Digital video broadcasting
Digital Video Broadcasting [ ˈdɪdʒɪtəl ˈvɪdiəʊ ˈbɹɔːdˌkɑːstɪŋ ] ( DVB ) stands for digital television (literally 'digital video broadcasting').
Technical DVB is the standardized process for transmitting digital content ( television , radio , multi-channel , surround sound , interactive services like MHP , EPG and Teletext , and other supplemental services) through digital technology . With data compression ( MPEG-2 , for HDTV especially H.264 and HEVC ), more programs can be transmitted per transmission channel (frequency) compared to analog television transmission. The quality can be adjusted in many ways; the more the data is compressed, the more programs can be transmitted simultaneously on a transponder (satellite) ; in return, the quality decreases or the computing effort increases.
Furthermore, offers such as subscriber or pay-TV , pay-per-view , video-on-demand are much cheaper and safer for the broadcasters by encrypting the signal.
Transmission routes
There are several technical sub-types of DVB for the different transmission paths, which differ mainly in the modulation method (the optimal choice depends crucially on the frequency range and transmission channel) and in the error correction:
- DVB-S for transmission through direct distribution S atelliten
- DVB-S2 current successor standard for DVB-S
- DVB-C for transmission over cable networks ( C able)
- DVB-C2 Successor standard for DVB-C
- DVB-T for transmission by t errestrische broadcasting networks in the VHF - or UHF range
- DVB-T2 Successor standard for DVB-T
- DVB-H for asynchronous transmission to mobile devices ( H terrestrial andhelds) also
- DVB-IPI for transmission over IP-based networks, e.g. Internet ( I nternet P rotocol I nfrastructure)
- DVB-RC (S / C / T) return channel ( R eturn C hannel) for the transmission of data services, such as broadband Internet
- DVB-SI for the transmission of S ervice I nformation
- DVB-SH for transmission over S atellit to mobile devices ( H andhelds)
Device requirements for the viewer
The vast majority of existing televisions and video recorders cannot handle the digital signals directly; therefore a digital receiver (as a set-top box , STB ) has to receive the data, decode it and convert it into an analog signal that is understandable for older electronics. But then the z. B. with ARD and ZDF in the DVB-S and DVB-C signal, existing high image quality is lost, because full digital TV reception also includes a digital video connection on the receiver and on the screen, i. H. with HDMI cable.
In the meantime there are also televisions with built-in or optional reception technology for DVB-C, -S, and -T on the market ( see also IDTV ). For mobile DVB-H reception, there are basically only fully integrated new devices, often mobile phone combinations. There are also plug-in cards and USB devices ( see also DVB-T stick ) for computers and laptops, which often only take over the reception and transfer the task of decoding and display to the computer.
History and background
In the European DVB project, over 270 member companies have come together to promote digital television. US, Japanese and Korean companies are involved through their European subsidiaries, with others from Australia and Canada. The members are program providers, device manufacturers, network operators and authorities. The European Commission ( Commission of the European Communities , CEC ), as well as other associations and standardization organizations such as ETSI and CENELEC are also involved in the work. By means of cooperation agreements it was agreed that ETSI and CENELEC would take over the technical specifications resulting from the DVB project. As a result, the specifications are available to everyone free of charge from the ETSI website. The Moving Picture Experts Group (MPEG) was involved in the work and has its work standardized in the ISO and IEC organizations . Therefore the results of the MPEG grouping are published there.
DVB-S and DVB-C were ratified in 1994, DVB-T in early 1997.
Basic driving ideas for the introduction of digital television technology are:
- The number of television programs per channel can be multiplied ( bouquet ).
- Encryption methods for pay TV are easier and more secure to implement.
- Additional distribution of radio programs is possible.
- Transmission of (also interactive) data services (see also MHP ) in the context of the programs offered.
- Image and sound quality can be increased so that a viewer who has a high-quality television set can also select and receive programs in high definition quality ( HDTV ). Even on non-high-resolution televisions, digital technology can enable a much lower-noise picture and surround sound .
See also: DAB , DRM , DTV , VDR , ISO 6937
Current situation of DVB
Dissemination and content
When DVB programs are broadcast via satellite, there is an extensive range of programs and all free-to-air programs in German-speaking countries can be received via DVB-S without additional monthly fees. Exceptions are some regional and local channels or windows that are broadcast via aerial television or cable television .
DVB-T has already established itself in the areas in which this transmission technology is offered ( see also DVB-T conversion ).
DVB-H has already been tested in many test networks around the world and has subsequently been introduced commercially in some countries. Success depends in particular on the underlying business models and is in strong competition with Internet-based services.
