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University of CanberraAnalog & Digital Communications

University of CanberraAnalog & Digital Communications

Elements of DigitalElements of DigitalTelevisionTelevision

by: Neil Pickfordby: Neil PickfordLecture 6Lecture 6Digital Digital

Modulation SystemsModulation Systems

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Enabling TechnologiesEnabling Technologies■■ Source digitisation (Rec 601 digital studio)Source digitisation (Rec 601 digital studio)■■ Compression technology (MPEG, AC-3)Compression technology (MPEG, AC-3)■■ Data multiplexing (MPEG)Data multiplexing (MPEG)■■ Transmission technology (modulation)Transmission technology (modulation)

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Digital TV Transmission TechnologyDigital TV Transmission Technology

■■ Transports data ratesTransports data ratesof around 20 Mb/sof around 20 Mb/s

■■ Transports data in individualTransports data in individualcontainers called packetscontainers called packets

■■ The transmission system is used to transport theThe transmission system is used to transport theinformation to the consumer.information to the consumer.

■■ The system protects the information beingThe system protects the information beingcarried from the transmission environmentcarried from the transmission environment

■■ The transmission system is aThe transmission system is a “data pipe” “data pipe”

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Digital TV Transmission SystemsDigital TV Transmission SystemsDTV & HDTV systems fall into three groupingsDTV & HDTV systems fall into three groupings■■ Europeans Europeans - Digital SDTV- Digital SDTV

- 8 MHz on UHF- 8 MHz on UHF- DVB-T (COFDM)- DVB-T (COFDM)

■■ AmericansAmericans - Digital HDTV- Digital HDTV- 6 MHz VHF/UHF- 6 MHz VHF/UHF- ATSC (8-VSB)- ATSC (8-VSB)

■■ Japanese Japanese - Integrated Broadcasting- Integrated Broadcasting- ISDB (BST-OFDM)- ISDB (BST-OFDM)

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8-VSB - USA8-VSB - USA

■■ Developed by the advance television systems committeeDeveloped by the advance television systems committeeATSCATSC

■■ Developed for use in a 6 MHz channelDeveloped for use in a 6 MHz channel◆◆ A 7 MHz variant is possible but has not been produced.A 7 MHz variant is possible but has not been produced.

■■ Uses a single carrier with pilot toneUses a single carrier with pilot tone■■ 8 level amplitude modulation system8 level amplitude modulation system■■ Single Payload data rate of 19.39 Mb/sSingle Payload data rate of 19.39 Mb/s■■ Relies on adaptive equalisationRelies on adaptive equalisation■■ Existing AM technology highly developedExisting AM technology highly developed

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COFDM - EuropeCOFDM - Europe■■ Developed by the digital videoDeveloped by the digital video

broadcasting project group - DVBbroadcasting project group - DVB■■ Uses similar technology to DRBUses similar technology to DRB■■ Uses 1705 or 6817 carriersUses 1705 or 6817 carriers■■ Variable carrier modulation types are defined allowingVariable carrier modulation types are defined allowing

Payload data rates of 5-27 Mb/s in 7 MHzPayload data rates of 5-27 Mb/s in 7 MHz■■ Developed for 8 MHz channelsDeveloped for 8 MHz channels

◆◆ A 7 & 6 MHz variants have been produced and tested.A 7 & 6 MHz variants have been produced and tested.

■■ Can use single frequency networks - SFNsCan use single frequency networks - SFNs■■ New technology with scope for continuedNew technology with scope for continued

improvement & developmentimprovement & development

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ISDB - JapanISDB - Japan■■ Japanese are developing integrated servicesJapanese are developing integrated services

digital broadcasting (ISDB)digital broadcasting (ISDB)■■ System integrates all forms of broadcastingSystem integrates all forms of broadcasting

services into one common data channel whichservices into one common data channel whichcan be passed by satellite, cable or terrestrialcan be passed by satellite, cable or terrestrialdelivery systemsdelivery systems

■■ Video servicesVideo services◆◆ Sound servicesSound services◆◆ Bulk data servicesBulk data services◆◆ Interactive data servicesInteractive data services

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ISDB - ConceptISDB - Concept

■■ Uses Band Segmented Transmission -Uses Band Segmented Transmission -Orthogonal Frequency Division MultiplexOrthogonal Frequency Division Multiplex(BST-OFDM)(BST-OFDM)

