DVB-T stands for Digital Video Broadcasting – Terrestrial; it is the DVB European consortium standard for the broadcast transmission of digital terrestrial television. For the chemical compound see Divinylbenzene. Digital Video Broadcasting ( DVB) is a suite of internationally accepted Digital Terrestrial Television ( DTTV or DTT) is an implementation of digital technology to provide a greater number of channels and/or better quality of picture and This system transmits a compressed digital audio/video stream, using OFDM modulation with concatenated channel coding (i. Orthogonal frequency-division multiplexing ( OFDM) — essentially identical to Coded OFDM ( COFDM) and Discrete multi-tone modulation ( In Computer science, a channel code is a broadly used term mostly referring to the Forward error correction code and Bit interleaving in communication and e. COFDM). The adopted source coding methods are MPEG-2 and, more recently, H.264/MPEG-4 AVC. MPEG-2 is a standard for "the generic coding of moving pictures and associated audio information" H264 is a standard for Video compression. It is also known as MPEG-4 Part 10, or MPEG-4 AVC (for Advanced Video Coding)

DVB-T is a method of transmission that is being adopted primarily for digital television broadcasting, for example in the UK, Freeview. The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom, the UK or Britain,is a Sovereign state located Freeview is an operator of free Digital terrestrial television in the United Kingdom, using the DVB-T standard OFDM works by splitting the wide-band digital signal into a large number of slower digital streams, and then transmitting them all on a set of closely spaced adjacent carrier frequencies, rather than just one. Orthogonal frequency-division multiplexing ( OFDM) — essentially identical to Coded OFDM ( COFDM) and Discrete multi-tone modulation ( Typically, transmitters miles apart can be operated on the same set of frequencies and a receiver in between will demodulate correctly the signal coming from both.

OFDM is also used for digital radio broadcasting.

Contents 1 DVB-T2 2 The DVB-T2 draft standard 3 Technical description of a DVB-T transmitter 4 Technical description of the receiver 5 Countries and territories using DVB-T[6] 5.1 Americas 5.2 Europe 5.3 Asia/Australasia 5.4 Africa 6 See also 7 Notes 8 References 9 External links

DVB-T2

In March 2006 DVB decided to study options for an upgraded DVB-T standard. In June 2006, a formal study group named TM-T2 (Technical Module on Next Generation DVB-T) was established by the DVB Group to develop an advanced modulation scheme that could be adopted by a second generation digital terrestrial television standard, to be named DVB-T2. ^[1]

According to the commercial requirements and call for technologies^[2] issued in April 2007, the first phase of DVB-T2 will be devoted to provide optimum reception for stationary (fixed) and portable receivers (i. e. , units which can be nomadic, but not fully mobile) using existing aerials, whereas a second and third phase will study methods to deliver higher payloads (with new aerials) and the mobile reception issue. The novel system should provide a minimum 30% increase in payload, under similar channel conditions already used for DVB-T. Expected technologies will probably include:

• LDPC/BCH code forward error correction, in compliance with the technique already adopted in the DVB-S2 satellite standard, and other newer standards. In Information theory, a low-density parity-check code (LDPC code is an Error correcting code, a method of transmitting a message over a noisy transmission In Telecommunication and Information theory, forward error correction (FEC is a System of Error control for Data transmission, whereby Digital Video Broadcasting - Satellite - Second Generation ( DVB-S2) is an enhanced specification to replace the DVB-S standard developed in 2003 and ratified
• Optional use of MIMO and other antenna diversity system. In Radio, multiple-input and multiple-output, or MIMO (pronounced mee-moh or my-moh) is the use of multiple antennas at both the transmitter Antenna diversity, also known as space diversity, is one in a superset of wireless Diversity schemes that utilizes two or more antennas to improve the quality and reliability
• Improved methods for reducing peak power to the antenna (PAPR reduction).
• More than 8k carriers. 16k and 32k carriers would minimize the overhead when single frequency networks are used. A single-frequency network or SFN is a Broadcast network where several Transmitters simultaneously send the same signal over the same Frequency Present SFN networks are likely to see gains of 50% or more in net bit rate.
• Improved channel estimation. Less overhead from fewer pilot carriers is likely.
• 30% larger distance between adjacent transmitters possible with SFN. Much larger SFN.
• Variable coding and modulation.
• Flexible multiplexing; several concurrent transport streams including Generic Stream Encapsulation for IP.
• New DVB-T2 receivers are expected to be able to receive DVB-T, but DVB-T receivers will not receive DVB-T2 as hardware changes are needed. Firmware upgrades will not be enough.

It is expected that work on the DVB-T2 specification will be completed and passed to ETSI for standardization during 2008. The European Telecommunications Standards Institute ( ETSI) is an independent non-for-profit Standardization organization of the Telecommunications First draft standard is expected by the end of June 2008. Market deployment is expected for 2009.

