Features of ISDB-T system
ISDB-T (Integrated Services Digital Broadcasting – Terrestrial) has been developed and deployed in Japan and Latin America.
In Japan, DTTB service has started since December 2003, and the migration from analog to digital had been smoothly completed. Also, "One-seg" service, which is a new portable reception service in the same channel, has been started since April 2006 in Japan.
|1.||Structure of ISDB-T (Japan)|
|2.||High quality / Service Flexibility|
|3.||Features of transmission system (Robustness, Reception System Flexibility, Frequency Utilization, Mobility & Portability)|
|3.1||OFDM transmission technology (robustness against multi-path, SFN)|
|3.2||Time Interleave (Robustness against urban noise, Mobility & Portability)|
|3.3||Segmented OFDM transmission (Portable reception in same channel)|
|3.4||Comparison of the transmission performance of 3 DTTB systems|
1. Technical requirements for Digital Terrestrial TV Broadcasting (DTTB) in Japan
When the research and development on digital broadcasting has started in Japan, it was expected HDTV would to be a main service of next generation of broadcasting, on the other hand, ordinal SDTV still would remain as an important broadcasting service. Hence, the harmonization between HDTV and SDTV had to be an important issue of next generation broadcasting in Japan.
In addition, because the condition of frequency in Japan was heavily crowded, "Effective utilization of frequency resource" was considered as one of the requirements of next generation broadcasting.
Moreover, internet service was on the way of penetration and it was forecasted to be the main service of communications in near future. That was a reason that the harmonization with Internet was set as an important requirement. To realize the interactive service, data–casting was also set as a requirement.
Further more, mobile and portable services were recognized as an important advantage of the new broadcasting service. Therefore, new technology should be developed and adopted for mobile and portable broadcasting services.
These requirements have been realized in ISDB-T system.
|1||High quality||HDTV should be possible in the bandwidth (6/7/8MHz)|
|2||Robustness||Robustness against multi-path, urban noise, fading and any other interference|
|2(1)||Service Flexibility||Any kinds of service are possible in the bandwidth||HD/SD possible|
|2(2)||Reception flexibility||Any kinds of reception system are possible, fixed/mobile/portable in the same bandwidth|
|3||Effective utilization of frequency resource||SFN (Single Frequency Network) is possible to reduce frequency.|
|4||Interactivity||Harmonization with internet|
|6||Commonality||Maximum commonality is need to reduce receiver cost. Especially, to digital radio, common standard is desirable.|
2. Technical features of ISDB-T
ISDB-T had been developed to realize the requirements shown in Table 1, therefore ISDB-T has many technical advantages described below.
For technical details, please refer ANNEX- AA.
(1) High quality / service flexibility
(a) Flexible multiplex technology (MPEG-2 systems) and (b) Flexible and high efficiency video/audio coding system (MPEG-2 and MPEG AAC) are adopted in ISDB-T. As a result, many types of broadcasting service, such as (a) HDTV, (b) HDTV+SDTV and (c) Multi-channel SDTV, are supported by ISDB-T.
(2) Robustness / reception flexibility
For designing the transmission system of digital terrestrial broadcasting, it is important to consider degradation factor of VHF/UHF band, such as thermal noise, multi-path interference (static and dynamic), urban noise, fading of mobile/ portable reception and others. To give the robustness against such degradation factor, ISDB-T adopts OFDM transmission system with "Time Interleave" technology. As a result, ISDB-T gives; (a) lower transmitter power, (b) possibility of indoor antenna reception and (c) mobile/portable reception service, etc.
(3) Effective utilization of frequency resource
OFDM transmission system contributes to construct Single Frequency Network (SFN), which makes possible to save the frequency resource for relay transmitter (repeater), use the same frequency for plural transmitters of the same network, and receive the programs by mobile or portable equipment without changing a receiving channel.
(4) Mobility/ Portability
To enable fixed, mobile or portable reception service in the same bandwidth, ISDB-T adopts new transmission technology, named "Segmented OFDM transmission system". This technology enables "One-seg" service, using 1 segment in the bandwidth. One seg receiver is easily mounted into mobile-phone, portable PDA, USB tuner ,etc, and it realizes the "Any time, Any place" broadcast service.
(5) One-seg service
One-seg service, that uses 1 segment in the same bandwidth, does not need another transmitter for the service. It leads saving of frequency resource and broadcaster's infrastructure cost. And more, Narrow band reception of One-seg receiver saves power consumption. As a result, long time reception is possible.
To reduce the cost of the receiver, the backend technology of ISDB-T is using the same technology as satellite, terrestrial and cable. As a result, the same backend chip can be mounted in these digital receiver. Actually integrated receiver equipped with both satellite and terrestrial tuner is ordinal.
(7) Utilization for disaster prevention
Utilization for disaster prevention is also important issue of digital broadcasting. ISDB-T has the advantage on portability and has the function EWBS (Emergency Warning Broadband System) [note].
[note] The purpose of EWBS is to start up receiver automatically by warning signal put into broadcast signal.
3. ISDB-T International
As well-known, Brazil adopted ISDB-T as a terrestrial broadcasting system in June,2006.
Brazilian system is not perfectly same as Japanese system, for example, H.264 for SDTV and HDTV coding technology, and another technology for middle-ware.
However, the structure of DTTB system is same, and transmission system is just same as Japanese system. Brazilian ISDB-T is one of ISDB-T family and has the same features of Japanese ISDB-T.
Following Brazil's adoption, many countries in Latin America and Asia adopted ISDB-T. That brings the expansion of the ISDB-T market and also the reduction of the receiver prices.
4. Current status of ISDB-T in Japan
In Japan, DTTB has started since December 2003 at 3 metropolitan areas, and expanded the cover area to all prefectures of the country. And One-seg service has been also started since April 2006. Japan has also succeeded in the complete digitalization of terrestrial television broadcasting by terminating analog broadcasting in July 2011 except some regions affected by the earthquake/tsunami damage where the termination was completed in March 2012. Moreover, since April 2012, a new mobile multimedia broadcasting has been introduced utilizing the frequency band after the termination of analog broadcasting. The new mobile multimedia broadcasting adopts ISDB-Tmm system, an advanced technology from ISDB-T system. In addition to this new mobile multimedia broadcasting, utilizing the frequency band after the termination of analog broadcasting, some new wireless telecommunication systems are introduced, such as, IMT mobile phone, ITS, public mobile broadband system.