Digital television ( DTV ) is the transmission of television signals, including voice channels, using digital encoding, in contrast to previous television technology, analog television, where video and audio are carried by analog signals. This is an innovative advancement that represents the first significant evolution in television technology since color television in the 1950s. Digital TV makes use of more economical rare spectrum radio spaces; can transmit multiple channels in the same bandwidth occupied by one analog television channel, and provide many new features that can not be analog television. The transition from analogue to digital broadcasting began around 2006 in some countries, and many industrialized countries have now completed transitions, while other countries are at various stages of adaptation. Different standards of digital television broadcasting have been adopted in different parts of the world; below is a more widely used standard:
- Digital Video Broadcasting (DVB) uses modulated orthogonal-division multiplexing (OFDM) modulation and supports hierarchical transmission. This standard has been adopted in Europe, Singapore, Australia and New Zealand.
- The Advanced Television System Committee (ATSC) uses an eight-level sideband vestigial (8VSB) for terrestrial broadcasting. This standard has been adopted by six countries: the United States, Canada, Mexico, South Korea, the Dominican Republic, and Honduras.
- Integrated Services Digital Broadcasting (ISDB) is a system designed to provide good reception for fixed recipients as well as portable or mobile receivers. It uses OFDM and interleaving two dimensions. It supports hierarchical transmission of up to three layers and uses MPEG-2 and Advanced Audio Coding video. This standard has been adopted in Japan and the Philippines. ISDB-T International is an adaptation of this standard using AVC H.264/MPEG-4 which has been adopted in most of South America and is also embraced by Portuguese-speaking African countries.
- Digital Terrestrial Multimedia Broadcasting (DTMB) adopts OFDM time-domain synchronization technology (TDS) with pseudo-random signal frame to serve as guard interval (GI) of OFDM blocks and training symbols. DTMB standards have been adopted in the People's Republic of China, including Hong Kong and Macao.
- Digital Multimedia Broadcasting (DMB) is a digital radio transmission technology developed in South Korea as part of a national IT project to deliver multimedia such as TV, radio and datacasting to mobile devices such as cell phones, laptops and GPS navigation systems.
Video Digital television
Histori
The roots of digital TV have been tied very closely to the availability of expensive and high-performing computers. It was not until the 1990s that digital TV became a real possibility.
In the mid-1980s, when Japanese consumer electronics companies advanced steadily with the development of HDTV technology, and as the MUSE analog format proposed by Japanese public broadcaster NHK as a worldwide standard, Japan's advancement was seen as a pacesetter that threatened the company's electronic eclipse. By June 1990, the Japanese MUSE standard - based on analog systems - was a pioneer among more than 23 different technical concepts under consideration. Then, the American company, General Instrument, shows the feasibility of a digital television signal. This breakthrough is so important that the FCC is convinced to delay its decision on ATV standards until a digital-based standard can be developed.
In March 1990, when it became clear that digital standards were feasible, the FCC made a number of important decisions. First, the Commission states that the new ATV standard should be more than an enhanced analog signal, but it can provide original HDTV signals with at least twice the resolution of existing television images. Then, to ensure that viewers who do not want to buy a new digital television can continue to receive conventional television broadcasts, it dictates that the new ATV standards must be able to "broadcast" on different channels. The new ATV standard also enables new DTV signals to be based on completely new design principles. Although not in accordance with existing NTSC standards, the new DTV standard will be able to incorporate many improvements.
Final standards adopted by the FCC do not require a single standard to scan formats, aspect ratios, or resolution lines. These results resulted from a dispute between the consumer electronics industry (followed by several broadcasters) and the computer industry (followed by the film industry and some public interest groups) in which two scanning processes - interlaced or progressive - were superior. Interlaced scanning, used in televisions around the world, scans the even numbered lines first, then the odd numbered. Progressive scanning, which is the format used on the computer, scans the line in descending order from top to bottom. The computer industry argues that progressive scanning is superior because it does not "blink" in an interlaced scanning mode. He also believes that progressive scanning enables easier connections with the Internet, and is cheaper to convert to interlaced formats than vice versa. The film industry also supports progressive scanning as it offers a more efficient way to convert programs that are filmed into digital format. For their part, the consumer electronics industry and broadcasters argue that interlaced scanning is the only technology that can deliver images of the highest quality then (and currently) feasible, that is, 1,080 lines per image and 1,920 pixels per line. Broadcasters also love interlaced scanning because large archives of interlaced programming do not match the progressive format.
