Digital television (DTV) uses digital modulation and compression to broadcast video, audio and data signals to television sets.
A major use of DTV can be to carry more channels in the same amount of bandwidth. Another can be high definition programming. The digital signal eliminates common analog broadcasting artifacts such as "ghosting", "snow" and static noises in audio. It can replace them with new MPEG compression artifacts, such as "blocking", when transmitted at too low a data rate, and may fail to work entirely in situations where analog television would have produced an impaired but watchable picture. Depending on the sophistication and level of the error correction defined by the standard and chosen by the broadcaster, DTV may either work perfectly or not work at all.
The switch-over to DTV systems often coincides with a change in picture format from a aspect ratio of 4:3 to one of 16:9. This enables TV to get closer to the aspect ratio of movies and human vision. On traditional screens this leads to "letterbox" black bars above and below the picture due to placing the 16:9 picture in a 4:3 frame. The previous aspect ratio of 4:3 was chosen to match the Academy standard ratio of the day.
Digital terrestrial television (DTT) is in the process of deployment in a number of countries.
- Governments see DTT as a "futuristic" technology that will push their country to the forefront of the "digital revolution" and free up existing TV frequencies for resale, eg to communications operators.
- Broadcasters see DTT as a way to fight competition from satellite and cable DTV and other digital program distribution technologies, such as personal digital video recorders (PVR) and video on demand (VoD).
- Hardware manufacturers see DTT as a way to sell set-top boxes first and new all-in-one TV sets later.
- Consumers see DTT as a way to obtain more programs from their existing TV antenna at the cost of a set-top box or new television.
In some countries, DTT is seen as a technology that is being pushed on a public that does not exhibit much demand for it. This is particularly so in countries where high definition programs are broadcast terrestrially, since HDTV sets are at the moment prohibitively expensive, and very little HDTV content exists apart from movies.
DTV has been shown to be commercially viable in the satellite television market, where it is used to multiplex large numbers of channels onto the available bandwidth. The business model for satellite DTV in the US and the UK is similar to that for cable TV. Satellite DTV operators tend to act as packagers for large numbers of channels, including pay-TV. The greater RF bandwidth available to satellite operators allows them to out-compete terrestrial DTV operators on both number of channels and picture quality. Satellite tv is 100% digital.
Where a cable set-top box was already required, cable DTV deployment makes little difference to the service seen by users, but allows operators to increase the carrying capacity of their networks with low marginal levels of investment.
In general, viewers who are happy with their existing analog TV systems tend not to adopt terrestrial DTV systems (so-called "digital refuseniks"). Many of those who want cable-TV-like services will either buy cable TV, where available, or satellite DTV.
Governments are responding to this with an attempt to force the issue by enforcing planned "switch-off" dates for analog television, but are encountering push-back from the public, as they fear that this will mean that they will need to replace every television they own, including portable TVs and bedroom TVs. Prices drop though as supply scales up to meet demand.
All digital TV variants can carry both standard definition television (SDTV) and high definition television (HDTV).
All early SDTV television standards were analog in nature, and SDTV digital television systems derive much of their structure from the need to be compatible with analog television. In particular, the interlaced scan is a legacy of analog television.
Attempts were made during the development of digital television to prevent a repeat of the fragmentation of the global market into different standards (i.e. PAL, SECAM, NTSC). However, the world could not agree on a single standard, and hence there are two major standards in existence: the European DVB system and the US ATSC system, plus the Japanese system ISDB.
Most countries in the world have adopted DVB, but several have followed the US in adopting ATSC instead (Canada, Mexico, South Korea). Korea has adopted ISDB for satellite mobile broadcasting.
There could be other specialized high-resolution digital video formats in the future for markets other than home entertainment. Ultra High Definition Video (UHDV) is a format proposed by NHK of Japan that provides a resolution 16 times greater than HDTV.
Coverage Maps: (from the DVB Project)
(Remark:DVB-T Map is not correct in South Korea,Mexico and China.
South Korea adopted ATSC, and Mexico will adopt ATSC.
China has been making their own system not DVB-T)
(Remark:DVB-C Map is not correct in Japan.
