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Communications, IEEE Transactions on

Issue 3 • Date March 1987

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Displaying Results 1 - 21 of 21
  • [Front cover and table of contents]

    Page(s): 0
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    Freely Available from IEEE
  • [Back cover]

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    Freely Available from IEEE
  • Delay Analysis Under a General Cut-Through Switching Technique in Computer Networks

    Page(s): 356 - 359
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    A general cut-through switching (GCTS) technique is proposed and analyzed. In GCTS, a message may cut through a node if the node becomes free before the message is completely received there. Under the GCTS mechanism, a message may cut through a node even though the node has more than one message in it. This results in minimizing the end-to-end delay time of messages as compared to the other cut-through mechanisms. Moreover, GCTS is more susceptible to exact mathematical treatment. View full abstract»

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  • DCTPSK--Differentially Detected Controlled Transition PSK

    Page(s): 349 - 352
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    An efficient modem is introduced for system applications which favor differential detection techniques. In differentially detected controlled transition PSK (DCTPSK), pulse-shaping techniques are used to achieve bandwidth and power efficiency in nonlinear channels. The baseband waveshapes, eye diagrams, and signal space diagram of DCTPSK are given; its bit error rate performance is calculated and its power spectral density is obtained. In a multicarrier adjacent channel interference environment, the compact spectrum of DCTPSK enables it to utilize the available bandwidth and power more efficiently than some well-known modulation techniques such as DQPSK and DMSK. View full abstract»

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  • BTC Image Coding Using Vector Quantization

    Page(s): 352 - 356
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    This paper describes source encoding of the outputs of a block truncation coder (BTC), namely, the overhead statistical information and the truncated block. The statistical overhead and the truncated block exhibit properties which can be effectively used for their quantization as vectors. Vector quantization of these BTC outputs results into reduction of the bit rate of the coder. The bit rate reduces up to 1.5 bits/ pel if vector quantization is used on one of the outputs; i.e., either the overhead information or the truncated block. By vector quantizing both the BTC outputs the bit rate can he reduced up to 1.0 bits/pel without introducing many perceivable errors in the reconstructed output. View full abstract»

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  • Videoconference Traffic and Network Design

    Page(s): 275 - 282
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    Recent technological progress is making possible the creation of a new form of videoconference service based on a public network interconnecting private studios located on user premises. We suppose that transmission links in such a network would be reserved in advance by users as and when they arrange their meeting. This and other significant differences with telephony-like services make the use of traditional teletraffic models inappropriate for network dimensioning and performance evaluation. In this paper, we propose an original model of the videoconference reservation traffic process in which essential parameters are the size and distribution of the studio population and the mean studio busy hour utilization rate. This model is used to study certain network architectures in order to identify the effect on link and node dimensions of major design options. First conclusions suggest that the most economical structure might be a simple star network where all studios are connected directly to a central switching facility. Advance reservation makes it possible to employ elaborate routing algorithms, such as call rearrangement, which might be exploited to optimize network or switching node design. View full abstract»

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  • Bounds on the Cross-Correlation Functions of State m-Sequences

    Page(s): 305 - 312
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    The performance of the periodic Hamming correlation function of the sequences of states ofm-sequence simple linear feedback shift register generators is evaluated. We call these sequences statemsequences. Theoretical lower and upper bounds on the peaks of the Hamming cross-correlation functions of those sequences, which are often used in frequency-hopped spread-spectrum systems, are derived. Numerical results in support of the theory are presented, and it is shown that the worst-case shift of the cross-correlation for relatively short sequences is of burst nature. The state position mapped (SPM) sequences of the statem-sequences are introduced. Their suitability for OR-channel code division multiplexing is numerically examined. The behavior of the periodic crosscorrelation function of these SPM sequences is used as the basis for judging their performance. It is explained also that the lower bound on the peak of the periodic Hamming cross-correlation function of the statem-sequences is naturally a lower bound on the peak of the periodic crosscorrelation function of SPM statem-sequences. This is due to the general relationship (a decimation relationship) between the two types of correlation functions. This relationship is explained and illustrated by an example. Tables of the peaks of both cross-correlation functions are presented for all sets of sequences for sequence generators of 5, 6, 7, and 8 stages. View full abstract»

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  • Blocking Probabilities for Trunk Reservation Policy

    Page(s): 313 - 318
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    This paper presents an analysis of the blocking phenomenon in circuit-switched routing policies with alternate routing and trunk reservation. From the usual assumptions on the offered traffic (Poisson) and the service time (exponential distribution), a classical Markov chain model is derived. Some approximate formulas are given to compute the blocking probabilities for first- and second-choice traffic. The accuracy of the proposed estimates is evaluated by direct comparison with already known results in simple cases and with the exact solution of the state equations. View full abstract»

