Digital Terrestrial Television ( DTTV or DTT ) is the technological evolution and advance from analogue terrestrial television, which broadcasts land based (terrestrial) signals. The purpose of digital terrestrial television, similar to digital versus analogue in other platforms such as cable, satellite, telecoms, is characterised reduced use of spectrum and more capacity than analogue, better-quality picture, and lower operating costs for broadcast and transmission after the initial upgrade costs. A terrestrial implementation of digital television technology uses aerial broadcasts to a conventional antenna (or aerial) instead of a satellite dish or cable connection.
Competing variants of digital terrestrial television technology are used around the world. Advanced Television Standards Committee ATSC is the one used in North America and South Korea, an evolution from the analogue National Television Standards Committee standard NTSC. ISDB-T is used in Japan, with a variation of it used in Brazil, Argentina, Peru, Chile and most recently Venezuela, while DVB-T is the most prevalent, covering Europe, Australia, New Zealand, Colombia, Uruguay and some countries of Africa.DMB-T/H is China's own standard (including Hong Kong, though Hong Kong's private operators use DVB-T); the rest of the world remains mostly undecided, many evaluating multiple standards. ISDB-T is very similar to DVB-T and can share front-end receiver and demodulator components. The United States of America has switched from Analogue to Digital terrestrial television, while Europe is hoping to have completed its switchover mostly by 2012.
Transmission
DTTV is transmitted on radio frequencies through the airwaves that are similar to standard analogue television, with the primary difference being the use of multiplex transmitters to allow reception of multiple channels on a single frequency range (such as a UHF or VHF channel).
The amount of data that can be transmitted (and therefore the number of channels) is directly affected by the modulation method of the channel. The modulation method in DVB-T is COFDM with either 64 or 16 state Quadrature Amplitude Modulation (QAM). In general a 64QAM channel is capable of transmitting a greater bitrate, but is more susceptible to interference. 16 and 64QAM constellations can be combined in a single multiplex, providing a controllable degradation for more important programme streams. This is called hierarchical modulation.ref
New developments in compression have resulted in the MPEG-4/AVC standard which enable three high definition services to be coded into a 24 Mbit/s European terrestrial transmission channel.
The DVB-T standard is not used for terrestrial digital television in North America. Instead, the ATSC standard calls for 8VSB modulation, which has similar characteristics to the vestigial sideband modulation used for analogue television. This provides considerably more immunity to interference, but is not immune — as DVB-T is — to multipath distortion and also does not provide for single-frequency network operation (which is in any case not relevant in the United States).
Both systems use the MPEG transport stream and H.262/MPEG-2 Part 2 video codec specified in MPEG-2; they differ significantly in how related services (such as multichannel audio, captions, and program guides) are encoded.
Advantages and disadvantages
Advantages:
- Digital reception tends to be better overall, particularly with a good signal. With a weaker signal there is little perceptible difference, in fact analogue can be better.
- It is easier to obtain the optimum digital picture than the optimum analogue picture.
- Many more channels can fit on the digital transmission.
- Interactive (red button) services can be provided.
Disadvantages:
- New equipment (Set-top box) may be required.
- Increased electricity consumption by the digital receiving equipment.
- An upgraded antenna installation may be required.
- Analogue requires lower signal strength to get a watchable picture. By extension, digital does not degrade as gracefully as analogue. For example, with low signal strength an analogue picture gets fuzzy (but is still viewable) while a digital picture freezes and stops updating.
- Switching channels is slower because of the time delays in decoding digital signals.
Reception
DTTV is received via a digital set-top box, or integrated receiving device, that decodes the signal received via a standard aerial antenna. However, due to frequency planning issues, an aerial with a different group (usually a wideband) may be required if the DTTV multiplexes lie outside the bandwidth of the originally installed aerial. This is quite common in the UK, see external links.