Initial launch
DirecTV in the US launched the first commercial digital satellite platform in May 1994, using the Digital Satellite System (DSS) standard. Digital cable broadcasts were tested and launched in the US in 1996 by TCI and Time Warner. The first digital terrestrial platform was launched in November 1998 as ONdigital in the UK, using the DVB-T standard.
Maps Digital television
Technical information
Bandwidth and format
Digital television supports a variety of different image formats determined by broadcast television system which is a combination of size and aspect ratio (width to height ratio).
With digital terrestrial television broadcasting (DTT), various formats can be divided into two categories: high definition television (HDTV) for high definition video transmission and standard definition television (SDTV). These terms alone are not very precise, and many cases of subtle transitions exist.
One of several different HDTV formats that can be transmitted via DTV is: 1280 × 720 pixels in progressive scanning mode (abbreviated to 720p) or 1920Ã, ÃÆ'â € Ã, 1080 pixels in an interlaced video mode ( 1080i ). Each uses a 16: 9 aspect ratio. HDTV can not be transmitted over an analog television channel due to channel capacity problems.
SDTV, by comparison, can use one of several different formats that take the form of various aspect ratios depending on the technology used in the broadcast country. In the case of rectangular pixels, NTSC states can provide 640 °, 480 resolution at 4: 3 and 854 °, 480 in 16: 9, while PAL can provide 768-576 in 4: 3 and 1024 ÃÆ'â € "576 in 16: 9 However, broadcasters may choose to reduce this resolution to reduce bit rate (for example, many DVB-T channels in the UK use horizontal resolution of 544 or 704 pixels per line).
Every terrestrial commercial terrestrial DTV channel in North America is allowed to broadcast at bit rate up to 19 megabits per second. However, the broadcaster does not need to use this entire bandwidth for just one broadcast channel. Instead of broadcasts can use channels to include PSIP and can also subdivide in multiple video sub-channels (alias feeds) of various quality and compression levels, including non-video data services that allow one-way high-bit data stream flow to computer such as National Datacast.
Broadcasters may choose to use standard definition digital signals (SDTV) rather than HDTV signals, since current conventions allow DTV channel bandwidth (or "multiplex") to be divided into multiple digital sub-channels, (similar to what most FM radio stations offer with Radio HD), providing multiple feeds from a completely different television program on the same channel. This ability to provide one HDTV feed or some lower-resolution feed is often referred to as distributing "bit budget" or multicasting. This can sometimes be set automatically, using a statistical multiplexer (or "stat-mux"). With some implementations, image resolution may be less directly constrained by bandwidth; for example in DVB-T, broadcasters may choose from several different modulation schemes, giving them the option to reduce the transmission bit rate and make reception easier for remote or further audiences.
Receiving digital signal
There are several different ways to receive digital television. One of the oldest ways of receiving DTV (and TV in general) is from a terrestrial transmitter using an antenna (known as air in some countries). This is known as terrestrial digital television (DTT). With DTT, viewers are limited to channels that have terrestrial transmitters within their antenna range.
Another way has been designed to receive digital television. Among the most familiar to people is digital cable and digital satellite. In some countries where TV signal transmission is usually achieved by microwaves, digital MMDS is used. Other standards, such as Digital multimedia broadcasting (DMB) and DVB-H, have been designed to enable mobile devices such as mobile phones to receive TV signals. Another way is IPTV, which is receiving TV via Internet Protocol, relying on digital subscriber line (DSL) or optical cable line. Finally, an alternative way is to receive digital TV signals over an open Internet (Internet television), either from a central streaming service or a P2P (peer-to-peer) system.