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  • Digital Radio Performance When the Transmitter Spectral Shaping Follows the Power Amplifier

    Page(s): 261 - 266
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    We analyze a digital radio link in which rectangular RF data pulses drive the high-power amplifier (HPA) and spectral shaping of the transmission is done after the HPA. The purpose of the analysis is to quantify detection performance for a variety of design possibilities. These include two approaches to predistortion in the transmitter and two ways of setting decision boundaries in the receiver. Also considered are different signal constellations and numbers of levels(M). We show that performance differences among practical system designs increase significantly withM. For example, the spread of minimum distance values among the various designs studied here grows from 4.4 dB forM = 16to 14.4 dB forM = 256. View full abstract»

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  • A Transmission Scheme for Integrated Services on Broad-Band Internal Private Business Networks

    Page(s): 328 - 335
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    Internal business networks are expected to present an economic area of application for broad-band communications. A star network with switches optimized for various services is envisaged. An asynchronous switch for video in square wave frequency modulation (SWFM) format can provide a practical solution for full bandwidth switched video services. A transmission scheme is described which combines a SWFM video service together with synchronous PCM data and voice services, asynchronous data up to 9.6 kbauds and network clocks at both 2 MHz and 160 kHz for ISDN, so that all services destined for one terminal site may be transmitted in binary format on cable or fiber. An experimental link is described which provides up to 10 Mbit/s data capacity together with the video service. The hardware is constructed with 74HC family CMOS. An analysis of the effects of data modulation on video quality is given. Measurements of video S/N and distortion are reported. Measured bit-error rate in a 64 kbit/s data channel is reported. The measurements relate to a coaxial cable link with link lengths from 200 to 400 meters. View full abstract»

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  • An Efficient DFE & ML Suboptimum Receiver for Data Transmission Over Dispersive Channels Using Two-Dimensional Signal Constellations

    Page(s): 336 - 339
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    The DFE & ML receiver is presented for data transmission systems using QAM modulation. A substantial improvement in performance results as compared to other one- or two-stage receiver structures at relatively low computational complexity. View full abstract»

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  • Motion-Compensated Coder for Videoconferencing

    Page(s): 297 - 304
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    A codec for videoconferencing purposes [8]-[12], [31] is proposed based on the one-at-a-time search (OTS) motion compensation algorithm [1], [30], [31]. The coder is implemented in an interframe hybrid mode using theC-matrix transform (CMT) [13]-[15]. The motion estimation algorithm employed is simple and reduces temporal redundancy, while the CMT reduces spatial redundancy in the transmitted prediction errors. The operation of the codec is presented. Simulation results based on three different scenes with varying levels of motion are presented. The coder operates in a feedback mode. View full abstract»

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  • Baseband Equalization and Carrier Recovery in Digital Radio Systems

    Page(s): 319 - 327
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    The influence of adaptive baseband equalization on decision-feedback carrier recovery performance is investigated. First, it is shown that the delay introduced by the equalizer in the carrier recovery loop does not have basic consequences on system performance. Second, the interaction between the two adaptive circuits is studied for four different equalizer adaptation algorithms. It is found that algorithms based on the zero-forcing criterion are unstable unless they are used with an appropriate constraint. With gradient-type algorithms based on the minimum mean square error criterion, the interaction leads to an improved carrier acquisition performance at the expense of a larger phase jitter. It is therefore concluded that even with these latter algorithms it is generally worthwhile to avoid the interaction by forcing the imaginary part of the equalizer reference tap to zero. The theoretical analysis (carried out with a single complex tap equalizer) is supported by experimental results and computer simulation. View full abstract»

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  • Content-Driven Progressive Transmission of Grey-Scale Images

    Page(s): 289 - 296
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    A lossless progressive transmission method for grey-scale images which concentrates early transmission efforts on areas of greater image information content is described. The receiver does not have a priori knowledge of which image areas are to receive preferential treatment, and the preferential level of resolution is the pixel. The method makes use of simultaneous geometric and information content decompositions. The method is computationally simple with a complexity which grows linearly with the number of pixels. Compression achieved approaches that obtained by nonprogressive lossless methods, and is approximately the same as for homogeneous progressive lossless methods. Extensions of the method for progressive transmission with limited distortion and greater compression are also discussed. View full abstract»

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  • On the Number of Switching Modes Generated by Time-Optimal Algorithms for SS/TDMA Systems

    Page(s): 359 - 362
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    An important parameter related to the efficiency of algorithms for data transmission on SS/TDMA systems is the number of switching modes they generate. It is shown in this note that time-optimal algorithms produce the maximum number of switchings only if the transmission durationLis exponential inN, whereNis the number of channels. This result explains the good performance exhibited by those algorithms in several simulation results. View full abstract»

