1. University of Canberra Advanced Communications Topics
Television Broadcasting into the Digital Era
Lecture 4
Error Correction,
DTTB Planning &
System Information
by: Neil Pickford 1

2. 64-QAM - Perfect & Failure
These figures are real 64-QAM system constellations for both a no noise “perfect” condition and at the failure threshold due to white noise. In the system on the right the data eye is no longer visible but the system is still just working. Again notice in the perfect case that there are some errant points in-between the main constellation points.

3. COFDM DTTB Block Diagram
Error Correction

4. Forward Error Correction (FEC)
Broadcast transmission
One way process - Tx to Rx
Not possible to repeat any errored data
Forward Error Correction is a technique used to improve the accuracy of data transmission
Extra redundant bits are added to the data stream
Error correction algorithms in the demodulator use the extra FEC bits to correct data errors
C OFDM uses a Convolutional FEC code
Encode
N bits
Tx/Rx
N+Code
Decode
N+Code+Error
N bits

5. Convolutional Coder X Output 1111001 Data Input 1-Bit Delay 1-Bit
Y Output

6. Puncturing Codes (FEC)
The X and Y outputs of the Convolutional coder are selected in a Puncturing pattern

7. Inner Coding Convolutional coder generates the X & Y codes
Puncturing operation selects X & Y in sequence
Result then scrambled with an interleaver X Y
Convolutional
Encoder
Coded
Data
Puncturing
Interleaver
Data

8. Viterbi Decoder
A special type of data decoder designed to work with convolutional FEC codes
Uses the past history of the data to identify valid future data values
Element in the Receiver Only

9. Reed Solomon (RS) RS is a Block data correcting Code
Hamming type cyclic Polynomial sequence
Code Generator Polynomial: g(x) = (x+l0)(x+l1)(x+l2)...(x+l15), l=02 Hex
Field Generator Polynomial: p(x) = x8 + x4 + x3 + x2 + 1
Has special ability to correct multiple bursts of errors in a code block
DVB-T uses 204 bytes for each 188 byte Packet (ATSC uses 207 bytes for each 187 byte Packet)
Can correct 8 bytes in each 204 byte packet

10. Error Protection - Order
188
Bytes
204
Bytes
Outer Code RS
(204,188)
Inner Code
FEC
(2/3)
Data
Input
306
Bytes
Interleaver
Interleaver
204
Bytes
2448
Bits
Mapper
Error
Protected
Data
6 bits x 1512 Carriers 6 bits x 6048 Carriers
64 QAM

11. DVB-T - Bit Rates [2k] 7 MHz Code Rate 1/2 2/3 3/4 5/6 7/8
D/Tu = 1/4
D/Tu = 1/8
D/Tu = 1/32
7 MHz
64 us
32 us
8 us
Code
Rate
QPSK
16 -
QAM
64 -
1/2
2/3
3/4
5/6
7/8
4.35
5.81
6.53
7.26
7.62
8.71
11.61
13.06
14.51
15.24
22.86
21.77
19.59
17.42
4.84
6.45
8.06
8.47
16.93
16.13
12.90
9.68
19.35
24.19
25.40
5.28
7.04
7.92
8.80
9.24
18.47
17.59
15.83
14.07
10.56
21.11
23.75
26.39
27.71
Page 21 Table A1 - AS

12. Simulated Theoretical Thresholds (bandwidth independent)
DVB-T - C/N Values
GAUSSIAN
RICEAN
RAYLEIGH
Code
16 -
64 -
QAM
16 -
64 -
16 -
64 -
QPSK
QPSK
QPSK
Rate
QAM
QAM
QAM
QAM
QAM
1/2
3.10
8.80
14.4
3.60
9.60
14.70
5.40
11.20
16.00
2/3
4.90
11.1
16.5
5.70
11.60
17.10
8.40
14.20
19.30
3/4
5.90
12.5
18.00
6.80
13.00
18.60
10.70
16.70
21.70
5/6
6.90
13.5
19.30
8.00
14.40
20.00
13.10
19.30
25.30
7/8
7.70
13.9
20.10
8.70
15.00
21.00
16.30
22.80
27.90
Simulated Theoretical Thresholds (bandwidth independent)

