DVB-T

List of digital television broadcast standards DVB family (Europe) DVB-S (satellite) DVB-S2 DVB-T (terrestrial) DVB-T2 DVB-C (cable) DVB-C2 DVB-H (handheld) DVB-SH (satellite) ATSC family (North America) ATSC (terrestrial/cable) ATSC-M/H (mobile/handheld) ISDB family (Japan/Latin America) ISDB-S (satellite) ISDB-T (terrestrial) 1seg (handheld) ISDB-C (cable) SBTVD/ISDB-Tb (Brazil) Chinese Digital Video Broadcasting standards DMB-T/H (terrestrial/handheld) ADTB-T (terrestrial) CMMB (handheld) DMB-T (terrestrial) DMB Family (Korean handheld) T-DMB (terrestrial) S-DMB (satellite) MediaFLO Codecs Video MPEG-2 H.264/MPEG-4 AVC AVS Audio MP2 MP3 AC-3 AAC HE-AAC Frequency bands VHF UHF SHF 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 publicated in 19971 and first broadcast in the UK in 1998.2 This system transmits compressed digital audio, video and other data in an MPEG transport stream, using coded orthogonal frequency-division multiplexing (COFDM or OFDM) modulation. Contents 1 Basics of DVB-T 2 Technical description of a DVB-T transmitter 3 Technical description of the receiver 4 Countries and territories using DVB-T[4] 4.1 Latin America 4.2 Europe 4.3 Asia & Australia 4.4 Africa 5 Channel data 6 See also 7 Notes 8 References 9 External links // Basics of DVB-T Rather than carrying the data on a single radio frequency (RF) 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 1,705 or 6,817 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 uses 6 MHz channels. Examples include the UK's Freeview. DVB-T receivers are generally manufactured so that they can be set up to work with all these different systems without being made for specific countries or regions. 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 3, the ETSI E-Book and Scandivia NorDig. DVB-T has been further developed into newer standards such as DVB-H (Handheld), now in operation, and DVB-T2, 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 (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 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-2 multiplexing (MUX) compressed video, compressed audio, and data streams are multiplexed into MPEG program streams (MPEG-PSs). One or more MPEG-PSs 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). MUX adaptation and energy dispersal 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. 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. 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. Spectrum of a DVB-T signal in 8k mode (note the flat-top characteristics). OFDM Modulation the sequence of blocks is modulated according to the OFDM 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). 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-analogue 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 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 4.976 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 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. Guard interval disposal: the cyclic prefix is removed. OFDM demodulation Frequency equalization: the pilot signals equalize the received signal. Demapping Internal deinterleaving Internal decoding: uses the Viterbi algorithm. External deinterleaving External decoding MUX adaptation MPEG-2 demultiplexing and source decoding Countries and territories using DVB-T4 DTT broadcasting systems Countries using DVB-T are shown in blue. Latin America  Colombia (decided on August 28, 2008) 5 (Uses DVB-T/H.264/MPEG-4 for SD and DVB-T2/H.264/MPEG-4 for HD transmissions.  Panama (decided on May 12, 2009) 6 (Uses DVB-T/MPEG-2 for SD and DVB-T2/H.264/MPEG-4 for HD transmissions.)  Trinidad and Tobago Europe  Albania  Andorra  Austria  Belgium  Belarus (uses MPEG-4 AVC /H.264 for SD transmission.)  Bulgaria (experimental in capital Sofia - MPEG-2, FEC=2/3, 16 QAM. Will shift soon to MPEG-4)  Croatia (See DVB-T in Croatia.)  Czech Republic  Cyprus (MPEG-4 video)  Denmark (Uses MPEG-2/MPEG-4) for SD and MPEG-4 for HD transmissions. See DVB-T in Denmark.)  Faroe Islands  Greenland (Nuuk tv)  Estonia (uses MPEG-4 video)  Finland  France (uses MPEG-2 for SD and MPEG-4 for HD transmissions.)  