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Communications, IEEE Transactions on

Issue 12 • Date December 1976

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Displaying Results 1 - 17 of 17
  • [Front cover and table of contents]

    Page(s): 0
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    Freely Available from IEEE
  • Editorial: Time for a Change

    Page(s): 1281
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    Freely Available from IEEE
  • Editorial

    Page(s): 1282
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    Freely Available from IEEE
  • [Back cover]

    Page(s): 0
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    Freely Available from IEEE
  • PCM-FDM System for Existing Microwave Radio Baseband

    Page(s): 1346 - 1350
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    Digital transmission over the empty lower baseband of an existing microwave radio system has the advantages of economical and easy construction. A 1.544 Mbit/s PCM-FDM converter (PF-B1) has been developed. Field test results show that the error-rate per bit is less than 10-8over 840 km with 3 basebands. View full abstract»

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  • An Equalizer Structure with Reduced Sampling Time Reference Sensitivity

    Page(s): 1337 - 1343
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    In the last decade the work on linear tapped delay line equalizers has proved successful in reducing intersymbol interferenceone of the largest problems in data communication systems. An adjoining problem is the selection of a sampling time reference. An equalizer structure less sensitive to sampling time reference is studied for adaptive equalization. The equalization is simply done by means of tap coefficient adjustment. The equalizer consists of two parallel branches, each containing a transversal filter with adjustable tap coefficients. The branches are connected by a fixed filter, the transfer function of which is selected such that the equalizer can perform a sampling time reference displacement and a cancellation of intersymbol interference simultaneously. The criterion of goodness is the conventional meansquare error (including noise) between the actual output and a desired output. The equalizer is applied in two examples showing-in contrast to a conventional equalizer with the same total number of tap coefficients-the insensitivity of the minimum mean-square error (MMSE) to how the the sampling time reference is selected. Thus no extra circuits are needed for this purpose, while a mean-square error that is as low as the best that can be obtained with a conventional equalizer is adaptively maintained. View full abstract»

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  • A New Approach to Computing Distortion of an FM Single-Tone Modulated Signal Due to Ideal Filtering

    Page(s): 1317 - 1321
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    By factorizing a finite sum of harmonics, an expression is obtained for an FM demodulator output when the modulating signal is a simple sinusoid and the RF filter is an ideal bandpass filter. Using this result, harmonic distortions and the signal-to-distortion ratio are defined and computed; several curves are drawn to show the variation of these quantities in terms of the modulation index and the normalized bandwidth. View full abstract»

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  • Mutual Synchronization Properties of a System of Two Oscillators with Sinusoidal Phase Detectors

    Page(s): 1321 - 1326
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    Mutual synchronization between two geographically separated phase-locked oscillators is investigated for two different interconnection methods. This includes the so-called single-ended (uncompensated delay) and the double-ended (compensated delay) methods. Explicit formulas for determining the steady-state frequency and phase errors are developed for both methods. Necessary conditions for the existance of a synchronous state are derived in terms of basic system parameters. Finally, a comparison Of the methods of oscillator interconnection is made as a function of the uncompensated channel delays. Graphical results are presented which are useful in determining steadystate system performance. View full abstract»

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  • A Simulation Study of Digital Modulation Methods for Wide-Band Satellite Communications

    Page(s): 1351 - 1354
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    A computer simulation study has been performed to evaluate the performance of a variety of digital modulation techniques in transmitting high-rate digital data over a satellite channel. Results are presented showing comparative performance of various techniques in the form of error-rate curves and signal-to-noise ratio (SNR) degradation curves. View full abstract»

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  • Timing Recovery for Equalized Partial-Response Systems

    Page(s): 1326 - 1331
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    It is shown that the sensitivity of the performance of least mean-square error (LMS) equalizers to the sampler phase is a function of equalizer length for partial-response systems. An LMS algorithm for the adjustment of sampler phase is derived for partial-response systems. This algorithm does not require the transmission of any pilot tones and is relatively easily implementable by digital circuits. A method of selecting a "good" initial sampler phase is also proposed. View full abstract»

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  • An Efficient Method of Simulation for Time-Sharing Systems

    Page(s): 1316 - 1317
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    Simulation of requests for service from a large number of low duty cycle independent users is apt to cause a severe computational load. A method is presented for the software implementation of an efficient simulator. It can be applied to the investigation of many time-sharing systems, such as satellite demand assignment (DA), computer time sharing, and traffic routing. More generally, the method generates independent multivariate Poisson distributions when the number of variables is very large and the value of the parameter in each distribution is very small. View full abstract»

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  • Receiver Designs for Fiber Optic Communications Optimization in Terms of Excess Noise Factors That Depend on Avalanche Gains

