Digital television

Digital television (DTV) uses digital modulation and compression to broadcast video, audio and data signals to television sets.

Introduction

A major use of DTV can be to carry more channels on the same amount of bandwidth. Another can be high-definition programming. The digital signal eliminates common artifacts from analog broadcasting, such as ghostly and snowy images, static noises in audio; although it can replace them with new MPEG compression artifacts, such as "painting" artifacts, when transmitted with too low data rate, and may entirely fail to work in situations where analog television would have produced an impaired but watchable picture. Depending on the sophistication of the error correction, 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 an aspect ration of 16:9. This enables TV to get closer to the aspect ratio of movies and human vision. On traditional screens this causes "letterbox" black stripes to be present in the picture in the attempt to place a 16:9 picture in a 4:3 frame. The previous aspect ratio of 4:3 was chosen due to the Academy standard ratio of the day.

Market

Terrestrial

Digital terrestrial television (DTTV) is in the process of deployment in a number of countries.

Governments see DTTV as a "futuristic" technology that will push their country to the forefront of the "digital revolution" and free up existing TV frequencies for resale to communications operators.
Broadcasters see DTTV 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). It also saves money due to lower power consumption.
Hardware manufacturers see DTTV as a way to sell set-top-boxes first and new all-in-one TV sets later.
Consumers see DTTV as a way to get more programs with the same simple antenna at the cost of a set-top box or new TV.

Terrestrial DTV is widely seen as an example of a technology that is being pushed on a public that does not exhibit much demand for it. This is particularly so for high definition (HDTV) broadcast, where HDTV sets are at the moment prohibitively expensive, and very little HDTV content exists apart from movies.

Satellite

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 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.

Cable

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.

Analog switch-off

In general, viewers who are happy with their existing analog TV systems tend not to adopt terrestrial DTV systems, and 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 significant push-back from the public, as they think that this will mean that they will need to replace every television they own, including portable TVs and bedroom TVs.

Technical

Formats

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 where 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 which is related to DVB.

Most countries in the world have adopted DVB, but several have followed the US in adopting ATSC instead (Canada, South Korea, Argentina and Taiwan). Japan is the only country to use ISDB.

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 grater than HDTV.

Coverage

Coverage Maps: (from the DVB Project)

Bandwidth

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) but allows the bandwidth of a DTV channel 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. DVB stations 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.

Reception

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 is 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.

Interaction

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. Digital teletext is supposed to provide interactive services, but for this a separate upstream channel such as a telephone line or ethernet connection is required.

Deployment

UK

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 analog spectrum to launch Channel 5 the last UK terrestrial analog channel, and ONdigital's short-sightedness in over-extending its use of available bandwidth, both in terms of using poor signal encoding to save money on replacing early set-top boxes, and in terms of 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 in an attempt to counter reception problems which dogged its predecessor. Instead of 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. The government (perhaps optimistically) remains hopeful that it can end analog television broadcasts by 2010.

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 £40 per month 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.

2004 will see the first areas of the United Kingdom losing there analogue signal in a pilot test. The residents of Ferryside and Llansteffan in Pembrokeshire Wales who have not already upgraded to digital television will be given a free Set Top Box to receive the Freeview television service, which includes Channel 4 previously unavailable through terrestrial transmissions in Wales and S4C~2 which broadcasts sessions of the National Assembly for Wales. If the pilot is a success it will pave the way for the switch off of the analogue television signals throughout the United Kingdom by the governments unofficial deadline of 2012.

U.S.

The U.S. 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. Apparently, the plan is behind schedule, as it is believed that the sheer number of TV sets and broadcast equipment that require upgrade, as well as the prohibitive expense to the average consumer (as of November 2001, DTV sets cost well over US$1000), slows the momentum of the implementation.

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.

Reference: ATSC

Canada

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 November 2003, only one Canadian television station, Citytv in Toronto, broadcasts a regular digital television signal.

Reference: CRTC Decision

Australia

All major capital city television stations, and many regional stations, now simulcast in both analogue (PAL G/K) 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.

Commercial stations are not yet allowed to multi-channel, with a few exceptions (for example, if a sports telecast runs overtime, they are allowed to continue the telecast on an additional channel and return to regular programming). 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. As of this writing, there is only one datacasting service - Channel 4 - which broadcasts primarily program information, news items, parliamentary broadcasts, sports results and some advertisements.

In December 2003, the countries first digital-only broadcaster began - Tasmanian Digital Television started as a Ten affiliate in Tasmania (Hobart initially, Launceston by July 2004, and the rest of the state 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.

Finland

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.

Germany

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 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) enforcment 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.

Sweden

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.