Digital television is a program gathering, from programme-making programs transport in digital mode until client-side processing signal end-to-end system. Based on the GuangBoShi DVB technical standard and interactive "digital television. Adopt advanced user management technique the quality and quantity of the contents of the programmes do perfect and bring more programs for the user choice and better program quality effect, compared with analog TV, digital TV program with high-quality image, great capacity (is analog TV program of transmission channels l0 times more capacity and sound effect good characteristic.
Digital signal
In a communication system, the signal transmission within the loads of information in time physical is discrete values, and are called scattered, also digital signal.
Transmission rate
Digital signal transmission rate is 19.39 megabytes per second, so big streams of data transfer guaranteed the digital TV high definition, overcome the congenital deficiency of analog TV. Also as a result of digital television can allow simultaneous presence of several rule signal, each digital channel can be divided into several son again under, thus can use channel a large data flow - 19.39 megabytes per second, also can he divided into several diversion, such as the speed of four, each is 4.85 megabytes per second, so although image clarity to discount, but can greatly increase the types of information, to meet different needs. For example at the broadcast a sports game, the audience need high definition images should be adopted, TV 19.39 megabytes per second of dissemination; And in radio news, people's attention is news content rather than announcer's image, so there is no need adopt such a high definition, then only three megabytes per second, the speed 16.39 megabytes left used to transport other content.
Now development
Digital TV is people talk about one of the most lively topic. As a result of digital TV is a fresh things, some related reports and articles in the introduction appear specious concepts, such as "digital TV", "full digital TV", "entire media TV", "multimedia TV" etc, causing confusion, mass loss. In fact, the meaning of "digital television" wasn't referring to the TV sets we generally somebody else, but that TV signal processing and transmission, sending and receiving process using digital signal TV system or TV equipment. Its specific transmission process is: by television sent the image and sound signal, the compressed digital and digital modulation, form, digital television signal through satellite, ground wireless broadcast or cable etc way by digital TV transmission, after receipt of the digital demodulation, through and digital audio decoding processing reduction of original image and sound out.
Working principle
Will the audio signal digital television, after the data quantity is big, very detrimental to transmission, therefore data compression technology to become the key. Realization of data compression techniques has two kinds:
One is the source coding process compressed
IEEE MPEG group has development made ISO/IEC13818 (mpeg-2,) international standard, mpeg-2, using different layer and level can satisfy the quality from family combination to broadcast quality and will be broadcast of HDTV quality different requirements, its application is very wide, it supports standard resolution 16:9 widescreen display and high definition TV etc. Various formats, from entering family DVD to satellite TV, radio and television microwave transmission are adopting this standard.
2 it is improving channel coding
Develop new digital modulation technology, improve unit bandwidth of data transfer rate. For instance, in Europe DVB carmountedly digital TV system, digital satellite TV system (dvb-s) the positive photograph shift keying modulation (QPSK); Digital cable TV system (DVB - C) adopt the quadrature am modulation (QAM); Digital TV system (open ground DVB - T) adopt more complex coded orthogonal frequency division multiplexing modulation (COFDM).
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