Digital television
Digital television is the transmission of television signals, including the sound channel, using digital encoding, in contrast to the earlier television technology, analog television, in which the video and audio are carried by analog signals. It is an innovative advance that represents the first significant evolution in television technology since color television in the 1950s. Digital TV transmits in a new image format called HDTV, with greater resolution than analog TV, in a wide screen aspect ratio similar to recent movies in contrast to the narrower screen of analog TV, it makes more economical use of scarce radio spectrum space. A transition from analog to digital broadcasting began around 2006 in some countries, many industrial countries have now completed the changeover, while other countries are in various stages of adaptation. Different digital television broadcasting standards have been adopted in different parts of the world; this standard has been adopted in Europe, Asia, total about 60 countries.
Advanced Television System Committee uses eight-level vestigial sideband for terrestrial broadcasting. This standard has been adopted by 6 countries: United States, Mexico, South Korea, Dominican Republic and Honduras. Integrated Services Digital Broadcasting is a system designed to provide good reception to fixed receivers and portable or mobile receivers, it utilizes two-dimensional interleaving. It supports hierarchical transmission of up to three layers and uses MPEG-2 video and Advanced Audio Coding; this standard has been adopted in Japan and the Philippines. ISDB-T International is an adaptation of this standard using H.264/MPEG-4 AVC that been adopted in most of South America and is being embraced by Portuguese-speaking African countries. Digital Terrestrial Multimedia Broadcasting adopts time-domain synchronous OFDM technology with a pseudo-random signal frame to serve as the guard interval of the OFDM block and the training symbol; the DTMB standard has been adopted in the People's Republic including Hong Kong and Macau.
Digital Multimedia Broadcasting is a digital radio transmission technology developed in South Korea as part of the national IT project for sending multimedia such as TV, radio and datacasting to mobile devices such as mobile phones, laptops and GPS navigation systems. Digital TV's roots have been tied closely to the availability of inexpensive, high performance computers, it wasn't until the 1990s. In the mid-1980s, as Japanese consumer electronics firms forged ahead with the development of HDTV technology, as the MUSE analog format was proposed by Japan's public broadcaster NHK as a worldwide standard, Japanese advancements were seen as pacesetters that threatened to eclipse U. S. 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. An American company, General Instrument, demonstrated the feasibility of a digital television signal; this breakthrough was of such significance that the FCC was persuaded to delay its decision on an ATV standard until a digitally based standard could be developed.
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 ATV 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. 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 allowed the new DTV signal to be based on new design principles. Although incompatible with the existing NTSC standard, the new DTV standard would be able to incorporate many improvements; the final standard adopted by the FCC did not require a single standard for scanning formats, aspect ratios, or lines of resolution. This outcome resulted from a dispute between the consumer electronics industry and the computer industry over which of the two scanning processes—interlaced or progressive—is superior.
Interlaced scanning, used in televisions worldwide, scans even-numbered lines first odd-numbered ones. Progressive scanning, 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 argued that progressive scanning enables easier connections with the Internet, is more cheaply converted to interlaced formats than vice versa; the film industry 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 feasible, i.e. 1,080 lines per picture and 1,920 pixels per line. Broadcasters favored interlaced scanning because their vast archive of interlaced
Set-top box
A set-top box or set-top unit is an information appliance device that contains a TV-tuner input and displays output to a television set and an external source of signal, turning the source signal into content in a form that be displayed on the television screen or other display device. They are used in cable television, satellite television, over-the-air television systems, as well as other uses. According to the Los Angeles Times, the cost to a cable provider for a set-top box is between $150 for a basic box to $250 for a more sophisticated box in the United States. In 2016, the average pay-TV subscriber paid $231 per year to lease their set-top box from a cable service provider; the signal source might be an Ethernet cable, a satellite dish, a coaxial cable, a telephone line, broadband over power lines, or an ordinary VHF or UHF antenna. Content, in this context, could mean any or all of video, Internet web pages, interactive video games, or other possibilities. Satellite and microwave-based services require specific external receiver hardware, so the use of set-top boxes of various formats has never disappeared.
