recent trends in digital television broadcasting

Description

LITERATURE REVIEW

OVERVIEW OF DIGITAL TELEVISION (DTV)

Television is probably the most cost-effective medium that informs, educates, and entertains the general public around the world. The television receiver is certainly the most popular home electronics device in the world. Based on the most recent data from the International Telecommunications Union (ITU), at the end of 2000, there were about 1.4 billion television sets in the world; many more than the number of fixed telephones (0.787 billion), cellular phones (0.75 billion), or personal computers (0.277 billion). Over the next 10–20 years, it is expected that these 1.4 billion analog TV sets will be replaced by digital sets, creating a multibillion dollar annual business for the broadcast equipment, consumer electronics, computer, and semiconductor industries.

Many countries have already started the transition from analog to digital television (DTV). DTV not only delivers interference and distortion-free audio and video signals; more importantly, it can do so while achieving much higher spectrum efficiency than analog television. DTV can also seamlessly interface with other communication systems, computer networks, and digital media, enabling data casting and multimedia interactive services; it is a key element of the ongoing digital revolution leading toward the information society.

There have been few, if any, tutorials that comprehensively cover all the worldwide DTV systems. This PROCEEDINGS OF THE IEEE special issue on DTV has been produced by a team of experts in DTV from around the world who, for the first time, have jointly developed a complete and systematic tutorial series of papers. This introductory paper puts the various current DTV systems into perspective and explains the differing paths each system took in development. The main focus is on the terrestrial DTV systems, but satellite and cable DTV are also covered, as well as emerging services such as Internet Protocol TV (IPTV) and DTV to handheld devices.

HISTORICAL BACKGROUND OF TELEVISION AND DEVELOPMENT

Analog TV System Development History

Many of the principles of television can be traced back to 19th-century work by European and North American inventors. The word “television” was first introduced in 1900 at the World’s Fair in Paris, France, where the First Inter- national Congress of Electricity was held (according to Broadcasting pioneers). Television is a hybrid word, coming from both Greek and Latin. “Tele” is Greek for “far,” while “vision” is from the Latin “visio,” meaning “vision” or “sight.” It is often abbreviated as TV. Research on television systems continued in the early 20th century, and by the 1920s was well under way on both sides of the Atlantic.

Monochrome Television: The early generations of television were mostly based on electromechanical systems. The display (TV screen) had a small motor with a spinning disc and a neon lamp, which worked together to give a blurry reddish-orange picture about half the size of a business card (Broadcasting pioneers). In 1926, in London, U.K., John Logie Baird demonstrated a 30-line system with such a display and an electromechanical optical scanner as a picture pickup device. Television broadcasting in the United Kingdom started with Baird’s system in 1932. The British Broadcasting Corpora- tion (BBC) television service started in 1936 with an on-air “bake-off” between an improved Baird 240-line mechanical system and a 405-line all-electronic system developed by the EMI and Marconi companies. In 1937, the 405-line monochrome system, known then as “high definition,” was selected as the U.K. standard. Development also occurred in several other European countries, with a variety of TV systems used for transmissions. By 1950, most European broadcasters had selected a standard based on 625 scanning lines with 50 fields (25 frames) per second, later adopted in many other parts of the world, although for many years France used a system with 819 lines.

Meanwhile, in the United States, Vladimir Zworykin and Philo Farnsworth had worked independently on television research, with major breakthroughs during the 1920s and 1930s. Farnsworth transmitted the first electronically produced pictures in 1927, with a fully working system in 1934. Numerous stations had experimental transmissions during the 1930s, with a variety of mechanical and electronic systems. A 300-line all-electronic service was started in Los Angeles, CA, in 1936, and other stations soon followed. Major development work was undertaken by the Radio Corporation of America (RCA), and by the late 1930s the Radio Manufacturers Association (RMA), the forerunner of the Electronics Industries Association (EIA), had established industry standards (Fink, 1999). The Federal Communications Commission (FCC) was not satisfied with the quality and level of performance of the RMA standard, and work on television development continued (Udelson, 1982). In 1942, the FCC adopted the work of the National Television System Committee (NTSC), and established a standard consisting of 525 scanning lines with 60 fields (30 frames) per second, which was also referred to as a “high definition” standard at that time. [5].

