Digital Video Broadcasting An Overview

1
Digital Video BroadcastingAn Overview

• Prof. Dr. Mehmet Safak
• Hacettepe University
• Dept. of Electrical and Electronics Engineering
• 06800 Beytepe, Ankara, Turkey
• msafak_at_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
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

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
• DVBs 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

5
Data Broadcasting
6
Data Broadcasting

• A 422 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.

7
Data Broadcasting

• nn

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.
• Todays 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.

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

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.

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.

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)

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.

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.

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

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

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)

20
Transmission

• Performance of LDPC codes over AWGN channel
  (N64800)

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

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 M360.
• 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.

23
Transmission

• DVB-C
• Published in 1994
• Modulation M-QAM with M16, 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

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

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

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

27
Hierarchical Modulation

• An example of a constellation diagram for
  hierarchical modulation

HP bit stream (QPSK)
LP bit stream (64-QAM)
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.

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

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)

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.

32
Transmission

• Minimum C/N ratio in the transmission channel
  required for quasi-error-free (QEF) reception for
  DVB-T
• QEF reception BER lt10-11 at the output
  of the RS decoder

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.

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

36
Interaction Channels

• The users 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.

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.

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 lt 0.5 W rms
• Time interleaving against impulsive interference

39
Interaction Channels
V. Paxal, DVB with return channel via
satellite, DVB-RCS200, www.dvb.org

• Simplified diagram of a network architecture for
  DVB return channel satellite systems (RCS)

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.

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.

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

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.

46
DVB over IP-based Networks

• Basic IPTV architecture
• www.dvb.org

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.

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)

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

51
DVB-Handheld

• The capacity of one DVB-T channel is split
  between three TV programs and an additional eight
  DVB-H services
• Slice duration
• 625 ms
• Bit rate
• 3.2 Mbps
• (2 Mb/625 ms)
• Average bir rate
• 0.4 Mbps(3.2/8)

625 ms
U. Reimers, DVB-the family of international
standards for DVB, Proc. IEEE, vol.94, no.1,
pp.173-181, Jan. 2006
52
DVB-Handheld

• Additional forward error correction (FEC) gives
  an improvement in
• carrier-to-noise (C/N) performance
• Doppler performance in mobile channels
• tolerance to impulsive interference
• e.g., ignition noise in cars.
• In view of the restricted data rates and small
  displays of handheld terminals, it is suggested
  to exchange MPEG-2 video by H.264/AVC.

53
DVB-Handheld

• The extensions to the physical layer of DVB-T
• Bits in transmitter parameter signaling (TPS) are
  upgraded to indicate the presence of DVB-H
  service
• A new 4K OFDM mode adopted for trading off
  mobility and single-frequency network (SFN) size
• All modulation formats (QPSK, 16QAM and 64QAM)
  with nonhierarchical or hierarchical modes can be
  used
• A new way of using the symbol interleaver of
  DVB-T has been defined (to provide tolerance
  against impulsive noise)
• The addition to DVB-T physical layer of a 5-MHz
  channel bandwidth to be used in non-broadcast
  bands.

54
DVB-Handheld

• DVB-H is intended to use the same broadcasting
  spectrum, which DVB-T is currently using.
• DVB-H services can be introduced
• in a dedicated DVB-H network
• now it is possible to select 4K mode or in-depth
  interleavers
• by sharing an existing DVB-T multiplex between
  DVB-H and DVB-T services
• by using the high-priority part of the DVB-T
  hierarchical modulation

55
DVB-Handheld

• Possible applications for DVB-H
• IP datacasting service to handheld terminals like
  mobile phones
• Broadcast services for the mobile phone users
• frequency allocation for simultaneous operation?
• DVB-H is very spectrum-efficient when compared
  with the traditional TV services
• One 8-MHz channel can deliver 30-50 video
  streaming services to the small screen terminals
• 10 times more than SDTV with MPEG-2
• 20 times more than HDTV with AVC

56
Hybrid Networks
57
Hybrid Networks

• Hybrid networks exploit the benefits of both DVB
  and mobile communications to enhance services
  provided to the consumer
• Broadcast networks typically involve wide area
  and high throughput at the expense of high Tx
  powers.
• Mobile communications offer low-power
  transmitters covering smaller areas (cells)
• Network cost per user is higher than for a
  broadcast network

58
Hybrid Networks

• Hybrid Networks
• www.dvb.org

59
Hybrid Networks

• The IP datacast, used by DVB for a system under
  development, integrates DVB-H in a hybrid network
  structure consisting of
• a mobile communications network such as GPRS or
  UMTS, and
• an additional DVB-H downstream.
• In the process of being standardized
• A paid service
• Possibility of handover

60
Hybrid Networks

• Architecture of the IP datacast system
• U. Reimers, DVB-the family of international
  standards for DVB, Proc. IEEE, vol.94, no.1,
  pp.173-181, Jan. 2006

61
Prospects for Future Developments
62
Future Developments

• Mobile communications, digital broadcasting and
  Internet are converging.
• Current achievements of DVB
• Broadcast delivery to fixed, portable and mobilr
  terminals
• Interactivity-capability in receivers
• Data broadcasting over IP-based networks
• Multimedia home platform (MHP) to run software
  applications on all sorts of terminal devices.
• To understand a persons current location,
  availability, and preferred method of
  communication at that moment e.g., a mobile phone
  or a DVB-H terminal.

63
Future Developments

• The focus is now moving to the content itself
• The ubiquitous access to media content requires
• content management, and
• copy protection measures
• Portable content formats
• To deliver or update the content over fixed and
  mobile IP networks (for portable video players)
• TV anytime/anywhere

64
References

• Special issue of Proc. IEEE on global digital
  television, vol.94, number 1, January 2006.
• DVB-T ETSI EN 300 744 V1.5.1 (2004-11)
• DVB-S2 Draft ETSI EN 302 307 V1.1.1 (2004-06)
• DVB-S EN 300 421 V1.1.2 (1997-08)
• http//www.dvb.org
• http//pda.etsi.org/pda/queryform.asp

65
Thanks