Set-top boxes can enhance source signal quality. Before the All-Channel Receiver Act of 1962 required US television receivers to be able to tune the entire VHF and UHF range, a set-top box known as a UHF converter would be installed at the receiver to shift a portion of the UHF-TV spectrum onto low-VHF channels for viewing; as some 1960s-era 12-channel TV sets remained in use for many years, Canada and Mexico were slower than the US to require UHF tuners to be factory-installed in new TVs, a market for these converters continued to exist for much of the 1970s. Cable television represented a possible alternative to deployment of UHF converters as broadcasts could be frequency-shifted to VHF channels at the cable head-end instead of the final viewing location. However, most cable systems could not accommodate the full 54-890 MHz VHF/UHF frequency range and the twelve channels of VHF space were exhausted on most systems. Adding any additional channels therefore needed to be done by inserting the extra signals into cable systems on nonstandard frequencies either below VHF channel 7 or directly above VHF channel 13.
These frequencies corresponded to non-television services over-the-air and were therefore not on standard TV receivers. Before cable-ready TV sets became common in the late 1980s, an electronic tuning device called a cable converter box was needed to receive the additional analog cable TV channels and transpose or convert the selected channel to analog radio frequency for viewing on a regular TV set on a single channel VHF channel 3 or 4; the box allowed an analog non-cable-ready television set to receive analog encrypted cable channels and was a prototype topology for date digital encryption devices. Newer televisions were converted to be analog cypher cable-ready, with the standard converter built-in for selling premium television. Several years and marketed, the advent of digital cable continued and increased the need for various forms of these devices. Block conversion of the entire affected frequency band onto UHF, while less common, was used by some models to provide full VCR compatibility and the ability to drive multiple TV sets, albeit with a somewhat nonstandard channel numbering scheme.
Newer television receivers reduced the need for external set-top boxes, although cable converter boxes continue to be used to descramble premium cable channels according to carrier-controlled access restrictions, to receive digital cable channels, along with using interactive services like video on demand, pay per view, home shopping through television. Set-top boxes were made to enable closed captioning on older sets in North America, before this became a mandated inclusion in new TV sets; some have been produced to mute the audio when profanity is detected in the captioning, where the offensive word is blocked. Some include a V-chip that allows only programs of some television content ratings. A function that limits children's time watching TV or playing video games may be built in, though some of these work on main electricity rather than the video signal; the transition to digital terrestrial television after the turn of the millennium left many existing television receivers unable to tune and display the new signal directly.
In the United States, where analog shutdown was completed in 2009 for full-service broadcasters, a federal subsidy was offered for coupon-eligible converter boxes with deliberately limited capability which would restore signals lost to digital transition. Professional set-top boxes are referred to as IRDs or integrated receiver/decoders in the professional broadcast audio/video industry, they are designed for rack mounting environments. IRDs are capable of outputting uncompressed serial digital interface signals, unlike consumer STBs which don't because of copyright reasons. Hybrid set-top boxes, such as those used for Smart TV programming, enable viewers to access multiple TV delivery methods. By integrating varying delivery streams, hybrids enable pay-TV operators more flexible application depl
Europe
Europe is a continent located in the Northern Hemisphere and in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west and the Mediterranean Sea to the south, it comprises the westernmost part of Eurasia. Since around 1850, Europe is most considered to be separated from Asia by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas and the waterways of the Turkish Straits. Although the term "continent" implies physical geography, the land border is somewhat arbitrary and has been redefined several times since its first conception in classical antiquity; the division of Eurasia into two continents reflects East-West cultural and ethnic differences which vary on a spectrum rather than with a sharp dividing line. The geographic border does not follow political boundaries, with Turkey and Kazakhstan being transcontinental countries. A strict application of the Caucasus Mountains boundary places two comparatively small countries and Georgia, in both continents.
