Internationalization of the Japanese Digital Terrestrial Television Broadcasting System, ISDB-T

2.1 TELETEXT and FM multiplexing broadcasting

NHK Science and Technical Research Laboratories (NHK STRL) carried out research and development from the 1970's into the mid-1980's on how to multiplex text with television broadcasts so that analog television could be viewed with subtitles. These systems were forerunners to digital broadcasting, with text information sent as digital 0's and 1's. At this time, researchers noticed that although the digital signal was robust with respect to noise, it was weak with respect to certain types of distortion such as ghost interference.

Then, from the mid-1980's, they began researching transmission system, called FM multiplexing broadcasting, which sent text, graphics and traffic information by multiplexing a digital signal over the FM-radio stereo base-band signal. This resulted in the broadcast system that is currently used for traffic information system (VICS) in car-navigation products. Over half of all FM radios were portable or in automobiles, and these mobile radios naturally needed to be capable of receiving the FM multiplexing broadcasting. However, mobile-receiver antennas have low antenna gain compared with fixed home receivers, and other issues including significant fading distortion made it very difficult for them to receive the multiplexed signal.

Both TELETEXT and FM multiplexing broadcasting use transmission techniques which multiplex a digital signal over an analog broadcast signal, and the development of ISDB-T was built on the experience of developing these technologies.

2.2 Integrated Services Digital Broadcasting (ISDB) Proposal

STRL published a document outlining the Integrated Services Digital Broadcasting (ISDB) concept as a vision for digital broadcasting from the 80's forward. ISDB provides high quality, performance, flexibility and extensibility in a broadcasting service by transmitting video, sound and other data as a digital signal in a unified format. It also attempts to create a common service across different media, whether satellite, cable or terrestrial transmission.

In the 1990's, new, high-performance encoding technologies for video and sound were being developed around the world created new possibilities. What began as an attempt to add new functionality by multiplexing a digital signal with a predominantly video and sound analog signal grew into genuine ISDB research: broadcasting a fully-digital, integrated signal.

Since the development of TELETEXT broadcasting, designs for data communications had become standardized based on the seven-layer Open Systems Interconnection (OSI) model established by the International Standards Organization (ISO). Following this trend, research progressed toward the unification of standards common across all media, such as encoding methods, and standardizing characteristics that differ across transport media, such as the physical layer, on a per-medium basis.

2.3 The beginning of digital terrestrial broadcasting research

Research of a digital terrestrial broadcasting system at STRL began in the latter half of the 80's. In contrast to satellite or cable transmission, digital terrestrial signals are affected by various types of distortion, including multi-path distortion due to reflections from buildings and geographical features, impulse noise from automobiles, and fading distortion from fluctuations in the received signal level. Even though digital broadcasting is robust with respect to noise, the experience gained in research and development of TELETEXT and FM multiplexing broadcasting made it clear that new technology tolerant to these types of distortion would be needed for digital terrestrial broadcasting. OFDM research began as one possible such technology.

The principles of OFDM had been known since the 1960's, but it had not yet been implemented practically.

Prompted by the use of OFDM for Digital Audio Broadcasting (DAB) in Europe in the 1980's, STRL began real research into OFDM. Although OFDM is susceptible to non-linear distortion, it is robust against multi-path distortion, and because the modulation method allows relay broadcasting on the same frequency, it also contributes to efficient use of bandwidth. Furthermore, when combined with time interleaving, it is excellent for portable and mobile reception, making it an excellent modulation technique overall.

So, computational simulations were begun in the late 1980's, prototype specifications were written starting in 1990, and development of prototype OFDM devices began. A prototype DQPSK-OFDM device was built first (Figure 1), followed by multi-level OFDM prototypes including 16QAM-OFDM and 64QAM-OFDM, as the rounds of testing progressed.

Research into multi-level OFDM, like 64QAM, was needed for transmission of High Definition TV programs in the 6 MHz band. Also at the time, related experiments on clock regeneration, frequency synchronization, frame synchronization, interference with analog broadcasts and Single Frequency Network (SFN) were done to determine the most promising transmission method.

Then, in 1993, STRL received the first license for an experimental station using OFDM modulator in Japan, installed a transmitting antenna on the STRL roof and began open-air field test with fixed and mobile receivers (Figure 2).