Japan adopted not DVB-C but ISDB-C)
In current practice, HDTV uses 1280 × 720 pixels in progressive scan mode (abbreviated 720p) or 1920 × 1080 pixels in interlace mode (1080i). SDTV has less resolution (704 × 480 pixels with NTSC, 768 x 576 or 1024 x 576 with PAL), but allows the bandwidth of a DTV channel (or "multiplex") to be subdivided into multiple sub-channels. The TV stations can use subchannels to carry multiple broadcasts of video, audio, or any other data, and can distribute their so-called "bit budget " as necessary, such as dropping one sub-channel down to a lower resolution in order to make another one available to show a wide-screen movie. Often, this is done automatically, using a statistical multiplexer (or "stat-mux").
Multiplexes can even reduce their overall bit budget and digital bandwidth, in order to reduce the transmission bitrate and make reception easier for more distant or mobile viewers.
Today most viewers receive digital television via a set-top box, which decodes the digital signals into signals that analog televisions can understand, but a slowly growing number of TV sets with integrated receivers are already available. Access to channels can be controlled by a removable smart card, e.g. via the Common Interface (CI) standard. Some signals carry encryption and specify use conditions (such as "may not be recorded" or "may not be viewed on displays larger than 1m in diagonal measure") backed up with the force of law under the WIPO Copyright Treaty and national legislation implementing it, such as the US Digital Millennium Copyright Act.
Digital teletext is an enhanced teletext service based on XHTML and CSS. Many countries, including Finland, use Multimedia Home Platform DVB-MHP for digital teletext. An alternative is the MHEG-5 platform used terrestrially in the UK. Digital teletext is supposed to provide interactive services, but for this a separate "return path", such as a telephone line or Internet connection is required.
ISDB has adopted ARIB STD-B24 for interactive services. ISDB has labeled interactive services as data broadcasting. ARIB STD-B24 system is base on BML. BML is modified XML language for data broadcasting. ISDB has been providing EPG, news, weather forecast, traffic information, stock market conditions, educational program, interactive game program, TV shopping via the internet etc.
The UK has three major forms of digital television, a direct-to-home satellite service provided by British Sky Broadcasting (commonly known as Sky), digital cable television services provided by Telewest and NTL and a free-to-air digital terrestrial service called Freeview.
The initial attempt at launching a digital terrestrial broadcasting service, ONdigital (later called ITV Digital), was unsuccessful and the company went into liquidation. Some observers have argued that this failure stemmed from the Government's eagerness in having sold off too much TV spectrum to launch Channel 5 (the last UK terrestrial analog channel), and ONdigital's short-sightedness in over-extending its use of available bandwidth: using poor signal encoding to maintain compatibility with early set-top boxes, optimising their broadcasts for capacity rather than reliability, and cramming too many channels into the available bit-rate.
ITV Digital was replaced in late 2002 by Freeview, which uses the same DVB-T technology, but with higher levels of error correction and more robust (but lower-capacity) modulation schemes in an attempt to counter the reception problems which dogged its predecessor. Rather than concentrating on Pay TV services, Freeview uses the available capacity to provide a free-to-air service that includes all the existing five free-to-air analog terrestrial channels and about twenty new digital channels. All services are transmitted in SDTV mode.
March 31st 2004 saw the return of a limited pay-television offering to the digital terrestrial platform with the launch of Top Up TV. This new service is designed to appeal to those who do not want to pay the high subscription fees that Sky Television and the Cable networks demand. The service carries some of the UK’s most watched channels including the Discovery Channel, UK Gold, Discovery Home and Leisure, E4 and Cartoon Network. The 10 channels are split into 5 different slots and broadcast for only part of the day.
2005 saw the first areas of the United Kingdom losing their analogue signal in a pilot test. The residents of Ferryside and Llansteffan in Carmarthenshire, Wales who had not already upgraded to digital television were given a free set-top box to receive the Freeview television service, which includes Channel 4 (previously unavailable terrestrially in Wales) and S4C~2, which broadcasts sessions of the National Assembly for Wales. Digital transmissions for this pilot commenced in December 2004, at which time a message was added to the analogue picture advising viewers that the analogue services would end in February 2005. If the pilot is a success it will have paved the way for switch-over to digital television signals throughout the United Kingdom by the Government's unofficial deadline of 2012.
