The ISDB-T System
Masafumi Saito
NHK Science & Technical Research Laboratories
(Japan Broadcasting Corporation)
Contents
1. Concept of ISDB
2. Requirements for ISDB-T
3. Transmission and Services
4. Experimental Results
5. Present Situation in Japan
6. Conclusions
Concept of ISDB
(Integrated Services Digital Broadcasting)
MPEG-2
Video
Satellite
Error correction
RS(204,188)
Coding
Modulation
TC-8PSK
Cable
Audio
Coding
Multiplexing
Error correction
RS(204,188)
Modulation
64QAM
Terrestrial
Data
Error correction
RS(204,188)
+Conv. code
Coding
Modulation
Segmented OFDM
Package Media, Communication Systems
or Other Media (DVB and ATSC)
MPEG-2 TS
Requirements for ISDB-T
(ISDB-Terrestrial)
ISDB-T should
- have the capability to provide various services, including
HDTV, multi-channel SDTV, data services, etc.
- have sufficient transmission quality for the portable
and mobile reception.
- ensure flexible use of transmission capacity.
- be able to achieve effective use of frequency using
SFN (Single Frequency Networks) technology.
Modulation Scheme of ISDB-T
(Band Segmented OFDM)
5.6 MHz
frequency
OFDM Segment
429 kHz
o
Bandwidth of an OFDM segment is 6/14 MHz (≅ 429 kHz).
o
All segments have a common structure.
Number of OFDM segments is 13 for wide-band ISDB-T
and 1 or 3 for narrow-band ISDB-T.
o
Multiplexing and Spectrum of ISDB-T
Wideband ISDB-T
Audio
Program
HDTV
Program
Audio SDTV for SDTV for
Stationary
Program Mobile
Reception Reception
Narrow band ISDB-T
(ISDB-TSB)
Audio
Audio
Program Program Data
Multiplexing
Spectrum
5.6 MHz
5.6 MHz
429 kHz 1.3 MHz
OFDM Segments
Wideband Receiver
(Integrated Receiver)
Narrow band Receiver
(Pocket-size)
Service Examples
Example 1
Example 2
Mobile
Reception
Stationary Reception
Example 3
Mobile
Reception
Stationary
Reception
Mobile
Reception
HDTV
SDTV
or
3 SDTV Programs
+
Data
Integrated Receiver
(all services)
+
Audio
and
Data
Car Receiver
(Audio and Data)
SDTV
+
Data
+
+
Still Picture
Data
Mobile Receiver
(SDTV, Audio and Data)
+
Data
Pocket-size Receiver
(Audio and Data)
Parameters of ISDB-T
Parameters
Number of OFDM segments
Useful bandwidth
Carrier spacing
Number of active carriers
Modulation
Number of symbols per frame
Active symbol duration
Guard interval duration
Inner code
Outer code
Time interleaving
Useful bit rate
(6MHz Bandwidth)
Mode 2
Mode 3
13
5.575 MHz
5.573 MHz
5.572 MHz
1.984 kHz
3.968 kHz
0.992 kHz
1405
2809
4992
QPSK , 16QAM , 64QAM , DQPSK
204
252ｵs
504ｵs
1.008 ms
Mode 1
1/4 , 1/8 , 1/16 , 1/32 of active symbol duration
Convolutional code (1/2 , 2/3 , 3/4 , 5/6 , 7/8)
RS (204,188)
0 ~ 0.44 s
3.651 Mbps ~ 23.234 Mbps
Channel Coding
- Single TS
- Constant clock rate
inserting null-TSP
TS
ReMultiplexer
Outer coder
RS (204,188)
Coded stream is divided
into up to three layers
Splitter
Energy
Dispersal
Delay
Adjustment
Byte-wise
Interleaving
Convulutional
coder
Energy
Dispersal
Delay
Adjustment
Byte-wise
Interleaving
Convulutional
coder
Energy
Dispersal
Delay
Adjustment
Byte-wise
Interleaving
Convulutional
coder
Code rate: 1/2, 2/3, 3/4, 5/6, 7/8
Compensating for the delay difference
among three layers caused by
Byte-wise interleaving
Modulation
Length of time interleaving:
0 ms, 110 ms, 220 ms, 440 ms, 880 ms
Bit
Interleaving
Pilot and
Control
signals
Mapping
Bit
Interleaving
Mapping
Bit
Interleaving
Mapping
Time
Interleaving
Frequency
Interleaving
Frequency Interleaver consists of
Intra-Segment Interleaver and
Inter-Segment Interleaver
- TMCC (Transmission and Multiplexing
Configuration Control)
- SP (Scattered Pilot)
- CP (Continual Pilot)
- AC (Auxiliary Channel)
OFDM
Frame
IFFT
Guard Interval
Insertion
Guard Interval Ratio:
1/32, 1/16, 1/8, and 1/4
Features of the Transmission Scheme
of ISDB-T
o
Different parameters can be set for each layer
→ Wide variety of services
o
Robust against fading in mobile environment
→ Suitable for mobile reception
o
Segment structure
→ Partial reception is possible
o
OFDM modulation → Effective use of frequency by
SFN (Single Frequency Networks)
Practical Experiments (Field Trials)
Tokyo Pilot Experiments
Phase 1 (November 1998 to March 1999)
HDTV, Multi-channel SDTV, Mobile reception, etc.