    Page(s): 1343 - 1346
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    The optimizations of signal-to-noise ratios (SNR's) and pulse error rates in fiber optic receivers are investigated in terms of an avalanche photo diode (APD) model in which excess noise factors depend on the avalanche gains. The optimization of SNR results in an analytical solution for the optimum avalanche gain. A numerical example compares the result with those of conventional SNR optimization where excess noise factors do not depend on avalanche gains. Improvements of around 2 dB in the accuracy of the optimum SNR's are expected. It is shown that the optimization of pulse error rates for digital transmissions can not be attained analytically. This problem is solved by the use of approximate representations of excess noise factors. Two approximate representations are illustrated that provide very simple and accurate analytical solutions. Numerical examples demonstrate the efficacy of these approximate solutions. View full abstract»

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  • Optimal Linear Coding for Vector Channels

    Page(s): 1283 - 1290
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    This paper is concerned with the problem of obtaining the optimal linear vector coding (transformation) method that matches anr-dimensional vector signal and ak-dimensional channel under a given channel power constraint and mean-squared-error criterion. The encoder converts thercorrelated random variables intorindependent random variables and selects at mostkindependent random variables which correspond to theklargest eigenvaiues of the signal covariance matrixQ. The encoder reinserts cross correlation into thekrandom variables in such a way that the largest eigenvalue ofQis assigned to the smallest eigenvalue of the channel noise covariance matrixRand the second largest eigenvalue ofQto the second smallest eigenvalue ofR, etc. When only the total power for allkchannels is prescribed, the optimal individual channel power assignments are obtained in terms of the total power, the eigenvalues ofQ, and the eigenvalues ofR. When the individual channel power limits are constrained byP_{1}, ..., P_{k}andRis a diagonal matrix, the necessary conditions of an inverse eigenvalue problem must be satisfied to optimize the vector signal transmission system. An iterative numerical method has been developed for the case of correlated channel noise. View full abstract»

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  • On Optimal Analog Repeater Systems

    Page(s): 1310 - 1315
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    In this paper, the optimal analog repeater system which transmits maximum mutual information (MI-system) is discussed. The solution is obtained by conventional variational method and the functional structure of the resulting optimal system is investigated. The system consists of a whitening filter, an "equivalent cable," and a "system equalizer," the concepts of which are newly introduced and defined in the paper. For comparison, the repeater system with minimum mean-square error (ME-system) is analyzed by the analogous method. It is shown that the whitening filter and the "equivalent cable" are invariant for both systems and that the only part which varies with the optimizing criterion is the "system equalizer." Finally, these results are applied to the special case of single stage and the relation to Shannon's water pouring theorem is discussed. View full abstract»

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  • Three-Level Subscriber's Loop Signaling for a Data Network

    Page(s): 1331 - 1336
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    This concise paper reports the result of a study leading to the design for a subscriber's loop signaling system in a data switching network. The data switching network is intended to have improved quality and versatility, and be less expensive than the existing data communication systems. Therefore, various requirements are imposed on the subscriber's loop signaling system. The three-level subscriber's loop signaling system described in this concise paper is considered to satisfy these requirements. In this system, signals are defined by three logical states in the subscriber's loop, i.e., +, -, andN. This system is applicable to both asynchronous and synchronous terminals. The data terminal equipment-data circuit terminating equipment (DTEDCE) interface and the subscriber's loop transmission system, suitable for this signaling system, are also described. View full abstract»

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  • Optimum Detection of Quantized PAM Data Signals

    Page(s): 1301 - 1309
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    The degree of complexity of a digital signal processor is closely related to the precision with which samples of an incoming analog waveform are represented. There is considerable interest in determining how coarse this representation can be without seriously degrading performance from that of an ideal processor of unquantized samples. This question is examined for a receiver of noisy, linearly distorted pulse amplitude modulation (PAM) signals. An optimum [maximum likelihood (ML)] detector, analogous to the Viterbi detector for unquantized samples, is derived for the case of a quantized sample sequence. Performance is evaluated under the assumption of high signal-to-noise ratio (SNR), and the resultant error probability is a good approximation for coarse quantization, and an upper bound for any degree of quantization. For a specified error probability, the degree of quantization suggested by this approach is conservative. Since receiver complexity is closely associated with the length of the digital representation of an input sample, an upper bound on receiver complexity is also suggested. Numerical evaluation of the error probability is quite tedious for an arbitrary channel; however, system performance may be readily evaluated for partial-response (PR) signaling. For the PR channels View full abstract»

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  • A Digital Receiver for Tone Detection Applications

    Page(s): 1291 - 1300
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    A digital circuit suitable for detection of tones in signaling applications is described. The amount of hardware required for the realization of the circuit is shown to be quite small. The circuit may be used for both analog and digital input signals. For analog signals, the necessary A/D conversion becomes very simple. Results of simulations on a digital computer are given that indicate the good performance of the circuit. 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.

 

 

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Robert Schober
University of British Columbia