The US Congress and Federal Communications Commission (FCC) mandated that TV stations convert to the digital TV standard by 2003 and that stations give up their analog TV spectrum by the end of 2006 or 2009.
The FCC has attempted to force the issue (at the behest of Congress, which wants to see the money from the auction of many old analog channels 52 to 69), by invoking the All Channels Act, to mandate DTV tuners be phased in to all new TV sets, beginning with the largest.
Japan adopted a unique DTTV system named ISDB-T. ISDB-T service was initiated on December 1, 2003 in the Tokyo, Osaka, and Nagoya metropolitan areas of Japan. Analog terrestrial television broadcasts in Japan should cease on July 24, 2011 according to the current Japanese broadcasting law.
The CRTC has adopted the same digital television standard for Canadian stations as the United States. The CRTC decided not to enforce a single date for transitioning to digital broadcasts, opting to let the economy decide when the switchover will occur. As of February 2005, three Canadian television stations broadcast a regular digital television signal: Citytv in Toronto, and CBFT and CBMT in Montreal.
Reference: CRTC Decision
All major capital city television stations, and many regional stations, now simulcast in both analogue (PAL-B) and digital (DVB-T) formats. Standard definition is the most common format - by law, broadcasters must deliver 100% of their feed in SD, and at least 20 hours a week of this must be simulcast in high definition format. As of June 2004, over 400,000 digital television receivers have been sold - roughly 4% of televisions.
Commercial stations are not yet permitted to multi-channel broadcast, unless the programming content is the same on multiple channels (for example: HD simulcasts, multiple camera angles, etc.). SBS has a second channel (a world news channel), and ABC had (until July 2003) ABC Kids and Fly TV, targeted to children and teenagers respectively.
Broadcasters need a special license for datacasting. In January 2005, there is are a number of datacasting services available only in Sydney, including a program guide (Channel 4), ABC news, sport and weather items (Channel 41), ChannelNSW: Government and Public Information (Channel 45), Australian Christian Channel (Channel 46), MacquarieBank TV (Channel 47), SportsTAB (Channel 48), Expo Home Shopping (Channel 49) and Federal parliamentary broadcasts (Audio only).
In December 2003, the country's first digital-only broadcaster began - Tasmanian Digital Television started as a Ten affiliate in Tasmania (Hobart initially, Launceston followed in July 2004 - the rest of the state is to follow). The introduction of this channel has caused digital television to have a much larger uptake in Hobart, as opposed to the minimal attention the format has received in the rest of the country.
The Australian government is requiring that all stations will switch to solely digital broadcasting by 2008 (however this date is to be reviewed), so the current analogue television frequencies can be freed for other uses. No new free-to-air stations will be licensed by the Australian Broadcasting Authority until 2007. Both these dates are to be reviewed in 2005.
External link: Digital Broadcasting Australia
At the moment, digital television broadcasts can be seen in the visibility areas of the radio and television stations of Anjalankoski, Espoo, Eurajoki, Jyväskylä, Kuopio, Lahti, Lapua, Oulu, Tampere and Turku. In addition, the television station in Vaasa broadcasts the channels of the Finnish Broadcasting Company (YLE). Also many cable providers in biggest cities provide basic and pay-tv as digital. Digital television broadcasts can be received DVB-T, DVB-C and DVB-S. There are altogether 9 channels at the moment. In addition to the basic channels of YLE, MTV3 and Nelonen — Finland, you can watch e.g. 24h news and sports channels. All the channels broadcast now are free of charge. It is possible that some of the new channels will be pay TV. It has planned, that analogue transmissions are ceased in 2007.
In France, digital TV broadcasts commenced on March 31, 2005, with 14 free channels covering around 35% of the population, scheduled to rise to 85% by 2007. Additional pay TV channels are due to be launched in September, 2005.
In Belgium, over 97% of all households have cable television, so (analog) terrestrial broadcasting is only used in very limited cases, like for example mobile viewing. Almost all cable channels are still analog, except for Canal Digitaal (Dutch name) or Canal Digital (French name) which is a pay-tv channel broadcasting several SDTV channels over 1 DVB-C multiplex.
