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Communications, IEEE Transactions on

Issue 5 • Date May 1987

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Displaying Results 1 - 19 of 19
  • [Front cover and table of contents]

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  • [Back cover]

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  • Code Acquisition for a Frequency-Hopping System

    Page(s): 566 - 568
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    Code acquisition for a frequency-hopping code-division multiple-access system using Reed-Solomon coding is investigated. The one-coincidence codes which minimize the user interference are shown to be well suited for initial synchronization but are less appropriate for regaining synchronism during transmission. A modified code construction is proposed, which has good capability of both startup and resynchronization. View full abstract»

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  • Routing in the Manhattan Street Network

    Page(s): 503 - 512
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    The Manhattan Street Network is a regular, two-connected network, designed for packet communications in a local or metropolitan area. It operates as a slotted system, similar to conventional loop networks. Unlike loop networks, routing decisions must be made at every node in this network. In this paper, several distributed routing rules are investigated that take advantage of the regular structure of the network. In an operational network, irregularities occur in the structure because of the addressing mechanisms, adding single nodes, and failures. A fractional addressing scheme is described that makes it possible to add new rows or columns to the network without changing the addresses of existing nodes. A technique is described for adding one node at a time to the network, while changing only two existing links. Finally, two procedures are described that allow the network to adapt to node or link failures. The effect that irregularities have on routing mechanisms designed for a regular structure is investigated. View full abstract»

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  • Comparison of Routing Procedures for Circuit-Switched Traffic in Nonhierarchical Networks

    Page(s): 535 - 544
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    In this paper, we compare the use of different types of routing procedures for circuit-switched traffic in nonhierarchical networks. The main performance criterion used is the end-to-end blocking probability. The results show that if the network traffic is light, alternate routing performs better than nonalternate routing, but if the network traffic is heavy, the situation is reversed. To improve the performance of networks using alternate routing, different types of strategies varying from fixed control to dynamic control are introduced. A comparison based on numerical examples shows the improvement in performance attained by using a dynamic control strategy compared to fixed control. Good control techniques result in nonalternate routing under heavy traffic loads; nonalternate routing is the most viable alternative in nonhierarchical networks under heavy traffic conditions. View full abstract»

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  • Analysis and Modeling of Intermodulation Distortion in Wide-Band Cable TV Channels

    Page(s): 568 - 572
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    This correspondence deals with the development of a practical approach for the assessment of intermodulation distortion in modern cable television (CATV) systems operating over the 400 MHz range. In particular, Volterra series expansions are used in establishing appropriate high-frequency models for the description of such wide-band CATV channels. Furthermore, experimental measurements made on a typical system are utilized to illustrate the development of Volterra models which may be used subsequently in the prediction of intermodulation distortion in such systems. View full abstract»

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  • Oversampled Sigma-Delta Modulation

    Page(s): 481 - 489
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    Oversampled sigma-delta modulation has been proposed as a practical implementation for high rate analog-to-digital conversion because of its simplicity and its robustness against circuit imperfections. To date, mathematical developments of the basic properties of such systems have been based either on simplified continuous-time approximate models or on linearized discrete-time models where the quantizer is replaced by an additive white uniform noise source. In this paper, we rigorously derive several basic properties of a simple discrete-time single integrator loop sigma-delta modulator with an accumulate-and-dump demodulator. The derivation does not require any assumptions on the correlation or distribution of the quantizer error, and hence involves no linearization of the nonlinear system, but it does show that when the input is constant, the state sequence of the integrator in the encoder loop can be modeled exactly as a linear system in an appropriate space. Two basic properties are developed: 1) the behavior of the sigma-delta quantizer when driven by a constant input and its relation to uniform quantization, and 2) the rate-distortion tradeoffs between the oversampling ratio and the average mean-squared quantization error. View full abstract»

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  • Time-Stamp Approach to Store-and-Forward Deadlock Prevention

