GérardGérard FARIA FARIA -- 20002000
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
Gerard FARIAGerard FARIAScientific DirectorScientific Director
ITIS ITIS -- FranceFrance
The Digital Video Broadcasting System:The Digital Video Broadcasting System:
The magic of the COFDMThe magic of the COFDM((Coded Orthogonal Frequency Division Multiplex)Coded Orthogonal Frequency Division Multiplex)
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
ITU seminar ITU seminar -- The Digital Video Broadcasting SystemThe Digital Video Broadcasting SystemKiev Kiev -- 13th November 200013th November 2000 GérardGérard FARIA FARIA -- 20002000
DIGITAL TERRESTRIAL BROADCASTDIGITAL TERRESTRIAL BROADCAST
Terrestrial Broadcast induces multiTerrestrial Broadcast induces multi--pathespathes and Doppler effects (if Mobile) : and Doppler effects (if Mobile) : COFDM is THE response to cope with these impairments !COFDM is THE response to cope with these impairments !
Distant transmitter
Nearest transmitter
Among the available Digital Broadcasting standards, three are baAmong the available Digital Broadcasting standards, three are based on the sed on the Coded Orthogonal Frequency Division Multiplex modulation.... WhyCoded Orthogonal Frequency Division Multiplex modulation.... Why ??
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
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Make subMake sub--carriers orthogonal (carriers orthogonal (dfdf=1/=1/dtdt) to avoid “inter) to avoid “inter--carriers” interference carriers” interference
COFDM : HOW ?COFDM : HOW ?qq 1 1 -- OrganiseOrganise the channel as a “timethe channel as a “time--frequency” cells partitionfrequency” cells partition
time
frequency
OFDMOFDMsymbolsymbol
8K system8K system 2K system2K system
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
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COFDM : HOW ?COFDM : HOW ?qq 2 2 -- Insert Guard Interval to avoid “interInsert Guard Interval to avoid “inter--symbol” interferencesymbol” interference
time
frequency
Useful symbolUseful symboldurationduration
Guard Guard IntervalIntervaldurationduration
OFDMOFDMsymbolsymbol
BUT : Guard interval introduces a first loss in transport capaciBUT : Guard interval introduces a first loss in transport capacity ty
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
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COFDM : HOW ?COFDM : HOW ?qq 3 3 -- Insert “Synchronization Pilots” to help Receivers to lock onto Insert “Synchronization Pilots” to help Receivers to lock onto the useful signalthe useful signal
FFTFFTtime windowstime windowsfor receiversfor receivers
OFDM FrameOFDM Frame(68 OFDM symbols)(68 OFDM symbols)
time
frequency
BUT : Synchronization markers introduce a second loss in transpBUT : Synchronization markers introduce a second loss in transport capacity ort capacity
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
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COFDM : HOW ?COFDM : HOW ?qq 4 4 -- Map protected payload bits onto OFDM symbols with frequency intMap protected payload bits onto OFDM symbols with frequency interleavingerleaving
time
frequency
DATA to broadcast
Protected DATA
0011
0000
11
Create frequency diversity to improve robustness against selectiCreate frequency diversity to improve robustness against selective fadingve fading
Guard Guard IntervalInterval
UsefulUsefulPeriodPeriod
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
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DVBDVB--T modes : the tradeT modes : the trade--off between Bitrate and Robustnessoff between Bitrate and Robustness
0 dB
3 dB
6 dB
9 dB
12 dB
15 dB
18 dB
21 dB
24 dB
27 dB
30 dB
33 dB
1/2 2/3 3/4 5/6 7/8 1/2 2/3 3/4 5/6 7/8 1/2 2/3 3/4 5/6 7/8
0 Mbps
3 Mbps
6 Mbps
9 Mbps
12 Mbps
15 Mbps
18 Mbps
21 Mbps
24 Mbps
27 Mbps
30 Mbps
33 Mbps
GérardGérard FARIA FARIA -- 20002000
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
The Digital Video Broadcasting System:
The Magic of Single Frequency Network (SFN) Operation
The Digital Video Broadcasting System:The Digital Video Broadcasting System:
The Magic of The Magic of Single Frequency Network (SFN) OperationSingle Frequency Network (SFN) Operation
Gerard FARIAGerard FARIAScientific DirectorScientific Director
ITIS ITIS -- FranceFrance
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
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Spectrum & Power Efficiency : the network point of viewSpectrum & Power Efficiency : the network point of view
63 dBµV/m
High Power Transmitters