Europe covers 2 % of the Earth's surface. Politically, Europe is divided into about fifty sovereign states of which the Russian Federation is the largest and most populous, spanning 39% of the continent and comprising 15% of its population. Europe had a total population of about 741 million as of 2016; the European climate is affected by warm Atlantic currents that temper winters and summers on much of the continent at latitudes along which the climate in Asia and North America is severe. Further from the sea, seasonal differences are more noticeable than close to the coast. Europe, in particular ancient Greece, was the birthplace of Western civilization; the fall of the Western Roman Empire in 476 AD and the subsequent Migration Period marked the end of ancient history and the beginning of the Middle Ages. Renaissance humanism, exploration and science led to the modern era. Since the Age of Discovery started by Portugal and Spain, Europe played a predominant role in global affairs. Between the 16th and 20th centuries, European powers controlled at various times the Americas all of Africa and Oceania and the majority of Asia.
The Age of Enlightenment, the subsequent French Revolution and the Napoleonic Wars shaped the continent culturally and economically from the end of the 17th century until the first half of the 19th century. The Industrial Revolution, which began in Great Britain at the end of the 18th century, gave rise to radical economic and social change in Western Europe and the wider world. Both world wars took place for the most part in Europe, contributing to a decline in Western European dominance in world affairs by the mid-20th century as the Soviet Union and the United States took prominence. During the Cold War, Europe was divided along the Iron Curtain between NATO in the West and the Warsaw Pact in the East, until the revolutions of 1989 and fall of the Berlin Wall. In 1949 the Council of Europe was founded, following a speech by Sir Winston Churchill, with the idea of unifying Europe to achieve common goals, it includes all European states except for Belarus and Vatican City. Further European integration by some states led to the formation of the European Union, a separate political entity that lies between a confederation and a federation.
The EU originated in Western Europe but has been expanding eastward since the fall of the Soviet Union in 1991. The currency of most countries of the European Union, the euro, is the most used among Europeans. In classical Greek mythology, Europa was a Phoenician princess; the word Europe is derived from her name. The name contains the elements εὐρύς, "wide, broad" and ὤψ "eye, countenance", hence their composite Eurṓpē would mean "wide-gazing" or "broad of aspect". Broad has been an epithet of Earth herself in the reconstructed Proto-Indo-European religion and the poetry devoted to it. There have been attempts to connect Eurṓpē to a Semitic term for "west", this being either Akkadian erebu meaning "to go down, set" or Phoenician'ereb "evening, west", at the origin of Arabic Maghreb and Hebrew ma'arav. Michael A. Barry, professor in Princeton University's Near Eastern Studies Department, finds the mention of the word Ereb on an Assyrian stele with the meaning of "night, sunset", in opposition to Asu " sunrise", i.e. Asia.
The same naming motive according to "cartographic convention" appears in Greek Ἀνατολή. Martin Litchfield West stated that "phonologically, the match between Europa's name and any form of the Semitic word is poor." Next to these hypotheses there is a Proto-Indo-European root *h1regʷos, meaning "darkness", which produced Greek Erebus. Most major world languages use words derived from Europa to refer to the continent. Chinese, for example, uses the word Ōuzhōu. In some Turkic languages the Persian name Frangistan is used casually in referring to much of Europe, besides official names such as Avrupa or Evropa; the prevalent definition of Europe as a geographical term has been in use since the mid-19th century. Europe is taken to be bounded by large bodies of water
DVB-T2
DVB-T2 is an abbreviation for "Digital Video Broadcasting — Second Generation Terrestrial". DVB has been standardized by ETSI; this system transmits compressed digital audio and other data in "physical layer pipes", using OFDM modulation with concatenated channel coding and interleaving. The higher offered bit rate, with respect to its predecessor DVB-T, makes it a system suited for carrying HDTV signals on the terrestrial TV channel; as of 2014, it was implemented in broadcasts in the United Kingdom, Finland, Sweden, Thailand Flanders, Ukraine, Denmark and some other countries. In March 2006 DVB decided to study options for an upgraded DVB-T standard. In June 2006, a formal study group named TM-T2 was established by the DVB Group to develop an advanced modulation scheme that could be adopted by a second generation digital terrestrial television standard, to be named DVB-T2. According to the commercial requirements and call for technologies issued in April 2007, the first phase of DVB-T2 would be devoted to provide optimum reception for stationary and portable receivers using existing aerials, whereas a second and third phase would study methods to deliver higher payloads and the mobile reception issue.