Phase 2 (April 1999 to March 2000)
Data broadcasting, Multimedia services, EPG, etc.
Phase 3 (April 2000 to March 2002)
Gap-fillers, Multimedia services, etc.
TOKYO TOWER
Transmitting Station of
Tokyo Pilot Experiments
Tx Antenna (261 m)
UHF 15 ch (485.15 MHz)
Tx power: 100 W
ERP: 395W
Field Trials (Fixed Reception)
BER (measured)
BER?2e-4
BER> 2e-4
Field Strength (calculated)
>70dBµV/m
>60dBµV/m
>50dBµV/m
0
50 km
Correct Reception Rate
(Fixed Reception)
Correct Reception Location Rates (%)
100
95
90
85
80
75
Mode 3, 64QAM, 5/6, 13 Seg.
Mode 2, DQPSK, 1/2, 1 Seg.
Mode 2, 64QAM, 7/8 12 Seg.
70
65
60
35
40
45
50
55
60
65
70
75
Measured Field Strength (dB ｵ V/m)
80
85
Field Trials (Mobile Reception)
Total measured distance
- about 3000 km
BER (measured)
BER?2e-4
BER> 2e-4
Field Strength (calculated)
>70dBµV/m
>60dBµV/m
>50dBµV/m
0
50 km
Correct Reception Time Rates (%)
Effect of Time Interleaving
(Mobile Reception)
100
99%
95
90
85
Mode 2, DQPSK, 1/2 , 13 seg.
80
Depth of time interleaving: 500ms
With Time Interleaving
Without Time Interleaving
75
70
35
40
45
50
55
60
Measured Field Strength (dBｵ V/m)
65
Pilot Experiments in 11 Areas
in Japan
Started in April 1999
Purposes:
ｷ Development of new services
suitable for each region
ｷ Confirmation of receiving
area
ｷ Training engineers, etc.
Sapporo
Sendai
Kanazawa
Nagano
Hiroshima
Tokyo
Nagoya
Fukuoka
Osaka
Naha
Takamatsu
Study on Single Frequency Networks
(Development of coupling cancelers)
q Distribution methods of ISDB-T signals from main
transmitters to relay transmitters
n Micro Wave
l Frequency for this purpose is necessary
n Optical Fiber
l Construction and running cost is high
n Relay Networks
l Low cost
l Interference by coupling waves is the problem
Coupling Waves at Relay Stations
Transmitting Antenna
Mountains,
Buildings, etc.
Wave from the
main transmitter
Coupling
Waves f 1
f1
f1
f1
Receiving
Antenna
NHK
SFN Relay Station
Principle of Coupling Cancelers
Receiving Antenna
Wave
from Main
Station
Coupling: C (? )
Transmitting
Antenna
Amplifier:
G (? )
+ _
_
W (? )
Transversal
Filter
Coupling Canceler
Condition for canceling: W (? ) = G (? ) C (? )
Output
Signal
Result of Field Trials
(Effect of Coupling Cancelers)
10-1
-2
BER
10
BER=7ﾗ 10
Mode 3
Guard Interval 1/8
-3
D/U=-6dB
10-3
D/U=8
D/U=0dB
-4
10
64QAM-OFDM,
Without FEC
10-5
20
25
30
C/N [dB]
35
Number of Transmission Stations for Analogue TV
Frequency Allocation in Japan
ISDB-T channels (An example)
700
Adjustment of
analogue channels
600
…
500
13 14 15 16 17 18 19 … … … 25 26 27 28 29 30 31 32
UHF lower channels
(Initial Allocation)
400
Adjustment of analogue
channels except for
major stations
300
200
100
0
1
2
3
4
5
6
7
8
VHF
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62
Channels
UHF
Schedule of Channel Planning in Japan
January 1999:
Start of a consortium on channel plan
April 2000:
Draft channel assignment for main stations
all over Japan
By the end of 2001
Draft channel assignment for major relay
stations
Schedule of Implementation
of ISDB-T in Japan
1999 2000 2001 2002 2003 2004 2005 2006 2007
Service
Final Standard
?
May
Service Start in Tokyo,
Osaka and Nagoya (2003)
?
Pilot Experiments
on a practical scale
Field
Experiments
Frequency
Planning
Channel Plan for
Main Stations
?
Apr.
Channel Plan for
Major Relay Stations
?
Service Start in
other areas (2006)
?
Conclusions
n ISDB-T system based on Band Segmented OFDM
was developed in Japan.
n The ISDB-T system was standardized as the
digital terrestrial television broadcasting system
in Japan in May 1999.
n Pilot experiments of ISDB-T are carried out in 11
major cities in Japan.
n ISDB-T services are planned to start before the
year 2003.