1. University of Canberra Advanced Communications Topics
Television Broadcasting into the Digital Era
Lecture 4
DTTB Types
Digital
Modulation Systems
by: Neil Pickford 1

2. Digital Terrestrial TV - Layers
. . . provide clean interface points
Picture
Layer
Multiple Picture Formats
and Frame Rates
1920 x 1080
1280 x 720
50,25, 24 Hz
Video Compression
Layer
MPEG-2
compression syntax or
Data
Headers
Motion
Vectors
Chroma and Luma
DCT Coefficients
Variable Length Codes
Transport
Layer
MPEG-2 packets
Video packet
Audio packet
Aux data
Packet Headers
Flexible delivery of data
DTTB is about layers.
Picture
Compression
Transport/Multiplexing
Transmission
Transmission
Layer
7 MHz
COFDM / 8-VSB
VHF/UHF TV Channel

3. Digital Television Encode Layers
Picture
Coding
Audio Coding
Data
MPEG-2 or AC-3
MPEG-2
Control
Video
Sound
Program 1 Multiplexer
MPEG Transport Stream Mux
Control Data
Bouquet Multiplexer
Program 2
Program 3
Service Mux
Other Data
Control Data
Modulator & Transmitter
Error Protection
Control Data
188 byte packets
MPEG Transport Data Stream
What are the inputs to these layers?
Delivery System

4. Digital Television Decode Layers
Data
Mon
Speakers
Audio Decoder
Data
Decoder
Picture
MPEG or AC-3
MPEG-2
MPEG Transport Stream
De-Multiplexer
MPEG DeMux
Transport Stream
Demodulator & Receiver
Error Control
At the receiver we simply select the portions of the existing data stream we wish to decode and throw away the rest.
Delivery System

5. Set top Box (STB) - Interfacing
Domestic and Professional interfaces still to be defined
Most probably Transport Stream via IEEE 1394 (Firewire)
Baseband Audio & RGB/YUV Video signals.
STB can convert between line standards so you do not have to have a HD display.
Display and transmitted information must be at same Frame/Field rate. (25/50)

6. 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
Broadband multimedia data, news, weather
Best of internet service
Interactive services
Software updates, games
Services can be dynamically reconfigured
DTTB can carry many other things than just television.
Interactive services need a back channel such as the telephone line or a cable/wireless modem.
The analog television we are used to uses a very dumb device to display the pictures.
Digital TV uses a smart box which can be dynamically re-configured. You can choose the change the channel/data structure mid program, upload new operating software with different funtions. No longer will the transmission be totally constrained by the dumb receiver at the other end.

7. DVB Data Containers
MPEG Transport Stream is used to provide DVB “data containers” which may contain a flexible mixture of:
Video
Audio
Data services
Streams with variable data rate requirements can be Statistically Multiplexed together.
Allows Six 2 Mb/s programs to be placed in a 8 Mb/s channel

8. Examples of DVB Data Containers
Channel bandwidth can be used in different ways:
SDTV 1
SDTV 2
SDTV 3
SDTV 4
SDTV 5
Multiple SDTV programs
Single HDTV program
HDTV 1
SDTV 1
HDTV 1
Simulcast HDTV & SDTV
Focusing on the TV aspects.
There are different ways the channel bandwidth can be used.
As has been done in the UK, you can have a multiplex which has multiple standard definition programs within it.
You can also have a multiplex which contains a single High Definition program which is the plan for many situations in Australia.
There is also the facility to have simulcast, where you cut down a bit on the High Definition to allow the older receivers that are there to decode the Standard Definition variant. This may well be used in the future in the UK when the analog transmissions are turned off. The plan in most of Europe is for High definition to be introduced as a second phase as part of the analog turn off.

9. 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
Digital TV will have a data capacity around 20 Mb/s.
For Sport or high action we can have relatively few services.
Films have high levels of temporal redundancy because both fields are scanned from the same frame. This allows the compression systems to perform higher levels of compression allowing spare data capacity and the ability to have more services.
Generally News & Soapies have lower data requirements so more channels are possible.
You do not ge more channels for nothing.
More Services Means Less Quality.

10. 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 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.
An example from tests in America.
Other non-real time services can use opportunistic use of the DTV data pipe to transmit data when the full bandwidth of the channel is not required for the main services. These services would be data specifically intended for broadcast application with no need for acknowledgement or a back channel. Teletext or Newspaper type information are good examples.