However, the two Belgian public TV stations, VRT on the Flemish side and RTBF on the Walloon side, are also broadcasting all their channels in DVB-T. Reception is said to be good in nearly the entire country. Both also have an internation channel on digital satellite (DVB-S) called BVN (as a cooperation between the Flemish VRT and the Dutch NOS) and RTBF Sat .
The Belgian commercial tv stations are currently only limited to cable distribution and are thus only available in analog at the moment. Terrestrial broadcasting is limited to public service TV stations by law in Belgium.
In two steps during 2003 terrestrial analog TV broadcasting in the area of Berlin and surrounding Brandenburg was switched completely to DVB-T with good reception in the public, because with its more than 20 channels it establishes a free competitor to cable TV. Other metropolitan areas are to follow in 2004. Terrestrial reception had lost most of its users in the 1990s and is believed to get a comeback now, especially in the mobile area.
Since early in the decade most of the 30+ TV stations broadcast their satellite signal analog and digital (DVB-S). 2003 the one digital-only bouquet is the one of Germany's only pay TV network Premiere , which (in form of its former owner Leo Kirch ) got into serious fiscal trouble due to its early and proprietary (Betacrypt , d-box ) enforcement of DTV.
Cable transmission is still mostly analog, again with the exception of Premiere (DVB-C) and some less important stations that didn't fit any more into the analog band. This situation is caused by the long and slow process of selling the infrastructure from former monopolist Deutsche Telekom to others, which for some years stopped nearly all new investments in that area.
Broadcast is always in DVB and SDTV PAL. No German network has announced HDTV broadcasts yet, but the pan-European network Euro1080 starts in 2004. All analog television broadcasting in Germany are to be terminated by law by 2010.
In 1996, the Swedish parliament decided that terrestrial digital broadcasts (DVB-T) were the future. The government presented its proposition to the parliament in March 2003. In the early summer of 2003, the parliament committed to a plan where the analog broadcasting would be shut down in February 2008 . As of May 2004, 23% of the population had access to equipment for receiving digital broadcasts. The digital broadcasts cover 90% of the population, and the plan is to cover 99.8% before the termination of the analog network.
The parliament and the ministry of culture determine what channels are allowed to broadcast digitally. The level of governmental control has generated some controversy.
The introduction of DVB-T is regulated by the ministry of culture and church affairs. So far Norway has developed slowly on DVB-T compared to main European countries, but pace is picking up as the Norwegian government now wants to close analogue tv broadcasting by 2009. In June 2002, a 12-year nationwide licence, including the roll-out of infrastructure, was publicly announced, met only by the application of Norges Televisjon as (NTV), a joint venture between the state-owned broadcaster NRK and the leading private broadcaster TV2. In February 2004, the Norwegian parliament passed the final regulations on digital broadcasting to the ministry of culture and church affairs, leaving the ministry to create a licence agreement for NTV. The ministry showed their proposal for a licence in December 2004. NTV was faced with more complicated regulations than they expected (such as the licence running already from roll-out of infrastructure). Therefore, in February 2005 NTV applied for extending their licence period from 12 yrs to 15 yrs, and consequently the ministry publicly announced the licence once again, announcement period expiring May 2, 2005. If licence is granted NTV during 2005, the company says it plans to roll-out infrastructure during 2006-2009, offering the Norwegian public between 15 and 18 TV stations; of them NRK1, NRK2, TV2, TV2 Xtra and a local channel. The EFTA competition authorities, ESA, has protested on the application process, saying the minstry is not in position to grant the DVB-T licence to a state-owned company like NTV, but ministry says this protest will not affect their decision. Here is a press release in Norwegian from the ministry dated March 7, 2005 annoncing the extended licence for digital television.
France is quite late in the deployment of digital terrestrial television (DVB-T) known under the acronym of TNT (Télévision Numérique Terrestre), however it will formally arrive on the 31st March 2005 after testings, like Freeview it will support many new channels as well as the current terrestrial television. The channels are TF1, France 2, France 3, Canal + (when programmes are non-encrypted), France 5, M6, ARTE, Direct 8, W9, TMC, NT1, NRJ 12, La Chaîne Parlementaire et France 4.
Regulators and organisations
Broadcasters and DTV Channel operators
Regulators and organisations
Broadcasters and DTV Channel operators
Regulators and organisations