Transcript Digital Television Talk v3

Communications Laboratory
Lecture Series
Digital television
broadcasting
Presentation by: Neil Pickford
1
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

2
Broad Objectives of DTB
Overcome limitations of the existing
analog television systems
 Improved picture

 High
quality (no interference)
 Resolution (HDTV)
 Format (16:9)
Enhanced service related features
 Additional data capacity available for other
value added services

3
Digital Media
First media systems were
analog
 Most media are
converting to digital

 Computer
4
storage
 Music (LP-CD)
 Telecommunications
 Multimedia
 Radio (DAB)
 Television
Standard Definition Television
SDTV
The current television display system
 4:3 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
5
lines - 704 pixels x 480 lines displayed
 60 frames/sec 30 pictures/sec
 337920 pixels total
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 - 16:9
 Multi-channel
sound

6
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

7
HDTV - Have We Heard This
Before?
The first TV system had just 32 lines
 When the 405 line system was introduced
it was called HDTV!
 When 625 line black & white came along
it was called HDTV!
 When the PAL colour system was introduced
it was called HDTV by some people.
 Now we have 1000+ line systems and digital
television - guess what? Its called HDTV!

8
Interlaced Vs Progressive Scan
Interlaced pictures. - 1/2 the lines presented each scan
1,3,5,7,9,11,13...............623,625 field 1
2,4,6,8,10,12,14.............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................623,624,625 picture
 No twitter or judder.
 But twice the information rate.

9
Question - HDTV
Have you seen
HDTV pictures?
10
Do You Use A PC?
All Current Generation
PCs use Progressive
Scan and display
Pictures which match
or exceed HDTV
resolutions although the
pixel pitch, aspect ratio
and colorimetry are
not correct.
11
HDTV
Digital Television
Why digital?





12
Noise free pictures
Higher resolution images
Widescreen / HDTV
No ghosting
Multi-channel sound
Other services.
Digital Television - Types

Satellite (DBS)
 DVB-S
 Program
interchange
 Direct view / pay TV
 SMATV
Uplink
13
Downlink
Digital Television - Types

Cable
 HFC
- pay TV
 MATV
 DVB-C / 16-VSB
Fibre
Main Coax
Tap
14
Spur
Tee
Digital Television - Types

Terrestrial (DTTB)
 DVB-T
/ 8-VSB
 Free to air TV (broadcasting)
 Narrowcasting/value added services
 Untethered - portable reception
15
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

16
Mobile Digital TV
Onboard a Tram in
Cologne - Germany
17
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.

18
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.

19
DTTB Transmission Systems

20
3 systems are being developed at present.
USA
ATSC
8-VSB
Europe
DVB
COFDM
Japan
ISDB
band segmented
OFDM
8-VSB - USA


Developed by the advance television systems
committee - ATSC
Developed for use in a 6 MHz channel
A7





21
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
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
A7
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
22
MHz variant has been produced and tested
Can use single frequency networks - SFNs
New technology with scope for continued
improvement & development
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
23
ISDB - Concept

24
Proposed to use band segmented transmission orthogonal frequency division multiplex (BSTOFDM)
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

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Individual band segments can be allocated to
separate services which can use different
modulation systems
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

26
8-VSB & COFDM - Spectrum
8-VSB
COFDM
27
Traditional SCPC Modulation
Minimum
Carrier Spacing
Frequency
28
COFDM - Orthogonal Carriers
Frequency
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Spectrum of COFDM DTTB
Carrier Spacing
2k Mode 3.91 kHz
8k Mode 0.98 kHz
Almost
Rectangular
Shape
1705 or 6817 Carriers
6.67 MHz in 7 MHz Channel
30
Digital Modulation - 8-AM
7
6
5
4
Before Equaliser
3
2
1
0
After Equaliser
8-VSB - Coaxial Direct Feed through Tuner on Channel 8 VHF
3 Bits/Symbol
31
QPSK
Q
I
2 Bits/Symbol
32
16-QAM
Q
I
4 Bits/Symbol
33
64-QAM
Q
I
6 Bits/Symbol
34
64-QAM - Perfect & Failure
35
64-QAM and QPSK
Q
I
6 or 2 Bits/Symbol
36
Non Uniform 64-QAM
Q
I
2 + 4 Bits/Symbol
37
Non Uniform 16-QAM
Q
I
2 + 2 Bits/Symbol
38
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

39
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

40
8-VSB - Transition Schedule
1/5/99
 1/11/99
 1/5/02
 1/5/03
 2006

41
coverage of 10 largest markets
coverage top 30 markets
all other commercials on air
all non commercial stations
switch off analog service and
recover 138 MHz of spectrum
42
8-VSB Equipment
Still at the
prototype
stage
 First chips
are being
tested now
 This year
domestic
receiver

43
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.

