前沿課題講座05_手機(jī)電視.ppt

1、手機(jī)電視,孫松林 北京郵電大學(xué) 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,四種不同的典型導(dǎo)頻分布圖,(a),(b),(c),(d),DVB-T系統(tǒng)中的導(dǎo)頻插入方案,DVB-T的幀結(jié)構(gòu),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,與DVB-T相比，DVB-H只是在參數(shù)的選擇和配置上有些改動(dòng)，它們擁有相同的物理層結(jié)構(gòu)。 有別于DVB-T提出的2K和8K模式，DVB-H使用了4K模式。,DVB-H發(fā)射系統(tǒng)的功能框圖,需要進(jìn)行4096點(diǎn)的IFFT/FFT運(yùn)算，支持QPSK、16-QAM和64-QAM符號(hào)映射。 發(fā)送信號(hào)由超幀（Super Fr

12、ame）組成，每個(gè)超幀包括4個(gè)OFDM幀。每個(gè)OFDM幀包括3409個(gè)導(dǎo)頻和數(shù)據(jù)子載波。 DVB-H基帶支持5、6、7和8 MHz的帶寬，在8MHz信道內(nèi)，傳送碼率為4.9831.67Mbps。 在射頻部分，標(biāo)準(zhǔn)建議下行鏈路使用與DVB-T相同的UHF頻段，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終端完全兼容DVB-T標(biāo)準(zhǔn)，這樣在傳輸網(wǎng)絡(luò)上，可以利用現(xiàn)有的DVB-T網(wǎng)絡(luò)傳送DVB-H碼流。 DVB-H的承載不僅僅是MPEG 2 TS流，還有封裝在MPE（MultiProtocol Encapsulation）區(qū)內(nèi)的IP數(shù)據(jù)報(bào)文或其他網(wǎng)絡(luò)層數(shù)據(jù)報(bào)文。,MPE-FEC,多協(xié)議前向糾錯(cuò)（MPE-FEC，MultiProtocol Encapsulation Forward Error Code）技術(shù)可以提高傳輸性能，并改善多普勒頻移帶來(lái)的影響，同時(shí)也能抵抗沖擊干擾。 引入了糾錯(cuò)技術(shù)，在每個(gè)獨(dú)立的MPE-FEC單元內(nèi)計(jì)算報(bào)文的奇偶校驗(yàn)信息，以信源的冗余換取移動(dòng)信道傳輸?shù)目煽啃浴?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系統(tǒng)中負(fù)載封裝

17、和傳輸?shù)氖疽鈭D,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),鏈路層部分引入了MPE-FEC和時(shí)間片（Time Slicing）技術(shù)。 時(shí)間片技術(shù)對(duì)降低終端功率，并確保無(wú)縫覆蓋和平滑切換具有重要作用。 時(shí)間片技術(shù)將一個(gè)服務(wù)周期分為若干個(gè)時(shí)隙，雖然發(fā)射端一直處于工作狀態(tài)，但接收機(jī)

21、只是在請(qǐng)求服務(wù)時(shí)隙有效的時(shí)候才處于工作狀態(tài)。,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是韓國(guó)推出的地面數(shù)字多媒體廣播系統(tǒng)。該標(biāo)準(zhǔn)在歐洲廠商開發(fā)的Eureka-147數(shù)字音頻廣播（DAB，Digital Audio Broadcasting）系統(tǒng)的基礎(chǔ)上做了一些修改，以便向手持設(shè)備播送數(shù)字電視節(jié)目。,T-DMB的分層

25、,T-DMB的視頻服務(wù)包括三層：內(nèi)容壓縮層、同步層和傳送層。 內(nèi)容壓縮層推薦使用ITU-T H.264對(duì)視頻進(jìn)行編碼，使用MPEG-4 BSAC對(duì)音頻進(jìn)行最高128kbps的編碼，使用MPEG-4 BIFS對(duì)交互數(shù)據(jù)進(jìn)行編碼。在幀率達(dá)到30fps時(shí)，圖像分辨率為352288。 同步層則使用MPEG-4 SL（Sync Layer）同步層從時(shí)間和空間上同步多媒體數(shù)據(jù)。 傳送層使用受限的MPEG-2 TS碼流來(lái)封裝音視頻數(shù)據(jù)。,T-DMB采用OFDM做為物理層技術(shù)，而衛(wèi)星傳輸?shù)腟-DMB（Satellite Digital Multimedia Broadcasting）則采用碼分復(fù)用CDM（Co

