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1、手机电视,孙松林 北京邮电大学 Email: Mobile: 13511017172,Content,DVB-H Digital Video Broadcasting for Handheld UMTS-PSS Universal Mobile Telecommunications System Packet Switched Stream,Introduction,Convergence of digital media and communication give users possibility to consume most digital content also in mobi
2、le environment The emerging DVB-H standard aims to provide digital TV reception in mobile devices Earlier known as DVB-X DVB-H is being standardized by and ad hoc group of the DVB organization Expected to be standardized in the first quarter of 2004 DVB-H combines traditional television broadcast st
3、andards with elements specific to handheld devices; mobility, smaller screens and antennas, indoor coverage and reliance on battery power,Motivation for creating DVB-H,Why not use UMTS? Not scalable for mass content delivery For delivery of mass media content, broadcast networks should be preferred
4、over point-to-point cellular networks Why not use DVB-T? Was designed for rooftop reception Need for an efficient power saving mechanism Inadequate impulse noise protection Why not use DAB? Designed for devices with similar power constraints but too narrow spectrum is assigned for data transmission,
5、DAB = Digital Audio Broadcasting,四种不同的典型导频分布图,(a),(b),(c),(d),DVB-T系统中的导频插入方案,DVB-T的帧结构,DVB-T,Terrestrial Digital Television Standard Used in 36 countries world wide One-to-many broadband wireless data transport Video, audio, data and importantly IP packets Scalable: cell size up to 100km (DVB-H cel
6、l size is smaller) Huge capacity: 54 channels each 5-32Mbit/s Shut down of analog TV will free up huge frequency capacity for DVB-T usage,DVB-T = Digital Video Broadcasting - Terrestrial,DVB-T (cont.),Developed for MPEG-2 stream distribution, but can basically carry any data Flexible, has many modes
7、, 4.98-31.67 Mbit/s C/N=25dB COFDM multicarrier modulation with 2k and 8k modes One DVB channel is 8MHz 1705 sub carriers (spacing: 4464 Hz) - 2k mode 6817 sub carriers (spacing: 1116 Hz) - 8k mode Carrier modulation: QPSK, 16 QAM or 64 QAM Error correction: convolutional code and Salomon-Reed Basic
8、 mode in Finland: 64 QAM, code rate = 2/3, guard interval 1/8 Gives 22.12 Mbits/s capacity when C/N=19.2 dB and 8 MHz channel,COFDM = Coded Orthogonal Frequency Division Multiplexing C/N = Carrier to Noise ratio,Mobile reception of DVB-T,DVB-T includes hierarchical modes where two transport streams
9、can be sent simultaneously Low capacity, high capacity DVB-T can also be used for broadcast to mobile devices, but a suitable mode have to be selected 8k 64 QAM: 400 km/h tolerable A separate network for DVB-H is desired Optimization of speed, coverage and capacity,2k, 4k or 8k and why?,A small numb
10、er of sub-carrier provides (like in 2k): large inter-carrier spacing - gives tolerance to the echoes affected by Doppler short symbol duration -limits the maximum delay of accepted echoes A large number of sub-carriers (like in 8k): small inter-carrier spacing but a large symbol duration In short, t
11、he choice of the sub-carrier number has no impact on the broadcast capacity but on the trade-of between Doppler acceptance and maximum echo delays,与DVB-T相比，DVB-H只是在参数的选择和配置上有些改动，它们拥有相同的物理层结构。 有别于DVB-T提出的2K和8K模式，DVB-H使用了4K模式。,DVB-H发射系统的功能框图,需要进行4096点的IFFT/FFT运算，支持QPSK、16-QAM和64-QAM符号映射。 发送信号由超帧（Super
12、 Frame）组成，每个超帧包括4个OFDM帧。每个OFDM帧包括3409个导频和数据子载波。 DVB-H基带支持5、6、7和8 MHz的带宽，在8MHz信道内，传送码率为4.9831.67Mbps。 在射频部分，标准建议下行链路使用与DVB-T相同的UHF频段，470862MHz。,DVB-H system elements,Time slicing for power saving Time between the bursts gives the power saving (off time) MPE-FEC for performance 4k mode was chosen to p
13、rovide mobility in medium SFNs Extended TPS bits for efficient signaling,MPE = Multiprotocoll encapsulation FEC= Forward Error Correction SFN= Single Frequency Network,IP Datacast (IPDC),“IP datacasting is a service where digital content formats, software applications, programming interfaces and mul
14、timedia services are combined through IP (Internet Protocol) with digital broadcasting.” All content delivered as IP packets Connectivity layer convergence DVB-H combined with IP datacasting enables distribution of many kinds of digital content TV broadcast, music, games etc.,DVB-T and DVB-H coexist
15、ence,DVB-H终端完全兼容DVB-T标准，这样在传输网络上，可以利用现有的DVB-T网络传送DVB-H码流。 DVB-H的承载不仅仅是MPEG 2 TS流，还有封装在MPE（MultiProtocol Encapsulation）区内的IP数据报文或其他网络层数据报文。,MPE-FEC,多协议前向纠错（MPE-FEC，MultiProtocol Encapsulation Forward Error Code）技术可以提高传输性能，并改善多普勒频移带来的影响，同时也能抵抗冲击干扰。 引入了纠错技术，在每个独立的MPE-FEC单元内计算报文的奇偶校验信息，以信源的冗余换取移动信道传输的可靠
16、性。,IPDC over DVB-H business,New forms of multimedia enjoyment for consumers New market opportunities for telecommunication and broadcasting industries High bandwidth and high transmission speeds but insensitive to number of recipients attractive from a business perspective,IPDC = IP Datacast,DVB-H系统中负载封装和传输的示意图,Network Design Flexibility & Signaling,Different datacast network operator and cellular network operator Digital broadcast infrastructure More transmission
