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Communications Systems, IRE Transactions on

Issue 2 • Date June 1961

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Displaying Results 1 - 14 of 14
  • [Front cover and table of contents]

    Publication Year: 1961 , Page(s): 0
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    Freely Available from IEEE
  • The Examination of Error Distributions for the Evaluation of Error-Detection and Error-Correction Procedures

    Publication Year: 1961 , Page(s): 101 - 106
    Cited by:  Papers (2)
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    The factors influencing the speed at which data can be transmitted, and those determining the error rate, are summarized as an introduction to a statement in respect to error rates measured. Different applications for data transmission are considered in relation to the amount of error correction which may be justified. Various forms of error detection and correction are illustrated, and the probability of undetected errors is considered from a theoretical point of view for a random distribution of errors. These results are then compared with records obtained by practical tests using various redundancy arrangements. It is concluded that there is a substantial advantage in the use of large (500-bit) rather than small (50-bit) blocks for detecting errors. It is also suggested that the practical evidence of error patterns which remain undetected should enable more effective detection designs to be produced. View full abstract»

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  • RF Spectra and Interfering Carrier Distortion in FM Trunk Radio Systems With Low Modulation Ratios

    Publication Year: 1961 , Page(s): 107 - 115
    Cited by:  Papers (11)
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    This paper provides formulas for evaluating RF spectral shape and interfering carrier distortion in connection with FM trunk radio systems having low modulation ratios. Numerical results are given for 1800-speech-channel systems. The curves showing interfering carrier distortion are of particular interest in connection with systems using RF multiplex (i.e., systems consisting of a number of carriers each modulated with a signal built up from a large number of speech channels). Preferred carrier spacings, originally determined for 600-channel systems, have been recommended by the CCIR 9th Plenary Assembly, 1959, for use with up to 1800 channel systems. It appears from the analysis that with these larger numbers of channels, a considerable amount of attenuation by filtering or by isolators will be required to give adequate protection against intermodulation distortion. View full abstract»

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  • Consideration of Nonlinear Noise and its Testing in Frequency Division Multiplex Voice UHF Radio Communication Systems

    Publication Year: 1961 , Page(s): 115 - 129
    Cited by:  Papers (1)  |  Patents (1)
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    In UHF radio communications systems, the thermal noise limits the performance under weak received signal conditions. When the signal is strong, the nonlinear noise (sometimes called the intermodulation noise) may become the limiting factor. it is, therefore, imperative to control the intermodulation distortion contribution from the system components by careful equipment design and from the medium by appropriate choice of system parameters. In single-sideband systems, nonlinear noise may be attributed to two main causes: 1) transmitter nonlinearity and 2) receiver nonlinearity. Multipath effects in the medium do not seem to produce any nonlinear distortion, except selective amplitude fading or frequency distortion. Amplitude nonlinearity is the sole contributing factor in nonlinear noise. There is no set rule on the subdivision of nonlinear noise among both the transmitter and the receiver. Equal distribution seems to be a reasonable assumption. In some cases, an entirely different distribution may be desired, according to actual requirements. How to distribute the transmitter or receiver nonlinear noise among its components depends on the characteristics of the components. The general principle is to have the most economical design on every piece of the components, if possible and practicable. The nonlinear noise in single-sideband systems may be assumed to consist of only 3rd- and 5th-order products. It is further assumed that 3rd- and 5th-order products contribute to the total nonlinear noise in equal amounts in power. In frequency modulation systems, nonlinear noise may be attributed to three main causes: 1) transmitter nonlinearity, 2) multipath effect in the medium, and 3) receiver nonlinearity. Both amplitude and phase nonlinearities are equally important in the contribution to the noise and each should be considered carefully. The subdivision of nonlinear noise may be done in two ways. It may be distributed among the transmitter, the path and the receiver, or- among the amplitude and phase nonlinearities. In either way, further subdivision is necessary in order to specify the amplitude or phase linearity requirements for the various components of the system. There is, again, no set rule on the distribution of nonlinear noise among the various causes. The same principle as applied to singlesideband systems as mentioned before may be used for frequencymodulation systems. The nonlinear noise in frequency-modulation systems, may be assumed to consist of only 2nd- and 3rd-order products. It is further assumed that 2nd- and 3rd-order products contribute to the total nonlinear noise in equal amounts. Methods for performance evaluation, based on signal-to-nonlinear-noise ratio, are given and sample calculations are made to illustrate the methods. In the test of a complete system, either two-tone or noise loading tests may be used. Assuming that only 3rd-order nonlinear noise is predominant and that a peak factor of 10 db for random noise is chosen, the noise loading test signal-to-nonlinear ratio is 8 db higher than the two-tone test ratio if the rms power in the two tests are equal. However, if the peak power in the two tests is equal, both ratios are the same. View full abstract»