The novel system should provide a minimum 30% increase in payload, under similar channel conditions used for DVB-T. The BBC, ITV, Channel 4 and Channel 5 agreed with the regulator Ofcom to convert one UK multiplex to DVB-T2 to increase capacity for HDTV via DTT, they expected the first TV region to use the new standard would be Granada in November 2009. It was expected that over time there would be enough DVB-T2 receivers sold to switch all DTT transmissions to DVB-T2, H.264. Ofcom published its final decision on 3 April 2008, for HDTV using DVB-T2 and H.264: BBC HD would have one HD slot after digital switchover at Granada. ITV and C4 had, as expected, applied to Ofcom for the 2 additional HD slots available from 2009 to 2012. Ofcom indicated that it found an unused channel covering 3.7 million households in London, which could be used to broadcast the DVB-T2 HD multiplex from 2010, i.e. before DSO in London. Ofcom indicated that they would look for more unused UHF channels in other parts of the UK, that can be used for the DVB-T2 HD multiplex from 2010 until DSO.
The DVB-T2 draft standard was ratified by the DVB Steering Board on 26 June 2008, published on the DVB homepage as DVB-T2 standard BlueBook. It was handed over to the European Telecommunications Standards Institute by DVB. ORG on 20 June 2008; the ETSI process resulted in the DVB-T2 standard being adopted on 9 September 2009. The ETSI process had several phases. Since the DVB-T2 physical layer specification was complete, there would be no further technical enhancements, receiver VLSI chip design started with confidence in stability of specification. A draft PSI/SI specification document was agreed with the DVB-TM-GBS group. Prototype receivers were shown in September IBC 2008 and more recent version at the IBC 2009 in Amsterdam. A number of other manufacturers demonstrated DVB-T2 at IBC 2009 including Albis Technologies, DekTec, Enensys Technologies, Pace, Rohde & Schwarz, Thomson Broadcast and TeamCast; as of 2012, Appear TV produce DVB-T2 receivers, DVB-T2 modulators and DVB-T2 gateways. Other manufacturers planning DVB-T2 equipment launches include Alitronika, CellMetric, Digital TV Labs, Humax, NXP Semiconductors, ProTelevision Technologies, Screen Service, SIDSA, Sony, ST Microelectronics and T-VIPS.
The first test from a real TV transmitter was performed by the BBC Research & Innovation in the last weeks of June 2008 using channel 53 from the Guildford transmitter, southwest of London: BBC had developed and built the modulator/demodulator prototype in parallel with the DVB-T2 standard being drafted. Other companies like ENKOM or IfN develop software based decoding. NORDIG published a DVB-T2 receiver specification and performance requirement on 1 July 2009. In March 2009 the Digital TV Group, the industry association for digital TV in the UK, published the technical specification for high definition services on digital terrestrial television using the new DVB-T2 standard; the DTG's test house: DTG Testing are testing Freeview HD products against this specification. Many tests broadcast transmission using this standard are being in process in France, with local Gap filler near Rennes CCETT. DVB-T2 was tested in October 2010, in Geneva region, with Mont Salève's repeater, in UHF band on Channel 36.
