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Communications, IEEE Transactions on

Issue 8  Part 2 • Date August 1980

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Displaying Results 1 - 25 of 46
  • [Front cover and table of contents]

    Page(s): 0
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    Freely Available from IEEE
  • Guest Editorial: Special issue on synchronization

    Page(s): 1105 - 1106
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    Freely Available from IEEE
  • Comments on "A study of users' buffer variations in random access satellite channels"

    Page(s): 1436
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    The commentors point out a problem with equation (6) of the above-named work (ibid., vol. COM-27, pp. 857-868, June 1979) that affects the subsequent values determined in the derivations presented and may make the paper's results inconclusive. View full abstract»

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  • Author's reply

    Page(s): 1436 - 1437
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    First Page of the Article
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  • Correction to "Receiver Windowing for FDM MFSK Signals"

    Page(s): 1437
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    An error to equation (25) in the above-named work (ibid., vol. COM-27, pp. 1519-1527, Oct. 1979) is corrected. View full abstract»

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  • [Back cover]

    Page(s): 0
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    Freely Available from IEEE
  • On Synchronization of Communication Networks with Varying Channel Delays

    Page(s): 1267 - 1268
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    Basic principles which ensure synchronization stability with respect to the delay variation are formulated. View full abstract»

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  • Synchronization of a Digital Network

    Page(s): 1285 - 1290
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    A brief description is given of synchronous and plesiochronous digital networks, with discussion of slip rate performance requirements. Various methods of synchronization are described with emphasis on the selection of the preselected alternate master-slave (PAMS) method. The evolution of a synchronized network is discussed, including basic topology rules, network stability, and domestic satellite considerations. To ensure that a given slip rate is maintained, a compatibility specification is proposed as the most effective method of defining equipment requirements for a synchronized network. View full abstract»

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  • Network Synchronization: Analysis of a Hybrid of Master-Slave and Mutual Synchronization

    Page(s): 1245 - 1259
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    The paper contains a proposal and an analysis of a hybrid method for synchronizing the clocks in a digital switching network to a more select group of "master clocks." The scheme is a hybrid of two well-known techniques, "mutual synchronization" and "masterslave," offering certain unique advantages. It allows different synchronizing disciplines for the masters (such as the toll switching machines) and the remaining subnetwork (composed, for example, of local switches). We begin by considering an idealized model containing only one master with constant clock frequency. The behavior of the controlled frequencies in the subnetwork is described by linear delay-differential equations with the delays determined by distances separating switches. We show that in all cases all clocks in the subnetwork approach in steady state the master clock frequency. Considerable emphasis is placed on the rate of synchronization, as determined by the principal root, the root with largest real part, of the characteristic function of the differential equations. The idealized model is extended in stages. First we consider the effects of many masters with constant but possibly nonidentical frequencies and show that the steady state frequencies in the subnetwork are narrowly bounded. Next, we allow clock drift and the master clocks to fluctuate about nominal centers with given tolerances. An expression for the residual steady-state departures from perfect synchronization shows the tradeoff between transient and stead-state behavior. Finally, two illustrative examples are numerically solved. View full abstract»

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  • An Electronic Hybrid with Adaptive Balancing for Telephony

    Page(s): 1399 - 1407
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    A new form of adaptive balancing hybrid is proposed for application to the two-wire to four-wire interface of a local digital switch. It is similar to an echo canceller but with a single degree of freedom and much simpler circuitry. In this paper a theory of operation of the hybrid is developed, and in a companion paper two circuit implementations and experimental results are reported. View full abstract»

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  • Phase Acquisition Statistics for Phase-Locked Loops

    Page(s): 1365 - 1372
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    Phase acquisition probabilities for phase-locked synchronizers are derived. Both self- and aided-acquisition techniques are investigated and compared. It is shown that so called "hang-up" can be prevented by using initial quadrant estimation to control appropriate slew voltage applied to VCO. View full abstract»

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  • Multilevel Quantized DPLL Behavior with Phase- and Frequency-Step Plus Noise Input

    Page(s): 1373 - 1382
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    A first-order nonuniform multilevel quantized DPLL is analyzed in the presence of a phase- and frequency-step signal plus Gaussian noise. The system is modeled as a homogeneous finite Markov chain. In this way, closed-form expressions are obtained for the steady-state probabilities, the mean and rms values of the phase error, and the mean number of samplings to slip a cycle or to reach acquisition. Numerical results are also presented. View full abstract»

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  • Synchronization for QPSK Transmission via Communications Satellites

