Analog Television

Digital broadcast television is viewed as a key market driver for RBB networking. Before considering digital television in more detail, though, it will be useful to review some important characteristics of analog television.

It's possible to argue that analog television is the most prevalent communications medium in the world. More televisions exist in the world than telephones, and the 1995 U.S. census reported that more homes had televisions than toilets.

The Three Standards

Three standards currently exist to encode and transmit analog TV worldwide: the National Television Standard Committee (NTSC), (sometimes referred to as Never Twice the Same Color), Phase Alternation Line (PAL), and Sequentiel Couleur Avec Memoire (Sequential Color with Memory, or SECAM). Table 1-1 shows some major characteristics of each standard.

Table 1-1. Characteristics of Analog Broadcast Standards

	NTSC	SECAM	PAL
Total lines/screen	525	625	625
Active lines/screen	480	575	575
Pixels/line	640	580	580
Bandwidth/channel	6 MHz	8 MHz	8 MHz
Picture rate/second	29.97	25	25
Megabits/second (Mbps) (uncompressed)	221.2	400.2	400.2
Countries	USA Japan Canada Rest of Europe	France French colonies Russia	Germany UK Australia

In the United States, TV channels are transmitted in increments of 6 MHz of bandwidth per channel. Channel 2 starts at 54 MHz, and Channel 6 ends at 88 MHz. (Between Channel 4 and Channel 5, 4 MHz of bandwidth is used for radio astronomy and radio navigation purposes). From 88 MHz to 108 MHz, FM radio is transmitted. Above the FM band, TV channels resume at 174 MHz with Channel 7 and continue upward in 6 MHz increments to Channel 13, ending at 216 MHz. Channels 2 through 13 are the very high frequency (VHF) stations. In addition, viewers can receive ultra high frequency (UHF) stations. UHF stations begin at 470 MHz for Channel 14 and continue upward in 6 MHz increments to Channel 69, ending at 806 MHz.

Table 1-2 shows spectrum allocation in the United States for frequencies covering broadcast television. Note that the broadcast TV frequencies are interspersed with other frequencies used mainly for governmental research, satellite communication, public safety, and amateur radio purposes.

Table 1-2. Spectrum Allocations for Broadcast Television Frequencies

Frequency Range (MHz)	Services
54 to 72	Channels 2, 3, and 4
72 to 76	Radioastronomy, aeronautical radionavigation, and fixed mobile
76 to 88	Channels 5 and 6
88 to 108	FM radio
108 to 174	Amateur radio, radioastronomy, aeronautical radionavigation space research (downlink), maritime, and fixed mobile
174 to 216	Channels 7 through 13
216 to 470	Amateur radio, satellite, mobile, public safety, radiolocation, and meteorology.
470 to 608	Channels 14 through 36
608 to 614	Radioastronomy
614 to 746	Channels 37 through 59
746 to 806	Channels 60 through 69 These frequencies are little used for broadcast TV. The FCC has recommended reallocating this spectrum for public safety.

Channelization rules are different elsewhere. In Europe, channel spacing is 8 MHz rather than 6 MHz, in either PAL or SECAM. Australia uses 7 MHz PAL encoding; more bandwidth per channel means clearer audio and video quality than with NTSC. On the other hand, for a given amount of aggregate bandwidth, fewer channels are available to the viewer.

Analog Screens Versus Computer Monitors

One of the assumptions on which residential broadband relies is that content can be received on computer monitors as well as television screens. This assumption poses some difficulties because the entrenched standard, analog television, differs from computer monitors in two important aspects: display format and color coding.

Display Format

In all analog television, interlacing is used as the display format. Interlacing means that horizontal lines of pixels are illuminated in an alternating pattern rather than sequentially. Figure 1-1 illustrates interlacing display. The television picture tube is a rectangular array of colored pixels that must be illuminated to present a picture. The solid lines show the first illumination pass of the screen. Illumination starts in the upper-left corner and proceeds to the right side at a slight angle downward. Then a line is skipped and the following line (the third line) is illuminated, the fourth is skipped, then the fifth is illuminated, and so on until the bottom of the monitor is reached. The entire vertical scan (called a frame) is performed 59.94 times per second, per NTSC.

