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Communications, IEEE Transactions on

Issue 6 • Date June 1984

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Displaying Results 1 - 16 of 16
  • [Front cover and table of contents]

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  • [Back cover]

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  • Computationally Optimal Metric-First Code Tree Search Algorithms

    Page(s): 710 - 717
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    Code tree search algorithms find wide applicability in source encoding, channel decoding, pattern recognition, and maximum likelihood sequence estimation. These algorithms search code trees and may be classified as depth-first, breadth-first, and metric-first depending on the search criterion employed. We define here a criterion for metric-first algorithms to be optimal. We show that implementations of metric-first searches proposed heretofore are not optimal, and we propose and analyze two algorithms which are. Experimental data obtained by encoding a voiced speech sound point to superiority of the proposed implementation over earlier versions. View full abstract»

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  • An Improved Broadcast Retransmission Protocol

    Page(s): 679 - 683
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    A recent paper by Calo and Easton proposes a broadcast protocol for identical file transfers toMdifferent sites wherein a large block of transmitted data is divided intoNframes ofBbits each, and in a second transmission cycle all frames not acknowledged by all sites are retransmitted. This paper shows several versions of a different technique which can result in better efficiency. In the technique, additional frames sent are not exact replicas of initially unacknowledged frames, but are chosen to provide additional information to all sites having one or more nondecodable frames. New frames are sent to provide additional information until all sites acknowledge the entire block. View full abstract»

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  • Probability of Error Analyses of a BFSK Frequency-Hopping System with Diversity Under Partial-Band Jamming Interference--Part I: Performance of Square-Law Linear Combining Soft Decision Receiver

    Page(s): 645 - 653
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    In this paper, error probability analyses are performed for a binary frequency-shift-keying (BFSK) system employingLhop/bit frequency-hopping (FH) spread-spectrum waveforms transmitted over a partial-band Gaussian noise jamming channel. The error probabilities for theLhop/bit BFSK/FH systems are obtained as the performance measure of the square-law linear combining soft decision receiver under the assumption of the worst-case partial-band jamming. The receiver in our analysis assumes no knowledge of jamming state (side information). Both exact and approximate (multiple bound-parameter Chernoff bound) solutions are obtained under two separate assumptions: with and without the system's thermal noise in the analyses. Numerical results of the error rates are graphically displayed as a function of signal-to-jamming power ratio withLand signal-to-noise ratio as parameters. All of our results, exact and approximate, indicated that the higher number of hops per bit produced higher error probabilities as a result of increased combining losses when the square-law linear combining soft decision receiver is employed in demodulating the multihop-per-bit waveform. View full abstract»

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  • Mathematical Models for Cochannel Interference in FH/MFSK Multiple-Access Systems

    Page(s): 670 - 678
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    FH/MFSK has been Proposed for a multiuser spread spectrum digital communication system to combat both self-jamming and intentional jamming. An independence assumption at the energy detector outputs is used to evaluate such a system for a digitized voice mobile radio system [11]. This paper presents a correlated model and compares its performance to an independence model under the symbol error probability criterion. A Gaussian process model is also developed for comparison. It is found that the conventional Gaussian approximation is inadequate in predicting the number of users that can be accommodated by an FH/MFSK system using the conventional receiver. Furthermore, for the cases we evaluated, the independence model provides an excellent approximation to the correlated model. Additionally, a conditional Chernoff bound is presented for the more general case of frequency-hopping systems with multiple hops per symbol. View full abstract»

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  • An Adaptive Receiver with Memory for Slowly Fading Channels

    Page(s): 654 - 659
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    We consider the problem of designing an adaptive receiver with anM-bit memory for binary orthogonal signaling over a slowly fading Rayleigh channel. Both the cases of decision-feedback and no decision-feedback are considered. We present a problem formulation by defining the contents of the receiver's memory. The structure of the Bayes receiver that makes optimum use of the memory information is then established. The LRT that defines the receiver is obtained explicitly, and it dictates a detector-estimator receiver structure. The detector can be interpreted as being partially coherent, with coherence being achieved asymptotically in the limit of perfect estimation of the fading process. Simulation results are given to show the improved error rate performance of the adaptive receiver. Our results also indicate that decision-feedback should be employed in a manner dependent on the SNR. View full abstract»

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  • Recursive Estimation of Local Characteristics of Edges in TV Pictures as Applied to ADPCM Coding

