Broadly speaking, DVB (Digital Video BroadcasTIng) technology refers to the broadcast of "data containers" that can transmit all types of data [1]. DVB simply transmits compressed images, sound or data to the receiving end through these "containers". DVB's "service information" plays the role of the container header, ensuring that the receiver knows how to decode. The key to the difference between DVB and other data broadcasting systems is that different data units in the container can carry independent timing information. For example, even if the sound and the image do not arrive at the receiver at the same time, the sound can be synchronized with the video information in the receiver, which is a different convenience from the traditional TV program.
The DVB method is highly adaptable. For example, a 38Mbit / s data container can support eight standard TV program (SDTV) channels, four enhanced TV program (EDTV) channels, or a high-definition digital TV (HDTV) channel. At present, the DVB satellite communication system is mainly used to transmit multiple SDTV programs and related sounds and data. DVB is also used for data broadcasting services, such as access to the Internet.
The MPEG-2 standard was adopted by DVB for encoding of sources such as sound and video information, and multiplexed a certain number of source data streams and auxiliary information into a single data stream suitable for transmission. Therefore, many parameters, domains, and structures in DVB baseband processing are the same as the definition of MPEG-2.
DVB service, it is a digital broadcasting technology based on source code MPEG-2 [2], this technology has three standards:
1. DVB-S, which is mostly used in satellite transponders, with a bandwidth of 26MHZ-72MHZ;
2. DVB-T, which is aimed at terrestrial broadcasting;
3. DVB-C is mainly used in cable TV. The signals of DVB-C digital video broadcasting system are usually transmitted by QAM (quadrature amplitude and phase modulation).
MPEG-2 takes into account both high-quality images and high compression ratios, from VHS image quality with a code rate of 2MB / s to high-definition television (HDTV) with a code rate of 18MB / s. The general MPEG-2 encoder can be selected by the user to compress the TV signal of one channel into digital signals of 2MB / s, 3MB / s, 4MB / s, 5MB / s, 6MB / s and 8MB / s. Actual observations show that the images compressed at 6MB / s and 8MB / s are basically the same as the images without compression, but the fast sports images compressed at 4MB / s can see the defects of the images. Therefore, sports programs generally use a code rate of 5MB / s or more, standard definition television (SDTV) uses a code rate of 4MB / s, and ordinary TV programs use a code rate of 2MB / s-3MB / s.
The simplified system structure of MPEG-2 is shown in Figure 1. This figure is a flowchart of MPEG-2 video and audio data signal processing. The simple working process is described as follows:
The hardware function of DVB-C set-top box is realized by eight functional modules, including high-frequency head, QAM demodulator, MPEG-2 demultiplexing, MPEG-2 decoding, video encoding, audio D / A, user control interface. Figure 2 is a schematic diagram of the composition of the DVB set-top box.
Digital compression cable TV receiver (set-top box DVB-C) is a new technology to realize the digital transmission of TV signals on the cable TV cable. The digital transmission of TV signals has the advantages of strong anti-interference, no transmission loss, convenient and reliable encryption, and high quality of received audio and video. Set-top boxes can open up channels in the future, laying the foundation for cable TV to set up high-speed Internet and other services.
The advanced applications of DVB technology include multimedia data broadcasting, Internet over-the-air transmission, interactive broadcasting services and mobile communication combined with GPRS technology.