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Communications, IEEE Transactions on

Issue 1 • Date January 1985

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Displaying Results 1 - 18 of 18
  • [Front cover and table of contents]

    Publication Year: 1985 , Page(s): 0
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    Freely Available from IEEE
  • [Back cover]

    Publication Year: 1985 , Page(s): 0
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    Freely Available from IEEE
  • Block Distortion in Orthogonal Transform Coding--Analysis, Minimization, and Distortion Measure

    Publication Year: 1985 , Page(s): 90 - 96
    Cited by:  Papers (13)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1072 KB)  

    Psychophysical considerations show that the block-shaped distortion peculiar to orthogonal transform coding (OTC) is ten times more objectionable than random noise distortion. Minimizing the blockshaped distortion is considered here by analyzing the process of generation of coding errors, and the required characteristics of the orthogonal transform function (OTF) are clarified. Computer simulations substantiate its validity. Graphical illustration and measures of the block-shaped distortion are proposed and substantiated. With the aid of these measures, one can evaluate the performance of OTC or a new OTF, if proposed, without conducting visual assessment tests. View full abstract»

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  • Backward Adaptive Lattice and Transversal Predictors in ADPCM

    Publication Year: 1985 , Page(s): 74 - 82
    Cited by:  Papers (30)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1008 KB)  

    Four different backward adaptive predictors and a fixed predictor are compared for use in an adaptive differential pulse code modulation (ADPCM) system for coding speech at 16 kilobits/second (kbits/s). For noise-free channels, the four adaptive predictors, a least squares lattice, a least mean square lattice, a Kalman transversal form, and a gradient transversal form, all exceed the fixed predictor performance as well as the performance of a continuously variable slope delta (CVSD) modulation system. For bit error rates (BER's) of 10-3or greater, the transversal predictor performance falls below that of the fixed predictor and CVSD; however, the lattice structures maintain their performance advantage. The least squares lattice predictor has the best objective and subjective performance for both noiseless and noisy channels. All systems perform poorly for a BER of 10-2. To extend the performance of ADPCM with a least squares lattice predictor down to a BER of 10-2, the sampling rate is reduced and a selective coding scheme is devised. The resulting ADPCM system maintains excellent performance through a BER of 10-2and outperforms CVSD for noise-free and noisy channels. The dynamic range, tandeming performance, and behavior for noisy inputs for the ADPCM system and CVSD are investigated. View full abstract»

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  • A Matrix Representation of CSMA/CD Networks

    Publication Year: 1985 , Page(s): 53 - 64
    Cited by:  Papers (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1360 KB)  

    A continuous time Markov chain model of asynchronous, nonpersistent CSMA/CD networks is developed which allows their complete characterization by a matrix whose dimensions are independent of the number of users in the network. The model provides an efficient reeursive algorithm for computing the performance of finite population networks. It also allows many analytical results to be obtained when an infinite population and a constant load retransmission policy are considered. These analytic results include necessary and sufficient conditions for stability, the distribution of the number of busy users, an exact closed form expression for the expected delay, and the exact upper bound on the throughput-all obtained via the properties of the matrix mentioned above. The results on stability show that, for this CSMA/CD model, the definitions of stability in terms of expected drift, nonnull recurrence, and maximum possible throughput exceeding actual loading are all equivalent. The model can approximate as closely as desired any distribution for the packet length, transmission detection time, and collision truncation time. Taking advantage of this freedom, the performance of CSMA/CD networks is shown to be very sensitive to the distribution of the transmission detection time. View full abstract»

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  • Measured Frequency Diversity Improvement for Digital Radio

    Publication Year: 1985 , Page(s): 106 - 109
    Cited by:  Papers (6)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (440 KB)  

    This paper presents the measured frequency diversity improvement factor for 6 GHz 16-QAM 90 Mbit/s digital radio on the 26.4 mi Atlanta-Palmetto path in Georgia. Two channels with a center frequency separation of 59.3 MHz were used in a one-by-one frequency diversity experiment. The 1980 data and the 1982 data indicate a frequency diversity improvement factor of 100 and 45, respectively, at the outage threshold of 10-3BER. This is in contrast to the improvement factor of 9 predicted for analog FM radio at the same fade margin. The measured one-by-one frequency diversity improvement factor is comparable to the measured space diversity improvement factor with 30 ft antenna spacing on the same path. We conclude that 1) frequency diversity can provide a large improvement factor for digital radio, 2) as an alternative to space diversity, frequency diversity can provide substantial cost savings for digital radio routes, and 3) the frequency diversity calculation based on analog FM radio experience is too conservative (i.e., pessimistic) for digital radio application. These experimental findings are in agreement with recent advances in digital radio diversity modeling. Digital radio performance depends heavily on the multipath dispersion in the channel. The measured data indicate that the power fade depths in the two channels are highly correlated, whereas the multipath dispersion in the two channels is decorrelated. This correlation difference provides insight into the measured large frequency diversity improvement factor for digital radio. View full abstract»

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  • Closed-Form Analytical Results for the Rejection of Narrow-Band Interference in PN Spread-Spectrum Systems--Part II: Linear Interpolation Filters

    Publication Year: 1985 , Page(s): 10 - 19
    Cited by:  Papers (46)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (832 KB)  

