DVB F.A.Q
DVB Project
DVB, short for Digital Video Broadcasting, is a suite of internationally accepted open standards for digital television. DVB standards are maintained by the DVB Project, an industry consortium with more than 270 members, and they are 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 at the ETSI website after registration. The interaction of the DVB sub-standards is described in the DVB Cookbook (DVB-Cook).
Transmission
DVB systems distribute data using a variety approaches, including by satellite (DVB-S, DVB-S2 and DVB-SH; also DVB-SMATV for distribution via SMATV); cable (DVB-C); terrestrial television (DVB-T) and terrestrial television for handhelds (DVB-H); and via microwave using DTT (DVB-MT), the MMDS (DVB-MC), and/or MVDS standards (DVB-MS)
These standards define the physical layer and data link layer of the 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) was published in November 2004.
These distribution systems differ mainly in the modulation schemes used, due to the different technical constraints. DVB-S (SHF) uses QPSK, 8PSK or 16-QAM. DVB-S2 uses QPSK, 8PSK, 16APSK or 32APSK, at the broadcasters decision. QPSK and 8PSK are the only versions regularly used. DVB-C (VHF/UHF) uses QAM: 16-QAM, 32-QAM, 64-QAM, 128-QAM or 256-QAM. Lastly, DVB-T (VHF/UHF) uses 16-QAM or 64-QAM (or QPSK) in combination with COFDM and hierarchical modulation
Content
Besides audio and video transmission, DVB also defines data connections (DVB-DATA - EN 301 192) with return channels (DVB-RC) for several media (DECT, GSM, PSTN/ISDN, satellite etc.) and protocols (DVB-IPI: Internet Protocol; DVB-NPI: network protocol independent).
Older technologies such as teletext (DVB-TXT) and vertical 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 physical Common Interface (DVB-CI) for accessing scrambled content. DVB-CA providers develop their wholly proprietary conditional access systems with reference to these specifications. Multiple simultaneous CA systems can be assigned to a scrambled DVB program stream providing operational and commercial flexibility for the service provider.
DVB is also developing a Content Protection and Copy Management system for protecting content after it has been received (DVB-CPCM), which is intended to allow flexible use of recorded content on a home network or beyond, while preventing unconstrained sharing on the Internet. DVB-CPCM has been the source of much controversy in the popular press and it's said that CPCM is the DVB's answer to the failed American Broadcast Flag [1]
DVB transports include metadata called Service Information (DVB-SI, ETSI EN 300468, ETSI TS 101211) that links the various elementary streams into coherent programs and provides human-readable descriptions for electronic program guides as well as for automatic searching and filtering.
Recently, DVB has adopted a profile of the metadata defined by the TV-Anytime Forum [2] (DVB-TVA, ETSI TS 102323). This is an XML Schema based technology and the DVB profile is tailored for enhanced Personal Digital Recorders. DVB lately also started an activity to develop a solution for IPTV (DVB-IPI, ETSI TR 102033, ETSI TS 102034, ETSI TS 102814) which also includes metadata definitions for a broadband content guide (DVB-BCG, ETSI publication expected December 2006).
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.
List of other user interaction software platforms.
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. DVB-RCT is short for Return Channel Terrestrial, specified by ETSI EN 301958.
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 (Canada, Mexico and South Korea) chose ATSC instead of DVB-T.
In Malaysia, a new Pay-TV station MiTV began service in September 2005 using IPTV over DVB-T technology while lone satellite programming provider ASTRO has been transmitting in DVB-S since its inception in 1996. DVB-T trials began in late 2006 with a simulcast of both RTM1 and RTM2 plus a new channel called RTM3/RTMi. In April 2007, RTM announced that the outcome of the test is favorable and expects DVB-T to go public by the end of 2007. Analog shut-off date is also announced to be sometime in 2015.
With the exception of Sky PerfecTV!, 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.
