-Digital Terrestrial Television/Sound/Data Broadcasting in Japan-
(Courtesy Asia-Pacific Broadcasting Union.)
Kenichi Tsuchida, Naohiko Iai, Masayuki Takada, Syunji Nakahara, Shigeki Moriyama and Makoto Sasaki
(Digital Broadcasting Networks)

Integrated Services Digital Broadcasting (ISDB) is an emerging digital broadcasting concept. With ISDB, everything is handled digitally. The three kinds of systems, ISDB-S (Satellite), ISDB-T (Terrestrial) and ISDB-C (Cable) were developed in Japan to provide flexibility, expandability and commonality for the multimedia broadcasting services using each network.
Since digital satellite broadcasting began service using ISDB-S in December of last year in Japan, we would like to introduce the three ISDB systems mentioned above. The ISDB-T system is explained in this article, the second in a series of three. This article is a reprint from ABU Technical Review No. 189.


The Integrated Services Digital Broadcasting - Terrestrial (ISDB-T) system was developed to provide flexibility, expandability, and commonality for multimedia broadcasting services using terrestrial networks. ISDB-T system adopted the Band Segmented Transmission - Orthogonal Frequency Division Multiplexing (BST-OFDM), which consists of a set of frequency blocks called OFDM segments. ISDB-T can provide services for both stationary and mobile receivers simultaneously, because BST-OFDM uses a set of OFDM segments with different transmission parameters to allow hierarchical transmission. To confirm the feasibility in real broadcast environments, pilot broadcast stations have been set up in 11 major areas of Japan. The results of the field trials showed the feasibility of ISDB-T system for digital terrestrial television/sound/data broadcasting services.

1. Introduction

The digital terrestrial broadcasting system has been discussed in Japan by the Telecommunications Technology Council (TTC), and detailed technical matters have been left to the Association of Radio Industries and Businesses (ARIB).

Based on the results of field trials, an ISDB-T system was found to offer superior reception characteristics; and consequently, the ISDB-T system was adopted as the Japanese standard for digital terrestrial television broadcasting (DTTB) and digital terrestrial sound broadcasting (DTSB) in 1999. To confirm the feasibility of the ISDB-T system in real broadcast environments, a pilot project was conducted in 11 major areas of Japan. In this paper, we describe the ISDB-T overview and describe its performance in field trials of DTTB and DTSB services.

2. Requirements for ISDB-T

The following are considered to be the main requirements for an ISDB-T system.
It should:
- be capable of providing a variety of video, sound, and data services,
- be sufficiently resistant to any multipath and fading interference encountered during portable or mobile reception,
- have separate receivers dedicated to television, sound, and data, as well as fully integrated receivers,
- be flexible enough to accommodate different service configurations and ensure flexible use of transmission capacity,
- be extendible enough to ensure that future needs can be met,
- accommodate single frequency networks (SFN),
- use vacant frequencies effectively, and
- be compatible with existing analogue services and other digital services.

To meet the above requirements, ISDB-T uses [1]. Three examples of ISDB-T transmission are shown in Figure 1. It can provide HDTV services for wide-band receivers during stationary reception, and multi-program services for wide-band receivers during both stationary and mobile reception. The DTSB system, by contrast, consists of either single or triple OFDM segments [2].

Figure 1: Examples of ISDB-T transmission

The OFDM segment bandwidth is equivalent to 1/14th of a television channel, for example, about 430 kHz (6/14 MHz) in Japan. Three kinds of modes are used, depending on the OFDM carrier spacing. These spacings are approximately 4 kHz (mode 1), 2 kHz (mode 2) and 1 kHz (mode 3). They translate into effective symbol durations of 252 (mode 1), 504 (mode 2), and 1,008s (mode 3). Guard intervals can be selected from among four lengths; 1/4, 1/8, 1/16, and 1/32 of the effective symbol duration. Multipath interference is suppressed by inserting a guard interval in the time domain, thus enabling the system to operate in SFN [3]. Four modulation schemes are supported: QPSK, 16QAM, 64QAM, and DQPSK. Error correction is handled by concatenated codes using convolutional code for the inner code and Reed-Solomon code for outer one. Any time interleaving length ranging between 0 sec and about 1 sec can be specified.

3. Field Trials on DTTB

Table 1: Tokyo Tower transmission conditions
485.15 MHz
(center frequency)
Transmitter 100 W
Power Polarization Linear-vertical
Antenna Height 261 m
E.R.P. 395 W
During the Tokyo DTTB field trials, the ISDB-T signal was transmitted in the UHF band [4]. The transmission conditions are listed in Table 1.
The transmission parameters used in the stationary reception experiments are listed in Table 2. The number of measured points is 127. These points are shown in Figure 2. The location rates of correct reception are plotted in Figure 3. The required minimum field strength for 99%-correct reception (S1 and S3) was about 57 dBV/m.
The transmission parameters used for the mobile reception experiments are listed in Table 3. The bit error rates and field strengths over the measured routes are shown in Figure 4. Figure 5 shows the time rates of correct reception. The required minimum field strength for 99%-correct reception (M1) was about 51 dBV/m. The figure compares the correct reception rates for transmission with (M1) and without (M2) time interleaving. The required minimum field strength for 99%-correct reception with time interleaving was about 10 dB lower. We conclude that time interleaving is very effective in mobile reception.

