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Communications, IEEE Transactions on

Issue 6 • Date December 1972

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Displaying Results 1 - 25 of 31
  • [Front cover and table of contents]

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  • [Back cover]

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  • Considerations of Nonlinear Effects in Phase-Modulation Systems

    Page(s): 1063 - 1073
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    A class of "optimum" phase modulation (PM) system treated in the past is one wherein a sinusoidal carrier is phase modulated linearly by a Gaussian (baseband) random process and demodulation is performed by a phase-locked loop (PLL). This paper is concerned with PM systems in which the phase modulation is allowed to be nonlinear. In practice, most phase modulators are restricted to finite ranges of linear operations. The performance (SNR) of the PLL demodulator is degraded when the linear range is exceeded by an amplitude of the modulating waveform. The occurrence of performance degradation is a random event whose frequency depends on the linear range and the statistics of the waveform amplitude. By interpreting the nonlinear phase modulation as a saturation phenomenon, we determine in this paper the performances of PLL de modulator as a function of varying degree of saturation (or limiting) level for several cases of baseband spectrums. We model the "saturation" by an error function limiter. Our results are general, and it is shown that the previous results of linear modulations are special cases of our results. We then move on to assume that the baseband waveform is a composite signal of multichannel frequency division multiplexed (FDM) signals. As a result, we compute the lower bounds of slgnal-to-crosstalk power ratio for several cases of baseband spectrums. View full abstract»

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  • Signal Processing, Modulation and Noise

    Page(s): 1202 - 1203
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    First Page of the Article
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  • On the Detection of Differentially Encoded Polyphase Signals

    Page(s): 1121 - 1128
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    Any digital communication system that employs coherent detection requires coherent reference signals for proper operation. This paper is concerned with the transmission and detection of differentially encoded multiple phase-shift-keyed (MPSK) signals and the ambiguity resolution problem that results from suppression of the transmitted carrier. In particular, the paper presents the analysis and performance of differentially encoded coherent MPSK systems that reconstruct coherent reference signals by means of generalized Costas orNth power loops. The performance of such systems is then compared with that of ideal reception of MPSK signals and differentially coherent detection of differentially encoded MPSK signals. Emphasis is placed upon the special cases of quadriphase and octaphase signaling. View full abstract»

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  • Complex Detection: A Waveform Preserving Technique for Single-Sideband Demodulation

    Page(s): 1097 - 1100
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    The full-carrier single-sideband signal is of the minimal phase type with limited phase excursion and contains sufficient information to recover completely the message waveform. A receiving system is described that makes use of both the envelope and the phase information in the signal. Operation is independent of input signal level and requires no wide-band quadrature network. View full abstract»

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  • A Theoretical Analysis of Telephone Dial Pulse Signaling

    Page(s): 1073 - 1079
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    This paper presents a theoretical analysis of the distortion of the dial pulse waveform and its effects on the response characteristics of the pulse-receiving circuit in the telephone office. To derive expressions for the waveform for dial speeds of 10 and 20 pulses per second (pps) Laplace transformation and matrix algebra are applied to the system, represented by two complementary linear lumped-constant time-invariant networks responsible for the generation of the leading and trailing edges of a dial pulse. Based on the known waveform and the operational requirements of the pulse-receiving circuit, a function is derived showing the percent break value of a pulse train as it arrives at the central office, and the dependence of the percent break on the number of extension (branch) telephones connected and the subscribers' loop parameters. Its inverse, shown in graphical form, presents the upper limits for the number of extensions to be associated with a transmission line of given electrical parameters. The conditions under which abrupt changes of the percent break value and quasi-pulses occur are analyzed. View full abstract»

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  • Amplitude- and Time-Limited Functions With Minimum Out-of-Band Energy

    Page(s): 1150 - 1153
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    The theory of time-limited functions with minimum out-of-band energy is extended to apply to functions whose amplitude is held constant and hence, are limited to phase modulation. In the absence of the amplitude constraint, the desired functions are prolate spheroidal functions of time, of order zero, with time-bandwidth product as a parameter. With the amplitude constraint, the desired functions can be expressed in terms of sums of even-order prolate spheroidal functions. An algorithm suitable for computations of the amplitude constrained functions is derived. View full abstract»

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  • Spectra and Efficiency of Binary Codes Without DC

    Page(s): 1182 - 1184
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    In digital transmission of binary (+1,-1) signals it is desirable that the stream of pulses which constitutes the signal have no dc, that is, that the power spectrum go to zero at zero frequency. It is desirable that, for a given efficiency or entropy, the spectrum rise slowly with increasing frequency. We have obtained the spectrum for selected blocks with equal numbers of plus ones and minus ones. For a given efficiency, this is better than the spectrum obtained by Rice, using the Monte Carlo method, for block encoding using polarity pulses. An algorithm given by Schalwijk should allow simple encoding into selected blocks. View full abstract»

