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Communications, IEEE Transactions on

Issue 6 • Date June 1987

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

    Publication Year: 1987 , Page(s): 0
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    Freely Available from IEEE
  • Correction to "A New Rapid Acquisition Technique for Direct Sequence Spread Spectrum Communications"

    Publication Year: 1987 , Page(s): 679
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (107 KB)  

    First Page of the Article
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  • [Back cover]

    Publication Year: 1987 , Page(s): 0
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    Freely Available from IEEE
  • Maximum Likelihood Symbol Synchronization for the Direct-Detection Optical On-Off-Keying Channel

    Publication Year: 1987 , Page(s): 626 - 631
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (544 KB)  

    The maximum-likelihood symbol synchronization statistic is derived from noisy observations of randomly modulated on-off-keying data for the direct-detection optical channel. A similar statistic for the case when the transmitter sends a special pattern of alternating O's and 1's for synchronization purposes only is also derived. Various approximations to the optimal statistic are introduced and their performance compared to the optimal one under a new criterion, believed to be more appropriate for the Poisson channel than the mean-square error criterion routinely used with other channels. It is shown that although the variable associated with symbol transitions is continuous, the possible values of it that maximize the maximum-likelihood (ML) statistic belong to a discrete set with relatively few elements. View full abstract»

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  • Proof that Timing Requirements of the FDDI Token Ring Protocol are Satisfied

    Publication Year: 1987 , Page(s): 620 - 625
    Cited by:  Papers (84)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (840 KB)  

    The fiber distributed data interface (FDDI) is an ANSI draft proposed standard for a 100 Mbit/s fiber-optic token ring. The FDDI timed token access protocol provides dynamic adjustment of the load offered to the ring, with the goal of maintaining a specified token rotation time and of providing a guaranteed upper bound on time between successive arrivals of the token at a station. FDDI also provides automatic recovery when errors occur. The bound on time between successive token arrivals is guaranteed only if the token rotates quickly enough to satisfy timer requirements in each station when all ring resources are functioning properly. Otherwise, recovery would be initiated unnecessarily. The purpose of this paper is to prove that FDDI timing requirements are satisfied, i.e., the token rotates quickly enough to prevent initiation of recovery unless there is failure of a physical resource or unless the network management entity within a station initiates the recovery process. View full abstract»

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  • Spectral Correlation of Modulated Signals: Part II--Digital Modulation

    Publication Year: 1987 , Page(s): 595 - 601
    Cited by:  Papers (94)  |  Patents (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (592 KB)  

    As a continuation of Part I, the spectral correlation function is presented for a variety of types of digitally modulated signals. These include digital pulse-amplitude, pulse-width, and pulse-position modulation, and various types of phase-shift keying and frequency-shift keying. The magnitudes of the spectral correlation functions are graphed as the heights of surfaces above a bifrequency plane, and these graphs are used as visual aids for comparison and contrast of the spectral correlation properties of different modulation types. View full abstract»

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  • Performance Evaluation of Multireject, Selective Reject, and Other Protocol Enhancements

    Publication Year: 1987 , Page(s): 659 - 666
    Cited by:  Papers (22)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (960 KB)  

    This study compared the effects on performance of four features of the LAPB and LAPD protocols. LAPB is the link level for the X.25 protocol, and LAPD is the link level for the ISDN "D" signaling channel. The features were: multireject in which additional reject or selective reject frames can be retransmitted under certain conditions, selective reject in which an entity can request selected frames to be retransmitted, the null information frame (NIF) with which additional control frames are sent to help detect missing frames, and multiple service access points (SAP's) in which several link-level protocol handlers are multiplexed on the same physical link (a feature unique to LAPD). Results indicate that the current standard LAPB/D protocol with multireject is the preferred protocol. Selective reject generally performed worse than the standard protocol, and offered improvement only with complex and expensive enhancements. The NIF feature yielded a virtually unnoticeable performance improvement. Multi-SAP introduced a virtually unnoticeable impairment when it was used to carry the same traffic load as a single SAP. View full abstract»

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  • Spectral Correlation of Modulated Signals: Part I--Analog Modulation

    Publication Year: 1987 , Page(s): 584 - 594
    Cited by:  Papers (95)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1192 KB)  

    The importance of the concept of cyclostationarity in design and analysis of signal detectors, synchronizers, and extractors in communication systems is briefly discussed, and the central role of spectral correlation, in the characterization of random processes that are cyclostationary in the wide sense, is explained. A spectral correlation function that is a generalization of the power spectral density function is described, and a corresponding generalization of the Wiener-Khinchine relation and several other fundamental spectral correlation relations also are described. Explicit formulas for the spectral correlation function for various types of analog-modulated signals are derived. This includes pulse and carrier amplitude modulation, quadrature amplitude carrier modulation, and phase and frequency carrier modulation. To illustrate the differing spectral correlation characteristics of different modulation types, the magnitudes of the spectral correlation functions are graphed or described in graphical terms as the heights of surfaces above a bifrequency plane. View full abstract»

