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Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 103
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 104
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 105
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 106
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 107
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 108
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 109
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 110
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 111
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 112
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
×
Page 113
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 114
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 115
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 116
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 117
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 118
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 119
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 120
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 121
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 122
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 123
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 124
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 125
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 126
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 127
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 128
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 129
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 130
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 131
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 132
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 133
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 134
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 135
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 136
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 137
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 138
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 139
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 140
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 141
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 142
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 143
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 144
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 145
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 146
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 147
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 148
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 149
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 150
Suggested Citation:"TRANSMISSION, MODULATION/DEMODULATION AND CODING." National Academy of Engineering. 1973. Telecommunications Research in the United States and Selected Foreign Countries: a Preliminary Survey. Report to the National Science Foundation. Washington, DC: The National Academies Press. doi: 10.17226/18640.
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Page 151

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

103 THE PROSPECT FOR U.S. TERRESTRIAL COMMUNICATIONS IN THE l980fs Telephone traffic has been increasing for the past decade at a rate of about 5% per year. Long-haul toll calls have been growing more rapidly; all toll at a rate of 7.8% per year and interstate calls at l0% per year. These trends are expected to continue for the next l0 to 20 years (Figure l). This projection leads to no absurdities, or even greatly different patterns and habits in telephone use. In l970, call- ing rates in the United States were 779 per capita for all calls and 49 per capita for toll calls. In 1990, the rate for all calls is projected to be about twice the present rate and for toll, about four times the present rate. This would be a call- ing rate for toll which is still only one-quarter the present total rate (Figure 2). Long-haul facility growth has paralleled traffic growth. The growth in calling rate along with a trend to longer holding times and greater average distance on calls has required a growth in facility capacity, measured in voice circuit miles, of over l5% per year (Figure 3). Projection at this rate indi- cates a required growth in long-haul facility capacity by a factor of 5 to l0 in the I960's(Figure 4). Radio has been the workhorse of the last two decades, but spectrum and system capacity limitations indicate a trend to guided systems (Figure 5). A "superhighway" approach to the interstate national network will accelerate this trend and, by concentrating traffic in fewer high cross-section links, will favor high capacity low unit cost systems such as waveguide. The capacity of these systems is such that even the enormous circuit mile requirements of continued l5% per year growth will not overtax our ability to design and build facilities to meet the needs through l990 (Figure 6). The toll facilities plant, following the trend already well established by T-Carrier in the exchange and short-haul (> 50 mile) plant, will become predominantly digital. Digital multiplexing with access at appropriate bit rates for all existing services already exists in part. Remaining levels and codecs for a com- plete hierarchy are under final development and will be avail- able well before 1980 (Figure 7). A series of digital

104 TRAFFIC 109 CALLS 1960 1970 1980 1990 TOTAL 94.0 159.6 — TOLL 3.43 7.24 17.7 39.9 INTERSTATE 1.04 2.71 7.3 17.9 Figure l

105 2000 r 1500 1000 500 CALLS/CAPITA/YEAR Total Toll • 1950 1960 4.1%/Year 189 7.4%/Year 49 1970 1980 1990 Figure 2

106 400 300 200 O DC O 100 0 CARRIER GROWTH BY FACILITY J I I I I 1950 Open Wire YEAR 1960 J I L 1970 Figure 3

107 FUTURE CARRIER GROWTH LLJ u cc PL o 15% 0 1950 1960 1970 1980 1990 Figure 4

108 4 KHz TELEPHONE CIRCUITS IN THE BELL SYSTEM CO LLJ D O cc O LL. O CO 1000 r- 500 200 100 50 20 10 5 2 1.0 I 1950 1955 1960 1965 YEAR END 1970 1975 Figure 5

109 FUTURE CARRIER GROWTH 111 0 c o 15% 5000 Miles of Waveguide 1950 1960 1970 1980 1990 Figure 6

110 DIGITAL TRANSMISSION HIERARCHY 1.5Mb/s 6.3Mb/s 45 Mb/s 274 Mb/s LINES MULTIPLEXES BANKS AND CODECS Figure 7

Ill transmission systjms on pairs, coaxial, waveguide, and probably domestic satellites, will become available before l980. They will capture a large share of long-haul growth and constitute a significant fraction of the long-haul plant by the mid-l980's. Continued growth, mostly by digital facilities, will make the plant predominantly digital by l990. The introduction of time division toll switching (No. 4 ESS) in the late l970's and its widespread use in the 1980's will be a strong factor in favor of digital transmission facilities, but both the transmission facilities and digital switch will compete economically in an otherwise analog plant. Exploitation of existing analog plant, as well as the large amount that will be added before digital facilities become a significant long-haul resource, will continue. Sig- nificant capacity for digital transmission can be realized by multilevel modulation in portions of the available spectrum on both radio and coaxial media. Economical mining of large num- bers of additional analog circuits may be possible by single sideband on microwave radio and follow-on systems to L5 on coaxial. The extent of this may be such as to alter the timing on the spread of new purely digital long-haul plant by two to four years, but not the conclusion that the plant will be pre- dominantly digital by l990. The advantages of digital plant and the ultimate limitations of the analog media point to this. The nature of new media, such as optical fibers, which may be important by the late l980's also favor the conclusion that digital transmission will prevail. An inescapable consequence is that we will have a hybrid plant, predominantly analog in the early years and predominantly digital by l990, but a mix for the entire decade of the l980's and beyond. Interfacing in the local plant will continue to be at voice frequency. In the long-haul plant, a key item will be the mastergroup codec which encodes a 2.5 MHz 600-channel analog mastergroup into a 45 mb (T3) digital signal and reconstructs the analog mastergroup signal from the T3 bit stream as required (Figures 8 and 9). Encoding smaller blocks of the analog hierarchy is obviously possible, but little need for doing so is expected. The MG codec will be especially important in the early stages when a small amount of digital plant is imbedded in a largely analog plant. E. F. O'Neill Bell Telephone Laboratories Holmdel, New Jersey

112 ANALOG DIGITAL INTERFACING CLEVELAND TERMINAL hill' DSX-3 CLEVELAND JUNCTION L5 M34 WT4 N.Y.C. Figure 8

113 MILWAUKEE L5 ANALOG DIGITAL INTERFACING CHICAGO TERMINAL Illl M34 T4 FEEDER CMG-3 CMG-3 CHICAGO JUNCTION DSX-3 Figure 9

114 OPTICAL COMMUNICATIONS I. Introduction The idea of using light for the transmission of informa- tion is an old one. Almost a century ago Alexander Graham Belli showed that speech could be transmitted over a beam of light. He called his invention the "Photophone". However, he (wisely, it turns out) decided to stick it out with an electric current on a metal wire. While optical communications received consideration on and off since then, the real impetus occurred a little over a decade ago with the invention of the laser - the source of coherent light. Today, research aimed at making optical communications a practical reality is being pursued vigorously in all industri- alized countries. The reasons are simple and obvious: the promise of truly enormous bandwidths; possible economic advan- tages (sand is cheaper than copper); and small size. An examina- tion of the progress made during the past decade toward the goal of making optical communications a practical reality2 shows: a) that the progress has been sufficiently rapid that we are today on the threshold of potential applications; and b) that a lion's share of this progress has been achieved through research carried out in the United States. Let us examine the veracity of this statement in greater detail by examining the progress made on the various components or parts of a possible communi- cation system. II. Sources In any communication system there is a source of the carrier over which information is transmitted. In an optical communi- cations system the source will be either a laser (a source of coherent light), or a light emitting diode (LED). Over the past decade, literally dozens of various lasers have been invented and developed to various stages of sophistication. It is strik- ing that almost every laser of possible use in optical communica- tions had its birth and was subsequently developed in the United States. The very long list starts with the pulsed ruby laser (at Hughes Research Labs); through the first cw gaseous He-Ne l) A. G. Bell, "Selenium and the Photophone", The Electrician 5., 2l4 (l880) . 2) By "practical reality" is meant a system or systems of interest and use to telecommunications utilities that can compete success- fully with present methods of communications. In some important sense "optical communications" is; a reality even today. For example, the lunar laser ranging experiment accomplished by the Apollo mission represents an optical communications system.

