Digital Television

List of digital television broadcast standards
DVB standards (countries)
terrestrial)

satellite)

cable)

DVB-H (handheld)

ATSC standards (countries)
terrestrial/cable)

ATSC-M/H (mobile/handheld)
ISDB standards (countries)
terrestrial)

ISDB-T International
satellite)
cable)
Brazil)
DTMB standards (countries)
DTMB (terrestrial)
CMMB (handheld)
DMB standard (countries)
Codecs
Video

Audio

Frequency bands
VHF
UHF
SHF

Digital television (DTV) is the transmission of audio and video by digitally processed and multiplexed signal, in contrast to the totally analog and channel separated signals used by [2]

Contents

[edit] Technical information

[edit] Formats and bandwidth

Digital television supports many different picture formats defined by the aspect ratio (width to height ratio).

With 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 channel capacity issues.

Standard definition TV (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. For [3]

Each National Datacast.

A broadcaster may opt to use a standard-definition (bitrate and make reception easier for more distant or mobile viewers.

[edit] Reception

There are a number of different ways to receive digital television. One of the oldest means of receiving DTV (and TV in general) is using an antenna (known as an aerial in some countries). This way is known as Digital terrestrial television (DTT). With DTT, viewers are limited to whatever channels the antenna picks up. Signal quality will also vary.

Other ways have been devised to receive digital television. Among the most familiar to people are digital cable and digital satellite. In some countries where transmissions of TV signals are normally achieved by microwaves, digital MMDS is used. Other standards, such as Digital multimedia broadcasting (DMB) and DVB-H, have been devised to allow handheld devices such as mobile phones to receive TV signals. Another way is IPTV, that 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 via the open Internet. For example, there is P2P (peer-to-peer) Internet television software that can be used to watch TV on a computer.

Some signals carry CableCard.

[edit] Protection parameters for terrestrial DTV broadcasting

[clarification needed]

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, and this is the reason a smaller range of channels can carry an all-digital set of television stations.[citation needed]

System Parameters
(protection ratios)
Canada [13] USA [5] EBU [9, 12]
ITU-mode M3
Japan & Brazil [36, 37][4]
C/N for AWGN Channel +19.5 dB
(16.5 dB[5])
+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[5])
+15.27 dB +19 dB +19 dB
Lower Adjacent Channel DTV into Analog TV −16 dB −17.43 dB −5 ~ −11 dB[6] −6 dB
Upper Adjacent Channel DTV into Analog TV −12 dB −11.95 dB −1 ~ −10[6] −5 dB
Lower Adjacent Channel Analog TV into DTV −48 dB −47.33 dB −34 ~ −37 dB[6] −35 dB
Upper Adjacent Channel Analog TV into DTV −49 dB −48.71 dB −38 ~ −36 dB[6] −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

[edit] Interaction

Interaction happens between the TV watcher and the DTV system. It can be understood in different ways, depending on which part of the DTV system is concerned. It can also be an interaction with the STB only (to tune to another TV channel or to browse the EPG).

Modern DTV systems are able to provide interaction between the end-user and the broadcaster through the use of a return path. With the exceptions of coaxial and fiber optic cable, which can be bidirectional, a dialup modem, Internet connection, or other method is typically used for the return path with unidirectional networks such as satellite or antenna broadcast.

In addition to not needing a separate return path, cable also has the advantage of a video on demand.

[edit] 1-segment broadcasting

cell phone.

[edit] Comparison analog vs digital

DTV has several advantages over analog TV, the most significant being that digital channels take up less bandwidth, and the bandwidth needs are continuously variable, at a corresponding reduction in image quality depending on the level of compression 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 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.

Digital and analog signals react differently to interference. For example, common problems with analog television include ghosting of images, noise from weak signals, and many other potential problems which degrade the quality of the image and sound, although the program material may still be watchable. With digital television, the audio and video must be synchronized digitally, so reception of the digital signal must be very nearly complete; otherwise, neither audio nor video will be usable. Short of this complete failure, “blocky” video is seen when the digital signal experiences interference.

[edit] Effect on existing 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, recorders) or may purchase set-top converter boxes to tune in the digital signals. In the United States, a [12] by 2015 in the Philippines and Uruguay and by 2017 in Costa Rica.

[edit] Disappearance of TV-audio receivers

Prior to the conversion to digital TV, analog television broadcast audio for TV channels on a separate FM carrier frequency from the video signal. This FM audio signal could be heard using standard radios equipped with the appropriate tuning circuits.

However, after the relatively recent DTV radio is not the same thing.)

[edit] 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 during [15]

While the hazardous material.

