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Communications, IEEE Transactions on

Issue 8 • Date August 1987

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Displaying Results 1 - 20 of 20
  • [Front cover and table of contents]

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  • [Back cover]

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  • Rearrangeability of the Five-Stage Shuffle/Exchange Network for N = 8

    Page(s): 808 - 812
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    In this paper we prove the rearrangeubility of a multistage shuffle/exchange network with eight inputs and outputs consisting of five stages. A lower bound of (2 log_{2} N - 1) stages for rearrangeability of a Shuffle/exchange network withN = 2^{n}inputs and outputs is known; we show its sufficiency forN = 8. We not only prove the rearrangeability, but also describe an algorithm for routing arbitrary permutations on the network and prove its correctness. In contrast to previous efforts to prove rearrangeability, which rely on topological equivalence to the Benes class of rearrangeable networks, our approach is based on first principles. We also show that two switches in the network are redundant. The results in this paper are useful for establishing an upper bound of (3 log_{2} N - 4) stages for rearrangeability of a multistage shuffle/exchange network withN geq 8, as demonstrated in [12]. View full abstract»

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  • Independent Stations Algorithm for the Maximization of One-Step Throughput in a Multiaccess Channel

    Page(s): 795 - 800
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    In the class of multiple-access schemes utilizing channel feedback information, one has generally to face a multistep control problem. In order to simplify the structure of the access strategies, a single-step horizon can be considered, so that the goal becomes the maximization of the probability of transmission at each slot. However, even in this case the optimal solution turns out to be intractable for a large number of stations. To avoid this intractability some simplifying assumptions can be made at the price of a certain degree of suboptimality. Our approach is based on an independence assumption and yields a scheme which can be termed an independent stations approach (ISA). View full abstract»

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  • Frame Synchronization for Gaussian Channels

    Page(s): 818 - 829
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    The problem of locating a periodically inserted frame synchronization pattern in random data for aM-ary digital communication system operating over the additive white Gaussian noise channel is considered. The optimum maximum-likelihood decision rule, high signal-to-noise approximate maximum likelihood decision rule, and ordinary correlation decision rule for frame synchronization are derived for both coherent and noncoherent phase demodulation. A general lower bound on synchronization probability is derived for the coherent correlation rule. Monte Carlo computer simulations of all three decision rules, along with evaluations of the lower bound for the coherent correlation rule, were performed for the coherent MPSK, coherent, and noncoherentMary orthogonal, and 16 QAM signaling schemes. These results show that in each case the high signal-to-noise maximum-likelihood rules have a performance nearly equal to that of the maximum-likelihood rules over a wide range of practically interesting signal-to-noise ratios (SNR's). These high SNR decision rules also provide significant performance improvement over the simple correlation rules. Moreover, they are much simpler to implement than the maximum-likelihood decision rules and, in fact, are no more complex than the correlation rules. View full abstract»

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  • Estimating Time Congestion from Traffic Parameters

    Page(s): 856 - 862
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    We address the problem of estimating the time congestion on a finite trunk group from the size of the group and the mean and peakedness factor of the offered traffic. In order to be able to assess the relative merits of the various estimates, we adopt a common setting where the offered traffic is simple overflow traffic. Next to giving brief descriptions of earlier results, we elaborate on some of the earlier suggestions, and discuss some new approaches to the problem. Our numerical evaluation of the various approximations for time congestion induced by simple overflow traffic distinctly reveals the superiority of a variant of Frederieks' approximation procedure. View full abstract»

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  • An Algorithm for Detecting and Resolving Store-and-Forward Deadlocks in Packet-Switched Networks

