前沿课题讲座05_手机电视.ppt

1、手机电视,孙松林 北京邮电大学 Email: MobileContent,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 mobile

2、 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 stan

3、dards 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 ov

4、er 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,DA

5、B = 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 cell

6、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 m

8、ode 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 MultiplexingC/N = Carrier to Noise ratio,Mobile reception of DVB-T,DVB-T includes hierarchical modes where two transport streams can

9、 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 number

10、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, the

11、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 Fr

12、ame）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 prov

13、ide mobility in medium SFNs Extended TPS bits for efficient signaling,MPE = Multiprotocoll encapsulationFEC= Forward Error CorrectionSFN= Single Frequency Network,IP Datacast (IPDC),“IP datacasting is a service where digital content formats, software applications, programming interfaces and multimed

14、ia 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 coexistence,

15、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性。,IP

16、DC 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

17、和传输的示意图,Network Design Flexibility & Signaling,Different datacast network operator and cellular network operator Digital broadcast infrastructure More transmission sites than normal broadcast networks required, but less than normal cellular phone networks existing masts can be reused Cellular networ

18、ks used for payment and administrative data Cellular network and broadcast network can share same core network,UTMS Base station,DVB-H transmitter,ISP,DVB-T Broadcasters,Core,Mux,Mobile Operator,Broadcast operator,IP Backbone,DVB-H Broadcasters,DVB-H features/pros,Cost efficient delivery of broadcas

19、t content to a large audience Low time to market Low complexity Not heavily affected of peak usage (during special events etc.) Flexible transport stream sharing between DVB-T and DVB-H possible Based on DVB-T with minimal changes Fulfils most commercial requirements Allows seamless handover No adve

20、rse effect on DVB-T IP allows encryption,DVB-H features/cons,Only IP based services possible Reduced power saving when total bit rate for DVB-H services is very low (no big “bursts” possible),链路层部分引入了MPE-FEC和时间片（Time Slicing）技术。 时间片技术对降低终端功率，并确保无缝覆盖和平滑切换具有重要作用。 时间片技术将一个服务周期分为若干个时隙，虽然发射端一直处于工作状态，但接收机

21、只是在请求服务时隙有效的时候才处于工作状态。,Mobile Terminal,FE = Front End, contains radio receiver and demultiplexor,FE,WLAN,Cellular Link,CPU,Media decoder,Display,Power consumption and handover,IP encapsulation allows sending the data in bursts to the mobile station and this saves energy (battery power) Power consump

22、tion and handover 2 Mbit buffer Handover possible during off time (services can be used even if the terminal has moved during off time),C/N Performance,RS decoder utilizing the Time Slice buffer Virtual time interleaver 10% TS PER tolerated Doppler and CN improved in mobile and portable Impulse inte

23、rference tolerance improved Possibility to vary the level of robustness,Nokias 7700 with support for DVB-H,“The Nokia 7700 will support the Nokia Streamer SU-6 accessory, the first mobile IP Datacast receiver designed to demonstrate the mobile phone television experience using the DVB-H network. The

24、 Nokia Streamer can be attached to the Nokia 7700 like a battery pack, and will be used in pilot projects to showcase the future of digital broadcasting on mobile devices.” ,T-DMB,T-DMB是韩国推出的地面数字多媒体广播系统。该标准在欧洲厂商开发的Eureka-147数字音频广播（DAB，Digital Audio Broadcasting）系统的基础上做了一些修改，以便向手持设备播送数字电视节目。,T-DMB的分层

25、,T-DMB的视频服务包括三层：内容压缩层、同步层和传送层。 内容压缩层推荐使用ITU-T H.264对视频进行编码，使用MPEG-4 BSAC对音频进行最高128kbps的编码，使用MPEG-4 BIFS对交互数据进行编码。在帧率达到30fps时，图像分辨率为352288。 同步层则使用MPEG-4 SL（Sync Layer）同步层从时间和空间上同步多媒体数据。 传送层使用受限的MPEG-2 TS码流来封装音视频数据。,T-DMB采用OFDM做为物理层技术，而卫星传输的S-DMB（Satellite Digital Multimedia Broadcasting）则采用码分复用CDM（Co

26、de Division Multiplexing）传输技术。 标准定义了4种传输模式，其中模式I适于单频网的地面广播，得到了广泛应用，其推荐的射频频率为小于375MHz的VHF，建议使用1.536 MHz的带宽，其子载波数目为1536个，IFFT/FFT的点数为2048个。,MediaFLO,在FLO网络中，内容提供商一般会将从卫星接收来的MPEG 2标准图像（704或720 480或576）转码为每秒30帧的QVGA（Quarter Video Graphics Array）图像（240320），音频为MPEG-4 HE-AAC（High Efficiency AAC）立体声，并可以传送IP

27、数据流。 FLO技术支持分层调制和编码，将信源分为基本层和增强层。所有用户都可以对基本层解码，而只有高信噪比的用户才可解码增强层数据。,FLO物理层是OFDM 4K模式，做4096点IFFT/FFT变换。 FLO的发送信号由超帧组成，每个超帧包括4帧数据。 支持5、6、7和8 MHz的带宽。在一个6MHz的信道上，FLO物理层速率可达11.2 Mbps。建议的射频范围为450MHz到3GHz。,三种标准的相同点,1.三种典型技术的物理层都应用了OFDM技术。 2.三种典型技术都采用了协议栈。在原先物理层之上构架了链路层，以传输网络层的数据承载。为了实现流业务和数据业务的共存和兼容，建立协议栈是

28、非常必要的。 3.三种典型技术都采用了功耗优化技术。这主要是针对移动终端的特点而引入的。虽然采用了不同的技术路线，但功耗已经引起了标准化组织和业界的足够重视。,物理层差异,DVB-H和T-DMB采用了RS码+卷积码的级联结构，而MediaFLO采用的是RS码+Turbo码的级联结构。 DVB-H和MediaFLO均采用了4096点的IFFT/FFT，而T-DMB采用了2048点IFFT/FFT。,Content,DVB-H Digital Video Broadcasting for Handheld devices UMTS-PSS Universal Mobile Telecommunications System Packet Switched Stream,PSS / 移动多媒体应用现状 PSS系统结构 PSS会话/协议栈 GPRS QoS,PSS,流媒体业务在3GPP的TS 26.233中被称为端到端分组交换流媒体业务（Transparent End-to-End Packet Switched Stream Service），简称为PSS业务。