In Hong Kong, several cable TV operators such as TVB Pay Vision and Cable TV have already started using DVB-S or DVB-C. The government has decided digital terrestrial broadcasting will start not later than 2007, and it is up to the broadcasters to decide which system to use. Originally it was thought that mainland China would adopt DVB-T, but instead they have decided to create their own digital television standard.
As of 2005, DVB-T television sets are not significantly more expensive than analog television sets. Most popular in Europe are the set-top boxes that enable DVB-T to be received through an ordinary analogue television, with the price dropping remarkably in the last year. An overview of the adoption of DVB-T can be found on the DVB Project website.
DVB-C
DVB-C stands for Digital Video Broadcasting - Cable and it is the DVB European consortium standard for the broadcast transmission of digital television over cable. This system transmits an MPEG-2 family digital audio/video stream, using a QAM modulation with channel coding.
Technical description of the transmitter
Source coding and MPEG-2 multiplexing (MUX): video, audio, and data streams are multiplexed into an MPEG-2 PS (MPEG-2 Programme Stream). One or more PSs are joined together into a 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). Allowed bitrates for the transported MPEG-2 depend on a number of modulation parameters: it can range from about 6 to about 64 Mbit/s (see the bottom figure for a complete listing).
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.
External encoder: a first level of protection 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.
External interleaver: convolutional interleaving is used to rearrange the transmitted data sequence, such way it becomes more rugged to long sequences of errors.
Byte/m-tuple conversion: data bytes are encoded into bit m-tuples (m = 4, 5, 6, 7, or 8).
Differential coding: the two most significant bytes in each m-tuple are encoded in order to give some ruggedness to the signal.
QAM Mapper: the bit sequence is mapped into a base-band digital sequence of complex symbols. There are 5 allowed modulation modes: 16-QAM, 32-QAM, 64-QAM, 128-QAM, 256-QAM.
Base-band shaping: the QAM signal is filtered with a raised-cosine shaped filter, in order to remove mutual signal interference at the receiving side.
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 by the RF front-end.
Available bitrates for a DVB-C system, range between 6.14 to 64.11 assuming a ratio of 1.15. These figures are dependant on the bandwidth and symbol rate. All (decimal) values in Mbit/s.
DVB-H
It is the latest development within the set of DVB transmission standards. DVB-H technology adapts the successful DVB-T (Digital Video Broadcasting - Terrestrial) system for digital terrestrial television to the specific requirements of handheld, battery-powered receivers. DVB-H can offer a downstream channel at high data rates which can be used as standalone or as an enhancement of mobile telecoms networks which many typical handheld terminals are able to access anyway. Time slicing technology is employed to reduce power consumption for small handheld terminals. IP datagrams are transmitted as data bursts in small time slots. Each burst may contain up to 2 Mbits of data (including parity bits). There are 64 parity bits for each 191 data bits, protected by Reed-Solomon codes. The front end of the receiver switches on only for the time interval when the data burst of a selected service is on air. Within this short period of time a high data rate is received which can be stored in a buffer. This buffer can either store the downloaded applications or playout live streams. The achievable power saving depends on the relation of the on/off-time. If there are approximately ten or more bursted services in a DVB-H stream, the rate of the power saving for the front end could be up to 90%. DVB-H is a technical system which was carefully tested by the DVB-H Validation Task Force in the course of 2004 (see ETSI Technical Report TR 102 401).
DVB-IPDC
The set of DVB specifications for IP Datacasting (DVB-IPDC) can most simply be described as the essential components required to deploy a commercial mobile TV service based on Internet Protocol. DVB-IPDC is a set of systems layer specifications originally designed for use with the DVB-H physical layer, but that will ultimately be used as a higher layer for all DVB mobile TV systems, including DVB-SH, and indeed as a higher layer for any other IP capable system. In short, with regard to mobile TV, these specifications define what is delivered, how it is delivered, how it is described, and how it is protected. They cover system architecture, use cases, DVB PSI/SI signalling, electronic service guide (ESG), content delivery protocols (CDP), and service purchase and protection (SPP). Almost all of these have now been published as formal ETSI standards. The full set of DVB-IPDC specifications is available from dvb-h.org
Trials
DVB-H trials are now underway in Malaysia, Singapore, Helsinki, Berlin, Oxford, Pittsburgh, Paris, Madrid, Sydney, South Africa, The Hague, Brussels, Bern, Vienna, Philippines, Copenhagen, Budapest [14] and Erlangen[5][6]. O2 Ireland commenced a trial in March 2007 with a single high site 1.2 kW transmitter at 3 Rock covering the Greater Dublin Area.