11. Enabling Technologies
Source digitisation (Rec 601 digital studio)
Compression technology (MPEG, AC-3)
Data multiplexing (MPEG)
Transmission technology (modulation)
Display technology (large wide screens)
Production
Digital TV has Key Technologies that make it possible. Most production within the current TV stations already happens in the digital domain using standards such as Rec 601 digital video. It only becomes analog when it is transmitted over the air to the viewer.
Display technology has not reached the level needed for HDTV to be fully implementable at present.

12. Digital Television - Types
Terrestrial (DTTB)
DVB-T / 8-VSB
Free to air TV (broadcasting)
Narrowcasting/value added services
Untethered - portable reception
DTTB allows both fixed or portable operation.

13. 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 an un-tethered portable service
What is DTTB?

14. 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
The transmission technology protects the data from the communications environment.
In something like the satellite environment it is very easy since there are not many variable sources of transmission impairment, A terrestrial system has to cope with obstructions, reflections, multipath, and various types of man made interference

15. 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
Being Digital, it is just like any computer data. You put a byte of data into the pipe, you must receive the same byte out the end of the pipe. If it is different at the other end it simply does not work. The testing of these systems had primarily been done (95%) looking at Bit Error Rates (BER), not the displayed pictures. The data is transported in 188 byte groups called packets. 4

16. Digital TV Transmission Systems
Australia has been following Digital TV & HDTV
Europeans - Digital SDTV MHz on UHF - DVB-T (COFDM)
Americans - Digital HDTV MHz VHF/UHF - ATSC (8-VSB)
Japanese - Integrated Broadcasting - ISDB (BST-OFDM)

17. 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 but has not been produced.
Uses a single carrier with pilot tone
8 level amplitude modulation system
Single Payload data rate of Mb/s
Relies on adaptive equalisation
Existing AM technology highly developed
ATSC developed out of the Grand Alliance which resulted at the end of the initial digital television race in America.

18. 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 Payload data rates of 5-27 Mb/s in 7 MHz
Developed for 8 MHz channels
A 7 & 6 MHz variants have been produced and tested.
Can use single frequency networks - SFNs
New technology with scope for continued improvement & development
Multicarrier System
Many different combinations of system parameters
To change the bandwidth of the system you change the master system clock. As the clock rate increases the system carrier spacing & thus bandwidth decreases as an inverse proportion.

19. 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

20. ISDB - Concept
Main TV menu
Newspaper - Categories - Headlines Downloaded overnight
Television Schedule
Weather
Preview of other stations
Time, ,Interactive services
16:9 Display.
Proposed to use band segmented transmission - orthogonal frequency division multiplex (BST-OFDM)

21. 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
The current Analog TV system has lots of problems which can arise in the transmission path and are reflected in a poor quality picture.
We also have problems with planning where to place these services, because we have to avoid known interference mechanisms.

22. 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
Digital modulation distributes the information across the channel bandwidth so the rectangular spectrum shown earlier is produced. This makes more efficient use of the spectrum.
Highly rugged transmission techniques are used for the system synchronisation data such as QPSK and 2 level data. This is because if the system clock is lost, the whole system immediately stops working and may take some time to reaquire lock.
Error correction techniques such as Reed Solomon and Viterbi Coding are used to correct errors in the data.

23. Conventional Single Carrier Multicarrier/Spread Spectrum
Digital Modulation
Two techniques:
Conventional Single Carrier
8VSB
Multicarrier/Spread Spectrum
OFDM
As we have discussed, each IRD contains components which are responsible for the decoding, demultiplexing and demodulation of signals and components which are responsible for decrypting of signals.
NDS licenses its technologies to a number of hardware manufacturers. These include Thomson, Sony, Hughes, Sanyo, Samsung and Panasonic for conditional access, and Pace and Mitsubishi for digital IRD technology
NDS receives upfront integration fees and ongoing royalties under these license arrangements
Core operating software and electronic program guide software are new offerings first being shipped this quarter to StarTV, NetSat and Innova initial licensee - Pace 38

24. 8-VSB & COFDM - Spectrum 8-VSB COFDM
This is a spectrum analyser plot of the two digital systems being considered in Australia. The little hump on the left side of the 8-VSB spectrum (yellow) is the pilot carrier.
These are averaged spectrums and have shoulder levels of around dB
The spectrums are basically rectangular in shape. The COFDM signal is wider since it is a 7 MHz system in a 7 MHz channel while 8-VSB is 6 MHz wide.