115 laser (Bell Labs); the ion lasers (Hughes); the Nd doped glass and YAG lasers (Bell Labs); the C02 laser (Bell Labs); the semi- conductor injection laser (IBM, GE, Lincoln Labs); the parametric oscillator (Stanford U.); the heterojunction GaAs-AlGaAs laser (Bell Labs); the dye laser (IBM). Others have made their con- tributions, to be sure. For example, the TE excitation of CC>2 lasers came from Canada, electron beam excitation received greatest attention in the USSR and very high power pulsed lasers (not really of much direct use in communications) in France and the USSR. But obviously the lion's share of the progress occurred in the United States. The U.S. industry today dominates the commercial laser market. It is also striking how broadly based this expertise in laser technology is in the United States. It is not limited to any one, or even half a dozen laboratories. The same is true of the LEDs. For reasons to be stated later, the most promising candi- dates for use as sources in a practical communication system are: l) the heterostructure GaAs-AlGaAs injection laser; 2) the Nd-YAG laser and a miniature LED. All of these emit adequate power (one would like more) at adequate efficiency (one would like more). Reliability, life, and cost remain a problem and must be improved. III. Transmission Medium Fog, rain and snow and other vagaries of the weather affect the transmission of optical waves through the atmosphere and, except for special application (transmission in space where there is no weather or for very short distances) the use of atmosphere as the transmission medium is not likely to prove practical. The use of lenses - either discrete or distributed (gas) - in shielded ducts remains a possibility. Such systems have shown to be tech- nically feasible again through research carried out in the United States (primarily at BTL). Economically they might be viable only if and when very large capacities are needed (hundreds of thousands of voice circuits). Such needs are well in the future. For more immediate application the optical fiber is thought today to offer the best promise as the transmission medium. It was Lord Rayleigh who first pointed out that dielectric wave- guides will guide light. But the more modern impetus came from the research sponsored by the British Post Office at STL in England. The modern fiber consists of a central core and a dielectric cladding whose index of refraction is lower than that of the core. The developers of this medium first faced the seemingly unsurmountable problem of reducing horrendous optical absorption losses. No more than five years ago the best optical fibers showed losses of hundreds of decibels per kilometer. But here, too, progress has been phenomenal. Liquid-filled optical fibers (developed at BTL and Australia) exhibit losses of less than l5 db/km and the best glass fiber most

l16 recently announced by the Corning Glass Co. shows a loss of only 4 db/km near 0.8 vim and l.05 urn region of the spectrum (where the GaAs, the Nd-YAG and the LEDs operate). Such low-loss fibers are already adequate for a variety of applications. But a myriad of problems remain to be solved. To mention just a few, we must learn how to control dispersion (here the Japanese Self Foe fiber is noteworthy), how to make sturdy cables out of the fragile fibers, how to splice such cables, and how to connect sources and other optical devices to such fibers. IV. Modulators, Detectors, etc, and Optical Repeaters The simplest optical communication system must have, in addition to the source and the transmission medium, a modu- lator of some sort and a detector. In more complex systems, optical repeaters will be required. The basic physical principles on which the operation of all these devices rests is, of course, well known. But in order to optimize the various devices, a body of knowledge has had to be developed on how light interacts with matter, and new materials have had to be invented which enhance the useful aspects of this interaction. An excellent example of the interaction of the quest for basic knowledge, the invention of new materials and construction of useful devices is the work leading to efficient electrooptic modulators. First there was quite extensive research on the physical nature of the electrooptic effect; new and/or exotic materials were examined and studied (for example LiNbOj, or the "bananas"). As a result, the improvement in modulator efficiency has been dramatic. It is now almost, but not quite as good as that in the microwave range of the spectrum. The accumulation of the body of knowledge on how light interacts with matter is now well on its way, again primarily through research in the United States. Here universities, industrial research laboratories, as well as government laboratories all have made important contributions. While the quest for this knowledge is far from complete, modulators and detectors can be built today which would be adequate for a communication system. Undoubtedly they will improve with time. An important contribution to this improvement will come from the new concept of integrated optics - a technology originated in the United States within the past few years. In summary, in the field of research and development leading to practical optical communications, as in almost any other area of telecommunication R&D, the United States has no equal. Its R&D enterprise is broadly based in universities, industry, and government labs. Although it has not been possible to generate dollar figures, judging by the results,

117 the enterprise has been adequately supported from a variety of sources. This enterprise has performed well in the past, and if not tinkered with, is likely to perform equally well in the future. Sol Buchsbaum Bell Telephone Laboratories Holmdel, N. J.

118 OPTICAL COMMUNICATIONS - IN THE 70'S AND BEYOND I. Summary Recent forecasts by the Stanford Research Institute (SRI)l and others have indicated growth or trends for tele- communications traffic over the switched network as more than doubling during the remainder of this decade. Although much of this expanding traffic can be accommodated by multiplexing and digital techniques over existing networks, the rapid growth of wide band services, principally video, cannot be readily accommodated on existing transmission systems without loss of quality of pictures, or degradation of information due to cross talk, bandwidth limitations, etc. To compound the transmission difficulties, proposals are being made for additional services, mainly wide band video and other wide band transmission services which will some day be introduced as part of the "wired city concepts" for dis- tribution through the "local loop" plant. (See references to articles by E. B. Carne, P. Goldmark, J. R. Pierce, etc.)2./3/4 and the excellent report by the NAE Committee on Telecommuni- cations, "Communications Technology for Urban Improvement."5 Alternative wide band communication transmission systems are discussed in this memorandum, namely, "optical transmis- sion" applying coherent or incoherent light sources, optical planar dielectric waveguide technology (integrated optical subsystem) and fiber optics, as the basic components for wide band information transmission as compared to the circular low loss millimeter waveguide system being developed by the Bell Laboratories. II. Traffic Forecasts An SRI report, "A Study of Trends in the Demand for Information Transfer," February, l970, by R. W. Hough, C. Fratessa and others, was prepared for the National Aeronautical and Space Administration, under Contract NAS2-5369 and SRI Project MU-7866. In tabular and graphic form reproduced from this report, is given the projected information transfer over the switched network for l980 and l990 as compared to l970 (see pages 1l9 and l20) . The expression chosen for this common denominator is bits (binary digits) per year. The method of conversion entailed first an assumption about the information transfer mode most likely to be used for the service - voice, video, alphanumeric coding, standard facsimile, high quality facsimile (newspaper and photo), etc. Next, a standard conversion method was assumed for each mode of operation, such as 30,000 bits per page for alpha coded text, 64,000 bits

119 Table l PROJECTED INFORMATION TRANSFER VOLUME, l970-l990 (Bits per Year) l970 l980 l990 Voice (x l0l7) Video (x l0l6) Record, data, and private wire (x l0l5) Written (x l0l5) Long Total Distance Total Long Distance Long Total Distance 20 l.0 50 37 l00 l0 0 .56 0.33 9.0 l.5 230 25 0 .38 0.34 3.5 3.l 30 27 l5 l0 20 14 30 2l Table 2 CLASSIFICATIONS USED TO SUMMARIZE RESULTS OF THE STUDY Voice Telecommunications Telephone Mobile Radiotelephone Radio Program Transmission Video Telecommunications Videotelephone Closed Circuit and Other Special Television Services Television Program Transmission Record, Data, and Private Wire Communications Public Message Telegraph Teletype service (TWX and TELEX) Data Transmission Private Wire Systems Written Books and Magazines Newspapers Mail

