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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
Digital terrestrial television

Digital Terrestrial Television is an implementation of digital technology to provide a greater number of channels and/or better quality of picture and sound using aerial broadcasts to a conventional Antenna instead of a satellite dish or cable connection....
. This system transmits compressed digital audio, video and other data in an MPEG transport stream, using COFDM modulation.

er than carrying the data on a single radio frequency carrier, OFDM works by splitting the digital data stream into a large number of slower digital streams, each of which digitally modulate a set of closely spaced adjacent carrier frequencies.






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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
Digital terrestrial television

Digital Terrestrial Television is an implementation of digital technology to provide a greater number of channels and/or better quality of picture and sound using aerial broadcasts to a conventional Antenna instead of a satellite dish or cable connection....
. This system transmits compressed digital audio, video and other data in an MPEG transport stream, using COFDM modulation.

Basics of DVB-T

Rather than carrying the data on a single radio frequency carrier, OFDM works by splitting the digital data stream into a large number of slower digital streams, each of which digitally modulate a set of closely spaced adjacent 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 1705 or 6817 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
DVB-T

DVB-T is an abbreviation for Digital Video Broadcasting ?? Terrestrial; it is the Digital Video Broadcasting European-based consortium standard for the broadcast transmission of digital terrestrial television....
), using mainly VHF 7 MHz and UHF 8 MHz channels whereas Taiwan uses 6 MHz channels. Examples include the UK's Freeview.

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
MPEG-2

MPEG-2 is a standard for "the generic coding of moving pictures and associated audio information". It describes a combination of Lossy compression video compression and lossy audio data compression methods which permit storage and transmission of movies using currently available storage media and transmission bandwidth....
 and, more recently, H.264/MPEG-4 AVC
H.264/MPEG-4 AVC

H.264 is a standard for video compression, and is equivalent to MPEG-4 Part 10, or MPEG-4 AVC . , it is the latest block-oriented motion-compensation-based codec standard developed by the ITU-T Video Coding Experts Group together with the International Organization for Standardization/International Electrotechnical...
 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 , the ETSI E-Book and Scandivia NorDig.

DVB-T has been further developed into newer standards such as DVB-H
DVB-H

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 European Telecommunications Standards Institute standard EN 302 304 in November 2004....
 (Handheld), now in operation, and DVB-T2
DVB-T2

DVB-T2 is an abbreviation for Digital Video Broadcasting ? Second Generation Terrestrial; it is the upcoming extension of the existing standard DVB-T, issued by the European-based consortium Digital Video Broadcasting, devised for the broadcast transmission of digital terrestrial television....
, which was recently finalised.

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
Single-frequency network

A single-frequency network or SFN is a broadcast network where several transmitters simultaneously send the same signal over the same frequency channel....
 (SFN) operation, where two or more transmitters carrying the same data operating 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 a 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 tradeoff between datarate and SFN capability. The longer the guard intervall the larger is the potential SFN area without creating Inter Symbol Interference (ISI). It can be 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
    Source coding

    In information theory, Shannon's source coding theorem establishes the limits to possible data compression, and the operational meaning of the Shannon entropy....
     and MPEG-2 multiplexing
    Multiplexing

    In telecommunications and computer networks, multiplexing is a process where multiple analog message signals or digital data streams are combined into one signal over a shared medium....
     (MUX):     compressed video, compressed audio, and data streams are multiplexed into PSs (Programme Streams
    Program stream

    Program stream is a container format for multiplexing digital audio, video and more. The PS format is specified in MPEG-1 Systems and MPEG-2 Part 1, Systems ....
    ). One or more PSs are joined together into an MPEG-2 TS (MPEG-2 Transport Stream
    Transport stream

    Transport stream is a communications protocol for Digital audio, Digital video, and Program and System Information Protocol which is specified in MPEG-2 Part 1, Systems ....
    ); this is the basic digital stream which is being transmitted and received by home Set Top Boxes (STB). Allowed bitrate
    Bitrate

    In telecommunications and computing, bitrate is the number of bits that are conveyed or processed per unit of time.The bit rate is quantified using the Data rate units unit, often in conjunction with an SI prefix such as kilo- , mega- , giga- or tera- ....
    s 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 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
    Carrier wave

    In telecommunications, a carrier wave, or carrier is a waveform that is Modulation with an signal for the purpose of conveying information....
    . 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-2 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
    Correlation

    In probability theory and statistics, correlation indicates the strength and direction of a linear relationship between two random variables....
    .


