Communications%20Laboratory%20Lecture%20Series

1
Communications Laboratory Lecture Series

• Digital television broadcasting

Presentation by Neil Pickford
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Digital Television Broadcasting DTB

• What is digital TV
• How was it developed
• What are the systems
• Enabling technologies
• Transmission technology
• Compression technology
• Content services
• What is happening in australia
• The future

3
Broad Objectives of DTB

• Overcome limitations of the existing analog
  television systems
• Improved picture
• High quality (no interference)
• Resolution (HDTV)
• Format (169)
• Enhanced service related features
• Additional data capacity available for other
  value added services

4
Digital Media

• First media systems were analog
• Most media are converting to digital
• Computer storage
• Music (LP-CD)
• Telecommunications
• Multimedia
• Radio (DAB)
• Television

5
Standard Definition Television SDTV

• The current television display system
• 43 aspect ratio picture, interlace scan
• Australia/Europe
• 625 lines - 704 pixels x 576 lines displayed
• 50 frames/sec 25 pictures/sec
• 405504 pixels total
• USA/Japan
• 525 lines - 704 pixels x 480 lines displayed
• 60 frames/sec 30 pictures/sec
• 337920 pixels total

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Enhanced Definition Television EDTV

• Intermediate step to HDTV
• Doubled scan rate - reduce flicker
• Double lines on picture - calculated
• Image processing - ghost cancelling
• Wider aspect ratio - 169
• Multi-channelsound

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High Definition Television HDTV

• Not exactly defined - number of systems
• System with a higher picture resolution
• Greater than 1000 lines resolution
• Picture with less artefacts or distortions
• Bigger picture to give a viewing experience
• Wider aspect ratio to use peripheral vision
• Progressive instead of interlaced pictures

8
HDTV - Have We Heard This Before?

• The first TV system had just 32 lines
• When the 405 line system was introducedit was
  called HDTV!
• When 625 line black white came alongit was
  called HDTV!
• When the PAL colour system was introducedit was
  called HDTV by some people.
• Now we have 1000 line systems and
  digitaltelevision - guess what? Its called HDTV!

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Interlaced Vs Progressive Scan

• Interlaced pictures. - 1/2 the lines presented
  each scan1,3,5,7,9,11,13...............623,625
  field 12,4,6,8,10,12,14.............622,624
  field 2
• Because the fields are recorded at separate times
  this leads to picture twitter judder
• Progressive pictures - all the lines sent in the
  one scan.1,2,3,4,5,6,7,8................623,624,6
  25 picture
• No twitter or judder.
• But twice the information rate.

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Question - HDTV

• Have you seen HDTV pictures?

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Do You Use A PC?
All Current Generation PCs use Progressive Scan
and display Pictures which match or exceed
HDTV resolutions although thepixel pitch, aspect
ratioand colorimetry are not correct.
HDTV
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Digital Television

• Why digital?
• Noise free pictures
• Higher resolution imagesWidescreen / HDTV
• No ghosting
• Multi-channel sound
• Other services.

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Digital Television - Types

• Satellite (DBS)
• DVB-S
• Program interchange
• Direct view / pay TV
• SMATV

Downlink
Uplink
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Digital Television - Types

• Cable
• HFC - pay TV
• MATV
• DVB-C / 16-VSB

Fibre
Main Coax
Spur
Tee
Tap
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Digital Television - Types

• Terrestrial (DTTB)
• DVB-T / 8-VSB
• Free to air TV (broadcasting)
• Narrowcasting/value added services
• Untethered - portable reception

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Digital Terrestrial Television Broadcasting - DTTB

• Regional free to air television
• Replacement of current analog PAL broadcast
  television services
• Operating in adjacent unused taboo channels
  to analog PAL service
• Carries a range of services HDTV, SDTV, audio,
  teletext, data
• Providing portable service

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Mobile Digital TV Onboard a Tram in Cologne -
Germany
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How Was Digital TV Developed

• Japanese Europeans wanted to improve analog TV
  - bigger pictures, more resolution
• Japanese developed muse 1125 lines 60 Hz
• Europeans worked on HD-MAC 1250 lines
• Americans broadcasters wanted to protect spare
  unused TV channels from the land mobile service
  and told FCC they required the channels for a
  future analog compatible HDTV system.

