The Digital Video Broadcasting System:
The magic of the COFDM
(Coded Orthogonal Frequency Division Multiplex)
Gerard FARIA
Scientific Director
ITIS - France
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
Gérard FARIA - 2000
ITU seminar - The Digital Video Broadcasting System
Kiev - 13th November 2000
Gérard FARIA - 2000
DIGITAL TERRESTRIAL BROADCAST
Among the available Digital Broadcasting standards, three are based on the
Coded Orthogonal Frequency Division Multiplex modulation.... Why ?
Distant transmitter
Nearest transmitter
Terrestrial Broadcast induces multi -pathes and Doppler effects (if Mobile) :
COFDM is THE response to cope with these impairments !
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
ITU seminar - The Digital Video Broadcasting System
Kiev - 13th November 2000
Gérard FARIA - 2000
COFDM : HOW ?
q
1 - Organise the channel as a “time-frequency” cells partition
8K system
2K system
time
OFDM
symbol
frequency
Make subsub-carriers orthogonal (df
(df=1/
=1/dt
dt)) to avoid “inter“inter-carriers” interference
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
ITU seminar - The Digital Video Broadcasting System
Kiev - 13th November 2000
Gérard FARIA - 2000
COFDM : HOW ?
q
2 - Insert Guard Interval to avoid “inter-symbol” interference
Guard
Interval
duration
Useful symbol
duration
time
OFDM
symbol
frequency
BUT : Guard interval introduces a first loss in transport capacity
capacity
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
ITU seminar - The Digital Video Broadcasting System
Kiev - 13th November 2000
Gérard FARIA - 2000
COFDM : HOW ?
q
3 - Insert “Synchronization Pilots” to help Receivers to lock onto the useful signal
OFDM Frame
(68 OFDM symbols)
time
frequency
FFT
time windows
for receivers
BUT : Synchronization markers introduce a second loss in transport
transport capacity
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
ITU seminar - The Digital Video Broadcasting System
Kiev - 13th November 2000
Gérard FARIA - 2000
COFDM : HOW ?
q
4 - Map protected payload bits onto OFDM symbols with frequency interleaving
interleaving
DATA to broadcast
Protected DATA
0
1
0
0
time
1
frequency
Guard
Interval
Useful
Period
Create frequency diversity to improve robustness against selective
selective fading
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
ITU seminar - The Digital Video Broadcasting System
Kiev - 13th November 2000
Gérard FARIA - 2000
DVB-T modes : the trade-off between Bitrate and Robustness
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 dB
0 Mbps
3 dB
3 Mbps
6 dB
6 Mbps
9 dB
9 Mbps
12 dB
12 Mbps
15 dB
15 Mbps
18 dB
18 Mbps
21 dB
21 Mbps
24 dB
24 Mbps
27 dB
27 Mbps
30 dB
30 Mbps
33 dB
33 Mbps
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
The Digital Video Broadcasting System:
The
The Magic
Magic of
of
Single
Single Frequency
Frequency Network
Network (SFN)
(SFN) Operation
Operation
Gerard FARIA
Scientific Director
ITIS - France
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
Gérard FARIA - 2000
ITU seminar - The Digital Video Broadcasting System
Kiev - 13th November 2000
Gérard FARIA - 2000
Spectrum & Power Efficiency : the network point of view
High Power Transmitters
Low Power Transmitters
+ Less Sites in Network
+ Higher “On“On
“On-air”
-air” Redundancy
+ Lower initial Investment
+ lower operational costs due to
higher Network Efficiency
- Lower “On“On
“On-air”
-air” Redundancy
- Higher operational costs due to
lower Power Efficiency
- More Sites in Network
- Higher initial Investment
63 dBµV/m
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
ITU seminar - The Digital Video Broadcasting System
Kiev - 13th November 2000
Gérard FARIA - 2000
SFN, the receivers point of view ...
Channel Impulse Response
Channel Spectrum
To
olved
To make
make receivers
receivers working
working with
with SFN
SFN signals,
signals, all
all transmitters
transmitters inv
involved
in
es” ::
in the
the Single
Single Frequency
Frequency Network
Network shall
shall comply
comply the
the “SFN
“SFN Golden
Golden Rul
Rules”
To
To radiate
radiate .. on
on the
the
.. at
at the
the
.. the
the
SAME
SAME FREQUENCY,
FREQUENCY,
SAME
SAME TIME,
TIME,
SAME
SAME DATA
DATA BIT(s).
BIT(s).