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  • Model of Impulsive Noise for Data Transmission

    Publication Year: 1961 , Page(s): 130 - 137
    Cited by:  Papers (44)
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    It has often been found more necessary in the engineering of data transmission systems to consider impulsive noise than conventional Gaussian white noise. A model is proposed for the impulsive noise, which describes empirically an amplitude distribution and a time distribution. Because the latter has been described in experimental work principally in terms of error occurrences, the description is translated into these. The notable characteristics of impulsive noise are that at low occurrence frequencies the amplitudes are much larger than for Gaussian noise, and that impulses or errors tend to be more "bunched" than expected from a Poisson distribution. View full abstract»

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  • Diversity Combining for Signals of Different Medians

    Publication Year: 1961 , Page(s): 138 - 145
    Cited by:  Papers (2)  |  Patents (15)
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    Over-the-horizon communication systems normally use two identical antennas at each end. It is shown that an asymmetrical arrangement, for example, 6o'( )60' 30'( )30' is better than a symmetrical arrangement when both antennas at one end are used for diversity reception and the larger antenna at the other end is used for transmitting. This arrangement is important because for a given performance it costs less than the symmetrical arrangement. Depending on the exact relationship between cost and antenna gain, the cost is a minimum when the difference in antenna gains lies between 3.2 and 4.8 db. Statistical performance for various combining methods and degrees of diversity are presented. As for the case of equal medians derived previously, selector diversity combining is decidedly inferior to equal gain combining, which in turn is about one db worse than maximal ratio combining. The "instantaneous" SNR's (applicable to data transmission) are derived and compared to the usual short-term SNR's applicable to telephony. View full abstract»

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  • Diversity Reception for Meteoric Communications

    Publication Year: 1961 , Page(s): 145 - 148
    Cited by:  Patents (1)
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    One of the first goals of the research effort on meteoric communications was to establish the advantage, if any, of diversity reception. Three types of diversity were investigated: frequency, space, and polarization. Nearly perfect correlation of the signals was found for frequency diversity reception with a frequency separation of 4 kc and for space diversity reception for antenna spacings of up to 1200 feet, Only polarization diversity appears to provide any advantage. Two identical eight-element yagi receiving antennas were erected. one horizontally polarized and the other vertically polarized. The transmitting antenna was horizontally polarized. Analysis of the data shows that about 34 per cent of the signals on the vertical antenna equal or exceed in amplitude the signals on the horizontal antenna, but the shapes of the bursts on the two antennas are identical in most cases. It is concluded that there is not enough increase in system performance to justify the use of any of the three types of diversity. View full abstract»

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  • Digital Computer Simulation for Prediction and Analysis of Electromagnetic Interference

    Publication Year: 1961 , Page(s): 148 - 159
    Cited by:  Papers (4)
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    A digital computer simulation program is described for use by communications systems and equipment designers who must consider electromagnetic interference. The program determines the interference experienced by a test receiver in a signal environment resulting from its associated transmitter, a large deployment of potentially interfering transmitters, and by atmospheric and cosmic noise sources. Simulation models are designed to represent such transmitter characteristics as antenna gain and scan patterns, polarization and emitted power spectrum; other models represent propagation phenomena such as scattering, reflection, fading and tropospheric refraction; and such receiver characteristics as antenna gain patterns, frequency selectivity and demodulator transfer characteristics. Signal acceptability criteria are included to permit system scoring. Program flexibility is stressed so that optimum system design may be achieved through rapid evaluation of successive approximations. View full abstract»

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  • Preliminary Study of a Miniature Underwater Cable System