    Page(s): 1302 - 1314
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    Carrier phase and symbol timing synchronization performances are determined for QPSK transmission over the nonlinear communications satellite channel with several typical modem filtering configurations. A computer simulation is used that models conventional or offset QPSK transmission, the modem filters, the nonlinear satellite TWTA, and the receive modem synchronizers. These simulations are used to obtain errors in carrier phase and symbol timing estimates caused by both thermal noise and the modulation-pattern-induced jitter. The statistics of these errors are obtained for several channel filtering combinations and TWTA backoff levels. These experiments are extended to examine the overall effect of synchronization errors on bit-error probability for one particular implementation of the synchronizers. View full abstract»

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  • Network Timing/Synchronization for Defense Communications

    Page(s): 1234 - 1244
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    The designers of synchronous switched digital communications networks have a large number of possibilities from which to choose a timing/synchronization system. Various combinations of the timing/synchronization system features described here can be used to characterize these possibilities. Advantages and disadvantages of employing different timing/synchronization features are examined, and their relationships to the more commonly discussed mutual and master-slave methods of network timing/synchronization are described. The need for particular timing system options is dependent on system applications. Significant differences in needed capability result from differences between civilian and military application. These differences are discussed, and the relationship between timing/ synchronization requirements of a wartime worldwide synchronous switched digital military communications network and timing system features is explored. View full abstract»

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  • Optimizing Pulse Shaping for Baseband Digital Transmission with Self-Bit Synchronization

    Page(s): 1164 - 1172
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    An effort is made to devise pulse shaping methods for self-bit-synchronizing systems that minimize both intersymbol interference and pattern-dependent jitter. Attention is confined to minimum-phase shaping which is considered from the standpoint of baseband applications. A short review of jitter analyses is also provided. It lays stress on discerning jitter components that accumulate along repeater chains from those that do not. Pulse shaping functions for the signal path, i.e., Nyquist's problem under minimum-phase constraint, are investigated first and found to result in Bessel filtering as well as its steepest descent modifications. It is observed that reducing intersymbol interference leads to increased pattern-dependent jitter. Next, pulse shaping functions for the timing path are developed. A broad sense symmetrical waveform concept produces a method of synthesizing shaping networks that can drastically reduce waveform dependent jitter, at the sacrifice of increased intersymbol interference. Finally, simultaneous minimizations of intersymbol interference and timing jitter are attempted. A minimal oscillatory tail shaping method incorporating a predistortion technique is shown to be quite efficient for this purpose and thus attractive for simple implementations. View full abstract»

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  • Carrier Recovery for Data Communication Systems with Adaptive Equalization

    Page(s): 1142 - 1153
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    This paper describes the problem of carrier recovery for adaptively equalized data communication receivers. A conventional receiver structure that employs baseband equalizers is considered first, and a practical method for jointly adjusting the demodulating carrier and the equalizer is briefly described. The reader is then introduced to an equalizer time delay problem critical to the system's performance. The first remedy for this problem involves the use of dual-mode carrier control loops. A method for designing such loops is presented and its use is illustrated by a conceptual design and a numerical example. The second remedy is to adopt a passband equalizer receiver structure. A tutorial introduction to this concept and a summary of the basic principles involved are presented. This paper concludes by reviewing related timing recovery problems. Joint design approaches such as the maximum likelihood estimate approach and the minimum mean-square error approach will be described and compared. View full abstract»

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  • Joint Carrier Phase and Symbol Timing Recovery for PAM Systems

    Page(s): 1121 - 1129
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    The detection of pulse amplitude modulation (PAM) carrier signals requires accurate symbol timing and carrier phase references. In most cases, it is desired to estimate these parameters directly from measurements on the received data signal. This paper adds to and unifies the theory of maximum likelihood [ML] estimation as applied to PAM timing and phase recovery. Several different estimation strategies are considered. Data-aided [DA] estimators are found which assume the transmitted data symbols are known at the receiver. Nondata-aided [NDA] estimators are found which require only knowledge of the statistics of the transmitted data symbols. Structures for estimation of symbol timing, carrier phase, and joint estimation of timing and phase are presented. The estimators are evaluated on the basis of their error variances. Relatively simple approximate expressions for these error variances are presented. These expressions allow the comparison of the effects of excess bandwidth, different modulation schemes, DA versus NDA recovery, and joint estimation versus estimation of only one parameter. A practical implementation of the ML estimator, termed a pseudo-maximum likelihood (PML) estimator, is proposed and analyzed. The performance of the PML estimator is shown to include a noise-independent, data-dependent jitter which dominates in many cases of practical interest. View full abstract»

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  • Statistical Performance of Single Dwell Serial Synchronization Systems

    Page(s): 1382 - 1388
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    Single dwell serial search techniques are common and useful for coarse time and frequency synchronization of spreadspectrum systems. A valuable system performance criterion, namely, the probability of successful synchronization for a single dwell serial synchronization system is derived. This probability is a function of the number of cells searched and is expressed in terms of the following four parameters: the dwell per cell, the detection probability, false alarm probability and the penalty time for a false alarm. Numerical results are presented to show the relationship between these parameters and system performance. View full abstract»