25. Sin(x)/x

26. Digital Modulation Amplitude, dB Frequency Fc - Fs Fc + Fs Fc
Spectrum of Conventional Multi-Phase Keyed Carrier Fc at Symbol Rate Fs
Sin X/X shaping
As we have discussed, each IRD contains components which are responsible for the decoding, demultiplexing and demodulation of signals and components which are responsible for decrypting of signals.
NDS licenses its technologies to a number of hardware manufacturers. These include Thomson, Sony, Hughes, Sanyo, Samsung and Panasonic for conditional access, and Pace and Mitsubishi for digital IRD technology
NDS receives upfront integration fees and ongoing royalties under these license arrangements
Core operating software and electronic program guide software are new offerings first being shipped this quarter to StarTV, NetSat and Innova initial licensee - Pace
Frequency
Fc - Fs
Fc + Fs Fc 38

27. Digital Modulation Amplitude, dB Frequency
Low Symbol Rate
Medium Symbol Rate
High Symbol Rate
Amplitude, dB
As we have discussed, each IRD contains components which are responsible for the decoding, demultiplexing and demodulation of signals and components which are responsible for decrypting of signals.
NDS licenses its technologies to a number of hardware manufacturers. These include Thomson, Sony, Hughes, Sanyo, Samsung and Panasonic for conditional access, and Pace and Mitsubishi for digital IRD technology
NDS receives upfront integration fees and ongoing royalties under these license arrangements
Core operating software and electronic program guide software are new offerings first being shipped this quarter to StarTV, NetSat and Innova initial licensee - Pace
Frequency 38

28. PSK

29. BPSK Modulation
I AXIS 1
180 Deg
Phase
Change

30. QPSK Modulation
Q AXIS
1 0
1 1
QPSK
Distance
I AXIS
0 0
0 1

31. 16QAM Modulation Q AXIS 1 0 1 1 I AXIS 0 0 0 1 16-QAM Distance 1 1 1 0
1 0
1 1
16-QAM
Distance
I AXIS
0 0
0 1

32. 8VSB Modulation Q AXIS 1 0 1 1 I AXIS 0 0 0 1 16-QAM Distance 1 1 1 0
1 0
1 1
16-QAM
Distance
I AXIS
0 0
0 1

33. Hierarchical Modulation
Distance
Q AXIS
1 0
1 1
QPSK
Distance
I AXIS
0 0
0 1

34. Digital Modulation Amplitude Frequency Fc - Fs Fc + Fs Fc
Typical Filtered Spectrum to give about half original bandwidth
Occupied Channel Bandwidth
As we have discussed, each IRD contains components which are responsible for the decoding, demultiplexing and demodulation of signals and components which are responsible for decrypting of signals.
NDS licenses its technologies to a number of hardware manufacturers. These include Thomson, Sony, Hughes, Sanyo, Samsung and Panasonic for conditional access, and Pace and Mitsubishi for digital IRD technology
NDS receives upfront integration fees and ongoing royalties under these license arrangements
Core operating software and electronic program guide software are new offerings first being shipped this quarter to StarTV, NetSat and Innova initial licensee - Pace
Frequency
Fc - Fs
Fc + Fs Fc 38

35. 8-VSB Digital Modulation
Amplitude
Application of Vestigial Sideband Filter to give reduced spectral occupancy BUT with destruction of pure Amplitude modulation causing incidental Phase modulation but some power in a small carrier
Occupied Channel Bandwidth
eg 6 MHz in US
As we have discussed, each IRD contains components which are responsible for the decoding, demultiplexing and demodulation of signals and components which are responsible for decrypting of signals.
NDS licenses its technologies to a number of hardware manufacturers. These include Thomson, Sony, Hughes, Sanyo, Samsung and Panasonic for conditional access, and Pace and Mitsubishi for digital IRD technology
NDS receives upfront integration fees and ongoing royalties under these license arrangements
Core operating software and electronic program guide software are new offerings first being shipped this quarter to StarTV, NetSat and Innova initial licensee - Pace
Frequency
Fc - Fs
Fc + Fs Fc
8VSB uses symbol Rate with period 93 nanoseconds 38

36. Normal FDM Guard Band Amplitude, dB Carrier 1 Carrier 2 Frequency
As we have discussed, each IRD contains components which are responsible for the decoding, demultiplexing and demodulation of signals and components which are responsible for decrypting of signals.
NDS licenses its technologies to a number of hardware manufacturers. These include Thomson, Sony, Hughes, Sanyo, Samsung and Panasonic for conditional access, and Pace and Mitsubishi for digital IRD technology
NDS receives upfront integration fees and ongoing royalties under these license arrangements
Core operating software and electronic program guide software are new offerings first being shipped this quarter to StarTV, NetSat and Innova initial licensee - Pace
Frequency 38