44
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

45
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

46
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

47
COFDM - Commercial Receiver

48
News data systems - system 3000
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

49
COFDM - Current Hardware
50
Dvbird - Receiver


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51
4 VLSI COFDM
receiver
Implements an 8K
FFT (2K/8K mode)
QPSK, 16QAM &
64QAM
1/4,1/8 & 1/32 guard
intervals
Onboard tuner
Enabling Technologies
Source digitisation (Rec 601 digital studio)
 Compression technology (MPEG, AC-3)
 Data multiplexing (MPEG)
 Transmission technology (modulation)
 Display technology (large wide screens)

52
Digital Terrestrial TV - Layers
. . . provide clean interface points. . . .
1920 x 1080
1280 x 720
60,30, 24 Hz
Picture
Layer
Video
Compression
Layer
Data
Headers
Motion
Vectors
Multiple Picture Formats
and Frame Rates
MPEG-2
compression
syntax
ML@MP
or
HL@MP
Chroma and Luma
DCT Coefficients
Variable Length Codes
Flexible delivery of data
Packet Headers
Transport
Layer
Transmission
Layer
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Video packet
Audio packet
Video packet
VHF/UHF TV Channel
7 MHz
Aux data
MPEG-2
packets
COFDM / 8-VSB
Digital Television Encode Layers
Control
Data
Video
Picture
Coding
Control Data
MPEG-2
Data
Data
Coding
Sound
Audio
Coding
MPEG Transport
Stream Mux
Program 1 Multiplexer
Program 2
Other Data
Control Data
MPEG-2
or AC-3
Program 3
Service
Mux
Bouquet Multiplexer
MPEG Transport Data Stream 188 byte packets
Control Data
Modulator & Transmitter
Delivery
54
System
Error
Protection
Digital Television Decode Layers
MPEG-2
Mon
Data
Picture
Decoder
Data
Decoder
MPEG Transport Stream
De-Multiplexer
Demodulator & Receiver
Delivery
55
System
Speakers
Audio
Decoder
MPEG
DeMux
Error
Control
MPEG
or AC-3
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

56
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

57
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
58
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
59
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 wide
on both VHF & UHF
 Australia uses:

 VHF
bands I, II & III
 UHF bands IV & IV
60
Digital Has to Fit In With PAL

World TV channel bandwidths vary
 USA /
28
japan 6 MHz
29
30
 Australian
28
29
 Europeans
28
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29
31
32
33
34
35
7 MHz
30
31
32
33
34
35
8 MHz
30
31
32
33
Affects:- tuning, filtering, interference
& system performance
34
35
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
62
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 6
Ch 7
Ch 8
VHF Television Spectrum
63
Ch 9
Ch 9A
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 6
8-VSB
Ch 7
Ch 8
COFDM
VHF Television Spectrum
64
Ch 9
Ch 9A
Digital Service Area Planning

Analog TV has a slow gradual failure
 Existing
PAL service was planned for:
50 % availability at
50 % of locations

Digital TV has a “cliff edge” failure
 Digital
TV needs planning for:
90-99 % availability at
90-99 % of locations
65
TV System Failure Characteristic
Good
Analog
Digital
Quality
Edge
of
Service
Area
Rotten
Close
Far
Distance
66
TV System Failure Characteristic
Good
Analog
Digital
Quality
Edge
of
Service
Area
Rotten
Close
Far
Distance
67
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
68
Compression Technology
When low bandwidth analog information is
digitised the result is high amounts of digital
information.
5 MHz bandwidth analog TV picture

170 - 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

69
Compression - Types
 Two
types of compression available
Loss-less
compression
2 to 5 times
Lossy
compression
5 to 250 times
70
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

71
Lookup tables
Compression - Lossy Types
 Quantisation
- rounding
 Motion vectors
 Prediction & interpolation
 Fractal coding
 Discrete cosine transform (DCT)
72
Compression - DCT
8x8 Pixels
73
MPEG-2 - I, P & B Frames
Uncompressed SDTV Digital Video Stream - 170 Mb/s
Picture 830kBytes
I Frame
100 kBytes
Picture 830kBytes
Picture 830kBytes
B Frame
B Frame
12 kBytes
12 kBytes
Picture 830kBytes
P Frame
33 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
74
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

75
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
Low level (LL)
Main level (ML)
High level (HL)
76
resolution
360 by 288
720 by 576
1920 by 1152
SIF
SDTV
HDTV
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.

79
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

80
Services can be dynamically reconfigured
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
81
Spare Data Capacity



82
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 second
BMW commercial
The Commercial was
shown 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.
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

83
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

84
NTA commenced own trials
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

85
Laboratory Tests - Test Rig
C/N Set & Attenuators
Control
Domestic
Computer Television
Receiver
86
Modulator
Control
Computers
EUT
PAL & CW
Spectrum Analysers
Plot &
Printing
Laboratory Tests - Test Rig
Power Meter
RF LO
PAL & CW
Interference
Generators
COFDM
Modulator
MPEG Mux
MPEG Mux
MPEG Encoder
MPEG Encoder
87
8-VSB
Modulator
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

88
A Future Digital System Concept
MMDS
Satellite
Hypermedia
Integrated Receiver
Decoder (IRD)
Terrestrial
Cable
Broadcast
Interactivity
B-ISDN
XDSL
89
CD, DVD
DVC
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?
91