Digital television
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List of digital television broadcast standards |
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DVB standards (countries) |
ATSC standards (countries) |
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ISDB standards (countries) |
DTMB standards (countries) |
DMB standard (countries) |
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Codecs |
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Terrestrial Frequency bands |
Satellite Frequency bands |
Digital television (DTV) is the transmission of
- Digital Video Broadcasting (DVB) uses coded orthogonal frequency-division multiplexing(OFDM) modulation and supports hierarchical transmission. This standard has been adopted in Europe, Africa, Asia, and Australia, for a total of approximately 60 countries.
- Advanced Television System Committee (ATSC) standard uses eight-level vestigial sideband (8VSB) for terrestrial broadcasting. This standard has been adopted by 9 countries: the United States, Canada, Mexico, South Korea, Bahamas, Jamaica, the Dominican Republic, Haiti and Suriname.[citation needed]
- .
- Digital Terrestrial Multimedia Broadcast (DTMB) adopts time-domain synchronous (TDS) OFDM technology with a pseudo-random signal frame to serve as the guard interval (GI) of the OFDM block and the training symbol. The DTMB standard has been adopted in China, including Hong Kong and Macau.[3]
- Digital Multimedia Broadcasting (DMB) is a digital radio transmission technology developed in South Korea[4][5][6] as part of the national information technology project for sending multimedia such as TV, radio and datacasting to mobile devicessuch as mobile phones, laptops and GPS navigation systems.
History
Background
Digital television's roots are tied to the availability of inexpensive, high performance
Development
In the mid-1980s,
A digital TV broadcast service was proposed in 1986 by
In the mid-1980s, as Japanese consumer electronics firms forged ahead with the development of
as a worldwide standard. Japanese advancements were seen as pacesetters that threatened to eclipse US electronics companies. Until June 1990, the Japanese MUSE standard—based on an analog system—was the front-runner among the more than 23 different technical concepts under consideration.Between 1988 and 1991, several European organizations were working on
In March 1990, when it became clear that a digital standard was feasible, the FCC made a number of critical decisions. First, the Commission declared that the new TV standard must be more than an enhanced analog signal, but be able to provide a genuine HDTV signal with at least twice the resolution of existing television images. Then, to ensure that viewers who did not wish to buy a new digital television set could continue to receive conventional television broadcasts, it dictated that the new ATV standard must be capable of being simulcast on different channels. The new ATV standard also allowed the new DTV signal to be based on entirely new design principles. Although incompatible with the existing NTSC standard, the new DTV standard would be able to incorporate many improvements.[7]
The final standard adopted by the FCC did not produce a universal standard for scanning formats, aspect ratios, or lines of resolution. This outcome resulted from a dispute between the consumer electronics industry (joined by some broadcasters) and the computer industry (joined by the film industry and some public interest groups) over which of the two scanning processes—interlaced or progressive—is superior. Interlaced scanning, which is used in televisions worldwide, scans even-numbered lines first, then odd-numbered ones. Progressive scanning, which is the format used in computers, scans lines in sequences, from top to bottom. The computer industry argued that progressive scanning is superior because it does not flicker in the manner of interlaced scanning. It also argued that progressive scanning enables easier connections with the Internet, and is more cheaply converted to interlaced formats than vice versa. The film industry also supported progressive scanning because it offers a more efficient means of converting filmed programming into digital formats. For their part, the consumer electronics industry and broadcasters argued that interlaced scanning was the only technology that could transmit the highest quality pictures then (and currently) feasible, i.e., 1,080 lines per picture and 1,920 pixels per line. Broadcasters also favored interlaced scanning because their vast archive of interlaced programming is not readily compatible with a progressive format.[7]
Inaugural launches
Technical information
Formats and bandwidth
Digital television supports many different picture formats defined by the
With digital terrestrial television (DTT) broadcasting, the range of formats can be broadly divided into two categories: high-definition television (HDTV) for the transmission of high-definition video and standard-definition television (SDTV). These terms by themselves are not very precise, and many subtle intermediate cases exist.
