Digital Terrestrial Television Broadcasting

outline and transmission scheme

Dec. 8, 2009
NHK Science and Technology Research Laboratories

ISDB-T,

Masayuki TAKADA

Contents
1. Introduction 2. Transmission scheme of ISDB-T
Digital modulation OFDM Interleaving Hierarchical transmission

3. 4. 5. 6.

Comparison of 3 DTTB systems Current services of ISDB-T in Japan ISDB-T receivers on the market Summary
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1. Introduction
Requirements for DTTB, and features of ISDB-T History and schedule of ISDB-T
DTTB (Digital Terrestrial Television Broadcasting) ISDB-T (Integrated Services Digital Broadcasting - Terrestrial)

Requirements for DTTB

For success of DTTB introduction
Requirements for DTTB
Attractive broadcasting service
High quality TV and sound (HDTV, 5.1 surround) Anytime information access (Data, Internet) Robustness against interference

Mobile and portable reception

Anytime, anywhere TV service (HD mobile and One-Seg)

Effective Frequency Utilization

SFN (Single Frequency Network)
4

What is ISDB-T ? ISDB-T is ...

One of the DTTB systems in the world
There are 3 systems recommended in ITU-R BT1306.
ISDB-T, DVB-T and ATSC

The most flexible system

HDTV, multi-SDTV, EPG, data-casting, internet-access, mobile reception, Cellular phone TV, etc.

The most robust system

OFDM, time-interleaving, etc. Brazilian comparison test results proved it.

Developed in Japan
5

ISDB-T transmission from the broadcaster to the receivers

One TV channel 13 Segments

Support 3 reception types by one channel

13 segment Fixed Reception

Internet / Telephone modem

TV station

Home Receiver
1 segment Handheld Reception 13 or 1 segment Mobile Reception diversity reception

Handheld terminal

Receiver in Vehicle
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ISDB-T realizes these services

HDTV

Multiple programs

Data broadcasting

Mobility

Merits
2

Advanced caption etc.

Interactive TV

History and schedule of DTTB in Japan

Jul. 2011 Analog TV Switched off

Dec. 2006 Apr. 2006 Dec. 2003

ISDB-T started (at main cities of the whole country) One-Seg service started

ISDB-T launched! (Tokyo, Nagoya, Osaka)

2000 ISDB-T recommended in ITU-R 1999 ISDB-T technical standard established in Japan
1994
End of 1980' Technical requirements for DTTB studied at Council OFDM study started in NHK Labs.
8

2. Transmission scheme of ISDB-T

Features and key technologies of ISDB-T
Digital modulation OFDM Interleaving Hierarchical transmission

ISDB-T (Integrated Services Digital Broadcasting - Terrestrial)

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Outline of digital transmission

Video/Audio Source (Analog)

Digitalization

Compression

Error correction coding

Digital modulation
Transmission

Source coding Video/Audio Signal (Analog)

Channel coding Error correction decoding

Source decoding

Digital demodulation

Noise, Multipath, Fading, etc

13

Receiving environment for terrestrial TV broadcasting

Fixed reception

Mobile reception

Multipath interference Fading interference Impulse, manmade noise Shadowing

Handheld reception

Receiving environment is very severe.

15

Key technologies of ISDB-T

Key technologies adopted in ISDB-T
To overcome the terrestrial severe receiving environment OFDM Time-interleaving (Freq.&Time interleave) To realize the effective and smart transmission Hierarchical transmission by segmented OFDM
Realization of One-Seg service for handheld reception
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Digital modulation
In the case of digital modulation, amplitude, frequency or phase of carrier changes digitally depend on digital data ASK (Amplitude Shift Keying) 1 0 1 0
modulate carrier amplitude

FSK (Frequency Shift Keying)

modulate carrier frequency

PSK (Phase Shift Keying)

modulate carrier phase
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PSK and QAM

BPSK (Binary Phase Shift Keying)
uses two phases of carrier

QPSK (Quadrature Phase Shift Keying)

uses four phases of carrier

8PSK (8 Phase Shift Keying)

uses eight phases of carrier

16QAM (16 Quadrature Amplitude Modulation)

uses 4 levels in orthogonal phases (in-phase and quadrature phase)