2.4 BST-OFDM Research

Analog terrestrial broadcasting in Japan is a general, national service which uses about 15,000 channels, including NHK and commercial stations. This results in channel congestion that is unprecedented in the world and conditions that make it extremely difficult to initiate digital broadcasting using the same frequency bands as analog television broadcasting. The BST-OFDM modulation method was conceived to address this problem (Figure 3). This technology broadcasts a wide-band signal by splitting it into several narrower bands for transmission. However, new technology soon made it possible to change the channel of an analog broadcast (analog-to-analog conversion) and thus secure the bandwidth needed for digital terrestrial broadcasting, so the need to split up the digital signal for transmission diminished. Instead, a modulation method was adopted with a digital signal transmitted in the 6 MHz band, dividing the signal into several segments, and allowing the modulation method to be configured separately for each segment. This resulted in ISDB-T, the current digital terrestrial broadcasting format. Note that BST was originally an abbreviation for Band Split Transmission, but this name was later changed to Band Segmented Transmission.

2.5 Collaborative research with DTV-Lab

In 1995, a time-limited company called the "Next-generation digital television broadcasting system laboratory Inc." (DTV-Lab) was established to accelerate the study of digital broadcasting transmission methods. STRL engaged in collaborative research with DTV-Lab from 1997 to advance the study of digital terrestrial broadcasting system for Japan. The current digital terrestrial broadcasting transmission method in Japan is the result of this collaborative research between the NHK STRL and DTV-Lab, which finalized various elements of the ISDB-T transmission method.

2.6 ISDB-T Features

To develop the digital terrestrial broadcasting method, the broadcasting system requirements were first decided, and then a method was developed to conform to these requirements. The main features of ISDB-T are described here. Figure 4 gives a conceptual representation of ISDB-T transmission.

1. Supports HDTV Services
2. Supports multi-channel SDTV services
3. Supports data transmission
4. Supports mobile and portable reception
5. Contributes to efficient use of frequency, supports SFN
6. Encoding and multiplexing methods are compatible with Broadcast Satellite (BS) digital broadcasting and use international standards
7. Considers compatibility with digital terrestrial audio broadcasting
8. Divides the 6-MHz band signal into 13 segments
9. Supports per-segment configuration of modulation parameters and hierarchical transmission up to three layers.

At first, the central segment, segment one, was allocated to allow partial reception of only the audio signal, but later with the advancement of video compression technology, it became possible to use it for the current One-Seg service.

3.1 Domestic standardization activity

To standardize a new transmission method in Japan, first an inquiry into the technical requirements is done by the Telecommunications Council (TC), which is an advisory body of the Ministry of Internal Affairs and Communications. Then, once the report on technical requirements has been completed and before the new standard is finally established, the Radio regulatory council conducts an inquiry and report into amendments to ministerial orders for related technology standards. In most cases, most of this practical work related to technical requirements is carried out by the private organization, the Association of Radio Industries and Businesses (ARIB). The particulars of the standardization of digital terrestrial broadcasting in Japan are summarized in Table 1.

In June, 1994, the Telecommunication Technology Council (TTC), which was an advisory body of the Ministry of Posts and Telecommunications at the time, established the Digital Transmission System Committee based on their inquiry No. 74, "Technical requirements for digital broadcasting systems". The second working group (WG2) under this committee conducted deliberations on digital terrestrial broadcasting method. In September, 1996, the digital terrestrial broadcasting system development section was established in ARIB, and concrete deliberations began.

STRL and DTV-Lab submitted a proposal in collaboration with ARIB for a digital terrestrial broadcasting transmission method resulting from their joint research. ARIB and the TTC deliberations then proceeded based on this proposed method. In September, 1997, the TTC settled on a tentative draft for the transmission portion of the digital terrestrial television broadcasting system. Prototype hardware was built based on this tentative draft, and laboratory experiments and basic-transmission open-air experiments were conducted, mainly by ARIB. A tentative digital terrestrial television broadcasting system was settled a year later in September, 1998, based on the results of these experiments.

Large-scale test was then done based on this tentative standard, with test stations in the Tokyo Tower and other locations; taking measurements including fixed and mobile reception and SFN characteristics to verify the performance of the system.