120 PROJECTED INFORMATION TRANSFER VOLUME, 1970-1990 1020 ' TOTAL 10 19 18 10 « 1017 UJ Q. 10 16 10 16 10 14 Voice Record Data and Private Wire - LONG DISTANCE Record Data and Private Wire 1970 1980 1990 1970 1980 1990 Figure l

l21 per second, for voice (assuming conventional PCM coding) , and l30 megabits per page for high quality newspaper facsimile. Finally, those factors were applied to the volume of trans- actions that had been projected for the various services. The result, then, was a statement of potential information transfer volume expressed in all cases in bits per year. It may be noted from the data presented in the tables, that the volume of voice transmission is presently greater by two orders of magnitude than all other information traffic combined which is being transmitted in l972. However, voice transmission appears to be following demographic trends while video is growing at 35% per year and data at approximately 25% per year. Data does not yet appear to be a factor in clogging up the transmission medium, except for the problems it presents in the form or kinds of modulation required and the problems of multiplexing. Video is another matter entirely when one recognizes that a single 6 MHz television channel will require l00 megabits/sec., or at least 50 MHz in channel bandwidth^ and a l MHz video phone channel would use up 6 megabits/sec. or approximately 3 MHz of bandwidth of an existing transmission medium. These are very large bandwidth bites out of the exist- ing radio transmission links. According to E. Bryan Game2, by mid-l980 "a wide range of services could be made available for the business com- munity," such as videotelephones, interactive TV electronic mail, data services, etc., if cost and transmission become feasible. With the additional requirement on bandwidth, how much further will the present transmission networks be taxed, particularly if to this new "wired city" one adds additional network traffic such as the following: - community affairs traffic (newspaper-like) - educational traffic - medical traffic - community management traffic - transportation information traffic Where will this transmission capacity come from, or how will the introduction of the above-mentioned new wide band services be affected by insufficient transmission capacity? How will such services be switched through the network? These are among the hard questions of great concern to the tele- communications industry and the people it serves, namely, all of us. In the following section we will look at some alternate projected transmission technologies that may soon be put into practice, or that can be "made to happen" if sufficient stress is applied by the research arms of the telecommunications

122 industry and by proper assists from the various government agencies. III. New Developments in Transmission Technology As discussed earlier it now appears from the "trend tables," compiled by various investigations that continued growth of traditional voice and data services at present rates will demand this doubling of present transmission capacity in less than ten years. Much of this increase can be accommodated by multiplexing the existing plant, mostly by digital tech- niques. On the other hand, high quality local video service presents technical and economic problems that need to be solved by long-range research. The latent demand for video transmission appears to be very large. If the price can be made reasonable and the quality improved substantially, there should be a considerable market for these services. The present loop plant has very limited capability of carrying video signals without developing excessive cross talk between the video and audio channels. A. Projected Technologies A number of new communications techniques for higher bandwidth are in various stages of development in laboratories throughout the world. The major ones are: - Optical Fibers - Laser Links - Circular Millimeter Wave Guides - Light Pipes - Digital Microwave - Improved Satellite Links B. Millimeter-Waves and Optical Transmission Communications engineers know that as the carrier fre- quency goes up, the amount of information that can be carried out on the carrier also increases. Since the frequency of light (lO^4 - l0^5 cycles/sec.) is several orders of magnitude greater than that of microwaves (l09 - lQl° cycles/sec.), then the potential for information capacity can be enormous. Earlier efforts to about l964 or l965 demonstrated optical communications experiments with modulation, detection, and

l23 simple transmission through the atmosphere, and the ability to carry one or even several TV signals over a laser beam. This capability, however, had some drawbacks. Laser light was, after all, "light." A laser beam is readily scattered by the atmosphere in conditions other than absolutely clear such as clouds, rain, or smoggy weather. The conclusion with regard to the mode of transmission was that the laser beam would necessarily have to travel through a pipe, or other friendly medium, and lenses and mirrors would be required to keep the beam directed along its chosen path, a costly and technologically difficult procedure. Also, the optical com- ponents which were developed to provide modulation or detec- tion themselves placed restrictions on the bandwidth that might be usefully employed in communications systems. At Bell Laboratories (in l966) , where much work had been going on to take advantage of the coherent and narrow spectral dis- tribution of laser beams, priorities for communications appeared to shift to the circular wave guides as the wide band transmission carrier, in spite of the recognized tech- nological problems and inherent high cost of such systems. An excellent presentation of the Bell Laboratory efforts in optical communications technology is the paper by R. Kompf- ner, Optics at Bell Laboratories - Optical Communications. In his article Dr. Kompfner outlines the history of R&D in optical communications at the Bell Laboratories from pre-laser days to the present. He also speculates on when optical com- munications systems will pass beyond the stage of engineering feasibility into the realm of practical applications. Circular waveguides are now emerging from the labora- tories into field trials. They are exclusively long-haul, very wide bandwidth systems (240,000 voice or l80 TV channels). Cost per channel will not be competitive until about 50% of the capacity is used. The minimum bending radius of the wave- guide is 200 feet, making it useless in congested areas. Incidentally, hollow light pipes would have the same kind of problems as circular wave guides with respect to bending radius. They do not appear at present to represent a serious approach. C. State-of-the Art of Optical Communications Optical fibers represent a very promising approach to the wide band transmission system. - In local distribution networks fibers will permit wideband video transmission with very small demands for duct space. (Bends can be as sharp as a few centimeters in radius.) - On interexchange trunk routes fibers can carry large amounts of voice, video and data, again with small duct space requirements.

124 - If\optical multiplexing techniques can be developed, fibers will prove useful on toll routes for carrying medium or heavy loads. The potential bandwidth available in an optical system surpasses the circular waveguide capacity. D. Optical Fibers for Information Transmission Although optical fibers have been in use for several years, their high attenuation (l000 db/km) had limited their use to special applications requiring only a few meters of transmission. The discovery? by Corning Glass Company less than two years ago that fibers could be made exhibiting losses less than 20 db/km has spurred work on fiber research in many laboratories throughout the world. In addition, the virtual certainty that low loss fibers will eventually become com- mercially available has triggered work on the many other com- ponents necessary for an optical communications system. Optical fibers can propagate either a single light mode (if their diameter is small enough) or many modes. A typical single mode fiber may have a core of only two microns diameter surrounded by a cladding of much larger (several mils) diameter and very slightly lower refractive index. The small diameter makes coupling of light into the fiber difficult, and only coherent laser sources can be efficiently coupled. However, the inherent bandwidth is limited only by the dispersion of light velocity in the fiber medium over the wavelengths contained in the message. Limiting bandwidths of l0 GHZ have been predicted. Corning has developed single mode fibers in 600-foot lengths with extrapolated attenuations of less than 10 db/km. Multimode fibers have core diameters in the order of l00 microns. This allows efficient coupling to less expen- sive light sources such as LED's. However, the different modes propagate with slightly different velocities, resulting in considerable dispersion of the signal and limitations of bandwidth. BTL studies of certain multimode fibers indicate a limiting bandwidth of 30 MHz for l km length. This limita- tion may be significantly reduced by a structures produced by Nippon Sheet Glass Company in which the refractive index decreases radially from the fiber center. This has the effect of self-focusing the light (hence the name SELFOC) and equalizing the path lengths, thereby reducing the dispersion. This fiber is available commercially in 200 meter lengths with attenuation less than l00 db/km. Laboratory samples of 40 db/km have been made. The lowest attenuations reported have been for fibers with liquid cores (BTL l3.5 db/km, and University of South- hampton, England l0 db/km, Australia!Government 5-7 db/km). These fibers are relatively easy to make with low attenuation,

125 but their practicability in a system is unknown. Most recently Corning has reported a loss of only 4 db/km for a glass core fiber. Laboratory techniques have been evolved^ at BTL and at Corning for splicing fibers with high optical throughput (97%) . However, this requires sub-micron tolerances. Field splicing of fibers will clearly demand sophisticated'techniques. At the Electro-Optics Conference, September l972, in New York City, several of the participants expressed strong confidence in adequate solutions to losses in single and multi- mode fibers, ability to provide low loss couplers, approaching the simplicity of UHF connectors, and the ability to achieve wave guide bundles for spatial distribution, etc. It was Coming's belief, backed by a sizable expenditure on fiber optics technology, that the day will come when the fiber bundle will replace coaxial cable economically for a large number of video and other wide band applications. To provide the light beam, light emitting diodes (LED) appear to represent the best sources for multimode fibers. BurruslO had developed a high radiance (small emitting area) LED and coupled it into a multimode fiber with an over-all conversion efficiency of 0.6%. This particular LED is presently limited in conversion efficiency, power output (2 mwatt), and life (3000 hours). For single mode fibers, lasers are necessary and no clear choice can be made. Double heterojunction diode lasersll perhaps have the most promise, if their very short lifetime (less than l00 hours) can be overcome. Other types under consideration include thin film lasers pumped by LED's and miniature gas lasers. The problems in all of these are some- what formidable at the present time. Assuming that lasers will be developed which are economic in price and have reasonable conversion efficiency and power, a modulator will be required in order to impress the informa- tion onto the light (LED's and diode lasers can be modulated directly by varying the current). While bulk modulators have long been known^, l3^ they are unsuitable both physically and economically for a practical system. A useful optical com- munications system will require optical signal processing and detection components which are rugged, efficient, and which can perform identical functions to that of their electrical counterparts. Thin film integrated optics consist of a deposition of thin optical film onto a substrate. The films may be amorphous or single crystal, and in some cases semiconductors. Thick- nesses are of the order of the wavelength of light, approximately