    Page(s): 718 - 728
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    In this paper, an algorithm is presented for extracting edges and estimating their local characteristics in TV pictures; the algorithm is designed for application to adaptive DPCM coding of TV pictures and it has the following properties: 1) it takes into account the causality constraint encountered in DPCM coding; 2) it is fitted to the line-by-line scanning of TV pictures; 3) it is fast, involving only a small amount of computation, and thus allowing real-time implementation. The whole processing is split into a local preprocessing and a global processing where the characteristics of the edges are renewed recursively line by line. This algorithm was used for implementing an adaptive choice of the prediction in DPCM coding of TV pictures. View full abstract»

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  • An Acknowledgement-Based Access Scheme in a Two-Node Packet-Radio Network

    Page(s): 741 - 744
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    A two-node packet-radio network with infinite buffers at the nodes is considered. The two nodes transmit data packets to a common station through a shared radio channel. One of the two nodes is granted full access rights to the channel, while the other node bases its decisions whether to transmit or not on the acknowledgments it receives about its transmissions. For this acknowledgment-based access scheme and for general arrival processes, we derive the joint generating function of the queue contents in steady state, as well as the condition for steady state. From the generating function, any moment can be derived, as well as average time delays. Numerical results are presented for independent Bernoulli arrival processes. View full abstract»

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  • Delay Analysis for a TDMA Channel with Contiguous Output and Poisson Message Arrival

    Page(s): 707 - 709
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    An analysis of the exact delay of a TDMA or a loop communication system with a contiguous output and a Poisson message arrival process is presented. The nonlinear relationship of a contiguous output with arbitrary arrival process can be expressed by an infinite series. In the case of a Poisson message arrival process, the series can be summed to a closed form. The derived result, which is validated by simulation, is a vast improvement over the previously used approximate model of multiple frames with single output. View full abstract»

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  • The Spatial Capacity of a Slotted ALOHA Multihop Packet Radio Network with Capture

    Page(s): 684 - 694
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    In this paper we determine throughput equations for a packet radio network where terminals are randomly distributed on the plane, are able to capture transmitted signals, and use slotted ALOHA to access the channel. We find that the throughput of the network is a strictly increasing function of the receiver's ability to capture signals, and depends on the transmission range of the terminals and their probability of transmitting packets. Under ideal circumstances, we show the expected fraction of terminals in the network that are engaged in successful traffic in any slot does not exceed 21 percent. View full abstract»

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  • Performance Analysis of Integrated Voice and Data Hybrid-Switched Links

    Page(s): 695 - 706
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    Numerical techniques for the solution of a class of twodimensional Markov processes are presented. These techniques are used to analyze the performance of several versions of hybrid switching including the movable boundary scheme with finite or infinite buffers, with flow control, and with or without TASI. Also included are results for TASI in which the number of off-hook calls is not fixed. Finally, the accuracy of the quasi-static approximation is evaluated for several problems. View full abstract»

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  • Bit Error Rate Evaluation for Spread-Spectrum Multiple-Access Systems

    Page(s): 660 - 669
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    A unified method for approximating and bounding the average bit error probability for spread-spectrum multiple-access communication systems is presented. Various forms of direct-sequence spreadspectrum modulation are considered including binary phase-shift keying, quadriphase-shift keying, and minimum-shift keying. The analysis of the multiple-access interference makes use of a number of moments sufficent to evaluate the error probability with a high degree of accuracy. A computationally efficient algorithm for computing the moments is also given. The subsequent transformation from the moments to the average bit error probability is carried out by means of Gauss-type numerical integration formulas. It is shown that the same approach can be exploited for evaluating two classes of upper and lower bounds on the bit error rate. Finally, some results and comparisons are reported. View full abstract»

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  • Interpolative DPCM

    Page(s): 729 - 736
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    Recent results have established that DPCM is quite inefficient when encoding tightly correlated autoregressive sources at low rates. This work presents a slightly more complex code generator based on interpolation for rate 1 encoding of such sources and evaluates its performance via simulation for Gaussian and Laplacian distributed general stationary autoregressive sources. Improvements in the range of 3 dB over the LMS predictive quantizer for speech-like correlated sources at rate 1 have been realized with no tree searching. Another 1 dB is gained with a moderate tree searching. The code generator is less sensitive to the quantizer step size and a locally mismatched source than DPCM, two desirable features for encod, ing quasi-stationary sources. View full abstract»

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  • On the Design of Optimal Policy for Sharing Finite Buffers

    Page(s): 737 - 740
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    An important analytic model of finite buffer systems is a multiclass single queue with typed servers. In the context of such a model, we address the problem of selecting an optimal buffer sharing policy. We show that with respect to weighted throughput, an optimal policy must be a stationary delayed resolution policy. An iterative procedure based upon the policy iteration method for Markov processes with rewards is used to efficiently search for the optimal delayed resolution policy for a given set of system parameters. A performance comparison of the optimal delayed resolution policy with other well-known buffer sharing policies is also provided. 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