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Showing papers in "IEEE Communications Magazine in 1977"


Journal ArticleDOI
TL;DR: In many applications, correlative coding or partial response signaling, which introduces intersymbol interference in a controlled way, is able to achieve high data rates with fewer levels and hence with better error rate performance.
Abstract: In most transmission channels, bandwidth is at a premium and an important attribute of any good digital signaling scheme is its ability to make efficient use of the bandwidth. Conventional Nyquist-type pulse amplitude modulation signaling schemes, which are designed to eliminate intersymbol interference, achieve high data rates only at the expense of a large number of signal levels. In many applications, correlative coding or partial response signaling, which introduces intersymbol interference in a controlled way, is able to achieve high data rates with fewer levels and hence with better error rate performance. In addition to higher data rates, correlative schemes achieve convenient spectral shapes and have error-detecting capabilities without introducing redundancy into the data stream. This paper explains how correlative schemes work and why they are advantageous.

50 citations


Journal ArticleDOI
S. Weinstein1
TL;DR: Why echo cancelers are advantageous and how they work is explained, an adaptive filter which selectively eliminates echoes.
Abstract: Most long-distance telephone connections generate echoes, which must be heavily attenuated in order to obtain satisfactory transmission quality. Voice-actuated switches (echo suppressors) are widely used to eliminate echoes but have an unfortunate tendency also to cut out part of the desired signal from the other end of the line. Because the distortion caused by echo suppressors is particularly noticeable on satellite-routed connections, the advent of telephone communication via satellite, including the recent introduction of satellite circuits into the U.S. domestic network, has motivated the search for a better way to eliminate echoes. The answer may be the echo canceler, an adaptive filter which selectively eliminates echoes. Advanced echo canceler designs have been undergoing field trials in recent years. This article explains why echo cancelers are advantageous and how they work.

49 citations


Journal ArticleDOI
E. Bedrosian1
TL;DR: It is shown that well-designed systems tend to operate near the "knee" of the power-bandwidth tradeoff curve for the ideal channel and that they are frequently within 10 dB or less of the performance of the ideal.
Abstract: The growth of the communication industry has resulted in ever-increasing demands on the radio spectrum. This, in turn, has spurred the exploitation of previously unused frequency bands and the development of techniques for making better use of those already available. In this paper, spectral utilization is examined using the information-theory techniques of Shannon. The power-bandwidth tradeoff for the ideal channel is established and the performance of practical analog and digital modulation techniques is compared with this ideal. It is shown that well-designed systems tend to operate near the "knee" of the power-bandwidth tradeoff curve for the ideal channel and that they are frequently within 10 dB or less of the performance of the ideal.

11 citations


Journal ArticleDOI
TL;DR: The cost effectiveness of the INTELSAT system has increased in the last decade as measured by the per-circuit-year cost of satellites in orbit, space segment charges, and earth station and total circuit costs.
Abstract: Global satellite communications, as the INTELSAT system has demonstrated, is a commercially successful business with over ten years of operating experience. The system provides high-quality reliable communications over a large number of links in successful competition with other modes of communications. The cost effectiveness of the INTELSAT system has increased in the last decade as measured by the per-circuit-year cost of satellites in orbit, space segment charges, and earth station and total circuit costs. Economies of scale and the use of progressively more advanced technology are expected to increase the cost effectiveness of global satellite communications in the future.

11 citations


Journal ArticleDOI
TL;DR: A TEM lens antenna is described that provides the capability of generating 61 low-sidelobe dual-polarized beams over a 17° field of view, at both 4 and 6 GHz.
Abstract: A TEM lens antenna is described that provides the capability of generating 61 low-sidelobe dual-polarized beams over a 17° field of view, at both 4 and 6 GHz. Isolation between these beams is examined, and it is concluded that 6 of the available 61 beams may be used simultaneously in many different positions, while maintaining at least 27 dB isolation, for a total of 12 times frequency reuse.

8 citations


Journal ArticleDOI
G. Nash1
TL;DR: This paper identifies the improvements due to large-scale integration [LSI] in the areas of cost, performance, size, reliability, and testing of data communication equipments.
Abstract: This paper identifies the improvements due to large-scale integration [LSI] in the areas of cost, performance, size, reliability, and testing of data communication equipments. An example using Motorola's MC6860 Digital Modem is given. Techniques for implementing linear functions using digital designs and processing methods are discussed along with future technology trends and projections.

6 citations


Journal ArticleDOI
TL;DR: The technologies, communications services, and applications that support effective network strategic planning are discussed, and the nature and levels of impairments experienced by system users have changed.
Abstract: Subjective testing of existing and proposed communication systems is an important element of network planning and equipment design. With the evolution over the years of world telecommunications, the nature and levels of impairments experienced by system users have changed,and as a consequence, a variety of subjective testing procedures have come into existence. Discusses the technologies, communications services, and applications that support effective network strategic planning.

3 citations


Journal ArticleDOI
TL;DR: During the first 11 years of its planetary program, the United States sent seven spacecraft to explore the inner planets: Venus, Mars, and Mercury; at the beginning of this period, the telemetry data rate was 8-1/3 bits/s; by the end of the period it was 120 kbits/s, a more than ten-thousand-fold increase.
Abstract: During the first 11 years of its planetary program, the United States sent seven spacecraft to explore the inner planets: Venus, Mars, and Mercury. At the beginning of this period, the telemetry data rate was 8-1/3 bits/s; by the end of the period it was 120 kbits/s, a more than ten-thousand-fold increase. To identify the major factors involved, the form of a deep space telemetry system is described and the values of the major factors for each of the seven spacecraft are given. The amount of the improvement in each is computed and the way in which the improvement was achieved is discussed. Finally, some possible directions for possible future improvements are suggested.