37. Traditional SCPC Modulation
Minimum Carrier Spacing
What is this COFDM modulation?
A Traditional Single Carrier Per Channel (SCPC) digital system there is a minimum spacing that you can put two individual carriers apart. It tends to be around 3 times the bessle frequency, where the modulation sidebands dimminish sufficiently to cause minimal interference to the adjacent carrier. SCPC is a type of Frequency Division Multiplex (FDM)
Frequency

38. Orthogonal Modulation
Amplitude, dB
As we have discussed, each IRD contains components which are responsible for the decoding, demultiplexing and demodulation of signals and components which are responsible for decrypting of signals.
NDS licenses its technologies to a number of hardware manufacturers. These include Thomson, Sony, Hughes, Sanyo, Samsung and Panasonic for conditional access, and Pace and Mitsubishi for digital IRD technology
NDS receives upfront integration fees and ongoing royalties under these license arrangements
Core operating software and electronic program guide software are new offerings first being shipped this quarter to StarTV, NetSat and Innova initial licensee - Pace
Frequency 38

39. Orthogonal Modulation
Amplitude, dB
As we have discussed, each IRD contains components which are responsible for the decoding, demultiplexing and demodulation of signals and components which are responsible for decrypting of signals.
NDS licenses its technologies to a number of hardware manufacturers. These include Thomson, Sony, Hughes, Sanyo, Samsung and Panasonic for conditional access, and Pace and Mitsubishi for digital IRD technology
NDS receives upfront integration fees and ongoing royalties under these license arrangements
Core operating software and electronic program guide software are new offerings first being shipped this quarter to StarTV, NetSat and Innova initial licensee - Pace
Frequency 38

40. COFDM - Orthogonal Carriers
COFDM is Coded Orthogonal FDM
If you observe the carrier spacing they are much closer together. This thing called “Orthogonality” is the key. It means that the peak of the yellow carrier (and all others) coincides with a null on every other carrier. Each peak sits directly above a null. You cannot generate these carriers by having individual oscillators mixed together. They are all generated at the same time using an Inverse Fast Fourier Transform (IFFT) using the same clock.
Frequency

41. Almost Rectangular Shape
Spectrum of COFDM DTTB
Carrier Spacing
2k Mode 3.91 kHz
8k Mode 0.98 kHz
Almost Rectangular Shape
These 1000s of carriers form the observed rectangular spectrum.
There are two modes for the system 2K & 8K. This referes to the size of the FFT used to generate and demodulate them. The 2k system has 1705 carriers and the 8k system uses 6817 carriers. The extra locations in the FFT are used to ensure that the signals have a sharp roll-off and good out of channel performance.
1705 or 6817 Carriers
6.67 MHz in 7 MHz Channel

42. OFDM Amplitude, dB Frequency Frequency Fcentre
Occupied bandwidth is: No. of Carriers x Spectral Width. Create with FFT
Amplitude, dB
As we have discussed, each IRD contains components which are responsible for the decoding, demultiplexing and demodulation of signals and components which are responsible for decrypting of signals.
NDS licenses its technologies to a number of hardware manufacturers. These include Thomson, Sony, Hughes, Sanyo, Samsung and Panasonic for conditional access, and Pace and Mitsubishi for digital IRD technology
NDS receives upfront integration fees and ongoing royalties under these license arrangements
Core operating software and electronic program guide software are new offerings first being shipped this quarter to StarTV, NetSat and Innova initial licensee - Pace
Frequency
Frequency
Spectral Width
2k is 4x wider than 8k
Fcentre 38

43. DIGITAL TERRESTRIAL BROADCASTING
Among the four Digital Broadcasting standards available, three are based on the Coded Orthogonal Frequency Division Multiplex modulation.... Why ?
Distant transmitter
Nearest transmitter
The Terrestrial Broadcasting has to cope with multipath propagation and Doppler effects: COFDM is the response for these impairments !

44. COFDM : HOW ?
1 - Organize time & frequency partitions in the RF channel
time
frequency RF
Channel
bandwidth
frequency
sub-band
time
segment

45. COFDM : HOW ? 2 - Spread sub-carriers over “time vs frequency” cells
symbol
Make sub-carriers orthogonal to avoid “inter-carriers” interference

46. COFDM : HOW ?
3 - Insert Guard Interval to avoid “inter-symbol” interference
time
frequency
Useful symbol
duration
Guard Interval
OFDM
symbol
Guard interval introduces a first loss in transport capacity

47. COFDM : HOW ?
4 - Insert “Synchronization Pilots” Helps Receivers to lock onto the signal
time
frequency
FFT
time windows
for receivers
OFDM Frame
(68 OFDM symbols)
Synchronization markers introduce the second loss in transport capacity