The process starts again at the top of the screen with the other lines being illuminated. These are shown as dotted lines in Figure 1-1. The total effect is to refresh the entire picture 29.97 times per second. The fact that lines are skipped does not affect the visual experience. The time spans and vertical spaces between the lines are too small for the human brain and eyes to notice.

In progressive scanning (or proscan, used in computer monitors), each line is illuminated sequentially, without skipping lines. This is a simpler approach than interlacing, and computer software (such as graphics and fonts) has been optimized for proscan. For computer monitors to display television signals, video cards need to perform scan conversion, which renders interlacing on progressive computer monitors.

Proponents of interlacing—namely the broadcasters and television manufacturers—maintain that it is superior to proscan for two reasons. First, interlacing is a form of bandwidth compression. Only half the image is broadcast at an instant, therefore allowing the full picture to be sent in half the bandwidth. Secondly, proponents assert that interlacing offers better, softer pictures, especially for outdoor, natural scenes. The human brain fills in the skipped lines, whereas progressive scanning tells too much and is too harsh because of its high resolution. Supporters of interlacing assert that proscan is viewed as upsetting to the psycho-visual experience over long-term viewing.

Color Coding

Computer monitors differ from TV in color coding as well. Whereas computer monitors use a red-green-blue (RGB) vector for each pixel to display color, television uses a luminance, hue, and intensity vector, called Y'UV coding for composite video and Y'CrCb coding for component video coding.

Television's system of color coding is an artifact of the transition from black-and-white to color. When television was only black-and-white, each individual pixel displayed only luminance, or brightness. To make color television backward-compatible with black-and-white TV, it was necessary to encode all colors using a luminance vector. That is, instead of coding colors using varying amounts of red, green, and blue, it was necessary to code colors in varying amounts of luminance and two other new vectors, called hue and intensity.

Additionally, the higher refresh rate for computer monitors is required due to higher contrast and luminance of display.

PC monitors were optimized for viewing static images (mostly printed fonts) from a distance of 2 feet. TV monitors are optimized for viewing objects in motion, thus offering lower resolution from a longer distance than PC range.

Table 1-3 summarizes the differences between televisions and computer monitors.

Table 1-3. Color TV Versus Computer Monitors

	Color TV Monitors	PC Monitors
Scanning	Interlaced	Progressive
Color coding	Luminance, hue, intensity (Y'UV)	Red, green, blue (RGB)
Pixels	640 x 480 (NTSC)	800 x 600 (SVGA) 1024 x 768 for larger monitors
Picture resolution	Relatively low	Relatively high
Frames/second	29.97	72, for high resolution
Viewing distance	More than 7 feet	2 feet
Viewing angle	Comparatively wide	For straight-on viewing
Monitor size	Now up to 66 inches	Normally less than 25 inches
Image motion	Optimized for motion	Optimized for static images

Because of these functional differences, it is difficult to merge the two monitor types into a single form factor. Even if performed, one wonders if the cost is worthwhile.

Business Environment

Individual television stations are generally one of three types: 1. network-owned and operated, 2. affiliate, and 3. independent. The network-owned and operated stations(O&Os) are owned directly by the big national networks, specifically ABC, NBC, CBS, and Fox. Legislation exists to prevent concentration of media power in too few hands. Until the Telecommunications Act of 1996 (Telecom 96), networks could own at most 12 stations, which were permitted to reach no more than 25 percent of the national television audience. As of Telecom 96, no limits govern the number of stations, but each network's stations are permitted to reach no more than 35 percent of the U.S. population.