Color Television: Following on from earlier research, during the 1940s various color television systems were pro- posed and demonstrated in the United States. The first all- electronic color television system, backward compatible with the existing monochrome television system, was developed in the early 1950s and submitted by the second National Tele- vision System Committee to the FCC in 1953 (Brown, 2012). The FCC approved the NTSC color TV standard on 17 December 1953 (Brown, 2012) and the first color live broadcast was of the Rose Parade in California on 1 January 1954. This standard was subsequently adopted by Canada, Mexico, Japan, and many other countries.

During the development of the NTSC color system, RCA had established a laboratory in Astoria, NY, three miles from the transmitter at the Empire State Building, where companies could bring receivers for testing. One night in April 1953, the RCA Princeton labs were conducting critical tests with test patterns, while receiver engineers asked repeatedly for live pictures. When the transmitter became available about 12:30 AM, the engineers requested that live talent and some colorful fruit be televised. George Brown of RCA noticed a can of blue paint nearby, and as a practical joke painted the bananas blue. The receiver engineers spent a half-hour unsuccessfully trying to get all the colors correct  (Pritchard, 2015). An apocryphal story tells of one manufacturer’s crew at Astoria who were so certain of their receiver design that they turned off the set, and proclaimed, “They have the phase wrong at the transmitter,” and went to a late dinner while waiting for the studio to correct their error. They never thought that the banana might be artificially made blue.

Color TV was not very successful in the United States until nearly a decade after its introduction. Few color TV sets were sold—they were expensive and did not perform well, and color programs were rare. Time magazine called color TV “the most resounding industrial flop of 1956” (Ninomiya, 1995). It was not until late 1960s that most TV programs were in color.

The countries of Europe delayed the adoption of a color television system, and in the years between 1953 and 1967, a number of alternative systems, compatible with the 625- line, 50-field existing monochrome systems, were devised ( Ninomiya, 1995). These had features intended to improve on NTSC, particularly to eliminate hue errors caused by phase errors of the color subcarrier in the transmission path.

An early system that received approval was one proposed by Henri de France of the Compagnie de Television of Paris. He suggested that the two pieces of coloring information (hue and saturation) could be transmitted as subcarrier modulation that is sequentially transmitted on alternate lines. Such an approach, designated as SECAM (SEquential Couleur Avec Memoire, for sequential color with memory) was developed and officially adopted by France and the USSR, and broad- cast service began in France in 1967.

The implementation technique of a one-line delay element for SECAM led to the development, largely through the efforts of Walter Bruch of the Telefunken Company, of the phase alternation line (PAL) system. The line-by-line alternation of the phase of one of the color signal components averages any colorimetric distortions to give the correct value. The PAL system was adopted by numerous countries in continental Europe, as well as in the United Kingdom, and other countries around the world. Public broadcasting began in 1967 in Germany and the United Kingdom using two slightly different variants.

DIGITAL TELEVISION SYSTEM DEVELOPMENT TREND

Development of high definition and advanced television systems proceeded in parallel in the United States, Europe, and Japan. For various technical, organizational, and political reasons, this has resulted in multiple sets of DTV standards, applicable in different regions of the world.

Currently, there are three main DTV standard groups:

• The Advanced Television Systems Committee (ATSC), a North America based DTV standards organization, which developed the ATSC terrestrial DTV series of In addition, the North American digital cable TV standards now in use were developed separately, based on work done by Cable Television Laboratories (CableLabs) and largely codified by the Society of Cable Telecommunications Engineers (SCTE).
• The DVB Project, a European based standards organization, which developed the DVB series of DTV standards, standardized by the European Telecommunication Standard Institute (ETSI).
• The ISDB standards, a series of DTV standards developed and standardized by the Association of Radio Industries and Business (ARIB) and by the Japan Cable Television Engineering Association (JCTEA).

It is believed that China is currently developing another terrestrial DTV standard, which is expected to be finalized in 2006.

1. ATSC and ACATS Process

Following in the footsteps of the two successful NTSC committees that established the 525-line monochrome and color TV standards in the United States, the ATSC was formed in 1982 by the member organizations of the Joint Committee on InterSociety Coordination (JCIC).1 The purpose of the ATSC was to explore the need for and, where appropriate, to coordinate development of the documentation of advanced television systems. Documentation was understood to include voluntary technical standards, recommended practices, and engineering guidelines. ATSC member companies recognized that the prompt, efficient, and effective development of a coordinated set of standards was essential to the future development of advanced televi sion services.