+ Less Sites in Network
+ Lower initial Investment
- Lower “On-air” Redundancy
- Higher operational costs due tolower Power Efficiency
High Power TransmittersHigh Power Transmitters
+ Less Sites in Network+ Less Sites in Network
+ Lower initial Investment+ Lower initial Investment
-- Lower “OnLower “On--air” Redundancyair” Redundancy
-- Higher operational costs due toHigher operational costs due tolower Power Efficiencylower Power Efficiency
Low Power Transmitters
+ Higher “On-air” Redundancy
+ lower operational costs due tohigher Network Efficiency
- More Sites in Network
- Higher initial Investment
Low Power TransmittersLow Power Transmitters
+ Higher “On+ Higher “On--air” Redundancy air” Redundancy
+ lower operational costs due to+ lower operational costs due tohigher Network Efficiencyhigher Network Efficiency
-- More Sites in NetworkMore Sites in Network
-- Higher initial InvestmentHigher initial Investment
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
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SFN, the receivers point of view ...SFN, the receivers point of view ...Channel Impulse Response Channel Spectrum
To make receivers working with SFN signals, all transmitters involved in the Single Frequency Network shall comply the “SFN Golden Rules” :To make receivers working with SFN signals, all transmitters invTo make receivers working with SFN signals, all transmitters involved olved in the Single Frequency Network shall comply the “SFN Golden Rulin the Single Frequency Network shall comply the “SFN Golden Rules” :es” :
To radiate . on the SAME FREQUENCY,. at the SAME TIME,. the SAME DATA BIT(s).
To radiate . on theTo radiate . on the SAME FREQUENCY,SAME FREQUENCY,. at the . at the SAME TIME,SAME TIME,. the . the SAME DATA BIT(s).SAME DATA BIT(s).
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
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SFN Golden rules SFN Golden rules ðð on the same frequencyon the same frequency
COFDMCOFDMmodulatormodulator
UpUpconverterconverter
UpUpconverterconverter
COFDMCOFDMmodulatormodulatorCOFDM
receiver
COFDMCOFDMreceiverreceiver
frequencyfrequency
frequencyfrequency
GPS10 Mhz
GPS10 Mhz
F0 in few Hertz !F0 in few Hertz !
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SFN : Frequency domain constraintsSFN : Frequency domain constraints
Modes 8K 2K I IV II III
Subcarriers / symbols 6817 1705 1536 768 384 192. Used for system 769 193 - - - -. Used to carry data 6048 1512 1536 768 384 192
Bits / symbols. D - QPSK - - 3072 1536 768 384. 4 - QAM (QPSK) 12 096 3 024 - - - -. 16 - QAM 24 192 6 048 - - - -. 64 - QAM 36 288 9 072 - - - -
Inter-Carrier spacing 1 116 Hz 4 465 Hz 1 kHz 2 kHz 4 kHz 8 kHzAbsolute precision ~ 1 Hz ~ 4 Hz ~ 10 Hz ~ 20 Hz ~ 40 Hz ~ 80 Hz
DVB-T (8 MHz) DAB-T (1,5 MHz)
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
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SFN Golden rules SFN Golden rules ðð at the same time : T0 in few at the same time : T0 in few µµs !s !Primary
DistributionNetwork
COFDMCOFDMmodulatormodulator
UpUpconverterconverter
UpUpconverterconverter
COFDMCOFDMmodulatormodulator
GPS1 pps
GPS1 pps
COFDMreceiverCOFDMCOFDMreceiverreceiver
timetime
timetime
freq
uenc
yfr
eque
ncy
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
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SFN : Time domain constraintsSFN : Time domain constraints
Modes 8K 2K I IV II III
Symbols / frames 68 68 78 78 78 155 Maximum. Used for system - - 2 2 2 2 distance. Used to carry data 68 68 76 76 76 153 between
Symbols duration 896 us 224 us 1000 us 500 us 250 us 125 us TxGuard Interval durations 7 us ~ 3 kms
14 us ~ 6 kms28 us 28 us 31 us ~12 kms56 us 56 us 62 us ~24 kms112 us 123 us ~48 kms224 us 248 us ~96 kms
Delivery Time Accuracy 2..22 us 0..5 us 24 us 12 us 6 us 3 us
DVB-T (8 MHz) DAB-T (1,5 MHz)
GérardGérard FARIA FARIA -- 20002000
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
The Digital Video Broadcasting System:
DVB-T Hierarchical modulation
The Digital Video Broadcasting System:The Digital Video Broadcasting System:
DVBDVB--T Hierarchical modulationT Hierarchical modulation
Gerard FARIAGerard FARIAScientific DirectorScientific Director
ITIS ITIS -- FranceFrance
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
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DVBDVB--T Hierarchical constellations : another way to use one RF channeT Hierarchical constellations : another way to use one RF channell
A basic 4 QAM named HP (High Priority) is used as a core modulation......
