Showing papers in "IEEE Communications Magazine in 1979"

Minimum shift keying: A spectrally efficient modulation

Abstract: The ever increasing demand for digital transmission channels, in the radio frequency (RF) band presents a potentially serious problem of spectral congestion and is likely to cause severe adjacent and cochannel interference problems. This has, in recent years, led to the investigation of a wide variety of techniques for solving the problem of spectral congestion. Some solutions to this problem include: 1) new allocations at high frequencies; 2) better management of existing allocations; 3) the use of frequency-reuse techniques such as the use of narrow-beam antennas and dual polarizing systems; 4) the use of efficient source encoding techniques; and 5) the use of spectrally efficient modulation techniques [l]. This article will consider the last approach and analyze, in particular, a modulation scheme known as minimum shift keying (MSK). The MSK signal format will be explained and its relation to other schemes such as quadrature phase shift keying (QPSK), offset QPSK (OQPSK), and frequency shift keying (FSK) pointed out. The main attributes of MSK, such as constant envelope, spectral efficiency, error rate performance of binary PSK, and self-synchronizing capability will all be explained on the basis of the modulation format.

Spread spectrum communications: myths and realities

Abstract: Spread spectrum communication techniques date back to the early fifties. Since the earliest applications, system improvements have been more evolutionary than revolutionary. Like most improvements in electronic systems, these are due primarily to the availability of ever higher speed integrated circuit components, which translate in this case to wider spread spectra. In three decades the achievable spreading factor has grown by about three orders of magnitude’ to the point that we are now limited more by bandwidth allocations than by technology limitations. Before we xamine the quantitative effects of spreading, let us catalog briefly the multiple purposes of spread spectrum communications. First, we note that spreading here refers to expansion of the bandwidth well beyond what is required to transmit digital data. Thus, a system transmitting data at a rate ( R ) of 100 Mbits/s using approximately 100 MHz of bandwidth (W) is not spread at all, while a system transmitting at 100 bits/s spread over a spectrum of about 100 MHz has a factor W/R = 106, or 60 dB of so-calledprocessing gain.

Surface acoustic wave devices

Abstract: bandwidth communication systems, most notably spread spectrum systems, puts greater demand on signal processing devices. For example, processing a 50 MHz bandwidth signal with current microprocessor technology is essentially out of the question due to the tremendously high clock rate that would be .needed. Surface acoustic wave (SAW) devices have certain general characteristics which make them ideal choices for use in systems which must process such high data rate signals. In what follows, the technology of the device will be briefly surveyed and various applications of SAW devices will be discussed. Also, a comparison wil l be given between SAW technology and its two prime competitors, charge-coupled devices and digital electronics (i.e., microprocessors).

Cellular land-mobile radio: Why spread spectrum?

Abstract: It is widely recognized that the electromagnetic spectrum is a beleaguered resource, and nowhere is this more evident than in the land-mobile radio service. The existing allocations of spectrum have long been oversubscribed in many major cities, and huge backlogs of potential users with no allocations have built up in many areas. Cellular land-mobile radio systems are widely recognized to provide a potential solution to this problem, and cellular systems using conventional analog modulation techniques have been proposed [l], [2]. This article discusses the authors' belief that spreadspectrum can substantially improve the spectral efficiency of a cellular land-mobile radio system, as well as making it more versatile and better adapted to the environment. It should be emphasized, however, that the theoretical work on which this belief is based is in a very preliminary stage and that much more study and simulation, as well as a field trial, are required before the validity of the claims made here can be established. Indeed, much of the work described here is controversial and, hence, a major function of this paper is to present these views to a wider audience and thereby encourage further discussion of them.

On resource sharing in a distributed communication environment

Abstract: A revolution is in the making! We are witnessing a growth rate in technological change which i s overwhelming. Thanks to enormous advances in data communications and in integrated chip technology, we are in the midst of a computer communication explosion which has already made significant changes in the field of data processing. The early phase of the revolution has passedwe have developed cost-effective data communication systems. Indeed in the last five years we have witnessed the rise of computer networks whose function it is to span intercontinental distances and provide communication among computers across nations and across the world. There now exists a large number of national networks which are in the process of interconnecting to each other in such a world network. These networks have hastened the next phase of the revolution, namely, the widespread acceptance and application of teleprocessing and networking by the business sector of our economy. As this second phase proceeds, we will see a stress placed on our computer networks in two areas. First, in the need for long-haul, wide-band inexpensive communications deep in the backbone of our networks; one answer to this need is the introduction of sophisticated packet satellite radio data communication systems. The other environment in which we will see stress is at the periphery of our networks where local accessis the major problem. The early

Digital communications--The silent (R)evolution?