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  • A Second-Order Frequency-Aided Digital Phase-Locked Loop for Doppler Rate Tracking

    Page(s): 1431 - 1436
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    A second-order digital phase-locked loop (DPLL) has a finite lock range which is a function of the frequency of the incoming signal to be tracked. For this reason, it is not capable of tracking an input with Doppler rate for an indefinite period of time. In this correspondence, an analytical expression for the hold-in time is derived. In addition, an all-digital scheme to alleviate this problem is proposed based on the information obtained from estimating the input signal frequency. View full abstract»

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  • Jitter Accumulation in PAM Systems

    Page(s): 1172 - 1183
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    A new approach to the jitter accumulation problem in a chain of regenerative repeaters for pulse amplitude modulation systems is described. In each regeneration section the timing circuit consists of a square-law device followed by a bandpass filter with center frequency close to the transmission rate. It is shown that, from the standpoint of jitter generation and propagation, the timing circuit is equivalent to a low-pass filter driven by the sum of the jitter generated in the previous regenerator plus a noise term. This is actually the jitter propagation mechanism suggested in [6] and referred to as Chapman's model. What makes a difference with the results published in [6] is that in our analysis an expression is given for the spectral density of the noise in the equivalent model in terms of system parameters such as pulse shape, bandpass filter mistuning, offset in the triggering level of the pulse generator, etc. In this way the various jitter sources can be qualified and their effects evaluated. View full abstract»

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  • Frame Synchronization Techniques

    Page(s): 1204 - 1213
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    A basic theory of frame synchronization for a singlechannel digital communication system is presented, along with extensive references to the literature. The design of frame markers is discussed and comparisons are drawn with more exotic techniques such as comma-free coding. View full abstract»

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  • Optimization of the Processing Gain of and M-ary Direct Sequence Spread Spectrum Communication System

    Page(s): 1389 - 1398
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    In most realistic communication systems, be they spread spectrum or conventional systems, some overall bandwidth constraint is usually placed upon the system. In the case of spread spectrum communications, this constraint limits the amount of processing gain that the system can employ. In addition to processing gain, factors such as alphabet size affect the total bandwidth. It is the purpose of this paper to combine these two effects to determine how one should trade off the amount of processing gain one uses relative to the underlying modulation bandwidth when one is operating under the constraint of fixed total system bandwidth. View full abstract»

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  • Synchronized Clock for DMS-100 Family

    Page(s): 1276 - 1284
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    The advent of digital telephone switches, interconnected by digital carrier systems, makes it possible to route and transmit telephone and data signals virtually without deterioration over many links and through many switching nodes. No bits of the digitized speech or data, however, should be lost en route; an economical method to ensure this is to operate the entire digital telephone system (of a country) synchronously. A highly stable master frequency reference is established from which all digital switching centers derive their clocking, either directly by national distribution of the reference frequency, or through the means of the (pulse-code modulation) PCM transmission systems which interconnect the switches. Operating considerations require that the synchronized clock systems of every switch can survive outages of equipment or synchronizing links without major impact on telephone service. The present paper is concerned with the design and performance of the synchronized clock system as an integral part of a large digital telephone switching office. Clocking and synchronization hardware and software algorithms have been developed to allow a switching office to be synchronized by external reference standards or over digital carrier links. The components of the synchronization system of an office are distributed in peripheral interface hardware, digitally controlled clock hardware, and a feedback algorithm implemented in the software of the switching computer. Steady-state and dynamic behavior are analyzed for a single switch and a timing network. Mathematical analysis is supported by simulation results. Special attention is given to quantization effects and maintenance considerations. View full abstract»

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  • Implementation of an Adaptive Balancing Hybrid

    Page(s): 1408 - 1416
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    Two implementations of an adaptive balancing hybrid are described. The first is predominly analog, in which the adaptation parameter θ is a continuous analog quantity, while the second is predominly digital, in which θ has a two-bit representation. Experimental results are reported. View full abstract»

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  • Survey of Synchronization Techniques for a TDMA Satellite-Switched System

    Page(s): 1291 - 1301
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    On-board processing of signals in a communications satellite system is rapidly becoming a reality. To meet the needs in high capacity systems, new technologies are being developed, and one of the most recent is the system called time-division multiple-access, satellite-switched (TDMA/SS) which employs multiple spot beam zones. Since TDMA is employed, it is necessary for all earth stations to synchronize their time bases to a common reference which, in this case, is the sync window connection of the satellite. Synchronization for this system is a major problem which has been examined in detail in a number of different papers. This paper provides a survey of the various techniques which have been proposed in the past and gives a comparative analysis of the advantages and disadvantages of each. Factors taken into account include timing accuracy, bit energy to noise density ratio of difference signals, estimated delay for acquiring acquisition, tracking features, microcomputer implementation, and possible improvements for the future. 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