Work on what would become the ATSC DTV system officially began in 1987, although the origins of HDTV can be traced back to the early 1980s with the first demonstrations of the NHK HDTV system. It was—in large part—the promise of HDTV that motivated the development of DTV.

• ACATS: On 21 February 1987 a “Petition for Notice of Inquiry” was filed with the U.S. FCC by 58 broadcasting organizations and companies requesting that the commission initiate a proceeding to explore issues arising from the introduction of advanced television technologies and their possible impact on the television broadcasting service. At the time, it was generally believed that HDTV could not be broadcast using 6-MHz terrestrial channels. The broad- casting organizations were concerned that only alternative media would be able to deliver HDTV to the viewing public, placing terrestrial broadcasting at a severe

The FCC agreed this was a subject of utmost importance and initiated a proceeding (MM Docket no. 87-268) to con- sider the technical and public policy issues of advanced television systems. The commission subsequently established ACATS, consisting of 25 leaders of the television industry. Richard E. Wiley, a former chairman of the FCC, was named to lead the committee, with hundreds of industry volunteers serving on numerous Advisory Committee subcommittees. Canada and Mexico also participated in the ACATS process. The Advisory Committee established subgroups to study the various issues concerning services, technical parameters, and testing mechanisms required to establish an advanced television system standard. It also established a system evaluation, test, and analysis process.

• Development of the ATSC DTV Standard: Initially, 23 different systems were proposed to the Advisory Committee (Hopkins, 2019). Mostly analog or hybrid analog/digital approaches, these systems ranged from “improved” systems, which worked within the parameters of the NTSC system to im- prove the quality of the video; to “enhanced” systems, which added additional information to the signal to provide an improved widescreen picture (Hopkins, 2019); and finally to HDTV systems using two 6-MHz channels per program, which were completely new services with substantially higher resolution, a wider picture aspect ratio, and improved sound (Hopkins, 2019). In January 1990, the FCC effectively rejected all of the proposed approaches by a policy announcement calling for:

• establishing a full HDTV transmission standard;
• using only a single 6-MHZ channel; and

3) locating it within the existing frequency bands allocated to analog TV broadcasting (Sikes et al., 2010).

In response to the FCC’s newly raised bar, a fundamental technological advance emerged when, in May 1990, General Instrument Corporation proposed the first all-digital HDTV. Their DigiCipher system proposal used the 1050i (“i” for interlaced scanning) video format, motion-compensated video compression, and QAM digital modulation (Sikes et al., 2010). Within seven months, three additional all-digital HDTV systems had been proposed, emerging from their secret development programs at leading research laboratories. Advanced Digital HDTV, proposed by Sarnoff, Thomson, Philips, and NBC, pioneered the use of multiple video formats, MPEG video compression, and packetized data transport (Joseph et al., 2012).Digital Spectrum Compatible Television, proposed by Zenith and AT&T, pioneered the use of the 720p progressive scan format and vestigial sideband digital modulation (Joseph et al., 2012). The Channel Compatible DigiCipher, proposed by General Instrument and the Massachusetts Institute of Technology (MIT), Cambridge, combined the use of the 720p format with QAM modulation (Joseph et al., 2012). Although the proponents high- lighted their differences, all of the proposed systems were similar in their use of motion-compensated discrete cosine transform based video compression to achieve the required reduction in data rate necessary for transmission in a single 6-MHz channel (Zou, 1991).

By 1991, the number of competing system proposals had been reduced to six, including the four all-digital HDTV systems. The Advisory Committee developed extensive test procedures to evaluate the performance of the proposed systems and required the proponents to provide fully implemented real-time operating hardware for the testing phase of the process. From July 1991 to October 1992, the six sys- tems were tested by three independent and neutral laboratories working together, following the detailed test procedures prescribed by the Advisory Committee (Bell, 1995) .

The Advanced Television Test Center (ATTC), funded by the broadcasting and consumer electronics industries, con- ducted transmission performance testing and subjective tests using expert viewers (Rhodes, 1990). CableLabs, a research and de- velopment consortium of cable television system operators, conducted an extensive series of cable transmission tests as well. The Advanced Television Evaluation Laboratory (ATEL) within the Canadian Communications Research Centre (CRC) conducted subjective assessment tests using nonexpert viewers (Rhodes, 1990).