A comprehensive list of DVB-H trials and service launches is available from dvb-h.org
Service launches
In Finland, the license to operate a DVB-H network was awarded to Digita in March 2006. In May 2006 they announced that they had signed a contract with Nokia to use its DVB-H platform for the service. The network was supposed to be launched on the 1st December 2006, but disagreements regarding copyrights of the broadcasted material have stalled the launch. Initially the network should cover 25% of the population with coverage area Helsinki, Oulu and Turku. Commercial service is supposed to start in the beginning of 2007; among the services available will be Voice TV and Kiss digital radio.
In India, Indian public broadcaster Prasar Bharti (also known as DD for Doordarshan) has teamed with Nokia to start a DVB-H. And trial is going in various metropolitan areas to test the reception quality of the broadcast coverage. The full service available from May 2007.
In Italy, 3 Italia launched nationwide services in May 2006, both Telecom Italia Mobile (TIM) and Mediaset in June 2006, Vodafone in December 2006.
In Singapore, TVMobile uses DVB technology to broadcast live news, entertainment and music content directly to over 1500 Singapore Bus Service buses islandwide, along with various other indoor and outdoor locations.
In the United States, a nationwide service will be rolled out by Modeo a company owned by Crown Castle. The service will begin in 2006 in New York City and will roll out to the top thirty markets in the USA during 2007. Modeo owns 5 MHz of spectrum nationwide at 1600 MHz. At the NAB trade show in April 2006, a second service launch was announced by SES Americom and Aloha Partners. Titled Hiwire Mobile Television, the service is set to begin trials in Las Vegas in Q4 2006. Hiwire owns two 6 MHz channels of spectrum at 700 MHz covering most of the country.
In Vietnam, VTC launched nationwide service on 21 December 2006.
In France, Germany, Spain and South Africa nationwide service launch is planned for 2007.
In China two companies have been issued licenses by the government, Shanghai Media Group and China Central Television. Trials are currently underway, with service launch expected before the 2008 Beijing Olympics.
· A 10-page article "DVB-H the emerging standard for mobile data communication" from European Broadcasting Union (EBU) Technical Review
· A collection of articles on DVB (including DVB-H) in the archive of EBU Technical Review
· ETSI Specifications 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)
· EN 302 304 "Digital Video Broadcasting (DVB);Transmission System for Handheld Terminals (DVB-H)"
· TS 102 470 "Digital Video Broadcasting (DVB);IP Datacast over DVB-H: Program Specific Information (PSI)/Service Information (SI)"
· TS 102 471 "Digital Video Broadcasting (DVB);IP Datacast over DVB-H: Electronic Service Guide (ESG)"
· TS 102 472 "Digital Video Broadcasting (DVB);IP Datacast over DVB-H: Content Delivery Protocols"
· TR 102 377 "Digital Video Broadcasting (DVB);DVB-H Implementation Guidelines"
· TR 102 401 "Digital Video Broadcasting (DVB);Transmission to Handheld Terminals (DVB-H);Validation Task Force Report"
· TR 102 469 "Digital Video Broadcasting (DVB);IP Datacast over DVB-H: Architecture"
· TR 102 473 "Digital Video Broadcasting (DVB);IP Datacast over DVB-H: Use Cases and Services"
· "Mobile DTV Alliance: Digital Video Broadcast for Handheld Devices; North American Implementation Guidelines Release 1.0" - DVB-H Implementation Guidelines for North America
Further information
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