126 l micron. The uniformity and optical behavior of such film make possible wave guiding of light, coupling, and frequency mixing. The technology is just in its earlier stages, having begun in 1969-l970. Success with integrated optical devices will provide many of the principal components which can serve as building blocks for a fully multiplexed PCM system at data rates impossible to transmit along coaxial lines. E. Optical Detectors Silicon avalanche detectors are commercially available with gain-bandwidth products of one hundred GHz and with quantum efficiencies of 50% or better. The detector, therefore, does not represent a present technical bottleneck, although sub- stantial cost reductions are necessary before an optical communications system could be economically viable. Recent developments of an extremely fast photomultiplier called the dynamic crossed-field photomultiplier (DCFP) makes possible direct optical detection to l.2 GHz.l4 IV. Program Considerations Programs to consider for monitoring and support to meet the needs for wide band services include: A. Fiber Technology - Develop and evaluate fibers for attenuation and dispersion. - Perform coupling and splicing experiments. - Investigate fiber handling techniques, including sheathing of fibers. - Perform theoretical studies on fiber bandwidth and attenuation. B. Light Sources - Develop high radiance LED's which may be directly modulated. - Study possibilities for film lasers and recommend most likely candidates for development (such a laser would be complementary to thin film modulation techniques). - Develop diode injection laser specifically for com- munications purposes. Power, life, and spectral output would be tailored to wide bandwidth requirements.

127 C. Modulation - Develop thin film modulator. - Develop coupling techniques. - Theoretical work to optimize modulator and coupling designs. D. Multiplexers - Development of optical multiplexers and demultiplexers. E. Electronic Subsystems - Development of drivers for PCM modulators. - Development of signal processors for high bit rates, l00 Mb/sec. F. Demonstrations of Wide Band Systems - Suggest and implement vehicles to demonstrate optical transmission and multiplexing. V. Concluding Remarks It is becoming increasingly evident by many studies of trends in the usage of the electromagnetic spectrum for telecommunications that bandwidth requirements are rapidly expanding and may soon become self-limiting due to over- crowding of the available information transmission channels. Exploitation of higher and higher frequencies into the milli- meter waves is well under way, but will entail expensive hardware and installation costs demanding almost from the beginning a high utilization or fill factor to be economical. For other practical reasons such wide band services provided by circular millimeter wave guide cannot readily be installed in built-up areas, areas which may be the early heavy users of video and high data rate services. The emerging technologies of low-loss fiber optic trans- mission lines, small efficient lasers or LED's, integrated optical components for modulating and detecting, may provide the answer to almost unlimited bandwidth and signal handling, as well as high degree of flexibility, gigahertz bit rate per second, and economic telecommunications systems for the urban communities. Many laboratories throughout the world are considering in piecemeal fashion the various components. Corning, Schott, Bell Labs, Bendix, American Optical, and others are doing glass fiber development for low-loss optical transmission. Processors and modulators, and other integrated optical circuits

128 are being studied in the laboratories at GTE, Bell, Hughes, Zenith, North American Rockwell, and many others. And, similarly, developments in fast optical detectors capable of stripping off hundreds of megabit/second signals from a carrier are being worked on at still other laboratories. A few large laboratories, like Bell or GTE, whose prime concern is to upgrade their telecommunications services, are examining the communications system in its entirety, as well as the components needed. From the numbers of documents made regarding optical communications by the various members of the Telecommuni- cations Research Panel, it would be desirable that the interested parties constitute themselves a Task Force on Optical Communications to review and recommend to the full Panel: l. Whether optical links are a viable approach to wide band services. 2. Who is doing what. 3. Where are the gaps in technology or systems approaches. 4. And if they are worthwhile, what incentive or support could be offered to implement these needs. The key to success will be the intensive research on materials and phenomena, with the same intensity as was required to make the integrated circuit field successful. To provide impetus and incentive, the Panel on Tele- communications Research may find it useful to recommend certain of these programs for NSF support, and better yet*, to set goals to tax the existing state of art on "tele- communications systems needs" where crowding of bandwidths, crowding of space, flexibility and social needs set the requirements for the extension of the radio frequency spectrum for telecommunications into the optical spectrum. Louis R. Bloom GTE Laboratories Stamford, Connecticut

129 REFERENCES l. R. W. Hough, C. Fratessa, V. Holley, A. H. Samuel, L. J. Wells, "A Study of Trends in the Demand for Information Transfer," SRI Final Report, Project MU-7866, February l970. 2. E. Bryan Carne, "Telecommunications: Its Impact on Business," Harvard Business Review, p. l25, July-August l972. 3. P. C. Goldmark, "Communication and the Community," Scientific American, 227, No. 3, p. l42, September l972. 4. J, R. Pierce, "Communication," Scientific American, 227, No. 3, p. 30, September l972. 5. "Communications Technology for Urban Improvement," Report to the Department of Housing and Urban Development, Contract No. H-l22l, June l97l. 6. "Transmission Systems for Communications," by Members of the Technical Staff, Bell Telephone Laboratories, Revises Third Edition, pps. 6l0-6ll. 7. F. P. Kapron, D. B. Kech, and R. D. Maurer, "Radi- ation Losses in Glass Optical Waveguides," Applied Phy. Letters, l7, 423 (l970). 8. R. H. Kita et al, "Light Focusing Glass Fibers and Roda," J, American Ceramics Society, 54, 32l (l97l). 9. D. J. Bisbee, "Optical Fibers Joining Technique," BLTJ, 50, 3l53 (l97l). l0. C. A. Burros, "Radiance of Small Area High Current Density Electroluminescent Diodes," Proc. IEEE, 60, 23l (l972) ll. M. B. Parish, "Heterostructure Injection Lasers," Bell Labs Record, 299 (Nov. l97l). l2. I. P. Kaminow, "Microwave Modulation of Light," Phys. Rev. Letters, 6_, 528 (l96l). 13. E. I. Gordon, "A Review of Acousto Optic Light Modulators," Proc. IEEE, 54, l324 (l966). l4. W. Connors, S. Green, L. Neal, "High Data Rate Optical Receiver," Developed under Contract AFAL-TR-72-l98 by McDonnell Douglas Corp., St. Louis, Mo.

l30 R&D TRENDS FOR COMMUNICATIONS SATELLITES: COMPARISON OF U. S. AND OTHER PROGRAMS This paper will cover a) major goals of communications satellite design; b) the approaches to be taken toward meeting these goals (in the process of spelling these out the R&D work needed will be apparent); c) status with respect to other countries in the field, and d) conclusions. I. Goals These can be stated quite simply as the desire to get more and more channels per satellite and to produce these at lower cost per channel. II. Approaches The general approaches can be estimated by looking at the trends from the first satellite through the present and extrapolating these. Early Bird started using a toroidal antenna pattern in which most of the energy was radiated away from the earth. Also, its bandwidth was only about l0% of that then allocated to communications satellites. Since that time the trend has been to satellites which fully utilize the allocated 500 MHz bandwidth and have directional antenna beams which illuminate the earth only, as well as narrower beams covering one sixteenth of the visible earth. The point of diminishing returns has already been reached as far as obtaining more channels by means of satellite radiated power. For example, in Intelsat IV, by going from a global beam to a spot beam a l6-fold increase in radiated power is obtained, but only a doubling in channel capacity results because of the limited bandwidth. In the future the trend will be to increase effectively the allocated bandwidth by using multiple antenna beams so designed that their overlap is suf- ficiently low so as to permit reuse of the spectrum in each beam. Thus, the use of four beams would yield a 4-fold increase in capacity per satellite. Sufficient work has been done to show the practicability of simultaneously using two polarizations in transmissions to and from the satellite. This provides another doubling of capacity for a given bandwidth.

