Digital television is largely based on analog television. The major changes concern the compression of the audio-visual sources and mode of delivery of audiovisual information.
Digital television can use different modes of broadcasts :
• the satellite,
• the cable, in big cities,
• the Internet, thanks to the advent of ADSL 1,
• the traditional terrestrial Hertzian channel
Digital Terrestrial Television is based on the terrestrial radio channel.
Currently in France the TNT is being deployed since April 1, 2005.
Around the world many countries already have their network of TNT. Among them are the United States, the Japan, the Germany and England...
ADSL (Asymmetric Digital Subscriber Line) : mode of transmitting high data rate.
The most advanced countries in terms of digital transmission of media are testing the convergence between digital TV and mobile offerings.
For example Japan, or even the South Korea offer the possibility to watch TV on their mobile phone.
1817 : discovery of the property which will create the photovoltaic cell. Cell that transforms the light running electric.
1897 : development of the cathode ray tube
1931 : René Barthélemy carried out the first transmission of an image of 30 lines in France.
1936 : broadcast of the Olympic Games in Germany. Over 150,000 viewers attend this event live.
1951 : first public show of color television
1969 : Live vision from the first step of man on the moon.
94 : first digital transmission in the USA for the general public.
98 : Britain launches its digital terrestrial television channels
: apparition de la nouvelle norme MPEG2
2000 : birth of standards MPEG 4 and 7
2003 : awarded frequency for DTT in France
2005 : deployment of DTT in France
As we saw previously, DTT is largely inspired by the classic television. Two delivery systems exist at first then in 2010
the analog broadcast will be stopped. The artisan frequency adjustments are performed so that systems do not interfere.
Emission range will be limited compared to the analog TV. Only the UHF frequency band will be used 2.
While analog television transmits a single program by channel, digital television to broadcast six.
The digital path of a film or a show is the following :
• 1 creating audiovisual source
• 2 digital coding of the source
• 3 compression of the source
• 4 multiplexing 3 and conversion to analog
• 5 issue of analog channels
• 6 channels analog reception
• 7 separation of channels in digital
• 8 return of the audiovisual source
Steps 1, 2, 3 depend on the chain that emits the program.
Steps 4 and 5 are performed by the broadcaster.
Steps 6, 7, 8 are carried out successively by the antenna, the decoder then television viewers.