Digital TV

Digital television is to show from the studio to launch, transmission and receiving all the links are using digital TV signals or of the system are all signal propagation by 0, 1 numeric string that form the digital streams to spread the TV type. The signal losses small, receiving the effect is good.

Content abstract

Digital television is from a program gathering, programme-manufacturing programs transport until client in digital signal processing methods of end-to-end system. Based on DVB technical standard AnBoShi and "interactive" digital television. Adopt advanced user management technology can be the quality and quantity of the contents of the programmes do perfect and bring more programs for the user choice and better quality of programs effect, and analog TV, compared to the digital TV to have high-quality image, show great capacity (is simulated television programmes transmission channels of l0 times more capacity and sound effect good characteristic.

Digital signal

In a communication system transmission from the inside, the load information physical quantities in time, but also is discrete values of discrete, it is known as a digital signal.

Transmission rate

Digital signal transmission rate is 19.39 megabytes per second, so big flow of data transfer guaranteed the digital television high-definition, overcoming the congenital deficiency of analog TV. Also as a result of digital television can allow several rule signal while exist, each digital channel and can be divided into several sub-systems channel, thus either by a large data flow - 19.39 megabytes per second, also can divide it into several shunting, for example, each of the four megabytes per second speed is 4.85, so although image clarity to sell at a discount greatly, but can greatly increase the types of information, to meet different needs. For example at the broadcast a sports, the audience need high-definition images, TV is should adopt the spread of 19.39 megabytes per second, And in the news broadcast, the audience attention is news content not announcer's image, so there is no need adopt such a high definition, then only three megabytes per second speed is ok, remaining 16.39 megabytes can be used to transmit other content.

Now the development

Digital television is people talk about the most lively one subject. As a result of digital television is a kind of new things, some related reports and articles in the introduction appear specious concepts, such as "digital television", "full digital TV", "entire media TV", "multimedia TV" etc, cause mass confusion, loss. Actually, the meaning of "digital television" does not mean we generally somebody else's watch TV, but means of TV signal processing and transmission, transmit and receive process using digital signal TV system or TV equipment. The specific transmission process is: by TV sent the image and sound signal, the digital compression and digital modulation, forming digital TV signals, through satellite, ground wireless radio or cable transmission, by way of digital TV receiving, through digital demodulation and digital audio decoding the original image processing reduction and sound.

Working principle

The TV of audio signal digital, the amount of data is very big, very disadvantageous to transmission, therefore data compression technology to become the key. Realization of data compression technology method 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 combination from family quality to broadcast quality and will broadcast of HDTV quality different requirements, its application is very wide, it supports standard resolution urbanus widescreen and HDTV etc. Various formats, from entering family DVD to satellite TV, radio and television microwave transfer has adopted the standard.

2 it is improving channel coding

Develop new digital modulation technology, improve unit bandwidth of data transfer rate. Be like, 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) orthogonal amplitude modulation (QAM); Digital TV system (open ground DVB - T) adopt more complex coded orthogonal frequency division multiplexing modulation (COFDM).

Specific classification

Digital television can press the following several ways classification:

According to the signal transmission classification

Can be divided into the ground wireless transmission (terrestrial digital TV DVB - T), satellite transmission (satellite digital TV dvb-s), cable transmission (cable digital TV DVB - C) three categories.

According to product type classification

Can be divided into digital TV monitor, digital TV top-box, integrated digital television receiver.

According to the definition classification

Can be divided into lower resolution digital television (HDTV image level than 250 line), the standard definition digital television (HDTV image level greater than 500 line), the high-definition digital television (HDTV more than 800 line image level, i.e. the HDTV). VCD of image formats belong to lower resolution digital television (LDTV) level, DVD image formats belong to standard definition digital television (SDTV) level.

According to the display screen picture type classification

Can be divided into the mire of picture type ratio and urbanus picture type than two types.

According to scan line number (display format) classification

Can be divided into HDTV scanline number (more than 1,000 line) and SDTV scan line number (600 ~ 800 line), etc.

Technical advantages

Digital television technology with the original analog TV technology, compared to have the following advantages:

(l) signals clutter ratio and the number of continuous treatment is irrelevant. Television signals through digital after is to use some binary two level to say, so the continuous process, or during transmission introducing clutter, after the clutter amplitude as long as no more than a rated level, through digital signal regeneration, are likely to get rid of it, even a clutter level, killing more than ratings ber, also can use correction encoder and decoder technology them to correct it. So, in digital signal transmission process, not reduce miscellaneous than letter. But in analog signal processing and transmission, each of which could introduce new clutter, in order to guarantee ultimate output have enough faith miscellaneous than it necessary for various processing equipment put forward higher than requirements. Letter miscellaneous Analog signal requirement S/N > 40dB, and digital signal only request S/N > 20dB. Analog signal during transmission noise gradually acumulate and digital signal during transmission, basically do not produce new noise, namely letter miscellaneous than the basic unchanged.

(2) can avoid system nonlinear distortions influence. While in simulation system, the nonlinear distortions can cause image obvious harm.

(3) digital equipment output signal is stable and reliable. For digital signal only "0", "l" two level, "l" low-levelcircuits simply meet processing circuit amplitude size can identify is "l" level can, bigger, a little irrelevant.

(4) easy to realize the signal of storage and storage time with the characteristics of signals is irrelevant. In recent years, large scale integrated circuits (semiconductor memory) development, can store multi frame television signals, thus completing with simulation technology cannot reach the processing function. For example, frame memory available to implement frame synchronization and format conversion etc processing, access to all kinds of new television image of special effects.

(5) due to adopting digital technology, and computer cooperation can realize the automatic control equipment and adjust.

(6) digital technology can be realized at road, make full use of channel capacity, using a digital TV signals boc, field vanishing time, can achieve text for broadcast (Teletext).

(7) compressed digital TV signals via digital modulation, can undertake open-circuit radio, in the design of service (ground broadcast), viewers will with great probability to realize "error-free receiving" (hair "0" accept "0", hair "l" accept "l"), watch the television picture and sound quality is very close to the studio quality.

(8) can be reasonably using various types of spectrum resources. In ground radio is concerned, digital TV can be enabled analog TV? Quot; Disable channel (any) taboo, and in the future can be used in a "single frequency network" (a) performance been technologies, such as l set of TV programs occupies only with a digital television channel and nationwide. In addition, the existing 6MHz analog TV channels, and can be used in the transmission l set of digital high-definition TV programs or 4 to 6 sets of high quality digital conventional TV program, or 16-24 sets and household VHS VCR quality of digital TV programmes. Quite

(9) in synchronous transfer mode (STM) of communication network, it can achieve a variety of business "dynamic combination" (dynamic together). For example, in high definition television in digital image details, often appear less time. At this time because of compressed image data quantity is less, can insert other business (such as the TV guide, fax, electronic game software, etc), and need not insert large meaningless "filling bits".

(10) easy to implement the encryption/decryption and add interference/perturbation technology, facilitate solutions specialized application (including military) and broadcast applications (especially in all kinds of charge service).

(DLL) with expansibility, grading sex and interoperability, facilitate in various communication channel is especially asynchronous transfer mode (ATM) network transmission, also facilitate and computer network unicom.

(12) can with computer "integration" and comprise one multimedia computer system.