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Digital Video Broadcasting An Overview

Digital Video Broadcasting An Overview. Prof. Dr. Mehmet Şafak Hacettepe University Dept. of Electrical and Electronics Engineering 06800 Beytepe, Ankara, Turkey msafak@hacettepe.edu.tr. Digital TV.

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Digital Video Broadcasting An Overview

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  1. Digital Video BroadcastingAn Overview Prof. Dr. Mehmet Şafak Hacettepe University Dept. of Electrical and Electronics Engineering 06800 Beytepe, Ankara, Turkey msafak@hacettepe.edu.tr

  2. Digital TV How come a man can be so sensitive as to distinguish between resolutions 1024 x 678 and 1365 x 768, but can not see the difference between 15 totally different woman shoes ? I could see the difference if they were on the TV DVB - An Overview

  3. Outline • Vision • Data Broadcasting • Integrated Receiver Decoders (IRD) • Transmission on Cable, Satellite and Terrestrially • Interaction Channels • The Multimedia Home Platform (MHP) • DVB-Handheld • Hybrid Networks • Prospects for Future Developments DVB - An Overview

  4. Vision • Initially, DVB concentrated on broadcasting of audio and video services. • In later phases, DVB addressed areas which lie outside of the classical broadcast world. • Vision defined in 2000: • DVB’s vision is to build a content environment that combines the stability and interoperability of the world of broadcast with the vigor, innovation, and multiplicity of services of the world of the Internet DVB - An Overview

  5. Data Broadcasting

  6. Data Broadcasting • A 4:2:2 picture requires a raw transmission rate of 13.5 Msamples/s x 16 bits/sample =216 Mbps. • The 216 Mbps just to transmit one digital TV channel is very high, so the need for compression is obvious. • Using compression techniques, the data rates on the order of 3.2 Mbps per TV channel are currently used. DVB - An Overview

  7. Data Broadcasting • nn DVB - An Overview

  8. Data Broadcasting • For real-time HDTV encoders, the rate of improvement in practice has been significantly less than for SDTV: • smaller number of channels per multiplex means that the introduction of statistical multiplexing techniques did not yield as much of a benefit for HDTV as it did for SDTV. • Today’s real-time HDTV encoders for H.264/AVC or VC-1 do not yet fully exercise all of the additional tools in the new algorithms, such as variable block sizes • Within a year, 8-10 Mbps is expected to be sufficient for the transmission of HDTV signals. DVB - An Overview

  9. Data Broadcasting Components inside the DVB data container U. Reimers, DVB-the family of international standards for DVB, Proc. IEEE, vol.94, no.1, pp.173-181, Jan. 2006 DVB - An Overview

  10. Data Broadcasting • The output of the MPEG-2 multiplexer (transport stream) consists of 188-byte packets, where different video, audio and data channels are multiplexed. • Depending on the usable data rate of the broadcast channel, the size of the container varies. • The program specific information (PSI) provides a list of packet ID (PID) values of the corresponding program numbers. • The service information (SI) contains the modulation parameters, translates program numbers into service names and electronic program guide. DVB - An Overview

  11. Data Broadcasting • Data services can be • program related (e.g., teletext), or • independent of any other service in the multiplex (e.g., software download, MHP applications, information services). • DVB data broadcasting offers fast Internet access via satellites. • Users may be connected to the Internet via standard modems and in addition install a satellite receiver card into their PCs for broadband downstream. DVB - An Overview

  12. Integrated Receiver Decoders (IRD)

  13. Integrated Receiver Decoders (IRD) • SDTV or HDTV • Baseline IRD or IRD with digital interface • whether or not they are intended for use with a digital bitstream storage device such as a digital VCR • Video coding formats: • MPEG-2 video or MPEG-4 AVC (H.264) • Audio coding formats: • Dolby AC-3, DTS and MPEG-4 AVC (H.264) DVB - An Overview

  14. Integrated Receiver Decoders (IRD) • Reception of DVB services delivered over IP-based networks • DVB-TXT replaces Teletext • which is transported during the period of the vertical blanking interval (VBI) of analog television. • DVB developed a generic means for the delivery of all VBI data, e.g., • to enable the control of video recorders, • the signaling of wide screen programs. DVB - An Overview

  15. Integrated Receiver Decoders (IRD) • As part of DVB signals, it is possible • to provide a translation of original soundtrack in the form of subtitles • add graphic elements to the transmitted images, e.g., station logos. • TV-Anytime information in DVB transport streams • help personal digital recorders (PDR) to search, select and acquire the content, the viewer wishes to record. DVB - An Overview