    Publication Year: 1961 , Page(s): 159 - 164
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    Certain aspects of feasibility of a miniature submarine cable-transmission system have been studied. The system is small and light, and designed for use in military applications as an expendable item where submarine cables of conventional design would be uneconomical. It weighs about 125 pounds per mile, transmits 1.35 million pulses per second of a pulse-code modulated (PCM) signal, and is powered by 4.5 ma with a voltage drop of about 2 volts per mile. Several armorless cables were tested. All have a steel core with a layer of copper for the center conductor, and extruded polyethylene dielectric. They differ in the way in which the center conductor is fabricated, in the materials of the outer conductor, and in the way in which it is held in place over the dielectric. The transistor repeater uses one transistor and eight passive components. It has a 17-db gain and an output of 0.8 volts into a 75-ohm line. The repeater housings are hollow cylinders of beryllium copper, 2 1/8 inches by 7/16 inches. The insulation of the transmission line is joined to the ends of the housing by an adhesive and by a mechanical seal. The cable tension is transferred to the housings by hollow ceramic insulating cones. The housings were tested in 13,200 psi hydrostatic pressure and to 120 pounds axial tension. A system of five repeaters in 18,000 feet of line was laid in Sandy Hook Bay and was operable for thirteen months. View full abstract»

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  • Development of Sydney, Nova Scotia-St. John's, Newfoundland Canadian National Telegraphs Microwave System

    Publication Year: 1961 , Page(s): 165 - 175
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    A 650-mile radio-relay system composed of 22 "lineof-sight" paths was constructed to supplement the Canadian National Communications between Sydney, Nova Scotia, and St. John's, Newfoundland. Relay repeater points were chosen by means of all available contoured maps and on-site surveys of the various points, bearing in mind radio transmission characteristics and also accessibility for maintenance. All the radio paths were field-tested to confirm their transmission capabilities. The overwater hop between Cape North and Red Rocks, which is 69 miles long, required careful consideration, and special arrangements were made to ensure that this hop would provide a satisfactory performance. Standard Telephones and Cables Ltd.,were requested to provide this system using their latest equipment. This is 5-watt equipment working on 4000 Mc and able to carry the equivalent of 600 toll quality message circuits or one video program. To handle the present Canadian National requirements, three channels were installed in an eastward direction and two in a westward direction. The system is divided into three sections with back-to-back terminals at Corner Brook and Gander for general communications and television branching circuits. Each section has a separate comprehensive supervisory control facility for providing dual information and controls at both section terminals. View full abstract»

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  • Analytical Prediction of Electromagnetic Environments

    Publication Year: 1961 , Page(s): 175 - 185
    Cited by:  Papers (2)
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    The problem of transmitting digital data through electromagnetic environments of high ambient-pulse density is one of growing concern. The appearance of pulsed radar in the lO-Mw range, and sensitive receivers in the - 100-dbm range, will aggravate this situation. This paper discusses three efforts made by the government to predict the status of future environments. In all cases, the basic technique of analytical prediction calls for the solution of mathematical models by digital computer. Results from these analyses are useful to the designer of future systems as well as to the operators who must use them. The responsibility of keeping the signal congestion within bounds rests with the designer and user alike. View full abstract»

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  • Theoretical limitations on frequency and time diversity for fading binary transmissions

    Publication Year: 1961 , Page(s): 186 - 187
    Cited by:  Papers (17)
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    The purpose of this note is to point out that for either frequency diversity or time diversity, the dependence of required transmitted power on number of branches is quite different than for space diversity. For both frequency- and time-diversity techniques the saving of transmitter power can come only from the first factor above (that is, the averaging of fluctuations), since the total mean received power is a fixed fraction of the scattered power. It will be shown that as a consequence: 1) The minimum required transmitter power for a specified reliability is strictly larger than zero. 2) Both the value of this minimum and the number of diversity branches yielding the minimum depend upon the diversity-combining method used. View full abstract»

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  • Evaluation of νth-law devices

    Publication Year: 1961 , Page(s): 188 - 189
    Cited by:  Papers (1)
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    Most of the work which has been done in the analysis of a νth-law device is concerned with the statistical properties of the output. Apparently, a general investigation to determine the optimum value of ν for a νth-law device has never been made. Therefore, a simple method of evaluating a νth-law device is necessary. This may be done by choosing the optimum value of ν based on the criterion for masimizing the detector output information capacity. It is shown that when the input of a νth-law detector consists of an amplitude modulated (AM) sine-wave signal and a stationary narrow-band white Gaussian noise, the square-law detector will give maximum output information capacity for very small input signal-to-noise ratio (SNR). In the case of a very large input SNR and a normally distributed signal modulating process on the AM sine wave signal, the linear detector will be considered as an optimum one. View full abstract»

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  • [Back matter]

    Publication Year: 1961 , 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