One of several different HDTV formats that can be transmitted over DTV is: 1280 × 720
SDTV, by comparison, may use one of several different formats taking the form of various aspect ratios depending on the technology used in the country of broadcast.
Each
A broadcaster may opt to use a standard-definition (SDTV) digital signal instead of an
Reception
There are several different ways to receive digital television. One of the oldest means of receiving DTV (and TV in general) is from terrestrial transmitters using an antenna (known as an aerial in some countries). This delivery method is known as digital terrestrial television (DTT). With DTT, viewers are limited to channels that have a terrestrial transmitter in range of their antenna.
Other delivery methods include
Some signals are protected by
Protection parameters
Digital television signals must not interfere with each other, and they must also coexist with analog television until it is phased out. The following table gives allowable signal-to-noise and signal-to-interference ratios for various interference scenarios. This table is a crucial regulatory tool for controlling the placement and power levels of stations. Digital TV is more tolerant of interference than analog TV.[19]
System Parameters (protection ratios) |
Canada | US | EBU ITU-mode M3 |
Japan & Brazil[A] |
---|---|---|---|---|
C/N for AWGN Channel | +19.5 dB (16.5 dB[B]) |
+15.19 dB | +19.3 dB | +19.2 dB |
Co-Channel DTV into Analog TV | +33.8 dB | +34.44 dB | +34 ≈37 dB | +38 dB |
Co-Channel Analog TV into DTV | +7.2 dB | +1.81 dB | +4 dB | +4 dB |
Co-Channel DTV into DTV | +19.5 dB (16.5 dB[B]) |
+15.27 dB | +19 dB | +19 dB |
Lower Adjacent Channel DTV into Analog TV | −16 dB | −17.43 dB | −5 ~ −11 dB[C] | −6 dB |
Upper Adjacent Channel DTV into Analog TV | −12 dB | −11.95 dB | −1 ~ −10[C] | −5 dB |
Lower Adjacent Channel Analog TV into DTV | −48 dB | −47.33 dB | −34 ~ −37 dB[C] | −35 dB |
Upper Adjacent Channel Analog TV into DTV | −49 dB | −48.71 dB | −38 ~ −36 dB[C] | −37 dB |
Lower Adjacent Channel DTV into DTV | −27 dB | −28 dB | −30 dB | −28 dB |
Upper Adjacent Channel DTV into DTV | −27 dB | −26 dB | −30 dB | −29 dB |
Interaction
People can interact with a DTV system in various ways. One can, for example, browse the electronic program guide. Modern DTV systems sometimes use a return path providing feedback from the end user to the broadcaster. This is possible over cable TV or through an Internet connection but is not possible with a standard antenna alone.
Some of these systems support video on demand using a communication channel localized to a neighborhood rather than a city (terrestrial) or an even larger area (satellite).
1seg
Comparison to analog
DTV has several advantages over analog television, the most significant being that digital channels take up less bandwidth, and the bandwidth allocations are flexible depending on the level of compression and resolution of the transmitted image. This means that digital broadcasters can provide more digital channels in the same space, provide high-definition television service, or provide other non-television services such as multimedia or interactivity. DTV also permits special services such as multiplexing (more than one program on the same channel), electronic program guides and additional languages (spoken or subtitled). The sale of non-television services may provide an additional revenue source to broadcasters.
Digital and analog signals react to interference differently. For example, common problems with analog television include ghosting of images, noise from weak signals, and other problems that degrade the quality of the image and sound, although the program material may still be watchable. With digital television, because of the cliff effect, reception of the digital signal must be very nearly complete; otherwise, neither audio nor video will be usable.
