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Communications, IEEE Transactions on

Issue 9 • Date September 1983

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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
  • Comments on "Optimal Retransmission Control of Slotted ALOHA Systems"

    Page(s): 1112
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    A controlled Markov model of the slotted ALOHA system in which the control parameter is the retransmission probability and a set of controls is the interval [0, 1] is considered. Numerical results are presented which show that the policy which maximizes the system's expected packet flow per time slot is not optimal. It is shown that, although it is not optimal, this policy can be considerably better than the optimal two-action control-limit policy. View full abstract»

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  • [Back cover]

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    Freely Available from IEEE
  • Frequency-Selective Fading Effects in Digital Mobile Radio with Diversity Combining

    Page(s): 1085 - 1094
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    we analyze the effects of frequency-selective fading in a cellular mobile radio system that uses 1) phase-shift keying (PSK) with cosine rolloff pulses, and 2) space diversity with maximal-radio combining. The distorting phenomena with which we deal are multipath fading (which produces the frequency selectivity), shadow fading, and cochannel interference. The relevant quality measure is defined to be the bit error rate averaged over the multipath fading, denoted by (BER). The relevant system performance characteristic is defined to be the probability distribution for (BER), taken over the ensemble of shadow fadings and locations of the desired and interfering mobiles. To obtain numerical results, we use a combination of analysis and Monte Carlo simulation, invoke widely accepted models for the multipath and shadow fadings, and assume a cellular system with seven channel sets and centrally located base stations. The outcome is a set of performance curves that reveal the influences of various system and channel parameters. These include: the number of modulation levels (two or four), the diversity order, the shape of the multipath delay spectrum, and the standard deviation (or delay spread, τ0) of the multipath delay spectrum. Practical factors accounted for in these assessments include fading- and interference-related timing recovery errors and combiner imperfections. Our results highlight the importance of the ratio \tau _{0}/T , where T is the digital symbol period. They show that the delay spectrum shape is of no importance for \tau _{0}/T \leq 0.2 , but can have a profound influence for \tau _{0}/T \geq 0.3 . We also find that using 4-PSK leads to better detection performance, in certain cases, than using 2-PSK. View full abstract»

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  • A Class of Phase Detector Characteristics for Symbol Synchronizers Yielding Unbiased Estimates

    Page(s): 1033 - 1036
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    Most practical synchronizers operating on a PAM waveform corrupted by additive noise can be analyzed by means of the theory of the phase-locked loop (PLL). In this paper, we present a class of synchronizers for which the equivalent phase detector characteristic is such that the timing instants generated by the voltage controlled clock (VCC) are unbiased with respect to the ideal sampling instants to be used in the data reconstruction path. As a consequence of this, the VCC output signal can directly activate the sampler in the data reconstruction path, without being properly delayed for bias compensation. View full abstract»

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  • An Incremental Capacity-Allocation Algorithm for Voice/Data Networks

    Page(s): 1113 - 1114
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    An algorithm is described by which TDM slots in many links of a network can be optimally allocated between voice and data. It is an adaptation of a convex-programming method due to Fox, by which a pool of resources is allocated to minimize a convex separable criterion function such as blocking probability for voice subject to a single convex separable constraint such as specified maximum mean delay to data. In our case the single pool of resources is the total of the available slots. The necessary adaptation of Fox's algorithm is described for the minimum blocking problem, and for minimum data delay subject to a blocking constraint. View full abstract»

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  • Dynamic Scheduling Protocols for a Multiple-Access Channel

    Page(s): 1046 - 1055
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    In this paper the multiple-access problem in a packet network is considered. A finite number of independent, packet transmitting users is assumed. Protocols are developed to allocate the channel resources among the users. Part of the channel capacity is assigned to control information. This information is used to make probabilistic inferences of the queue lengths and delay characteristics of the users. The probabilistic inferences are used to develop dynamic scheduling protocols for data transmission. Protocols are developed for two different levels of control information. An analysis of the relationship between amount of control information and system performance is carried out, and a study of the frequency of transmission of control information is also provided. View full abstract»

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  • A Simple Lower Bound on the Linearized Performance of Practical Symbol Synchronizers

    Page(s): 1029 - 1032
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    In this paper we present a lower bound on the linearized mean-square timing error resulting from a practical synchronizer estimating the delay of a baseband PAM waveform which is corrupted by stationary Gaussian noise. This lower bound is easily evaluated, and applies to a broad class of synchronizers. View full abstract»

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  • Optimal Symbol-by-Symbol Detection for Duobinary Signaling

