http: // 2006-11-20Beijing Ocean Industrial Technology Co., Ltd.
Abstract: Under the premise of introducing the basic concepts and background of digital TV, this article introduces the main parameters and main instruments of digital TV testing, and introduces the development status of digital TV testing industry.
Keywords: digital TV test, transmission code stream, signal source one, digital TV concept and its advantages
Digital TV classification Digital TV can be divided into three types according to its transmission channels: digital satellite TV (DVB-S), digital cable TV (DVB-C) and digital terrestrial broadcast TV (DVB-T), digital handheld TV (DVB-H) ).
Digital TV can be roughly divided into three levels according to the bit rate of its transmitted video (moving image): universal digital TV (PDTV), standard definition digital TV (SDTV) and high definition digital TV (HDTV). Among them, PDTV belongs to the lowest level of SDTV. At present, the development direction of digital TV is to take SDTV as the main development direction, and HDTV is used in the source of digital TV or in some fields.
Advantages of digital TV Compared with analog TV, digital TV has the following advantages:
â‘ The image transmission quality is high and the distance is long. During the transmission of digital TV signals, interference and noise accumulation will not occur after multiple relays (or duplications). At the same time, error correction coding technology can be used to improve anti-interference ability. Therefore, the digital TV keeps the signal-to-noise ratio basically unchanged, the image quality of the receiving end remains basically the same as the sending end, and the transmission distance is not limited.
â‘¡ High utilization of spectrum resources. Spectrum resources are important national resources, and analog television has limited spectrum resources. A set of analog TV programs requires a satellite transponder with a bandwidth of 36 MHz and a terrestrial TV broadcast and cable TV frequency of 8 MHz. Digital TV uses compression coding technology, which can transmit 5 sets of SDTV programs in a 36MHz satellite transponder and more than 4 sets of SDTV programs in an 8MHz channel.
â‘¢ Provide brand new business and realize high-speed data transmission. In digital TV communication, multiple digital information such as text, data, language, and still images can be transmitted simultaneously without interference.
â‘£ The information is stable and reliable, and the equipment maintenance and use are simple.
⑤ Save transmission power and cover a wide range.
â‘¥ Flexible and friendly man-machine interface, easy to achieve conditional access.
Therefore, technologically advanced digital TV systems will inevitably replace analog TV. Digital TV System Introduction Digital TV broadcasting systems mainly include terrestrial broadcasting, cable broadcasting and satellite broadcasting systems.
The digital TV broadcasting system is mainly divided into the following parts:
â‘ Digital studio system;
â‘¡ Compression coding part of video and audio signals;
â‘¢ System business reuse part;
â‘£ ICT coding part;
⑤ Modulation transmission part.
Digital TV broadcasting system block diagram: (Figure 1-1)
Picture 1-1
2. Digital TV Standard
Digital TV standards include two major parts: digital TV studio standards and digital TV broadcast standards. Digital TV studio standards define the format of uncompressed audio and video, interfaces between devices, etc., mainly related to the production of programs. Digital television broadcasting standards involve audio and video compression, digital signal transmission, conditional access systems, and other standards related to digital television broadcasting services. International Digital TV Standards Currently, there are three international digital standards, namely the American standard ATSC (Advanced Television Systerm Committee); the European standard DVB (Digital Video BroadCasting); the Japanese standard ISDB (Intetarted Services Digital Broadcasting).
The European DVB standard is divided into three parts: satellite digital TV is DVB-S, using orthogonal key modulation (QPSK); cable digital TV is DVB-C, using quadrature amplitude modulation (QAM); terrestrial digital TV is DVB -T, using orthogonal frequency division multiplexing modulation (COFDM).
The DVB standard has many advantages, because DVB-S has been adopted globally, and DVB-C has also been adopted in Europe, Australia, North America, South America and other countries. It can be said that digital satellite TV and digital cable TV both adopt the European DVB standard in principle. The major difference is terrestrial TV. For DVB digital TV system test standards, in principle, according to "DVB system test standard TR101290", this standard tests MPEG-2TS streams, common parameters of satellite and TV network transmission media, TV network, satellite, terrestrial, MMDS / The specific tests of MVDS give specific methods and requirements. China's Digital TV Standards China is the country with the most TV users in the world, and should have its own intellectual property digital TV standards. For digital cable TV and digital satellite TV, the country has clearly adopted the DVB standard, that is, the use of DVB-S and DVB-C, all areas are in order. The main reason is that the terrestrial television standards with independent intellectual property rights have not yet been formulated.
China has determined to independently develop terrestrial broadcasting and television standards. In 2001, the National Special Working Conference on Digital TV was collected for the domestic digital TV terrestrial transmission scheme. Five ground transmission schemes were collected from four standard research units before April 30, 2001. From 2002 to 2003, these 5 sets of schemes were tested, and two schemes were selected for further improvement, namely the scheme DMB-T standard proposed by Tsinghua University and the scheme ADTB-T proposed by Shanghai Jiaotong University. In the final stage of the formulation of digital TV terrestrial transmission standards, the DMB-T standard dominated by Tsinghua University and the ADTB-T standard dominated by Shanghai Jiaotong University were stalemate, and eventually the two moved towards "fusion".
On August 18, 2006, the China National Standards Commission issued the "Framework, Channel Coding and Modulation of Digital TV Terrestrial Broadcasting Transmission System" in the "Announcement on the Approval and Release of Chinese National Standards No. 8 (General No. 95) in 2006". The national mandatory standard was formally implemented on August 1, 2007. There are three kinds of receiving methods for terrestrial digital TV broadcasting: fixed terrestrial receiving, mobile receiving and handheld device receiving. The terrestrial digital TV standards in China are mainly applicable to the first two receiving methods, and mobile multimedia broadcasting standards will be specially formulated for handheld receiving.
Second, the digital TV standard Digital TV test can be roughly divided into four levels, namely the application layer, protocol layer, transmission layer, physical layer. The application layer test is mainly aimed at the SD / HD program production and broadcast department. The test instrument should provide a multi-format, multi-standard test platform to perform quality tests on digital TV audio baseband signals. Protocol layer testing is mainly used to measure the compliance of equipment with standards and protocols. It is required that such instruments have as many current general protocols as possible to conduct protocol testing, such as MPEG-2, MPEG-4, H.264 / AVC and VC- 1 Wait. The transmission layer test is used to evaluate the debugging performance of various debugging methods, such as constellation diagram, modulation error rate, and bit error rate. Physical layer testing includes specific physical interface testing, such as output power and port resistance
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