Table 2: Stationary reception parameters
Stationary Reception
No. S1 S2 S3
Mode 3 2
Guard Interval Ratios 1/16 (63s) 1/8 (63s)
Number of Segments 13 1 12
Carrier Modulations 64QAM DQPSK 64QAM
Inner Code Rates 5/6 1/2 7/8
Time Interleaving 0 ms 0 ms 0 ms
Information Rates 21.47Mbps 312kbps 19.66Mbps

Figure 2: Measured BER for S3 condition

Figure 3: Correct reception location rates

Table 3: Mobile reception parameters
Mobile Reception
No. M1 M2
Mode 2
Guard Interval Ratios 1/8 (63s)
Number of Segments 13
Carrier Modulations DQPSK DQPSK
Inner Code Rates 1/2 1/2
Time Interleaving 427.5 ms 0 ms
Information Rates 4.06 Mbps 4.06 Mbps

Figure 4: Measured BER in M1 condition

Figure 5: Time rates of correct reception

4. Field Trials on DTSB

ISDB-TSB (ISDB-T for Sound Broadcasting system has two kinds of bandwidths: a single segment, and an extended version using triple segments. The information bit rate of the system ranges from 280 kbps to 5.3 Mbps depending on the combination of transmission parameters. Table 4 shows two service examples using coding rate of covolutional code 1/2, which is the robustest coding rate of this system. In the case of carrier modulation scheme DQPSK, one stereo audio program, Electric Programming Guide (EPG), still pictures and files can be broadcasted within the bit rate of about 330 kbps. In the case of 16QAM, two stereo audio programs, EPG, motion picture and files can be broadcasted within the bit rate of about 660 kbps.

Table 4: Service examples of narrow-band ISDB-TSB
Number of Segments 1-segment
Guard interval ratio 1/16
Inner code rate 1/2
Carrier modulation DQPSK 16QAM
Information bit rate 330.42 kbps 660.84 kbps
Stereo audio 144 kbps (1 program) 288 kbps (2 programs)
Character (include EPG) 16 kbps 16 kbps
Picture 64 kbps (still) 256 kbps (motion)
File (ex. newspaper) 32 kbps 32 kbps
Control 64 kbps 64 kbps
Total bit rate 320 kbps 656 kbps

Table 5: Outline of experimental transmitter
Transmitter Frequency 190 MHz
Transmitter Power 100 W
Polarization Linear-vertical
Antenna Height 247.5 m
Max. ERP 800 W
In Tokyo area, the trials of mobile reception were carried out using the single-segment system. The transmission condition and parameters used in the trials are listed in Table 5 and Table 6 respectively. For the receiver antenna, a dipole antenna was installed on the roof of a vehicle. The height of the receiver antenna is 1.8 m. The receiving vehicle ran approximately 700km on main roads including expressway and main arterial road.
Figure 6 shows the correct reception time rates on the measurement course. For example, to obtain a correct reception time rate of 99%, it was found that the DQPSK modulation requires a field strength of 38 dBV/m and the 16QAM requires a field strength of 44 dBV/m. From the results, it was found that DQPSK was approximately 6dB more robust than 16QAM in mobile reception environment.

Table 6: Transmission parameters of mobile reception trial for ISDB-TSB
Mode Guard ratio Time interleaving Carrier modulation Error correction
3 1/16 407ms DQPSK 1/2+RS
3 1/16 407ms 16QAM 1/2+RS

Figure 6: Correct reception time rates for each field strength of wide-area mobile reception trial

5. Multimedia Services

In the Tokyo pilot project, application tests that involved the transmission of video, sound, and data, using signals that were close to those of actual services, were conducted. In these test, function verifications for the reception of data transmitted in conjunction with TV programs were carried out. These verifications focused on the transmission and reception of independent data services (i.e., news and weather forecasts) and program-linked data services.

6. ISDB-T Facilities in Japan

Figure 7: ISDB-T facilities in Japan
The Ministry of Posts and Telecommunications (MPT) launched several facilities to accelerate DTTB and DTSB services throughout Japan. The pilot broadcast stations were set up in 11 major areas in 1998 (Figure 7). The output powers of the main stations are over the kW range. Some stations have a number of relay stations used to verify SFN. All the facilities are capable of providing HDTV, SDTV and data services with multimedia applications and interactive functions.

7. Conclusions

Digital satellite broadcasting began service using ISDB-S in December of last year in Japan. ISDB-T is designed to be compatible with ISDB-S. ISDB-T receivers can use the same devices as ISDB-S receivers, except for the ISDB-T-oriented OFDM chip. The common receiver will be also available. Regarding multimedia facilities, Digital Satellite Broadcasting using ISDB-S provides datacasting services and interactive services. It is obvious that the same technologies and facilities will be easily implemented for ISDB-T.

[1] T. Kuroda and M. Sasaki : "Terrestrial ISDB System using Band Segmented Transmission Scheme", International Television Symposium, ITVS 20, pp. 641-654 (1997)
[2] M. Takada, M. Sasaki, T. Ikeda: "Draft Standard for Digital Terrestrial Sound Broadcasting in Japan", NAB 53rd Annual Broadcasting Engineering Conference (1999)
[3] S. Nakahara, S. Moriyama, T. Kuroda, M. Sasaki, S. Yamazaki, and O. Yamada : "Efficient Use of Frequencies In Terrestrial ISDB System", IEEE Trans. On Broadcasting, Vol. 42, No. 3, pp. 173-178 (1996)
[4] S. Moriyama, M. Takada, S. Nakahara, H. Miyazawa : "Progress Report of ISDB-T System", Broadcast Asia 2000

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