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Development Race

• Americans embarked on a HDTV race to develop an
  analog HDTV system
• Digital television was seen as impossible.
• General instruments developed first digital TV
  system for satellite pay TV from experience with
  NASA deep space probes
• HDTV race became a digital HDTV race.
• Race outcome - poor performance but demonstrated
  digital could be done.

20
DTTB Transmission Systems

• 3 systems are being developed at present.
• USA ATSC 8-VSB
• Europe DVB COFDM
• Japan ISDB band segmented OFDM

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8-VSB - USA

• Developed by the advance television systems
  committee - ATSC
• Developed for use in a 6 MHz channel
• A 7 MHz variant is possible.
• Uses a single carrier with pilot tone
• 8 level amplitude modulation system
• Payload data rate of 19.3 Mb/s
• Relies on adaptive equalisation
• Existing technology developed to near limit

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COFDM - Europe

• Developed by the digital video broadcasting
  project group - DVB
• Uses similar technology to DRB
• Uses 1705 or 6817 carriers
• Variable carrier modulation types are defined
  allowing data rates of 5-27 Mb/s in 7 MHz
• Developed for 8 MHz channels
• A 7 MHz variant has been produced and tested
• Can use single frequency networks - SFNs
• New technology with scope for continued
  improvement development

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ISDB - Japan

• Japanese are developing integrated services
  digital broadcasting (ISDB)
• System integrates all forms of broadcasting
  services into one common data channel which can
  be passed by satellite, cable or terrestrial
  delivery systems
• Video services
• Sound services
• Bulk data services
• Interactive data services

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ISDB - Concept

• Proposed to use band segmented transmission -
  orthogonal frequency division multiplex (BST-OFDM)

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BST-OFDM - Japan

• BST-OFDM is a variant of the European COFDM
  system which allows segmenting of the data
  spectrum into 100 kHz blocks.
• 2 receiver bandwidths proposed.
• 500 kHz portable / mobile for sound and data
• 5.6 MHz fixed / mobile for SDTV and LDTV
• 5.6 MHz fixed for HDTV
• Individual band segments can be allocated to
  separate services which can use different
  modulation systems

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BST-OFDM - Japan

• Allows separate services to be replaced for local
  area broadcasting
• Allows for variable ruggedness for fixed / mobile
  / portable reception
• Could straddle other existing services.
• Primarily being developed for japan as a solution
  to cluttered broadcasting spectrum.
• In early stages of development
• No hardware available at this stage

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8-VSB COFDM - Spectrum
8-VSB COFDM
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Traditional SCPC Modulation
MinimumCarrier Spacing
Frequency
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COFDM - Orthogonal Carriers
Frequency
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Spectrum of COFDM DTTB
Carrier Spacing 2k Mode 3.91 kHz 8k Mode 0.98 kHz
AlmostRectangularShape
1705 or 6817 Carriers
6.67 MHz in 7 MHz Channel
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Digital Modulation - 8-AM
7
6
5
4
3
2
1
0
Before Equaliser
After Equaliser
8-VSB - Coaxial Direct Feed through Tuner on
Channel 8 VHF
3 Bits/Symbol
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QPSK
Q
I
2 Bits/Symbol
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16-QAM
Q
I
4 Bits/Symbol
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64-QAM
Q
I
6 Bits/Symbol
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64-QAM - Perfect Failure
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64-QAM and QPSK
Q
I
6 or 2 Bits/Symbol
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Non Uniform 64-QAM
Q
I
2 4 Bits/Symbol
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Non Uniform 16-QAM
Q
I
2 2 Bits/Symbol
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8-VSB - DTV - Development

• 1987 FCC inquiry into future TV systems and
  advisory committee on ATV service was
  established - ACATS
• 1990 digital TV systems developed
• Competitive testing race undertaken
• 1993 poor results announced - grand
  alliance (GA) formed by the contestants.
  - Extra development
• 1994 re-testing of GA system

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8-VSB - DTV - Development

• 1996 FCC adopted ATSC standard
• 1997 each full-power broadcaster loaned a
  second 6 MHz TV channel for
  simalcasting DTV.
• 1997 FCC announced DTV service and mandated
  8 year transition schedule
• 1997 demonstration, laboratory testing and
  field trials of 8-VSB in Australia

