The huge advantages of digital TV over analog TV make it a recognized next-generation TV system. To turn digital TV into reality, the industry needs to complete complex and systematic work, and the most important part is the formulation of digital TV standards. The role of the standard is to define the specific implementation details of the entire digital TV system, and the main content covers the pre-production of digital programs, the display format of digital programs, and the transmission of digital programs. After all these standards are determined, the entire digital TV system can be combined and run, and the entire digital TV industry can really start.
Digital TV is divided into three types: terrestrial, satellite and cable according to the transmission mode. In 1995, 150 European organizations established the DVB (Digital Video Broadcasting, Digital Video Broadcasting) alliance, which now has nearly 200 members. In 1997, the DVB Alliance published its technical specifications for data broadcasting, including the satellite digital television transmission standard DVB-S, the cable television transmission system standard DVB-C and the terrestrial transmission standard DVB-T, for the transmission of high-speed satellite, cable and terrestrial television channels. Data paves the way. Among them, DVB-S stipulates the modulation standard of satellite digital broadcasting, so that the original channel that transmits one set of PAL programs can broadcast four sets of digital TV programs, which greatly improves the efficiency of satellites. DVB-C specifies the modulation standard for broadcasting digital TV in the cable television network, so that the channel that originally conveyed a set of PAL programs can distribute four to six sets of digital TV programs. DVB-S and DVB-C, the two globalized satellite and cable transmission standards, have been accepted by most countries (including China) as the world's unified standard. For terrestrial digital television broadcasting standards, there are three approved by the International Telecommunications Union (ITU), namely: the DVB-T standard of the European Union, the ATSC (Advanced Television System Committee, Advanced Television System Committee) standard of the United States and the ISDB of Japan -T (Integrated Services Digital Broadcasting, Integrated Services Digital Broadcasting) standard, therefore, the digital TV standard battle is mainly concentrated in the terrestrial digital broadcasting system.
European DVB-T Standard
A large number of pilot signal insertion and guard interval technologies adopted by the DVB-T standard make the system have strong multipath reflection adaptability, and can also receive good reception in dense buildings. In addition to mobile reception, it can also establish a single frequency network , suitable for mountainous areas with shielded signals. In addition, the European system also combines parameters such as the number of carriers, the length of the guard interval, and the number of modulation constellations to form a variety of transmission modes for users to choose. However, the European standards also have defects: 1. The frequency band loss is serious; 2. Even if a large number of pilot signals are prevented, the channel estimation is still insufficient; 3. There are obvious deficiencies in the performance of interleaving depth, anti-impulse noise interference and channel coding; 4. Coverage smaller.
American ATSC Standard
On December 24, 1996, the United States decided to adopt ATSC based on HDTV as the US national digital television standard. The US Federal Communications Commission (FCC) has decided to complete the historic transition from analog TV to digital TV within 9 years.
The ATSC standard has the main technical advantages of low noise threshold (close to the theoretical value of 14.9dB), large transmission capacity (6MHz bandwidth transmission of 19.3Mbps), long transmission, wide coverage and easy implementation of receiving solutions. But there are also a series of problems, the main one is that it cannot effectively deal with strong multipath and rapidly changing dynamic multipath, resulting in unstable fixed reception and no support for mobile reception in some environments.
Japanese ISDB-T Standard
Japan started its independent digital TV standard research and development project in 1996. On the basis of European COFDM technology, it added technology with independent intellectual property rights to form ISDB-T terrestrial digital broadcasting transmission standard. passed at the deliberation meeting. In 2001, the standard was officially accepted by ITU as the third international standard for digital TV transmission in the world.
Spectrum segmented transmission and enhanced mobile reception are the two main features of the Japanese ISDB-T standard. They are the result of objective analysis and optimization of numerous parameters and related performance of the terrestrial digital television system. Development strategies are trade-offs. While realizing the specific functions of the system, it also pays a corresponding price, such as the impact of spectrum segmented transmission on the frequency diversity performance and payload rate of the system, and adopting spectrum segmentation as the basis to implement layered transmission with different bit error protection rates has a negative impact on the system. The impact of complexity, the use of delays up to hundreds of milliseconds of interleaving links in the inner layer of the system, the impact of the system and business synchronization response, etc.
At present, all countries in the world have carefully selected terrestrial digital TV standards according to their own specific conditions. From a global perspective, in addition to the United States, there are also Canada, Argentina, South Korea and other countries that adopt the American ATSC standard. And all European countries and Australia, Singapore, India and other countries have chosen the DVB-T standard of the European Union.