64QAM (16 Quadrature Amplitude Modulation)

uses 8 levels in orthogonal phases (in-phase and quadrature phase)
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Constellations
BPSK
Q
[C] [01]

QPSK
Q
A

8PSK
[C1 C0] [00]

Q
[010] [100]
A

[C2 C1 C0]
[011] [001] [000]
A

[1]
-A

[0]
A

-A

-A

[11]
-A

[10]

[101]

-A

[110] [111]

1bit/symbol

2bits/symbol

3bits/symbol

16QAM Q I

64QAM Q I

4bits/symbol

6bits/symbol

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BPSK modulation
input data input pulses
0 1 0 0 1

cosine
=0 = =0 =0 =

=0

Signal space diagram

BPSK signal

20

QPSK modulation
=3/4 Q = /4 (00) I (10) = 7/4

binary input

(01) (11) =5/4

010100011010010101 Level Conv. I data

Modulated : I

+A -A

0 0 0 0 1 1 0 0 0 Modulated : Q

Q data

+A -A

1 1 0 1 0 0 1 1 1 QPSK out (I+Q)

01 01 00 01 10 10 01 01 01 11
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Comparison of PSK modulations

overlap
2

Noise
Q

(01)

(00)
1

(011)
(010) (100) (001) (000) (111)
0

(1)

(0)

0 -1

-1 -2 -2

-1 -1 0 1 2 -2

(11)
-1 0

(10)
1 2

(101)
-1

(110)
1 2

-2 -2

BPSK
Strong

QPSK
Robustness
Transmission capacity

8PSK
Weak

Low

High
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Bit Error Rate / Carrier-to-Noise Ratio

10-1 BER

10-3
BPSK -5 10

8PSK
QPSK

16QAM

Good

10-7 5

10 15 C/N (Nyquist)

20 Good
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OFDM
Orthogonal Frequency Division Multiplexing Multicarrier modulation method
500 8000 carriers

Modulation method of each carrier is BPSK, QPSK, 16QAM, 64QAM, etc.

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Features of OFDM
Robustness against multipath interference
symbol duration is longer than single carrier modulation guard interval is provided

Robustness against frequency-selective fading

OFDM uses many carriers

SFN (Single Frequency Network)

frequency effective usage

Signal process using IFFT/FFT Poor against non-linearity

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OFDM waveform and spectrum

Time domain signal
Carrier #1
+
+

Frequency domain signal

Carrier #2
+ +

Carrier #k
+ =

+ +

Transmitting Signal

S (t ) cn e j ( 2 ( nf )t n )
n 0

N 1

GI

Effective symbol duration

transmitting symbol S(t)

FFT/ IFFT

Frequency

Addition of various carriers !!

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Fast Fourier Transform

Enables Frequency Analysis
Time Domain Frequency Domain

FFT

wave (1KHz)

IFFT

1KHz

FFT

IFFT wave (containing various frequency)

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Overview of OFDM modulation

Modulation
Frequency domain
QAM Mapping

Transmission
Time domain

Demodulation
Frequency domain
QAM Demapping

IFFT
n= n=2

FFT
time
n= n=2 n=N-1 freq n=N

n=N-1 freq n=N

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Multipath Echo Interferences

Multipath echo = Delayed wave

NHK

Main path

Multipath echo interferes the receiving performance

30

Signal Distortion by Multipath Echo

10MHz

10MHz

Transmitted signal

Received signal

= includes Main path and Multipath Echo

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Why signal distorted ?

Carrier combined with opposite phase / C/N=small Carrier combined with same phase : / C/N=large

Power

Frequency
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Why Signal Distorted ?

Case of same phase composition
Power

Main path
Freq

Delay path
Looking on one carrier

Received Signal
=Main path +Delay path

Amplitude increase

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Why Signal Distorted ?

