Showing papers in "IEEE Communications Magazine in 1987"

Trellis-coded modulation with redundant signal sets Part I: Introduction

Abstract: rellis-Coded Modulation (TCM) has evolved over the past decade as a combined coding and modulation technique for digital transmission over band-limited channels. Its main attraction comes from the fact that it allows the achievement of significant coding gains over conventional uncoded multilevel modulation without compromising bandwidth efficiency. T h e first TCM schemes were proposed in 1976 [I]. Following a more detailed publication [2] in 1982, an explosion of research and actual implementations of TCM took place, to the point where today there is a good understanding of the theory and capabilities of TCM methods. In Part 1 of this two-part article, an introduction into TCM is given. T h e reasons for the development of TCM are reviewed, and examples of simple TCM schemes are discussed. Part I1 [I51 provides further insight into code design and performance, and addresses. recent advances in TCM. TCM schemes employ redundant nonbinary modulation in combination with a finite-state encoder which governs the selection of modulation signals to generate coded signal sequences. In the receiver, the noisy signals are decoded by a soft-decision maximum-likelihood sequence decoder. Simple four-state TCM schemes can improve. the robustness of digital transmission against additive noise by 3 dB, compared to conventional , uncoded modulation. With more complex TCM schemes, the coding gain can reach 6 dB or more. These gains are obtained without bandwidth expansion or reduction of the effective information rate as required by traditional error-correction schemes. Shannon's information theory predicted the existence of coded modulation schemes with these characteristics more than three decades ago. T h e development of effective TCM techniques and today's signal-processing technology now allow these ,gains to be obtained in practice. Signal waveforms representing information sequences ~ are most impervious to noise-induced detection errors if they are very different from each other. Mathematically, this translates into therequirement that signal sequences should have large distance in Euclidean signal space. ~ T h e essential new concept of TCM that led to the afore-1 mentioned gains was to use signal-set expansion to I provide redundancy for coding, and to design coding and ' signal-mapping functions jointly so as to maximize ~ directly the \" free distance \" (minimum Euclidean distance) between coded signal sequences. This allowed the construction of modulation codes whose free distance significantly exceeded the minimum distance between uncoded modulation signals, at the same information rate, bandwidth, and signal power. The term \" …

Trellis-coded modulation with redundant signal sets Part II: State of the art

Abstract: I the,art in trellis-coded modulation (TCM) is given for the more interested reader. First, the general structure of TCM schemes and the principles of code construction are reviewed. Next, the effects of carrier-phase offset in carrier-modulated TCM systems are discussed. The topic i s important, since TCM schemes turn out to be more sensitive to phase offset than uncoded modulation systems. Also, TCM schemes are generally not phase invariant to the same extent as their signal sets. Finally, recent advances in TCM schemes that use signal sets defined in more than two dimensions are described, and other work related to trellis-coded modulation is mentioned. The best codes currently known for one-, two-, four-, and eight-dimensional signal sets are given in an Appendix. T h e trellis structure of the early hand-designed TCM schemes and the heuristic rules used to assign signals to trellis transitions suggested that TCM schemes should have an interpretation in terms of convolutional codes with a special signal mapping. This mapping should be based on grouping signals into subsets with large distance between the subset signals. Attempts to explain TCM schemes in this manner led to the general structure of TCM encoders/modulators depicted in Fig. 1. According to this figure, TCM signals are generated as follows: When m bits are to be transmitted per encoder/modulator operation, m 5 m bits are expanded by a rate-rYd(m-t 1) binary convolutional encoder into rii-t 1 coded bits. These bits are used to select one of 2' \" + I subsets of a redundant 2'11+1-ary signal set. The remaining mm uncoded bits determine which of the 2 \" '-' \" signals in this subset is to be transmitted. The concept of set partitioning is of central significance for TCM schemes. Figure 2 shows this concept for a 32-CROSS signal set [ 11, a signal set of lattice type \" Z2 \". Generally, the notation \" Zk \" is used to denote an infinite \" lattice \" of points in k-dimensional space with integer coordinates. Lattice-type signal sets are finite subsets of lattice points, which are centered around the origin and have a minimum spacing of A,. Set partitioning divides a signal set successively into smaller subsets with maximally increasing smallest two-way. The partitioning is repeated iii 4-1 times until A,,+, is equal to or greater than the desired free distance of the TCM scheme to be designed. T h e finally …

The application of error control to communications

Abstract: Aprll 4987-Vol. 25, No. 4 IEEE Communlcatlonr Magazine E rror Control is an area of increasing importance in communications. This is partly because the issue of data integrity is becoming increasingly important. There is downward pressure on the allowable error rates for communications and mass storage systems as bandwidths and volumes of data increase. Certain data cannot be wrong; for example, no one can be complacent about the effect of an undetected data error on a weapons control system. More generally, in any system which handles large amounts of data, uncorrected and undetected errors can degrade performance, response time, and possibly increase the need for intervention by human operators. Just as important as the data integrity issue is the increasing realization that error control is a system design technique that can fundamentally change the trade-offs in a communications system design. To take some examples:

Photonic switching using directional couplers

Abstract: May 1987-Voi. 25, No. 5 IEEE Communications Magazine I n the past few years the term photonic interconnection network (a photonic switch) has expanded and taken on several different meanings. In the most general case, a photonic switch refers to a system where both the inputs and outputs to an interconnection network are information encoded streams of photoris. An example of this would be a switching system that is used to interconnect a large collection of fiber-optic cables. In this general case a photonic switching system can be treated as a black box that operates on the inputs to connect them to the desired outputs. The fabric used within this black box can be divided into three classes. In the first class, this black box can include an optical-to-electrical conversion (o/e) followed by a conventional electronic switch, which is then followed by an electrical-to-optical conversion (e/o). Here there is a large inefficiency added by the o/e and e/o conversions in addition to imposing a rate constraint on the bit-rate of the photonic signal. T h e second class of switching fabric is an interconnection network that has the capability of switching the light entering the network without having to convert to the electrical domain. In this class, the control of the network remains in the electronic domain. A directional coupler, which is discussed in detail, is an example of an element in this fabric. The final class of switching fabric is similar to the previous class in that no ole or e/o conversions take place. The difference is that the control of this class of photonic switch is optical. This class of switch could be composed of optical logic that has been designed to perform switching functions. This article deals exclusively with the second class of switches based on an electro-optic device known as a directional coupler. Directional couplers can be fabricated in several materials but the focus of this article will be on LiNbOg based devices. T h e article begins by describing the basic principles behind the operation of the directional coupler. After the operation of directional couplers has been described, some of the current system design constraints are discussed. Finally, there is a brief description of the switching environment best suited for directional couplers along with some potential applications.

Photonic switch with optically self-routed bit switching

Abstract: hotonic switches capable of routing wideband optical signals will be an important element of ultrahigh-capacity fiber-optic networks of the future [ 1,2]. A photonic switch generally consists of a multistage connecting network-each stage comprising switching devices and controllers-which routes optical information between input and output ports. We restrict our attention here to photonic switching devices which maintain signals in optical form as they traverse the switch. The controllers process address information supplied by the source. This processing can be performed either electronically or optically. The controller output sets u p the appropriate switch permutation to route the signal to its destination. This control signal may be either electrical or optical, depending upon whether switching is accomplished by an electro-optic or opto-optic effect. Photonic switching devices which have been previously demonstrated include 2x2 integrated-optic wave-guide switches, controlled electrically [3-51. Arrays of these 2x2 switching devices have been organized in NXN crossbar configurations [6-91. Crossbar switch arrays can be further cascaded into photonic switching networks [ 101. Recently, optically-controlled photonic switching devices have also been developed [11,12] and are expected to ultimately switch at speeds in excess of 1 THz [ 131. Whatever photonic switching device is used, the speed of future photonic switches will be limited not only by the device switching speed, but by the speed of the controller. A severe data flow bottleneck will occur at the controller if electronic processing is used. This bottleneck can be eliminated with optical processing. In switches requiring electro-optic control, the output of the optical processor must be converted to an electrical signal to activate the switch. In future photonic switches employing opto-optic control, this conversion would not be necessary. T h e speed of such a switch would then be limited by the speed of the optical decision-making process or the speed of the photonic switching device itself. There have been few proposals of photonic switches with optically-processed control. Haque and Arozullah [14] have proposed that some of the electronic functions in a conventional electronic switch be replaced by their optical or electro-optic counterparts. We propose to improve the performance of photonic switches by developing a novel optical architecture with optically-processed control which could not be implemented with electronic components. Distinguishing characteristics of optical processing include its inherent parallelism and non-interfering nature as well as its high speed [ 151. We report the experimental demonstration of a photonic switch using optically self-routed …

Broadband communication and its realization with broadband ISDN

Abstract: In addition to narrowband services, future broadband networks will also include broadband services for applications like: high-speed communication of data, text and graphics person-to-person video communication, access to video information as well as broadcast of programs and data. Low terminal costs and service charges are essential with respect to a growing demand for new services, especially in the home. Broadband ISDN, to be developed on the basis of ISDN and using glass-fiber subscriber lines, will enable a wide range of applications satisfying the needs and requirements of the business and private sectors. The best technical solution from the aspect of user-friendliness and economy is to implement this broadband ISDN for all services with an evolutionary and flexible design. The broadband ISDN concept is not restricted to the public network and terminal equipment but also comprises private networks, information and program centers, etc. Many countries are pursuing the goal of this universal network for the future "information society". However, the approaches for setting up the broadband ISDN differ from country to country, depending on the particular technical and political situation. Standardization plays an important role with regard to "open broadband telecommunication", the worldwide trouble-free communication and information exchange of one party with any other.