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
ITU seminar - The Digital Video Broadcasting System
Kiev - 13th November 2000
Gérard FARIA - 2000
SFN Golden rules ð on the same frequency
COFDM
modulator
GPS
10 Mhz
Up
converter
GPS
10 Mhz
Up
converter
COFDM
COFDM
receiver
receiver
F0 in few Hertz !
frequency
frequency
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
COFDM
modulator
ITU seminar - The Digital Video Broadcasting System
Kiev - 13th November 2000
Gérard FARIA - 2000
SFN : Frequency domain constraints
DVB-T (8 MHz)
Modes
DAB-T (1,5 MHz)
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
-
-
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 kHz
~ 10 Hz
~ 20 Hz
~ 40 Hz
~ 80 Hz
Bits / symbols
. D - QPSK
Absolute precision
~ 1 Hz
~ 4 Hz
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
ITU seminar - The Digital Video Broadcasting System
Kiev - 13th November 2000
Gérard FARIA - 2000
SFN Golden rules ð at the same time : T0 in few µs !
Primary
Distribution
Network
GPS
1 pps
frequency
Up
converter
frequency
GPS
1 pps
COFDM
modulator
COFDM
COFDM
receiver
receiver
Up
converter
time
time
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
COFDM
modulator
ITU seminar - The Digital Video Broadcasting System
Kiev - 13th November 2000
Gérard FARIA - 2000
SFN : Time domain constraints
DVB-T (8 MHz)
DAB-T (1,5 MHz)
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
896 us
224 us
1000 us
500 us
250 us
125 us
Tx
Symbols duration
Guard Interval durations
7 us
~ 3 kms
14 us
~ 6 kms
28 us
28 us
56 us
56 us
31 us
62 us
112 us
224 us
Delivery Time Accuracy
2..22 us 0..5 us
~24 kms
123 us
~48 kms
248 us
24 us
~12 kms
~96 kms
12 us
6 us
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
3 us
The Digital Video Broadcasting System:
DVB
-T Hierarchical modulation
DVB-T
Gerard FARIA
Scientific Director
ITIS - France
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
Gérard FARIA - 2000
ITU seminar - The Digital Video Broadcasting System
Kiev - 13th November 2000
Gérard FARIA - 2000
DVB-T Hierarchical constellations : another way to use one RF channel
A basic 4 QAM named HP (High Priority) is used as a core modulation......
4QAM - HP
4QAM - HP
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
ITU seminar - The Digital Video Broadcasting System
Kiev - 13th November 2000
Gérard FARIA - 2000
DVB-T Hierarchical constellations : another way to use one RF channel
Then, a Low Priority stream (LP) “over-modulates” the HP one to constitute a....
HIERARCHICAL 16 QAM
made of
4QAM (LP) over 4QAM (HP)
HIERARCHICAL 64 QAM
made of
16QAM (LP) over 4QAM (HP)
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
ITU seminar - The Digital Video Broadcasting System
Kiev - 13th November 2000
Gérard FARIA - 2000
DVB-T : Hierarchical modulation for what ?
To define modulation parameters, the network planning follows “usually”
“usually” these rules :
• to reach a given bitrate, Physical Modulation & Coding rate are determined,
• 2K / 8K format is selected relative to the transmission cell sizes,
sizes,
• Guard Interval value is chosen relative to the nature of the terrain,
terrain,
The
-off ::
The Hierarchical
Hierarchical Modulation
Modulation feature
feature offers
offers aa further
further trade
trade-off
to broadcast TWO services on ONE radio channel
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
ITU seminar - The Digital Video Broadcasting System
Kiev - 13th November 2000
Gérard FARIA - 2000
Hierarchical Modulation : Stationary vs Portable receivers
REG 64QAM 2/3
HP 4QAM 1/2
0
LP
REG
HP
3
6
9
12
15
18
21
24
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
LP 16QAM 2/3
ITU seminar - The Digital Video Broadcasting System
Kiev - 13th November 2000
Gérard FARIA - 2000
Hierarchical Modulation : Mobile vs Static reception
Channel RF2
RF1
+
RF2
REGULAR
LP for Fixed
for
FIXED
Channel
RF1
RF1 + RF2
HPREGULAR
for Mobile
for
MOBILE
0
REG
RF1
16Q
1/2
REG
HP
LP
RF2
RF1.1 RF1.2
64Q 4Q 16Q
2/3 1/2 3/4
6
12
18
24
30
36
42
48
54
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
HP
RF2.1 LP
RF2.2
4Q 16Q
1/2 3/4
The Digital Video Broadcasting System:
Use of DVB-T with Mobile Receivers