DTT Around the world
Main article: List of digital television deployments by countryEurope
United Kingdom
The United Kingdom (1998), Sweden (1999) and Spain (2000) were the first to launch DTT with platforms heavily reliant on pay television. All platforms experienced many starter problems, in particular the British and Spanish platforms which failed financially. Nevertheless, Boxer, the Swedish pay platform which started in October 1999, proved to be very successful.
DTT in the United Kingdom was launched in November 1998 as a primarily subscription service branded as ONdigital, a joint venture between Granada Television and Carlton Communications, with only a few channels being available free to air. ONdigital soon ran into financial difficulties with subscriber numbers below expectations, and in order to attempt to reverse their fortunes, it was decided that the ITV and ONdigital brands should align, and the service was rebranded ITV Digital in 2001. Despite an expensive advertising campaign, ITV Digital struggled to attract sufficient new subscribers and in 2002 closed the service. After commercial failure of the Pay TV proposition it was relaunched as the free-to-air Freeview platform in 2002. Top Up TV, a lite pay DTT service, became available in 2004.
DSO has begun in the UK in some areas and will begin soon in others and over the next three years will be completed in all by the end of 2012. One multiplex for public service broadcasters has been given freed up and given over to HD on DTT and some areas will be able to receive Freeview HD in advance of digital switchover using the new 2nd generation DVB-T2 and MPEG4 set top boxes according to Freeview.
Republic of Ireland
In the Republic of Ireland the establishment of DTT has been somewhat problematic. Initially, in the mid-1990s It's TV was the sole applicant for a digital terrestrial television license under the provisions of the Irish Broadcasting Act 2001 which also established Telífís na Gaeilge, now TG4. It proposed a triple play deployment with Broadband, TV and Digital Radio services. However, following financial difficulties with other DTT deployments, most particularly in the neighbouring UK and in Spain and Portugal, it's TV failed to get its license conditions varied or to get a time extension to securing funding and its license was eventually withdrawn for non performance.
Under subsequent legislation in May 2007, RTÉ and the spectrum regulator (ComReg)and the broadcasting regulator BCI (now BAI) were mandated to invite applications during 2008 under the Broadcasting (Amendment) Act 2007and RTÉ and the BCI received licenses from ComReg and the BCI advertised and invited multiplex submissions by 2 May 2008. RTÉ Networks is required to broadcast in digital terrestrial TV (aerial TV) under the that and the more recent The Netherlands
The Netherlands launched its DTT service 23 April 2003, and terminated analogue transmissions nationwide on 11 December 2006. KPN own Digitenne which provides pay DTT services. DTT is now proving to be an able competitor to cable in a highly cable dominated country. It also provides a mobile broadcast DVB-H service as well as an IPTV service, with DTT the most popular of its products.
Portugal
Portugal launched its DTT service on 29 April 2009 available to around 20% of the Portuguese population and Portugal Telecom expects to reach 80% of the population by the end of the 2009. Airplus TV Portugal that was set up to compete for a licence to manage Portugal’s pay-TV DTT multiplexes, will dissolve as it didn't get the license and a Portuguese court ruled not to suspend the process for the awarding of a licence to Portugal Telecom, based on a complaint submitted by Airplus TV Portugal. The start of the pay-TV multiplexes will take place later in the year.
Spain
In Spain most multiplexes closed after the failure of Quiero TV, the country's original pay DTT platform. DTT was relaunched on 30 November 2005, with 20 free-to-air national TV services as well as numerous regional and local services. Nearly 11 million DTT receivers had been sold as of July 2008. Positive approval for pay DTT services have reportedly been given by Spain’s Ministry of Industry in a surprise move on 17 June of the Advisory Council on Telecommunications and the Information Society (Catsi). IT will now be included in a Royal Decree. A number of leading Spanish media pla
Digital terrestrial television - Wikipedia, the free encyclopedia
Digital Terrestrial Television (DTTV or DTT) is the technological evolution and advance from analogue terrestrial television, which broadcasts land based (terrestrial) signals.
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