The BBC, ITV, Channel 4 and Five have agreed with the regulator Ofcom to convert one UK multiplex (B, or PSB3) to DVB-T2 to increase capacity for HDTV via DTT. Independent Television (generally known as ITV) is a public service network of British commercial television broadcasters set up under the Independent Channel 4 is a public-service Television and Radio broadcaster in the United Kingdom centred around a television channel of the same name which began The Office of Communications (Y Swyddfa Gyfathrebiadau or as it is more often known Ofcom is the independent regulator and competition authority for the Communication ^[3] They expect the first TV region to use the new standard will be Granada in November 2009 (with existing switched over regions being changed at the same time). Granada Television is the United Kingdom ITV contractor for North West England. It is expected that over time there will be enough DVB-T2 receivers sold to switch all DTT transmissions to DVB-T2, and MPEG-4 Part 10. H264 is a standard for Video compression. It is also known as MPEG-4 Part 10, or MPEG-4 AVC (for Advanced Video Coding)

Ofcom recently published its final decision for HDTV using DVB-T2 and MPEG-4 ^[4]: BBC HD will have one HD slot after DSO at Granada and ITV, C4 and Five will compete for the two remaining HD slots from 2009 until 2012. BBC HD is a High-definition television channel provided by the BBC. Granada Television is the United Kingdom ITV contractor for North West England.

The DVB-T2 draft standard

From documents published on the Internet by RAI and others, the following characteristics are expected for the T2 standard:^[5]

• Modulation will be standard COFDM in one of the modes QPSK, 16-QAM, 64-QAM, or 256-QAM (but not 128-QAM). Rai - Radiotelevisione Italiana, known until 1954 as Radio Audizioni Italiane, is the Italian public service broadcaster, and is considered
• OFDM modes will be 1k, 2k, 4k, 8k, 16k and 32k. The symbol length for 32k mode will be about 4 ms.
• Guard intervals will be 1/128, 1/32, 1/16, 19/256, 1/8, 19/128, and 1/4. (For 32k mode, the maximum is 1/8. )
• FEC will be LDPC and BCH (as in DVB-S2), with rates 1/2, 3/5, 2/3, 3/4, 4/5, and 5/6.
• There will be fewer pilots, in 8 different pilot-patterns, and equalization will be based also on the RAI CD3 system.
• In the 32k mode, a larger part of the standard 8 Mhz channel can be used, adding about 2% extra capacity.
• DVB-T2 will be specified for 1. 7, 5, 6, 7, 8, and 10 MHz channel bandwidth.
• MISO (Multiple-Inputs Single-Output) may be used (Alamouti scheme), but MIMO will not be used. In Radio, multiple-input and multiple-output, or MIMO (pronounced mee-moh or my-moh) is the use of multiple antennas at both the transmitter Diversity receivers can be used (as they are with DVB-T).
• Bundling of more channels into a SuperMUX (called TFS) is not in the standard, but may be added later.

An example for a UK MFN DVB-T profile (QAM64, 2k, CR2/3, GI1/32) and a DVB-T2 equivalent (QAM256, 32k, CR3/5, GI1/128) shows an increase in bit rate from 24. 13 Mbit/s to 35. 4 Mbit/s (+46. 5%).
Another example is an Italian SFN DVB-T profile (QAM64, 8k, CR2/3, GI1/4) and a DVB-T2 equivalent (QAM256, 32k, CR3/5, GI1/16): it shows an increase in bit rate from 19. 91 Mbit/s to 33. 3 Mbit/s (+67%).

Status of the DVB-T2 specification (early April 2008)

• The DVB-T2 physical layer specification is complete and there will be no further technical enhancements.
• The receiver VLSI chip design can be started with confidence in stability of specification (the DVB internal standard document is available to all DVB members including the leading chip companies)
• Draft PSI/SI (program and system information) specification document agreed with the DVB-TM-GBS group.

Some information can be found in this document DVB-T2 Fact Sheet June 2008

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 PSs (Programme Streams). For multiplexing in electronics and signal processing see Multiplexer. Program stream ( PS or MPEG-PS) is a container format for multiplexing Digital audio, Video and more One or more PSs are joined together into an MPEG-2 TS (MPEG-2 Transport Stream); this is the basic digital stream which is being transmitted and received by home Set Top Boxes (STB). Transport stream ( TS, TP, MPEG-TS, or M2T) is a Communications protocol for audio, video, and data A set-top box (STB or set-top unit (STU is a device that connects to a Television and an external source of signal, turning the signal into 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). In Telecommunications and Computing, bitrate (sometimes written bit rate, data rate or as a Variable R or f b In telecommunications Bit rate or Data transfer rate is the average number of Bits characters or blocks per unit time passing between equipment in a data transmission

• 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. High-definition television (HDTV is a Digital television Broadcasting system with higher resolution than traditional television systems (standard-definition In Telecommunications, a carrier wave, or carrier is a Waveform (usually Sinusoidal) that is modulated (modified with an input signal 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). In Information technology, a packet is a formatted unit of Data carried by a Packet mode Computer network. With a technique called energy dispersal, the byte sequence is decorrelated. In Probability theory and Statistics, correlation, (often measured as a correlation coefficient) indicates the strength and direction of a linear