Analog TV began with monophonic sound and later developed
Digital TV signals require less transmission power than analog TV signals to be broadcast and received satisfactorily.[21]
Compression artifacts, picture quality monitoring, and allocated bandwidth
DTV images have some picture defects that are not present on analog television or motion picture cinema, because of present-day limitations of bit rate and compression algorithms such as
Because of the way the human visual system works, defects in an image that are localized to particular features of the image or that come and go are more perceptible than defects that are uniform and constant. However, the DTV system is designed to take advantage of other limitations of the human visual system to help mask these flaws, e.g. by allowing more
Broadcast, cable, satellite, and Internet DTV operators control the picture quality of television signal encoders using sophisticated, neuroscience-based algorithms, such as the
Quantising effects can create contours – rather than smooth gradations – on areas with small graduations in amplitude. Typically, a very flat scene, such as a cloudless sky, will exhibit visible steps across its expanse, often appearing as concentric circles or ellipses. This is known as
Effects of poor reception
Changes in signal reception from factors such as degrading antenna connections or changing weather conditions may gradually reduce the quality of analog TV. The nature of digital TV results in a perfectly decodable video initially, until the receiving equipment starts picking up interference that overpowers the desired signal or if the signal is too weak to decode. Some equipment will show a garbled picture with significant damage, while other devices may go directly from perfectly decodable video to no video at all or lock up.[23] This phenomenon is known as the digital cliff effect.[24]
Block errors may occur when transmission is done with compressed images. A block error in a single frame often results in black boxes in several subsequent frames, making viewing difficult.
For remote locations, distant channels that, as analog signals, were previously usable in a snowy and degraded state may, as digital signals, be perfectly decodable or may become completely unavailable. The use of higher frequencies add to these problems, especially in cases where a clear line-of-sight from the receiving antenna to the transmitter is not available, because usually higher frequency signals can't pass through obstacles as easily.
Effect on old analog technology
Television sets with only analog tuners cannot decode digital transmissions. When analog broadcasting over the air ceases, users of sets with analog-only tuners may use other sources of programming (e.g. cable, recorded media) or may purchase set-top converter boxes to tune in the digital signals. In the United States, a government-sponsored coupon was available to offset the cost of an external converter box.
The digital television transition began as early as the late 1990s and has been completed on a country-by-country basis in most parts of the world.
Disappearance of TV-audio receivers
Prior to the conversion to digital TV, analog television broadcast audio for TV channels on a separate FM
However, after the digital television transition, no portable radio manufacturer has yet developed an alternative method for portable radios to play just the audio signal of digital TV channels; DTV radio is not the same thing.
Environmental issues
The adoption of a broadcast standard incompatible with existing analog receivers has created the problem of large numbers of analog receivers being discarded. One superintendent of public works was quoted in 2009 saying; "some of the studies I’ve read in the trade magazines say up to a quarter of American households could be throwing a TV out in the next two years following the regulation change".[25] In Michigan in 2009, one recycler estimated that as many as one household in four would dispose of or recycle a TV set in the following year.[26] The digital television transition, migration to high-definition television receivers and the replacement of CRTs with flatscreens are all factors in the increasing number of discarded analog CRT-based television receivers. In 2009, an estimated 99 million analog TV receivers were sitting unused in homes in the US alone and, while some obsolete receivers are being retrofitted with converters, many more are simply dumped in landfills where they represent a source of toxic metals such as lead as well as lesser amounts of materials such as barium, cadmium and chromium.[27][28]
See also
- Autoroll
- Broadcast television systems
- Digital television in the United Kingdom
- Digital television in the United States
- Digital terrestrial television
- Text to Speech in Digital Television
References
- ISBN 1-59033-502-3.
- ^ "HDTV Set Top Boxes and Digital TV Broadcast Information". Archived from the original on 22 May 2016. Retrieved 28 June 2014.
- ^ Ong, C. Y., Song, J., Pan, C., & Li, Y.(2010, May). Technology and Standards of Digital Television Terrestrial Multimedia Broadcasting [Topics in Wireless Communications], IEEE Communications Magazine, 48(5),119–127
- ^ "Korea's Terrestrial DMB: Germany to begin broadcast this May". ZDNet Korea. 2006-04-06. Retrieved 2010-06-17.