In February 1993, a Special Panel of the Advisory Committee convened to review the results of the testing process, and—if possible—to choose a new transmission standard for terrestrial broadcast television to be recommended by the Advisory Committee to the FCC. After a week of deliberations, the Special Panel determined that there would be no further consideration of analog technology, and that based upon analysis of transmission system performance, an all- digital approach was both feasible and desirable. Although all of the all-digital systems performed well, each of them had one or more aspects that required further improvement. The Special Panel recommended that the proponents of the four all-digital systems be authorized to implement certain modifications they had proposed, and that supplemental tests of these improvements be conducted. The Advisory Com- mittee adopted this recommendation of the Special Panel, but also expressed its willingness to entertain a proposal by the remaining proponents for a single system that incorporated the best elements of the four all-digital systems (ATSC, 1993).

The Grand Alliance: In response to this invitation, in May 1993, as an alternative to a second round of intense competitive testing, the proponents of the four all-digital systems formed the Digital HDTV Grand Alliance. The members of the Grand Alliance were AT&T, General Instrument, North American Philips, MIT, Thomson Consumer Electronics, the David Sarnoff Research Center, and Zenith Electronics Corporation. In forming the Grand Alliance, the formerly competing proponents agreed to several key system principles, including: 1) accommodating both interlaced and progressive picture formats; 2) basing the video compression on the newly emerging MPEG-2 standard and 3) utilizing a packetized data transport as part of a layered system architecture. However, many difficult choices remained, including whether or not to use bidirectional predicted B-frames, consideration of possible extensions to the MPEG syntax, which digital audio sub- system to use and which digital modulation technique to employ. After a thorough review of the Grand Alliance’s initial proposal, the Advisory Committee worked, in collaboration with the Grand Alliance during 1993 and early 1994, to finalize the design of the system, which eventually included the use of the 1920   1080 interlaced format and the 1280 720 progress format with square pixels, Dolby AC-3 (Dolby Digital) audio, and the use of 8-VSB modulation, which had demonstrated better performance than QAM during comparative transmission subsystem testing.

By 1994, the Grand Alliance companies proceeded to build a final prototype system based on specifications approved by the Advisory Committee (Hopkins, 1993). The prototype Grand Alliance system was built in a modular fashion at various locations. The video encoder was built by AT&T and General Instrument, the video decoder by Philips, the multichannel audio subsystem by Dolby Laboratories, the transport system by Thomson and Sarnoff, and the transmission system by Zenith. The complete system was integrated at Sarnoff Labs (Challapali et al., 1995)

Testing of the complete Grand Alliance system began in April 1995 and was completed in August of that year.

The Advisory Committee testing of the Grand Alliance system was similar to that conducted for the four individual all-digital systems; however, additional tests were conducted to more fully evaluate the proposed system. These new tests included format conversions between the progressive and interlace modes (both directions) and compliance with the MPEG-2 video compression syntax. Subjective audio tests and long form viewing of video and audio programming were also conducted. Field tests were conducted in Charlotte, NC, utilizing the complete Grand Alliance system.

Working closely with the Advisory Committee throughout the U.S. DTV process, the ATSC was responsible for developing and documenting the detailed specifications for the ATV standard based on the Grand Alliance system (Hopkins et al., 1994). In addition, the ATSC developed the industry consensus around several SDTV formats that were added to the Grand Alliance HDTV system to form a complete DTV standard. Among other things, these SDTV video formats provided for inter- operability with existing television standards and supported the convergence of television and computing devices.

1. Documenting the DTV Standard: The ATSC assigned the work of documenting the advanced television system standards to specialist groups, dividing the work into five areas of interest:

• video, including input signal format and source coding;
• audio, including input signal format and source coding;
• transport, including data multiplex and channel coding;
• RF/transmission, including the modulation subsystem;
• receiver

A steering committee consisting of the chairs of the five specialist groups, the chair and vice-chairs of the Technology Group on Distribution (T3), and liaison among the ATSC, the FCC, and ACATS was established to coordinate development of the documents.

