The American DTV PLATFORM - TvTechnology

The American DTV PLATFORM

This month marks the 10th anniversary of the FCC's formal adoption of the American DTV standard. For those of us who work in this industry, this anniversary
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This month marks the 10th anniversary of the FCC's formal adoption of the American DTV standard. For those of us who work in this industry, this anniversary represents a good point to look back at the technological journey that brought us to this solution.

The beginning

The genesis of high-definition television (HDTV) is generally attributed to NHK. At the 1981 SMPTE Conference in San Francisco, NHK demonstrated what it called a Hi-Vision analog HDTV transmission system. The technology was initially designed not for home reception but as a satellite link. The system was based on an analog PAL composite video signal that had been scaled up to 1125 lines with 60 fields. The transmission link required 20MHz of bandwidth.

SMPTE attendees were stunned by the high-resolution images. Some recognized that they were viewing the future of over-the-air television. For them, this was an exciting development. Others were less enthusiastic. Some saw the demonstration as an attempt by the Japanese to set standards for the U.S.

The U.S. effort to establish an HD transmission standard began with the creation of the ATSC in 1982. The committee was initiated at the direction of the Joint Committee on Inter-Society Coordination (JCIC). The ATSC was given the task to develop voluntary technical standards to replace the 50-year old NTSC standard. The initial ATSC committee included members from the EIA, IEEE, NAB, NCTA and SMPTE.

In September 1984, the State Department submitted an ATSC-recommended 1125/60 proposal to the CCIR for a worldwide HDTV production standard. Motivating the action was the feeling that a global HD production standard would benefit the U.S. TV industry for international program distribution.

This proposal was adopted in 1985 by Study Group 11 and was passed on to the plenary assembly for further consideration. With heavy resistance from Thomson and Philips in particular, in 1986 the CCIR postponed any action on the proposal until 1990. Some feared that an NHK-based proposal would kill the MAC systems under development. It was also seen as an attempt by Japan to dominate the consumer electronics economy.

While the ATSC persisted and attempted to gain support for the 1125/60 Japanese standard, U.S. broadcasters were turning their attention to over-the-air transmission of HDTV.

Why develop a U.S. HD standard?

The motivation to develop an American HDTV transmission standard was influenced by many factors, including the potential loss of TV spectrum to mobile services. Local stations were certainly less interested in providing HD services at this point than just protecting their future spectrum.

Certainly the U.S. consumer electronics industry under the leadership of the Consumer Electronics Association (CEA) was keen to see a new entertainment technology develop. While the CEA was publicly supportive from a U.S. perspective, the reality was that America had little entertainment manufacturing left in this country. As the HD standard was debated, virtually all television set manufacturing was being moved outside U.S. borders.

There was also a pride issue. American engineers were loath to have Japan set the standards for the key U.S. entertainment industry. In addition, broadcasters thought that broadcasting HD might also help stem the loss of viewers to cable. NTSC was technologically antiquated, as the high-definition demonstrations clearly showed. Finally, broadcasters, NAB and the CEA recognized that the NTSC standard was old and needed to be replaced.

The FCC starts the process

In July 1987, the FCC issued its First Notice of Inquiry on Advanced Television Service. Later that year, the commission appointed a 25-member advisory panel, calling it the Advisory Committee on Advanced Television Service (ACATS). Chaired by former FCC Chairman Richard E. Wiley, the panel, which included Joe Flaherty of CBS, was charged with reviewing the technical issues and then recommending an advanced television system to the FCC. Twenty-three systems, many only existing in simulations, were submitted and competed for the blessing of the FCC and adoption as the U.S. standard.

One proposal, Sarnoff's Advanced Compatible Television (ACTV) system, required a two-step approach to HD. Another came from the Philips laboratory and was called High Definition System - North America (HDS-NA). This represented an adaptation of Multiple Analog Commanding (MAC) technology. Both systems provided NTSC compatibly that met the FCC's NTSC compatibility requirement, but required more than a standard 6MHz transmission channel.

Two of the proponents, MIT and Zenith, advocated an alternative called simulcasting. In a simulcast approach, a channel is used to convey an independent advanced television signal that is not NTSC-compatible. To receive advanced television, only the simulcast channel needs to be received. The concern was whether HDTV could be achieved within a single TV channel.

The initial 23 systems were reduced to six during “Hell Week” in November 1988. ACATS now realized a laboratory was necessary to properly test the surviving proposed HDTV systems. With the broadcasters' backing, the committee built the Advanced Television Test Center (ATTC).