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Terrestrial Transmission ProblemsTerrestrial Transmission Problems✘✘ Multipath interference - ghostsMultipath interference - ghosts✘✘ Noise interference - snowNoise interference - snow✘✘ Variable path attenuation - fadingVariable path attenuation - fading✘✘ Interference to existing servicesInterference to existing services✘✘ Interference from other servicesInterference from other services✘✘ Channel frequency assignment -Channel frequency assignment -

where to place the signalwhere to place the signal

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Digital Modulation - FunctionsDigital Modulation - Functions✔✔ Spreads the data evenly across the channelSpreads the data evenly across the channel✔✔ Distributes the data in timeDistributes the data in time✔✔ Maintains synchronisation well below dataMaintains synchronisation well below data

thresholdthreshold✔✔ Employs sophisticated error correction.Employs sophisticated error correction.✔✔ Equalises the channel for best performanceEqualises the channel for best performance

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Digital Modulation

Two techniques:Two techniques:■■ Conventional Single CarrierConventional Single Carrier➣➣ 8VSB, QPSK or QAM8VSB, QPSK or QAM

■■ MulticarrierMulticarrier/Spread Spectrum/Spread Spectrum➣➣ OFDM OFDM

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8-VSB & COFDM - Spectrum8-VSB & COFDM - Spectrum

8-VSBCOFDM

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As power is an absolute As power is an absolute quantity the negative quantity the negative

amplitudes also amplitudes also resolve as real power resolve as real power

Sin(x)/xSin(x)/xAmplitude dB

FrequencyFrequency

A Carrier phase or frequency A Carrier phase or frequency modulated at a low symbol ratemodulated at a low symbol rate

will exhibit a Sin(X)/X typewill exhibit a Sin(X)/X typespectral occupancyspectral occupancy

Digital Modulation

Frequency

Amplitude, dBLow Symbol Rate

Medium Symbol Rate

High Symbol RateSpectrum Spectrum ofof

a Conventionala ConventionalMultiMulti-Phase -Phase KeyedKeyed

CarrierCarrier FcFc at at aaSymbolSymbol Rate Fs Rate Fs

FcFc - Fs Fc + Fs

Sin(X)/Xshaping

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PSKPSKDigital Information

Phase Shift Keying Modulation

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BPSK Modulation

I AXIS0 1

180 DegPhase

Change

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QPSK Modulation

I AXIS

Q AXIS

QPSKDistance

0 0

1 1

0 1

1 0

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16QAM Modulation

I AXIS

Q AXIS

16-QAMDistance

1 1 0 0 1 1 0 1

1 1 1 0

0 0

1 1

0 1

1 01 1 1 1

0 0 0 0

0 0 1 0 0 0 1 1

0 0 0 1

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64QAM Modulation

I AXIS

Q AXIS

64-QAMDistance 110011 110111

111011

0 0

1 1

0 1

1 0111111

000000

001000 001100

000100

111001

110001

001110

000110

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1 1

0 0

Hierarchical Modulation

I AXIS

Q AXIS

QPSKDistance

HierarchicalDistance

1 1 0 0 1 1 0 1

1 1 1 0 1 1 1 1

0 0 0 0

0 0 1 1

0 0 0 1

0 1

1 0

0 0 1 0

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Digital Modulation

Frequency

Amplitude

FcFc - Fs Fc + Fs

Occupied ChannelBandwidth

Typical FilteredSpectrum to giveabout half original

bandwidth

Normal FDMAmplitude, dB

Frequency

Carrier 1 Carrier 2

GuardBand

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Frequency

Amplitude, dB

Orthogonal Modulation

Frequency

Amplitude, dB

Orthogonal Modulation

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COFDM - Orthogonal CarriersCOFDM - Orthogonal Carriers

Frequency

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Spectrum of COFDM DTTBSpectrum of COFDM DTTB

6.67 MHz in 7 MHz Channel

AlmostRectangular

Shape

1705 or 6817 Carriers

Carrier Spacing2k Mode 3.91 kHz8k Mode 0.98 kHz

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OFDMAmplitude, dB

FrequencyFrequencyFcentre

Occupied bandwidth is: No. ofCarriers x Spectral Width.

Create with FFT

Spectral Width

2k is 4x wider than 8k

DIGITAL TERRESTRIALBROADCASTING

The Terrestrial Broadcasting has to cope with multipath propagation and DopplerThe Terrestrial Broadcasting has to cope with multipath propagation and Dopplereffects: COFDM is the response for these impairments !effects: COFDM is the response for these impairments !

