subject: Mobile Digital Tv-related Technology - China Turbo Kits - China Turbo Parts [print this page] Introduction With the rapid communication and information technology development, human development trend is to obtain information from fixed to mobile, from voice to multimedia. At present, to a large number of viewers in the mobile environment to provide multimedia content to the network architecture there are three: mobile communication network (2.5/3G); wireless local area network (WLAN); terrestrial digital broadcasting network. In addition, DVB organization has formally announced the adoption of terrestrial digital television broadcasting network to the portable / handheld devices to provide multimedia services are tailored to the DVB-H standard (DigitalVideoBroadcastingHandheld) [1], thus making this area more competitive.
Chengdu Sunbeam Microwave Engineering Co., Ltd. is China's earlier research and the launch of digital TV modulation systems company, has successfully developed an important component of mobile digital TV DVB-T modulator, is developing DMB-T Modulator, Digital TV transmitters have been put into use. Now mobile digital TV related technology research, can often released, and we encourage each other.
1, mobile digital TV technology and applications related
Divided by function, digital TV system consists of three parts: source section, channel section and the residential part of the letter. Figure 1 shows a digital television system, the basic block diagram. The system application can be divided into 2 sub-transmission and reception system (Figure 1 to two parts). Technically, digital TV system can be divided into source and channel two (corresponding to Figure 1 in order to reuse reuse reconciliation around the field two parts).
Basic digital TV system block diagram
Source coding part, including source (audio / video) encoders and multiplexers. Source coding of video / audio signal compression, compression rate in a certain subject to get the highest image quality decoding; source part of the algorithm is mainly in accordance with MPEG-2 standard (or MPEG-4 standard) (multi-channel audio codec also according to Dolby AC-3 algorithm), video encoder performance of the DTV system performance has a decisive impact on the image. Multiplexer to ensure the system operational flexibility and scalability, to complete a combination of various digital bit stream to adjust and provide a variety of transmission networks (such as telecommunications networks, satellite transmission channel, cable, ground-launched, etc.) to fit interface.
Channel transmission section includes channel coding and modulation, transmitter, transmission medium, receiver and channel demodulation and decoding, in which transmission can be CATV, satellite, terrestrial (including MMDS / MUDS) and so on. According to the different media in the transmission section of the channel will take a different channel coding and modulation, channel transmission parts corresponding to three criteria: terrestrial broadcasting, satellite broadcasting and cable television (including HFC and MMDS). As the terrestrial broadcasting channel is not ideal conditions, various kinds of interference and clutter to signal the error rate increased, decreased quality of service, in order to more effectively overcome the hostile environment, but also support mobile reception, terrestrial broadcasting channel technology used is relatively the other two types of complex. This section mainly elaborates terrestrial digital television broadcasting related technologies.
1.1 digital terrestrial television transmission standard
As noted above, the task of the transmission channel is transmitted in a given transmission channel bandwidth, and considering the existence of various kinds of interference under the premise of ensuring the correct maximum flow capacity data transmission, it is a transparent relative to the source The data stream transmission public platform, and the transmission of data unrelated to the content. Digital signal encoding and modulation scheme determines the major part of the channel transmission performance of different coding and modulation constitutes a national digital terrestrial television transmission standard different.
1.1.1 Foreign TV terrestrial transmission standard
Currently there three mature international digital TV terrestrial transmission standard, namely: the United States Advanced Television Systems Committee in 1996 (ATSC) developed "Trellis coded 8-level vestigial sideband" (8-VSB), Europe 1997 put forward in digital video terrestrial broadcasting (DVB-T) using coded orthogonal frequency division multiplexing (COFDM), Japan, in 1999 proposed Terrestrial Integrated Service Digital Broadcasting (ISDB-T).
U.S. ATSC8-VSB system. ATSC 8-level use of vestigial sideband modulation, it is a pilot of the single-carrier modulation, also the AM modulation of existing mature technologies. It can be used reliably within the 6MHz 8-VSB modulation transfer 19.36Mbps data. 8-VSB system has joined 0.3dB pilot signal for the auxiliary carrier recovery, and joined the segment sync signal, for the 8-VSB system synchronization. Low system noise threshold (theoretical value 14.9dB), anti-multipath and anti-jamming capability relies on a complex adaptive equalizer, but very sensitive to changes in echo delay. System provides a fixed receiver, does not support mobile reception.
European DVB-T system. European DVB-T system uses COFDM modulation, the transmission bit split into thousands of dollars in low bit-rate subcarrier (for example, 2k mode with 1705 carriers; 8k mode with 6817 carriers). The European system placed a large number of pilot signals, interspersed among the data, and 3dB higher than the power to send data. The completion of the pilot signal synchronization, carrier recovery, clock adjustment and channel estimation. Large number of pilot signals and the scattered data can be more timely estimates channel characteristics change. To further reduce the multipath effects caused by ISI, the European system also use the "guard interval" technology, to withstand the impact of multipath. It that a large number of pilot signals and guard interval insertion technology is the technical core of the European system is designed to allow the European systems to strong multi-path and dynamic anti-multipath and the measured performance of mobile reception is better than the United States ATSC8- VSB system. In addition, the European systems also guard interval length and combination of parameters such as modulation constellation to form a variety of transmission modes for users to choose. However, the integrated DVB-T bandwidth efficiency of the VSB program lower than the United States, it is the system transmission capacity overhead expense for the system with multipath fading. Notably, the European DVB-T system in the cutting depth of anti-impulsive noise interference and channel coding, etc. There is obviously inadequate performance. The system capacity, while DVB-T system is developed for the 8MHz channel, but can be used for any channel bandwidth, (6,7,8 MHz), 8MHz channel net within the effective transmission bit rate in the range of 4.98 ~ 31.67Mbps the actual channel bandwidth, depends on the channel coding parameters, modulation type and the choice of guard interval. On the European DVB-T system, do the next section details