131 Work is underway on time division modulation methods to achieve greater numbers of channels per repeater and also to permit interconnection of the various beams. Beyond this, the l97l World Administrative Radio Conference allocated bandwidths at ll and l4 gc; and at 20 and 30 gc to the fixed satellite service. The first pair of bands total l000 MHz, the same as the presently allocated 4 and 6 gc bands, while the bandwidth of the latter pair is five times as great. This should permit a 6-fold increase in channel capacity. Work is needed to develop suitable satellites and earth station RF components for these new bands; and also to improve our knowledge of propaga- tion at these frequencies. Considering the above, a satellite including a number of beams could have a total two-way telephone capacity in the order of l/4 million circuits. In addition to working on the communication aspects mentioned above, work will proceed on the spacecraft aspects of trying to get more power from a given weight-size satellite. This, coupled with development leading to light-weight components, should ultimately permit a given capacity to be obtained in a smaller satellite, thus further decreasing the cost per channel. Improvement in reducing earth station antenna sidelobes would be useful in permitting closer satellite spacing along the geostationary orbit. Similar work on satellite antennas should permit closer spacing of illuminated areas on the ground. III. Foreign Communication Satellite Activities A. Canada Canada started in the communications satellite area by designing and building the communications repeaters for the Relay satellite in l96l, and also the Alouette scientific satellite in the same period. Some subsystems for the Intelsat IV satellite were built in Canada. More recently, in November l972 the Canadians launched a satellite for their domestic use. This satellite was built by Hughes and was launched by NASA for Canada. Several dozen earth stations have been built, ranging in size from 25 foot to 97 foot diameter antennas, with the majority of them being of the smaller size. A substantial number of these stations are of Canadian manu- facture, but for the most part the Canadian manufacturers are

132 subsidiaries of, or affiliated with, American companies. The system will be used for transmission of TV and two-way telephony. The Canadians and NASA are jointly working on an experi- mental "Communications Technology Satellite." Canada is to build the entire satellite, except for the 200 watt l2 gc power amplifier. NASA is to supply the Delta rocket and the 200 watt amplifier. The satellite, to be launched in late l975, will be used for the experimental transmission of TV to small stations. ESRO (European Space Research Organization) is sup- plying a 20 watt traveling wave amplifier and flexible solar cell arrays to the Canadians for use on this satellite. B. France/Germany In order to provide a background in satellite technology for French and German industrial concerns, the Symphonie satel- lite project was started in l967. Two flight models were to be built for launch in l972 in connection with the satellite and rocket (Europa II). This rocket, the first model of which was launched early in l972, failed and several major subsystems have to be redesigned. Because of this, it has not yet been decided whether to continue with this rocket or to use an American Delta rocket to launch the satellite. The schedule has slipped from l972 to late l973, or possibly early l974. The cost for development and construction of two satellites and two rockets had risen from the original $65,000,000 to about $l50,000,000 by early l972. By comparison, the cost of develop- ing, building and launching eight simpler Intelsat III satel- lites each of about three quarters the weight, including the cost of eight rockets, was about $l00,000,000. The Symphonie satellite itself will weigh about 450 pounds, which is well under the 600-700 pound capacity of the Delta rocket. It will have two repeaters of 90 megacycle bandwidth and two elliptical beams, one covering most of Europe and Africa and the other covering most of South America and the eastern part of North America. The satellite will be stabilized with a momentum wheel, an approach which has been used in the American ITOS series. Both French and German manu- facturers have built subsystems for the Intelsat IV satellites. C. Italy In l967 Italy initiated the SIRIO program which called for the development, construction, and launching of a

133 geostationary satellite for space research on physics of the magnetosphere and propagation experiments in the ll/l8 gc region (which was being considered for communication satellites at the time). This program has been delayed so that the original launch date of the last quarter of l97l is now scheduled for the first half of l974. The satellite itself is technically some- what similar to the Intelsat III, but would operate at milli- meter wavelengths, and use a narrower beam antenna. Italy has participated in Intelsat IV subcontracting work. D. japan japan has plans for a communications satellite to be launched in the l977 period. A contract for system engineer- ing and preparation of specifications for this satellite has been awarded to Philco-Ford, but it is likely that the satellite would be designed and built in Japan. A Japanese manufacturer has also built subsystems for the Intelsat IV satellite. E. United Kingdom The award of a 6-month project definition phase contract for the U.K. Geostationary Technology Satellite (GTS)* has been announced. The project definition phase is for approximately £0.5 million and is expected to lead to a development and con- struction contract in the amount of Ll5-20 million for a l976 launch using a Delta rocket. The satellite will be 3-axis stabilized and will utilize the same 5.5 foot diameter antenna for l2/l4 GHz coverage of the British Isles and offset L-band feeds for elliptical coverage of part of the North Atlantic for maritime communica- tions experiments. The TV broadcast experiments will involve primarily propagation investigations as well as the utilization of various ground antenna sizes for community and direct-to- home TV receptions. Several British manufacturers have built subsystems for Intelsat IV satellites. F. U.S.S.R. The U.S.S.R. launched its first communications satellite, Molniya I, in l965 and since then has launched at least 20 of *Previously named the U.K. Applications Technology Satellite.

134 this series. Based on the available information, this satellite is primarily used for TV transmission to several dozen earth stations inside the U.S.S.R., but it also has the capability for limited telephony transmission. The orbit is elliptical, with approximately a l2-hour period, and an inclination of 64° North, resulting in an apogee of about 24,000 miles which focuses the satellite on the Northern Hemisphere and provides coverage over all Northern latitudes. Transmission is in the 900 MHz region. Reports have been received of the launch of a more advanced communications satellite, Molniya II, with a similar orbit, but higher capacity repeaters in the 3400 to 3900 MHz band. In l968 the U.S.S.R. filed with the International Frequency Registration Bureau for allocations in this band for a geostationary satellite, "Statsionar" to be launched by the end of l970, but none have yet been reported in orbit. Both the Molniya II and Statsionar use 20 repeaters for telephony each with l0 MHz bandwidth and 7 watt transmitter power, working into an antenna beam covering the visible earth plus a higher power, wider band repeater for TV. Using avail- able characteristics of their earth stations and the above satellite data yields a repeater capacity of l20 one-way telephony channels, and a total capacity of l200 two-way telephone circuits, in addition to one TV channel. It is estimated that the solar array for these repeaters must produce at least three times the power output of an Intelsat IV, and that the satellite's 2l repeaters probably weigh about twice or more than Intelsat IVs l2 repeaters of 36 MHz bandwidth. However, using the U.S.S.R. earth stations in both cases, an Intelsat IV should have twice the capacity of the Statsionar because of its greater bandwidth, and with Intelsat's earth stations, four times the capacity. IV. Comparison with U.S. Systems Communications satellite technology in the U.S. is well advanced over that of other countries because: — the need existed, and — spacecraft technology and launch .vehicles from NASA and Department of Defense satellite programs could be applied to communications satellite design. Other countries of the world outside the U.S.S.R. have a need in that most of them are members of Intelsat and therefore

135 eligible to participate in the design and construction of its satellites. Their lack is an extensive space technology back- ground. The U.S.S.R. has the space experience, but apparently has relatively limited need, judging by its communications satellite objectives. While the Franco-German Symphonie project has experienced difficulties, there is little doubt that these countries will eventually launch a communications satellite. While Symphonie won't be economically viable, future designs may well be economic, based on the Symphonie experience and also on their participation in Intelsat R&D programs (approximately 28%* of the Intelsat IV satellite program was subcontracted outside of the U.S.). Their problems have been due to their relatively limited number of space projects, aggravated by politics. The U.K., Canada and Japan should be better off in this respect. Because U.S. communications needs are much greater domes- tically than internationally, the introduction of a domestic satellite system will undoubtedly provide the stimulus for development of the ll/l4 gc, 20/30 gc bands, and also the greater exploitation of the 4/6 gc bands. Meanwhile, Japan and Western Europe are also developing microwave components for ll/l4 gc and 20/30 gc for use in ter- restrial relay systems as well as for satellite use. They have a good background acquired in developing and building substan- tial numbers of similar components for 2, 4 and 6 gc relay systems and must be considered serious competitors in this field. Their disadvantage vis-a-vis the U.S. is mainly in the spacecraft and launch vehicle area. Because of their rela- tively limited needs and experience, their space programs thus far have moved at a slower pace and have become obsolete more quickly. It was pointed out that the Europa II rocket to be used for the Symphone satellite may be scrapped. This rocket is a follow-on to the Europa I series. Together, they repre- sent ll launch attempts without a single successful orbiting of a satellite and an expenditure of over 2/3 of a billion dollars spread over most of a decade. *Corresponding to foreign subcontracts of $29.7 million out of a $l06 million total. This figure covers the development and the construction of eight satellites.

