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University of Canberra Advanced Communications Topics. Television Broadcasting into the Digital Era. Lecture 4 Error Correction, DTTB Planning & System Information. by: Neil Pickford. 64-QAM - Perfect & Failure. COFDM DTTB Block Diagram. Error Correction.

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University of canberra advanced communications topics l.jpg

University of Canberra Advanced Communications Topics

Television Broadcasting into the Digital Era

Lecture 4

Error Correction,

DTTB Planning &

System Information

by: Neil Pickford



Cofdm dttb block diagram l.jpg
COFDM DTTB Block Diagram

Error Correction


Forward error correction fec l.jpg
Forward Error Correction (FEC)

N bits

Encode

Tx/Rx

Decode

N bits

N+Code

N+Code+Error

  • 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


Convolutional coder l.jpg
Convolutional Coder

1111001

X Output

1-Bit

Delay

1-Bit

Delay

1-Bit

Delay

1-Bit

Delay

1-Bit

Delay

Data

Input

1-Bit

Delay

Y Output

1011011

6 5 4 3 2 1 0


Puncturing codes fec l.jpg
Puncturing Codes (FEC)

  • The X and Y outputs of the Convolutional coder are selected in a Puncturing pattern


Inner coding l.jpg
Inner Coding

X

Coded

Data

Data

Y

  • Convolutional coder generates the X & Y codes

  • Puncturing operation selects X & Y in sequence

  • Result then scrambled with an interleaver

Convolutional

Encoder

Puncturing

Interleaver


Viterbi decoder l.jpg
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


Reed solomon rs l.jpg
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


Error protection order l.jpg
Error Protection - Order

Inner Code

FEC

(2/3)

Data

Input

Interleaver

Interleaver

Error

Protected

Data

Mapper

188

Bytes

204

Bytes

Outer Code

RS

(204,188)

306

Bytes

204

Bytes

2448

Bits

6 bits x 1512 Carriers6 bits x 6048 Carriers

64 QAM


Dvb t bit rates 2k l.jpg
DVB-T - Bit Rates [2k]

16 -

64 -

16 -

64 -

16 -

64 -

QPSK

QPSK

QPSK

QAM

QAM

QAM

QAM

QAM

QAM

1/2

4.35

8.71

13.06

4.84

9.68

14.51

5.28

10.56

15.83

2/3

5.81

11.61

17.42

6.45

12.90

19.35

7.04

14.07

21.11

3/4

6.53

13.06

19.59

7.26

14.51

21.77

7.92

15.83

23.75

5/6

7.26

14.51

21.77

8.06

16.13

24.19

8.80

17.59

26.39

7/8

7.62

15.24

22.86

8.47

16.93

25.40

9.24

18.47

27.71

D/Tu = 1/4

D/Tu = 1/8

D/Tu = 1/32

7 MHz

64 us

32 us

8 us

Code

Rate

Page 21 Table A1 - AS4599-1999


Dvb t c n values l.jpg
DVB-T - C/N Values

64 -

QAM

GAUSSIAN

RICEAN

RAYLEIGH

16 -

16 -

64 -

16 -

64 -

Code

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)


C n signal level performance l.jpg
C/N - Signal Level Performance

28

24

20

16

C/N Threshold (dB)

12

8

4

0

10

15

20

25

30

35

40

45

50

55

60

Receiver Signal Level (dBuV)


General parameters aust tests l.jpg
General Parameters - Aust Tests

Parameter DVB-T ATSC

Data Payload 19.35 Mb/s 19.39 Mb/s

Carriers 1705 1

Symbol Time 256 us 93 ns

Time Interleaving 1 Symbol 4 ms

Reed Solomon code rate 188/204 187/207

IF Bandwidth (3 dB) 6.67 MHz 5.38 MHz

19



7 mhz cofdm modulator spectrum l.jpg
7 MHz COFDM Modulator Spectrum

0

-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

0

1

2

3

4

5

6

7

8

Frequency Offset (MHz)


Frequency planning l.jpg
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??


Digital has to fit in with pal l.jpg
Digital Has to Fit In With PAL

28

29

30

31

32

33

34

35

28

29

30

31

32

33

34

35

  • 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


Channel spacing l.jpg
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 9A

Ch 9

Ch 7

Ch 6

Taboo

Taboo

Taboo

VHF Television Spectrum


Digital challenges l.jpg
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 9A

Ch 9

Ch 7

Ch 6

8-VSB

COFDM

VHF Television Spectrum



Uhf channels london l.jpg
UHF Channels: London

Photograph by courtesy and © BBC R&D


Planning issues l.jpg
Planning Issues

  • Channel Disturbances:

    • 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


Signal strength l.jpg
Signal Strength

SIGNAL STRENGTH, MicroVolts

REGION OF SERVICE

FAILURES FOR

PERCENTAGE

OF TIME

MEAN

RECEIVER C/N LIMIT

TIME


Digital service area planning l.jpg
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