Distant transmitter

Nearest transmitter

Among the four Digital Broadcasting standards available, three are based onAmong the four Digital Broadcasting standards available, three are based onthe Coded Orthogonal Frequency Division Multiplex modulation.... Why ?the Coded Orthogonal Frequency Division Multiplex modulation.... Why ?

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COFDM : HOW ?COFDM : HOW ?■■ 1 - Organize time & frequency partitions in the RF channel1 - Organize time & frequency partitions in the RF channel

time

frequency

RFRFChannelChannel

bandwidthbandwidth

frequencyfrequencysub-bandsub-band

timetimesegmentsegment

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Make sub-carriers orthogonal to avoid “inter-carriers” interference

COFDM : HOW ?■■ 2 - Spread sub-carriers over “time 2 - Spread sub-carriers over “time vsvs frequency” cells frequency” cells

time

frequency

OFDMOFDMsymbolsymbol

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COFDM : HOW ?■■ 3 - Insert Guard Interval to avoid “inter-symbol” interference3 - Insert Guard Interval to avoid “inter-symbol” interference

time

frequency

Useful symbolUseful symboldurationduration

Guard IntervalGuard Intervaldurationduration

OFDMOFDMsymbolsymbol

Guard interval introduces a first loss in transport capacity Guard interval introduces a first loss in transport capacity

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COFDM : HOW ?■■ 4 - Insert “Synchronization Pilots”4 - Insert “Synchronization Pilots”

Helps Receivers to lock onto the signalHelps Receivers to lock onto the signal

FFTFFTtime windowstime windowsfor receiversfor receivers

OFDM FrameOFDM Frame(68 OFDM symbols)(68 OFDM symbols)

time

frequency

Synchronization markers introduce the second lossSynchronization markers introduce the second lossin transport capacityin transport capacity

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COFDM : HOW ?■■ 5 - Prepare data to be carried on OFDM symbols5 - 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 capacityProtection codes introduce the third loss in transport capacity

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COFDM : HOW ?■■ 6 - Map bits onto OFDM:6 - Map bits onto OFDM:

Spread contiguous data bits over distant sub-carriersSpread contiguous data bits over distant sub-carriers

time

frequency

DATA to broadcast

Protected DATA

0 1 0 01

Create frequency diversity to improve robustness against fadingCreate frequency diversity to improve robustness against fading

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DTTB - Channel EstimationDTTB - Channel Estimation■■ The Terrestrial transmission channel isThe Terrestrial transmission channel is

continuously varying (position & time)continuously varying (position & time)■■ Variations occur inVariations occur in

Amplitude, Phase & FrequencyAmplitude, Phase & Frequency■■ To correct for this variation Information needsTo correct for this variation Information needs

to be added to the transmission to quantify theto be added to the transmission to quantify thechannels response at any instant - Pilotschannels response at any instant - Pilots

■■ Equalisers in the Digital receiver use thisEqualisers in the Digital receiver use thisinformation to remove these transmissioninformation to remove these transmissionimpairmentsimpairments

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DVB-T - Carriers + Pilots

KminKmin

SYMBOLS IN SEQUENCE - 68 PER BLOCK.SYMBOLS IN SEQUENCE - 68 PER BLOCK.

KmaxKmax1704 for 2K or1704 for 2K or 6816 for 8K6816 for 8KKmax =Kmax =

Modulated CarriersModulated Carriers

0.977/3.906 kHz0.977/3.906 kHz

Scattered PilotsScattered Pilots

SSYYMMBBOOLLSS

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TPS PilotsTPS Pilots■■ Transmission Parameter Signalling is added onTransmission Parameter Signalling is added on

selected carriers within the OFDM spectrumselected carriers within the OFDM spectrum(17 pilots for 2k & 68 pilots for 8k)(17 pilots for 2k & 68 pilots for 8k)