In May, 1999, the "Digital Terrestrial Television Broadcasting System Technical Requirements" report from the TTC was accepted by the Ministry of Posts and Telecommunications.

In September, 1999, the Ministry of Posts and Telecommunications submitted amendments to related ordinances to the Radio Regulatory Council, as required to finalize the technical standards and adopt the digital terrestrial broadcasting system, and in November, 1999, they received partial approval for the draft from the council.

Through ARIB, STRL actively contributed to investigation of the format, laboratory and open-air basic tests, SFN test, and large-scale test for the digital terrestrial broadcasting system.

3.2 International Standardization Activities

International standards dealing with radio frequencies in the telecommunications field come in the form of reports from the International Telecommunication Union (ITU). In order to have the Japanese digital terrestrial broadcasting system classified as an international standard, it needed to be accepted and recognized as an ITU recommendation, so from the beginning of development, NHK actively contributed to ITU standardization activities for the system. We describe the process leading to acceptance of the Japanese digital terrestrial broadcasting system as an ITU recommendation below. An overview of this process is shown in Table 2.

At the time, deliberation on recommendations for digital terrestrial television broadcasting were carried out by the Study Group 11 (SG11) of the radio-communication sector (ITU-R) of the ITU, which presided over all television-broadcasting-related matters. The new research topic, Question ITU-R 31/6 (formerly 121/11) "Digital terrestrial television broadcasting", describing multiplexing, error-correction, modulation and other methods applicable to digital terrestrial television broadcasting was approved in 1992. In January, 1992, task group TG 11/3 under SG11 was established to deliberate on recommendations related to the new research topic. Then, at a meeting in November, 1996, in Sydney, TG 11/3 completed the final several draft recommendations related to digital terrestrial television broadcasting.

The International standard recommendation for digital terrestrial television broadcasting, BT.1306 ("Error-correction, data framing, modulation and emission methods for digital terrestrial television broadcasting") was adopted in October, 1997, at the ITU-R wireless communications general meeting (RA97). Within this recommendation, it was recommended that one of two methods, ATSC (USA) or DVB-T (Europe) be used, and descriptions of their respective error correction, framing, modulation, and emission methods were given in Annex 1. The Japanese proposal, ISDB-T, was described in Annex 2 as still-under-development and not yet accepted in its domestic market.

Since being established in 1992, TG 11/3 contributed various documents towards NHK's eventual adoption of the standard in the future. TG 11/3 was disbanded in November, 1996, and deliberations on digital terrestrial television broadcasting moved to WP11A, a working section of SG11. We continued submitting information on the development status and test results for the Japanese system, ISDB-T, even after the broadcast recommendation BT.1306 was adopted, and in May, 1999, the ISDB-T system was accepted domestically. Japan then proposed to the ITU-R that the ISDB-T system be added to the international recommendation.

Proposed revision to the BT.1306 recommendation was accepted at the general meeting of SG11 in February, 2000, adding the ISDB-T system to the already-accepted ATSC and DVB-T systems. Then a poll was conducted through the mail by the supervisory board, and finally, in October 2000, the revised recommendation was officially adopted.

Note that the proactive effort by the ITU-R towards standardization of ISDB-T was one of the reasons Brazil became aware of the system and lead to the correspondence that followed.

4.1 DiBEG

In September, 1997, when most of the transmission portion of ISDB-T had taken shape, the Digital Broadcasting Experts Group (DiBEG) was inaugurated to promote its adoption overseas in parallel with efforts to gain recommendation status with the ITU-R. The specific objective of DiBEG was to promote adoption of ISDB-T internationally, and initially it focused efforts on giving seminars and demonstrations to various countries in Asia that had not yet decided on a digital terrestrial television broadcasting system. This effort only later came to focus Brazil.

DiBEG originally began as a private organization and a liaison group for international collaborative research in digital broadcasting technology, but was later re-formed as a section under the ARIB promotional committee for the international promotion of digital broadcasting technology. NHK has collaborated with the international promotion of ISDB-T through DiBEG. Table 3 summarizes the major DiBEG activities, including its collaboration with NHK.

4.2 Early activities of DiBEG

One of the early activities of DiBEG was to promote ISDB-T by attending the International Broadcasting Equipment Exhibition, InterBEE, in 1997 and 1998, exhibiting prototype equipment to visiting technologists from the various Asian countries, and explaining the principles and characteristics of the ISDB-T system.

