The Digital Video Broadcasting System.ppt [Read-Only] · ITU seminar - The Digital Video...

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)


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 ??



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



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



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



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



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



The Digital Video Broadcasting System:

The Magic of Single Frequency Network (SFN) Operation


The Magic of The Magic of Single Frequency Network (SFN) OperationSingle Frequency Network (SFN) Operation





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



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).



SFN Golden rules SFN Golden rules ðð on the same frequencyon the same frequency

COFDMCOFDMmodulatormodulator

UpUpconverterconverter


COFDMCOFDMmodulatormodulatorCOFDM

receiver

COFDMCOFDMreceiverreceiver

frequencyfrequency

frequencyfrequency

GPS10 Mhz

GPS10 Mhz

F0 in few Hertz !F0 in few Hertz !



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)



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





GPS1 pps

GPS1 pps

COFDMreceiverCOFDMCOFDMreceiverreceiver

timetime

timetime

freq

uenc

yfr

eque

ncy



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)



The Digital Video Broadcasting System:

DVB-T Hierarchical modulation


DVBDVB--T Hierarchical modulationT Hierarchical modulation





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



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



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,



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



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






Use of DVBUse of DVB--T with Mobile ReceiversT with Mobile Receivers



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



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



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)



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



« 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



"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



« 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



Mobile DVBMobile DVB--T demonstrated at IBC 98T demonstrated at IBC 98

Courtesy of Courtesy of



THANK YOU FOR YOUR ATTENTIONTHANK YOU FOR YOUR ATTENTION

Gérard [email protected]

ITIS - Francewww.itis.fr

The Digital Video Broadcasting System.ppt [Read-Only] · ITU seminar - The Digital Video...

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