■■ TPS pilots Carry:TPS pilots Carry:◆◆ Frame Number in Super Frame: 00 / 01 / 10 / 11Frame Number in Super Frame: 00 / 01 / 10 / 11◆◆ Constellation Type QPSK / 16-QAM / 64-QAMConstellation Type QPSK / 16-QAM / 64-QAM◆◆ OFDM Mode 2k or 8kOFDM Mode 2k or 8k◆◆ Constellation Mode Normal/Hierarchical + Constellation Mode Normal/Hierarchical + α α valuevalue◆◆ Inner FEC Code rate (1/2, 2/3, 3/4, 5/6, 7/8)Inner FEC Code rate (1/2, 2/3, 3/4, 5/6, 7/8)◆◆ Guard Interval (1/4, 1/8, 1/16, 1/32)Guard Interval (1/4, 1/8, 1/16, 1/32)◆◆ System Bandwidth (6, 7, 8 MHz)System Bandwidth (6, 7, 8 MHz)

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DVB-T Transmission FrameDVB-T Transmission Frame

Data

Scattered Pilot

TPS - Pilot

Continuous Pilot

Kmin=0 KmaxCarrier Spacing & Position 2k mode - 3906 Hz - Kmax=17048k mode - 977 Hz - Kmax=6816

Symbol Duration 256 us (2k) or 1024 us (8k)

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DVB-T - Estimating the ChannelDVB-T - Estimating the Channel

AABBCCDDEE

AAB=3/4A+1/4EB=3/4A+1/4EC=1/2(A+E)C=1/2(A+E)

EED=1/4A+3/4ED=1/4A+3/4E

A to E A to E - 1.024 ms (2k)- 1.024 ms (2k) - 4.096 ms (8k)- 4.096 ms (8k)

For a varying transmission channel For a varying transmission channel DVB-T estimation is 23.5 times faster than ATSCDVB-T estimation is 23.5 times faster than ATSC

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DVB-T - Estimating the ChannelDVB-T - Estimating the Channel

A B C D E F GA B C D E F G

A to D - 11.724 kHz (2k)A to D - 11.724 kHz (2k) - 2.931 kHz (8k) - 2.931 kHz (8k)

For a varying transmission channel For a varying transmission channel DVB-T estimation is 23.5 times faster than ATSCDVB-T estimation is 23.5 times faster than ATSC

A B C D E F GA B C D E F GB=2/3A+1/3DB=2/3A+1/3DC=1/3A+2/3DC=1/3A+2/3D

E=2/3D+1/3GE=2/3D+1/3GF=1/3D+2/3GF=1/3D+2/3G

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Estimation Rate DVB-TEstimation Rate DVB-T■■ Equaliser is updated every symbol periodEqualiser is updated every symbol period

(256 us). (256 us). 11//1212 of data carriers are pilots of data carriers are pilots■■ Full Channel estimate is available everyFull Channel estimate is available every

4 symbols (1.024 ms)4 symbols (1.024 ms)

■■ OFDM is better than Single carrier systems underOFDM is better than Single carrier systems underMultipathMultipath Echo conditions due to the addition of Echo conditions due to the addition ofa Guard interval in the modulation system.a Guard interval in the modulation system.

■■ The Guard interval is added onto the symbol timeThe Guard interval is added onto the symbol timewasting some potential data capacity.wasting some potential data capacity.

Guard IntervalGuard Interval

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Transmitted Symbol Transmitted Symbol

Guard IntervalGuard Interval

Useful Symbol Useful Symbol

TTGG

TTSS

TTUU

11//44

11//88

11//1616

11//3232

GuardGuard

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COFDM - MultipathTRANSMITTER A

SIGNAL

REFLECTIONS

DIRECT PATH

1 Microsecond=

300 Metres

RECEPTION POINTSYMBOL PERIOD [1 ms]

Several µseconds disturbance from echoes.OFDM inherently resistant. 8VSB needs Time DomainEqualiser, symbol period short at 93ns

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COFDM - MultipathTRANSMITTER A

GUARDINTERVAL

SIGNAL

REFLECTIONS

DIRECT PATH

SAFEAREA

1 Microsecond=

300 Metres

RECEPTION POINTSYMBOL PERIOD

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COFDM - Pre-EchoTRANSMITTER A

SIGNAL

REFLECTIONS

1 Microsecond=

300 Metres

GUARDINTERVAL RECEPTION POINTSYMBOL PERIOD

SAFEAREA

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COFDM - SFN

GUARDINTERVAL[Variable]

SIGNAL

REFLECTIONS

DIRECT PATH

SAFEAREA

1 Microsecond=

300 Metres

RECEPTION POINTSYMBOL PERIOD

TRANSMITTER ATRANSMITTER B

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Mobile Services■■ Antenna PerformanceAntenna Performance

➣➣ Poor Directivity, Low Gain Poor Directivity, Low Gain➣➣ Multipath Dominated environment Multipath Dominated environment

■■ DopplerDoppler➣➣ High Speeds for Main Roads and Railways High Speeds for Main Roads and Railways➣➣ Low Speeds for Public Transport in Cities Low Speeds for Public Transport in Cities

■■ Needs to be RuggedNeeds to be Rugged➣➣ Choose version of DVB-T that is suitable Choose version of DVB-T that is suitable➣➣ Low Bit Rate, Low C/N, Long Guard Interval? Low Bit Rate, Low C/N, Long Guard Interval?

