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Communications, IEEE Transactions on

Issue 4 • Date April 1985

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Displaying Results 1 - 14 of 14
  • [Front cover and table of contents]

    Publication Year: 1985 , Page(s): 0
    Save to Project icon | Request Permissions | PDF file iconPDF (179 KB)  
    Freely Available from IEEE
  • [Back cover]

    Publication Year: 1985 , Page(s): 0
    Save to Project icon | Request Permissions | PDF file iconPDF (230 KB)  
    Freely Available from IEEE
  • A Predictor Switching Scheme for DPCM Coding of Video Signals

    Publication Year: 1985 , Page(s): 373 - 379
    Cited by:  Papers (8)  |  Patents (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (496 KB)  

    In DPCM coding of video signals, for improved data compression efficiency, the predictor is often switched adaptively between two or more different predictions. For low-bit-rate coders, the predictor switching is done on a pel-by-pel basis. In this paper, a new scheme for predictor switching on a pel-by-pel basis is proposed. This new scheme is a modification of an existing adaptive predictor switching scheme which has been implemented in pel-recursive motion compensated coding of video signals. To evaluate the efficiency of the new scheme, a theoretical expression for the output bit rate is derived. It is pointed out under what conditions it is advantageous to use the new scheme for predictor switching. Some details of implementation are discussed. Results of computer simulation on natural scenes are presented. These results validate the theoretical conclusions derived in the paper. The simulation results also indicate that the picture quality is improved significantly, for approximately the same output bit rate, with the new predictor switching scheme as compared to the existing scheme for predictor switching. View full abstract»

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  • Linear Receivers for Correlatively Coded MSK

    Publication Year: 1985 , Page(s): 338 - 347
    Cited by:  Papers (30)  |  Patents (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (944 KB)  

    In this paper we show that many spectrally efficient modified MSK schemes, termed generalized MSK, although not representable as OQPSK, may nevertheless be (suboptimally) demodulated using an I-Q receiver with a proper choice of carrier-phase offset. Correlatively coded MSK schemes with I-Q receivers are studied, and it is concluded that duobinary MSK and (1 + 2D + D^{2})/4 MSK represent good performance-bandwidth tradeoffs among first- and second-order correlative coding polynomial schemes. The optimal design of these receivers are considered subject to the constraint of a finite duration impulse response, especially for asymptotic cases of arbitrarily small and large SNR. Filter design based on a zero-intersymbol interference constraint for PAM-based approximations of the signals is also considered. The optimized linear I-Q receivers for (1 + D)/2 MSK and (1 + D)^{2}/4 MSK are presented. These receivers are only 0.28 and 1.24 dB poorer than the optimal (Viterbi) receivers at high SNR. View full abstract»

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  • Coding and Decoding for Code Division Multiple User Communication Systems

    Publication Year: 1985 , Page(s): 310 - 316
    Cited by:  Papers (14)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (792 KB)  

    A new algorithm is introduced which decodes code division multiple user communication signals. The algorithm makes use of the distinctive form or pattern of each signal to separate it from the composite signal created by the multiple users. Although the algorithm is presented in terms of frequency-hopped signals, the actual transmitter modulator can use any of the existing digital modulation techniques. The algorithm is applicable to error-free codes or to codes where controlled interference is permitted. It can be used when block synchronization is assumed, and in some cases when it is not. The paper also discusses briefly some of the codes which can be used in connection with the algorithm, and relates the algorithm to past studies which use other approaches to the same problem. View full abstract»

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  • Asymptotic Upper Bounds on the Minimum Distance of Trellis Codes

    Publication Year: 1985 , Page(s): 305 - 309
    Cited by:  Papers (20)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (520 KB)  

    A trellis code is a "sliding window" method of encoding a binary data stream as a sequence of signal points in Rn. When a trellis code is used to encode data at the rate of k bits/channel symbol, each channel input depends not only on the most recent block of k bits to enter the encoder, but will also depend on a set of ν bits preceding this block. The ν bits determine the state of the encoder and the most recent block of k bits generates the channel symbol conditional on the encoder state. The performance of a trellis code depends on a suitably defined minimum distance property of that code. This paper obtains upper bounds on this minimum distance that are better than any previously known. View full abstract»

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  • A Review of Models for Estimating 1 min Rainfall Rates for Microwave Attenuation Calculations

    Publication Year: 1985 , Page(s): 361 - 372
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1136 KB)  

    A search for information on short-duration precipitation rates uncovered several sources of data, primarily for North America and Europe. However, the data available, especially for 1 min rainfall rates, are insufficient to permit direct calculation of precipitation-rate frequency distributions for all but a few locations in the world. Due to the need for these statistics for microwave attenuation calculations, researchers developed models that can be used to estimate 1 min rainfall-rate distributions. Some require climatic data, while others divide the globe into regions, each of which is associated with a representative distribution. A survey of the available data and a comparison of models for determining short-duration precipitation rate distributions is presented, with particular emphasis on 1 min rates. View full abstract»

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  • Joint Baud and Frame Synchronization in Direct Detection Optical Communications

    Publication Year: 1985 , Page(s): 357 - 360
    Cited by:  Papers (19)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (392 KB)  