In March 1990, the FCC ruled in favor of simulcast HDTV. Broadcasters would be granted a second 6MHz channel for HDTV broadcasts. At some time in the future, NTSC transmission would cease and the second channel would be returned for reuse and auction.

The switch to digital

Some of the engineers involved with these early systems realized that an analog transmission scheme would not meet the FCC's interference requirements, especially when scaled to national proportions. They began looking at a digital solution.

General Instrument (GI) beat everyone to the punch and announced it had built an all-digital HD system. GI also claimed that its system could compress HDTV into a 6MHz signal. Now that was something significant. Not only could an all-digital system be built, it would also fit within the current NTSC channel allocations.

By 1990, broadcasters, the NAB, the consumer industry and the FCC were pushing for a working solution. The proponent HDTV systems were only in the R&D prototype stage. Demonstrations were under limited, controlled conditions. Confirmation that one of these systems could successfully be deployed nationally was still to be estblished.

By now, the players realized there were only two possible outcomes from the current battle for supremacy. First, a company's proposal might be selected as the winning design, and the company would reap billions in licensing fees.

The second, and more likely scenario, was that a company's proposal would be rejected. Not only would the company's R&D money already spent be lost, but more importantly, the billions in licensing fees they hoped to reap would be forever lost. So, when faced with getting all of the pie or none of the pie, seven of the companies decided to cooperate. Through a combined approach, they would hedge their costs and increase the odds of getting at least something for their efforts.

Four groups resulted and developed digital systems. (See Table 1.) NHK also submitted its analog system for consideration. Proponent testing was scheduled.

The tests begin

After the first round of proponent tests were completed, the NHK analog system was eliminated.

The ACATS decided that only digital systems would remain under consideration. It also decided that no one system was sufficiently satisfactory. The four groups of players were asked to submit proposed system improvements and undergo another round of tests.

The Grand Alliance

By late 1992, as improvements made each system virtually indistinguishable from each other, it seemed likely that the ACATS was going to be unable to select a winning proposal from the four remaining players. At this point, the players recognized that the only way each could be guaranteed to receive a portion of future licensing revenues was for them to cooperate and form a single entity to finish the project. Thus, the Grand Alliance (GA) was formally established in May 1993. The seven members of the Grand Alliance were AT&T, General Instrument, MIT, Philips, Sarnoff, Thomson and Zenith.

This arrangement solved two issues. The first was that sharing patents between Grand Alliance members ensured that everyone would receive at least a share of the profits. From the FCC's viewpoint, with only one system to consider, the commission was provided with political cover. The commission wanted no potential for a repeat of its embarrassing 1953 color standard reversal and 1982 AM stereo fiasco. This became the politicians' win-win scenario.

For engineers, the GA became a logical, technically sound architecture that incorporated the best features from each of the four proponent prototypes.

The remainder of 1993 was spent defining system architecture and dividing the design and construction of sub systems among GA members. Once the system's specifications were established, ACATS approved them, and a prototype was built.

National Information Infrastructure

Often lost in the telling of HD's development is the influence the National Information Infrastructure (NII) initiative had on prototype system design. The NII was Washington-speak for what would later become the World Wide Web.

Key among the NII's requirements was high-digital interoperability with other systems. In many respects, the ATSC transport system became the core platform and helped extend services beyond audio and video. A/65 PSIP, the A/90 Data Broadcast Standard and A/9x data services standards series have resulted from this capability.

The GA spent much of 1994 developing a working prototype. AT&T and GI developed the MPEG video encoder, and Philips the MPEG video. Sarnoff built the transport encoder and Thomson the transport decoder. Zenith built the modulation/demodulation system.

Key solutions still needed

Performing format conversion proved to be an early issue. Converting between 1080i and 720p in real time had never been done before, but it was also an important aspect of the final test procedure. This required the design and construction of a format converter.

Two format converters were available. The first was developed during the competition phase by the ATTC and built by Tektronix. It was expensive, having cost approximately $600,000. The second was developed by the Grand Alliance, with the design and construction shared across companies.

The battle for progressive scan

In November 1995, the ACATS recommended the ATSC Grand Alliance system be accepted by the FCC. While broadcasters thought the path was now clear, the computer industry had not yet begun to fight. Scheming behind the scenes were two groups, the PC folks and the film industry. The computer industry contended that to promote interoperability between DTV and PC devices, any ATSC standard should rely exclusively on progressive displays. The film industry demanded that movies be broadcast in their original aspect ratio. Thus, just at the point broadcasters thought the issues were almost resolved, two outsiders began to throw stones on the entire process.