13. C/N - Signal Level Performance28 24 20 16
C/N Threshold (dB) 12 8 4 10 15 20 25 30 35 40 45 50 55 60
Receiver Signal Level (dBuV)

14. General Parameters - Aust Tests
Parameter DVB-T ATSC
Data Payload Mb/s Mb/s
Carriers
Symbol Time us 93 ns
Time Interleaving 1 Symbol 4 ms
Reed Solomon code rate 188/ /207
IF Bandwidth (3 dB) MHz 5.38 MHz
There are 120 modulation options available for 7 MHz DVB-T. We chose a mode which was comparable with ATSCs one mode. DVB-T was a 7 MHz system in a 7 MHz channel while ATSC was tested as a 6 MHz system in a 7 MHz channel 19

15. 8VSB vs COFDM Latest

16. 7 MHz COFDM Modulator Spectrum
-10
-20
Power Spectrum Density (dB)
-30
-40
8k 1/32 Guard
2k 1/32 Guard
-50 -8 -7 -6 -5 -4 -3 -2 -1 1 2 3 4 5 6 7 8
Frequency Offset (MHz)

17. Frequency Planning Fundamental Matter - Scarce Resource
Analogue Rules set limit to more Services
No NEW TV Spectrum is Available
Digital Transmission changes Rules
Signals have different behaviour
Digital Signals can occupy unused space - “Taboos”
Digital Needs to fit in with Existing PAL
Eventually Digital Only - but long wait??

18. 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 28 29 30 31 32 33 34 35 28 29 30 31 32 33 34 35
Why would the channel spacing matter?
It means that we need a special 7 MHz channel varient for us. The diagram shows 6,7 & 8 MHz channel spacings at UHF starting at channel 28. You can see that by the time we get to channel 35 we are over a channel out. If nothing else this means that Digital TV receivers for Australia will need a flexible tuning system which allows for 7 MHz spacings instead of 6 or 8 MHz. This would mean a software change. 28 29 30 31 32 33 34 35

19. 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
Ch 9
Ch 9A
I talked earlier about there being problems with channel spacing and taboo channels. Analog TV cannot cope with another analog service in the adjacent channel without some interference occuring. An analog service in channel 8 above would interfere with channel 7 & 9 in the same area. Digital has been designed to use these inbetween channels without interfering with the Analog service.
Taboo
Taboo
Taboo
VHF Television Spectrum

20. 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
Ch 7
Ch 8
Ch 9
Ch 9A
The digram here shows the spectrums of both 8-VSB and COFDM in the adjacent channels 6 & 8. Note that the 8-VSB has a lot more room at the edge of the channel. This is because it is a 6 MHz system operating in a 7MHz channel. The COFDM signal gets very close to the sound subcarriers of channel 7.
Because it is in the same area as current transmissions the antennas & towers can be shared by combining the signals. This avoids constructing new towers but does need some complex combiners to be built.
8-VSB
COFDM
VHF Television Spectrum

21. DTTB & PAL

22. UHF Channels: London Photograph by courtesy and © BBC R&D
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

23. Planning Issues Channel Disturbances: Antenna Pattern?
Noise, at edge of area with NO interference
Interference, Co Channel Interference and Adjacent Channel Interference
Multipath, Echoes:How Many, How Large, Moving?
Antenna Pattern?
Static Roof Top? Directional? Wideband?
CCIR Antenna Rec BT-419-3
Portable Receivers? No Antenna?
Frequency Re-Use Distances
Terrain Data
Propagation Models
Protection Ratios

24. Signal Strength SIGNAL STRENGTH, MicroVolts MEAN RECEIVER C/N LIMIT
REGION OF SERVICE
FAILURES FOR
PERCENTAGE
OF TIME
MEAN
RECEIVER C/N LIMIT
TIME

25. 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: % availability at % of locations
At the edge of the analog service area at 50% of the locations in that area you will have a “good” service at least 50% of the time. This is because analog TV has a slow and gradual failure mechanism.
Digital has a cliff edge failure, Its either perfect or its nothing. So we have to change these planning numbers to achieve 90-99% availability at 90-99% of locations.