Slide26 l.jpg

TV System Failure Characteristic

Good

Quality

Edge

of

Service

Area

Rotten

Far

Close

Distance


Slide27 l.jpg

TV System Failure Characteristic

Good

Quality

Edge

of

Service

Area

Rotten

Far

Close

Distance


Slide28 l.jpg

TV System Failure Characteristic

Good

HDTV

PAL

Quality

SDTV

Edge

of

Service

Area

Rotten

Far

Close

Distance


Service area planning l.jpg
Service Area Planning

Modulation

Typical

Choice of

C/N

Dependent

Variation

PICTURE

QUALITY

DIGITAL

5

4

ANALOGUE

3

THRESHOLD OF

ACCEPTABILITY

2

ANALOGUE

FAILURE

C/N

1

NO

SERVICE

40

45

35

15

20

25

30

10


Service areas current l.jpg
Service Areas - Current

50 - 100 KILOMETRES

TRANSMITTER B

TRANSMITTER A


Service areas sfn l.jpg
Service Areas - SFN

50 - 100 KILOMETRES

TRANSMITTER B


Digital provides new concepts l.jpg
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 asexactly the same program is carried

    • Allows lower power operation

    • Better shaping of coverage

    • Improved service availability

    • Better spectrum efficiency




Packetisation approaches l.jpg
Packetisation Approaches

Fixed Length

Variable Length


Transport stream l.jpg
Transport Stream

Link Header Format


System information si l.jpg
System Information (SI)

  • Required for :

    • Automatic Tuning of receiver upon selection

    • Program location

    • EPG (Electronic Program Guide)

    • API (Application Programming Interface)

    • CA (Conditional Access)


Dvb si model l.jpg
DVB SI Model

Networks

Terrestrial

Satellite

Cable

Transport Streams

Transponder

1

Transponder

2

Transponder

3

Transponder

T

Channel

2

Channel

C

Channel

2

Channel

C

Channel

1

Channel

1

Services

Bouquet

Service

1

Service

2

Service

S

Service

1

Service

2

Service

S

Service

1

Service

2

Service

3

Service

S

Components

Video

Audio 1

Audio 2

Data


System information l.jpg
System Information

  • The DVB SI structure has it’s derivation in MPEG ISO/IEC 13818-1 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


What is si l.jpg
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


Psi and dvb si tables l.jpg
PSI and DVB SI Tables

NIT

ACTUAL

Delivery Sys.

PID=0x0010

PID=0x0000

NETWORK

INFORMATION.

PID=P

BOUQUET

INFORMATION.

PMT

BAT

SDT

ACTUAL

TS

SERVICE

DESCRIPTION.

PID=Ox0011

EIT

ACTUAL

TS

EIT

OTHER

TS

PID=Ox0001

CAT

EIT

ACTUAL

TS

EVENT

INFORMATION.

PID=0X0012

PID=0X0002

PCR

TSDT

TOT

PID=0X0012

TDT

TIME

OFFSET.

DVB OPTIONAL

MPEG DVBMANDATORY

NIT

OTHER

Delivery Sys.

PID=0x0010

PAT

PID=Ox0011

SDT

OTHER

TS

PID=Ox0011

ST

RST

STUFFING

TABLE.

PROGRAMME

CLOCK REF.

RUNNING

STATUS.

TIME AND

DATE.


Mpeg program pids l.jpg
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


Virtual channels pcr timing l.jpg
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.


Decoding the program l.jpg
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 :


Pat pmt cat tables l.jpg
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.


Dvb si features l.jpg
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


  • Si features nit l.jpg
    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


    Si features sdt bat l.jpg
    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”


    Si features eit l.jpg
    SI Features: EIT

    • Present/Following

      • 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


  • Si features tdt tot rst l.jpg
    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


  • Electronic program guide epg l.jpg
    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.






    Application program interface api l.jpg
    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.


    Dvb conditional access l.jpg
    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).



    A future digital system concept l.jpg
    A Future Digital System Concept

    MMDS

    HypermediaIntegrated ReceiverDecoder (IRD)

    Satellite

    Terrestrial

    Cable

    Broadcast

    Interactivity

    B-ISDNXDSL

    CD, DVDDVC


    Dttb systems doppler performance limits l.jpg
    DTTB Systems Doppler Performance Limits

    for currentimplementations

    300

    250

    UHF

    200

    VHF - Band III

    DOPPLERSHIFT(Hz)

    COFDM 2K, 3dB degrade

    140

    COFDM 2K

    100

    50

    0

    0

    100

    200

    300

    400

    500

    600

    700

    800

    900

    1000

    ATSC

    seeseparatecurves

    SPEED (Km/Hr)

    Vehicles

    AIRCRAFT

    Over Cities

    COFDM implementations will inherently handlepost andpre-ghostsequally within the selected guard interval.


    Main results lab tests l.jpg
    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


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