Gerard FARIA
Scientific Director
ITIS - France
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
Gérard FARIA - 2000
ITU seminar - The Digital Video Broadcasting System
Kiev - 13th November 2000
Gérard FARIA - 2000
Mobile Receivers behaviour characteristic
C/N
PT1
Working
Reception
Area
(C/N)
+3dB
min
(C/N)min
Not
Working
Area
PT3
PT4
10Hz
PT2
fd,max/2
fd,3dB
fd,max
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
Doppler
frequency
ITU seminar - The Digital Video Broadcasting System
Kiev - 13th November 2000
Gérard FARIA - 2000
Receiver ’s characteristics Dispersion
40 dB
DVB-T mode : 2K, 16QAM, CR: 1/2, GI: 1/4
Classical : 1st Generation chipset
Classical : 2nd Generation chipset
34 dB
Reference Receiver Model
Antenna Diversity : Packet switching
Experimental : Large Filtering
Antenna Diversity : Sub-Carriers switching
C/N
28 dB
22 dB
16 dB
Doppler Frequency
10 dB
0 Hz
50 Hz
100 Hz
150 Hz
200 Hz
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
250 Hz
ITU seminar - The Digital Video Broadcasting System
Kiev - 13th November 2000
Field tests : recorded spectra
Antenna 1
Antenna 2
Gérard FARIA - 2000
(dense urban environment)
-72
MRC
-77
-82
dBµV
-87
-92
-97
distance between Antennae = 20 cm (λ = 38 cm)
789
791
793
795
frequency (Hz)
797
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
-102
799
ITU seminar - The Digital Video Broadcasting System
Kiev - 13th November 2000
Gérard FARIA - 2000
Signal to Noise Ratio vs Doppler
33
8K
SNR (dB)
28
2K
23
18
Gains with MRC
6 dB & 100 Hz
13
8
25
75
125
175
225
275
325
375
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
Doppler (Hz)
425
Speed Limit for 2K
Gain with enhanced
Time Interpolation
Speed Limit for 8K
38
ITU seminar - The Digital Video Broadcasting« Maximum
SystemDoppler Frequency »
vs
Kiev - 13th November 2000
Gérard FARIA - 2000
DVB-T Modes & Channel Profiles
8K 64QAM reg 2/3
19,91 Mbps
2K 64QAM reg 2/3
8K 64QAM reg 1/2
14,93 Mbps
2K 64QAM reg 1/2
8K 16QAM reg 2/3
13,27 Mbps
2K 16QAM reg 2/3
9,95 Mbps
8K 16QAM reg 1/2
2K 16QAM reg 1/2
8K 64QAM a=1 2/3
8K 16QAM a=2 2/3
6,68 Mbps
8K 4QAM reg 2/3
2K 64QAM a=1 2/3
2K 16QAM a=2 2/3
2K 4QAM reg 2/3
8K 64QAM a=1 1/2
4,98 Mbps
8K 16QAM a=2 1/2
8K 4QAM reg 1/2
2K 64QAM a=1 1/2
2K 16QAM a=2 1/2
2K 4QAM reg 1/2
0 Hz
50 Hz
100 Hz
150 Hz
200 Hz
250 Hz
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
300 Hz
350 Hz
ITU seminar - The Digital Video Broadcasting System
Kiev - 13th November 2000
Gérard FARIA - 2000
DAB III (192)
10000 km/h
"Maximum Speed vs RF frequency"
for DVB-T in 2K & 8K modes and DAB
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
CH40
2K 64QAM a=1 1/2
626 MHz
2K 16QAM reg 1/2
1000 km/h
2K 16QAM reg 2/3
Maximum Speed
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
100 km/h
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
10 km/h
100 MHz
Band III
VHF
UHF
Band IV
Band V
8K 64QAM reg 2/3
1000 MHz
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
CH40 - 626 MHz
« MaximumSystem
Speed » using CH40-626 MHz
ITU seminar - The Digital Video Broadcasting
vs
Kiev - 13th November 2000
Gérard FARIA - 2000
2K
4Q
AM
2K
RE
16
G
Q
AM
2K
a=
2
64
Q
AM
8K
4Q a=1
AM
8K
RE
G
16
Q
AM
8K
a=
2
64
Q
AM
2K
a=
4Q
1
AM
2K
RE
16
G
Q
AM
2K
a=
2
64
Q
AM
8K
a=
1
4Q
AM
8K
RE
16
G
Q
AM
8K
a=
2
64
Q
AM
2K
a=
16
1
Q
AM
8K
RE
16
G
Q
AM
2K
RE
16
G
Q
AM
8K
RE
16
G
Q
AM
2K
RE
64
G
Q
AM
8K
RE
64
G
Q
AM
2K
RE
64
G
Q
AM
8K
RE
64
G
Q
AM
RE
G
DVB-T Modes using GI:1/4
60 km/h
3 Mbps
120 km/h
6 Mbps
180 km/h
9 Mbps
240 km/h
12 Mbps
300 km/h
15 Mbps
360 km/h
18 Mbps
420 km/h
21 Mbps
480 km/h
24 Mbps
540 km/h
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
27 Mbps
ITU seminar - The Digital Video Broadcasting System
Kiev - 13th November 2000
Gérard FARIA - 2000
Mobile DVB-T demonstrated at IBC 98
Courtesy of
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization
ITU seminar - The Digital Video Broadcasting System
Kiev - 13th November 2000
Gérard FARIA - 2000
THANK YOU FOR YOUR ATTENTION
Gérard FARIA
gfaria@harris.com
ITIS - France
www.itis.fr
Gerard FARIA - Copyright 2000 - This document cannot be duplicated without a prior written authorization