  16. Transmission on Cable, Satellite and Terrestrially

  17. Transmission Block diagram of the DVB-T encoder (Blue blocks are used in DVB-C and DVB-S as well) U. Reimers, Digital Video Broadcasting, IEEE Comm. Mag., pp.104-110, June 1998 DVB - An Overview

  18. Transmission • DVB-S • Published in 1993 • Modulation: QPSK and BPSK • Convolutional codes concatenated with RS codes • DVB-S2 • Published in 2003 • Modulation: QPSK, 8-PSK (broadcast applications), 16-APSK and 32-APSK (professional applications) • Backward-compatibity with existing DVB-S receivers • Reasonable receiver complexity • Interactivity (i.e., Internet access) • Professional services, such as digital satellite news gathering DVB - An Overview

  19. Transmission • DVB-S2 • Best transmission performance • LDPC codes concatenated with BCH codes • Variable and adaptive coding and modulation (recovers rain margin) • Approximately 30 % capacity increase compared to DVB-S • Maximum flexibility • framing structure • variable and adaptive coding and modulation • can operate in any existing satellite transponder • accommodates any input stream format (188-byte MPEG-2 transport streams (packets), continuous bit streams, IP, ATM) DVB - An Overview

  20. Transmission Performance of LDPC codes over AWGN channel (N=64800) DVB - An Overview

  21. Transmission M. Eröz et al., An innovative LDPC code design with near-Shannon-limit performance and simple implementation, IEEE Trans. Communications, vol.54, no.1, pp.13-17, January 2006. Comparison of DVB-S2 (LDPC+ BCH) codes to DVB-S (convolutional+ RS) and channel capacity DVB - An Overview

  22. Transmission • For each code rate, a parity-check matrix is specified by listing adjacent check nodes for the first bit node in a group of M=360. • Irregular LDPC codes are used, where degrees of bit nodes are varying. • DVB-S2 offers more than 30% capacity improvement • DVB-S2 is, on average, about only 0.7-0.8 dB away from Shannon limits. DVB - An Overview

  23. Transmission • DVB-C • Published in 1994 • Modulation: M-QAM with M=16, 32, 64,128 or 256. • Only RS coding is used (no convolutional coding). • DVB-H • Published in November 2004 • Enables the reception of digital TV signals by handheld devices • Additional FEC, in-depth interleaving and time slicing DVB - An Overview

  24. Transmission • DVB-T, published in 1997, uses OFDM transmissions • OFDM has 2K (subcarriers), 4K and 8K versions • OFDM allows single-frequency network (SFN) operation • Modulation: QPSK, 16-QAM or 64-QAM. • Hierarchical modulation: High and low priority streams are modulated onto a single DVB-T stream for SDTV and HDTV • Reception by roof-top antenna, portable and mobile reception • DVB-T is adopted in large parts of the world with • built-in front-ends set-top-boxes • PCI cards and USB boxes for desk-top PCs • PCMCIA modules for lap-top PCs • DVB-T reception in cars in driving speeds DVB - An Overview

  25. SFN Range vs Mobility Trade-off • OFDM with 2K: • widest subcarrier spacing, hence least susceptible against Doppler shifts (suitable for high-mobility applications) • shortest symbol duration, hence provides the minimum range for SFN. • OFDM with 8K: • narrowest subcarrier spacing, hence most susceptible against Doppler shifts (suitable for low-mobility applications) • longest symbol duration, hence provides the maximum range for SFN. • OFDM with 4K provides a trade-off between 2K and 8K DVB - An Overview

  26. Hierarchical Modulation • Two separate data streams modulated onto a single DVB-T stream, • high-priority (HP) (low data rate) stream is embedded within a low-priority (LP) (high data rate) stream • Receivers with good reception conditions can receive both streams • Only HP streams are received in bad channel conditions, e.g., mobile and portable reception DVB - An Overview

  27. Hierarchical Modulation HP bit stream (QPSK) An example of a constellation diagram for hierarchical modulation LP bit stream (64-QAM) DVB - An Overview

  28. Hierarchical Modulation • Broadcasters can target two different types of DVB-T receiver with two completely different (LP or HP) services • LP stream is of higher bit rate, but lower robustness than the HP one; • hence, a trade-off between service bit-rate versus signal robustness • A broadcast could choose to deliver HDTV in the LP stream. DVB - An Overview

  29. Transmission Choice of parameters for non-hierarchical DVB-T transmission U. Ladebusch and C.A. Liss, Terrestrial DVB, Proc. IEEE, vol.94, no.1, pp. 183-193, Jan 2006 DVB - An Overview

  30. Transmission • Useful bit rate (Mbit/s) for all combinations of guard interval, constellation and code rate for non-hierarchical systems for 8 MHz channels (irrespective of the transmission modes) DVB - An Overview