136 By comparison, the rapid U.S. growth is epitomized by the U.S. Delta program, with its synchronous orbit payload capa- bility increasing as follows: 85 pounds - l965; l90 pounds - l966; 300 pounds - l968; and 700 pounds - l973. All of these increases were due to improvements in the various stages which originated in programs other than communications satellites. Actually, of a total of over 80 Delta and Atlas/Centaur rockets launched since the launch of Early Bird (the first commercial communications satellite in l965), only about 20% have been for commercial communications satellites. Thus, the growth of the commercial program has been due in large part to the broad space technology base provided by NASA and Department of Defense satellite and rocket programs. These programs have maintained a number of highly skilled spacecraft and rocket engineering teams around the country, together with subsystem and component manufacturers. Their expertise grows as new programs pose problems of increasing sophistication. The recent NASA and Department of Defense cutbacks have already slowed down this growth. While no country outside the U.S. and U.S.S.R has yet built a commercial communications satellite, there is little doubt that toward the end of the l970's Canada, Italy, France/Germany, Japan and the United Kingdom will have the capacity to do so. V. Aerosat and Maritime Satellites Serious consideration of the use of satellites for com- munications between planes and land based stations started in about l964. In early l973 there is still no firm plan to proceed. Initially, with the limited payloads available from rockets which could be considered for such a project, the basic question was economic viability. Other questions were debated, e.g.,- the channel capacity needed; the power required per channel; the choice of frequency (VHF or UHF); and an important nontechnical question of who was to own and operate the system. These tended to be secondary issues at the time. As the payload capability of the Delta increased year by year, and as tests on the Applications Technology Satellites (ATS) yielded useful experimental data, the relative importance of the various questions changed and that of choice of frequency became paramount.

137 Finally, in the last two years the U.S. Government has endorsed the use of UHF, and the Delta payload capacity has reached the point of assuring useful capacity, so that the major question remaining has been that of ownership and opera- tion of the system. For the past year the program has remained stalled at dead center pending a resolution of this problem. Technically, an aeronautical communications satellite can be designed with today's technology; what is needed is a resolution of the non-technical problems. Recently ESRO has been selected by the West European countries to manage their share of this program, in conjunction with a U.S. partner yet to be chosen. While the application of satellite communications to mari- time use is easier than to aeronautical, since a physically larger shipboard antenna can be used, substantial interest of the maritime community has arisen only in the last couple of years. The l97l World Administrative Radio Conference allocated frequencies for such use adjacent to the aeronautical satellite service in the l600 me region, both exclusive and for sharing with aeronautical satellites. Since the frequencies are adjacent, and the applications similar, it would appear technically and economically desirable to build one type of satellite for both services simultaneously. However, there are some groups in each of the two camps who feel that some "sovereignty" will be lost by such joint use. The cost comparison of a joint system versus separate systems may resolve this issue. A more important problem, similar to that which has arisen in the Aerosat program, is the decision on how the maritime system is to be established and operated. Here, too, no clear solution is yet in sight. VI. New Applications of Communications Satellites The l960's have seen the growth of the international com- munications satellite system from its first experiments to one with 80 operational antennas. The l970's will see the appli- cation of communications satellites to domestic and regional use, and to special applications. As regards domestic service, Canada will have its system in operation by early l973; and the U.S. has a number of specific proposals pending. The special applications area is somewhat nebulous. Various uses of satellites for communication via stations with relatively small antennas, 7 to

138 l8 ft. in diameter have been proposed for remote areas whose only communication means has been H.F. radio. While there is no question as to the technical feasibility of such systems,* their economic feasibility is still open to question. It is difficult, if at all possible, to predict the extent of future use of such new systems. The approach will likely be one of adapting existing systems to demonstrate and test new appli- cations, in addition to testing more advanced satellite con- cepts with NASA's ATS series of satellites. The NASA ATS-F satellite, to be launched in l974, will also test the feasibility of TV broadcast to small stations. VII. Conclusions The U.S. lead thus far is based on satellites and rocket technology from NASA and Department of Defense programs. Until now no other country, except the U.S.S.R., has had available our broad range of rockets for launching satellites. However, the U.S. has recently agreed to launch satellites for all countries subject to rather nominal restrictions. There- fore, all countries are now on an essentially equal basis as far as availability of launch vehicles is concerned. During the last decade other countries have begun to develop their own satellite technology. While by far the major portion of this work has been funded by the countries them- selves, their participation in Intelsat R&D programs and in actual development and production of Intelsat III and IV satel- lites (totalling over $25 million) has given them a close coupling to U.S. technology programs. The future application of communications satellites for special purposes - domestic, regional, aeronautical, maritime and broadcast - will result in a need for development and construction of new satellites. Even with these new uses the relatively few satellites needed make it uneconomical for most countries to build up a capability in this field. Furthermore, Since the beginning of l972 Intelsat has provided 24 hours per day communications via its Pacific satellite between an 8 ft. antenna station in the Antarctic and the U.S. earth station at Jamesburg, California, at 800 bps with an error rate of approximately l/l0 .

139 all of these services will operate with synchronous satellites so that it will be technically and economically desirable to use a given spacecraft design for several different services by suitable modification of the communications package, thus further decreasing the potential market. Regardless, other countries are continuing development in this field based on considerations of national posture rather than economics. This incentive, coupled with the availability of rockets and the recent growth of satellite know-how as mentioned above, will provide the means for other countries to enter this field. From the U.S. viewpoint, this should provide a market for rockets, but there will be a loss in satellite markets. Offsetting this is the fact that the use of satellites for U.S. domestic purposes should open up a market for satellites with one and even two orders of magnitude greater capacity than for international use at least for a number of years. The development and production of such satellites should provide the stimulus to keep a leading U.S. position. This assumes that non-technical considerations which stalled this program from l966 to l972 and resulted in a Canadian domestic satellite (built in the U.S.) before ours, are re- solved expeditiously in the future as they arise. The U.S. leadership in satellite design is based on the existence of a number of highly experienced engineering and manufacturing teams built up over the past l0-l5 years for the development of NASA and Department of Defense satellites. The techniques and know-how which they developed on these government programs have formed the basis of the Intelsat family of satellites. In the case of the Hughes Aircraft Co., which developed and built 3 of the 4 types of Intelsat satellites, one can trace their evolution from Syncom (NASA) via Intelsat I, Intelsat II, ATS-l through 5 (NASA), TACSAT (Defense), and finally to Intelsat IV. Each satellite design was nourished by its predecessors and in turn contributed new information (sometimes in the form of what not to do) to successor designs. These evolutionary changes had their troubles, but judged in comparison with other satellite pro- grams, even greater troubles can be expected when initiating more radical changes from previous designs. The government is the only organization financially able to support development of radically new satellite designs and techniques. For example, the ATS-F program includes satellites which will, in orbit, extend members supporting the solar arrays to form a structure over 50 feet long, and also deploy a para- bolic antenna 30 feet in diameter. Included experiments cover ion engines, precision pointing to better than O.io, TV broad- cast, navigation, millimeter wave propagation, and radiation