    Page(s): 490 - 495
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    This paper deals with the problem of store-and-forward deadlock prevention in store-and-forward networks. The presented solution uses time stamping of all messages in the network, and a nonpreemptable message exchange mechanism. By combining these ideas, a new distributed flow control procedure is derived which guarantees that all messages are delivered to their own destinations, thus avoiding both deadlock and livelock without any message loss. It is shown that some properties of this procedure depend on the policy of the allocation of exchange buffers to nodes. On the one hand, an optimal allocation strategy is presented which results in a maximally optimal deadlock prevention procedure. The procedure is network sizeand topology-independent and allows unrestricted packet routing. On the other hand, the allocation of one exchange buffer per node is discussed, which, even if not optimal, makes the derived deadlock prevention procedure completely independent of network reconfigurations. The last feature is extremely important from the practical point of view and, therefore, such a solution is strongly recommended. When compared to store-and-forward deadlock prevention procedures described so far, which lack some or all of these desirable properties, the procedure presented here behaves favorably. However, it imposes other drawbacks, i.e., the possibility of extra hops as a result of exchange operations. It is argued that this drawback appears rarely in practice, and some strategies which aim at a reduction of it are proposed. View full abstract»

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  • Announced Arrival Random Access Protocols

    Page(s): 513 - 521
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    In this paper we propose and evaluate several protocols for a random access channel. The channel is divided into a control subchannel which is used to inform all users of the approximate times of arrival of new packets and a data subchannel which is used to transmit the data. Packets arriving at different users at approximately the same time may cause a collision on the control subchannel. Such collisions are resolved on the data subchannel by a collision resolution algorithm. Eight protocols that differ in the feedback available on both channels and the time that the feedback is available are described and evaluated. The expected delay of each protocol is determined by modeling the system as a slotted concentrator. Comparisons are made among the protocols described and analyzed in this paper and between these protocols and other protocols that have been studied previously. View full abstract»

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  • Configuration and Characteristics of a Fiber-Optic Video Distribution System

    Page(s): 522 - 528
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    A multiservice fiber-optic subscriber system using wavelength division multiplexing technology has been developed by Nippon Telegraph and Telephone Corporation to provide both 64 kbits/s and broad-band communication services on a single multimode fiber. The subscriber network is formed in a star topology to facilitate bidirectional connection. The system was put in service in March, 1985, as part of the information network system (INS) model system. This paper describes the configuration and characteristics of the video distribution system of this fiber-optic subscriber system. The distribution system uses analog baseband video transmission at a 0.89μm wavelength. The video channel selection is made by an FDM video tuner installed in a central office. The overall performance successfully met design objectives. View full abstract»

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  • A Minimum Mean-Square Error Equalizer for Nonlinear Satellite Channels

    Page(s): 556 - 560
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    The problem of designing and evaluating the performance of a minimum mean-square error equalizer (MMSEE) for binary PSK transmission over band-limited nonlinear satellite channels is considered in this correspondence. The effect of intersymbol interference followed by AM/AM and AM/PM conversions are taken into account while optimizing the performance in the presence of the downlink white Gaussian noise. In analyzing the problem, the decision is made on a typical signal in a received sequence taking into account past and future interfering signals, i.e., ISI. As an illustrative example of the receiver, a typical channel model is considered in details. Based on the analysis, an alternative receiver structure which is more suitable for implementation is introduced. The taps gain coefficients for minimum mean-square error, between the received sample and the actual transmitted bit, are obtained using numerical methods. The performance of the equalizer is evaluated using computer simulation techniques and it is shown that significant performance improvement over the single-sample sign detector can be obtained. View full abstract»

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  • The Minimum Likelihood--A New Concept for Bit Synchronization

    Page(s): 545 - 549
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    A new bit synchronization concept based on the "minimum likelihood" criterion instead of the conventional "maximum likelihood" concept is developed. The minimum likelihood situation is even easier to reach than the maximum likelihood because the derivative of the log likelihood function becomes identically zero there. Minimum likelihood implies "least likely" for synchronization (the worst case synchronization error) or an "orthogonal" timing condition which simply means that the locally generated clock is synchronized correctly, but with a delay of a half bit period. The structure and performance of the minimum likelihood bit synchronizer are discussed in detail in this paper. The results indicate that the minimum likelihood bit synchronizer has a much simpler structure, but with performance very close to the optimal maximum likelihood synchronizer. View full abstract»