Case of opposite phase composition
Power

Main path
Freq

Looking on one carrier

Delay path

Received Signal
=Main path +Delay path

Amplitude decrease
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Guard Interval
Time Domain copy signal copy signal

ISDB-T Signal
Guard Interval Effective Symbol

Tg
126ms (*)

Ts
1008ms (*)
(*) figure of NHK actually its flexible

Transmitting Symbol

In transmittingAdd partial copy of Effective Symbol In demodulation extract only effective symbol duration length from transmitting symbol and execute FFT Able to eliminate the effects of multipath echo interference within delay time of Tg [sec]
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Effect of Guard Interval

Time

Symbol #N-1
Looking on one carrier Guard Interval

Symbol #N
Transmitting symbol Effective symbol

Symbol #N+1

Main path

Delay path
Delay time

Received Signal
=Main path +Delay path

Non Continuous !!

Only use here for demodulation (FFT)

Able to eliminate non continuous part 36

Performance of OFDM
under multipath distortion
D/U Ratio of Desired wave (mainpath) and Undesired wave(echo)

D/U = 0 dB

10-1
Bit Error Rate

10-2 10-3 6 dB
10
-4

10 dB

guard interval
10-5 0

64QAM-OFDM C/N = 30 dB
150
37

50 100 Delay time [usec]

Interleaving
Interleaving
Randomization of data symbols Carrier arrangement time-sequence of symbols

An order is randomly changed.

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What is interleaving ?
Actual data

Data 1

Data 2 Data 3
Shuffle order of data

Data k

Data

Transmit after interleaving

Mass Data error in specified area or frequency

Transmitting data Reorder Received data

Error Error Correction Correction Error Correction Error Correction

Deinterleave after receiving

Able to fix the mass data error by Interleaving !!

Data after error correction

Frequency or time duration

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Effect of frequency interleaving

Cumulative correct reception rate (%)

100
3.5MHz

98
1.5MHz

100kHz

96
500kHz

94
92
Time interleave length : 48msec Maximum Doppler frequency : 15Hz

Spectrum (Multipath distorted)

90

10-2

Bit error rate

10-1
40

Good

Effect of time interleaving

Laboratory test results
flat fading,DQPSK,Mode=1,GI=1/8,FEC=1/2,RS=OFF 1.00E+00 1.00E-01

Better

1.00E-02
BER

Fd = 7 Hz Fd = 20 Hz Without time interleaver

1.00E-03 1.00E-04 1.00E-05

Fd = 20 Hz Fd = 70 Hz Fd = 7 Hz

Fd = 70 Hz

Without time-interleaver (Error remains even in With time interleaver high C/N) of 440 ms

1.00E-06 5 10 15 20 25 30 C/N[dB] 35 40 With time-interleaver (No error at more than C/N=20dB)

Far from Tx

Near to Tx

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Hierarchical transmission
ISDB-T adopts hierarchical transmission system
by FDM (frequency division multiplexing) of Segment

Hierarchical transmission is realized by changing following parameters

Modulation : QPSK, 16QAM, 64QAM, (DQPSK)

QPSK
More robust

16QAM

64QAM

Higher capacity

Error correction : Coding rate of convolutional code (1/2 - 7/8) 1/2

More robust Higher capacity
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2/3

3/4

5/6

7/8

Flexible hierarchical transmission by segmented OFDM

ISDB-T - Consists of 13 OFDM segments - Hierarchical transmission by segmented OFDM - Up to 3 layers Examples
1 layer 2 layers 3 layers
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6MHz
(13 segments)

frequency

For fixed receivers

For mobile receivers For handheld receivers

Example of hierarchical transmission

Layer A

Example
(2 layers transmission)
1 channel
(13 segments)

Handheld reception (One-Seg service)

For handheld service

Robust transmission mode

frequency

Layer A
LDTV, Audio, Data

QPSK FEC=2/3 Layer B

Fixed reception, Mobile reception (HDTV,etc)

For HDTV
or Multi-SDTV

Layer B
HDTV or Multi-SDTV programs with Data

service
High capacity transmission mode
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64QAM FEC=3/4

Transmission parameters used in Japan

Used bandwidth Number of carriers Carrier spacing 5.572 MHz 5617 (8k FFT) 0.992 kHz

Usable symbol duration

Guard interval ratio (length)