    Page(s): 801 - 807
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    Freedom from store-and-forward (S/F) deadlocks in a packet-switched network can be guaranteed with the use of deadlock avoidance protocols. However, these protocols put so many restrictions on the use of buffers that even under normal circumstances the buffer utilization is small. We propose instead a deadlock detection and resolution algorithm that is completely invisible under normal circumstances. As soon as certain channels in the network have trouble in accepting and transmitting packets due to the lack of buffers, the deadlock detection phase of the algorithm is invoked. When a deadlock is identified, the deadlock resolving phase of the algorithm is executed. Once the deadlock is resolved, the control is removed. The algorithm can be used in conjunction with either the complete partitioning or the sharing with maximum queue lengths output buffer allocation strategies. A proof on the correctness of the algorithm is given. Simulation results show that the network can maintain a relatively high throughput even when deadlocks are being detected and resolved. In addition, several properties of deadlocks are shown: i) deadlocks start to increase abruptly once the network operates beyond its capacity; and ii) under heavy load conditions, increasing the buffer pool size will not delay the occurrence of deadlocks. View full abstract»

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  • Timing Recovery in the Presence of a Residual Echo Signal

    Page(s): 830 - 833
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    This paper deals with the problem of symbol timing recovery at the subscriber end of a full duplex two wire digital subscriber loop employing echo cancellation. Both nondecision-aided and decisionaided synchronization are considered. It is demonstrated that the presence of a residual echo signal can substantially degrade the synchronizer performance. This degradation is shown to be larger for nondecisionaided synchronizers than for decision-aided synchronizers. The smaller the synchronizer bandwidth and the signal-to-echo ratio, the more the decision-aided synchronizer outperforms the nondecision-aided synchronizer. View full abstract»

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  • Group Testing Protocol with Capture for Random Access Communication

    Page(s): 849 - 854
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    The capture property of a receiver is used to design a collision resolution algorithm for a ternary feedback random access channel. Group testing techniques are employed under the assumption of finite users model. Users are assumed to generate a packet with probabilitypduring a collision resolution interval. Two groups of users with different transmission powers are assumed to exist in the system. Performance of this algorithm is shown to be considerably better than that of the algorithm without capture. Effect of varying the number of users in both groups on the expected collision resolution interval is studied. One of the features of this algorithm is that it is always superior to TDMA for any probabilitypas long as there is at least one user in the high power group. View full abstract»

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  • The Performance of Random and Optimal Scheduling in a Time-Multiplex Switch

    Page(s): 813 - 817
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    In a time-multiplex switching system, the incoming traffic must be scheduled to avoid conflict at the switch output (two or more users converging simultaneously upon a single output). Two scheduling algorithms, random scheduling and optimal scheduling, are explored in this paper. Random scheduling is computationally simple, whereas optimal scheduling is currently very difficult. We have found, using a traffic model appropriate for circuit switched traffic that increases of typically 10 to 15 percent in offered load can be obtained through optimal scheduling (as compared to the much simpler random scheduling algorithm). The improvement is a function of the number of time slots (or circuits) per time-multiplexed frame, and falls to zero for both very small and very large frame sizes. Thus, in many circuit switching applications, providing a computationally expensive optimal schedule may not be warranted. This conclusion has important ramifications for both electronic and emerging photonic switching systems since it reduces the importance of the costly design feature of optimal scheduling. View full abstract»

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  • VLSI Implementation of a DPCM Compression Algorithm for Digital TV

    Page(s): 854 - 856
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    Future video services in the loop plant may be based on digital transmission through optical fibers. A small and inexpensive codec is required for a variety of services based on digital television. We have demonstrated a compression algorithm for transmission of NTSC color television over a DS3 channel (44.736 Mbits/s). This predictive coding algorithm has been implemented using circuits built with conventional TTL logic. The resulting picture is visually unimpaired, but may not have network quality. The major portion of the compression or reconstruction circuit has also been implemented in one CMOS VLSI chip. Compression is accomplished using this chip with two small ROM chips. Reconstruction is done with the same VLSI chip and one ROM chip. View full abstract»

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  • Digital Subscriber-Loop Performance Using Echo-Cancellation with WAL I and WAL II Coding

    Page(s): 862 - 865
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    The performance of the echo-cancelling method of transmission using the WAL I and WAL II line codes is investigated for a loop model which is based on a statistical survey of the subscriber loopnetwork in New Zealand. Extensive simulation results are given for linear equalizers and decision-feedback equalizers operating at 144 kbit/s. It is found that, provided a good sampling phase can be assumed, simple DFE's and WAL I line code are generally adequate for a loop population penetration of over 95 percent. View full abstract»