26. TV System Failure Characteristic
Good
Quality
Edge of
Service
Area
The real problem arises in the shaded area where people outside the analog service area have been receiving “fortuitos” reception of analog, usually with a poor picture, but will receive no digital service.
This will be a difficult problem to deal with, as some of the people in these areas have gone to great lengths to get capital city reception.
Rotten
Close
Far
Distance

27. TV System Failure Characteristic
Good
Quality
Edge of
Service
Area
The real problem arises in the shaded area where people outside the analog service area have been receiving “fortuitos” reception of analog, usually with a poor picture, but will receive no digital service.
This will be a difficult problem to deal with, as some of the people in these areas have gone to great lengths to get capital city reception.
Rotten
Close
Far
Distance

28. TV System Failure Characteristic
Good
HDTV
PAL
Quality
SDTV
Edge of
Service
Area
The real problem arises in the shaded area where people outside the analog service area have been receiving “fortuitos” reception of analog, usually with a poor picture, but will receive no digital service.
This will be a difficult problem to deal with, as some of the people in these areas have gone to great lengths to get capital city reception.
Rotten
Close
Far
Distance

29. Service Area Planning DIGITAL 10 15 20 25 30 35 40 45 PICTURE QUALITY
Modulation
Dependent
Variation 4
ANALOGUE 3
THRESHOLD OF
ACCEPTABILITY 2
Typical
Choice of
C/N
ANALOGUE
FAILURE
C/N 1 NO
SERVICE 10 15 20 25 30 35 40 45

30. Service Areas - Current
KILOMETRES
TRANSMITTER A
TRANSMITTER B

31. Service Areas - SFN
KILOMETRES
TRANSMITTER B

32. 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
I mentioned SFNs earlier. This is a feature of the COFDM modulation technology which allows reuse of the same spectrum in the same coverage area, and thus greater spectrum efficiency. The circles represent the coverage in Canberra, Green being the main transmitter and the other circles being existing or future translators which all use separate channels with Analog TV. Using a SFN all these fill in transmitters could be on the same frequency. Unfortunately we cannot use the digital SFN technique in channels adjacent to existing analog services, so this will be a restriction on the use of this technique, until the analog services can be switched off at the end of the simualcast period.
SFNs must have exactly the same data on each transmitter.

33. MPEG Packet

34. System Level Multiplexing Approaches
Video PES
Video Data
Video Encoder
Packetizer
PS Mux
Program Stream
Audio Data
Audio Encoder
Packetizer
Audio PES
TS Mux
Transport Stream

35. Packetisation Approaches
Fixed Length
Audio
Video
Audio
Audio
Video
Video
Video
Audio
Audio
Video
Video
Audio
Video
Audio
Audio
Transport Stream
Audio
Video
Audio
Video
Program Stream
Variable Length

36. Adaptation Header (Variable Length)
Transport Stream
188 Bytes
Adaptation Header (Variable Length)
4 Bytes
Payload
not to scale
Link Header
Link Header Format
sync_byte (0x47)
Adaptation header packet payload
13 bit PID or
4 bit: continuity_counter
1 bit: transport_priority
1 bit: payload_unit_start_indicator
2 bit: adaptation_field_control
1 bit: transport_packet_error_indicator
2 bit: transport_scrambling_control

37. System Information (SI)
Required for :
Automatic Tuning of receiver upon selection
Program location
EPG (Electronic Program Guide)
API (Application Programming Interface)
CA (Conditional Access)

