Features of ISDB-T system

  ISDB-T Report (published in June, 2007)

Foreword

ISDB-T (Integrated Service Digital Broadcasting - Terrestrial) has been developed and now on service in Japan, and adopted by Brazil.
ISDB-T proves best performances in Japanese DTTB service for more than 3 years.
Since Dec. 2003, start of Japanese DTTB service, DTTB service is rapidly migrated because of its advantages, and new service, named "One-seg", portable reception service in same channel, has been started from April 2006.
But, because of late start of ISDB-T, ISDB-T is not so popular in the world, so, we will submit this report to South America countries to understand the ISDB-T system and its advantages on technical aspect.

Contents

ANNEX

1. Structure of ISDB-T (Japan)
2. High quality / Service Flexibility
2.1 High quality
2.2 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
4. Commonality

1. Technical requirements for Digital Terrestrial TV Broadcasting (DTTB) in Japan

In 1990s, research and development of digital broadcasting has started in Japan. In Japan, NHK led research/development of HDTV, and implementation of HDTV was almost on market at this time. So, HDTV was expected to be a main service of next generation of broadcasting. But, SDTV seemed to be a important broadcasting service, so, harmonization of HDTV and SDTV had to be a important issue of next generation broadcasting.

In addition, in Japan, frequency resource is not enough to start next generation broadcasting, therefore, "Effective utilization of frequency resource" had to be one of requirement of next generation.

And more, at that time, internet service was on the way of penetration and forecasted to be main service of communications in near future, so, harmonization with Internet was also set as important requirement. To support interactive service and as a new broadcasting service, data-casting was also set as a requirement.

Further more, mobile and portable service was recognized as a important advantage of broadcasting which uses radio wave. Therefore, new technology should be developed and adopted in next generation broadcasting to enable mobile and portable service.

These requirements have been realized in ISDB-T system and now on service.
How to realize these requirements in ISDB-T system and features of ISDB-T is described in section 2.

2. Technical features of ISDB-T

As described Section 1, requirements for DTTB system were set shown in Table 1 in Japan.
Table 1-1 Requirements for Digital Terrestrial TV Broadcasting in Japan.

No. Item Requirement Note
1 High quality HDTV should be possible in 6MHz bandwidth
2 Robustness Robustness against multi-path, urban noise, fading and any other interference
2 Flexibility
2(1) Service Flexibility Any kinds of service are possible in 6MHz bandwidth HD/SD possible
2(2) Reception flexibility Any kinds of reception system are possible, fixed/mobile/portable in same bandwidth
3 Effective utilization of frequency resource SFN (Single Frequency Network) is possible to reduce frequency.
4 Interactivity Harmonization with network
5 Data casting
6 Commonality Maximum commonality is need to reduce receiver cost. Especially, to digital radio, common standard is desirable.

ISDB-T in Japan has been developed to realize above requirement shown in Table as a next generation broadcasting, and now ISDB-T has many technical advantages described below.
For technical details, please refer ANNEX- AA.

(1) High quality / service flexibility

Following technologies are adopted in ISDB-T; (a)Flexible multiplex technology (MPEG-2 systems), (b)Flexible and high efficiency video/ audio coding system (MPEG-2 and MPEG AAC).
As a result, many kinds of broadcasting service, such as (a)HDTV, (b)HDTV+SDTV, (c)Multi-channel SDTV, are possible in one standard. ISDB-T receiver receives any type of service described above.
Technical details are described in ANNEX- AA section 2.

(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, of course 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 following features compare to other DTTB systems; (a) lower transmitter power, (b) possibility of indoor antenna reception, (c) mobile/portable reception service, etc.
Technical details are described in ANNEX- AA section 3.

(3) Effective utilization of frequency resource

By adopting OFDM transmission system, it is possible to construct Single Frequency Network (SFN). As a result, possible to reduce frequency resource for relay transmitter (repeater). Further more, using same frequency for plural transmitters of same network, mobile/ portable receiver is not required to change receiving channel.
Technical details are described in ANNEX- AA section 3.

(4) Mobility/ Portability

To enable fixed/ mobile/portable reception service in same channel, ISDB-T developed new transmission technology, named "Segmented OFDM transmission system".
As a result, fixed/mobile & portable service in same channel is possible.
"One-seg" service, its unique portable service of ISDB-T, uses 1 segment of 6MHz.
One seg receiver is easily mounted into mobile-phone, portable PDA, USB tuner ,etc, so it enable the broadcast service of "Any time, Any place".
Technical details are described in ANNEX- AA section 3.

(5) One-seg service

One-seg service, uses 1 segment of 6MHz, dose not need another channel, so not need more transmitter.. it leads save of frequency resource and broadcaster's infrastructure cost. And more, One-seg receiver operates as narrow band reception, this operation saves consumption power. As a result, long time reception is possible by battery.
Technical details are described in ANNEX- AA section 3 and ANNEX- BB.

(6) Commonality

To reduce the receiver cost, backend of digital receiver, for satellite/ terrestrial/ cable, has common technology. As a result, backend chip is common used for these digital receiver. In Japan, integrated receiver , in which both satellite tuner and terrestrial tuner are equipped, is very popular type of receiver. This type of receiver save cost by using commonly backend circuit.
In addition above, Japanese digital audio broadcasting, named ISDB-Tsb just now trail service stage, adopts common standard of ISDB-T for coding/transmission system. As a result, common receiver for One-segment audio service and One-seg TV service has been on market.
Technical details are described in ANNEX- AA section 4 and ANNEX- BB.

(7) Utilization for disaster prevention

Utilization for disaster prevention is also important issue of digital broadcasting.
To realize for this use, 2 technical measure are necessary; one is portability, other is EWS(Early Warning System)(note). For former measure, already realized as One-Seg receiver, for later measure, now on research and development stage by NHK.
(note)the purpose of EWS is to wake 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. From this time, ISDB-T became ISDB-T International.
Brazilian system is not perfectly same as Japanese system. Brazilian standard is now on standardization stage, its will adopt new technology, such as H.264 for SDTV and HDTV coding technology, and another technology for middle-ware.
But, structure of DTTB system is same, and transmission system is just same as Japanese system. Therefore, Brazilian ISDB-T is one of ISDB-T family and has same features of Japanese ISDB-T.
By Brazil adoption, ISDB-T market expand to 300 million people, it means that cost down of receiver will be expected.

4. Current and future of ISDB-T in Japan
4.1 Current situation in Japan

In Japan, DTTB has started in December, 2003 at 3 metropolitan area, and widen the cover area to all prefecture of country. And One-seg service has been also started in April, 2006.
In Japan, digital receiver extremely penetrated, accumulated number of digital receiver in market is around 20 Million at end of March. In addition, One-seg receiver hs been sold over than 5 million by February this year, and forecasted over 10 million at August this year.

4.2 Future in Japan

Japanese government announced that analog TV service will be stopped in July, 2011.
Only 4 years for the end of analog TV service.
The most important subject is to accelerate the penetration of digital receiver.
To accelerate the penetration, low price STB is necessary, recently several manufacturers started to develop low price STB and will be on market in near future.
One more important subject is to cover any place by digital radio-wave. Small power repeater is necessary to cover mountain area and shadow of big building in urban area.
In Japan, now on standardization stage of such small power transmitter, it will be available in near future.