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DVB 技術介紹

R &D Center. DVB 技術介紹. Presented by: Jiader Chen / 陳家德. Jiader@action-sz.com. Section 1: Digital TV Standards Section 2: Transmission Standards Section 3: Conditional Access Section 4: Middleware. Agenda. 数据来源 ： CCW Research, 2005.2. 美規 ATSC

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DVB 技術介紹

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  1. R&D Center DVB 技術介紹 Presented by: Jiader Chen / 陳家德 Jiader@action-sz.com

  2. Section1: Digital TV Standards Section 2: Transmission Standards Section 3: Conditional Access Section 4: Middleware Agenda 数据来源：CCW Research, 2005.2

  3. 美規ATSC 由「美國先進電視系統委員會」Advanced Television Systems Committee 制定 歐規DVB Digital Video Broadcasting 由European Telecommunication Standard Institute 制定 日規ISDB Integrated Service Digital Broadcasting 由「日本數位廣播專業集團」Japanese Digital Broadcasting Expert Group 制定 Digital TV Standards

  4. The Comparison List of Digital TV Standards

  5. DVBStandards

  6. DVB-S(ETS 300 421): 为数字卫星广播系统标准。 卫星传输具有覆盖面广、节目容量大等特点。 数据流的调制采用四相 相移键控调制(QPSK)方式，工作频率为11/12GHz。 在使用MPEG-2MP@ML格式时，用户端若达到 CCIR 601演播室质量，码率为9Mb/s；达到PAL质量，码率为5Mb/s。一个54MHz转发器传送速率 可达68Mb/s，可用于多套节目的复用。 DVB-C(ETS 300 429): 为数字有线电视广播系统标准。 具有16、32、64QAM(正交调幅)三种调制方式，工作频率在10 GHz以下。 采用64QAM时，一个PAL通道的传送码率为41.34Mb/s，可用于多套节目的复用。 系统 前端可从卫星和地面发射获得信号，在终端需要电缆机顶盒。 DVBStandards

  7. DVB-T(ETS 300 744): 为数字地面电视广播系统标准。 这是最复杂的DVB传输系统。 地面数字电视发射的传输容量，理论 上与有线电视系统相当，本地区覆盖好。 采用编码正交频分复用(COFDM)调制方式，在8MHz带宽 内能传送4套电视节目，传输质量高。 DVB-SMATV(ETS 300 473): 为数字卫星共用天线电视(SMATV)广播系统标准 它是在DVB-S和DVB-C基础上制定的。 DVB-MS(ETS 300 748):为高于10GHz的数字广播MMDS分配系统标准。 它基于DVB-S，使携带大量节目的微波信号直接入户。用DVB-S接收机配上一个MMDS频率变换器， 就可接收DVB-MS信号。 DVB-MC(ETS 300 749): 为低于10GHz的数字广播MMDS分配系统标准。 它基于DVB-C，使携带大量节目的微波信号直接入户。用DVB-C接收机配上一个MMDS频率变换器， 就可接收DVB-MC信号。 DVBStandards

  8. Digital Transmission System

  9. Tuner Front-end Descrambler Smart card / CA Module MPEG-2 demultiplexer SDRAM MPEG-2 decoder Graphics processor CPU Flash memory Middleware Block diagram of a typical receiver

  10. Channel coding: Transforming signals to improve communications performance by increasing the robustness against channel impairments (noise, interference, fading, ..) Waveform coding: Transforming waveforms to better waveforms Structured sequences: Transforming data sequences into better sequences, having structured redundancy. “Better” in the sense of making the decision process less subject to errors. What is channel coding?

  11. 传输信道中常见的错误有以下三种： 随机错误：错误的出现是随机的，一般而言错误出现的位置是随机分布的，即各个码元是否发生错误是互相独立的，通常不是成片地出现错误。这种情况一般是由信道的加性随机噪声引起的。因此，一般将具有此特性的信道称为随机信道。 突发错误：错误的的出现是一连串出现的。通常在一个突发错误持续时间内，开头和末尾的码元总是错的，中间的某些码元可能错也可能对，但错误的码元相对较多。这种情况如移动通信中信号在某一段时间内发生衰落，造成一串差错；汽车发动时电火花干扰造成的错误；光盘上的一条划痕等等。这样的信道我们称之为突发信道。 混合错误：既有突发错误又有随机差错的情况。这种信道称之为混合信道。 Error Correction Coding

  12. Automatic Repeat reQuest (ARQ) Full-duplex connection, error detection codes The receiver sends a feedback to the transmitter, saying that if any error is detected in the received packet or not (Not-Acknowledgement (NACK) and Acknowledgement (ACK), respectively). The transmitter retransmits the previously sent packet if it receives NACK. Forward Error Correction (FEC) Simplex connection, error correction codes The receiver tries to correct some errors Hybrid ARQ (ARQ+FEC) Full-duplex, error detection and correction codes Error Control Techniques

  13. 正交振幅调制(QAM)：调制效率高，要求传送途径的信噪比高，适合有线电视电缆传输。 键控移相调制(QPSK)：调制效率高，要求传送途径的信噪比低，适合卫星广播。 残留边带调制(VSB)：抗多径传播效应好（即消除重影效果好），适合地面广播。 编码正交频分调制(COFDM)：抗多径传播效应和同频干扰好，适合地面广播和同频网广播。 Digital Modulation Techniques