38. DVB SI Model
Satellite
Cable
Terrestrial
Networks
Transponder 1 2 3 T
Channel C
Transport Streams
Service 1 2 3 S
Services
Bouquet
To describe the model for DVB Service Information we have a fairly straightforward hierarchy here.
The networks which are the physical delivery media, which typically provides you several transport streams.
Within a transport stream you have one or more services and the service it’s self is mad up of several components.
If it is a TV service it is at least Audio and Video, you may have several audio components for different languages, you may have subtitling on top of the video or data components.
You can view the services in the time domain when they are made up of a sequence of events for the individual TV programs.
Video
Audio 1
Audio 2
Data
Components

39. System Information
The DVB SI structure has it’s derivation in MPEG ISO/IEC and is defined in a set of tables.
The primary link between DVB SI and MPEG is the“PSI” (Program Specific Information) in MPEG and is contained primarily in the “PAT”, “PMT” and “CAT” set of tables

40. What is SI? SI data provides information for:
Automatic tuning to transport stream
User Information for:
Service selection
“Event” selection
“Component” selection
PSI data provides information for:
Configuration of decoder for selected Service
DVB extensions for non-MPEG components
DVB has added data on top of the PSI to complement it, so you get an environment which supports automatic tuning and information for user selection.
So relative to the analogue environment where the user is very coupled to what is going on in the technical sense, choosing physical channels, and then if you want some program information you need to be aware there is a teletext system which you need to select. You go to that and select a particular page, which is all very primitive compared to what you can do with the PSI and SI data streams. They allow a pretty seamless environment for a user interface on a digital TV system.
DVB extensions to the PSI have been defined for teletext and subtitling.

41. PSI and DVB SI Tables DVB OPTIONAL MPEG DVB MANDATORY NIT NIT PAT PMT
ACTUAL
Delivery Sys.
PID=Ox0011
PID=0x0010
PID=0X0012
NIT
OTHER
Delivery Sys.
PID=Ox0001
PID=0x0000
PID=0X0002
PID=P
PID=0x0010
PAT
SERVICE
DESCRIPTION.
NETWORK
INFORMATION.
EVENT
BOUQUET
BAT
PMT
PID=Ox0011
SDT
OTHER TS
CAT
SDT
ACTUAL TS
PID=Ox0011
TSDT
EIT
ACTUAL TS
EIT
OTHER TS
ACTUAL
PCR
TDT
TOT
TIME
OFFSET.
RST ST
PROGRAMME
CLOCK REF.
TIME AND
DATE.
RUNNING
STATUS.
STUFFING
TABLE.

42. MPEG Program PIDs What is a program ?
MPEG has a definition which is different to that normally understood.
A “program” in broadcasting is a collection of elements with a common time base and the same start and stop times.
A program in MPEG is a collection of elements with a common time base only. That is a collection of elementary streams with same PCR_PID and referenced to the same program_number

43. Virtual Channels & PCR Timing
A conventional Broadcaster of a TV channel or service having one program would be composed of a series of “broadcaster programs” or events with the same program_number and a common PCR_PID.
In other words the PCR time base effectively creates a virtual channel which may be associated with a single or multiple program_numbers.
A TV channel having multiple programs would have multiple program_numbers with either single or multiple PCR_PID between program streams.
NOTE : Services with different program_numbers may draw upon the same video as with the case of multilingual services.

44. Decoding the Program Decoding the correct program (ie “channel”) ?
Where there are several Transport Streams available to a decoder, in order to successfully demultiplex a program, the decoder must be notified of both the transport_stream_id (to find the correct multiplex) and the program_number of the service (to find the correct program within the multiplex).
Note again the program here refers to the channel not the event or actual broadcast program.
Now to the various main table purposes :

45. PAT, PMT & CAT Tables PAT (Program Association Table)
provides the link between the transport_stream_id, the program_number and the program_map_id (PMT).
PMT (Program Map Table)
when pointed to from the PAT, the PMT provides the associated group of elements (video, audio etc) with the program_number.
CAT (Conditional Access Table)
provides the association between CA system(s) and their EMM (Entitlement Management Messages) streams and any special parameters associated with them.