They also conducted demonstrations and equipment loans overseas, including participation in experiments comparing the three major systems in Singapore in 1998 and Hong Kong in 1999. However, even though the ISDB-T system produced the best results in these experiments, the format was not chosen for other, non-technical reasons and because real broadcasting in the system had not yet begun (Japan had not yet begun digital broadcasting by ISDB-T domestically).

4.3 Activities promoting the format in Brazil

In 1998, the CTO, F. Bittencourt, of the largest television station in South America, TV Globo, requested Osamu Yamada, ex-director general of STRL, to give an introductory presentation of ISDB-T at the Brazil Television Association Conference (SET1998). This was the first contact with Brazil regarding ISDB-T. Thereafter, Brazil asked to borrow ISDB-T equipment so that they could conduct fair technical evaluations and select the system that really was the best, so DiBEG participated in experiments comparing the three major systems in Brazil.

Laboratory and field tests were carried out in Sao Paolo from January to March in 2000 (see Figure 5 and Figure 6). This was the first time that the three systems had been tested under the same conditions. Brazil published the results of these tests, making it clear that ISDB-T yielded the best results of the three (see Figure 7 and Figure 8). A major reason that ISDB-T proved the best was that it uses time interleaving. In addition to the performance of ISDB-T, Brazil also focused on the flexibility of the system. The ability to reorganize the system according to regional characteristics or changes in the business model of the broadcaster, features like HDTV, multi-channel, vehicle-oriented mobile reception, and services for "One-Seg" phones was evaluated highly. These features were made possible through the segmented architecture, hierarchical transmission, MPEG2 multiplexing and other technical features of ISDB-T. In spite of Brazil's good evaluation of ISDB-T, the biggest obstacle to adopting the system was the fact that Japan did not commence broadcasting in ISDB-T until 2003.

After that, there was a change of political power in Brazil, resulting in policy changes toward developing their own system. Even in those conditions, DiBEG continued its efforts, with presentations and demonstrations focusing on Brazil and South America. TV Globo and the major television broadcasters also continued their support of ISDB-T.

Then, when Communications Minister Costa (formerly of TV Globo) assumed the post of Third Communications Minister in the President Lula administration in July, 2005, suddenly major developments began to emerge. Development of Brazil's own system, which was not making progress, was abandoned, and it was announced that a system would be selected by February 10, 2006. They held hearings to discuss various aspects including technical strengths, equipment costs, and technical collaboration. From November, 2005 till April, 2006, a group representing Japan visited Brazil three times to attend negotiations. Then, on April 13, 2006, the Japanese government and the Federal Republic of Brazil signed a memorandum that Brazil would implement ISDB-T as the base digital television system, and for cooperation with the development of Brazil's electrical and electronic industries related to this decision. Then, on June 29, 2006, government guidelines for implementing the content of this memorandum were signed in Brasilia, finally bringing the efforts of DiBEG to fruition after seven years since the first contact with Brazil.

While STRL was collaborating with DiBEG, it also worked to build the trust-relationship with Brazil, supporting their thorough understanding of ISDB-T transmission technology by accepting three technicians from Brazil TV Globo in 2002 and a professor from Mackenzie University in Sao Paolo in 2005 as visiting researchers.

Note that the Brazil system is called "ISDB-T based" because additional features were added, such as H.264 video encoding, which is used for HDTV transmission in Brazil.

4.4 Activity promoting ISDB-T throughout South America

Brazil's selection of a system for digital terrestrial broadcasting affected the surrounding South American countries, prompting them to begin deliberation to select their own systems. DiBEG has been actively pursuing the spread of ISDB-T throughout South America, receiving requests for seminars and demonstrations from Argentina, Chile, Venezuela, Colombia, Peru and others. In December, 2006, demonstrations of ISDB-T in indoor and outdoor mobile reception were carried out in Buenos Aires, Argentina. In Buenos Aires, a promotional video called "ISDB-T One signal, unlimited reception" was hastily created, but in spite of this it was exceptionally well received. Then, in February, 2007, the same demonstration as in Argentina was held in Santiago, Chile. The demonstration in Argentina is shown Figure 9 and Figure 10.