    Page(s): 1077 - 1085
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    An optimal symbol-by-symbol detection scheme for duobinary signaling (Class I PRS) which exploits the inherent correlation properties of partial response signaling (PRS) is postulated. Analytical results indicate a maximum improvement of approximately 0.7 dB over conventional split shaping duobinary detection at a 10-4error rate. Although duobinary signaling is emphasized, sufficient generality within the formulation is maintained to accommodate any class of PRS. View full abstract»

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  • A Systematic Methodology for Analyzing Security Threats to Interprocess Communication in a Distributed System

    Page(s): 1055 - 1063
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    It is observed that a direct mapping exists between a distributed system's physical configuration and the security threats that can be mounted against interprocess communication in that system. A systematic methodology is presented which implements that mapping for a large class of distributed systems. The methodology includes a model of threats to interprocess communication as well as a model of distributed system security configurations. This methodology is useful in situations where certain major characteristics of the distributed system physical configuration will remain stable over a long time. View full abstract»

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  • A Simple Method of Estimating Multipath Fade Model Parameters from Measurements on Existing Analog Links

    Page(s): 1103 - 1109
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    A theoretical analysis of the problem of estimating frequency selective fade model parameters from measurements on existing analog links is presented. These measurements essentially consist of obtaining records of AGC and continuity pilot level variations from which a first approximation of a, \alpha , \omega _{0} , and τ (fade model parameters) can be obtained. Field results obtained on a working link in New Zealand are reported. View full abstract»

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  • Design and Performance of WDM Transmission Systems at 6.3 Mbits/s

    Page(s): 1095 - 1102
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    One- and two-way 6.3 Mbit/s optical transmission systems employing wavelength-division-multiplexing (WDM) are designed for application to telephone networks. Multiplexing at two wavelengths, 1200 and 1300 nm, as well as that at 810 and 890 nm, is found to be effective after taking the application fields and present fabrication techniques for optical multiplexers into account. Requirements for optical multiplexers are clarified through SNR design in which crosstalk is dealt with effectively. Optical multiplexers composed of newly developed dielectric multilayer thin-film filters are designed to meet the systems' requirements, and good transmission quality is confirmed for the systems by experiments. View full abstract»

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  • Interfade Interval Statistics of a Rayleigh-Distributed Wave

    Page(s): 1114 - 1116
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    This paper presents distributions of the intervals between fades measured on a hardware-simulated Rayleigh-fading mobile radio channel. For intervals between deep fades, these distributions take on a Poisson form. Measured results are in good agreement with a simple analytical model. Distributions for the intervals between shallower fades exhibit preferred durations caused by peaks in the Doppler fading spectrum. View full abstract»

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  • Synchronous and Channel-Sense Asynchronous Dynamic Group-Random-Access Schemes for Multiple-Access Communications

    Page(s): 1063 - 1077
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    Adaptive random-access schemes are introduced and analyzed to provide access-control supervision for a multiple-access communication channel. The dynamic group-random-access (DGRA) schemes introduced in this paper implement an adaptive GRA structure. An active terminal transmits its ready packet at random within the next specified time period. Colliding packets are retransmitted at a random slot within the next time period. The duration of each time period is dynamically determined in accordance with the observed state of the channel during the previous time period. Synchronous and carrier-sense asynchronous DGRA procedures, the latter employing collision detection and/or idle detection, are considered. The schemes are shown to exhibit good delay-throughput characteristics. The carrier-sense ADGRA/ID scheme, employing idle detection, is shown to yield superior performance to that exhibited by other carrier-sense schemes, over a wide range of operational parameters. View full abstract»

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  • Decoding with Stretched Pulses in Laser PPM Communications

    Page(s): 1037 - 1045
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    The design and performance of optical PPM communication systems with ideal (rectangular) pulses have been well documented. However, many optical channels (fibers, atmosphere, clouds) are extremely dispersive to narrow pulses, producing receiver pulses that are spread (stretched) in time. This stretching produces interslot interference within a PPM frame, and if severe enough, can stretch over several frames (intersymbol interference). In this paper, laser pulse stretching in optical PPM formats is investigated in terms of performance degradation and decoder design alternatives. Several methods are considered for combating the pulse stretching, including pulse equalization, extended pulse integration, and pulse shape matching. Performance of these methods is compared for the case of exponential stretching and Gaussian statistics. View full abstract»

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  • Signal Sets with Optimal Correlation Properties

    Page(s): 1109 - 1112
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    Rowe has developed an upper bound on the number of vectors possible in a d -dimensional space, given that the vectors of the set are divided into orthogonal alphabets and subject to an appropriately defined root-mean-square correlation constraint Crms. Here, signal set design procedures are presented that are near optimal with respect to Rowe's upper bound. The specific parameters of these signal set construction techniques are significant as they illustrate the tightness of the upper bound for situations that have not been previously addressed. Finally, a signal set design procedure is presented that serves as an improvement to a lower bound originally reported by Rowe. 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