Two major types of broadcasting exist for television; the so-called analogue and digital television.
The analogue television appeared the first. This is widely spread around the world. However, this type of diffusion is ageing and not very innovative.
For this reason analogue television is currently tending to disappear to give way to digital television.
Digital television is largely based on analogue television. The major changes concern the compression of audiovisual sources and the way in which audiovisual information is routed.
Digital television can use different broadcast modes :
• the satellite,
• cable, in major cities,
• the Internet, in particular thanks to the advent of ADSL 1,
• the traditional terrestrial radio channel
Terrestrial digital television relies on the terrestrial radio channel.
Currently in France TNT is being deployed since April 1, 2005.
Elsewhere in the world many countries already have their network of TNT. These include the United States, Japan, Germany, England...
ADSL (asymmetric digital subscriber line) : high data rate transmission mode.
The most advanced countries in terms of digital media transmission are currently testing the convergence between the digital television and mobile supply.
Japan for example or South Korea offer the possibility to watch TV on its mobile phone.
1817 : discovery of the property that will generate the photovoltaic cell. Cell that allows to turn light into electric current.
1897 : focusing the cathode ray tube
1931 : René Barthélemy performs in France the first transmission of an image of 30 lines.
1936 : retransmission of the Olympic Games in Germany. More than 150000 viewers attend this event live.
1951 : first public television broadcast colour
1969 : live vision of the first man's step on the moon.
94 : first digital transmission in the USA for the general public.
98 : Britain launches digital terrestrial television channels
: apparition de la nouvelle norme MPE
2000 : birth of MPEG 4 and 7 standards
2003 : frequency allocation for TNT in France
2005 : TNT deployment in France
As we have seen previously, TNT is largely inspired by classical television. The two diffusion systems will co-habitate in the first time and then in 2010
analogue broadcasts will be stopped. Adjustments of frequencies are made so that the systems do not interfere.
The emission range will be limited compared to analogue television. Only the UHF frequency band will be used 2.
While analogue television transmits only one program per channel, digital television broadcasts six.
The digital path of a movie or broadcast is as follows :
• 1 creation of the audiovisual source
• 2 digital source coding
• 3 source compression
• 4 multiplexing 3 and conversion to analogue
• 5 analogue channel transmission
• 6 analog channel reception
• 7 digital channel separation
• 8 restitution of the audiovisual source
Steps 1, 2, 3 depend on the channel that emits the program.
Steps 4 and 5 are carried out by the diffuser.
Steps 6, 7, 8 are carried out successively by the antenna, the decoder and the television of the Viewer.