Germany (usually MPEG-2, SD only, Überallfernsehen)  Greece (ERT Digital and Digital Union use MPEG-2 but will shift to MPEG-4. Digea uses MPEG-4)  Hungary (branded MinDigTV, uses H.264/MPEG-4 AVC video exclusively.)  Iceland7  Ireland (Will use MPEG-4 video, see DVB-T in Ireland.)  Italy (MPEG2 for SD, MPEG 4 AVC for HD)  Latvia (uses H.264/MPEG-4 AVC)  Lithuania (uses H.264/MPEG-4 AVC)  Luxembourg  Macedonia (DVB-T in Macedonia)  Malta  Moldova (uses MPEG-2. MPEG-4 is being tested.)  Montenegro  Netherlands (uses MPEG-2)  Norway (Uses MPEG-4) for SD and MPEG-4 for HD transmissions. See DVB-T in Norway.)  Poland (Uses MPEG-4/H.264 video)  Portugal (Uses MPEG-4 video/H.264)  Romania (uses MPEG-2 for SD and MPEG-4 for HD transmissions.)  Russia (experimental)  Serbia (testing, will use MPEG-4 video and DVB-T28)  Slovakia  Slovenia (Use MPEG-4 video since 2007. See DVB-T in Slovenia)  Spain (Uses DVB-T/MPEG-2 for SD and DVB-T/H.264/MPEG-4 for HD transmissions.)  Sweden (Uses MPEG-2/MPEG-4) for SD and DVB-T2 with MPEG-4 for HD transmissions. See DVB-T in Sweden.)  Switzerland  Turkey (experimental)  United Kingdom (Uses DVB-T/MPEG-2 for SD and DVB-T2/H.264/MPEG-4 for HD transmissions. See DVB-T in United Kingdom.)  Ukraine (uses MPEG-4) Asia & Australia  Australia (Uses DVB-T/MPEG-2 for both SD and HD transmissions.)  Bahrain (In Assessment)  India (Uses MPEG-4 and MPEG-2 Video)  Indonesia (Experimental target in 2015 full covered all city)  Iran (uses MPEG-4/H.264 SD video and DVB-T/H.264/MPEG-4 for SD transmissions)  Iraq (In Assessment)  Israel (uses MPEG-4/H.264 video)  Jordan (In Assessment)citation needed  Kuwait (Will use MPEG-2 for SD and MPEG-4 for HD transmissions.)  Lebanon (In Assessment)citation needed  Malaysia (experimental, may also adopt DMB-T/H)  Maldives  Myanmar  New Zealand (see Freeview New Zealand)  Oman (In Assessment)  Palestine (In Assessment)citation needed  Qatar (In Assessment)  Singapore  Saudi Arabia (Will use MPEG-2 for SD and MPEG-4 for HD transmissions.)  Syria (Will use DVB-T , MPEG-2 and MPEG-4.)citation needed  Sri Lanka (pilot service 9)  Taiwan (Uses DVB-T/MPEG-2 for SD and DVB-T2/H.264/MPEG-4 for HD transmissions.)  Thailand (May use either DVB-T or ISDB-T)  Vietnam  United Arab Emirates (Will use MPEG-2 for SD and MPEG-4 for HD transmissions.)  Yemen (In Assessment) Africa  Algeria  Ghana  Cape Verde  Kenya (Will use MPEG-4)  Mauritius  Morocco  Namibia  South Africa (Will use DVB-T2, after briefly considering ISDB-T)1011  Tunisia (experimental) Channel data Some DVB-T receiver can upload channel data to a USB device (i.e. external hard disk).citation needed 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 DVB-T2 Digital terrestrial television DMB-T - Digital Multimedia Broadcast-Terrestrial Interactive television ISDB - Integrated Services Digital Broadcasting ISDB-T International OFDM system comparison table Personal video recorder Spectral efficiency comparison table Teletext Notes ^ "What is DVB-T". http://www.radio-electronics.com/info/broadcast/digital-video-broadcasting/what-is-dvb-t-basics-tutorial.php. Retrieved 2009-07-19.  ^ "What is DVB-T". http://www.radio-electronics.com/info/broadcast/digital-video-broadcasting/what-is-dvb-t-basics-tutorial.php. Retrieved 2009-07-19.  ^ "DGTVi - Per la Televisione Digitale Terrestre". http://www.dgtvi.it.  ^ DVB.org, Official information taken from the DVB website ^ El Espectador, Colombia adopta el estándar europeo para la tv digital terrestre, 28 August 2008 ^ Panama adopts DVB-T ^ "Digital Ísland" (in Icelandic). fjarskiptahandbokin.is. http://www.fjarskiptahandbokin.is/index.php?option=com_content&task=view&id=75&Itemid=125. Retrieved 2009-10-27.  ^ "DVB-T2" (in Serbian). http://www.mtid.gov.rs/digitalizacija/digitalizacija.639.html. Retrieved 2009-12-08.  ^ Lankanewspapers.com, Dialog TV launches another South Asia's first DVBT, 2008-01-24. Retrieved on 2008-01-26. ^ "BusinessDay - State U-turn on Nyanda's digital-TV signal plan". http://www.businessday.co.za/articles/Content.aspx?id=127899. Retrieved 2010-11-26.  ^ "DVB-T2 chosen as digital TV standard". http://mybroadband.co.za/news/broadcasting/17491-DVB--chosen-digital-standard.html. Retrieved 2011-01-03.  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.) 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