26、de Division Multiplexing）傳輸技術(shù)。 標(biāo)準(zhǔn)定義了4種傳輸模式，其中模式I適于單頻網(wǎng)的地面廣播，得到了廣泛應(yīng)用，其推薦的射頻頻率為小于375MHz的VHF，建議使用1.536 MHz的帶寬，其子載波數(shù)目為1536個(gè)，IFFT/FFT的點(diǎn)數(shù)為2048個(gè)。,MediaFLO,在FLO網(wǎng)絡(luò)中，內(nèi)容提供商一般會(huì)將從衛(wèi)星接收來(lái)的MPEG 2標(biāo)準(zhǔn)圖像（704或720 480或576）轉(zhuǎn)碼為每秒30幀的QVGA（Quarter Video Graphics Array）圖像（240320），音頻為MPEG-4 HE-AAC（High Efficiency AAC）立體聲，并可以傳送IP

27、數(shù)據(jù)流。 FLO技術(shù)支持分層調(diào)制和編碼，將信源分為基本層和增強(qiáng)層。所有用戶都可以對(duì)基本層解碼，而只有高信噪比的用戶才可解碼增強(qiáng)層數(shù)據(jù)。,FLO物理層是OFDM 4K模式，做4096點(diǎn)IFFT/FFT變換。 FLO的發(fā)送信號(hào)由超幀組成，每個(gè)超幀包括4幀數(shù)據(jù)。 支持5、6、7和8 MHz的帶寬。在一個(gè)6MHz的信道上，F(xiàn)LO物理層速率可達(dá)11.2 Mbps。建議的射頻范圍為450MHz到3GHz。,三種標(biāo)準(zhǔn)的相同點(diǎn),1.三種典型技術(shù)的物理層都應(yīng)用了OFDM技術(shù)。 2.三種典型技術(shù)都采用了協(xié)議棧。在原先物理層之上構(gòu)架了鏈路層，以傳輸網(wǎng)絡(luò)層的數(shù)據(jù)承載。為了實(shí)現(xiàn)流業(yè)務(wù)和數(shù)據(jù)業(yè)務(wù)的共存和兼容，建立協(xié)議棧是

28、非常必要的。 3.三種典型技術(shù)都采用了功耗優(yōu)化技術(shù)。這主要是針對(duì)移動(dòng)終端的特點(diǎn)而引入的。雖然采用了不同的技術(shù)路線，但功耗已經(jīng)引起了標(biāo)準(zhǔn)化組織和業(yè)界的足夠重視。,物理層差異,DVB-H和T-DMB采用了RS碼+卷積碼的級(jí)聯(lián)結(jié)構(gòu)，而MediaFLO采用的是RS碼+Turbo碼的級(jí)聯(lián)結(jié)構(gòu)。 DVB-H和MediaFLO均采用了4096點(diǎn)的IFFT/FFT，而T-DMB采用了2048點(diǎn)IFFT/FFT。,Content,DVB-H Digital Video Broadcasting for Handheld devices UMTS-PSS Universal Mobile Telecommunications System Packet Switched Stream,PSS / 移動(dòng)多媒體應(yīng)用現(xiàn)狀 PSS系統(tǒng)結(jié)構(gòu) PSS會(huì)話/協(xié)議棧 GPRS QoS,PSS,流媒體業(yè)務(wù)在3GPP的TS 26.233中被稱為端到端分組交換流媒體業(yè)務(wù)（Transparent End-to-End Packet Switched Stream Service），簡(jiǎn)稱為PSS業(yè)務(wù)。