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8-VSB - Transition Schedule

• 1/5/99 coverage of 10 largest markets
• 1/11/99 coverage top 30 markets
• 1/5/02 all other commercials on air
• 1/5/03 all non commercial stations
• 2006 switch off analog service and recover
  138 MHz of spectrum

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(No Transcript)
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8-VSB Equipment

• Still at the prototype stage
• First chips are being tested now
• This year domestic receiver

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European Development - DVB

• 1991 European launching group (ELG)
• 1992 ELG developed MoU for cooperation
• 1993 ELG became digital video broadcasting (DVB)
  project - a forum for all interested in digital
  TV to participate in research and development as
  a unified group.
• DVB is a consortium of over 200 network
  operators, broadcasters, manufacturers and
  regulators in 30 countries working together.

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DVB Project

• The DVB philosophy - open, interoperable,
  flexible, market-led, global standards for
  digital TV
• 1980s MAC systems under development gave way to
  all digital technology
• Based on common MPEG-2 coding system
• Integrated set of standards allowing flexible
  operation across cable, microwave, satellite and
  terrestrial distribution

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DVB - COFDM - Development

• Easier satellite (DVB-S) cable (DVB-C) systems
  were developed first.
• DVB-T is the terrestrial member of the DVB family
  of standards.
• OFDM transmission originally developed for cable
  systems, adapted to digital radio broadcasting,
  extended by DVB to digital TV
• DVB-T based on COFDM technology

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COFDM - Transition Schedule

• DTTB test transmission programs are currently
  occurring in Denmark, Holland, Finland, France,
  Germany Italy
• 1998 Britain Sweden on air with SDTV DTTB
  system using UHF band.
• 2001 Spain plans DTTB to be operational,
  achieving 100 coverage by 2010.
• Simulcasting is expected to be around 20 years in
  Europe. Focus is SDTV to EDTV

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COFDM - Commercial Receiver

• News data systems - system 3000

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COFDM DTTB Equipment

• System 3000 - NDS
• Project mummy bear - NDS zenith
• Dvbird - Thomson SGS Philips
• 3 chip receiver - Philips
• Test receiver - ITIS Harris
• Chip set - Hokia Siemens
• Over 20 manufacturers showing hardware

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COFDM - Current Hardware
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Dvbird - Receiver

• 4 VLSI COFDM receiver
• Implements an 8K FFT (2K/8K mode)
• QPSK, 16QAM 64QAM
• 1/4,1/8 1/32 guard intervals
• Onboard tuner

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Enabling Technologies

• Source digitisation (Rec 601 digital studio)
• Compression technology (MPEG, AC-3)
• Data multiplexing (MPEG)
• Transmission technology (modulation)
• Display technology (large wide screens)

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Digital Terrestrial TV - Layers

. . . provide clean interface points. . . .
1920 x 1080 1280 x 720 60,30, 24 Hz
Picture Layer
Multiple Picture Formats and Frame Rates
MPEG-2 compression syntax ML_at_MPorHL_at_MP
Video Compression Layer
Data Headers
Chroma and Luma DCT Coefficients
Motion Vectors
Variable Length Codes
Flexible delivery of data
Packet Headers
Transport Layer
MPEG-2packets
Video packet
Video packet
Audio packet
Aux data
VHF/UHF TV Channel
COFDM / 8-VSB
Transmission Layer
7 MHz
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Digital Television Encode Layers
Video
Data
Sound
Picture Coding
AudioCoding
Data Coding
Control Data
MPEG-2or AC-3
MPEG-2
MPEG TransportStream Mux
Program 1 Multiplexer
Control Data
Program 2
Program 3
Other Data
ServiceMux
Bouquet Multiplexer
Control Data
188 byte packets
MPEG Transport Data Stream
Error Protection
Modulator Transmitter
Control Data
Delivery System
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Digital Television Decode Layers
Speakers
Data
Mon
AudioDecoder
Data Decoder
Picture Decoder
MPEGor AC-3
MPEG-2
MPEG Transport Stream De-Multiplexer
MPEG DeMux
Demodulator Receiver
Error Control
Delivery System
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Transmission Technology

• The transmission system is used to transport the
  information to the consumer.
• The system protects the information being carried
  from the transmission environment
• Current Australian analog television uses the
  PAL-B AM modulation system

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Digital TV Transmission Technology