140 detectors of various types. The program involves an expendi- ture of over $200 million, or over twice Intelsat's gross annual revenues. From such programs will come the basis for future commercial satellite designs, as well as for new military and scientific satellites. Other governments are proceeding with their own communi- cations satellite programs. Japan and Germany are looking into the development of high powered satellites for broadcast use. The U.K. and the CEPT are planning experimental com- munications satellites for the l976 period. Japan is proceeding on a similar schedule, and an Italian experimental satellite is now scheduled for l974 launch. Canada is building an experi- mental satellite to test operation of a relatively high powered transmitter at l2 gc (involving light weight deployable solar arrays of over l kw output) which could be the forerunner of a broadcast TV system. This complete satellite will be built in Canada, except for the high power amplifier and the Delta rocket, which will be supplied by NASA for a l975 launch. Thus, at a time when all major countries are engaged in breaking new ground in this field in order to insure a place for the future, the U.S., already in the lead, has cancelled the ATS-G, H and I. The effects of this cancellation should appear in the second half of the l970's because of the anticipated need for advanced aeronautical, maritime, domestic, regional, and inter- national satellites. Commercial satellite ventures must, because of the high costs of satellites and rockets, take a conservative design approach. Radically new approaches involving expenditures of many tens of million dollars, can't be funded by today's satellite business. For example, Intelsat's l972 gross revenues were just under $90 million. Several other countries are developing entire satellites, including communications packages. I recommend that the detailed design of satellites for operational commercial purposes (com- munications, broadcast, aeronautical, and maritime) be funded by non-government entities; but the U.S. Government should continue to sponsor the advanced satellite techniques and com- ponents useful to all satellites*, government and non-government, in addition to its sponsorship of new satellites for specific non-commercial purposes, i.e., government, military, and scien- tific applications, and demonstrations of satellite technology for systems having no early commercial potential. S. Metzger COMSAT Washington, D.C. *This includes new designs of attitude control, structures, thermal systems, power sources, mechanisms, and RF systems, including in-orbit tests and demonstrations.

l4l EARTH STATIONS This paper will briefly review the l0-year history of communication satellite earth stations with emphasis on the trends in design during this period. I. Antennas and General Station Considerations The first commercial earth station antenna, built by AT&T at Andover, Maine, was a 60-foot aperture horn which was scaled from the 20-foot aperture horn used in terrestrial radio relay stations designed for the Echo satellite experi- ment. This design was chosen to maximize the gain and to minimize the noise temperature for a given size aperture. Although the antenna was designed to withstand l00 mile per hour winds, a radome was added in order to simplify the operational problems during the heavy snowfalls of a Maine winter. This antenna worked well for the experiments for which it was intended; however, it was not satisfactory as a model for future production because of its high cost and because of the radome loss which could be as much as 6 to 9 dB from rain or wet snow. Later models used parabolic reflectors and Cassegrain feeds in order to eliminate the waveguide loss which would occur in a lower cost front-fed antenna. Initially, 85-foot diameter reflectors were used from available NASA and Department of Defense designs. The development sequence has gone as follows: — Learning how to get the desired gain and noise temperature over the 500 MHz bandwidth (centered at 4000 MHz) and the transmitting gain over an equal band cen- tered at 6000 MHz. — Having achieved the electrical performance, the next step was to modify the mechanical design so that an operator working on equipment behind the feed cone could stand on a horizontal floor regardless of the elevation angle of the antenna. — The next step was to achieve the above, but at lower cost. — About the time the above items were accomplished, communication satellites had matured to the point where performance and reliability compared favorably with

l42 terrestrial systems and the emphasis was then placed on decreasing the number of men needed to operate a station. — This trend has led to the design now being built by most manufacturers. This consists of a circular concrete structure about 50 feet in diameter and one story high on the top of which the 97-foot antenna is mounted on a wheel-and-track arrangement. The low noise paramps are in an upper room behind the feed and all other equipment usually in the room below the antenna. — Recently some new antennas incorporate multiple reflectors so that the terminals of the feed are at ground level, avoiding the need for an upper equipment room. — Development is underway for feeds capable of operating with two orthogonal polarizations simultaneously, and providing adequate isolation between these to permit reuse of the frequency spectrum. — With approval of new frequency bands by the World Administrative Radio Conference in l97l, new equipment will be needed at ll/l4 gc, and also at 20/30 gc. — The antennas in general use shaped reflectors and achieve aperture efficiencies of 70% and noise tem- peratures as low as 50°K at 5° elevation. It is doubtful that much more can be accomplished in these areas. Each of the major industrial countries design and build their own feeds and antennas. Equipment is now fairly standardized and sufficiently reliable so that in most of the smaller stations it is technically feasible to employ one man per shift for two of the three shifts per day. The costs of earth stations having 97-foot diameter antennas have dropped from the range of $6 - $l2 million in l965 to $4 - $8 million in l969, and to $3 - $6 million at the present time. Costs vary widely depending on the number of countries with which it is desired to communicate cost of land, and the austerity of the design. For most countries of the world the earth stations represent their entry into the space age and facilities are therefore pro- vided for visitors. Funds are also allocated for an architectural design of which the country can be proud.

l43 In the U.S. the cost of land for ground stations has varied from several tens of thousands of dollars (West Virginia) to several hundreds of thousands of dollars (Hawaii). II. Electronic Equipment A. Power Amplifiers At the present time, of the 80 antennas and related electronics in the Intelsat system, the traffic per station varies from 4 to l200 circuits and the number of countries with which a given country communicates varies from l to 28. The amplifier output can accordingly range from several watts to several kW. Until now the highest power amplifier has been an 8 kW TWT 500 MHz wide, but recently l2 kW tubes have been developed. Life has been very satisfactory, ranging from l-l/2 years to 3 years. For smaller stations 3kW klystrons and TWT's are used and air-cooled versions of these are now available, thus simplifying maintenance. For still smaller stations, 300 W air-cooled TWT's are typically used. The tubes for these amplifiers are manu- factured in the U.S., Japan and Europe. In future satellites, when the narrower antenna beams will be used for the satel- lite receiver, earth station transmitter power will decrease. B. Paramps While the 25 MHz bandwidth masers were used in the early stations, the need for more bandwidth resulted (l966) in l50 MHz masers. With the desire for still more band- width, the trend shifted to paramps of 500 MHz useful band, since masers could not realistically be designed for such wide bands. The paramps resulted in an increase in noise which was compensated by going from 85-foot diameter antennas to approximately 97-foot, which is the size now used in practically all earth stations. While such paramps are built mainly in the U.S., but also in Japan and Italy, and to a lesser extent in France and Germany (both of whom have only built for their own use), the cryogenics are supplied only by Arthur D. Little Company (Boston, Mass). Extensive work is underway on uncooled paramps mainly for proposed domestic satellite systems. The leading companies in this field are in the U.S. and their expertise in both cooled and uncooled versions can be traced back to government requirements for similar equipment. During the last two years the performance of such amplifiers has improved from 200°

l44 to l00° and is now down to 50 to 60°K. Recently some international stations located in southerly latitudes have gone to uncooled paramps, which, in conjunction with l05- foot diameter antennas, results in the required antenna gain-to-system-noise temperature. C. Low Level Electronics Equipment The accepted method of modulation in the Intelsat system today is FDM/FM. Therefore the multiplex equipment, IF amplifiers, modulators, demodulators, and up and down con- verters are all similar to those used in terrestrial radio relay systems and are built in most of the heavily indus- trialized countries of the world. The major difference in earth station equipment as compared to radio relay systems, is that greater flexibility is needed in the former as compared to the latter. This has resulted in the design of dual conversion up and down converters permitting rapid change of frequency with little or no retuning of ampli- fiers. D. New Multiplex Systems Because of the wide range of traffic carried by the different stations, work has been underway on developing multiplex and modulation methods which can be most effici- ently adapted to the differing traffic requirements. In particular, initial installations are now underway for the so-called SPADE system which has been designed for countries having relatively few channels to relatively many other countries. In this system a time division orderwire is shared by up to 50 countries on an automatic basis. A voice channel is then automatically assigned any unused carrier frequency, transmitted by PCM/PSK, which may be on a different frequency for each new call. Each station has a computer which keeps track of the status of the various assignments. This system decreases the cost of the earth station and increases the number of channels per satellite repeater as compared to the conventional FDM/FM system. At the present time this equipment is being built in Japan and in the U.S. E. TDM (Time Division Multiplex) While the SPADE system is more efficient in the case of a few channels and FDM/FM is most efficient in the case of a large number of channels directed at one country, it