4QAM 4QAM -- HPHP 4QAM 4QAM -- HPHP
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
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Then, a Low Priority stream (LP) “over-modulates” the HP one to constitute a....
HIERARCHICAL 16 QAMHIERARCHICAL 16 QAMmade ofmade of
4QAM (LP)4QAM (LP) overover 4QAM (HP)4QAM (HP)
HIERARCHICAL 64 QAMHIERARCHICAL 64 QAMmade ofmade of
16QAM (LP)16QAM (LP) overover 4QAM (HP)4QAM (HP)
DVBDVB--T Hierarchical constellations : another way to use one RF channeT Hierarchical constellations : another way to use one RF channell
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
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DVBDVB--T : Hierarchical modulation for what ?T : Hierarchical modulation for what ?
The Hierarchical Modulation feature offers a further trade-off :
to broadcast TWO services on ONE radio channel
The Hierarchical Modulation feature offers a further tradeThe Hierarchical Modulation feature offers a further trade--off :off :
to broadcast TWO services on ONE radio channelto broadcast TWO services on ONE radio channel
To define modulation parameters, the network planning follows “uTo define modulation parameters, the network planning follows “usually” these rules :sually” these rules :
•• to reach a given bitrate, Physical Modulation & Coding rate areto reach a given bitrate, Physical Modulation & Coding rate are determined,determined,
•• 2K / 8K format is selected relative to the transmission cell si2K / 8K format is selected relative to the transmission cell sizes, zes,
•• Guard Interval value is chosen relative to the nature of the teGuard Interval value is chosen relative to the nature of the terrain,rrain,
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
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HPHP
LPLP
Hierarchical Modulation : StationaryHierarchical Modulation : Stationary vsvs Portable receiversPortable receivers
REGREG
0
3
6
9
12
15
18
21
24
REG 64QAM 2/3 HP 4QAM 1/2 LP 16QAM 2/3
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RF1 + RF2RF1 + RF2HP for MobileHP for Mobile
RF1 + RF2RF1 + RF2LP for FixedLP for Fixed
Hierarchical Modulation : MobileHierarchical Modulation : Mobile vsvs Static receptionStatic reception
Channel RF1Channel RF1REGULARREGULAR
for for MOBILEMOBILE
Channel RF2Channel RF2REGULARREGULAR
for for FIXEDFIXED
06
1218243036424854
RF1 RF2 RF1.1 RF1.2 RF2.1 RF2.2REGREG16Q16Q1/21/2
REGREG64Q64Q2/32/3
HPHP4Q4Q1/21/2
LPLP16Q16Q3/43/4
HPHP4Q4Q1/21/2
LPLP16Q16Q3/43/4
GérardGérard FARIA FARIA -- 20002000
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
Gerard FARIAGerard FARIAScientific DirectorScientific Director
ITIS ITIS -- FranceFrance
The Digital Video Broadcasting System:The Digital Video Broadcasting System:
Use of DVBUse of DVB--T with Mobile ReceiversT with Mobile Receivers
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
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Mobile Receivers behaviour characteristicMobile Receivers behaviour characteristic
(C/N)min
PT2
(C/N)min+3dB
fd,max/2 fd,maxfd,3dB
C/N
Dopplerfrequency
PT1
PT3
WorkingReception
Area
NotWorkingArea
10Hz
PT4
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
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ReceiverReceiver ’s ’s characteristics characteristics DispersionDispersion
10 dB
16 dB
22 dB
28 dB
34 dB
40 dB
