3 DVB-C of DVB standard wired Transmission System
3.1 composition of DVB standard wired Transmission System
Figure
Figure 3 Composition of DVB standard wired Transmission System
The composition of the DVB standard wired transmission system is as follows:
A. Signal Source
(1) Output of local broadcasting devices, such as video recorders, DVDs/VCD players, and video servers;
(2) A variety of TV signals, such as satellite TV signals, cable TV signals, and open-circuit TV signals;
(3) On-site signal collection, such as live broadcasting in the studio and competition;
(4) data streams from telecommunication networks and IP networks.
B. Video Encoder
The main function is to convert the above signal source to a digital video transmission stream conforming to the DVB standard after being collected by the encoder. The output trend can be divided:
(1) offline encoding: The converted programs are stored on the video server in the form of transmission stream files (TS;
(2) Real-time Encoding; program information is encoded in real time to form a transmission stream, which is directly output to the multipleer without the video server.
C. Video Server
The video server uses a large array disk to store audio and video streaming files, effectively manage the program editing process and material library, prepare program series orders, and broadcast multiple programs through the broadcast control platform.
D. DTS
The multi-channel MPEG-2 data transmission stream (SP, single-program TS) from the video server and real-time Encoding Equipment is reused as one-way transmission data stream (MP, multi-program TS Stream ), to save and optimize bandwidth resources.
E. QAM modulation
By using the QAM modulation, the input 38 m code stream can be modulated to 8 M bandwidth, so that 6 ~ transmission can be performed on the bandwidth of a simulated CATV channel ~ 8 digital video programs.
F. Automatic Broadcasting Control System
Programs can be input and stored in hard disks or disk arrays. You can use a computer to compile the program's broadcast time, times, length, and broadcast mode to make a program broadcast list; the program in the hard disk is automatically called by the system according to the program at the specified time, and is automatically broadcast on a regular basis.
G. Conditional Receiving System
By disturbing signals, encrypting users' electronic keys, and establishing a user management system that ensures authorized users can receive disturbing programs, ensure that the DVB service is only received by authorized users.
H. User Management System
This is a commercial center that issues electronic keys, sends bills, and charges to users. The main task of the user management system is to establish the user information, decoder serial number, and manage the information database for which services are ordered and received.
3.2 main functions and advantages of DVB standard wired Transmission System
(1) Production and broadcasting of high-quality digital TV programs
According to the GB 1583-79 "Color TV Image Transmission" standard, china's analog TV has passed the television center, microwave, satellite, transmitter and receiver after each link is five-level quality evaluation of 3.25 level (the receiver has automatic Tone Control) and level 2.75 (no automatic Tone Control ).
In the digital TV signal transmission, noise is not accumulated, and the signal quality of each user is the same, which improves the transmission quality. The MPEG-2 video encoding standard, video bit rate is 4 ~ 5 Mb/s, using these digital signal sources, the Digital CATV network is used for transmission to users, the number of images is 704 (720) × 576 (480), the display definition can be raised to 480 lines, the subjective rating is about 4.3 Points. Compared with the simulated score of about 3 points, the image grade is improved by 1 level.
(2) Improve frequency band Utilization
The analog system of Chinese TV is pal D/K, and the channel bandwidth is 8 MHz. CATV uses 64QAM digital modulation. One 8 MHz Analog channel can transmit 8 ~ 10 sets of digital TV programs. 200 ~ 200 can be transferred within MHz bandwidth ~ 250 sets of programs. Some overseas users are recommended to use 550 ~ 250 MHz band, some cable TV stations in China are occupied by analog channels, and ~ 450 MHz supplementary band. In this way, VOD, HDTV, and other multimedia information services can be carried out in the CATV system.
(3) Receiving and forwarding of satellite TV programs
Over the past year, hundreds of digital compression satellite channels have emerged in Asia. China has 28 provincial units carrying out digital satellite broadcasting, and 11 sets of digital satellite broadcasting on CCTV, there are more than 40 sets of digital satellite broadcasting in China. China's satellite digital TV program sources are already rich.
At present, China does not allow families to directly receive satellite TVs. Digital live broadcast satellites do not pose a threat to cable TV networks. Many viewers, especially urban audiences, watch programs through cable TV networks, therefore, opening a digital TV in the cable TV network will be welcomed by the audience. In addition, it is much easier to implement than digital television broadcasting on the ground.
(4) rich value-added services
The adoption of digital technology is conducive to the convergence of television broadcasting and the Internet, thus greatly expanding service content. This means that users can change from passive watching to active quasi-interactive (local interaction) and interactive watching. In addition, with the rich program sources, users can get more game and entertainment programs and various targeted information, such as financial information. Other services include: new value-added services such as pay-as-you-go programs, pay-as-you-go programs, on-demand videos, singing on-demand videos, news selection, distance education, TV shopping, interactive games, home banking, and Web page surveys.
(5) effective user management
It is easy to implement encryption and decryption, and to facilitate various billing services. Applications with conditional receipt systems can effectively manage users and ensure the operator's return on funds.