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  • Simulated Performance of an Adaptive Multielement Integrated Receiver Structure in Impulse or Burst Noise

    Page(s): 834 - 845
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    We consider the convergence and tracking properties of an adaptive multielement integrated receiver structure operating in the presence of impulsive or burst noise. The receiver structure is integrated in the sense that it incorporates both the spatial/temporal predetection processing and demodulation functions in a single entity. This integrated receiver structure has been developed in previous work to approximate maximum-likelihood (ML) reception in the presence of both intersymbol interference (ISI) and spatially distributed interference (SDI) when the latter is modeled as zero-mean Gaussian noise. The present paper is devoted to a simulation study of the convergence properties of this receiver structure when the SDI is replaced by non-Gaussian impulsive or burst noise. Results indicate that the convergence characteristics are relatively insensitive to the statistics of the SDI provided that secondorder properties are held fixed, at least for moderate deviations from Gaussian behavior. For highly impulsive SDI environments, however, the adaptive system exhibits a complete failure to converge. View full abstract»

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  • Penalties of Sample-and-Sum and Weighted Partial Decision Detectors in Gaussian Noise

    Page(s): 777 - 785
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    The deterioration in performance, measured in the probability of error sense, of sample-and-sum and weighted partial decision detectors are analyzed for arbitrary signal-to-noise ratios. These suboptimal detectors have more modest computational requirements than the optimal digital matched filter making them amenable to simple digital implementations. The effects on the penalties of the signaling waveform employed, the number of samples processed, and the signal-to-noise ratio are considered in detail. Included are the penalties for the optimum weighted partial decision detector. The optimum weighted partial decision detector is the optimum detector, in the minimum probability of error sense, for hard-limited samples. The penalty of the optimum weighted partial decision detector relative to the digital matched filter detector represents the fundamental loss in signal detectability due to hard-limiting in a sampled system. View full abstract»

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  • A Phase-Adaptive Echo Canceller with Reduced Sensitivity to Power Variations

    Page(s): 865 - 867
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    In a previous correspondence [1], we have studied an echo canceller (EC) compensating far-end echos affected by frequency offset. It has been shown that the sensitivity of the loop gain versus the powerPof the echo and the powerSof the signal, can be reduced by adoption of a normalized gain multiplied by the echo power. In this correspondence a novel and very simple algorithm is described that further reduces this sensitivity and yields an optimum phase loop gain proportional to(S/ p)^{1/6}. View full abstract»

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  • Detection Using a Noise Estimation-Cancellation Technique

    Page(s): 786 - 794
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    This paper introduces a novel class of detectors, which has a symbol-by-symbol, multisample, transversal filter-based structure. The essence of the proposed detectors is based on a noise estimationcancellation technique. By exploiting the noise correlation among the received samples, a linear minimum mean-squared estimate of the existing noise is made and subsequently cancelled. As an illustration of the detection principle, partial response signaling systems of the form1 pm D^{m}are considered. The effects of the system bandwidth, the number of exploited samples and filtering allocation, on the system performance are thoroughly examined. It is shown that with optimum filtering allocation, the proposed detectors, while having simple structures, give substantial performance gains over conventional one-sample detectors. View full abstract»

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  • Extension to the Rude-CSMA Analysis

    Page(s): 848 - 849
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    This paper extends the rude-CSMA analysis by removing the restriction that each node have the same average arrival rate and average service time. Additionally, some minor errors are corrected. View full abstract»

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  • Error Recovery of Decision Feedback Equalizers on Exponential Impulse Response Channels

    Page(s): 846 - 848
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    In this correspondence we determine an upper bound on the error recovery time of a decision feedback equalizer (DFE) operating on a high signal to noise ratio channel of exponential impulse response to be used for binary transmission. This bound is related to the channel time constant and we show that exponential impulse response channels form a favourable class of channels with regard to DFE error recovery properties. 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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Editor-in-Chief
Robert Schober
University of British Columbia