  31. Transmission • For the hierarchical schemes the useful bit rates can be obtained from the table as follows: • HP stream: figures from QPSK columns; • LP stream, 16-QAM: figures from QPSK columns; • LP stream, 64-QAM: figures from 16-QAM columns. DVB - An Overview

  32. Transmission Minimum C/N ratio in the transmission channel required for quasi-error-free (QEF) reception for DVB-T • QEF reception: BER <10-11 at the output of the RS decoder DVB - An Overview

  33. Interaction Channels

  34. Interaction Channels • The data belonging to a certain interactive service is transmitted in the broadcast channel • The interaction channel enables the user to respond in some way (for instance via the standard remote control ) to the interactive service. • The service provider or network operator listens and reacts to that response. DVB - An Overview

  35. Interaction Channels Generic system reference model used by DVB for interactive services U. Reimers, DVB-the family of international standards for DVB, Proc. IEEE, vol.94, no.1, pp.173-181, Jan. 2006 DVB - An Overview

  36. Interaction Channels • The user’s response may take the form of some simple commands, like • voting in a game show, • purchasing goods advertised in a shopping program. • Interactive services may take the form of full Internet access at the receiver. DVB - An Overview

  37. Interaction Channels • DVB broadcast channels can deliver information at typical rates of • 20 Mbps per channel for terrestrial broadcast networks, • 38 Mbps per channel for broadcast networks via satellite and cable. • Capacity of interaction channel may range from a few kbps to up to 10 Mbps in cable networks. DVB - An Overview

  38. Interaction Channels • Return Channel Terrestrial (RCT): • Multiple access: OFDMA • Coding: Turbo or RS+ convolutional • Several kbps per TV viewer in cells with 65 km radius • Can handle large peaks in traffic • Use any gaps or under-utilised spectrum • Serve portable and mobile devices • Can operate in 6, 7 and 8 MHz channels • Transmit power < 0.5 W rms • Time interleaving against impulsive interference DVB - An Overview

  39. Interaction Channels Simplified diagram of a network architecture for DVB return channel satellite systems (RCS) V. Paxal, DVB with return channel via satellite, DVB-RCS200, www.dvb.org DVB - An Overview

  40. The Multimedia Home Platform (MHP)

  41. The Multimedia Home Platform • The MHP specification defines an interface between a digital TV and the network to be connected to in order to support interactive services. • It provides features and functions required for the • Enhanced Broadcast, • Interactive Broadcast, • Internet Access. • The right to use the MHP logo is only granted to those MHP implementations that pass some 10000 tests, defined by ETSI. DVB - An Overview

  42. The Multimedia Home Platform • MHP offers true multimedia services to TV users. • MHP provides a technical solution for the user terminal enabling the reception and presentation of applications in an environment that is • independent of specific equipment vendors, • application authors, • broadcast service providers. DVB - An Overview

  43. The Multimedia Home Platform • Some examples: • Electronic program guides for the channels/services provided by a broadcaster • Information services (superteletex, news tickers, stock tickers) • Enhancements to TV content (sporting and voting applications and local play-along games) • E-commerce, e-government and other applications relying upon secure transactions • Educational applications DVB - An Overview

  44. DVB over IP-based Networks

  45. DVB over IP-based Networks • A typical IPTV service involves the delivery of broadcast television, radio and similar on-demand services over IP networks, • hence, a bi-directional IP communication. • An open IP infrastructure is used to reach the customers that can not be reached via classical broadcast networks. • Thus, the geographical reach of DVB services can be extended using broad-band IP networks. DVB - An Overview

  46. DVB over IP-based Networks Basic IPTV architecture www.dvb.org DVB - An Overview

  47. DVB over IP-based Networks • The work on IPTV can be divided into three areas: • Set-top boxes and personal video recorders (PVR), • Home networking, • Additions to the Multimedia Home Platforms (MHP). • A specification has been developed that describes the transport of MPEG-2 based DVB services over IP-based networks. • Creation of a wireless home network segment is soon expected. DVB - An Overview

  48. DVB-Handheld

  49. DVB-Handheld • The system takes into account the specific properties of typical DVB-H terminals: • Battery-powered • User mobility • Handover between cells • Mobile multipath channels (antenna diversity) • High levels of man-made noise • Indoor and outdoor operation • Flexibility to operate in various transmission bands and channel bandwidths (to operate in various parts of the world) DVB - An Overview

  50. DVB-Handheld • DVB-H requires some additional features in the link layer of the existing DVB-T standard; • Existing receivers for DVB-T are not disturbed by DVB-H signals • The additional elements in the link layer: • Time slicing • to reduce the average power in the receiver front-end significantly (significant power savings in the receiver) • to enable smooth and wireless handover when the users leave one service area as they enter a new cell DVB - An Overview

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