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  • Optimum Joint Slot and Symbol Synchronization for the Optical PPM Channel

    Publication Year: 1987 , Page(s): 632 - 636
    Cited by:  Papers (10)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (368 KB)  

    A maximum-likelihood statistic for pulse-position-modulation (PPM) symbol synchronization in the absence of slot synchronization is derived for the direct-direction optical channel from noisy observations of randomly modulated data, observed through a window M symbols wide. Two approximations to the optimal rule that are easier to implement are also derived and their performance analyzed by computer simulations. It is seen that the performance of one approximation, which is quite easy to implement, is almost identical to the more complex approximation. View full abstract»

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  • 15/30 Mbit/s Universal Digital TV Codec Using a Median Adaptive Predictive Coding Method

    Publication Year: 1987 , Page(s): 637 - 645
    Cited by:  Papers (23)  |  Patents (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1136 KB)  

    This paper describes a 15/30 Mbit/s TV codec with a new approach to high-efficiency coding for TV signals, i.e., median adaptive prediction. The 15/30 Mbit/s codec, commonly applicable to NTSC, PAL, and SECAM (525/60 and 625/50) systems, uses adaptive prediction incorporating a motion-compensated interframe, an interfield, and an intrafield predictor. Its performance for digital transmission is presented. This universal codec is designed, based on CCIR recommendations concerning digital TV coding parameters for studios (Rec. 601) and general principles on long-distance digital TV transmission (Rec. 604). A field trial of 15 Mbit/s digital TV transmission using this codec between earth stations with a 30 m diameter antenna and a 5 m diameter antenna is reported. View full abstract»

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  • Derivation of Gardner's Timing-Error Detector from the Maximum Likelihood Principle

    Publication Year: 1987 , Page(s): 684 - 685
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (216 KB)  

    In a recent paper [1], Gardner described a new timing-error detector for sampled receivers. The detector derives timing information without decision direction from a BPSK or QPSK signal sampled at rate 2/T (symbol interval T ). We will show how this detector can be derived from the maximum likelihood principle, and thus give insight into the nature of the algorithm. View full abstract»

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  • Time Slot Assignment in SS/TDMA Systems with Intersatellite Links

    Publication Year: 1987 , Page(s): 602 - 608
    Cited by:  Papers (18)  |  Patents (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (904 KB)  

    In this paper we study the time slot assignment problem in clusters of SS/TDMA satellite systems interconnected through intersatellite links. We show that the problem of finding an assignment which minimizes the total transmission time is NP-complete, i.e., computationally intractable, even for quite restricted intersatellite link patterns and simplified system models. Successively, we focus our attention on clusters of two satellites, proposing a branch-and-bound optimal algorithm and two fast heuristic algorithms. We investigate the performance of the proposed heuristic algorithms both by a theoretical worst case bound and by simulation trials showing that the produced solutions are close to the optimal on the average. View full abstract»

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  • Efficiency of Digital Synchronous Communication Systems

    Publication Year: 1987 , Page(s): 679 - 684
    Cited by:  Papers (5)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (512 KB)  

    A novel criterion for digital synchronous communication system efficiency estimation is defined. All system attributes such as bit error probability, coding efficiency, initial system synchronization time, efficiency of detection of timing anomalies and system sync recovery, reliability of the lock indication, and the amount of redundancy insertion in the data stream for synchronization and error-correcting coding purposes are included in a single parameter called "system efficiency." The expression for this parameter is derived under the assumption of signal ergodicity and steady-state system operation. In its final form, this parameter seems obvious almost by inspection. Even so, until now, it has not been used in the analysis of communication system efficiency. The analysis of this parameter for several different systems is presented as an illustration. View full abstract»

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  • A Petri Net Control Unit for High-Speed Modular Signal Processors

    Publication Year: 1987 , Page(s): 577 - 583
    Cited by:  Papers (3)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (672 KB)  

    This paper proposes a hierarchical representation of digital signal processing algorithms suitable for real-time implementations. Petri net models are used to demonstrate every possible operating parallelism in their graphical expression, the marked Petri graph. Moreover, a hierarchical algorithm execution control based on delayed Petri graphs is presented. A strictly modular system architecture suitable for VLSI implementation and data-driven processing is reviewed in its main components. The algorithm representation is then applied to the design of the control part of the system modules. Details at the logic level of the controllers for an array of digital signal processors are presented as an application of the proposed methodology. View full abstract»

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  • A Prototype Switching System Employing a Matching-Based Language

