Digital terrestrial television

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Digital Terrestrial Television (DTTV or DTT) is an implementation of digital technology to provide a greater number of channels (SDTV) and/or better quality of picture (EDTV, HDTV) and sound (AC3, Dolby Digital) through a conventional antenna (or aerial) instead of a satellite dish or cable connection. The technology used is ATSC in North America, ISDB-T in Japan, and DVB-T in Europe and Australia; the rest of the world remaining mostly undecided. ISDB-T is very similar to DVB-T and can share front-end receiver and demodulator components.

1 Transmission
2 Reception
3 DTT Around the world
- 3.1 Table
4 See also
5 External links

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Transmission

DTTV is transmitted on radio frequencies that are similar to standard analog 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.

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 less immunity to interference, and effectively does not provide for single-frequency network operation (which is in any case not relevant in the United States, where ATSC was invented).

Both systems use the MPEG-2 transport stream and video codec; they differ significantly in how related services (such as multichannel audio, captions, and program guides) are encoded.

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Reception

DTTV is received via a set-top box, or integrated receiving device, that decodes the signal received via a standard aerial. However, due to frequency planning issues, an aerial upgrade may be required if the DTTV multiplexes lie outside the bandwidth of the installed aerial (quite common in the UK).

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DTT Around the world

Main article: List of digital television deployments by country

The United Kingdom, Sweden and Spain were the first to launch DTT with platforms heavily reliant on pay television. All three pay platforms suffered from problems, and the British and Spanish pay television platforms failed financially. Since 2004, the Swedish pay platform, operated by Boxer, has proven to be very successful.

The UK DTT was relaunched as a free-to-air platform ("Freeview") in 2002 and the UK DTT currently leads the world in terms digital television penetration (along with Finland). A "lite" pay DTT service became available in the UK in 2004 with the Top Up TV offer.

In Spain, most muxes were closed after the failure of the pay DTT platform, Quiero TV. DTT was relaunched on 30 November 2005 with around 30 national and autonomous TV and radio channels broadcasting their DTTV signals free-to-air.

Germany launches a free-to-air platform region-by-region, starting in Berlin in November 2002. The analogue broadcasts ceases soon after the digital ones are started, and Berlin became completely digital on 4 August 2003. It is estimated that by the end of 2005, 59% of the population could access DTT services.

France's DTT platform, TNT (télévision numérique terrestre), offers 18 free channels and 11 pay channels. It is expected that by 2008 70% percent of the population will be able to receive TNT.

In Sweden, DTT was launched in 1999 operating solely with pay television. Pay television still dominates the platform with only the channels financed by the license fee and a few commercial channels broadcasting in the clear. Switch-off of the analogue signal started in 2005 and finishes in 2007. Finland launched DTT in 2001, and closes down all analogue signals in 2007. Most Finnish broadcasts are in the clear.

In December 2005 the EU recommended that its Member-States cease all analogue television transmissions by the year 2012. It also recommend that those members that have not yet launched DTT services should do so. Some EU member states have decided to complete this analogue switch-off as early as 2008 (e.g. Sweden). Two member states (not specified in the announcement) have expressed concerns that they might not be able to proceed to the switchover by 2012 due to technical limitations, the rest of the EU member states are expected to stop analogue television transmissions by 2012.

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Table

The following table show launches of DTT and the closing down of analogue television in several countries:

Country	Official launch	Start of closedown	Closedown finished	System used
United Kingdom	15 November 1998	Planned 2008	Planned 2012	DVB-T
Sweden	April, 1999	19 September, 2005	21 November 2007	DVB-T
Spain	May 2000	2008 (Local channels)	3 April 2010 (Other channels; 2009 in Catalonia)	DVB-T
Finland	August 27, 2001	August 31, 2007		DVB-T
Germany	November 2002	August 2003	Planned 2008	DVB-T
Portugal	2002/2003		2010	DVB-T
Faroe Islands	2002/2003	December 2002		DVB-T
Belgium	2002/2003			DVB-T
Netherlands	2003			DVB-T
Italy	January 1, 2004			DVB-T
Switzerland	Began 2001			DVB-T
France	March 31, 2005			DVB-T
Greece	January 16, 2006			DVB-T
Denmark	March 31, 2006	November 1, 2009		DVB-T
Turkey	February 2006 (trial services)			DVB-T
Albania	August 2005			DVB-T
Australia	January 1, 2001	Planned 2010		DVB-T
South Africa	March, 2006	Planned 2009		undecided
Hong Kong	2007		2012	undecided