DVB
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DVB, short for Digital Video Broadcasting, is a suite of internationally accepted, open standards for digital television maintained by the DVB Project, an industry consortium with more than 300 members, and published by a Joint Technical Committee (JTC) of European Telecommunications Standards Institute (ETSI), European Committee for Electrotechnical Standardization (CENELEC) and European Broadcasting Union (EBU). The standards can be obtained for free at the ETSI website (http://www.etsi.org/services_products/freestandard/home.htm) after registration.
How the several DVB sub-standards interact is described in the DVB Cookbook (DVB-Cook).
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Transmission
DVB systems distribute data by:
- satellite (DVB-S and DVB-S2)
- cable (DVB-C)
- terrestrial television (DVB-T)
- terrestrial television for handhelds (DVB-H)
These standards define the physical layer and data link layer of a distribution system. Devices interact with the physical layer via a synchronous parallel interface (SPI), synchronous serial interface (SSI), or asynchronous serial interface (ASI). All data is transmitted in MPEG-2 transport streams with some additional constraints (DVB-MPEG). A standard for temporally compressed distribution to mobile devices (DVB-H) is in testing.
These distribution systems differ mainly in the modulations used, due to the requirements of different frequency bands. The high frequency DVB-S uses QPSK, lower hertz DVB-C uses QAM (64-QAM in general) and DVB-T (in VHF and/or UHF band) uses COFDM.
Content
Besides audio and video transmission, DVB also defines data connections (DVB-DATA) with return channels (DVB-RC) for several media (DECT, GSM, PSTN/ISDN etc.) and protocols (DVB-IPI: Internet Protocol, DVB-NPI: network protocol independent).
Legacy technologies like teletext (DVB-TXT) and video blanking interval data (DVB-VBI) are also supported by the standards to ease conversion. However for many applications more advanced alternatives like DVB-SUB for sub-titling are available.
Encryption and metadata
The conditional access system (DVB-CA) defines a common scrambling algorithm (DVB-CSA) and a common interface (DVB-CI) for accessing scrambled content . DVB system providers develop their proprietary conditional access systems within these specifications. DVB transports include metadata called service information (DVB-SI) that links the various elementary streams into coherent programs and provides human-readable descriptions for electronic program guides.
Software platform
The DVB Multimedia Home Platform (DVB-MHP) defines a Java-based platform for the development of consumer video system applications. In addition to providing abstractions for many DVB and MPEG-2 concepts, it provides interfaces for other features like network card control, application download, and layered graphics.
Return channel
DVB has standardised a number of return channels that work together with DVB-S/T/C to create bi-directional communication. RCS is short for Return Channel Satellite, and specifies return channels in C-, Ku- and Ka frequency-bands with return bandwidth of up to 2 Mbit/s.
Adoption
DVB-S and DVB-C were ratified in 1994. DVB-T was ratified in early 1997. The first commercial DVB-T broadcasts were performed by the United Kingdom's Digital Terrestrial Group (DTG) in late 1998. In 2003 Berlin, Germany was the first area to completely stop broadcasting analog TV signals. Many European countries aim to be fully covered with digital television by 2010 and switch off PAL/SECAM services by then.
In its origin Europe, in Australia, South Africa and India DVB is used throughout the areas it covers or is at least decided to be. This also holds true for cable and satellite in most Asian, African and many South American countries. Many of these have not yet selected a format for digital terrestrial broadcasts (DTTV) and a few (Argentina and South Korea) chose ATSC instead of DVB-T for now.
With the exception of SkyPerfect, Japan uses different formats in all areas (ISDB), which are however quite similar to their DVB counterparts. SkyPerfect is a satellite provider using DVB on their 124 and 128 degrees east satellites. Their satellite at 110 degrees east does not use DVB however.
In North America DVB-S is often used in signal compression and encoding of digital satellite communications alongside Hughes DSS. Unlike Motorola's DigiCipher 2 standard, DVB has a wider adoption in terms of the number of manufacturers of receivers. Cable operators either use DVB-C or OpenCable. Terrestrial HDTV broadcasts use ATSC digital encoding with 8VSB modulation instead of DVB-T's COFDM.
As of 2004, DVB-T television sets are still significantly more expensive than analog television sets. This is creating serious consternation among consumers in countries such as Australia that have mandated to switch off analog television in a few years. However, the high prices of digital television sets are expected to diminish shortly. Elsewhere, television sets with built-in DVB receivers are still not widely sold.
World maps
- DVB-S (http://www.dvb.org/graphics/internal/Adoption-Map_DVB-S_April_20.jpg),
- DVB-C (http://www.dvb.org/graphics/internal/Adoption-Map_DVB-C_April_20.jpg),
- DVB-T (http://www.dvb.org/graphics/internal/Adoption-Map_DVB-T.jpg),
- MHP (http://www.mhp.org/graphics/mhp-sitewide/Adoption-Map_mhp.jpg).
See also
External links
- DVB Project (http://www.dvb.org/)
- Mediacast Trade Fair (http://www.mediacast.net).
- DVB-T Channels in Europe (http://www.kswindells.34sp.com/freeview/ta.php/world/)
- War of the standards (http://news.bbc.co.uk/2/hi/technology/4278567.stm)de:Digital Video Broadcasting
es:DVB fr:Télévision numérique terrestre fi:Digi-tv pl:Digital Video Broadcasting ja:DVB sk:DVB