48. Protected DATA (convolutionnal error protection codes)
COFDM : HOW ?
5 - Prepare data to be carried on OFDM symbols
time
frequency
DATA to broadcast
Protected DATA (convolutionnal error protection codes)
Protection codes introduce the third loss in transport capacity

49. COFDM : HOW ?
6 - Map bits onto OFDM: Spread contiguous data bits over distant sub-carriers
time
frequency
DATA to broadcast
Protected DATA 1
Create frequency diversity to improve robustness against fading

50. DTTB - Channel Estimation
The Terrestrial transmission channel is continuously varying (position & time)
Variations occur in Amplitude, Phase & Frequency
To correct for this variation Information needs to be added to the transmission to quantify the channels response at any instant
Equalisers in the Digital receiver use this information to remove these transmission impairments

51. Data Multiplex - 8-VSB

52. 8-VSB Segment Sync & Data
Symbol Duration 93 ns

53. Digital Modulation - 8-AM7 6 5 4 3 2 1
Before Equaliser
After Equaliser
8-VSB - Coaxial Direct Feed through Tuner on Channel 8 VHF
3 Bits/Symbol

54. Field Sync is Repeated Every 24 ms
8-VSB - Field Sync
Field Sync is Repeated Every 24 ms

55. 8-VSB - Field Sync 7 6 5 4 3 2 1
Before Equaliser
After Equaliser

56. 8-VSB Frame Sync 832 Symbols per Data Segment of 77.3 µs 313 Data
Training Sequence
313 Data
Segments
of 24.2 ms
Data
Sync
Training Sequence
As we have discussed, each IRD contains components which are responsible for the decoding, demultiplexing and demodulation of signals and components which are responsible for decrypting of signals.
NDS licenses its technologies to a number of hardware manufacturers. These include Thomson, Sony, Hughes, Sanyo, Samsung and Panasonic for conditional access, and Pace and Mitsubishi for digital IRD technology
NDS receives upfront integration fees and ongoing royalties under these license arrangements
Core operating software and electronic program guide software are new offerings first being shipped this quarter to StarTV, NetSat and Innova initial licensee - Pace
Data
The Training Sequence is only 0.3% of signal time
Total Sync is only 0.8% of time 38

57. DVB-T - Carriers + Pilots
0.977/3.906 kHz
Kmin
1704 for 2K or
6816 for 8K
Kmax =
Kmax
SYMBOLS IN SEQUENCE - 68 PER BLOCK.
Modulated Carriers
Scattered Pilots

58. Co- Incident with Scattered pilots
DVB-T Super Frame
45/177
TPS Carriers
Fixed Pilots
Frame 1
Frame 2
Frame 3
Frame 4 54 48 34 50
17/68
1512:
1705
in 2k
6048:
6817
in 8k
Co- Incident with Scattered pilots
Super
Frame
4 x 68
Symbols =
N MPEG
Packets

59. DVB-T Transmission Frame
2k mode Hz - Kmax=1704
8k mode Hz - Kmax=6816
Kmin=0
Carrier Spacing & Position
Kmax
Data
TPS - Pilot
Scattered Pilot
Continuous Pilot
Symbol Duration 256 us (2k) or 1024 us (8k)

60. DVB-T - Estimating the Channel
B=3/4A+1/4E C
C=1/2(A+E) D
D=1/4A+3/4E E E
A to E ms (2k) ms (8k)
For a varying transmission channel
DVB-T estimation is 23.5 times faster than ATSC

61. DVB-T - Estimating the Channel
A B C D E F G
A B C D E F G
B=2/3A+1/3D
C=1/3A+2/3D
E=2/3D+1/3G
F=1/3D+2/3G
A to D kHz (2k) kHz (8k)
For a varying transmission channel
DVB-T estimation is 23.5 times faster than ATSC

62. Channel Estimation & Equalisation
ATSC
Time
DVB-T
Time

63. Estimation Rate Comparison
ATSC Equaliser is updated every 24 ms (~ symbols)
DVB-T Equaliser is updated every symbol period (256 us). 1/12 of data carriers are pilots
DVB-T Full Channel estimate is available every 4 symbols (1.024 ms)
For a varying transmission channel DVB-T estimation is at least 23.5 times faster than ATSC

64. OFDM - Features Multicarrier - many carriers sharing
Reduced C/N compared to Analogue
Resistant to echoes, Interference etc
Low symbol rate per carrier
~ 1 kBaud: Long Symbol Period, can Extend with Guard Interval
With FEC becomes COFDM
Uses Fast Fourier Transform [FFT]
”2k” and “8k” versions
Single Frequency Networks [SFN]