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Bus Route 7 Singapore - 1999Bus Route 7 Singapore - 1999

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OFDM - Features■■ MulticarrierMulticarrier - many carriers sharing- many carriers sharing

■■ Reduced C/N compared to Analogue Reduced C/N compared to Analogue■■ Resistant to echoes, Interference etc Resistant to echoes, Interference etc■■ Low symbol rate per carrier Low symbol rate per carrier

➣➣ ~ 1 ~ 1 kBaudkBaud: Long Symbol Period, can Extend with Guard: Long Symbol Period, can Extend with GuardIntervalInterval

■■ With FEC becomes With FEC becomes CCOFDMOFDM■■ Uses Fast Fourier Transform [FFT] Uses Fast Fourier Transform [FFT]

➣➣ ”2k” and “8k” versions”2k” and “8k” versions

■■ Single Frequency Networks [SFN] Single Frequency Networks [SFN]

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64-QAM - Perfect & Failure64-QAM - Perfect & Failure

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COFDM DTTB Block DiagramCOFDM DTTB Block Diagram

Error CorrectionError Correction

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Forward Error Correction (FEC) Forward Error Correction (FEC) ■■ Broadcast transmissionBroadcast transmission

◆◆ One way process - One way process - TxTx to Rx to Rx◆◆ Not possible to repeat any Not possible to repeat any errorederrored data data

■■ Forward Error Correction is a technique used toForward Error Correction is a technique used toimprove the accuracy of data transmissionimprove the accuracy of data transmission

■■ Extra redundant bits are added to the data streamExtra redundant bits are added to the data stream■■ Error correction algorithms in the demodulatorError correction algorithms in the demodulator

use the extra FEC bits to correct data errorsuse the extra FEC bits to correct data errors■■ C C OFDM uses a OFDM uses a ConvolutionalConvolutional FEC code FEC code

EncodeEncodeN bitsN bits N bitsN bitsTxTx/Rx/Rx

N+CodeN+Code

DecodeDecode

N+Code+ErrorN+Code+Error

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Convolutional CoderConvolutional Coder

1-Bit1-BitDelayDelay

1-Bit1-BitDelayDelay

1-Bit1-BitDelayDelay

1-Bit1-BitDelayDelay

1-Bit1-BitDelayDelay

1-Bit1-BitDelayDelay

DataDataInputInput

Y OutputY Output10110111011011

X OutputX Output11110011111001

6 6 5 4 3 5 4 3 2 1 2 1 0 0

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Puncturing Codes (FEC) Puncturing Codes (FEC) ■■ The X and Y outputs of the Convolutional coderThe X and Y outputs of the Convolutional coder

are selected in a Puncturing patternare selected in a Puncturing pattern

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Inner CodingInner Coding■■ Convolutional coder generates the X & Y codesConvolutional coder generates the X & Y codes

ConvolutionalConvolutionalEncoderEncoder PuncturingPuncturing InterleaverInterleaverDataData

CodedCodedDataData

XX

YY

■■ Puncturing operation selects X & Y in sequencePuncturing operation selects X & Y in sequence■■ Result then scrambled with an interleaverResult then scrambled with an interleaver

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Viterbi DecoderViterbi Decoder■■ A special type of data decoder designed to workA special type of data decoder designed to work

with with convolutionalconvolutional FEC codes FEC codes■■ Uses the past history of the data to identify validUses the past history of the data to identify valid

future data valuesfuture data values■■ Element in the Receiver OnlyElement in the Receiver Only

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Reed Solomon (RS)Reed Solomon (RS)■■ RS is a Block data correcting CodeRS is a Block data correcting Code■■ Hamming type cyclic Polynomial sequenceHamming type cyclic Polynomial sequence

