# DVB-T

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DVB-T is an abbreviation for "Digital Video Broadcasting — Terrestrial"; it is the DVB European-based consortium standard for the broadcast transmission of digital terrestrial television that was first published in 1997 [1] and first broadcast in the UK in 1998. [1] This system transmits compressed digital audio, digital video and other data in an MPEG transport stream, using coded orthogonal frequency-division multiplexing (COFDM or OFDM) modulation. It is also the format widely used worldwide (including North America) for Electronic News Gathering for transmission of video and audio from a mobile newsgathering vehicle to a central receive point.

Digital Video Broadcasting (DVB) is a set of international open standards for digital television. DVB standards are maintained by the DVB Project, an international industry consortium, and are published by a Joint Technical Committee (JTC) of the European Telecommunications Standards Institute (ETSI), European Committee for Electrotechnical Standardization (CENELEC) and European Broadcasting Union (EBU).

Digital terrestrial television is a technology for broadcast television in which land-based (terrestrial) television stations broadcast television content by radio waves to televisions in consumers' residences in a digital format. DTTV is a major technological advance over the previous analog television, and has largely replaced analog which had been in common use since the middle of the 20th century. Test broadcasts began in 1998 with the changeover to DTTV beginning in 2006 and is now complete in many countries. The advantages of digital terrestrial television are similar to those obtained by digitising platforms such as cable TV, satellite, and telecommunications: more efficient use of limited radio spectrum bandwidth, provision of more television channels than analog, better quality images, and potentially lower operating costs for broadcasters.

The United Kingdom, officially the United Kingdom of Great Britain and Northern Ireland but more commonly known as the UK or Britain, is a sovereign country lying off the north-western coast of the European mainland. The United Kingdom includes the island of Great Britain, the north-eastern part of the island of Ireland and many smaller islands. Northern Ireland is the only part of the United Kingdom that shares a land border with another sovereign state‍—‌the Republic of Ireland. Apart from this land border, the United Kingdom is surrounded by the Atlantic Ocean, with the North Sea to the east, the English Channel to the south and the Celtic Sea to the south-west, giving it the 12th-longest coastline in the world. The Irish Sea lies between Great Britain and Ireland. With an area of 242,500 square kilometres (93,600 sq mi), the United Kingdom is the 78th-largest sovereign state in the world. It is also the 22nd-most populous country, with an estimated 66.0 million inhabitants in 2017.

## Basics

Rather than carrying one data carrier on a single radio 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.

Radio frequency (RF) is the oscillation rate of an alternating electric current or voltage or of a magnetic, electric or electromagnetic field or mechanical system in the frequency range from around twenty thousand times per second to around three hundred billion times per second. This is roughly between the upper limit of audio frequencies and the lower limit of infrared frequencies; these are the frequencies at which energy from an oscillating current can radiate off a conductor into space as radio waves. Different sources specify different upper and lower bounds for the frequency range.

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 and Trinidad and Tobago use 6 MHz channels. Examples include the UK's Freeview.

Freeview is the United Kingdom's digital terrestrial television platform. It is operated by DTV Services Ltd, a joint venture between the BBC, ITV, Channel 4, Sky and transmitter operator Arqiva. It was launched in 2002, taking over the licence from ITV Digital which collapsed that year. The service provides consumer access via an aerial to the six DTT multiplexes covering the United Kingdom. In April 2014 it had some 60 DVB-T TV channels, 26 digital radio channels, 10 HD channels, six text services, 11 streamed channels, and one interactive channel. A number of new HD channels launched in 2014, from a new group of multiplexes awarded to Arqiva. The new HD channels were launched in selected areas on 10 December 2013 with a further roll-out during 2014.

The DVB-T Standard is published as EN 300 744, Framing structure, channel coding and modulation for digital terrestrial television. This is available from the ETSI 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 for MPEG-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 the D-book in the UK, the Italian DGTVi, [2] the ETSI E-Book and the Nordic countries and Ireland NorDig.

The European Telecommunications Standards Institute (ETSI) is an independent, not-for-profit, standardization organization in the telecommunications industry in Europe, headquartered in Sophia-Antipolis, France, with worldwide projection. ETSI produces globally-applicable standards for Information and Communications Technologies (ICT), including fixed, mobile, radio, converged, broadcast and internet technologies.

MPEG-2 is a standard for "the generic coding of moving pictures and associated audio information". It describes a combination of lossy video compression and lossy audio data compression methods, which permit storage and transmission of movies using currently available storage media and transmission bandwidth. While MPEG-2 is not as efficient as newer standards such as H.264/AVC and H.265/HEVC, backwards compatibility with existing hardware and software means it is still widely used, for example in over-the-air digital television broadcasting and in the DVD-Video standard.

H.264 or MPEG-4 Part 10, Advanced Video Coding is a block-oriented motion-compensation-based video compression standard. As of 2014, it is one of the most commonly used formats for the recording, compression, and distribution of video content. It supports resolutions up to 8192×4320, including 8K UHD.

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

DVB-H is one of three prevalent mobile TV formats. It is a technical specification for bringing broadcast services to mobile handsets. DVB-H was formally adopted as ETSI standard EN 302 304 in November 2004. The DVB-H specification can be downloaded from the official DVB-H website. From March 2008, DVB-H is officially endorsed by the European Union as the "preferred technology for terrestrial mobile broadcasting". The major competitors of this technology are Qualcomm's MediaFLO system, the 3G cellular system based MBMS mobile-TV standard, and the ATSC-M/H format in the U.S. DVB-SH now and DVB-NGH in the future are possible enhancements to DVB-H, providing improved spectral efficiency and better modulation flexibility. DVB-H has been a commercial failure, and the service is no longer on-air. Finland was the last country to switch-off its signals in March 2012.