Abstract: “Do’you speak digitease?” (Or digits with ease?) You probably have “spoken in digitease” many times without being aware of the fact. With digital facilities your speech signal is sampled, digitized in an analog-to-digital (A/D) converter and interleaved in time with those digits representing your neighbors’ speech (or data). This composite digital signal is transmitted over the ordinary telephone wires that may have been under the streets for a number of years. Sharing a pair of wires over many conversations increases the system capacity in a’cost-effective way. By “mining” additional circuits from the existing copper we conserve a precious resource and we avoid tearing up the concrete. For these, and other reasons to be developed,’ many countries in the world have introduced digital systems. Thus we can answer our lead-off question in the affirmative. Virtually, all of us have spoken “digitease” (some since 1962) and all of us will speak in bits (1’s and 0’s) and bytes (groups of bits) in the future. Thus, in a real sense, the evolution to digital has been quiet-no trip-hammers, no bulldozers. Of course, until we are fitted with a digital ear, it is necessary to convert “digitease” back to the domain of continuous time and amplitude before presentation to the human receiver:For this translation to succeed, we must make sure that almost all of the pulses that enter

The 1979 world administrative radio conference

Abstract: This September in Geneva the International Telecommunication Union (ITU) will convene a World Administrative Radio Conference called WARC-79 The purpose of this gathering is to review and revise where necessary essentially all the International Radio Regulations, so that the benefits of wireless communication may be equitably shared and enjoyed by all the world’s inhabitants The increasing importance of telecommunications cannot be overemphasized; fast, reliable communication is essential to the economic, political and social well-being of modern nations The treaty formulated at WARC-79 will represent the cooperative effort of the 154 member nations of the ITU to ensure the

Information and communication in the third millenium

Abstract: This paper presents the author's views on what the information and communication industry will be like at the start of the third millennium, with emphasis on the implications to information and communication theorists. The main conclusions are that communication will play a greater role in Society in the third millennium. Communication Theory will be more concerned with channel complexity than with channel capacity. More communication theorists will be needed, and they will be more broadly trained.

Looking backward and looking forward: Right or wrong

Abstract: The future doesn't shape itself to fit prophesies. Rather, it follows a path paved by the successful work of those with a yen for more.

New services and their introduction into existing networks

Abstract: Past telecommunication needs of the general public have mainly focused on the transmission of speech; however, new services are currently of growing interest. In many countries, activities are going on to investigate this trend and evaluate the demand for new services, their realization and their benefit to the public. In the Federal Republic of Germany, for instance, a “Commission on the Future of Telecommunications” (KtK) has recently explored this field and found that remarkable innovative effects may be achieved by implementing new forms of telecommunication in the existing networks [l]. In the following, a systematic review of possible future services is given. For the purpose of illustration, it is based largely on the results of the KtK-Commission and the situation in the Federal Republic of-Germany (FRG) [2]. However, it is assumed that the situation and findings in other European countries are quite similar [3].

Communicating through the earth

Abstract: people beyond the horizon? What can be made to follow the curve of earth’s surface? Of course, we can send electrical signals through wires around any curves. In the Nineteenth Century, copper wires were strung across the continents and ocean floors and the world was united through telegraphy. That takes a lot of copper, though, and a lot of maintenance. We could send light-wave signals and do away with wires, but light waves move in a straight line and won’t curve around the earth’s bulge. We would have to set up relay stations or place mirrors in orbit to make that work. Radio waves, like light waves but a million times longer, do better. They travel in straight lines, too, but the upper atmosphere contains regions rich in chargedparticles (the ionosphere) that tend to reflect the radio waves. It is as though there were natural mirrors in the sky. That makes it possible to send radio signals long distances, and in theTwentieth Century the world was united without wires. However, the ionosphere is affected by the solar wind. When the sun produces flares, an electrical storm can take place that will disrupt radio communication. But short radio waves (microwaves) can go right through ‘the ionosphere and be amplified and sent on by communications satellites. As communications ,satellites improve, signals will be sent from place to place on earth with so little trouble that it would seem unreasonable to ask for anything better. But what about signals that go through the body of the earth and Isaac Asimov

Greetings from the chairman

Abstract: (NACADA) recognized FACT FORUM with a 2002 Institutional Advising award. FACT FORUM is the name of our innovative, intensive year-long orientation, advising, mentoring program that has been in place since Fall 1999. The name stands for Freshman Advising Contact Term and Faculty Overview of Research and Undergraduate Mentoring. This learnercentered program was designed to facilitate Freshman integration into the Department, give them the tools to do thoughtful, proactive curriculum planning, become familiar with research opportunities here in the Department, and interact meaningfully with faculty and other students.