    The maximum-likelihood frame synchronizer was recently derived for direct-detection optical communications assuming baud synchronization. In this paper we present an extension to those results when pulse-position modulation is used and jointly derive baud and frame synchronization from slot synchronization. The optimum rule is seen to consist of a simple correlation term and a nonlinear correction term. Simulation results for the optimum rule compared to analytical and simulation results for the simple correlation rule show that equivalent performance for the simple correlation rule requires a substantial increase in signal power. To design good synchronization patterns, we use a divergence measure derived from the optimum rule. A simple algorithm is derived to test whether a given sequence is good or not. View full abstract»

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  • The Effect of Capture on Collision-Resolution Algorithms

    Publication Year: 1985 , Page(s): 317 - 324
    Cited by:  Papers (15)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (856 KB)  

    In many communication systems, the stronger of two or more overlapping packets might capture the receiver and thus be received without error. The effect of capture on collision-resolution algorithms in a slotted ALOHA type broadcasting network is investigated here. Extensions to the algorithms are suggested for both the situations in which the receiver can or cannot distinguish between success slots and capture slots. In particular, we present a class of retransmission schemes for packets that have been transmitted during capture slots but have not been received correctly. The performance analysis is confined to a simplified model in which the nodes of the network are divided into two groups and only packets sent by the nodes of one of them might be captured. For this simplified model and for each extended algorithm, explicit recursive equations are given, from which the average conditional collision-resolution interval length, as well as the maximal throughput, can be determined. As expected, we show that in the presence of capture, the performance of the network is improved and the maximal attainable throughput is increased. Extensions of the simplified model such as dividing the nodes into K groups instead of two, or considering the situation that capture depends on relative distances and transmission powers, are also discussed. For the latter situation we give simulation results. View full abstract»

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  • Simulation of a Multiprocessor Switching System Using Model Aggregation

    Publication Year: 1985 , Page(s): 325 - 329
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (560 KB)  

    Multiprocessor systems find wide application in telecommunications. Simulation techniques are often incorporated in the performance analysis of these systems. Simulation models enable an operating system to be represented in detail, e.g., multitasking, message handling, and concurrent processing. This level of detail is useful in evaluating software design. However, the complexity of such models can lead to costly simulations. Aggregation techniques can often be used to reduce model complexity. Aggregation typically involves the representation of only part of the system in detail, i.e., the primary subsystem. The remainder of the system is represented by a simplified composite. Parametric analysis is performed on the primary subsystem. The role of the composite is to introduce interactive effects to the primary subsystem. Aggregation techniques are accurate for certain classes of analytic models. The purpose of this study is to apply aggregation to the simulation model of a multiprocessor switching system. A model for real-time performance evaluation is described. An aggregation technique is derived from basic queueing models. The accuracy of the aggregated model is assessed through the simulation of realistic test cases. The results demonstrate that good accuracy can be obtained with aggregation. Substantial simulation cost savings are also demonstrated. View full abstract»

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  • A Proposed Receiver Structure for Optical Communication Systems that Employ Heterodyne Detection and a Semiconductor Laser as a Local Oscillator

    Publication Year: 1985 , Page(s): 382 - 384
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (296 KB)  

    Coherent heterodyne detection in optical communication is degraded by phase instabilities present when a semiconductor laser is used as a local oscillator. Postdetection processing that accounts for these instabilities is suggested, based on a diffusion-process model for oscillator instabilities and a maximum-likelihood sequence-estimator of information symbols modulating the received light. View full abstract»

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  • Adaptive Lattice Decision-Feedback Equalizers--Their Performance and Application to Time-Variant Multipath Channels

    Publication Year: 1985 , Page(s): 348 - 356
    Cited by:  Papers (66)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (944 KB)  

    This paper presents two types of adaptive lattice decisionfeedback equalizers (DFE), the least squares (LS) lattice DFE and the gradient lattice DFE. Their performance has been investigated on both time-invariant and time-variant channels through computer simulations and compared to other kinds of equalizers. An analysis of the self-noise and tracking characteristics of the LS DFE and the DFE employing the Widrow-Hoff least mean square adaptive algorithm (LMS DFE) are also given. The analysis and simulation results show that the LS lattice DFE has the faster initial convergence rate, while the gradient lattice DFE is computationally more efficient. The main advantages of the lattice DFE's are their numerical stability, their computational efficiency, the flexibility to change their length, and their excellent capabilities for tracking rapidly time-variant channels. View full abstract»

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  • On "A Simple Protocol Whose Proof Isńt": The State Machine Approach

    Publication Year: 1985 , Page(s): 380 - 382
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (360 KB)  

    We discuss how to model a synchronous protocol (due to Aho, Ullman, and Yannakakis) using communicating finite state machines, and present a proof for its safety and liveness properties. Our proof is based on constructing a labeled finite reachability graph for the protocol. This reachability graph can be viewed as a sequential program whose safety and liveness properties can be stated and verified in a straightforward fashion. View full abstract»

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  • A Simple Protocol Whose Proof Isn't

    Publication Year: 1985 , Page(s): 330 - 337
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (848 KB)  

    Aho, Ullman, and Yannakakis have proposed a set of protocols that ensure reliable transmission of data across an error-prone channel. They have obtained lower bounds on the complexity required of the protocols to assure reliability for different classes of errors. They specify these protocols with finite-state machines. Although the protocol machines have only a small number of states, they are nontrivial to prove correct. In this paper we present proofs of one of these protocols using the finite-state-machine approach and the abstract-program approach. We also show that the abstract-program approach gives special insight into the operation of the protocol. 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