  • External encoder: a first level of error correction is applied to the transmitted data, using a nonbinary block code
    Block code

    In computer science, a block code is a type of channel coding. It adds redundancy to a message so that, at the receiver, one can decode with minimal errors, provided that the information rate would not exceed the channel capacity....
    , 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
    Convolutional code

    In telecommunication, a convolutional code is a type of error-correcting code in which each m-bit information symbol to be encoded is transformed into an n-bit symbol, where m/n is the code rate and the transformation is a function of the last k information symbols, where k is the constraint length of the code....
    , which is often denoted in STBs menus as FEC (Forward error correction
    Forward error correction

    In telecommunication and information theory, forward error correction is a system of error control for data transmission, whereby the sender adds Redundancy to its messages, also known as an error correction code....
    ). 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
    Modulation

    In telecommunications, modulation is the process of varying a Periodic function waveform, i.e. a tone, in order to use that signal to convey a message, in a similar fashion as a musician may modulate the tone from a musical instrument by varying its volume, timing and Pitch ....
     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). A frame
    Frame synchronization

    While receiving a stream of data frame data, frame synchronization is the process by which incoming frame alignment signals, i.e., distinctive bit sequences , are identified, i.e., distinguished from data bits, permitting the data bits within the frame to be extracted for decoding or retransmission....
     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
    Orthogonal frequency-division multiplexing

    Orthogonal frequency-division multiplexing ? essentially identical to Coded OFDM and Discrete multi-tone modulation ? is a frequency-division multiplexing scheme utilized as a digital multi-carrier modulation method....
     technique, using 2048, 4096, or 8192 carriers (2k, 4k, 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
    Cyclic prefix

    In an Orthogonal frequency-division multiplexing symbol the cyclic prefix is a repeat of the end of the symbol at the beginning. The purpose is to allow multipath to settle before the main data arrives at the receiver....
    ). 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 analog signal, with a digital-to-analog converter
    Digital-to-analog converter

    In electronics, a digital-to-analog converter is a device for converting a digital code to an analog signal .An analog-to-digital converter performs the reverse operation....
     (DAC), and then modulated to radio frequency (VHF
    Very high frequency

    VHF is the radio frequency range from 30 megahertz to 300 megahertz. Frequencies immediately below VHF are denoted High frequency , and the next higher frequencies are known as Ultra high frequency ....
    , UHF
    Ultra high frequency

    Ultra high frequency designates a range of Electromagnetic radiation waves with frequency between 300 megahertz and 3 gigahertz . Also known as the decimetre band or decimetre wave as the wavelengths range from ten to one decimetres....
    ) by the RF
    RF

    Rf or RF is an abbreviation for:* ** Radiative forcing, is an IPCC unit that nominates the global, annual average of radiative imbalance in net heating of the Earth's lower atmosphere as a result of human activities since the beginning of the industrial era....
     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 samples/s, where is the channel bandwidth expressed in Hz.


Available bitrates (Mbit/s) for a DVB-T system in 8 MHz channels
Modulation Coding rate Guard interval
Guard interval

In telecommunications, guard intervals are used to ensure that distinct transmissions do not interfere with one another. These transmissions may belong to different users or to the same user ....
1/41/81/161/32
QPSK
Phase-shift keying

Phase-shift keying is a digital modulation scheme that conveys Data#Uses of data in computing by changing, or modulating, the Phase of a reference Signal ....
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
Quadrature amplitude modulation

Quadrature amplitude modulation is a modulation scheme which conveys data by changing the amplitude of two carrier waves. These two waves, usually sinusoids, are out of phase with each other by 90degree and are thus called Quadrature phase carriers?hence the name of the scheme....
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
Quadrature amplitude modulation

Quadrature amplitude modulation is a modulation scheme which conveys data by changing the amplitude of two carrier waves. These two waves, usually sinusoids, are out of phase with each other by 90degree and are thus called Quadrature phase carriers?hence the name of the scheme....
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 analog RF signal is converted to base-band and transformed into a digital signal, using an analog-to-digital converter
    Analog-to-digital converter

    An analog-to-digital converter is a device which converts continuous signal to Discrete signal digital numbers. The reverse operation is performed by a digital-to-analog 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
    Doppler effect

    The Doppler effect , named after Austrian physicist Christian Doppler who proposed it in 1842, is the change in frequency and wavelength of a wave for an observer moving relative to the source of the waves....
    , inaccuracies in either the transmitter or receiver clock, and so on.