A mobile van was testing BER, quality reception, with special PCs used as spectrum analysers, constellation testers. The van was moving in Canton Geneva, France. However, none were demonstrated in TELECOM 2011 at Palexpo; the following characteristics have
Teletext
Teletext, or broadcast teletext, is a videotex standard for displaying text and rudimentary graphics on suitably equipped television sets. Teletext sends data in the broadcast signal, hidden in the invisible vertical blank interrupt area at the top and bottom of the screen; the teletext decoder in the television buffers this information as a series of "pages", each given a number. The user can display chosen pages using their remote control, it was created in the United Kingdom in the early 1970s by John Adams, Philips' Lead Designer for video display units. Public teletext information services were introduced by major broadcasters in the UK, starting with the BBC's Ceefax service in 1974, it offered a range of text-based information including news, weather and TV schedules. Paged subtitle information was transmitted using the same system. Similar systems were introduced by other UK broadcasters, including ITV's ORACLE and Teletext Ltd. while the General Post Office introduced the Prestel system using the same display standards but run over telephone lines using bi-directional modems rather than the send-only system used with televisions.
Teletext formed the basis for an extended version of the same basic system. This saw widespread use across Europe starting in the 1980s, with all televisions including a decoder; the teletext system was used for a number of experimental systems, notably in the United States, but these were never as popular as their European counterparts and most closed by the early 1990s. Most teletext systems survived in one form or another into the 2000s, when the internet had become ubiquitous. Teletext is broadcast in numbered "pages." For example, a list of news headlines might appear on page 110. The broadcaster sends out pages in sequence. There will be a delay of a few seconds from requesting the page and it being broadcast and displayed, the time being dependent in the number of pages being broadcast. More sophisticated receivers use a memory buffer to store some or all of the teletext pages as they are broadcast, allowing instant display from the buffer; this basic architecture separates from other digital information systems, such as the internet, whereby pages are'requested' and then'sent' to the user – a method not possible given the one-way nature of broadcast teletext.
Unlike the Internet, teletext is broadcast, so it does not slow down further as the number of users increase, although the greater number of pages, the longer one is to wait for each to be found in the cycle. For this reason, some pages are broadcast more than once in each cycle. Teletext proved to be a reliable text news service during events such as the September 11 terrorist attacks, during which the webpages of major news sites became inaccessible because of the high demand. Teletext is used for carrying special packets interpreted by TVs and video recorders, containing information about subjects such as channels and programming. Although the term "teletext" tends to be used to refer to the PAL-based system, or variants, the recent availability of digital television has led to more advanced systems being provided that perform the same task, such as MHEG-5 in the UK, Multimedia Home Platform. Teletext is a means of sending text and simple geometric shapes to a properly equipped television screen by use of one of the "vertical blanking interval" lines that together form the dark band dividing pictures horizontally on the television screen.
Transmitting and displaying subtitles was easy. It requires limited bandwidth. However, it was found that by combining a slow data rate with a suitable memory, whole pages of information could be sent and stored in the TV for recall. In the early 1970s work was in progress in Britain to develop such a system; the goal was to provide UK rural homes with electronic hardware that could download pages of up-to-date news, reports and figures targeting U. K. agriculture. The original idea was the brainchild of Philips Laboratories in 1970. In 1971, CAL engineer John Adams created a proposal for UK broadcasters, his configuration contained all the fundamental elements of classic Teletext including pages of 24 rows with 40 characters each, page selection, sub pages of information and vertical blanking interval data transmission. A major objective for Adams during the concept development stage was to make Teletext affordable to the home user. In reality, there was no scope to make an economic Teletext system with 1971 technology.
However, as low cost was essential to the project's long term success, this obstacle had to be overcome. Meanwhile, the General Post Office, whose telecommunications division became British Telecom, had been researching a similar concept since the late 1960s, known as Viewdata. Unlike Teledata, a one-way service carried in the existing TV signal, Viewdata was a two-way system using telephones. Since the Post Office owned the telephones, this was considered to be an excellent way to drive more customers to use the phones. In 1972 the BBC demonstrated their system, now known as Ceefax, on various news shows; the Independent Television Authority announced their own service in 1973, known as ORACLE. Not to be outdone, the GPO announced a 1200/75 baud videotext service under the name Prestel; the first teletext test transmissions were made by Ceefax in 1973. After proliferation of the BBC system in the UK, it was adopted in Europe and standardised as World System
DVB-T
DVB-T is an abbreviation for "Digital Video Broadcasting — Terrestrial". This system transmits compressed digital audio, digital video and other data in an MPEG transport stream, using coded orthogonal frequency-division multiplexing modulation, it is the format used worldwide for Electronic News Gathering for transmission of video and audio from a mobile newsgathering vehicle to a central receive point. Rather than carrying one data carrier on a single radio frequency channel, COFDM works by splitting the digital data stream into a large number of slower digital streams, each of which digitally modulates a set of spaced adjacent sub-carrier frequencies. In the case of DVB-T, there are two choices for the number of carriers known as 8K-mode; these are 1,705 or 6,817 sub-carriers that are 4 kHz or 1 kHz apart. DVB-T offers three different modulation schemes. DVB-T has been adopted or proposed for digital television broadcasting by many countries, using VHF 7 MHz and UHF 8 MHz channels whereas Taiwan, Colombia and Trinidad and Tobago use 6 MHz channels.