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  • A Digital Echo Suppressor for Satellite Circuits

    Page(s): 1176 - 1181
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    An echo suppressor that is composed solely of digital logic circuits and based on a digital voice detector [1] has been designed. The unit is simple and requires no adjustment. Its basic application is to the SPADE [2] PCM channel, although it can be adapted to work with other systems. Results of initial subjective tests are included. View full abstract»

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  • Signal Detection in the Presence of Cochannel Interference and Noise

    Page(s): 1153 - 1158
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    The problem of detection of a sinusoidal signal in the presence of white Gaussian noise and an interfering sinusoid at a nearby frequency is discussed. In the case of coherent detection, several possible receivers are analyzed and probability of error curves are calculated. In some cases it is possible to reduce the effect of cochannel interference significantly by proper choice of a receiver. In the case of incoherent detection, error probability curves have been calculated for the standard envelope detector for several values of frequency separation. The performance of the envelope detector can be degraded substantially by the presence of an interfering sinusoid. View full abstract»

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  • A Tabulation of Hilbert Transforms for Electrical Engineers

    Page(s): 1194 - 1198
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    The Hilbert transform has found application in the analysis of single-sideband signals and angle modulation in communication systems. This extensive tabulation of this transform should prove handy for engineers as much as the more popular Laplace transform tabulations. Such a comprehensive listing of Hilbert transforms is not available in any published work so far. View full abstract»

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  • Statistical Behavior of Deep Fades of Diversity Signals

    Page(s): 1100 - 1107
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    This paper presents the results of a statistical analysis of diversity combining systems. Previous theoretical work on this topic often assumes that the input signals are jointly Rayleigh distributed, which may not hold for a practical fading environment. In this paper, we use a new formulation and analysis to show that the major results of previous theoretical work are actually valid without the restrictive assumption of a joint Rayleigh distribution. The statistics include the probability of fade, the expected number of fades per unit time, and the average fade duration. We also extend the analysis to include the effect of a dominant interfering signal such as the water-reflected ray of an overwater radio link. The statistics of diversity signals on these radio links are different and are not treated in the literature. View full abstract»

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  • The Performance of a Noncoherent FSK Receiver Preceded by a Bandpass Limiter

    Page(s): 1128 - 1136
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    Many applications of the bandpass limiter involve either coherent or noncoherent demodulation following the limiter. In this paper we study the performance of a noncoherent frequency-shift keying (FSK) receiver when it is preceded by a bandpass limiter. In particular, we obtain expressions for signal suppression- factor, output signal-to-noise ratio (SNR), and error probability from which one can assess the degradation in performance of the receiver due to the presence of the limiter. Both narrow-band and wide-band cases are treated thus covering situations where no frequency uncertainty exists (i.e., known carrier frequency) as well as large-frequency uncertainties. Also discussed is the first-order signal plus noise probability density function (pdf) following noncoherent demodulation. View full abstract»

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  • Carrier Phase-Jitter Extraction Method for VSB and SSB Data Transmission Systems

    Page(s): 1169 - 1175
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    Theoretical analysis of the phase-jitter problem for a vestigial sideband (VSB) or single sideband (SSB) high-speed data transmission system is discussed in detail in this paper. Particular attention is paid to the effect of the phase shift introduced to the phase-jitter sideband components by various circuits in the carrier recovery system. Based on this theoretical analysis, a practical carrier recovery system, which will extract the phase jitter with minimum phase shift introduced to the phase-jitter sideband components, is proposed so that the overall effect of the phase jitter on the demodulated signal will be minimized. View full abstract»

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  • Optimum Detection and Signal Design for Channels With Non- but Near-Gaussian Additive Noise

    Page(s): 1087 - 1096
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    The Gram-Charlier series representation of the noiseprobability density function is used to determine an optimum detector for signals in non-Gaussian but near-Gaussian (NGNG) noise. Solutions are obtained for coherent and incoherent detection. Optimal detectors for several typical transmitting systems are determined. Generally these detectors consist of the standard detector for Gaussian noise with the addition of a few, not too sophisticated, nonlinear elements. The performance of a detector, specified by the upper bound on the probability of error, is assessed and is seen to depend on the signal shape, the time-bandwidth product, and the signal-to-noise ratio. The optimal signal to minimize the probability of error is determined and is seen to result as a solution to Duffing's second-order nonlinear differential equation. View full abstract»

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  • Analysis of Variance of Traffic Usage Data