With the spread of DVB-C , however, there were some problems with the large cable providers in Germany . For a long time there was no nationwide broadcasting of private channels via DVB-C. Only the public broadcasters as well as Sky and other pay-TV offers could be received. Since January 2006, channels from the RTL family and ProSiebenSat.1 can also be received digitally after the cable companies reached an agreement with the channels. These programs, which can be freely received via all other distribution channels, have long been encrypted with most providers and can only be viewed with an additional one-off or monthly fee. A few smaller local cable network operators, often in more rural regions, fed the DVB satellite signals from the large German broadcasting families such as ARD, ZDF, RTL, ProSiebenSat.1 and of course Sky as well as some other German broadcasters (DSF, Tele 5, etc.) right from the start and at no extra charge .) into the cable network, even if you need a DVB-C receiver - Sky customers still need a smart card, for example. The basic encryption was eventually discontinued by the majority of the cable companies due to antitrust concerns.
In some cases, the operators of cable networks also require that the serial number of a Sky-certified receiver must be given in order to receive DVB-C channels, even if there is no Sky subscription at all or is not desired.
In Germany, digital television (DVB) has replaced analog television ( PAL ) in DVB-T from August 2003, DVB-S in April 2012 and DVB-C from June 2017 ( see also analogue switch-off ).
technology
Several television and radio programs broadcast via DVB share one channel or transponder . The data streams of the individual programs are "muxed" to form an overall data stream (derived from " multiplexer "). Data rates of 2–8 Mbit / s are usual for each television program or up to 27 Mbit / s for HDTV programs, whereby it should be noted that the video bit rate is often variable and the maximum value is usually not reached permanently, while the audio and other data streams have a constant bit rate; z. B. 256 kbit / s for standard MP2 audio as television sound or radio program.
Compared to analog broadcasting, the DVB signal reaches the TV sets with a clearly perceptible delay. This phenomenon caused some irritation during the 2006 World Cup , as the celebrations for goals could often be heard from households supplied with analog TV, while DVB users only saw the triggering scene a few seconds later.
differences
| satellite | electric wire | Terrestrial | ||||
|---|---|---|---|---|---|---|
| DVB-S | DVB-S2 | DVB-C | DVB-C2 | DVB-T | DVB-T2 | |
| Modulation types | QPSK | QPSK, 8PSK, 16APSK or 32APSK | 16-256 QAM | 16-4096 QAM | QPSK , 16- QAM , 64- QAM | |
| Transmission method | QAM | COFDM | COFDM | |||
| Transmission capacity | typ. 33 Mbit / s – 38 Mbit / s | typ. 38 Mbit / s (64 QAM) 51 Mbit / s (256 QAM) |
typ. 38 Mbit / s (64 QAM) 83 Mbit / s (4096 QAM) |
typ. 4 Mbit / s – 22 Mbit / s | ||
| reception | Parabolic antenna | BK network connection | Depending on the location, indoor, outdoor or roof antenna | |||
| mobility | stationary, partially portable (mobile) | stationary | stationary, portable, mobile | |||
| Return channel / others | no / telephone networks | yes / telephone networks | no / telephone networks | |||
criticism
Since digital signals can easily be encrypted, the shift in the market from free TV to paid content is favored.
Critics also see the possibilities of free access and anonymous use of the media ( free-to-air ) through the use of digital processes and the possible digital rights management ( DRM ) through smart cards, HDCP and the like. similarly limited.
Where only one analog TV station is broadcast on a transponder , some digital stations can be broadcast in the same frequency range because of the data compression. Therefore, unlike the introduction of DVB-T, the analog satellite channels are not threatened with closure for bandwidth reasons, but primarily economic considerations on the part of the broadcasters (and in some cases also on the part of the satellite operator) decide whether and when analog satellite channels are set; for example, the migration of viewers to DRM-capable systems (e.g. Entavio ) should be forced.
Because the rights holders are interested in protecting the broadcast material from high-quality copies, it is planned for new DVD or hard disk recorders with built-in DVB receivers that the broadcasters can transmit a signal that prohibits or restricts the recording. The recorder manufacturers could then be obliged to modify their recorders technically so that this signal is evaluated during a recording and thus possibly prevents a recording - similar to the Macrovision copy protection for physical media.
literature
- Ulrich Reimers: DVB (Digital Video Broadcasting): The Family of International Standards for Digital Video Broadcasting (Signals and Communication Technology) . 2nd Edition. Springer, Berlin, 2004, ISBN 978-3-540-43545-7 .
- Markus Vorhauer: Integration of an Electronic Program Guide (EPG) in IPTV: Structure and evaluation of DVB (Digital Video Broadcasting) and EPG, and integration in IPTV . Vdm Verlag Dr. Müller, 2008, ISBN 978-3-639-03239-0 .