46. DVB SI Features Data structured as several “Tables”
Structures use “fixed format” for essential data, and descriptors for optional or variable-length data (similar to PSI)
Efficient data transmission
Extensible while maintaining compatibility
Support for “private” extensions
Can provide standard EPG data-stream
“Look and Feel” determined by receiver software
Resident or Downloaded
We have items called tables.
Combination of “Fixed format” and “variable length” descriptors.
Fixed format - particular bytes in a table have a pre-determined meaning. The structure is particularly efficient as the definitions are already pre-known to the decoder.
The variable length descriptors are a sequence known as TLV. Tag Length Value. Where the tag identifies the data that is to follow, the length indicates the length of the data. You have a very flexible format with a sequence of descriptors which allows you to carry almost anything, which is extremely useful when you want flexibility, but obviously not as efficient as fixed format because of the overhead of the T and the L instead of just the V.
The combination is also used for PSI transmission. The descriptors give the right combination of efficiency and we use descriptors to achieve extensibility. It also gives support for additions to the specification whether defined by DVB or in particular implementations which add their own extensions without interfering with the basic specification.
DVB-SI can be regarded as a standard EPG format, in terms of the transmitted data but the presentation, look and feel is determined by the receiver software. That software could be a fixed or temporary application downloaded as part of the broadcasters bitstream. This allows particular broadcasters can have their own look and feel for the EPG.

47. SI Features: NIT Network Information Table
Identification of transmission as a member of a group of multiplexes - “Network”
Network Name
Tuning parameters with support for various delivery media
List of additional frequencies for terrestrial transmission
Designed for simple transcoding of transport streams
This provides the description of the transport streams that is carried by the physical media. This is known as a Network.
The user can select the Network name.
A special challenge for terrestrial media is that you typically have a number of signals carrying the same transmission by virtue of relay transmissions. To allow this the specification added a list of additional frequencies.
NTI designed to allow moving the transport stream from one delivery medium to another, like from satellite to cable or terrestrial to cable. The NIT is relatively small and is easy to replace in the transport stream, without having to modify the whole transport stream. That is an operation you can do on a transport stream at relatively low cost.

48. SI Features: SDT & BAT Service Description Table
Identifies all Service names and Service types in TS
Linked Services
Pointer to MPEG Program in PSI
Service_id = MPEG Program Number
Bouquet Association Table (Optional)
Groupings of Services
May convey “logical channel number”
SDT
Linkages between services can be identified. If one service is a part time service then when it stops running you can identify another service that would be good for the receiver to select automatically.
BAT
This is optional. You do not have to transmit it but in some situations it could be useful.
Logical channel numbers
This is a way of identifying particular service by a number which is the way we view analogue services today. When DVB developed the Service Information specification they very much thought there would be so many channels, you would never remember the numbers, and obviously you would want to select them by the service names. In practice where every system has been implemented it actually makes use of logical channel numbers.

49. SI Features: EIT Present/Following Schedule (optional)
Information on current and next events
Schedule (optional)
Up to 64 days ahead - ordered by service and time
Event Information
Title, short description
Start time & duration
Content classification & parental rating
Longer text description
Information on components
The EIT comes in two flavors.
The present / following information which tells you what is on now and what is on next
The EIT Schedule which allows you to give the information for further ahead.

50. SI Features: TDT,TOT, RST
Time and Date Table
Transmission of current time for automatic setting of receiver clock
Time Offset Table (optional)
Transmission of time offset by zone - both current, and next offset values, with date at which next occurs
Running Status Table (optional)
Mechanism for signalling status transitions with greater timing precision
The transmission of the time and date is done in UTC, and the SI event times are also done in UTC which avoids the complications and confusions which always arise in software at daylight saving transitions.
Daylight savings transitions are handled by the Time Offset Table.
The RST is probably a rather futuristic table, with current implementations not having the speed of operation in the decoder to take advantage of the greater timing precision. It is rather difficult to generate a data stream that achieves the greater timing accuracy that this could offer.