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  • The Effect of Idle Server First Random Routing on the Behavior of a Finite Queue

    Page(s): 496 - 502
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    This paper studies the effect of routing on the behavior of a finite queue which accepts batch Poisson inputs and receives service from multiple synchronous servers. Upon the arrival of a group of customers idle or pseudoidle servers will be considered first in routing decisions. Otherwise routing will be determined randomly in accordance with a preset probability distribution. Results obtained include state probability, blocking probability, delay, and throughput. Validity of analysis has been verified by computer simulations. These results can he used in evaluating the performance of a computer communication network. View full abstract»

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  • Time-Stamp Approach to Prevention of Different Deadlock Types in Store-and-Forward Networks

    Page(s): 564 - 566
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    This correspondence is concerned with the prevention of four types of deadlock in store-and-forward networks, i.e., progeny, copy-release, reassembly, and resequence deadlocks. The approach presented makes use of time stamping of all messages and generalizes the method of store-and-forward deadlock prevention. View full abstract»

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  • Common Pitfalls in the Application of Stationary Process Theory to Time-Sampled and Modulated Signals

    Page(s): 529 - 534
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    The common practice of applying the theory of stationary stochastic processes to a cyclostationary process by introducing random phase(s) into the probabilistic model in order to stationarize the process can lead to erroneous results, such as incorrect formulas for power spectral density. This is illustrated by showing that commonly used formulas for signals that have undergone frequency conversion or time sampling can be incorrect. The source of error is shown to be inappropriate phase-randomization procedures. The correct procedure is described, and corrected formulas are given. The problem is further illustrated by showing that commonly used resolution and reliability (mean and variance) formulas for spectrum analyzers must be corrected for cyclostationary signals. It is explained that all corrections to formulas reflect the effects of spectral correlation. These effects are inappropriately averaged out by inappropriate phase-randomization procedures. It is further explained that these inappropriate procedures destroy the important property of ergodicity of the probabilistic model. View full abstract»

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  • Optimization of Generalized Tamed Frequency Modulation Bit Error Rate Performance Subject to a Bandwidth Constraint

    Page(s): 560 - 564
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    This paper deals with the optimization of coherent generalized tamed frequency modulation (GTFM). The optimization is carried out over certain parameters of the modulation scheme to give the best BER (bit error rate) performance, subject to a bandwidth constraint. The optimization is done by an algorithm which uses the upper bound on the squared Euclidean distance as a metric of the BER performance and the power spectra at a certain frequency as a metric of the bandwidth. It is concluded that when the modulation index is not restricted to 0.5, a theoretic improvement of 1.9 dB over the BER performance of GTFM is achievable, with equal bandwidths as a basis of comparison. View full abstract»

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  • Adaptive Diversity Reception Over a Slow Nonselective Fading Channel

    Page(s): 572 - 574
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    We extend some previous results on adaptive receivers with memory for slow nonselective Rayleigh fading channels to the case of diversity reception. The Bayes receiver in this case is shown to be a generalized maximal ratio combiner. Error probability performance is obtained for antipodal signals such as BPSK. A simple performance upper bound is also derived. Numerical performance results are presented for the particular case of a Markov channel model. View full abstract»

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  • Performance of RS-BCH Concatenated Codes and BCH Single-Stage Codes on an Interference Satellite Channel

    Page(s): 550 - 556
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    In this correspondence, a model is analyzed that was designed to study interference on satellite channels. We developed this model to obtain performance results for a coherent phase-shift keyed (CPSK) system in which RS-BCH concatenated codes and BCH singlestage codes are applied to a satellite channel corrupted by cochannel interference. These results make use of earlier work on performance analysis of an m -phase CPSK system operating in the presence of random Gaussian noise and non-Gaussian interference. Earlier work on performance evaluation of concatenated codes on an equierror channel is also used. Our model incorporates features that account for the burst behavior of the interference sources. Results indicate that the use of RS-BCH concatenated coding provides significant performance improvement over no coding as well as single-stage BCH coding. 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