  • Guard interval disposal: the cyclic prefix is removed.
  • OFDM demodulation
  • Frequency equalization
    Equalization

    Equalization, equalisation or EQ is the process of using passive or active electronic elements or digital algorithms for the purpose of altering the frequency response characteristics of a system....
    :     the pilot signals equalize the received signal.
  • Demapping
  • Internal deinterleaving
  • Internal decoding: uses the Viterbi algorithm
    Viterbi algorithm

    The Viterbi algorithm is a dynamic programming algorithm for finding the most likelihood function sequence of hidden states – called the Viterbi path – that results in a sequence of observed events, especially in the context of Markov information sources, and more generally, hidden Markov models....
    .
  • External deinterleaving
  • External decoding
  • MUX adaptation
  • MPEG-2 demultiplexing and source decoding


Countries and territories using DVB-T


Americas

  • (experimental)
  • (decided in August 28, 2008)
  • (decided in September 2007, but not effective yet)


Europe

  • (Plan to switch by 2011)
  • (experimental)
  • (experimental)
  • See DVB-T in Croatia.)*
  • (See DVB-T in Denmark.)
    • ()
  • (uses MPEG-4
    MPEG-4

    MPEG-4 is a collection of methods defining Video compression of audio and visual digital data. It was introduced in late 1998 and designated a standardization for a group of sound and video coding formats and related technology agreed upon by the International Organization for Standardization/International Electrotechnical Commission Moving...
     video)* (uses MPEG-2
    MPEG-2

    MPEG-2 is a standard for "the generic coding of moving pictures and associated audio information". It describes a combination of Lossy compression video compression and lossy audio data compression methods which permit storage and transmission of movies using currently available storage media and transmission bandwidth....
     for SD and MPEG-4
    MPEG-4

    MPEG-4 is a collection of methods defining Video compression of audio and visual digital data. It was introduced in late 1998 and designated a standardization for a group of sound and video coding formats and related technology agreed upon by the International Organization for Standardization/International Electrotechnical Commission Moving...
     for HD transmissions.)*
  • (branded , uses MPEG-4
    MPEG-4

    MPEG-4 is a collection of methods defining Video compression of audio and visual digital data. It was introduced in late 1998 and designated a standardization for a group of sound and video coding formats and related technology agreed upon by the International Organization for Standardization/International Electrotechnical Commission Moving...
     video exclusively.)* (Will use MPEG-4
    MPEG-4

    MPEG-4 is a collection of methods defining Video compression of audio and visual digital data. It was introduced in late 1998 and designated a standardization for a group of sound and video coding formats and related technology agreed upon by the International Organization for Standardization/International Electrotechnical Commission Moving...
     video, see DVB-T in Ireland.)* (experimental)
  • (uses H.264/MPEG-4 AVC)*** (uses MPEG-4
    MPEG-4

    MPEG-4 is a collection of methods defining Video compression of audio and visual digital data. It was introduced in late 1998 and designated a standardization for a group of sound and video coding formats and related technology agreed upon by the International Organization for Standardization/International Electrotechnical Commission Moving...
     video)
  • (experimental, uses MPEG-4
    MPEG-4

    MPEG-4 is a collection of methods defining Video compression of audio and visual digital data. It was introduced in late 1998 and designated a standardization for a group of sound and video coding formats and related technology agreed upon by the International Organization for Standardization/International Electrotechnical Commission Moving...
     video)
  • (experimental, uses MPEG-4 video)* (experimental)*
  • (Use MPEG-4
    MPEG-4

    MPEG-4 is a collection of methods defining Video compression of audio and visual digital data. It was introduced in late 1998 and designated a standardization for a group of sound and video coding formats and related technology agreed upon by the International Organization for Standardization/International Electrotechnical Commission Moving...
     video fom 2007. See DVB-T in Slovenia)* (Uses MPEG-2
    MPEG-2