◆◆ Code Generator Polynomial:Code Generator Polynomial: g(x) = (x+ g(x) = (x+λλ00)(x+)(x+λλ11)(x+)(x+λλ22)...(x+)...(x+λλ1515), ), λλ=02 Hex=02 Hex

◆◆ Field Generator Polynomial:Field Generator Polynomial: p(x) = x p(x) = x88 + x + x44 + x + x33 + x + x22 + 1 + 1

■■ Has special ability to correct multiple bursts ofHas special ability to correct multiple bursts oferrors in a code blockerrors in a code block

■■ DVB-T uses 204 bytes for each 188 byte PacketDVB-T uses 204 bytes for each 188 byte Packet(ATSC uses 207 bytes for each 187 byte Packet)(ATSC uses 207 bytes for each 187 byte Packet)

■■ Can correct 8 bytes in each 204 byte packetCan correct 8 bytes in each 204 byte packet

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Error Protection - OrderError Protection - Order

Outer CodeOuter CodeRSRS

(204,188)(204,188)

DataDataInputInput

InterleaverInterleaver InterleaverInterleaver

Inner CodeInner CodeFECFEC(2/3)(2/3)

ErrorErrorProtectedProtected

DataDataMapperMapper

188188BytesBytes

204204BytesBytes

204204BytesBytes

306306BytesBytes

6 bits x 1512 Carriers6 bits x 1512 Carriers6 bits x 6048 Carriers6 bits x 6048 Carriers

24482448BitsBits

64 QAM64 QAM

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DVB-T - Bit Rates [2k]

CodeRate

QPSK 16 -QAM

64 -QAM

QPSK QPSK16 -QAM

64 -QAM

64 -QAM

16 -QAM

D/Tu = 1/4 D/Tu = 1/8 D/Tu = 1/32

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

13.06 4.84

6.45

7.26

8.06

8.47 16.93

16.13

14.51

12.90

9.68 14.51

19.35

21.77

24.19

25.40

5.28

7.04

7.92

8.80

9.24 18.47

17.59

15.83

14.07

10.56 15.83

21.11

23.75

26.39

27.71

64 us 32 us 8 us7 MHz

Page 21 Table A1 - AS4599-1999Page 21 Table A1 - AS4599-1999

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DVB-T - C/N Values

CodeRate QPSK

16 -QAM

64 -QAM QPSK QPSK

16 -QAM

64 -QAM

64 -QAM

16 -QAM

1/2

2/3

3/4

5/6

7/8

3.10

4.90

5.90

6.90

7.70

8.80

11.1

12.5

13.5

13.9 20.10

19.30

18.00

16.5

3.60

5.70

6.80

8.00

8.70 15.00

14.40

13.00

11.60

9.60 14.70

17.10

18.60

20.00

21.00

5.40

8.40

10.70

13.10

16.30 22.80

19.30

16.70

14.20

11.20 16.00

19.30

21.70

25.30

GAUSSIAN RICEAN RAYLEIGH

27.90

14.4

Simulated Theoretical Thresholds (bandwidth independent)

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C/N - Signal Level PerformanceC/N - Signal Level Performance

64QAM 7/8 FEC64QAM 5/6 FEC64QAM 3/4 FEC64QAM 2/3 FEC64QAM 1/2 FEC16QAM 7/8 FEC16QAM 5/6 FEC16QAM 3/4 FEC16QAM 2/3 FEC16QAM 1/2 FECQPSK 7/8 FECQPSK 5/6 FECQPSK 3/4 FECQPSK 2/3 FECQPSK 1/2 FEC8VSB Test Rig

Receiver Signal Level (dBuV)

C/N

Thr

esho

ld (d

B)

1010 1515 2020 2525 3030 3535 4040 4545 5050 5555 6060

8

0

16

4

12

20

24

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7 MHz COFDM Modulator Spectrum7 MHz COFDM Modulator Spectrum

8k 1/32 Guard8k 1/32 Guard2k 1/32 Guard2k 1/32 Guard

00

-10-10

-20-20

-30-30

-40-40

-50-50

00-1-1-2-2-3-3-4-4-5-5-6-6-7-7-8-8 11 22 33 44 55 66 77 88Frequency Offset (MHz)Frequency Offset (MHz)

Pow

er S

pect

rum

Den

sity

(dB

)Po

wer

Spe

ctru

m D

ensi

ty (d

B)

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Frequency Planning■■ Fundamental Matter Fundamental Matter - - Scarce ResourceScarce Resource■■ Analogue Rules set limit to more ServicesAnalogue Rules set limit to more Services■■ No NEW TV Spectrum is AvailableNo NEW TV Spectrum is Available■■ Digital Transmission changes RulesDigital Transmission changes Rules➣➣Signals have different behaviourSignals have different behaviour

■■ Digital Signals can occupy unused spaceDigital Signals can occupy unused space --“Taboos”“Taboos”

■■ Digital Needs to fit in with Existing PALDigital Needs to fit in with Existing PAL■■ Eventually Digital Only Eventually Digital Only - - but long wait??but long wait??