Some signals carrying encryption and determining conditions of use (such as "not to be recorded" or "not to be viewed on the screen larger than 1 m in diagonal size") are supported by legal force under the Copyright Agreement (WIPO Copyright Treaty) and national legislation that implements them, such as the US Digital Millennium Copyright Act. Access to encrypted channels can be controlled by removable smart cards, for example through the Common Interface (DVB-CI) standard for Europe and through Point Of Deployment (POD) for IS or named different CableCards.
Protective parameters for terrestrial DTV broadcast
Digital television signals should not interfere with each other, and they must also co-exist with analog television until deleted. The following table provides the signal-to-noise and signal-to-interference ratios allowed for various interference scenarios. This table is an important setting tool for controlling station placement and station power levels. Digital TVs are more tolerant of interference than analog TVs, and this is the reason that smaller channels can carry a set of all-digital television stations.
Interactions
People can interact with DTV systems in various ways. One can, for example, browse the electronic program guide. Modern DTV systems sometimes use return paths that provide feedback from end users to the broadcaster. This is possible with coaxial or fiber optic cable, dialup modem, or Internet connection but not possible with standard antenna.
Some of these systems support video on demand using localized communication channels to the environment rather than the city (terrestrial) or larger areas (satellites).
1-segment broadcasting
1seg (1-segment) is a special form of ISDB. Each channel is subdivided into 13 segments. The 12 segments of them are allocated to HDTV and the remaining segment, the 13th one, is used for narrow band receivers such as cellular or cellular telephones.
Transition timeline
Comparison vs digital vs
DTV has some advantages over analog TV, the most significant is that digital channels take up less bandwidth, and bandwidth requirements are constantly changing, on the corresponding reduction in image quality depending on the compression level as well as the resolution of the transmitted image. This means that digital broadcasters can provide more digital channels in the same space, provide high definition television services, or provide other non-television services such as multimedia or interactivity. DTV also enables specialized services such as multiplexing (more than one program on the same channel), electronic program guide and additional languages ​​(oral or subtitle). Sales of non-television services can provide an additional source of revenue.
Digital and analog signals react to interference differently. For example, common problems with analogue television include image shadows, noise from weak signals, and many other potential problems that degrade image and sound quality, even though the program material is still viewable. With digital television, audio and video must be digitally synchronized, so the reception of digital signals should be almost complete; otherwise, neither audio nor video will be usable. Short of this complete failure, the "yellow" video is seen when the digital signal is interfering.
Analog TV begins with monophonic sound, and then develops multicultural television sounds with two independent audio channel channels. DTV allows up to 5 channels of audio signals plus sub-woofer bass channels, with similar broadcasts in quality for cinema and DVDs.
Compression artifacts, image quality monitoring and allocated bandwidth
DTV images have some image defects that do not exist on analog television or cinema movies, due to current bit rate limitations and compression algorithms such as MPEG-2. These defects are sometimes referred to as "mosquitoes".
Due to the way the human visual system works, the defects in the image are localized to certain features of the image or that come and go more clearly than uniform and constant deformities. However, the DTV system is designed to take advantage of the limitations of the human visual system to help cover this deficiency, eg. by allowing more compression artifacts during fast motion where the eye can not trace and solve them easily and, on the other hand, minimize the background artefacts that can still be examined strictly in a scene (due to time permitting).
Broadcast, cable, satellite, and Internet DTV operators control the image quality of television signal encoding using advanced neuroscience-based algorithms, such as the Structural Similarity (SSIM) video quality tool, which is given every discoverer, Primetime Emmy because of its global usage. Another tool, called Visual Information Fidelity (VIF), is the best performing algorithm at the core of VMAF Netflix video quality monitoring system, which accounts for about 35% of all US bandwidth consumption.
Poor reception effect
Changes in signal reception from factors such as decreased antenna connections or gradual changes in weather conditions can reduce the quality of analog TVs. The nature of the digital TV results in a perfectly decoded video at first, until the receiving device begins to take on interference beyond the desired signal strength or if the signal is too weak to decode. Some tools will display chaotic images with significant damage, while other devices may be directly from a video that can be decoded to video or locked. This phenomenon is known as the cliff effect of digital.