Reed Hundt, FCC chairman was sympathetic to the computer industry's position. The Computer Industry Coalition on Advanced Television Service (CICATS) had not participated in the formal standards development process. But that didn't stop it from lobbying hard through 1996 to get progressive scanning adopted as part of any standard. The result was that the FCC refused to act on ACATS' proposed DTV standard.

Final agreement

In late 1996, FCC Commissioner Susan Ness demanded that the warring groups — the GA, CICATS, Consumer Electronics Manufacturers Association and Film Coalition — enter negotiations to resolve the remaining contentious issues.

Once again, politics came to the rescue. The ATSC initially implemented the infamous Table 3 with 18 different resolution and scan rates. (See Table 2.) However, in an effort to streamline the standard and simplify displays, it was removed from the final FCC DTV regulations. This change resolved the concerns of the computer industry.

The Film Coalition held steadfast, demanding that a film's original aspect ratio be protected. However, being a small group without lobbying funds and big names, its opinion got little attention. Its concerns were steamrolled by the Ness-forced negotiations.

So, after a long and arduous HDTV standards quest, on Christmas Eve 1996, the FCC adopted the proposed ATSC digital television terrestrial broadcast standard.

Key provisions of the adopted standard include: MPEG- 2 video compression; ATRC derived packetized transport; Dolby's AC-3 multichannel audio; and Zenith's 8-VSB transmission system.

Into the analog sunset

In the 10 years that have passed since the standard's adoption, DTV transmissions now cover the U.S. Cable operators offer HDTV services on virtually every system, and HD satellite broadcasts have a national footprint.

The final step in this transformation is scheduled for February 17, 2009. On that day, broadcasters will turn off their analog transmitters for the last time.

Today, most prime-time programming is produced in HD. DTV has reached 30 percent household penetration and is predicted to top 80 percent by 2009. Vouchers for digital-to- analog converter boxes will be subsidized by the government to enable every household in America to continue to receive over-the-air broadcasts after the analog shutdown.

Beyond the commercial success and DTV's rapid market penetration, the fact that the system has a layered architecture may be the most important aspect of platform. Each of the layers — presentation, compression, transport and transmission — has already been augmented or replaced by other, newer technologies. Because the U.S. DTV system is so flexible, Americans can expect it to continue to take advantage of new developments and provide a long-lived service to viewers, which will help ensure that it has a long and successful life.

Philip J. Cianci has been in the TV business for 21 years and has done circuit design in the Grand Alliance ATSC prototype system. He is seeking first-person memories from engineers and technical personnel who participated in any phase of HDTV R & D, early broadcasts, standards committees, facility construction and equipment manufacture for an insider's view book. For more information about this effort, to contribute or comment about this article, visitwww.HDTVArchiveProject.com.

Table 1. ATTC Round 1 proponent systems Proponent Members Proposed system Scanning format Source coding Modulation Advanced Television Research Consortium (ATRC) Philips/Thomson/Sarnoff/CLI AD-HDTV 1050/59.94/2:1 MC-DCT AA-QAM
Zenith/AT&T DSC-HDTV Digital Spectrum Compatible 787.5/59.94/1:1 MC-DCT 4-Level-VSB American Television Alliance GI/MIT DigiCipher 1050/59.94/2:1 MC-DCT 16/32-QAM American Television Alliance MIT/GI CC-DigiCipher 787.5/59.94/1:1 MC-DCT 16/32-QAM Table 2. 18 ATSC video presentation formats # PIXELS/Line LINES/Frame ASPECT RATIO Refresh Rate (Hz) SCAN MODE 18 1920 1080 16:9 30 Interlaced 17 1920 1080 16:9 30 Progressive 16 1920 1080 16:9 24 Progressive 15 1280 720 16:9 60 Progressive 14 1280 720 16:9 30 Progressive 13 1280 720 16:9 24 Progressive 12 704 480 16:9 30 Interlaced 11 704 480 16:9 60 Progressive 10 704 480 16:9 30 Progressive 9 704 480 16:9 24 Progressive 8 704 480 4:3 30 Interlaced 7 704 480 4:3 60 Progressive 6 704 480 4:3 30 Progressive 5 704 480 4:3 24 Progressive 4 640 480 4:3 30 Interlaced 3 640 480 4:3 60 Progressive 2 640 480 4:3 30 Progressive 1 640 480 4:3 24 Progressive