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Digital Has to Fit In With PALDigital Has to Fit In With PAL

■■ World TV channel bandwidths varyWorld TV channel bandwidths vary◆◆ USA / Japan 6 MHzUSA / Japan 6 MHz

◆◆ Australian 7 MHzAustralian 7 MHz

◆◆ Europeans 8 MHzEuropeans 8 MHz

■■ Affects:-Affects:- tuning, filtering, interferencetuning, filtering, interference& system performance& system performance

2828

2828

2828

3030

30302929

2929

3131

3131 3232 3333 3434 3535

3535

35353434

34343333

3333

3232

3232

313130302929

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Channel SpacingChannel Spacing■■ Existing analog TV channels are spaced so they do notExisting analog TV channels are spaced so they do not

interfere with each other.interfere with each other.■■ Gap between PAL TV servicesGap between PAL TV services

◆◆ VHF 1 channelVHF 1 channel◆◆ UHF 2 channelsUHF 2 channels

■■ Digital TV can make use of these gapsDigital TV can make use of these gaps

Ch 7 Ch 8 Ch 9Ch 6 Ch 9A

VHF Television Spectrum

Taboo Taboo Taboo

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Digital ChallengesDigital Challenges■■ Digital TV must co-existDigital TV must co-exist

with existing PAL serviceswith existing PAL services◆◆ DTV operates at lower powerDTV operates at lower power◆◆ DTV copes higher interference levelsDTV copes higher interference levels◆◆ Share transmission infra-structureShare transmission infra-structure◆◆ DTV needs different planning methodsDTV needs different planning methods

Ch 7 Ch 8 Ch 9Ch 6 Ch 9A

VHF Television Spectrum

8-VSB COFDM

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DTTB & PALDTTB & PAL

UHF Channels: London

Photograph by courtesy and © BBC R&D

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Planning Issues■■ Channel Disturbances:Channel Disturbances:

➣➣ Noise, at edge of area with NO interferenceNoise, at edge of area with NO interference➣➣ Interference, Co Channel Interference and Adjacent Interference, Co Channel Interference and Adjacent

Channel InterferenceChannel Interference➣➣ Multipath, Echoes:How Many, How Large, Moving? Multipath, Echoes:How Many, How Large, Moving?

■■ Antenna Pattern?Antenna Pattern?➣➣ Static Roof Top? Directional? Wideband? Static Roof Top? Directional? Wideband?➣➣ CCIR Antenna CCIR Antenna RecRec BT-419-3 BT-419-3➣➣ Portable Receivers? No Antenna? Portable Receivers? No Antenna?

■■ Frequency Re-Use DistancesFrequency Re-Use Distances➣➣ Terrain Data Terrain Data➣➣ Propagation Models Propagation Models➣➣ Protection Ratios Protection Ratios

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Signal StrengthSIGNAL STRENGTH, MicroVolts

TIME

MEAN

RECEIVER C/N LIMIT

REGION OF SERVICEFAILURES FORPERCENTAGE

OF TIME

36

71

Digital Service Area PlanningDigital Service Area Planning■■ Analog TV has a slow gradual failureAnalog TV has a slow gradual failure

◆◆ Existing PAL service was planned for:Existing PAL service was planned for:50 % availability at50 % availability at50 % of locations50 % of locations

■■ Digital TV has a “cliff edge” failureDigital TV has a “cliff edge” failure◆◆ Digital TV needs planning for:Digital TV needs planning for:

90-99 % availability at90-99 % availability at90-99 % of locations90-99 % of locations

