Digital television is that from the studio to the launch, transmission, reception of all aspects of the use of digital television signals or all the signals of the system are transmitted through the 0, 1 digital strings of digital streams composed of the type of television to spread. Digital signal propagation rate is 19.39 megabytes per second, such a large stream of data transmission to ensure that the high definition of digital television, to overcome the inherent shortcomings of analog television. Also due to the fact that digital television allows the simultaneous existence of several standardized signals, each digital channel can be divided into several sub-channels under the channel, so that both a large data stream - 19.39 megabytes per second - can be used, but also can be divided into several sub-streams, for example, four, each of which the rate of 4.85 megabytes per second, so that, although the clarity of the image to be a big discount, but can greatly increase the variety of information to meet the different needs. For example, in the broadcast of a sports game, the audience needs high-definition images, the TV station should be used 19.39 megabytes per second transmission; and in the news broadcast, the audience is concerned about the content of the news rather than the announcer's image, so there is no need to use so high definition, then only 3 megabytes per second speed can be used, the remaining 16.39 megabytes can be used to transmit other content.

Digital television technology has the following advantages over the original analog television technology:

(l) The signal clutter ratio is independent of the number of consecutive processing. Television signals are digitized with a number of binary levels to represent the two levels, and thus in the continuous processing or in the transmission process after the introduction of clutter, the clutter amplitude as long as it does not exceed a certain rated level, through the digital signal regeneration, may be able to remove it, even if a certain clutter level exceeds the rated value, resulting in errors, but also the use of error-correcting coding and decoding technology to correct them. Therefore, in the digital signal transmission process, will not reduce the signal-to-noise ratio. The analog signal processing and transmission, each time may introduce new noise, in order to ensure that the final output has sufficient signal to noise ratio, it is necessary to put forward a variety of processing equipment for a higher signal to noise ratio requirements. Analog signals require S/N>40dB, while digital signals only require S/N>20dB. analog signals in the transmission process noise gradually accumulated, while digital signals in the transmission process, basically does not produce new noise, that is, the signal to noise ratio is basically unchanged.

(2) The effect of nonlinear distortion of the system can be avoided. In contrast, in analog systems, nonlinear distortion can cause significant damage to the image.

(3) The output signal of digital devices is stable and reliable. Because the digital signal is only "0", "l" two levels, "l" level amplitude size as long as the processing circuit may be recognized as "l" level can be. "level can be, a little bigger, a little smaller does not matter.

(4) easy to realize the signal storage, and storage time and the characteristics of the signal has nothing to do. In recent years, the development of large-scale integrated circuits (semiconductor memory), you can store multiple frames of television signals, thus completing the processing functions that are not possible with analog technology. For example, the frame memory can be used to achieve frame synchronization and standard conversion processing, to obtain a variety of new television image effects.

(5) due to the use of digital technology, with the computer can realize the automatic control and adjustment of equipment.

(6) digital technology can realize the time division multiplex, make full use of the channel capacity, the use of digital television signals in the line, field fading time, can realize the text multiplex broadcasting (Teletext).

(7) compressed digital TV signal after digital modulation, can be open-circuit broadcasting, in the design of the service area (terrestrial broadcasting), the audience will be a great probability of realizing "error-free reception" (send "0" to receive), "0", "0", "0", "0", "0", "0", "0", "0", "0", "0", "0", "0". "0", "l", "l"), the television image and sound quality is very close to the quality of the studio.

(8) can reasonably utilize various types of spectrum resources. In terms of terrestrial broadcasting, digital television can be enabled analog television?quot; disable the channel (taboo channel), and in the future to be able to use "single frequency network" (single frequency network) technology, such as l sets of television programs only occupy the same 1 digital television channel and cover the whole country. The whole country will be covered by the same digital TV channel. In addition, the existing 6MHz analog TV channel can be used to transmit l digital high-definition TV programs or 4-6 digital regular TV programs of higher quality, or 16-24 digital TV programs of comparable quality to home VHS recorders.

(9) In the synchronous transfer mode (STM) of the communication network, a variety of services can be realized "dynamic combination" (dynamic combination). For example, in digital high-definition television programs, there are often moments when the image details are less. At this time, because of the compressed image data is small, it can be inserted into other services (such as TV program guide, fax, video game software, etc.), without having to insert a large number of meaningless "filler bits".

(10) It is easy to realize encryption/decryption and scrambling/descrambling technology, which is convenient for professional applications (including military) and broadcasting applications (especially for various kinds of fee-based services).

(ll) It is scalable, hierarchical, and interoperable, and is easy to transmit over various types of communication channels, especially Asynchronous Transfer Mode (ATM) networks, and is also easy to interconnect with computer networks.

(12) It can be "integrated" with computers to form a class of multimedia computer systems that will be an important part of the future National Information Infrastructure (NII).