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Analysis: Mobile TV Technology and Development
Broadcast receiver installed in the bus terminal first car, subway, train suburban, taxis, commercial vehicles and the system in other public places, television, the second is a handheld receiver (such as mobile phones, laptop, PMP, PC ultra portable, etc.) to meet the needs of people viewing mobile TV system. This article discusses the support of the second category of mobile terminals, namely handheld applications of mobile TV technology. handheld products Mobile TV now has the absolute number is mobile TV.
The key technologies for Mobile TV in January, the wireless transmission wireless receiving environment of the multi-path problems, receive signals from different paths of overlapping signaling vector. The introduction of different routes of different delay and phase, if the delay extend the canal to send signals during the symbol, the signal have a frequency selective fading and cause interference between symbols, resulting in system performance.
Mobile TV business must be in a different type of movement of mobile users with high quality and reliable video transmission, including basic domestic users fixed low speed mobile users (less than 30km / h) and high-speed motion of the vehicle users (over 100 km / h). Get the Games against the sender generate Doppler frequency shift. This change in frequency is proportional to the speed and relative motion, resulting in adjacent carrier interference, affect the orthogonality between the companies. This demodulator should have a wider range of Doppler frequency shift, which is a measure of the channel time selectivity scale radio.
2, the power consumption of mobile phone problems
The design of the telephone system, power consumption is one of the designers of the factors that most concern. The introduction of mobile TV services can not be too much to sacrifice the cost of waiting time, users want a single charge for more than four hours of continuous viewing of TV programs. Past standards digital terrestrial broadcasting, like DVB-T, although the reception of high speed in a good performance, but not the power consumption for mobile reception design special optimization, now facing the energy-end DVB-T also consume about 300-500mW of power, which is Mobile battery, Economics is not enough. The introduction of mobile TV services with the power consumption of mobile phone, the receiver front-end to represent approximately 80% of the balance of power to choose devices specifically designed for mobile television standard, low-power design tuner and demodulator.
3, spectrum planning in the spectrum, mainly related to the four bands Frequency: VHFIII (174 ~ 240MHz), UHF (470 ~ 862MHz) and L1 (1452 ~ 1492MHz), L2 (1660 ~ 1685MHz). States in the planning of mobile TV spectrum not is uniform. Multi-standard, multi-band world roaming as a problem of users in the U.S. Japan may not be able to enjoy mobile TV services. To resolve this problem, move the receiver tuner and demodulator, and the signal processor and software stack must have the flexibility to support multiple standards and multiple frequency bands.
4 codec technology
For full use of spectrum resources, limited bandwidth to provide all channels, you must use high compression ratio and audio coding techniques video, such as the latest video compression standard H.264 (MPEG-4Part10) and AAC audio coding standard, including H.264, MPEG-2 compression higher proportion of 2-3 times, 1Mb / s of image data about the image quality MPEG-2DVD, so mobile TV is the most appropriate source coding standard. H.264 motion compensation with DCT techniques, and directional intra prediction, variable motion segmentation based on blocks, arithmetic context-based binary coding, the filter ring, block-based 4 × 4 integer transform quarter of accuracy as part of compensation movement, such as layered coding syntax, these technologies are highly efficient H.264 compression, the same image quality, you can save over rate MPEG-4/H.263 of about 50%.
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