• The transmission system is a data pipe
• Transports data rates of around 20 Mb/s
• Transports data in individual containers called
  packets

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Terrestrial Transmission Problems

• Multipath interference - ghosts
• Noise interference - snow
• Variable path attenuation - fading
• Interference to existing services
• Interference from other services
• Channel frequency assignment - where to place
  the signal

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Digital Modulation - Functions

• Spreads the data evenly across the channel
• Distributes the data in time
• Maintains synchronisation well below data
  threshold
• Employs sophisticated error correction.
• Equalises the channel for best performance

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Digital Has to Fit In With PAL

• We need a digital system that can co-exist with
  the existing analog broadcast TV currently in use
  in Australia
• We use the PAL-B with sound system G
• Australian TV channels are 7 MHz wideon both VHF
  UHF
• Australia uses
• VHF bands I, II III
• UHF bands IV IV

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Digital Has to Fit In With PAL

• World TV channel bandwidths vary
• USA / japan 6 MHz
• Australian 7 MHz
• Europeans 8 MHz
• Affects- tuning, filtering, interference
  system performance

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35
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33
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30
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35
28
35
34
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Digital Has to Fit In With PAL

• Digital television system development is focused
  in Europe USA
• The systems standards are designed to meet the
  needs of the developers
• They focus on their countries needs first
• Australian input is through standards
  organisations such as the ITU-R

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Channel Spacing

• Existing analog TV channels are spaced so they do
  not interfere with each other.
• Gap between PAL TV services
• VHF 1 channel
• UHF 2 channels
• Digital TV can make use of these gaps

Ch 8
Ch 7
Ch 9
Ch 6
Ch 9A
VHF Television Spectrum
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Digital Challenges

• Digital TV must co-exist with existing PAL
  services
• DTV operates at lower power
• DTV copes higher interference levels
• Share transmission infra-structure
• DTV needs different planning methods

Ch 8
Ch 7
Ch 9
Ch 6
Ch 9A
8-VSB
COFDM
VHF Television Spectrum
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Digital Service Area Planning

• Analog TV has a slow gradual failure
• Existing PAL service was planned for50
  availability at 50 of locations
• Digital TV has a cliff edge failure
• Digital TV needs planning for90-99
  availability at 90-99 of locations

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TV System Failure Characteristic
Good
Quality
Edge of Service Area
Rotten
Close
Far
Distance
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TV System Failure Characteristic
Good
Quality
Edge of Service Area
Rotten
Close
Far
Distance
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Digital Provides New Concepts

• Single frequency networks (SFNs) can help solve
  difficult coverage situations
• SFNs allow the reuse of a transmission frequency
  many times in the same area so long as exactly
  the same program is carried
• Allows lower power operation
• Better shaping of coverage
• Improved service availability
• Better spectrum efficiency

69
Compression Technology

• When low bandwidth analog information is
  digitised the result is high amounts of digital
  information.
• 5 MHz bandwidth analog TV picture º170 - 270
  Mb/s digital data stream.
• 270 Mb/s would require a bandwidth of at least
  140 MHz to transport
• Compression of the information is required

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Compression - Types

• Two types of compression available
• Loss-less compression 2 to 5 times
• Lossy compression 5 to 250 times

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Compression - Loss-less Types

• Picture differences - temporal
• Run length data coding - GIF
• 101000100010001001101 1 4x0100 1101
• 21 bits source 12 bits compressed
• Huffman coding - PKZIP
• Short codes for common blocks
• Longer codes for uncommon blocks
• Lookup tables

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Compression - Lossy Types

• Quantisation - rounding
• Motion vectors
• Prediction interpolation
• Fractal coding
• Discrete cosine transform (DCT)

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Compression - DCT
8x8 Pixels
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MPEG-2 - I, P B Frames
Uncompressed SDTV Digital Video Stream - 170 Mb/s
Picture 830kBytes
Picture 830kBytes
Picture 830kBytes
Picture 830kBytes
I Frame
B Frame
P Frame
B Frame
100 kBytes
12 kBytes
33 kBytes
12 kBytes
MPEG-2 Compressed SDTV Digital Video Stream - 3.9
Mb/s

• I - intra picture coded without reference to
  other pictures. Compressed using spatial
  redundancy only
• P - predictive picture coded using motion
  compensated prediction from past I or P frames
• B - bidirectionally-predictive picture using both
  past and future I or P frames