DVB-T2 is an abbreviation for "Digital Video Broadcasting — Second Generation Terrestrial"; it is the extension of the television standard DVB-T, issued by the consortium DVB, devised for the broadcast transmission of digital terrestrial television. DVB has been standardized by ETSI.

DVB-T as a digital transmission delivers data in a series of discrete blocks at the symbol rate. DVB-T is a COFDM 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 allows single-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 to GPS.

The length of the Guard Interval can be chosen. It is a trade-off between data rate and SFN capability. The longer the guard interval the larger is the potential SFN area without creating intersymbol 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

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

Source coding and MPEG-2 multiplexing (MUX)
Compressed video, compressed audio, and data streams are multiplexed into MPEG program streams (MPEG-PS's). One or more MPEG-PS's are joined together into an MPEG transport stream (MPEG-TS); this is the basic digital stream which is being transmitted and received by TV sets or home Set Top Boxes (STB). Allowed bitrates for the transported data depend on a number of coding and modulation parameters: it can range from about 5 to about 32 Mbit/s (see the bottom figure for a complete listing).
Splitter
Two different MPEG-TSs can be transmitted at the same time, using a technique called Hierarchical Transmission. It may be used to transmit, for example a standard definition SDTV signal and a high definition HDTV signal on the same carrier. 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).
The MPEG-TS is identified as a sequence of data packets, of fixed length (188 bytes). With a technique called energy dispersal, the byte sequence is decorrelated.
External encoder
A first level of error correction is applied to the transmitted data, using a non-binary block code, a Reed-Solomon RS (204, 188) code, allowing the correction of up to a maximum of 8 wrong bytes for each 188-byte packet.
External interleaver
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 punctured convolutional 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 valid modulation schemes: QPSK, 16-QAM, 64-QAM.
the complex symbols are grouped in blocks of constant length (1512, 3024, or 6048 symbols per block). A frame is generated, 68 blocks long, and a superframe is built by 4 frames.
Pilot and TPS signals
In order to simplify the reception of the signal being transmitted on the terrestrial radio 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.
OFDM Modulation
The sequence of blocks is modulated according to the OFDM 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 same carrier frequency.
DAC and front-end
The digital signal is transformed into an analogue signal, with a digital-to-analog converter (DAC), and then modulated to radio frequency (VHF, UHF) by the RF front end. The occupied bandwidth is designed to accommodate each single DVB-T signal into 5, 6, 7, or 8 MHz wide channels. The base band sample rate provided at the DAC input depends on the channel bandwidth: it is ${\displaystyle f_{s}={\frac {8}{7}}B}$samples/s, where ${\displaystyle B}$ is the channel bandwidth expressed in Hz.
Available bit rates (Mbit/s) for a DVB-T system in 8 MHz channels
ModulationCoding rate Guard interval
1/41/81/161/32
QPSK 1/24.9765.5295.8556.032
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-QAM 1/29.95311.05911.70912.064
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-QAM 1/214.92916.58817.56418.096
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

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 an analogue-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 new OFDM 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 by Doppler 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.
• Frequency equalization: the pilot signals are used to estimate the Channel Transfer Function (CTF) every three subcarriers. 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 the Viterbi 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
• MPEG-2 demultiplexing and source decoding

## Notes

1. "What is DVB-T" . Retrieved 2009-07-19.
2. DVB.org, Official information taken from the DVB website
3. "About - DVB" . Retrieved 26 June 2016.
4. "News - DVB" . Retrieved 26 June 2016.
5. "KTV Ltd" . Retrieved 26 June 2016.
6. "Plan for the introduction of terrestrial digital television broadcasting(DVB-T) in the Republic of Bulgaria" (in Bulgarian). Ministry of Transportation, Information Technology and Communications. Retrieved 2012-12-17.
7. "Digital Television". NURTS (TV tower operator). Retrieved 2012-12-17.
8. "Digital Ísland" (in Icelandic). fjarskiptahandbokin.is. Retrieved 2009-10-27.
9. "ETV: trial DVB-T2 network" (in Serbian). Archived from the original on 16 April 2012. Retrieved 22 March 2012.
10. "100,000 likes – Oqaab reaches over 1 Mio TV Households". 31 March 2015. Retrieved 26 June 2016.
11. "Samart eyes Middle East market for digital TV-enabled smartphone" . Retrieved 26 June 2016.
12. "PERSYARATAN TEKNIS ALAT DAN PERANGKAT PENERIMA TELEVISI SIARAN DIGITAL BERBASIS STANDAR DIGITAL VIDEO BROADCASTING TERRESTRIAL – SECOND GENERATION" (PDF). Kominfo. Retrieved 1 April 2017.
13. Hawkes, Rebecca (26 February 2014). "Kuwait TV opts for Harris DVB-T2 technology". www.rapidtvnews.com/. Retrieved 2014-04-11.
14. "Qatar Goes DVB-T2". https://www.dvb.org . 11 December 2013.External link in |website= (help)
15. 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. Retrieved 26 November 2010.
16. "DVB-T2 chosen as digital TV standard" . Retrieved 2011-01-03.

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## References

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