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Communications Systems, IRE Transactions on

Issue 3 • Date September 1961

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Displaying Results 1 - 24 of 24
  • [Front cover and table of contents]

    Page(s): 0
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    Freely Available from IEEE
  • Our expanding resposibilities

    Page(s): 193
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    Freely Available from IEEE
  • A Technique for Lowering the Noise Threshold of Conventional Frequency, Phase and Envelope Demodulators

    Page(s): 194 - 206
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    Envelope, phase and frequency demodulators exhibit a stronger-signal capture phenomenon which enables the noise to suppress the signal when the signal is the weaker of the two, and the signal to suppress the noise when the reverse is true. The presence of the noise thus imposes a threshold that must be exceeded by the signal for proper envelope, phase or frequency demodulation. A general discussion is presented of the relative signal and noise content of the envelope, phase and frequency of the resultant of an amplitude- or exponent-modulated sinusoid plus random-fluctuation noise, when one or the other is heavily dominant. An analysis is then presented of the effect of regenerative feedback around an amplitude limiter upon a sinusoid plus random noise in order to define the conditions under which a CW-type signal will be enhanced over a strong random-fluctuation noise. It is shown that an oscillating limiter whose output maintains a high degree of coherence in the presence of a pure random-noise excitation will boost a wide class of relatively weak coherent signals into predominance over the noise when such a signal is added to the noise. Substantial threshold reductions which have been demonstrated in the laboratory are thereby made possible. View full abstract»

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  • Binary Error Rates in Fading FDM-FM Communications

    Page(s): 206 - 214
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    This paper discusses the transmission of binary data over a fading frequency-division multiplexed FM (FDM-FM)radio system. The important results are convenient design formulas for binary error rate in terms of the symbol duration, the IF bandwidth, the per channel rms frequency deviation, the average received carrier-to-noise ratio, and the particular types of binary detection and diversity combining techniques used. By using accepted telephone talker statistics and the CCIF recommendations with regard to data channel loading in a combined voice-data system binary error rate is further related to FM deviation ratio, and the pre-emphasis time constant etc., which are of more specific interest to system design. An important corollary of the analysis is that in a fading environment FDM-FM offers relatively inefficient means for data transmission. In particular it is shown that an FDM-FM data system does not perform as well as does the equivalent FDM-SSB system by an amount in the order of 10 db. View full abstract»

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  • Reduced-Time Facsimile Transmission by Digital Coding

    Page(s): 215 - 222
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    The growing importance of digital communication links has resulted in a family of coding methods designed to achieve reduced-time digital facsimile transmission. This paper reports on a study of the effectiveness and feasibility of one of these methods, Run Length Coding (RLC). RLC is a well-known digital method in which the area and shade of the copy are quantized to form a mosaic pattern. Neighboring elements of the mosaic are successively scanned, and redundancy is removed by coding and transmitting only lengths between shade changes (run lengths) rather than individual area elements. Measurements of the statistical distribution of run lengths of various copy were made to determine the possible transmission time reduction. Digital equipment and a drum scanner were used to measure the statistics of weather maps, topographic maps, text, diagrams, and continuous-tone pictures (quantized to four shade levels). The maximum possible time reduction was calculated for each type of copy, and practical codes were then designed and evaluated. The average time reduction factor for black and white copy was four, compared to a theoretical optimum of 4.7. Since the maximum bit rate of the transmission line should be continuously utilized, and since time reduction factors for particular runs depend on the lengths of the runs, a practical RLC facsimile system must possess either a variable speed scan, a large and elastic buffer storage, or some combination of the two. A system is proposed whose encoding principle permits a feasible compromise between these two extremes, and whose implementation involves a flying-spot scanner that is converted into a digital device by means of optical reference gratings. View full abstract»

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  • A Technique for Improving the Intelligibilty of Speech Transmitted by Amplitude Modulation over Noisy Channels

    Page(s): 222 - 225
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    This paper describes a limited experimental study of a technique for enhancing the intelligibility of speech transmitted by amplitude modulation over noisy channels. The technique requires that the two sidebands of the received signal be demodulated separately by conventional single-sideband methods, and that the resulting audio signals be presented to the listener via headphones as binaural stimuli. The experimental results indicate that when white noise is the only form of interference, the technique yields better intelligibility scores than conventional AM detection for most values of SNR. Although practical applications appear to be limited, the technique is interesting because it exploits a perceptual faculty of human listeners. View full abstract»

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  • Jamming Vulnerability of Communication Systems

