The digital broadcasting system was discussed in Japan by the Telecommunications Technology Council (TTC) of the Ministry of Post and Telecommunications – MPT (current MIC: Ministry of Internal Affairs and Communications), and detailed technical matters have been discussed at the Association of Radio Industries and Businesses (ARIB).
ISDB (Integrated Services Digital Broadcasting) 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.
Based on the results of field trials, ISDB-T system was found to offer superior reception characteristics; and consequently, the ISDB-T system was adopted in Japan as the digital terrestrial television broadcasting (DTTB) system and digital terrestrial sound broadcasting (ISDB-TSB) system in 1999.
8.2 Time schedule for digital terrestrial television
Figure 49 shown below presents the time schedule for Digital Broadcasting in Japan.
Digital terrestrial broadcasting was launched in December 2003 in Tokyo, Osaka and Nagoya metropolitan areas. In addition, digital terrestrial broadcasting has started at the main cities in all other prefectures as of the end of 2006. The service areas become wider step by step. Analog terrestrial television broadcasting will be terminated in 2011.
8.3 Frequency Situation
Analog terrestrial broadcasting utilizes MFN (Multi-Frequency Network), a transmission scheme that uses a different transmitting frequency in each service area. MFN with many transmitting stations is a solution for delivering programs to the national audience without causing harmful radio interference among service areas. Approximately 15,000 transmitting stations for analog terrestrial television broadcasting were constructed throughout Japan. So there are not enough frequencies for digital television broadcasting.
The Japanese Government is undertaking a huge program which will cost around 180 billion Yen (approx. 1.8 billion US $) to move a quantity of analog television stations to the upper part of the spectrum in order to free up the frequencies for digital television.
8.4 TV channels in Tokyo
Nine digital TV channels are transmitted from Tokyo tower.
8.5 Transmission Antennas
In the Tokyo area, broadcasters have placed new antennas at a height of 250 m on Tokyo Tower. A transmitter room was built under the tower's large observatory. In the Nagoya area, a new facility with a
246-m steel tower and a broadcasting station has opened in Seto city. In the Osaka area, broadcasters installed antennas on their own towers. An overview of these facilities is shown in Fig. 52.
Although digital terrestrial broadcasting started only approximately 4 years ago (December 2003), over
25 million ISDB-T receivers have been shipped to date (50 million households in Japan).
8.7 Technical Characteristics of ISDB-T
The system compatibility between digital television and digital sound broadcasting is taken into consideration in ISDB-T. ISDB-T with full segments serves digital terrestrial television broadcasting and ISDB-TSB using one segment or three segments serves digital terrestrial sound broadcasting.
ISDB-T is also capable of providing data broadcasting consisting of text, diagrams, still pictures, and video image for handheld devices, in addition to high quality pictures and stereo sound. In contrast with digital satellite broadcasting, it is able to feature detailed local interest information. Furthermore, it has great potential to diffuse information to mobile multimedia terminals, such as car radios and pocket-sized receivers.
The following requirements were considered in the development of ISDB-T.
− 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 analog services and other digital services.
To comply with all the specified requirements ISDB-T made use of a series of unique tools such as the OFDM modulation system associated with band segmentation, which gives the system great flexibility and the possibility of hierarchical transmission, time interleaving which contributes to achieving the necessary robustness for mobile and portable reception besides giving the system powerful robustness against impulsive noise and TMCC (Transmission and Multiplex Configuration Control) which allows dynamic change of transmission parameters in order to set the system for optimized performance depending on the type of broadcasting (HDTV, mobile reception, etc).
These unique characteristics make ISDB-T able to provide a wide range of applications such as those presented in the next chapter.