0 Hz 50 Hz 100 Hz 150 Hz 200 Hz 250 Hz
Doppler Frequency
C/N
Classical : 1st Generation chipsetClassical : 2nd Generation chipsetReference Receiver ModelAntenna Diversity : Packet switchingExperimental : Large FilteringAntenna Diversity : Sub-Carriers switching
DVB-T mode : 2K, 16QAM, CR: 1/2, GI: 1/4
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
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Field tests : Field tests : recorded spectra recorded spectra (dense urban environment)(dense urban environment)
-102
-97
-92
-87
-82
-77
-72
789 791 793 795 797 799frequency (Hz)
dB
µV
Antenna 1 Antenna 2 MRC
distance distance betweenbetween AntennaeAntennae = 20 cm (= 20 cm (λλ = 38 cm)= 38 cm)
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Signal to Noise Ratio Signal to Noise Ratio vs vs DopplerDoppler
8
13
18
23
28
33
38
25 75 125 175 225 275 325 375 425
Doppler (Hz)
SN
R (
dB)
Sp
eed L
imit for 2K
Sp
eed L
imit for 8K
2K8K
Gain Gain with enhancedwith enhancedTime InterpolationTime Interpolation
Gains with MRC6 dB & 100 Hz
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
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« Maximum Doppler Frequency »vs
DVB-T Modes & Channel Profiles
0 Hz 50 Hz 100 Hz 150 Hz 200 Hz 250 Hz 300 Hz 350 Hz
2K 4QAM reg 1/2
2K 16QAM a=2 1/2
2K 64QAM a=1 1/2
8K 4QAM reg 1/2
8K 16QAM a=2 1/2
8K 64QAM a=1 1/2
2K 4QAM reg 2/3
2K 16QAM a=2 2/3
2K 64QAM a=1 2/3
8K 4QAM reg 2/3
8K 16QAM a=2 2/3
8K 64QAM a=1 2/3
2K 16QAM reg 1/2
8K 16QAM reg 1/2
2K 16QAM reg 2/3
8K 16QAM reg 2/3
2K 64QAM reg 1/2
8K 64QAM reg 1/2
2K 64QAM reg 2/3
8K 64QAM reg 2/319,91 Mbps
14,93 Mbps
13,27 Mbps
9,95 Mbps
6,68 Mbps
4,98 Mbps
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
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"Maximum Speed vs RF frequency"for DVB-T in 2K & 8K modes and DAB
10 km/h
100 km/h
1000 km/h
10000 km/h
100 MHz 1000 MHz
Max
imum
Spe
edDAB III (192)
DAB II (384)
2K 4QAM reg 1/2
2K 16QAM a=2 1/2
2K 4QAM reg 2/3
2K 16QAM a=2 2/3
2K 64QAM a=1 1/2
2K 16QAM reg 1/2
2K 16QAM reg 2/3
DAB IV (768)
2K 64QAM a=1 2/3
2K 64QAM reg 1/2
2K 64QAM reg 2/3
DAB I (1536)
8K 4QAM reg 1/2
8K 16QAM a=2 1/2
8K 4QAM reg 2/3
8K 16QAM a=2 2/3
8K 64QAM a=1 1/2
8K 16QAM reg 1/2
8K 16QAM reg 2/3
8K 64QAM a=1 2/3
8K 64QAM reg 1/2
8K 64QAM reg 2/3
CH40 - 626 MHzBand III Band IV Band V
CH40626 MHz
VHF UHF
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
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« Maximum Speed » using CH40-626 MHzvs
DVB-T Modes using GI:1/4
60 km/h
120 km/h
180 km/h
240 km/h
300 km/h
360 km/h
420 km/h
480 km/h
540 km/h
2K 4Q
AM RE
G
2K 16
QAM a=
2
2K 64
QAM a=
1
8K 4Q
AM RE
G
8K 16
QAM a=
2
8K 64
QAM a=
1
2K 4Q
AM RE
G
2K 16
QAM a=
2
2K 64
QAM a=
1
8K 4Q
AM RE
G
8K 16
QAM a=
2
8K 64
QAM a=
1
2K 16
QAM RE
G
8K 16
QAM RE
G
2K 16
QAM RE
G
8K 16
QAM RE
G
2K 64
QAM RE
G
8K 64
QAM REG
2K 64
QAM RE
G
8K 64
QAM REG
3 Mbps
6 Mbps
9 Mbps
12 Mbps
15 Mbps
18 Mbps
21 Mbps
24 Mbps
27 Mbps
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
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Mobile DVBMobile DVB--T demonstrated at IBC 98T demonstrated at IBC 98
Courtesy of Courtesy of
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
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THANK YOU FOR YOUR ATTENTIONTHANK YOU FOR YOUR ATTENTION
Gérard [email protected]
ITIS - Francewww.itis.fr