1008 s
1/8 (126 s) A 1 QPSK

Hierarchical transmission
Number of segments Carrier modulation Coding rate of inner code (convolutional code) Outer error correction code Time interleaving length Information bit rate Required CN ratio for AWGN

B
12 64 QAM 3/4 RS(204,188) 215 ms 16.85 Mbps 20.1 dB

2/3
RS(204,188) 430 ms

416 kbps
6.6 dB

Features of ISDB-T transmission system

1. Robustness against interference
(1)Adopt OFDM transmission system (2)Adopt time interleaving; very effective for various kinds of interference (3)Adopt concatenated error correction with plural interleaver

2. HDTV for fixed/mobile and One-Seg for portable/handheld can be transmitted simultaneously in one TV channel
(1)Hierarchical transmission by segmented OFDM (2)Partial reception of center one-segment for handheld service

3. Efficient frequency utilization

(1)Adopt OFDM transmission system; SFN operation (2)Adopt hierarchical transmission; service for different type of reception in one frequency channel

4. Flexibility for several type of service/reception style

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3. Comparison of 3 DTTB systems

Features of 3 DTTB systems Results of comparison tests Summary of comparison

47

Key parameters of 3 DTTB systems

System
Modulation Interleaving Frequency
time
Excess Bandwidth/ Guard Interval
Bit/Symbol

ATSC
8VSB Yes -

DVB-T
OFDM (QPSK, 16QAM,64QAM) Yes Yes -

Segmented OFDM (DQPSK,QPSK, 16QAM,64QAM) Yes Yes 0s, 0.1s,0.2s,0.4s

ISDB-T

11.5%
-

1/4,1/8,1/16,1/32 1/4, 1/8,1/16,1/32

TPS TMCC

Configuration

Information bit rate Channel bandwidth

19.39 Mbps 6 / 7 / 8 MHz

3.69 -23.5Mbps 6 / 7 / 8 MHz

3.65 -23.2 Mbps 6 / 7 / 8 MHz

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Results of Brazilian Tests

Comparison tests for three DTTB systems - ATSC, DVB-T, ISDB-T Carried out from Aug. 1999 to April 2000 Selected transmission parameters
- Almost same transmission bit rate

ATSC
Fixed, 8VSB FEC=2/3 (19,39 Mbit/s)

DVB-T
DVB-2K : 64QAM FEC=3/4 GI=1/16 2K (19,75 Mbit/s)

ISDB-T
ISDB-4k : 64QAM FEC=3/4 GI=1/16 4K 0,1s (19,33 Mbit/s)
(From the presentation of the Brazilian SET/ABERT study group at NAB2000)

50

Impulse noise
Relation between the noise pulse width & interference to signal ratio
ATSC - Chip A
30
25

DVB - NDS - 3/4 1/16 2K

ISDB-T

ISDB - NEC - 3/4 1/16 4K 0,1s

20

"I"/C (dB)

15 10 5

Better

ATSC

0 -5
-10

DVB-T

-15
0 100 200 300 400

Pulse width (us)

Better performance of the ISDB-T system, by introducing time interleaving

(From the presentation of Brazilian SET/ABERT study group at NAB2000)
51

Outdoor : Coverage
Success on Receiving - Cumulative Function Criterion: Number of Errors < 5
100%

ISDB-T
Percentage of Sites
90%

DVB-T

Better

80%

70%

ATSC

60% 0

10

15

20

25

30

35

40

Distance (km)
ATSC DVB-2k

ISDB-T

(From the presentation of Brazilian SET/ABERT study group at NAB2000)

52

Essence of comparison test results

The OFDM modulation scheme is suitable for DTTB in real broadcast circumstances.
Time interleaving scheme, adopted in ISDBT, is a key technology for mobile digital transmission and is also effective to cope with impulse noise degradation.

ISDB-T showed the best results in Brazils comparison tests, and other countries such as Chile, Peru, Philippine, etc.
55

4. Current services of ISDB-T in Japan

HDTV, SDTV multi-program, EPG (Electric Program Guide) Data broadcasting, Interactive One-Seg (Handheld) EWS (Emergency Warning System)

56

Powerful applications of ISDB-T

HDTV Multi-channel program Data broadcasting

High quality image on wide screen and CD quality sound.