Examples include the UK's Freeview. The DVB-T Standard is published as EN 300 744, Framing structure, channel coding and modulation for digital terrestrial television; this is available from the ETSI website, as is ETSI TS 101 154, Specification for the use of Video and Audio Coding in Broadcasting Applications based on the MPEG-2 Transport Stream, which gives details of the DVB use of source coding methods for MPEG-2 and, more H.264/MPEG-4 AVC as well as audio encoding systems. Many countries that have adopted DVB-T have published standards for their implementation; these include the D-book in the UK, the Italian DGTVi, the ETSI E-Book and the Nordic countries and Ireland NorDig. DVB-T has been further developed into newer standards such as DVB-H, a commercial failure and is no longer in operation, DVB-T2, finalised in August 2011. DVB-T as a digital transmission delivers data in a series of discrete blocks at the symbol rate. DVB-T is a COFDM transmission technique, it allows the receiver to cope with strong multipath situations.
Within a geographical area, DVB-T allows single-frequency network operation, where two or more transmitters carrying the same data operate on the same frequency. In such cases the signals from each transmitter in the SFN needs to be time-aligned, done by sync information in the stream and timing at each transmitter referenced to GPS; the length of the Guard Interval can be chosen. It is a trade-off between SFN capability; the longer the guard interval the larger is the potential SFN area without creating intersymbol interference. It is possible to operate SFNs which do not fulfill the guard interval condition if the self-interference is properly planned and monitored. With reference to the figure, a short description of the signal processing blocks follows. Source coding and MPEG-2 multiplexing: Compressed video, compressed audio, data streams are multiplexed into MPEG program streams. One or more MPEG-PS's are joined together into an MPEG transport stream. Allowed bitrates for the transported data depend on a number of coding and modulation parameters: it can range from about 5 to about 32 Mbit/s.
Splitter: Two different MPEG-TSs can be transmitted at the same time, using a technique called Hierarchical Transmission. It may be used to transmit, for example a standard definition SDTV signal and a high definition HDTV signal on the same carrier; the SDTV signal is more robust than the HDTV one. At the receiver, depending on the quality of the received signal, the STB may be able to decode the HDTV stream or, if signal strength lacks, it can switch to the SDTV one. MUX adaptation and energy dispersal: The MPEG-TS is identified as a sequence of data packets, of fixed length. With a technique called energy dispersal, the byte sequence is decorrelated. External encoder: A first level of error correction is applied to the transmitted data, using a non-binary block code, a Reed-Solomon RS 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, in such a way that it becomes more rugged to long sequences of errors.
Internal encoder: A second level of error correction is given by a punctured convolutional code, denoted in STBs menus as FEC. There are five valid coding rates: 1/2, 2/3, 3/4, 5/6, 7/8. Internal interleaver: Data sequence is rearranged again, aiming to reduce the influence of burst errors; this time, a block interleaving technique is adopted, with a pseudo-random assignment scheme. Mapper: The digital bit sequence is mapped into a base band modulated sequence of complex symbols. There are three valid modulation schemes: QPSK, 16-QAM, 64-QAM. Frame adaptation: the complex symbols are grouped in blocks of const