    Page(s): 226 - 232
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    This paper presents the procedure for evaluating the jamming vulnerability of a communication system. The factors considered include system performance under laboratory conditions, characteristics of transmission channels, power and transmitter design of jammer, and the costs of desired communication and jamming systems. View full abstract»

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  • The Sideband Intermediate Frequency Radio Communications System

    Page(s): 232 - 238
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    A communications system is described which eliminates oscillator-frequency drift problems by incorporating an amplitude modulated transmitter modulated by an oscillator tuned to half the intermediate frequency of the receiver. The use of a balance modulator elimates the carrier and allows energy at the two sideband frequencies to be propagated to a receiver. In the receiver these two sidebands are beat against each other to produce the IF signal. No receiver local oscillator is required. Only one high-frequency oscillator, the transmitter carrier oscillator, is used in the entire system, and frequency drift problems are reduced to those of low-frequency oscillators. However, preliminary investigation indicates that a bandwidth of twice that of a regular communications system is required in most cases. The system may prove useful at frequencies between the microwave and infrared regions. View full abstract»

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  • Techniques for Comparing Modulation Methods for Data Transmission over Telephone Channels

    Page(s): 239 - 243
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    A program has been initiated for study of complete data communication systems by a general purpose analog computer. Complete PM and FM systems including transmitter, receiver, and channel have been simulated. Illustrative results and a discussion of criteria of performance are presented. View full abstract»

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  • New Equipment for Experiments on Data Transmission and Error Analysis

    Page(s): 244 - 246
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    This paper describes the test equipment which was used jointly in 1959 by Post Office authorities and IBM for evaluation of the data transmission feasibility over European telephone networks. A summary of the results gained is displayed and demonstrates the feasibility of data transmission even if many problems are still to be solved. In the second part of the paper a method for recording and analyzing the errors is explained briefly. This method uses a conventional way of programming a computer and will be used in the future for statistical studies on error distributions. View full abstract»

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  • The Telephone Channel in a Global Communications System

    Page(s): 247 - 252
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    The nominal 4-kc telephone channel is by far the most dominant parameter of contemporary telecommunication networks. It is, directly or otherwise, underwritten by a world-wide investment of the order of fifty billion dollars. The engineering of present and future global communication networks must therefore provide for working with and into such channels, concomitantly with finding avenues out of their limitations as a device for partitioning and and utilizing communications space. This paper is a characterization of the telephone channel to a first order of approximation-its loss, phase and noise characteristics and some related operational factors. View full abstract»

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  • Start-Stop Data Transmission Without the Stop Element

    Page(s): 252 - 258
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    The existing start-stop telegraph system as used in the telex service allows for the transmission of 400 telegraph characters per minute when the CCIT recommended speed of 50 bauds is used. The signals comprise a start element and 5 information elements, each of unit length (20 msec), and a stop element with a duration of I 1/2 units, so that a telegraph signal of this type has a duration of 150 msec. This system allows for the transmission of 52 different letters and figures and six functionals, two of which are used for the change from letter shift to figure shift and vise versa. In this paper it is shown that it is possible to omit the stop element in a start-stop transmission of telegraph signals. This increases the telegraph speed from 400 characters per minute to 500 characters per minute. When special means are used and when it is possible to limit the the system to the transmission of numerical information, only a start element and four information elements are required. The telegraph speed will increase in that case to 600 characters per minute. This gain in speed may be exchanged for a parity check on the correct transmission. Various possibilities and their consequences are discussed in this paper. View full abstract»

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  • Telegraph Distortion on High-Speed Frequency Shift Data Transmission Systems

    Page(s): 259 - 270
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    First, the distortion due to the telephone channel is calculated by considering the instantaneous frequency of the transmitted signal, the telephone channel being defined in terms of its frequency characteristics: attenuation and group delay. The results are easily obtained when the signal is recurrent. Calculations have been carried out on a particular binary signal, for some typical telephone lines, the results being presented as time variations of instantaneous frequency and amplitude. Then, consideration is given to the distortion coming from other disturbances, such as frequency stability, imperfect limitation and, more specially, noises. Two typical sources of noise are examined: noise consisting of a sine wave, and white noise. Distortion is evaluated in each case by calculating the maximum disturbance, this being done for an ideal binary signal, and also for a signal already affected by some typical inperfection of the telephone channel. View full abstract»

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  • Some Results of Data Transmission Tests Over Leased Telephone Circuits