  14. OFDM Technique

  15. Multicarrier - many carriers sharing Reduced C/N compared to Analogue Resistant to echoes, Interference etc Low symbol rate per carrier ~ 1 kBaud: Long Symbol Period, can Extend with Guard Interval With FEC becomes COFDM Uses Fast Fourier Transform [FFT] ”2k” and “8k” versions Single Frequency Networks [SFN] OFDM - Features

  16. Advantages over satellite Lower cost Reduced latency Non line-of-sight Flexibility Mobility The COFDM Digital Microwave Advantage • Advantages over analog • Less bandwidth required • Robust Signal • Quality consistency • Non line-of-sight • Scalable performance • Encryption

  17. Anti-piracy system for pay-TV Decrypts some or all of the data Depending what was encrypted by the network operator Usually based around some kind of physical token Smart card or similar device Only that token will work with that receiver Each STB usually has one CA system integrated This is enough for most pay-TV systems The box is tied with the subscription, so only used on one network and one CA system Most common CA vendors: Conditional access (CA) • Canal + (MediaGuard) • Philips (Cryptoworks) • Irdeto (IrdetoAccess) • General Instrument (DigiCypher II) • NDS (VideoGuard) • Nagravision-Kudelski (Nagravision) • Conax (Conax) • Motorola • France Telecom (Viacess)

  18. Some CA systems require special hardware support e.g. NDS Usually features built into the CPU Most systems will use a standard Smart Card slot Some receivers will use two, one for CA and one for banking card, etc. Some network operators are now using pure software CA systems No need for extra hardware module Makes it quicker to roll out new encryption when the old one is cracked May still use smart cards for authentication CA systems may do more than just encryption Pair a smart card to a single receiver Smart card can not be moved to other receivers Provide a way of uniquely identifying the receiver Smart card serial number Prevent STBs moving to other household Second STB usually provided at lower price by network operator CA system may stop that box being given to neighbor, friend, other family member Every household must have their own subscription Conditional Access (CA)

  19. Integrated CA systems are unsuitable for some markets May use a pluggable CA module instead Entire decryption solution on a PCMCIA card Smart card plugs in to PCMCIA card Used on retail systems to allow use with any network Common systems include: DVB Common Interface (DVB-CI) ATSC Point Of Deployment (POD) module OpenCable CableCARD (based on POD) This has several limitations More expensive (PCMCIA card vs. integrated smart card reader) Very few vertical markets will use pluggable CA modules because there is no need or benefit Also perceived as being less secure, in the case of DVB-CI Not all CA systems will support pluggable modules Conditional Access (CA)

  20. Provides a common software platform for application development Usually in C or Java Every middleware platform has basically the same features Graphics & video manipulation, return channel access, access to service information, etc. Most middleware platforms today are proprietary OpenTV (OpenTV Core) NDS (NDS Core) Canal+ (MediaHighway) PowerTV (PowerTV) Microsoft (Microsoft TV) Nagravision-Kudelski (Tsunami) Liberate (Liberate) But open middleware platforms are now being deployed MHP, OCAP, ACAP, JavaTV, ARIB-B23 Middleware

  21. DVB-MHP Overview • The DVB “Multimedia Home Platform” (MHP) is an open standard specification for an interactive TV platform. • Enables digitalcontent providers to address all types ofterminals ranging from low-end to high-end settop boxes, integrated digital TV sets andmultimedia PCs • MHP extends the existing,successful DVB open standards forbroadcast andinteractive services in all transmission networks.

  22. MHP Architecture

  23. Money from Your Pocket 新一代多媒体移动标准：DVB-H （Digital Video Broadcasting Handheld） 通过地面数字广播网络向便携/手持终端提供多媒体业务 基于DVB-T标准，但和DVB-T相比，具有下列特点： DVB-H终端具有更低的功耗 H.264（MPEG4, Part 10）音视频编码和压缩（IP? Microsoft Windows Media Codec 9?） 移动接收和抗干扰性能更为优越 适用于移动电话、手持计算机等便携终端通过地面数字电视广播网络接收音视频及数据信息。 TV in Your Pocket

  24. Possible interactive services for mobile TV can be grouped into five categories • Route planer • Event calendar • ... Information services • News • Weather • Traffic information • Tourist information • Restaurant-, hotel guide • Horoscope, biorhythm • Screensavers • Ring tones • ... Downloads • Video clips • Audio clips • Games Purchasing services • Ticketing • Shopping • Auctioning • Banking • ... • Casino • ... Entertainment services • Voting • Lottery, quiz • Betting Socialising services • Chat • Flirt • Dating • Friend finder • ...

  25. Why DVB-H ? DVB-H stands for Digital Video Broadcasting for Handhelds • Using 3G to deliver high speed high bite rate services to a large number of users is costly • Broadcasting is a relatively inexpensive way of distributing lots of data at high speed to a large number of users • Handheld devices have particular requirements in terms of power consumption, screen size and mobility

  26. Why Time Slicing ? • Time slicing is the mechanism DVB-H uses to transmit data in periodic bursts with significantly higher instantaneous bit rates than the bit rates required if the data are transmitted continuously. region 1 (SFN) DVB-H playout DVB core Playout Server service Application provider region 2 (SFN)

  27. Time Slicing Structure Continuous Transmission Structure

  28. Summary • Using DVB spectrum for services that are not recognised as traditional broadcast will have regulatory implications • There are some major problems in DVB-T standard with regards to mobility • The actors are aware of these problems and standardisation of DVB-H has received high priority • Different business models are suggested but they must be proven in a real market • Broadcasters and other media companies should consider how they can utilise the new possibilities in this new platform

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