l45 appears that for intermediate numbers of channels, TDM may be advantageous. Experiments are underway on a 50 megabit system which will provide about 800 channels shared among several countries. Development on such systems has been undertaken in Japan, Germany and the U.S. Extensions of this system to permit switching of channels on a TDM basis among various beams of a satellite are also under study. In addition, digital speech interpola- tion, a more sophisticated form of TASI, is being developed in Italy, Germany, Japan and the U.S., which should provide a doubling in channel capacity for the same power and band- width. III. Summary Satellite earth stations have generally reached a fair degree of maturity. As an example, the eight U.S. stations for the past year and a half have achieved cir- cuit continuity of 99.99% (ratio of circuit hours on the air to circuit hours possible during a year). While the U.S. has been the major supplier of such stations through- out the world,* the choice has not always been made on the basis of technical quality or price, but also on national considerations of mutual trade and long-term loans. In this respect the U.S. has been at a disadvan- tage as compared to other countries where there exist closer ties between the government and its manufacturers. For future domestic, regional, special purpose, and broadcast services (the latter funded thus far by NASA), small stations with antennas ranging from 32 feet down to 7 feet in diameter may be more economical considering *The U.S. has supplied approximately 43%; Japan 20%; U.K. l3%; France 9%; Canada 8%; Italy 5%; and Germany 3%.

l46 the number of stations and the number of channels in the system. Several U.S. companies are taking the lead in developing such stations for the anticipated future market; however, for export the problem mentioned above will exist here also. S. Metzger COMSAT Washington, D.C.

147 ATS ALASKA TELEMEDICINE EXPERIMENT I. ATS-l Project Description The objective of the ATS-l Alaska telemedicine communi- cations experiment is to demonstrate and evaluate the use of communications satellite technology to provide reliable, voice-grade, intrastate communications to isolated communities using small, inexpensive ground stations. These villages are isolated by geography, weather conditions, unreliable radio communications, and a lack of telephone service. Village medical aides and their patients depend on infrequent contacts with doctors in larger towns and cities for consultation, diagnosis and treatment. The inadequate communications services in Alaska have forced the State to examine alternate technologies which can provide communications facilities to all areas of the State. This ATS-l experiment provides the Alaskan health care community, and the Department of Health, Education and Welfare with information necessary for planning and implementing future systems. Continuing experiments are planned for the follow-on ATS-F satellite. Twenty-eight villages and towns in Alaska have been out- fitted with inexpensive (about $2,000) VHF, voice-bandwidth, transceiver ground stations.* Access to the VHF transponder on the ATS-l satellite has been made available to the experi- menters. Communications takes place among the villages and with the larger stations in Fairbanks and Anchorage. The health care experiments were started in March l97l with two villages (Allakaket and Venetie) communicating with the hospital in Fairbanks via the VHF voice channel on ATS-l. The objective of the scheduled one-hour per day "Doctor Call" was to determine the value of the reliable, but time-limited voice channel to provide health care services, and to provide some experience for the village medical aides operating with a small low-cost satellite terminal. The experiment was expanded in August l97l, to include l8 other villages in the Tanana River region northwest of Fairbanks, and eight larger towns and cities equipped with Public Health Field Service Hospitals. This expanded experiment provides medical education programming, remote health care diagnosis and treatment to each of the villages. The satellite receiving terminal equipment is located in the village medical aide work area. In the 20 villages in the Tanana region, the equipment is time-shared with the school teacher who has a remote line from the terminal. One of the *See page151for their characteristics

148 joint educational/medical experiments includes the evaluation of specially designed listening equipment for the native Alaskan children, who generally have a severe hearing disability. A second,but equally important aspect of the health care experi- ment is being conducted by the National Library of Medicine's Lister Hill National Center for Biomedical Communications. It uses satellite channels to transfer medical records, diagnosis data and research materials among the Field Service Hospitals. The National Institutes of Health, in cooperation with the University of Washington, Stanford University, and Uni- versity of Wisconsin, conducts a program of consultation to sub-professional health personnel in the villages as part of the "Doctor Call" experiment. This is a potentially important new health care service for remote, sparsely populated regions. II. ATS-l Findings The availability of a reliable and regular form of com- munication to the remote areas has resulted in an improvement in the medical care available to the residents of these remote villages. Some lives have been saved and considerable allevi- ation of patient distress has been achieved through the ability to secure prompt attention by medical personnel. The growing effectiveness of medical communications between the Service Unit Hospitals and the remote villages is demonstrated by the striking growth in utilization of satellite channels as compared to HF channels as shown by the following table: "Satellite Village" "HF" Village Average number of days Tanana Doctor contacted: l0/l/70 to 7/3l/7l (via HF) 49.6 39.5 l0/l/7l to 7/3l/72 230.7 20.0 (via HF) Average number of cases treated: l0/l/70 to 7/3l/7l (via HF) 43.6 22.0 l0/l/7l to 7/3l/72 l52.9 l4.8 (via HF) Service Unit Hospitals that serve only villages without satellite ground stations do not tend to use the satellite channels to other hospitals or major centers. This is because alternate telephone or TTY circuits are available and are apparently preferred. In cases where a village has reliable

149 HF service as well as a satellite ground station, the HF circuits are preferred because their use is not limited by the ATS-l schedule. III. ATS-F Project Description A somewhat more extensive telemedicine communications experiment is being planned in Alaska using the 2.5 GHz trans- mitter on ATS-F, which will be launched in the spring of l974. The three federal organizations cooperating with the State of Alaska are the National Library of Medicine, the Bureau of Health Manpower Education, and the Health Services and Mental Health Administration. This experiment will be under the direction of the Federation of Rocky Mountain States, with the University of Washington as coordinator. The use of the 2.5 GHz, l5 watt transmitter and high gain antenna on the ATS-F satellite provides a much higher flux density at the ground receivers, and thus video signals as well as voice signals can be transmitted to the remote village sites. In addition to the extension of communications capacity to include television, schedule flexibility with ATS-F may permit appreciably more time to be devoted to Alaskan experiments, at least on occasion, than has been possible with ATS-l. The criteria of approval for each experiment proposal are that they must be part of an ongoing program with an existing data base, they must have measurable objectives, and they must not unduly raise the expectations of the people in the experiment. For operations in Alaska, an operations center is planned for Fairbanks. Somewhere between 20 and 40 receive-only terminals are planned, with five transmit stations, consisting of fixed terminals in Anchorage, Fairbanks, Bethel, and Juneau, and one transportable station. Figure l shows the ATS-F foot- print (-3db and -l0 db) over Alaska as well as the location of the various medical centers, hospitals, and villages parti- cipating in the ATS-l experiment. (See page l50.) Richard B. Marsten Donald P. Rogers Office of Applications, NASA HQ Washington, D.C. J

150 O LLJ 3 DC 0. C/J O I- O _ li 13 8? LU S I-01 LU LU < h- LU LU QC Q. 0. xfc LU O 0) M 5 01 S P » 1

151 Description of Terminal Equipment l. Low Power Stations - ERP + 6l.4 dBm A. Transceiver - Motorola Micor T73 RTN Series l. Receiver frequency - l35.60 MHz 2. Transmitter frequency - l49.22 MHz 3. Frequency deviation - + 5 KHz 4. Rated transmitter output power - ll0 watts B. Antenna - 8 turn helical l. Antenna gain - l4 db With a 3 dB transmission line loss, the ERP of the low power station is 6l.4 dBm. 2. High Power Stations - ERP + 66.7 dBm A. Transmitter-Receiver - Motorola Base Station Model B93MPIB-l000B l. Receiver frequency - l35.60 MHz 2. Transmitter frequency - l49.22 MHz 3. Frequency deviation - + 5 KHz 4. Rated transmitter output power - 375 watts B. Antenna - 8 turn helical l. Gain - l4 dB With a 3dB transmission line loss, the ERP of the high power stations is 66.7 dBm.

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