51. Electronic Program Guide - EPG
EPG (Electronic Program Guide)
Combining primarily the EIT and the SDT, both the time and description is provided to the viewer via some form of EPG ranging from “vanilla EPG’s”, simple “eye plate style” displays to full blown EPG’s, either from Receiver manufacturers designs or downloaded EPG’s with GUI interfaces designed by the Networks.
This information so constructed and displayed can be used to provide a Parental Guidance lock function through PIN number access.

52. Example EPG using DVB SI
As an illustration this is a screen shot of an electronic program guide (EPG) implemented entirely using DVB-SI.
We have services down the side and time across the page.
The services are identified by their service name and also here by the logical channel number.
The event name is displayed from the EIT, with a sequence of event names with the start time and duration reflected by their position relative to the top scale.
The current time is shown, taken from the TDT.
Where the item does not fit in the space, it is not part of the transmission to determine how you truncate it. The receiver software determines this which is part of the look and feel of the box.
What you see on the screen from a different implementation might have more or less time, a different number of channels or the whole appearance could be completely different.
The basic information is all conveyed by the DVB-SI specification.

53. Example: Event Details
When an event is selected additional information is displayed.
Channel Name, Event name
Start time and duration's are worked out.
The General Rating from the parental rating
Some private data has been used here to indicate family viewing.

54. Example: Selection by Genre
Another way of selecting programs is via the content classification
Here is a list of some of the DVB classifications.
You can scroll along the table to reveal more than what are shown on the screen.

55. Example: Selection by Genre
If you select on a particular classification you get a list of events in order of start time which fit that classification.

56. Application Program Interface API
API (Application Programming Interface)
some form of API must be used to allow the control by the viewer or installer of the decoder / receiver. The API software provides the connection between the applications (eg. EPG) and the hardware.
Some API’s may employ MHEG-5 multimedia support and Java programming language for EPG generation.
CA in practice is reliant upon EPG’s and the API’s.

57. DVB - Conditional Access
CA (Conditional Access)
Access to the EMM (Entitlement Management Message) is provided by the CAT.
The EMM allows a single decoder to view the program material which is scrambled via a DVB “common scrambling algorithm” by providing the key to the code word which is involved in the scrambling. The code word is sent via the ECM (Entitlement Control Message).

58. Typical Conditional Access System

59. A Future Digital System Concept
MMDS
Hypermedia Integrated Receiver Decoder (IRD)
Satellite
Terrestrial
Cable
Broadcast
Interactivity
What will the future home digital system components be? The IRD will be the central hub of the home television and information system.
Interactivity will be via Cable or the Telephone line. Inputs can be from Satellite, MMDS, Cable or Terrestrial.
It will primarily be controlled by a IR remote control and on screen menus. It will most likely link not only to a display device and DVD/DVC but also your home computer, allowing data applications.
B-ISDN XDSL
CD, DVD DVC

60. DTTB Systems Doppler Performance Limits
for current implementations
300
250
UHF
200
VHF - Band III
DOPPLER SHIFT (Hz)
COFDM 2K, 3dB degrade
140
COFDM 2K
100 50
Some interesting doppler effects due to large vehicles were experienced during the field test. ATSC failed when Busses & Trucks passed the field vehicle. The data on this plot comes from the Lab tests but demonstrates the doppler speed sensitivity of the DVB-T system. Note the small red circle in the bottom left corner.
100
200
300
400
500
600
700
800
900
1000
ATSC
see separate curves
SPEED (Km/Hr)
Vehicles
AIRCRAFT
Over Cities
COFDM implementations will inherently handle post and pre-ghosts equally within the selected guard interval.

61. Main Results - Lab Tests
C/N ATSC 4 dB better than DVB-T. This Advantage offset by Poor Noise Figure
DVB-T is better than ATSC for Multipath
ATSC is better than DVB-T for Impulse Noise
ATSC cannot handle Flutter or Doppler Echoes
ATSC is very sensitive to Transmission system impairments and IF translation
DVB-T is better at handling Co-channel PAL
DVB-T is better rejecting on channel interference (CW) 13