About 200 network affiliates exist for each national network. The national networks pay their affiliates to retransmit network programming, normally consisting of prime-time programming, national news, weekend sports, and soap operas. The compensation paid to the affiliates is a function of market size and competitive over-the-air stations. The network sells advertising during the national programs. Affiliates can obtain their own programming, schedule permitting, and make much of their independently derived money on local news.

Finally, there are the independent stations, which have no network affiliation. They purchase programming from the networks, syndicators, and independent producers, or they develop it themselves.

In total, there are more than 1500 broadcasters in the United States. A trade association called the National Association of Broadcasters (NAB) functions as the industry's lobbying arm.

Local content and advertising insertion are important services for affiliates and especially small independent stations, which do not have a guaranteed flow of network programming. Local content is also important for the national networks because consumers like to watch local events, traffic, weather, and advertising.Local content and ad insertion raises new technical problems as stations transition to digital transmission. New techniques to merge national content with local content will be required and will require new investment.

The point of this discussion is that the transition from analog to digital transmission will be costly, and the majority of stations in the United States—namely the independents and some affiliates—will face financial hardship during the transition.

Regulation

In the United States, as elsewhere, the broadcast television industry is regulated by national authorities: The U.S. Federal Communications Commission(FCC) regulates many aspects of broadcast television. Among these aspects are ownership rules of stations, media control, spectrum allocation, and technical specifications

In the past, the FCC and Congress have required backward-compatibility for TV innovations. For example, the FCC mandated that color television sets be capable of receiving and displaying black-and-white signals when color television was just becoming available in the 1950s. In the 1960s, a congressional mandate stated that TV sets must be capable of receiving UHF as well as VHF stations, over the objections of the TV industry. Requiring the combined reception of UHF and VHF was viewed as excessive government meddling, but it created new channel capacity and opportunities for programmers.

Regulations in the public interest also exist with regard to Must Carry rules imposed on cable operators (cable companies must carry local broadcast stations), foreign ownership of U.S. television stations (foreigners can't own majority shares of a broadcaster), and closed captioning (required by Telecom 96). There is every reason to believe that similar regulations will carry over to digital television.

In Canada, the Canadian Radio and Television Commission (CRTC) performs regulation. The jurisdictions of the FCC and CRTC are comparable, with the CRTC having greater oversight of the cable industry than the FCC. In the United States, municipalities have a strong regulatory role in cable, particularly with respect to franchise renewals, requirements for upgraded facilities, and the granting of bandwidth for public affairs and educational and governmental (PEG) uses.

Key Pressures on Analog TV

A convergence of interest is taking place among broadcasters, cable operators, TV manufacturers, and the government to change the existing analog television regime. Their various concerns can be summarized as follows:

• Channel lineup and scarcity— The Must Carry rule highlights a fundamental problem of analog TV, both over-the-air and cable. There is insufficient channel capacity for all the networks that broadcasters and cable operators want or need to get on the air.

• Conditional Access (CA)— Conditional access is the capability to preclude viewers from stealing programming. Cable operators experience significant pirating of signals, and analog scrambling has not been effective in stopping it.

• Picture quality— Picture and audio quality could stand some improvement. Screens are getting larger, and the proliferation of channels is stimulating increased production of made-for-TV film production. These should be presented more attractively.

• Slow TV sales— Even though roughly 110 million television sets are sold annually around the world, profit margins on TV sales are poor. There have been relatively few innovations in recent years to motivate sales; consumers tend to keep TV sets for a decade or longer. The TV industry needs a shot in the arm.

• Spectrum auctions— From the government's point of view, analog TV is wasteful of spectrum. The government would like to see other, more efficient uses of spectrum emerge. Then analog TV spectrum could be returned to the government and auctioned to feed the government's coffers in a relatively painless way.

• Desire for new revenue streams— Analog television provides little opportunity for new programming options and revenue streams, such as interactive service and e-commerce.

For more complete discussions of analog TV, see [Jack] and [Watkinson].