System applications for wireless indoor communications

Abstract: Buildings present a hostile environment for radio communications, with in-building radio propagation difficult to predict and continuously changing. W ireless indoor communications can be used in a bride range of applications to provide for user mobility, easy setup, and reconfiguration of terminals, telephones, and so forth. Such applications can be divided $#to two classes: (1) Narrowband applications, such as paging or wireless PBX systems for voice and low rate data and (2) Wideband applications, such as a wireless local area network capable of handling data rates u p to several Megabits per second. Buildings, however, present a hostile environment for radio communications, with in-building radio propagation difficult to predict and continuously changing. Problems include multipath and shadow fading, which reduce the coverage region, and dispersion due to delay spread, which limits the maximum data rate. Furthermore, in buildings with multiple users, interference among users can be a serious problem, and the available spectrum might be much less than that required to handle all potential users. In this article we describe various antenna diversity techniques, including selection, maximal ratio and optimum combining, and show how diversity, in combination with other techniques, can be used to overcome these problems. One such technique is resource sharing, which recognizes that, at any moment, only ;I small fraction of all users are experiencing transmission difficulties, and assigns extra system resources (for example, bandwidth or time slots) as needed to protect those users.\" We first briefly describe the indoor radio environment and show why diversity can be effective. We then describe techniques for narrowband applications , such as wireless PBX's, that can be used to increase the coverage region, eliminate interference problems, and permit frequency reuse within the same coverage region, thereby dramatically increasing system capacity. Finally, we describe techniques for wide-band applications, such as wireless local area networks , that can be used to increase both the maximum data rate and the coverage region. With indoor radio communication, there is rarely a line of sight between the transmitter and receiver, and multiple signal propagation paths exist. The signals from these paths combine both constructively and destructively at the receiver to produce multipath fading. For narrowband transmission, where the propagation delays associated with the various paths are extremely small compared to the inverse of the signal bandwidth, the channel can be considered as a Rayleigh fading channel with frequency flat fading [ 141. This Rayleigh fading …

Status and future trends in terrestrial optical fiber systems in North America, Europe, and Japan

Abstract: In North America Peter Kaiser Bell Communications Research T elecommunication on optical fiber has grown to more than a billion dollar annual business in the world today-with about half that amount being spent in the United States-and is expected to grow by a factor of three by the end of this decade. The total fiber installed in the United States alone will have reached about 3.2 million kilometers by the end of 1987 [ l ] (Table I). These numbers reveal the enormous importance telecommunication on fiber has assumed, with the United States leading the application of fiber technology as the most communication-intensive country in the world. In the following article, we will describe the evolution of fiber communication in North America, which started with the achievement of low-loss silica fibers and room-temperature semiconductor lasers in the early 70s, and culminated in the recent completion of several trans-continental single-mode fiber links in the US (Figs. 1 and 2). The construction of a TransCanadian fiber system has also been started. T h e expected completion of the first Trans-Atlantic and Trans-Pacific submarine optical cable links in 1988 will interconnect the regional networks and enable worldwide communication on optical fiber. In the US, fiber transmission systems are being installed by longdistance carriers such as AT&T Communications, US Sprint, MCI, Lightnet, he National Telecommunication Network Group (NTN), and by the Bell Operating Companies and independent Operating Telephone Companies.

Photonic switching: Technology and applications

Abstract: As fiber optics and optoelectronics technologies become, more and more, the technologies of choice for a wide range of communications transmission facility applications. It is useful to ask what role optoelectronic technologies can play in implementing communications switching facilities. What are the basic technologies which can be used to realize all-optical switching functions? How can these basic technologies be applied to implement various types of switching subsystem? What are the time frames anticipated for these various applications of photonic switching technology?

A view from Europe

Abstract: M. J. Pagones and V. K. Prabhu, “Effect of Interference from geostationary satellites on the terrestrial radio network,” Conf. Record, GLOBECOM 1985, pp. 47.7.147.7.5, Dec. 1985. I. Godier, “DRS-8 digital radio for long-haul transmission,” Conf. Record, ICC 1977, pp. 5.4.102-5.4.105. JUW 1977. R . A. Roadhouse, T. G. Fellows, and J. L. Cpencrr, “The trans-Cmada digital radio network.” Co71f. liecord. ICC 1977, pp. 5.1.91-5.1.95, June 1977. C. P. Bates, W. G. Robinson, 111. and M. A. Skinner. “DK-6-135 system design and applications,” Conf. liecord, GLOBECOM 1984, pp. 16.7.1-16.7.8, Nov. 1984. D. P. ‘raylot-and P. R. Hartmann, “Telc.cornmunic~~tiorls b y rnicl-owave digital radio,” I E E E Cornmunicatiorzs Magazine, vol. 24, no. 8, pp. 11-16, Aug. 1986. T. Noguchi. Y. Daido, and J. A. Nossek, “Modulation techrliqurs for microwave digital radio,” IEEE Communications Magazine, vol. 24, no. 10, pp. 21-30, Oct. 11186. W. D. Rummler, R. P. Coutts, and M. Linigcr, “Multipath Fading Channel Models for Microwave Digital Kadio,” lEEE Comnzunicatio?~~ Muguzine, vol. 24, no. 11, pp.

