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Introduction to DTV Receivers and Transmitters
DTV Receivers
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Introduction to DTV Receivers and Transmitters
- 1. Copyright © StevenMorris 2005 All Rights Reserved Downloaded from http://www.interactivetvweb.org An introduction to DTV receiver technology Steve Morris [email protected]
- 2. Copyright © StevenMorris 2005 All Rights Reserved Downloaded from http://www.interactivetvweb.org What does a DTV receiver do? • Receives digital TV broadcasts from a cable, satellite or terrestrial network • Decodes them • Outputs them to a television or other display device – This display device is usually a television • May do other things – E.g. execute applications included with the broadcast
- 3. Copyright © StevenMorris 2005 All Rights Reserved Downloaded from http://www.interactivetvweb.org Types of digital TV receiver • Set-top box (STB) – The most common type – Varies in functionality and features from very basic to very advanced – May be integrated with other types of device • E.g. a DVD player or PVR system • Integrated Digital TV (IDTV) – Receiver is built into a TV set – Can receive digital or analog broadcasts with no extra hardware • PC with digital tuner card – Similar to analog TV tuners, except it decodes digital TV signals
- 4. Copyright © StevenMorris 2005 All Rights Reserved Downloaded from http://www.interactivetvweb.org Block diagram of a typical receiver Tuner Front-end Smart card / CA Module MPEG-2 decoder CPU Middleware SDRAM Flash memory Graphics processor Descrambler MPEG-2 demultiplexer
- 5. Copyright © StevenMorris 2005 All Rights Reserved Downloaded from http://www.interactivetvweb.org The Front End • The part of the receiver that actually receives the analog signal and converts it into a stream of bits – Two main components, the tuner and the front end – These may be integrated into a single package – Usually specific to cable, satellite or terrestrial networks – Some may support both analog and digital signals • The tuner – Receives a signal on the frequency specified by the rest of the STB – Demodulates the signal – Turns the analog signal into a digital bitstream • The front-end – Performs first level of error correction – Removes the first level of packetization in the stream – Outputs an MPEG-2 transport stream in digital format
- 6. Copyright © StevenMorris 2005 All Rights Reserved Downloaded from http://www.interactivetvweb.org The Demultiplexer • Takes an MPEG-2 transport stream and locates those elements that the STB is interested in – All elements of the current channel • Audio and video streams • Broadcast data streams • Service information – Some service information for the network as a whole • Passes these streams on to other parts of the system – Service information and data streams to the CPU (if it is interested) – Audio and video to the MPEG decoder • Other data from the transport stream is thrown away – But demultiplexer may include section filtering capability to filter other MPEG-2 sections as requested by applications
- 7. Copyright © StevenMorris 2005 All Rights Reserved Downloaded from http://www.interactivetvweb.org The MPEG Decoder • Decodes audio and video streams and displays them on the screen • May include support for graphical overlays – Cursor, graphics – Some receivers support up to five graphics planes • Background, video, two graphics planes, cursor • May include support for scaling, clipping and repositioning video – But this may be limited • Typically combined with the graphics processor – Makes it easier to integrate different elements of the display
- 8. Copyright © StevenMorris 2005 All Rights Reserved Downloaded from http://www.interactivetvweb.org The CPU • Handles all of the other tasks in the system – Decoding and handling service information – Decoding broadcast data streams – User interaction – Running built-in or downloaded applications • Often integrated with the MPEG-2 decoder and other components • Typical CPUs – STMicroelectronics 551x family – NEC EMMA2 – ATI Xilleon – Broadcom BCM3560
- 9. Copyright © StevenMorris 2005 All Rights Reserved Downloaded from http://www.interactivetvweb.org Conditional access (CA) • 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: – Canal + (MediaGuard) – Philips (Cryptoworks) – Irdeto (IrdetoAccess) – General Instrument (DigiCypher II) – NDS (VideoGuard) – Nagravision-Kudelski (Nagravision) – Conax (Conax) – Motorola – France Telecom (Viacess)
- 10. Copyright © StevenMorris 2005 All Rights Reserved Downloaded from http://www.interactivetvweb.org Conditional Access (CA) • 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
- 11. Copyright © StevenMorris 2005 All Rights Reserved Downloaded from http://www.interactivetvweb.org Conditional Access (CA) • 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