- ^ "picturephoning.com: DMB". Textually.org. Archived from the original on 2010-08-09. Retrieved 2010-06-17.
- ^ "South Korea : Social Media 답변 내용 : 악어새 – 리포트월드". Reportworld.co.kr. Archived from the original on 2009-08-17. Retrieved 2010-06-17.
- ^ Benton Foundation. 2008-12-23.
- ^ a b c Lea, William (1994). Video on demand: Research Paper 94/68. House of Commons Library. Retrieved 20 September 2019.
- ^ a b c Barbero, M.; Hofmann, H.; Wells, N. D. (14 November 1991). "DCT source coding and current implementations for HDTV". EBU Technical Review (251). European Broadcasting Union: 22–33. Retrieved 4 November 2019.
- ISSN 0032-4558.
- ^ Bateman, Selby (April 1986). "New Technologies: The Converging Digital Universe". Compute!. No. 71. pp. 21-29 (26-8).
- ^ Barbero, M.; Stroppiana, M. (October 1992). "Data compression for HDTV transmission and distribution". IEE Colloquium on Applications of Video Compression in Broadcasting: 10/1–10/5.
- ^ "History of U.S. Satellite Broadcasting Company, Inc. – FundingUniverse". www.fundinguniverse.com. Retrieved 9 August 2018.
- ^ "Business Insider: Digital satellite TV has Indy roots". Retrieved 9 August 2018.
- ^ "NextLevel signs cable deal - Dec. 17, 1997". money.cnn.com. Retrieved 9 August 2018.
- ^ "TCI faces big challenges - Aug. 15, 1996". money.cnn.com. Retrieved 9 August 2018.
- ^ "CANAL+ TECHNOLOGIES and the world's first digital terrestrial television service in the United Kingdom". Retrieved 9 August 2018.
- ^ Latest snapshots - Freeview/DTT bitrates Archived 2007-11-22 at the Wayback Machine (Mendip transmitter, UK)
- ^ "Frequently Asked Questions -- What Is Digital TV?". ABC News. Retrieved 2020-09-30.
- ^ "Digital TV: A Cringley Crash Course — Digital Vs. Analog". Pbs.org. Retrieved 2014-01-13.
- ^ "Report ITU-R BT.2140-3 (05/2011)" (PDF). Archived (PDF) from the original on 10 June 2020.
- ^ Le Dinh, Phuc-Tue; Patry, Jacques (February 24, 2006). "Video compression artifacts and MPEG noise reduction". Video Imaging DesignLine. Archived from the original on March 14, 2006. Retrieved April 30, 2010.
- ^ "Digital TV Info". Antenna Direct. 2013-09-25. Retrieved 2022-07-22.
- ^ "Steering clear of the digital cliff". Connected Magazine. 2010-03-01. Retrieved 2024-01-05.
- ^ North Tonawanda: council discusses future TV disposal Archived 2009-01-31 at the Wayback Machine, Neale Gulley, Tonawanda News, January 27, 2009
- Detroit News, January 23, 2009
- ^ Old Toxic TVs Cause Problems, USA TODAY, January 27, 2009
- Milwaukee Journal-Sentinel, January 23, 2009
Further reading
- ISBN 0-521-82624-1
External links
- Overview of Digital Television Development Worldwide Proceedings of the IEEE, VOL. 94, NO. 1, JANUARY 2006 (University of Texas at San Antonio)
- The FCC's US consumer-oriented DTV website Archived 2011-07-23 at the Wayback Machine
- Digital TV Consumer test reports - UK Government-funded website to support Digital Switchover
- How to Set up a DTV Digital Converter Box and Antenna, a how-to article from wikiHow
- How to Scan for DTV Channels Using a Digital TV Converter Box (and why this must be done 11 June 2009 in US), a how-to article from wikiHow
- How to Use Your Older VCR, TiVo, or DVR With a DTV Converter Box, a how-to article from wikiHow