Retrieved26 November 2010.
  38. ^Etherington-Smith, James (3 January 2011)."DVB-T2 chosen as digital TV standard".MyBroadband.co.za. Retrieved3 January 2011.

References

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  • ETSI Standard: EN 300 744 V1.5.1,Digital Video Broadcasting (DVB); Framing structure, channel coding and modulation for digital terrestrial television, available atETSI 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.)

External links

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