    MPEG-2 is a standard for "the generic coding of moving pictures and associated audio information". It describes a combination of Lossy compression video compression and lossy audio data compression methods which permit storage and transmission of movies using currently available storage media and transmission bandwidth....
     for SD and MPEG-4
    MPEG-4

    MPEG-4 is a collection of methods defining Video compression of audio and visual digital data. It was introduced in late 1998 and designated a standardization for a group of sound and video coding formats and related technology agreed upon by the International Organization for Standardization/International Electrotechnical Commission Moving...
     for HD transmissions. See DVB-T in Sweden.)* (experimental)
  • (See DVB-T in United Kingdom.)
  • (Uses MPEG-2
    MPEG-2

    MPEG-2 is a standard for "the generic coding of moving pictures and associated audio information". It describes a combination of Lossy compression video compression and lossy audio data compression methods which permit storage and transmission of movies using currently available storage media and transmission bandwidth....
     - experimental, Kyiv only, 19 TV channels and 3 radio channels. Regular broadcasts will use MPEG-4
    MPEG-4

    MPEG-4 is a collection of methods defining Video compression of audio and visual digital data. It was introduced in late 1998 and designated a standardization for a group of sound and video coding formats and related technology agreed upon by the International Organization for Standardization/International Electrotechnical Commission Moving...
     exclusively )


Asia/Australasia

  • (Uses MPEG-4
    MPEG-4

    MPEG-4 is a collection of methods defining Video compression of audio and visual digital data. It was introduced in late 1998 and designated a standardization for a group of sound and video coding formats and related technology agreed upon by the International Organization for Standardization/International Electrotechnical Commission Moving...
     and MPEG-2
    MPEG-2

    MPEG-2 is a standard for "the generic coding of moving pictures and associated audio information". It describes a combination of Lossy compression video compression and lossy audio data compression methods which permit storage and transmission of movies using currently available storage media and transmission bandwidth....
     Video)* (pilot service)* (experimental)* (see Freeview)
  • (experimental)*
  • (pilot service )**


Africa

  • (Uses MPEG-4
    MPEG-4

    MPEG-4 is a collection of methods defining Video compression of audio and visual digital data. It was introduced in late 1998 and designated a standardization for a group of sound and video coding formats and related technology agreed upon by the International Organization for Standardization/International Electrotechnical Commission Moving...
    )
  • (experimental)


See also

  • ATSC (Advanced Television Systems Committee, North American Standard)
  • Digital audio broadcasting
    Digital audio broadcasting

    Digital Audio Broadcasting , also known as EUREKA, is a digital radio technology for broadcasting radio stations, used in several countries, particularly in the UK and Europe....
     (low bitrate video suitable for moving receivers)
  • DTV channel protection ratios
    DTV channel protection ratios

    Terrestrial digital television will co-exist with analog television for many years. The issue of electromagnetic compatibility between the two systems still looms....
  • DVB over IP
  • Interactive television
    Interactive television

    Interactive television describes a number of techniques that allow viewers to interact with television content as they view it....
  • Digital terrestrial television
    Digital terrestrial television

    Digital Terrestrial Television is an implementation of digital technology to provide a greater number of channels and/or better quality of picture and sound using aerial broadcasts to a conventional Antenna instead of a satellite dish or cable connection....
  • DMB-T - Digital Multimedia Broadcast-Terrestrial
  • ISDB
    ISDB

    Integrated Services Digital Broadcasting is a Japanese standard for digital television and digital radio used by the country's radio station and television stations....
     - Integrated Services Digital Broadcasting
  • OFDM system comparison table
    Orthogonal frequency-division multiplexing

    Orthogonal frequency-division multiplexing ? essentially identical to Coded OFDM and Discrete multi-tone modulation ? is a frequency-division multiplexing scheme utilized as a digital multi-carrier modulation method....
  • Spectral efficiency comparison table
    Spectral efficiency

    Spectral efficiency, spectrum efficiency or bandwidth efficiency refers to the information rate that can be transmitted over a given Bandwidth in a specific communication system....


External links