- 12. Copyright © StevenMorris 2005 All Rights Reserved Downloaded from http://www.interactivetvweb.org Return channel • Used to communicate with the network operator or other service operator – Ordering pay-per-view services, home shopping, home banking • May be used for general network access – Web browsing, email, chat • Many types in use – PSTN modem (usually 56K) is still the most common – Cable modem and ADSL modem are becoming more common – Exotic technologies such as GSM, DVB RCS (return channel via satellite) etc. also in limited use • Not every receiver will have a return channel – Adds to the cost – Not all subscription services will need or use one
- 13. Copyright © StevenMorris 2005 All Rights Reserved Downloaded from http://www.interactivetvweb.org Middleware • 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
- 14. Copyright © StevenMorris 2005 All Rights Reserved Downloaded from http://www.interactivetvweb.org Integration • Cost is a major factor in STB manufacture – Especially in vertical markets – Everyone wants the product cheaper – Lots of competition – Typical cost is ~100 USD to the network operator for a standard STB • Retail is more expensive • Many components get integrated to save cost – Tuner and front end – Demultiplexer/MPEG decoder/CPU/graphics processor • Most current STBs are one- or two-chip solutions – Depends on features needed • Pressure is always towards more integrated solutions
- 15. Copyright © StevenMorris 2005 All Rights Reserved Downloaded from http://www.interactivetvweb.org Block diagram of a typical receiver Tuner Smart card / CA Module MPEG-2 decoder CPU Middleware SDRAM Flash memory Graphics processor Descrambler MPEG-2 demultiplexer Front-end Standard STB with pay-TV support (integrated) BOM Cost: ~80 USD Integrated into front-end Integrated into CPU
- 16. Copyright © StevenMorris 2005 All Rights Reserved Downloaded from http://www.interactivetvweb.org Three distinguishing features • To use a receiver on a given network, we care about three things: – Middleware • The APIs used to develop interactive applications – Conditional access system • The type of encryption used to protect pay-TV content – Type of network it receives the signal from • Terrestrial, cable or satellite • Does it use ATSC, OpenCable, or DVB standards? • These determine whether a receiver will work on a that network – Other specifications are less important – All of these features will be determined by the network operator in a vertical market
- 17. Copyright © StevenMorris 2005 All Rights Reserved Downloaded from http://www.interactivetvweb.org Receiver markets • Two types of market for digital TV receivers – Horizontal market (receivers sold in retail stores) • Free-to-air networks • Some cable networks in the USA – Vertical market (receivers supplied by network operators) • Pay-TV networks in Europe and Asia • Some Pay-TV networks in the USA • These markets have very different business models – Thus, the pressures on the receiver manufacturer and on the spec of the receiver are also different – Which market type is best for a given manufacturer depends on their skills and strengths – Neither type of market will go away • Both will likely grow in the short term • Becoming more common with more digital terrestrial TV deployments and the use of open standards for middleware
- 18. Copyright © StevenMorris 2005 All Rights Reserved Downloaded from http://www.interactivetvweb.org Horizontal markets • Receivers are sold through retailers – E.g. electronics store, supermarket • Often used for free-to-air channels only – Especially in Europe and Asia – No subscriptions needed • User may be able to buy subscription from pay-TV company – Some US cable networks – Provides access to pay-TV channels as well as free-to-air channels – Uses a pluggable CA module to ensure receiver works on all networks • But not every receiver in every horizontal market will include this! – More choice for the user – More scope for different types of receiver – Means the network operator doesn’t have to own the boxes • Less capital investment
- 19. Copyright © StevenMorris 2005 All Rights Reserved Downloaded from http://www.interactivetvweb.org Vertical markets • Boxes are bought by the network operator and supplied to customers – Either rented or as part of subscription package • The main model for pay-TV systems at the moment – Especially in Europe & Asia – Usually used by pay-TV satellite or cable networks • Gives the network operator more control over their network – Network operator defines the hardware and software specification for the boxes – May still be supplied by more than one vendor – Gets better price because of volume discounts and guaranteed order numbers • But has the costs associated with owning all of the receivers – Large capital investment – More support needed • Logistics, tech support, installation, repair, etc.