    Page(s): 1051 - 1062
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    Procedures are developed and illustrated by application to real usage data of analysis of variance techniques for measuring components of variance in the data due to trend and arbitrary random variability in usage of equipment in a group as a whole. The usage data are obtained by periodic scanning of the equipment group at fixed intervals. Procedures for fitting the Polya distribution to the data are presented. Fitted Polya distributions are used to estimate the effects of trend on blocking. The procedures are extended to measuring and estimating the effects on blocking of day-to-day traffic variation and are illustrated by application to real usage data. A procedure is presented for adjusting estimates of variance for autocorrelation due to the usage measurement procedure and call holding times. The adjustment procedure is based on incomplete research and is, therefore, tentative. The effects of using a variance-stabilizing transformation of the data are shown. Other areas of application of the theory and procedures are discussed. View full abstract»

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  • Efficient Synchronization for Digital TV Phone Transmission

    Page(s): 1158 - 1159
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    We describe a technique for jointly encoding the rasterscan sync and data framing information for digital TV phone systems in which synchronous sampling is employed for picture encoding. The technique yields: 1) fast acquisition and hard locking synchronization; 2) highly stable picture displays; and 3) reduced channel capacity requirements. View full abstract»

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  • Phase and Frequency Tracking Accuracy in Direct-Detection Optical-Communication Systems

    Page(s): 1139 - 1142
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    Lower bounds are given on the attainable mean-square performance in causally tracking the phase and frequency of a subcarrier that modulates an optical carrier in a direct-detection opticalcommunication system. View full abstract»

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  • Effect of Mutual Coupling on a Mobile-Radio Maximum Ratio Diversity Combiner With a Large Number of Branches

    Page(s): 1188 - 1193
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    The effect of mutual coupling on a space diversity combined signal from an optimum resistive load network lessens when the antenna spacingdand the number of elementsMincrease. Whendis greater than 0.2λ, the cumulative distribution curves of anM-branch signal with mutual effects included show only a small difference compared to an array with no coupling, and are close to the cumulative distribution curve of an array withMindependent branches. For the average SNR of an array with 100 branches obtained from an optimum resistive load network to be within -3 dB of the SNR from independent branches the required antenna spacing is at least 0.25λ, for an in-line array and 0.5λ, for a planar array. Since a planar array is much smaller than an in-line array for equal performance, the planar array is a more desirable configuration. View full abstract»

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  • A Double-Loop Tracking System

    Page(s): 1142 - 1150
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    A nonlinear analysis which can be used to assess certain statistical characteristics of double-loop tracking systems is presented. It takes into account the mutual coupling effects of the loops in the system. Two approaches are taken to obtain steady-state probability density functions (pdf's) of the system phase errors, φ1and φ2From these pdf's, important system performance statistics, e.g., the phaseerror variances, can be calculated, thus illustrating the application and usefulness of the analysis. The analysis is applied to a satellite transponder as an example. View full abstract»

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  • On Bandwidth Requirements for Multilevel PCM Encoders

    Page(s): 1165 - 1169
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    Most receivers for multilevel pulse-code modulation (PCM) signals incorporate a sample-and-hold circuit in the analog-analog-to-digital converter. The sample-and-hold circuits cannot respond instantaneously in practice, and this paper considers the effects on system performance of their finite response time. To provide guidelines for system designers, the problem is analyzed in some generality and numerical results are obtained for a specific example. It is shown that a definite tradeoff exists between the bandwidth of the operational amplifiers in the sample-and-hold circuit and the follow time, and that system performance deteriorates rapidly if the bandwidth is reduced past a certain critical value. Unless the bandwidth is much larger than the critical value, there is a strong advantage in using follow times larger than onehalf the symbol interval. The bandwidth required for good eight-level transmission is about twice that required for binary transmission. View full abstract»

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  • An Adaptive Electronic Hybrid Transformer

    Page(s): 1184 - 1188
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    A hybrid transformer is used to couple simultaneously both a transmitter and a receiver to the same end of a telephone line with minimum crosstalk. Under ideal circumstances the transformer provides a cancellation signal at the input terminals of the receiver to exactly cancel the signal induced by the local transmitter. This paper describes a simple electronic device that closely behaves as a hybrid transformer operating under ideal conditions. Rejection on dial-up lines is between 50-80 dB. Adaption time is on the order of 50 ms. View full abstract»

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Aims & Scope

IEEE Transactions on Communications focuses on all telecommunications including telephone, telegraphy, facsimile, and point-to-point television by electromagnetic propagation.

 

 

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Meet Our Editors

Editor-in-Chief
Robert Schober
University of British Columbia