• External encoder: a first level of error correction is applied to the transmitted data, using a nonbinary 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. In Computer science, a block code is a type of Channel coding. Reed-Solomon error correction is an Error-correcting code that works by Oversampling a Polynomial constructed from the data

• 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. Interleaving in Computer science is a way to arrange Data in a non- Contiguous way in order to increase performance

• 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). In Telecommunication, a convolutional code is a type of Error-correcting code in which (a each m - Bit Information symbol (each In Telecommunication and Information theory, forward error correction (FEC is a System of Error control for Data transmission, whereby 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. In Telecommunications, modulation is the process of varying a periodic Waveform, i Phase-shift keying (PSK is a Digital Modulation scheme that conveys data by changing or modulating the phase of a reference signal

• Frame adaptation: 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. While receiving a stream of framed Data, frame synchronization is the process by which incoming frame alignment signals i

• 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. Radio is the transmission of signals by Modulation of electromagnetic waves with frequencies below those of visible Light. 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. It should be noted that 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 2048, 4096, or 8192 carriers (2k, 4k, 8k mode, respectively). Orthogonal frequency-division multiplexing ( OFDM) — essentially identical to Coded OFDM ( COFDM) and Discrete multi-tone modulation ( 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). In an OFDM symbol the cyclic prefix is a repeat of the end of the symbol at the beginning 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 (DAC), and then modulated to radio frequency (VHF, UHF) by the RF front-end. In Electronics, a digital-to-analog converter ( DAC or D-to-A) is a device for converting a digital (usually binary code to an Analog signal Very high frequency (VHF is the Radio frequency range from 30 MHz to 300 MHz. Front-end and back-end are generalized terms that refer to the initial and the end stages of a process The occupied bandwidth is designed to accommodate each single DVB-T signal into 5, 6, 7, or 8 MHz wide channels. The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. The base band sample rate provided at the DAC input depends on the channel bandwidth: it is samples/s, where B 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
		1/4	1/8	1/16	1/32
QPSK	1/2	4. In Telecommunications, guard intervals are used to ensure that distinct transmissions do not interfere with one another Phase-shift keying (PSK is a Digital Modulation scheme that conveys data by changing or modulating the phase of a reference signal 976	5. 529	5. 855	6. 032
	2/3	6. 635	7. 373	7. 806	8. 043
	3/4	7. 465	8. 294	8. 782	9. 048
	5/6	8. 294	9. 216	9. 758	10. 053
	7/8	8. 709	9. 676	10. 246	10. 556
16-QAM	1/2	9. 953	11. 059	11. 709	12. 064
	2/3	13. 271	14. 745	15. 612	16. 086
	3/4	14. 929	16. 588	17. 564	18. 096
	5/6	16. 588	18. 431	19. 516	20. 107
	7/8	17. 418	19. 353	20. 491	21. 112
64-QAM	1/2	14. 929	16. 588	17. 564	18. 096
	2/3	19. 906	22. 118	23. 419	24. 128
	3/4	22. 394	24. 882	26. 346	27. 144
	5/6	24. 882	27. 647	29. 273	30. 160
	7/8	26. 126	29. 029	30. 737	31. 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 (ADC). An analog-to-digital converter (abbreviated ADC, A/D or A to D) is an electronic integrated circuit which converts continuous signals to

• Time and frequency synchronization: the digital base band signal is searched to identify the beginning of frames and blocks. Any problems on 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. The Doppler effect (or Doppler shift) named after Christian Doppler, is the change in Frequency and Wavelength of a Wave for

• Guard interval disposal: the cyclic prefix is removed.
• OFDM demodulation
• Frequency equalization: the pilot signals equalize the received signal. Equalization (or equalisation, EQ) is the process of changing the frequency envelope of a sound in Audio processing.
• Demapping
• Internal deinterleaving
• Internal decoding: uses the Viterbi algorithm. The Viterbi algorithm is a Dynamic programming Algorithm for finding the most likely sequence of hidden states &ndash called the Viterbi path
• External deinterleaving
• External decoding
• MUX adaptation
• MPEG-2 demultiplexing and source decoding

Countries and territories using DVB-T^[6]

See also

• ATSC (Advanced Television Systems Committee, North American Standard)
• Digital audio broadcasting (low bitrate video suitable for moving receivers)
• DTV channel protection ratios
• DVB over IP
• Interactive television
• Digital terrestrial television
• DMB-T - Digital Multimedia Broadcast-Terrestrial
• ISDB - Integrated Services Digital Broadcasting
• OFDM system comparison table
• Spectral efficiency comparison table

Notes

References

• ETSI Standard: EN 300 744 V1. The European Telecommunications Standards Institute ( ETSI) is an independent non-for-profit Standardization organization of the Telecommunications 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. )

External links

• Website of the DVB Project
• DVB-H.org
• DigiTAG website
• OFCOM DTT future
• BBC press

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