- 20. Copyright © StevenMorris 2005 All Rights Reserved Downloaded from http://www.interactivetvweb.org Classes of receiver • Different groups have different needs from an STB – Some people want something cheap – Most people want an average box that lets them do a little bit more – Some people will pay extra for more advanced features – A few want to add DTV support to their PC • Products are available for most of these groups – But some groups don’t have much choice • Pay-TV operators will only support a few types of product – Supporting more is expensive – Typically will only provide an average box with some support for interactivity – May provide a more advanced box (as part of a more expensive subscription) • Retail products have wider range of features and prices
- 21. Copyright © StevenMorris 2005 All Rights Reserved Downloaded from http://www.interactivetvweb.org Classes of receiver – Basic ‘zapper’ • Very basic hardware – Limited memory and CPU power, no return channel • Usually sold retail • Can receive free channels only – No support for subscription or pay-per-view channels • Simple features – Channel up/down – Control audio language – Control subtitles – No program guide or other features – No interactivity
- 22. Copyright © StevenMorris 2005 All Rights Reserved Downloaded from http://www.interactivetvweb.org Block diagram of a basic receiver μController SDRAM ROM Free-to-Air ‘zapper’ box BOM Cost: ~30-40 USD MPEG-2 decoder SDRAM MPEG-2 demultiplexer Tuner / Front-end
- 23. Copyright © StevenMorris 2005 All Rights Reserved Downloaded from http://www.interactivetvweb.org Classes of receiver - Standard • Slightly more advanced STB – More memory, faster CPU, maybe a return channel • Usually sold retail or as part of a subscription • May receive some pay-TV channels – Usually tied to a specific network in subscription systems – May include support for pluggable CA module in retail products • Some interactivity – Program guide – Maybe games or features associated with a specific show – Maybe other interactive services offered by the network operator
- 24. Copyright © StevenMorris 2005 All Rights Reserved Downloaded from http://www.interactivetvweb.org Classes of receiver - Advanced • Advanced features – More memory, faster return channel, extra hardware (e.g. keyboard) • Usually sold retail or as part of an advanced subscription package • Receives some pay-TV channels – As for standard STB • Integrates other features – E.g. PVR • May include more interactive features – More applications, e.g. web browser or email – Makes use of improved hardware to offer more services
- 25. Copyright © StevenMorris 2005 All Rights Reserved Downloaded from http://www.interactivetvweb.org Classes of receiver – Very advanced • Typically a PC with digital tuner card – Either internal or external • May not be able to receive pay-TV channels – Piracy concerns may prevent this • May include many advanced features – PVR, web browsing, email, DVD playback – All PC applications – But the actual DTV functionality may also be very limited • Not usually the main device in a home – Typically will not replace the TV/STB combination in the living room • except in a very small urban home – May be used in a young person’s bedroom or university accommodation • Combination device to save space
- 26. Copyright © StevenMorris 2005 All Rights Reserved Downloaded from http://www.interactivetvweb.org Conclusion • All DTV receivers are fairly similar – Most differences are in the software • E.g. middleware, CA system • Feature sets range from extremely basic to very advanced – But most boxes currently sold will have roughly the same features • Middleware to provide some interactive applications (e.g. program guide and downloaded apps) • PSTN modem or cable modem for return channel • The move towards horizontal markets is giving more opportunities for receiver manufacturers – Markets are growing – Wider range of feature sets can be sold • As markets grow, more televisions will include this functionality – Just like TVs now include cable as well as terrestrial reception