    Publication Year: 1987 , Page(s): 653 - 658
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (712 KB)  

    This paper describes an experimental switching system employing a nonprocedural language. It presents a study of the appropriate architecture for implementing the language, and examines the system's performance characteristics. Furthermore, it identifies the critical part of the architecture, and provides two strategies for throughput improvement and indicates their effects. View full abstract»

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  • Accurate Calculation of TWT Intermodulation in the Many-Carrier Case

    Publication Year: 1987 , Page(s): 685 - 687
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (304 KB)  

    The formulas derived by Stette [1] permit the calculation of TWT output carrier power and intermod power when the input to the TWT consists of an infinite number of infinitesimal carriers. The formulas for these quantities involve an integration of the TWT singlecarrier characteristic over a semi-infinite range, and for most of the TWT's one considers, a simple approximation of the integration by a summation gives satisfactory answers. However, when one considers special TWT's, e.g., linearized TWT's or the piecewise linear limiter [2], simple approximations are often not good enough. To get accurate results, a multipoint Gaussian quadrature must be used. View full abstract»

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  • A Code-Division Multiple-Access Local Area Network

    Publication Year: 1987 , Page(s): 667 - 671
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (520 KB)  

    In this paper, we propose a code-division multiple-access (CDMA) approach as a method of local area networking, and analyze its physical performance. The proposed system has the advantage of a multiehannel multiaccess local area network, and provides the capability of easy access to different kinds of traffics, such as voice and data. View full abstract»

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  • Adaptive Median Filtering for Impulse Noise Elimination in Real-Time TV Signals

    Publication Year: 1987 , Page(s): 646 - 652
    Cited by:  Papers (10)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (880 KB)  

    A two-dimensional (3 × 3) median filter with controlled turn-on is employed in an adaptive fashion for selective removal of impulse noise interference in real-time television signals. Various filters and threshold conditions are selected from programmed PROM's as a function of impulse noise detected and counted during a vertical interval window period. The adaptive median filter is used in conjunction with a satellite FM communication downlink system and can effectively improve the onset of threshold performance by about 3 dB carrier-to-noise ratio. The particular FM system discussed employs a multiplexed analog component, MAC, formatted TV signal. Use of the filter for standard NTSC composite signals is indicated. View full abstract»

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  • Message Delays with Prioritized HOLP and Round-Robin Packet Servicing

    Publication Year: 1987 , Page(s): 609 - 619
    Cited by:  Papers (5)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1144 KB)  

    Three disciplines for prioritized transmission of messages in packet switching systems are considered. Messages from a finite number of classes having their lengths drawn independently from general service time distributions are assumed to arrive to the system according to independent Poisson processes. After entering the switch, the messages are divided into packets, overhead is added, and then the packets join a queue to be served according to one of the following disciplines: head-of-the-line (HOL), HOL with message preemption, and prioritized round robin (RR). Preemption of packet transmission is not allowed in any of the disciplines, and the service disciplines of different classes need not be the same. One result of the work presented here is a model to assess delays in the case of the prioritized RR; this work appears to be the first in which messages are not of fixed length and all quanta from a given message are served at the same priority. Numerical results which illustrate effects of choice of packet lengths and service disciplines upon delay of messages from the different classes are presented. View full abstract»

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  • Conditional Run-Length and Variable-Length Coding of Digital Pictures

    Publication Year: 1987 , Page(s): 671 - 677
    Cited by:  Papers (5)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (816 KB)  

    In earlier publications, we have presented two coding schemes which take into account the conditional statistics of input signals. In the first scheme, the codewords are assigned in such a way as to provide a signal with long runs of zeros and ones. In the second scheme, each picture element is coded by variable-length codewords according to the values of previously transmitted PEL's. In this paper, by providing further results, we examine these coding schemes in greater detail. The performance of both schemes in terms of entropy and bit rate are compared with an optimum predictive coder. The simulation results indicate that these schemes have a significant advantage over standard predictive encoders. Methods to reduce the storage requirement for the encoder and decoder codebooks are also discussed. View full abstract»

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  • An Efficient Nearest Neighbor Search Method

    Publication Year: 1987 , Page(s): 677 - 679
    Cited by:  Papers (26)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (336 KB)  

    A simple, but efficient, nearest neighbor search algorithm is proposed and simulation results demonstrating its effectiveness in the case of vector quantization for a given source are presented. The simulation results indicate that use of this approach reduces the number of multiplications and additions to as low as 9 percent of those required for the conventional full search method. The reduction in the number of subtractions is also considerable. The increase in the number of comparisons is moderate, and therefore, the total number of operations can be as low as 28 percent of those required by the full search method. An additional advantage of the described algorithm is the fact that it requires no precomputations and/or extra memory. 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