3 citations


Journal ArticleDOI
TL;DR: Reports on the technologies, applications, systems, and communications facilities that have been developed over the past 25 years are presented.
Abstract: Reports on the technologies, applications, systems, and communications facilities that have been developed over the past 25 years.

1 citations


Journal ArticleDOI
TL;DR: Reports on the technologies, applications, systems, and communications facilities that have been developed over the past 25 years are presented.
Abstract: Reports on the technologies, applications, systems, and communications facilities that have been developed over the past 25 years.

1 citations


Journal ArticleDOI
TL;DR: The modem as the authors know it today is a product of research done for the Defense Department by MIT Lincoln Laboratory and Bell Telephone Laboratories in the 1950’s.
Abstract: The modem as we know it today is a product of research done for the Defense Department by MIT Lincoln Laboratory and Bell Telephone Laboratories in the 1950’s. Encouraged by advances in data processing technology, scientists at these research centers concentrated on finding ways to improve the speed and the accuracy of data transmission using existing facilities of the nation’s vast elephone network. A great deal of study went into understanding telephone line parameters and deriving techniques that could work efficiently parameters.

Journal ArticleDOI
TL;DR: This paper examines the projected needs for satellite communications services of two fundamental types, point-to-point and broadcast, through the end of the 20th century, and relates the needs to systems architecture by considering factors which affect systems architecture and by relating the service needs to available and developing technologies.
Abstract: This paper examines the projected needs for satellite communications services of two fundamental types, point-to-point and broadcast, through the end of the 20th century, and relates the needs to systems architecture. This is done by considering factors which affect systems architecture, and by relating the service needs to available and developing technologies for satellite communications Systems. Some of these technologies originate from requirements on the different types of systems to share the communications channel capacity of the orbital are in allocated spectral bands. Consideration of the technologies applied to different systems architectures leads to the conclusion that developing capabilities are converging on elimination of the distinction between point-to-point and broadcast services at 12 GHz. This emerges in the discussion of systems architectures that completes the paper.


Journal ArticleDOI
TL;DR: The combination of topical content and the clarity of explanation in this book when mixed with proven technical writing successes of the authors over the last 30 years assures this reviewer that this volume will become a well-recognized text for practical engineering in digital integrated electronics.
Abstract: digital and digital-to-analog conversion techniques and the circuitry for implementation are explored in Chapter 14. The concluding chapter of the book presents various timing circuits for monostable and astable multivibrators. Timing circuit operation is illustrated for CMOS, ECL, and TZL gates, and for use with the 555 timer. In evaluating this bo.ok a s a course textbook or for self study, this reviewer gives it very high marks. The explanations are clear and well illustrated with example calculations and problems. There are more than 400 homework problems provided, and a solution manual and an answer book are also available to instructors. Also, the authors state in the Preface that they"wil1 be happy to furnish a set of laboratory experiments currently used at CCNY (City College of the City University of New York) in conjunction with this text." In summary, the combination of'the topical content and the clarity of explanation in this book when mixed with proven technical writing successes of the authors over the last 30 years assures this reviewer that this volume will become a well-recognized text for practical engineering in digital integrated electronics.

Journal ArticleDOI
TL;DR: The Mariner missions during the next decade will concentrate on the outer planets, with requirements to operate over greatly increased ranges in hostile radiation environments, and for reduced weight to allow the transportation of probes.
Abstract: The past Mariner missions to the inner planets have greatly increased our knowledge about Mars, Venus, and Mercury. The continued success of these missions has been enhanced by the evolution of communication technology, with the main growth in the ground capability. The missions during the next decade will concentrate on the outer planets, with requirements to operate over greatly increased ranges in hostile radiation environments, and for reduced weight to allow the transportation of probes. The communication requirements will be mainly achieved by increases in flight equipment performance, new larger antennas, and operation at higher frequencies. The rate of growth of the communication capability is heavily dependent on the type of missions planned. However, we do have the capability to provide significant data return from the outer planets.

Journal ArticleDOI
TL;DR: The technical issues involved in determining what is wrong with circuit equipmant are discussed and how to fix problems are examined.
Abstract: Discusses the technical issues involved in determining what is wrong with circuit equipmant and examines how to fix problems.

Journal ArticleDOI
TL;DR: The workshop was held September 19-21, 1976, at Bryce Mountain, VA, and speakers included representatives of telephone operating companies, and representatives of the manufacturers or laboratories intimately associated with the design and technology.
Abstract: The workshop was held September 19-21,1976, at Bryce Mountain, VA. The speakers included: representatives of telephone operating companies, who indicated their points of view on the need, advantages, and economics of digital switching for the local plant: persons involved in planning the application of local digital switching, who presented the results of studies: and representatives of the manufacturers or laboratories intimately associated with the design and technology. The following is a brief summary of topics that were discussed in greater detail. At the request of Mr. Russell DeWitt, organizer and chairman of this excellent Workshop, the writer agreed to act as reporter.