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MPEG-2

• Compresses source video, audio data
• Segments video into I, P B frames
• Generates system control data
• Packetises elements into data stream
• Multiplexes program elements - services
• Multiplexes services - transport stream
• Organises transport stream data into 188 byte
  packets

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MPEG-2 - Formats ML HL

• MPEG-2 defines profiles levels
• They describe sets of compression tools
• DTTB uses main profile.
• Choice of levels
• Higher levels include lower levels
• Level resolution
• Low level (LL) 360 by 288 SIF
• Main level (ML) 720 by 576 SDTV
• High level (HL) 1920 by 1152 HDTV

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Video Formats - SDTV - 50 Hz
All these formats are Interlaced
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Video Formats - HDTV - 50 Hz
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Common Image Format CIF

• 1920 pixels x 1080 lines progressive scan is now
  being promoted as the world CIF.
• All HDTV systems will need to support this image
  format and then allow conversion to any other
  display formats that are supported by the
  equipment.

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DTTB - Content Services

• DTTB was designed to carry video, audio and
  program data for television
• DTTB can carry much more than just TV
• Electronic program guide, teletext
• Best of internet service
• Broadband multimedia data, news, weather
• Interactive services
• Software updates, games
• Services can be dynamically reconfigured

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Video Program Capacity
For a payload of around 19 Mb/s

• 1 HDTV service - sport high action
• 2 HDTV services - both film material
• 1 HDTV 1 or 2 SDTV non action/sport
• 3 SDTV for high action sport video
• 6 SDTV for film, news soap operas
• However you do not get more for nothing.
• More services means less quality

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Spare Data Capacity

• Spare data capacity is available even on a fully
  loaded channel.
• Opportunistic use of spare data capacity when
  available can provide other non real time data
  services.
• Example 51 secondBMW commercial

The Commercial wasshown using 1080
Lines Interlaced. 60 Mb of data was transferred
during it. In the Final 3 seconds the BMW Logo
was displayed allowing 3 Phone Books of data to
be transmitted.
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Navigation Systems

• The concept of channel numbers for networks may
  disappear with DTV
• Television becomes one of a number of services
  carried within the data pipe.
• Users will select what service or program they
  wish to decode. The box then finds it.
• Each digital transmission can carry program
  directories for all service providers
• This area is still under heavy development

84
Australian Activity

• ABA report on digital television in Australia
  recommended using HDTV
• FACTS have set up a specialists group to advise
  and direct commercial advanced television
  development
• Represents commercial television (7,9,10)
• ABA and communications lab have been assisting
  this group
• NTA, ABC and SBS are not represented
• NTA commenced own trials

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Laboratory Tests

• Tested both COFDM 8-VSB systems
• Investigated operation within the existing
  Australian broadcasting infrastructure
• Systems evaluated as data pipes
• Both systems operate satisfactorily with only
  small operational differences evident
• Report on measurements was produced for the FACTS
  specialists group

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Laboratory Tests - Test Rig
EUT
C/N Set Attenuators
PAL CW
Spectrum Analysers
ControlComputer
DomesticTelevisionReceiver
ModulatorControlComputers
Plot Printing
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Laboratory Tests - Test Rig
Power Meter
PAL CWInterferenceGenerators
RF LO
COFDMModulator
MPEG Mux
MPEG Mux
MPEG Encoder
8-VSBModulator
MPEG Encoder
88
Field Tests

• Field tests conducted in Sydney on VHF channel 8
  during oct-nov 1997
• Both COFDM 8-VSB systems evaluated at over 150
  sites using an ABA field vehicle
• Comparison of the digital and existing PAL
  systems performance at each site
• Concentrating on difficult reception sites
• Report on field trials was produced for the
  FACTS specialists group

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A Future Digital System Concept
MMDS
HypermediaIntegrated ReceiverDecoder (IRD)
Satellite
Terrestrial
Cable
Broadcast
Interactivity
B-ISDNXDSL
CD, DVDDVC
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Future - Things to Be Done

• Decide on digital transmission standard
• Policy HDTV vs multiple SDTV
• Minimum data rates / quality ?
• Multiplex / content provider relationships
• Pay vs free to air
• Sort out service provider issues
• Conditional access systems
• Ancillary data

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The End

• Thankyou for your attention
• Any questions?