elements of digital television - .auhappy.emu.id.au/lab/info/digtv/files/uocdtv46w.pdf · digital...
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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
70
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.