Standard quality multi-channel service

Local news and weather forecast for viewers at any time.

Interactive service

One-Seg service

Mobile reception

Offers Interactive service

Anytime, anywhere, TV service

Stable reception service 57

HDTV
High

Definition Television Program

The high quality images on a 169 wide screen and CD-quality sound make you feel as if you were at the theater. European broadcasters have opted for multichannel strategy, but Japanese broadcasters have chosen to take advantages of high definition pictures. HDTV is a killer application.

58

Multi channel program (SDTV)

ISDB-T can transmit multiple SDTV programs simultaneously in one TV channel.

SD-1

SD-2

-----

SD-8
59

EPG
EPG (Electronic Program Guide)
An Electronic Program Guide (EPG) is an interactive schedule of current and upcoming programs that a viewer can display on-screen simply by pressing a button on a remote control unit.

63

One-Seg service for handheld receiver

Display Image

On-air program
Example parameter Transmission Mode 3 Guard Interval 1/8 Modulation QPSK Code Ratio 2/3 Bit Rate 416 Kbps

Video (H.264)
180-256kbps

Audio (AAC-SBR)
32-64kbps

Data-cast (BML)
20-80kbps

Data service
64

Emergency Warning System

Application to Disaster Prevention
Schematic diagram for disaster prevention service
PossibilityText of a flood in the xxx river has increased. Residents in the surrounding areas should evacuate. Areas affected are as follows.

Image
Emergency evacuation areas

Transmission without congestion

Start signal

On-air waves

Mobile base station

Screen

TV station
Tuner power ON

Master room EMG-button

Test Server

Evacuation recommenda tion order

BML automatic converter

Screen display

65

5. ISDB-T Receivers on the Market

TV set (PDP, LCD, CRT) (fixed reception home receiver) STB (Set Top Box) HDD/DVD recorder with digital tuner One-Seg receiver (Cellular phone) HDTV mobile receiver for car TV Portable player
70

Wide variety of ISDB-T receivers

TV set
STB HDD/DVD recorder Cell phone

PC

Laptop / handheld PC
Car TV

Handheld TV

71

ISDB-T receivers for fixed reception

Panasonic

SONY

Toshiba

Hitachi

SANYO

Victor

Pioneer

Sharp

Mitsubishi

NANAO

EPSON

72

Types of fixed reception digital receivers (HDTV)

(Plasma Display type)

(LCD type)

(CRT type)
(Rear Projection type)
73

PCs with ISDB-T tuner (HDTV)

74

Set Top Box (DTTB Tuners)

SONY DST-TX1

PANASONIC TU-MHD500

SHARP TU-HD200
75

HDD/DVD recorders with DTTB tuner

HITACHI SHARP

Panasonic

SONY

Pioneer

TOSHIBA

SANYO

Victor

76

Cellular Phones for One-Seg

77

PCs with ISDB-T tuner (One-Seg)

Tune r

78

USB type ISDB-T Tuners for One-Seg

79

Portable DVD Players with ISDB-T tuner (One-Seg)

80

Other Portable One-Seg devices

Portable Audio Player

Portable Electronic Dictionary

Portable Navigator

Portable TV
81

Mobile receivers for car TV system (HDTV / One-Seg)

Panasonic TU-DTV100, TU-DTV20

SANYO NVP-DTA10

Mitsubishi TU-100D

Pioneer GEX-P7DTV

Fujitsu Ten DTV105

Alpine TUE-T300

82

6. Summary

83

Summary
ISDB-T is the most robust transmission system
Adopting OFDM and time-interleaving Brazil, Chile, Peru, Philippine, etc. confirmed ISDB-T performance is the best.

HDTV (or SDTV multi-channel) and One-Seg (handheld TV service) can be transmitted simultaneously in a channel
ISDB-T enables both digital TV service for fixed and mobile (handheld) by just one transmission facility

HDTV and mobile TV (One-Seg) using ISDB-T is successfully progressing in Japan.

84

Muchas Gracias!
Thank You for Your Attention!

85