    Page(s): 271 - 275
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    Data transmission tests were performed on leased telephone circuits using two different sets of terminal equipments. The first applied phase-reversal modulation (PM), the second, frequency-shift keying (FSK). The transmission speeds were 750 or 1625 baud in the former and 750 or 1500 baud in the latter case. Nine different circuits, having an average length of 980 km, were tested. Only erroneous blocks were recorded, the blocklength being in the PM case one quarter and in the FSK case one half of the 250 bits provisionally recommended by the CCITT. A block error occurred, on the average, in every 1000-10,000 correct blocks. On shorter circuits or under special conditions average error rates of one in 100,000 seem possible. On the average, 250-millions bits were transmitted per test. The test procedure is illustrated in one selected example, which is also particularly interesting because of the unusually high outage time of the circuit during the test period. View full abstract»

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  • Oblique-Sounding and HF Radio Communication

    Page(s): 275 - 279
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    The sweep-frequency oblique sounder is a powerful tool for the study of ionospheric propagation over actual communication circuits. In addition, since it provides the pulse response of the ionosphere as a function of frequency it is potentially a powerful tool for improving communication via the ionsphere. The Defence Research Telecommunications Establishment's (DRTE) experience in using sweep-frequency sounding for the study of HF radio propagation over both short and long paths is described. These include difficult communication circuits in the auroral zone where unreliability is frequently encountered. These studies have revealed many inadequacies in our present prediction systems. Preliminary attempts to use oblique-sounding information for improving present HF communication circuit reliability have been made, but to obtain full advantage of this technique improved communication systems are required. A description is given of a proposal, which is only one of many possible, for using the obliquesounding technique on HF radio circuits to obtain more reliable long distance communication. View full abstract»

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  • Information Bandwidth of Tropospheric Scatter Systems

    Page(s): 280 - 287
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    A set of design curves of peak intermodulation distortion due to frequency selective fading, as a function of information bandwidth, is derived for tropospheric scatter systems. These curves are applicable to systems frequency-modulated with frequency-division multiplexed telephone and telegraph channels. A two-ray tropospheric scatter model was selected in order to derive general results. This, however, restricts the use of the design curves to the region where the information bandwidth is less than the propagation bandwidth. Equations for intermodulation distortion are evaluated for parameters normally encountered in tropospheric scatter systems. A method of obtaining a probability distribution of the distortion is indicated, and an example is worked out in detail. The intermodulation distortion due to frequency selective fading will exceed the thermal noise in some systems, and should be taken into consideration when designing tropospheric scatter systems. View full abstract»

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  • The Economical Design of Radio Communication Systems by Matching the Message Urgency to the Fading Conditions

    Page(s): 288 - 291
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    A "matched-traffic technique" is proposed to control the hourly traffic volume so that the capability of the system is designed only to carry the urgent messages that require immediate transmission at the desired reliability. The urgent messages carried by preferred channels will be transmitted as usual all the times while the nonurgent messages carried by delayed channels will be transmitted when the fading conditions improve. This technique may permit reductions in required transmitter power and antenna size. View full abstract»

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  • Universal Combined Radio Relay and Tropospheric Scatter Equipment [Equipment Group AN/FRC-( )]

    Page(s): 292 - 297
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    The characteristic distinguishing this equipment group resides in the words "Equipment", "Universal" and "Combined''. As conceived by Rome Air Development Center, this approach is aimed to bring about a matrix of least-common buildingblock equipments with the built-in flexibility for mutual fit to make up any required radio relay or tropospheric scatter subsystem. It is intended that the resulting subsystem designs will enable a closer approach to the ideal "universal" trunk line radio communication subsystems for AIRCOM than has been hitherto possible. This is so mainly because the AN/FRC-( ) design objectives hew closely to the over-all comprehensive AIRCOM system plan, assuring fit and interface within a well-defined architectural scheme. The equipment group presently specified for development is characterized by the inherent versatility to compose line-of-sight radio or trope subsystems for AIRCOM applications demanding a high order of signal reliability (99.9 per cent), heavy baseband capacity (to 600 4-kc voice channels, or video equivalent), long trunk line distances (up to 6000 miles), and signal quality standards up to CCITT recommended values. The radio relay or tropospheric scatter subsystems so derived should compatibly feed from or into existing long-distance commercial communications facilities in the North American continent, and Air Force systems expected to be served by AIRCOM. This fresh departure from the conventional piecemeal subsystem design and fabrication was derived from the fundamental philosophy expressed by Strom and Kunze. As applied to radio relay and tropo scatter, this universality-andcombinability concept may well prove a forerunner to similar embodiments in related communication fields, with consequent benefits in uniformity, versatility, compatibility, growth potential and economy in time, money and logistics. View full abstract»

