[Graphic] Wuxi terrestrial digital mobile TV system implementation

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Of: Radio and Television Technical Center in Wuxi, Jiangsu Province Lu Jianhua Zhang Wei Shen Hao Chen






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  Wuxi in Jiangsu Province to achieve the "two first" pilot areas, demonstration areas, has become the fastest-growing economy, one of the most dynamic regions. Wuxi to meet the social, economic and cultural development, the establishment of terrestrial digital mobile TV system platform, full-capacity digital broadcasting, transmission efficiency, flexibility, good benefits is necessary to carry out mobile TV services. In countries where standards are not introduced, after extensive research, testing and comprehensive consideration, we chose Tsinghua University, "MC" DMB-T program.
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A digital mobile TV system planning


1. Coverage Planning With full use of existing resources, save investment and gradually expand the coverage of the development principles, Wuxi digital mobile TV system is divided into three specific implementation:








Phase: Mao Feng in Hyesan two transmitters with 800W digital transmitter to a single point of emission, broadcast a program, covering the urban areas.








II: According to the income test results and network planning, the establishment of suitable locations in the outskirts of the Deputy launch point, the composition of a single frequency network, or to cover up spots, to further improve the city and suburban coverage.








III: According to the development of mobile TV services, plans in Jiangyin, Yixing, vice launching point to establish, and fight with Suzhou, Changzhou cities such as Shanghai-Nanjing Line co-operation to further expand coverage, inter-city roaming implementation.








2. Business Planning Digital mobile TV as a new kind of media, they can conduct a variety of business:








* Bus, taxi, commercial vehicle, private car, car mobile TV;


* Focus TV; * Wearable, handheld, mobile TV;


* Multi-channel pay-TV; * IP data broadcasting. Digital mobile TV terminal products with the development of the next few years will gradually be extended to individuals from the car TV handsets and personal information terminals. Expected to be complete within five years will form a covering of Wuxi city and the surrounding region of the digital mobile network, which would be great Wuxi development of mobile television, for our business development objectives are:








First step: the establishment of mobile TV broadcasting platform based on one-way, the development of car mobile TV.








Second step: the establishment of one-way fee-based mobile television platform to provide multi-channel pay mobile TV services, providing electronic program guide, the development of mobile individuals.








Third step: the establishment of mobile-based video, audio and data services, multimedia broadcast platform to provide digital audio radio services, mobile stock information, shopping information and electronic newspapers and journals, the development of mobile personal multimedia devices, and to achieve international roaming.








Two digital mobile TV system components


Digital mobile TV system consists of front-end parts, transmission network, the transmitter and receiver part. System block diagram shown in Figure 1. Wuxi








Figure 1 Block diagram of digital mobile TV system


Complete front-end some of the major program production, editing, broadcast, video and audio coding, data conversion, bit stream multiplexing. Lord, prepare encoder we chose Harley MV50, it is a broadcast quality encoder, full compliance with the MPEG-2 standard, with excellent image quality. In the first phase, because only the broadcast of a program, so not need to stream multiplexer equipment.








Transmission networks digital television streams transmitted to the transmitter, and the complete restoration of streams and synchronization. TS code stream using LEITCH6800 + Digital Optical and NEC digital microwave transmission for two-way, to ensure the safety route.








Transmitter is sent to the TS transmission network stream directly into the exciter modulation, frequency conversion, the output RF signal, and then carried out by the transmitter power amplifier, through the antenna and feeding system for wireless transmitters. Wireless transmitter with 29 channels, the launch point 300 meters above sea level, 80 meters high tower, the antenna is surrounded by eight layers of double-dipole antenna, gain 12dB.








Launched in part by the R & SSV702 actuator (main, equipment), good omen 800W all solid state digital TV transmitter (master) and 3kW tube TV transmitter (prepared) form. As the R & S all digital exciter with a unique I / Q modulation signal directly from baseband to radio frequency signal modulation, and automatic adaptive digital pre-correction function, to ensure that the emission signals technical indicators, to facilitate the transmission equipment use and maintenance.








Received in part by special receiving antenna, car DMB-T receiver and liquid crystal televisions, audio amplifiers, car speakers, etc. Antenna to receive terrestrial TV signals sent to the car receiver, receiver frequency, demodulation, receive digital TV streams, further demultiplexing, decoding, output video and audio signals, through the LCD TV and speakers to reproduce the moving television programs, to achieve vehicle mobile reception.








Working parameters: Comparison of urban poor mobile reception conditions, signal attenuation and shelter problem, the channel conditions change rapidly, generally choose QPSK sub-carrier modulation or 16QAM, select the guard interval 1 / 9, channel coding options 4 / 9 or 2 / 3. QPSK modulation is to select at least 1 / 9 guard interval, 4 / 9 channel code rate, in this case, the receiving and demodulation of the signals required minimum, you can cope with the worst reception environments, such as the built-up area, a short tunnel. Subcarriers using 4K mode, suitable for mobile reception, which can effectively resist the Doppler effect, but also suitable for handheld devices to receive. Wuxi mobile TV system currently uses QPSK modulation, the mode of 4K, stream 5.414Mb / s, guard interval 1 / 9, channel coding rate 4 / 9.








Three digital mobile TV system test


In the specific implementation process, we conducted a major technical indicators transmitter test and after using 800W digital TV transmitter coverage area in Wuxi test.








1. Transmitter test Transmitter test equipment specifications, instrument connection shown in Figure 2. Transmitter output power (average power)> 800W, in-band frequency response ± 0.5dB, around the shoulder Yue Luo (± 4.3MHz) -38dB, adjacent channel suppression (± 8MHz) -45dB,-band unwanted emissions (second harmonic) -60dB. Measured curve shown in Figure 3.








Figure 2 targets digital mobile TV test transmitter schematic


Figure 3 transmitters technical indicators measured curve