For remote locations, remote channels which, as analog signals, may previously be used in snow and degraded conditions may, as digital signals, be decoded perfectly or become completely unavailable. Higher frequency usage will add to this problem, especially in cases where a clear line of sight from the receiving antenna to the transmitter is unavailable.
Effect on old analog technology
Television set only with analog tuner can not decode digital transmission. When analogue broadcasting over the air stops, the user sets with an analog tuner alone can use other programming sources (eg cables, recorded media) or can purchase a set-top converter box to set up a digital signal. In the United States, government sponsored coupons are available to offset the cost of an external converter box. The analog switch-off (full power plant) took place on December 11, 2006 in the Netherlands, June 12, 2009 in the United States for power stations, and then for the Class-A Station on September 1, 2016, July 24, 2011 in Japan, August 31, 2011 in Canada, February 13, 2012 in Arab countries, May 1, 2012 in Germany, October 24, 2012 in the UK and Ireland, October 31, 2012 in certain Indian cities, and December 10, 2013 in Australia. The analog switch-off completion is scheduled for 31 December 2017 across India, December 2018 in Costa Rica and about 2020 for the Philippines.
Audio-TV receiver
Prior to conversion to digital TV, analog TV broadcast audio for TV channels on FM carrier signal is separate from the video signal. This FM audio signal can be heard using a standard radio equipped with a proper tuning circuit.
However, after the transition of many countries to digital TV, there is no portable radio manufacturer that has not developed an alternative method for portable radios to simply play the audio signal of digital TV channels. (Radio DTV is not the same thing.)
Environmental issues
The adoption of a broadcast standard incompatible with existing analog receivers has created the problem of a large number of analogue receivers being discarded during the transition of digital television. One of the public works inspectors quoted in 2009 said, "Some of the research I've read in trade magazines says up to a quarter of American households can issue TVs within the next two years after regulatory changes." In 2009, an estimated 99 million analog TV receivers were sitting unused in homes in the US alone and, while some outdated receivers were being installed with converters, many were thrown away in landfills where they represented a toxic metal source such as lead as well as less amount of material such as barium, cadmium and chromium.
According to one campaign group, CRT or TV computer monitors contain an average of 8 pounds (3.6 kg) of lead. According to other sources, embankments in CRT glasses vary from 1.08 pounds to 11.28 pounds, depending on the size and type of display, but lead in the form of "stable and immobile" lead oxide mixed into the glass. It is said that lead can have long-term negative effects on the environment if disposed of as a landfill. However, glass envelopes can be recycled at well-equipped facilities. Other parts of the receiver may be disposed of as hazardous materials.
Local limitations on the disposal of these materials vary widely; in some cases used stores refuse to accept color television receivers for resale due to the increasing cost of discarding unsold TVs. Secondhand stores that still receive donated TVs have reported a significant increase in the use of well-functioning television channels left by viewers who often hope they will not work after the digital transition.
In Michigan in 2009, one recycler estimated that as many as one household in four homes would dispose or recycle a TV set the following year. The transition of digital television, migration to high definition television receivers and the replacement of CRTs with flatscreens are all factors in the growing number of abandoned CRT-based analog television receivers.
See also
- Television broadcast system
- Text to Speech on Digital Television
Notes and references
Further reading
- Hart, Jeffrey A., Television, technology, and competition: HDTV and digital TV in the United States, Western Europe, and Japan , New York: Cambridge University Press, 2004. ISBN : 0-521-82624-1
External links
- Digital TV Development Overview Worldwide Proceedings of IEEE, VOL. 94, NO. 1, JANUARY 2006 (University of Texas at San Antonio)
- DCC AS consumer oriented DTV website
- Digital TV Consumer testing report - UK Government funded website to support Digital Switchover
- How to Set Up a Box and Digital DTV Converter Antenna, a help article from wikiHow
- How to Scan DTV Channels Using Digital TV Converter Box (and why this should be done June 11, 2009 in the US), help article from wikiHow
- How to Use Your Old VCR, TiVo, or DVR With DTV Converter Box, help article from wikiHow
Source of the article : Wikipedia
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