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  • Correction [to "Some recent developments in digital feedback communication systems"]

    Page(s): 297
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    Summary form only given, as follows. The author of the above-named work, which appeared on pages 51-57 of the March, 1961, issue of these Transactions, requested the following addition to his paper: "The research reported was performed at New York University, N.Y., under the sponsorship of the Air Force Command and Control Development Division, Air Research and Development Command, Laurence G. Hanscom Field, Bedford, Mass." View full abstract»

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  • Planning Aspects of Globe-Circling Communications System of High Capacity, Reliability, and Performance Quality

    Page(s): 298 - 311
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    The need for very long-haul circuits of high-quality has developed considerably over the last few years. Recent developments in the under-seas cable field indicate that a global cable network might be devised to solve much of this traffic problem. A review is made of the basic considerations which enter into the planning of such a network, and it is pointed out that political difficulties may today pose far greater problems than any other single factor. Present and planned world cable systems are disclosed and it is pointed out that if advantage is taken of the alternate routing capabilities so offered, the required network can be reduced to a single globe-circling trunk. The factors which definitize the routing, such as economics, logistics, international agreements, presence of volcanic zones, and other inhospitable environments, are briefly discussed. It is shown that a 2-Mc cable, providing a 1-Mc band in each direction of transmission, is feasible. Performance capability may be based on a 10,000-nantical-mile section, and preliminary calculations indicate that toll-quality circuits over this length are possible. Preferred location of switching, centers is also given. Traffic from areas surrounding the global trunk can be readily fed in by spur circuits using tropospheric-scatter or microwave relay, submarine cable, or radio relays utilizing special long-endurance aircraft, according to requirements and terrain. It is suggested that the trans-African route should be a nine-link tropospheric-scatter system rather than a cable round the Cape. It is then shown that by these means, toll interconnections may be made between any two points over most of the globe, including most of the habitable part of the earth, and the major seaways and airways. It is concluded that this basic trunk could readily integrate with satellite trunks when these ultimately become operational. View full abstract»

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  • Integration of Independently Designed Military Communication Systems

    Page(s): 312 - 316
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    The existence of many special purpose military communication systems will be pointed out, and the efficiency resulting from integrating these separate systems is discussed, as against the technical complexities involved in modifying them for interconnection. The various degrees of integration is considered, from maintaining separate channels on shared-baseband systems to complete interconnection facilities among the end instruments or input-output devices of the systems concerned. The constraints on switching arrangements dictated by minimum over-all transmission quality are considered, particularly as they affect alternative routing. Also examined is the practicality of reducing these constraints by limiting certain end-instrument stations to access to a limited number of other stations in the many cases in which such end-instrument stations have no occasion to be connected to more than a very limited group of other stations. Automatic interconnection between systems having different numbering plans presents problems which are not always easily solved. The solution by the establishment of a common over-all numbering plan might require small systems with short messages to use too large a precentage of circuit time in establishing a connection. Considerations involved in integrating voice and data systems are discussed, as well as considerations in combining message-switching and line-switching systems. Finally, the importance of definitely established quantitative standards in integrating systems is emphasized, and various activities involved in the establishment of such standards are reviewed. View full abstract»

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  • System Utilization of Electronic Frankensteins

    Page(s): 316 - 319
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    Short-sighted system planning has resulted in the evolution and system mix of both megawatt and microwatt power level equipments with little concern for the over-all system degradations which result from sub-system interactions. Unfortunately the effects of these interactions are often felt far beyond the immediate system. As a result, the full use of extremely sensitive sensors and detectors, which are often very susceptible to spurious and background noise and to interference, may not be economically feasible in view of the cost or impracticability of the accessory background noise and spurious signal elimination devices. As pulsed equipment powers increase to megawatts and pulse lengths become longer than communications bit lengths, spurious suppression far beyond state-of-the-art is necessary if the over-all system is not to be degraded. The problem is serious in that the industrial managers or military commanders will not realize problems exist until the system fails when it is needed. Graphical analysis methods and guidelines for future developments are presented. View full abstract»

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  • A Laboratory Comparison of Maximal-Ratio Combiners and Optimal Selectors for Fading HFSK Channels

    Page(s): 320 - 321
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    Experimental results are described to demonstrate the superiority of a maximal ratio combiner (or ratio squarer) over an optimal selector in the reception of fading HFSK signals. View full abstract»

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  • [Back matter]

    Page(s): 0
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    Freely Available from IEEE

Aims & Scope

This Transactions ceased publication in 1962. The current retitled publication is  IEEE Transactions on Communications.

Full Aims & Scope