Local restrictions on disposal of these materials vary widely; in some cases second-hand stores have refused to accept working color television receivers for resale due to the increasing costs of disposing of unsold TVs. Those thrift stores which are still accepting donated TVs have reported significant increases in good-condition working used television receivers abandoned by viewers who often expect them not to work after digital transition.[20]

In Michigan, one recycler has estimated that as many as one household in four will dispose of or recycle a TV set in the next year.[21] 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.

[edit] Technical limitations

[edit] Compression artifacts 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 bandwidth and compression algorithms such as MPEG-2. This defect is sometimes referred to as “mosquito noise“.[22]

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 compression artifacts during fast motion where the eye cannot track and resolve them as easily and, conversely, minimizing artifacts in still backgrounds that may be closely examined in a scene (since time allows).

[edit] 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. This phenomenon is known as the digital cliff effect.

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 will add to these problems, especially in cases where a clear line-of-sight from the receiving antenna to the transmitter is not available.

[edit] Timeline of transition

[edit] See also

[edit] Notes & references

  1. ^ Kruger, L. G. (2001). Digital Television: An Overview. Hauppauge, New York: Nova Publishers.
  2. ^ Ong, C. Y., Song, J., Pan, C., & Li, Y.(2010, May). Technology and Standards of Digital Television Terrestrial Multimedia Broadcasting [Topics in Wireless Communications], Communications Magazine, IEEE , 48(5),119-127
  3. ^ Latest snapshots – Freeview/DTT bitrates (Mendip transmitter, UK)
  4. ^ ISDB-T (6 MHz, 64QAM, R=2/3), Analog TV (M/NTSC).
  5. ^ b The Canadian parameter, C/(N+I) of noise plus co-channel DTV interface should be 16.5 dB.
  6. ^ d Depending on analog TV systems used.
  7. ^ “The Digital TV Transition: Will You Be Affected?”. FCC. http://www.dtv.gov/affected.html. Retrieved 2009-11-02.
  8. ^ “New DTV Hard Date: July 24, 2011?”. B&C. http://www.broadcastingcable.com/blog/BC_DC_Eggerton_on_Washington/15430-New_DTV_Hard_Date_July_24_2011_.php. Retrieved 2009-11-02.
  9. ^ “DTV Post-Transition Allotment Plan” (PDF). Spectrum Management and Telecommunications. http://www.ic.gc.ca/eic/site/smt-gst.nsf/vwapj/DTV_PLAN_Dec08-e.pdf/$file/DTV_PLAN_Dec08-e.pdf. Retrieved 2009-11-02.
  10. ^ “When do I switch?”. Digital UK. http://www.digitaluk.co.uk/when_do_i_switch. Retrieved 2009-11-02.
  11. ^ “Digital Terrestrial Television for Ireland – What are the benefits, when will it happen? New website to answer questions”. http://www.digitaltelevision.ie/News/launch+of+website.htm.
  12. ^ “When do I switch?”. Digital Ready AU. http://www.digitalready.gov.au/. Retrieved 2010-05-14.
  13. ^ Unloading that old TV not quite so simple, Lee Bergquist, Milwaukee Journal-Sentinel, January 23, 2009
  14. ^ North Tonawanda: council discusses future TV disposal, Neale Gulley, Tonawanda News, January 27, 2009
  15. ^ Old Toxic TVs Cause Problems, USA TODAY, January 27, 2009
  16. ^ Campaigners highlight ‘toxic TVs’, Maggie Shiels, BBC News, 9 January 2009
  17. http://www.premierinc.com/quality-safety/tools-services/safety/topics/computers/downloads/k_3_lead_in_crts.pdf. Retrieved 2009-09-29.
  18. http://ewasteguide.info/biblio/management-cr. Retrieved 2009-09-29. “number of studies have demonstrated that the neck and funnel glasses of CRT are hazardous wastes, while the panel glass exhibits little toxicity.”
  19. ^ What To Do With Your Old TV’s, Mike Webster, WCSH-TV, January 28, 2009
  20. ^ Many people throwing out perfectly good TVs over digital confusion, Daniel Vasquez, Sun-Sentinel, Florida, January 19, 2009
  21. ^ Trashing the tube: Digital conversion may spark glut of toxic waste, Jennifer Chambers, Detroit News, January 23, 2009
  22. ^ Le Dinh, Phuc-Tue; Patry, Jacques (February 24, 2006). “Video compression artifacts and MPEG noise reduction”. ideo Imaging DesignLine. http://www.videsignline.com/howto/180207350. Retrieved April 30, 2010.

[edit] Further reading

[edit] External links



Source: Wikipedia