Following completion of its work to document the U.S. ATV standard, the ATSC membership approved the specification as the ATSC Digital Television Standard (document number A/53) on 16 September 1995. On 28 November 1995, the FCC Advisory Committee issued its Final Report, providing the following conclusions.

• The Grand Alliance system meets the Committee’s performance objectives and is better than any of the four original digital ATV
• The Grand Alliance system is superior to any known alternative
• The ATSC Digital Television Standard fulfills all of the requirements for the S. ATV broadcasting standard.

Accordingly, the Advisory Committee recommended to the FCC that the ATSC DTV Standard be adopted as the standard for digital terrestrial television broadcasting in the United States (Reimers, 2004).

1. DTV Standard Adopted by the FCC: On 24 December 1996, the commission adopted the major elements of the ATSC Digital Television Standard, mandating its use for digital terrestrial television broadcasts in the United 2 In 1997 the FCC adopted companion DTV rules as- signing additional 6-MHz channels to approximately 1600 full-power broadcasters in the United States to permit them to offer digital terrestrial broadcast in parallel with their existing analog services during a transition period while consumers made the conversion to digital receivers or set-top boxes. The FCC also adopted a series of rules governing the transition to DTV, including a rather aggressive schedule for the transition. Under the FCC’s timetable, stations in the largest U.S. cities were required to go on the air first with digital services, while stations in smaller cities would make the transition later.

Under the FCC’s plan, more than half of the U.S. population would have access to terrestrial broadcast DTV signals within the first year, all commercial stations would have to be on the air within five years, and all public TV stations would have to be on the air within six years. Analog broad- casts were planned to cease after nine years (on 31 December 2006), assuming that the public had embraced digital TV in adequate numbers by that time. Part of the FCC’s motivation in mandating a rapid deployment of digital TV was to hasten the day when it could recapture 108 MHz of invaluable nationwide spectrum that would be freed up by the use of more spectrum-efficient DTV technology.

In accordance with the FCC plan, DTV service was launched in the United States on 1 November 1998, and more than 50 percent of the U.S. population had access to terrestrial DTV signals within one year. By 1 March 2003, there were more than 750 DTV stations on the air in the United States, and nearly 5 million DTV displays had been sold. By 1 March 2005, there were nearly 1400 DTV stations on the air and over 16 million DTV displays had been sold, including over 2.5 million with integrated ATSC tuners. According to CEA data, consumer adoption of HDTV in the United States is occurring at roughly twice the rate as the adoption of color TV.

The ATSC DTV Standard was submitted to Task Group 11/3 of the ITU-R, and in 1997 it was included as System A in ITU Recommendations BT.1300 and BT.1306.

Ongoing Work of the ATSC: Since the primary ATSC DTV Standard was adopted in 1995, the ATSC has con- ducted a wide-ranging program for developing supplemental DTV and DTV-related standards, and for addressing implementation issues that have arisen in the countries that have adopted the ATSC DTV Standard. Highlights of this work include a standard for program and system information protocol (PSIP), a conditional access standard to permit restricted or pay services, a suite of data broadcasting standards, a standardized software environment for digital receivers, a standard for distributed transmitter synchronization, a standard for satellite contribution and distribution services, and a standard for direct-to-home satellite services. All segments of the television industry in North America and elsewhere are now represented within the ATSC, including broadcasters, cable companies, satellite service providers, consumer and professional equipment manufacturers, computer and telecommunications companies, and motion picture and other content providers. A current organizational illustration of the ATSC is given in Fig. 4. A Board of Directors, formed of members of the parent committee, manages the overall activities and directions of the ATSC. Two main subcommittees exist:

• the Technology and Standards Group (TSG);
• the Planning Committee (PC).

From time to time, the board can establish one or more task force groups to address specific items. Within the TSG structure, specialist groups are organized into specific areas of interest. Ad hoc groups may be formed for specific issues or projects.

Satellite and Cable Delivery of DTV Services in North America: It should be mentioned that the terrestrial broadcasting is no longer the only method for delivery of DTV services. In North America today, a large percentage of households are serviced by digital cable and digital satellite direct-to-home (DTH) systems. There are two papers entitled “Carriage of Digital Video and Other Services by Cable in North America” and “Satellite Direct-To-Home” in this special issue, which provide detailed technical information on digital cable and digital satellite systems in North America.