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  • Polling with a General-Service Order Table

    Page(s): 283 - 288
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    This paper derives exact results for a polling system such as a token bus or token ring with exhaustive service and priority polling. The results can also be used to analyze a terminal controller with a generalservice order table. There areNstations in the system and the token is passed among them according to a polling table of lengthM (geq N). Stations are given higher priority by being listed more frequently in the polling table. By a straightforward extension of results of Ferguson and Aminetzah [5] for systems with circular polling and exhaustive service, it is shown that in general, theNmean waiting times require the solution of a set ofM - Nsimultaneous equations and a set ofM(M - 1)simultaneous equations. We show that partial symmetry in the polling table and the station characteristics can be used to significantly reduce the number of equations which must be solved. We present the reduced equation set for a two-priority class system and apply the results to a large token-passing bus network in which a few nodes account for a substantial portion of the network traffic. We show that in the latter case, the overall_ average message waitmg time can be significantly reduced by using priority polling: average waiting times at the high-priority nodes have large reductions in return for a smaller increase at low-priority nodes. View full abstract»

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  • Bandwidth Compressive 16-State SQAM Modems Through Saturated Amplifiers

    Page(s): 339 - 345
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    The performance of new bandwidth compressive 16 SQAM (Superposed-QAM) modems, operating in a highly power-efficient saturation mode, is analyzed. Nonlinearly amplified 16 SQAM retains the out-of-band energy much lower than 4-level rectangular (i.e., 16 QAM) or sinusoidal shaped (i.e., MAMSK) QAM, and operates within 0.7 dB of theoretical (i.e., 16 QAM in Nyquist linear channel) performance atP(e) = 10^{-6}using simple 4th-order Butterworth LPF's. Effects of baseband pulse shaping, receive filter BTs, power level variations and propagation time difference (or static phase shift) of transmit HPA's are analyzed in terms of BER. View full abstract»

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  • Improved Methods of Accelerating the Convergence of Adaptive Equalizers for Partial-Response Signals

    Page(s): 257 - 260
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    In order to accelerate the convergence of adaptive equalizers for partial-response signals it is necessary to transform the input signal, and use the transformed values in one of two ways-to calculate both the equalizer output and the tap updates, or to calculate only the tap updates. These methods are called double-sided and single-sided orthogonalizalion, respectively; this paper confirms previous suggestions that the latter is preferable. In an early implementation of the double-sided orthogonalization (DSO) the number of multiplications was proportional to the square of the number of taps (N2); this was later reduced to2Nmultiplications; the only implementation of single-sided orthogonalization (SSO) that has been described used of the order of N2multiplications. This paper describes an implementation of SSO that needs only2Nmultiplications,and gives explicit formulas for the two partial-response systems of most interest-I and IV. Two examples of the improved convergence are given, and the application of this method to complex equalizers is discussed. View full abstract»

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  • An Algorithm for an Adaptive Multifrequency Receiver

    Page(s): 345 - 349
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    This paper presents a simple and effective algorithm for an adaptive multifrequency receiver that can be used for several types of multifrequency signals. This algorithm uses the ability of frequency detection of signal processing using extreme and zero-crossing points in the multifrequency signals and an adaptive second-order notch filter. View full abstract»

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  • Throughput Analysis in Multihop CSMA Packet Radio Networks

    Page(s): 267 - 274
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    In this paper, we use a Markov model to develop a product form solution to efficiently analyze the throughput of arbitrary topology multihop packet radio networks that employ a carrier sensing multiple access (CSMA) protocol with perfect capture. We consider both exponential and nonexponential packet length distributions. Our method preserves the dependence between nodes, characteristic of CSMA, and determines the joint probability that nodes are transmitting. The product form analysis provides the basis for an automated algorithm that determines the maximum throughput in networks of size up to 100 radio nodes. Numerical examples for several networks are presented. This model has led to many theoretical and practical extensions. These include determination of conditions for product form analysis to hold, extension to other access protocols, and consideration of acknowledgments. View full abstract»

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  • Packet-Switched Performance with Different Circuit-Switched Routing Procedures in Nonhierarchical Integrated Circuit-Switched and Packet-Switched Networks

    Page(s): 362 - 366
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    It is shown in [13] that different types of routing procedures for circuit-switched traffic in a nonhierarchical network exhibit various performance tradeoffs. It is, however, not clear if the network is also allowed to carried packet-switched traffic, how the packet-switched traffic will be affected by using different routing procedures for the circuit-switched traffic. In this paper, we examine the average time delay of the packet-switched traffic assuming that the network uses a movable boundary scheme to allocate bandwidth dynamically 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