Multiple access protocols for data communications via VSAT networks

Abstract: Follow this and additional works at: http://opensiuc.lib.siu.edu/ece_articles Published in Wolejsza, C. J., Taylor, D., Grossman, M., & Osborne, W. P. (1987). Multiple access protocols for data communications via VSAT networks. IEEE Communications Magazine, 25(7), 30-39. ©1987 IEEE. Personal use of this material is permitted. However, permission to reprint/ republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE. This material is presented to ensure timely dissemination of scholarly and technical work. Copyright and all rights therein are retained by authors or by other copyright holders. All persons copying this information are expected to adhere to the terms and constraints invoked by each author's copyright. In most cases, these works may not be reposted without the explicit permission of the copyright holder.

The intelligent home of 2010

Abstract: 0163-6804/87/0012-0081$01.0001987 IEEE Introduction B y the year 2010, activities within the home will be heavily influenced by a wide variety of interactive information and control systems. A new appliance will be incorporated into the home; a control processor, which will monitor and control many household functions and provide a gateway to communicate with the outside world. This paper will discuss technological developments which will be critical in the evolution to the intelligent home. It will describe the intelligent home and give examples of how these technologies will be employed both within the home and to interact with the external world.

A 1.7 gigabit-per-second, time-multiplexed photonic switching experiment

Abstract: Current experimental Ti:LiNbO 3 switching systems need electronics for control, regeneration, and compensation for the imperfections of the photonic switching fabric. These early photonic switches do, however, have advantages over their electronic counterparts: 1) They can carry 100 Mb/s or 10 Gb/s with little modification to the switching fabric, 2) They are synergistic with fiber transmission, especially when optical amplifiers can be used, 3) They provide valuable experience in optics and photonic switching, 4) They give insight into the future of optical switching and how the signaling and protocols of the network need to evolve to accommodate this emerging technology.

Overview of optical switching technologies in Japan

Abstract: Optical Switching Systems can be divided into three groups-space division, time division, and wavelength division. This article describes each in detail and gives the present status and projects the future of each M any studies on ISDN are being made in a number of countries in an attempt to provide enhanced services that integrate voicr, data, and video. In order to provide high-speed, broadband services, a new network, consisting of high-speed transmission lines and highspeed, broadband switching systems, must be constructed. Currently, cost-effective transmission systems are being developed, due to remarkable progress in optical fiber transmission technologies. The penetration of optical fiber into the subscriber loop network f copper wires is expected soon. High-speed, broadband switching systems require high-speed operation, in which electronic circuits have many problems, such as high power consumption and low isolation. Optical switching technology is a highly promising candidate for solving these problems. It may be said that switching systems, using optical switching technologies, will most likely provide the future highspeed, broadband services. In view of the non-inductiveness and broad bandwidth of optical devices, studies on optical switches have been conducted in Japan with stress placed upon mechanical switches. However, recent technological progress, based on the electro-optic effect, has accelerated the development of true optical switches, and the application of these devices to optical switching systems is now being considered. In this article, we classify optical switching systems into three categories. The present status and'the future of each optical switching, system and optical device technologies in Japan are then described. It describes only optical devices, without using electronic-optical and optical-electronic onverters. Therefore,'optoelectronic integrated circuits (OEIC's), which are believed a principal candidate for constructing optical switching systems in the near future, are not discussed.

Integrated office systems: 1995 and beyond

Abstract: December 1987-Vol. 25, No. 12 IEEE Communications Magazine 74 Introduction N o one can predict what office systems will be like a decade from now. If one were pressed to make a guess, however, the answer should be based on two questions: in what directions are the desires of users heading, and in what directions is the technology developing? The answers to these questions are important because the course of future development will be determined by the extent to which technological progress will be able to fulfill the desires of users. As Dr. Koji Kobayashi, the Chairman of the Board of NEC, has previously stated in his book ( l ) , the future information society will see the support of human creative and intellectual activities through the fusion of Computers and Communications (C&C). He refers to this as “modern communications,” and calls the resulting society supported by modern communications “Man and C&C.” T h e most desirable office systems of the future will beachieved primarily hy the implementation of modern communications, a C&C system unifying computers and communications, in the office.