72

TV System Failure CharacteristicTV System Failure Characteristic

A nalog

D igital 1

Good

RottenClose Far

Distance

Quality

Edgeof

ServiceArea

37

73

TV System Failure CharacteristicTV System Failure Characteristic

A nalog

D igital 1

Good

RottenClose Far

Distance

Quality

Edgeof

ServiceArea

74

A nalog

D igital 1

D igital 2

TV System Failure CharacteristicTV System Failure Characteristic

Good

RottenClose Far

Distance

Quality

Edgeof

ServiceArea

SDTV

HDTV

PAL

38

75

Service Area PlanningPICTUREQUALITY

C/N

ANALOGUE

DIGITAL

THRESHOLD OFACCEPTABILITY

5

4

3

2

1 NOSERVICE

10 15 20 25 30 40 45

ANALOGUEFAILURE

35

ModulationDependent Variation

TypicalChoice of

C/N

76

Service Areas - Current

50 - 100 KILOMETRES

TRANSMITTER BTRANSMITTER A

39

77

Service Areas - SFN

TRANSMITTER B

50 - 100 KILOMETRES

78

Digital Provides New ConceptsDigital Provides New Concepts■■ Single frequency networks (SFNs)Single frequency networks (SFNs)

can help solve difficult coveragecan help solve difficult coveragesituationssituations◆◆ SFNs allow the reuse of aSFNs allow the reuse of a

transmission frequency many timestransmission frequency many timesin the same area so long asin the same area so long as exactly the same program is carriedexactly the same program is carried

◆◆ Allows lower power operationAllows lower power operation◆◆ Better shaping of coverageBetter shaping of coverage◆◆ Improved service availabilityImproved service availability◆◆ Better spectrum efficiencyBetter spectrum efficiency

40

79

Analog

Black Mt

Analog

Black Mt

Analog

Black Mt

Analog

Black Mt

Analog

Black Mt

Analog

Fraser

Analog

Fraser

Analog

Tugg Hill

Analog

Tugg Hill

Analog

Tugg Hill

Analog

Tugg Hill

Analog

Tugg Hill

Analog

Mt Taylor

Analog

Mt Taylor

Analog

Mt Taylor

Analog

Mt Taylor

Analog

Mt Taylor

Analog Canberra TelevisionAnalog Canberra Television

2828 30302929 3131 3232 3333 3434 3535

5353 55555454 5656 5757 5858 5959 6060

6161 63636262 6464 6565 6666 6767 6868 6969

66 8877 99 9A9A 1010 1111 1212Band III

Band IV

Band V

80

Digital

Black Mt

Digital

Black Mt

Digital

Black Mt

Digital

Black Mt

Digital

Black Mt

Digital

Black Mt

Digital SFN

Tugg HillMt Taylor

Digital

Tugg Hill

Digital

Tugg Hill

Digital

Tugg Hill

Digital Canberra TelevisionDigital Canberra Television

2828 30302929 3131 3232 3333 3434 3535

5353 55555454 5656 5757 5858 5959 6060

6161 63636262 6464 6565 6666 6767 6868 6969

66 8877 99 9A9A 1010 1111 1212Analog Analog

Analog Analog Analog

Analog Analog Analog Analog Analog Analog

Analog Analog Analog Analog Analog Analog

Black Mt Black Mt

Black Mt Black Mt Black Mt

Fraser FraserTugg Hill Tugg Hill

Tugg HillTugg HillTugg Hill

Mt Taylor Mt Taylor

Mt Taylor Mt Taylor Mt Taylor

Band III

Band IV

Band V

41

81

A Future Digital System ConceptA Future Digital System Concept

Integrated ReceiverDecoder (IRD) / Personal

Video Recorder (PVR)

MMDS

Satellite

Terrestrial

Cable

B-ISDNADSL CD, DVD,

DV, D8

Broadcast Interactivity

82

WebCTWebCT■■ The Course presentations have been put in WEBCT:The Course presentations have been put in WEBCT:

http://teaching.canberra.edu.au/SCRIPT/IS1512/scripts/serve_homehttp://teaching.canberra.edu.au/SCRIPT/IS1512/scripts/serve_home

■■ You will see "MODULE4" when you login this page.You will see "MODULE4" when you login this page.

■■ Open "MODULE4", and you will find two pages calledOpen "MODULE4", and you will find two pages called"MATERIAL1" and "MATERIAL2", which are the"MATERIAL1" and "MATERIAL2", which are theAcrobat handout versions of the power-point filesAcrobat handout versions of the power-point files"uocdtv43w."uocdtv43w.pdfpdf" and "uocdtv46w." and "uocdtv46w.pdfpdf", respectively.", respectively.