    The performance of PN spread-spectrum communication systems in the presence of narrow-band interference is studied when linear interpolation filters are employed for the estimation and subsequent suppression of the interference. Closed-form analytical expressions for the system's performance are established for a broad class of interference processes. The advantages of linear interpolation filters over predictive filters with identical number of taps are examined analytically and some unexpected results are obtained. The analytical results are illustrated by examples. View full abstract»

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  • Convolutional Coding Combined with Continuous Phase Modulation

    Publication Year: 1985 , Page(s): 20 - 29
    Cited by:  Papers (68)  |  Patents (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (928 KB)  

    Background theory and specific coding designs for combined coding/modulation schemes utilizing convolutional codes and continuous-phase modulation (CPM) are presented. In this paper the case of r = 1/2 coding onto a 4-ary CPM is emphasized, with short-constraint length codes presented for continuous-phase FSK, double-raised-cosine, and triple-raised-cosine modulation. Coding buys several decibels of coding gain over the Gaussian channel, with an attendant increase of bandwidth. Performance comparisons in the power-bandwidth tradeoff with other approaches are made. View full abstract»

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  • A Note on Contention with Reference to Communication Networks

    Publication Year: 1985 , Page(s): 103 - 104
    Cited by:  Papers (1)
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    In this paper we give a solution to a contention problem with reference to communication networks. A and B simultaneously try to access a communication channel. They attempt access again at some later time chosen at random. From what probability density function should the time be chosen to minimize conflict? They are not allowed to communicate with one another. View full abstract»

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  • On the Spectral Skewness of a Narrow-Band Gaussian Process

    Publication Year: 1985 , Page(s): 99 - 101
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    This correspondence discusses techniques for estimating the spectral skewness of the baseband spectrum of the complex envelope of a narrow-band Gaussian process from its undistorted and distorted (by memoryless nonlinear devices) in-phase and quadrature components. Some applications of the spectral skewness in communication theory are also mentioned. View full abstract»

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  • Bandwidth Efficient Quadrature Overlapped Squared Raised-Cosine Modulation

    Publication Year: 1985 , Page(s): 101 - 103
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (312 KB)  

    This correspondence describes staggered quadrature overlapped squared raised-cosine (QOSRC) modulation. The power spectrum of QOSRC attains good spectral characteristics over a bandpass hardlimited channel compared to quadrature overlapped raised-cosine (QORC) modulation because of less fluctuation of the signal envelope. It is found that QOSRC has better bit error probability performance than QORC. View full abstract»

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  • Analysis and Optimization of Correlative Code-Tracking Loops in Spread-Spectrum Systems

    Publication Year: 1985 , Page(s): 30 - 43
    Cited by:  Papers (65)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1328 KB)  

    The purpose of this paper is to apply the renewal theory approach for analyzing aperiodic finite S -curve code-tracking loops developed by Meyr [9] to the case of a noncoherent, arbitrary offset, early-late, delay-locked loop ("noncoherent δ-DLL"). The exact (renewal) approach is compared to the approximate (periodic-extension) approach of using the periodic S -curve or phase-locked loop theory, as well as to the linear theory developed herein for the aforementioned codetracking loop. Finally, loop optimization with respect to the offset δ is carried out according to certain performance criteria. The results indicate that, for low SNR, the exact and approximate theories could deviate significantly while, for high SNR, all three theories yield identical performance, as expected. Furthermore, it is shown that the optimal δ for both low and high SNR could differ from the commonly accepted choice \delta = 1/2 . View full abstract»

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  • Echo Cancellation of Voiceband Data Signals Using Recursive Least Squares and Stochastic Gradient Algorithms

    Publication Year: 1985 , Page(s): 65 - 73
    Cited by:  Papers (24)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (928 KB)  

    The convergence properties of adaptive least squares (LS) and stochastic gradient (SG) algorithms are studied in the context of echo cancellation of voiceband data signals. The algorithms considered are the SG transversal, SG lattice, LS transversal (fast Kalman), and LS lattice. It is shown that for the channel estimation problem considered here, LS algorithms converge in approximately 2N iterations where N is the order of the filter. In contrast, both SG algorithms display inferior convergence properties due to their reliance upon statistical averages. Simulations are presented to verify this result, and indicate that the fast Kalman algorithm frequently displays numerical instability which can be circumvented by using the lattice structure. Finally, the equivalence between an LS algorithm and a fast converging modified SG algorithm which uses a maximum length input data sequence is shown. View full abstract»

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  • A Simpler Approach to "Analysis of Integrated Voice/Data Multiplexing"

    Publication Year: 1985 , Page(s): 104 - 106
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    This paper gives a conceptually and algorithmically much simpler method for the model of a moving-boundary, fixed frame length, integrated multiplexor of the above paper. The method uses a Markov chain to obtain H_{[0,R]} and H_{R+t,s} , which can then be used to solve for the same joint distributions of queue length and expected waiting time as in the paper. This method enables a practitioner to use available standard packages to obtain system performance measures. View full abstract»

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  • Serial MSK-Type Detection of Partial Response Continuous Phase Modulation

    Publication Year: 1985 , Page(s): 44 - 52
    Cited by:  Papers (26)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (904 KB)  

    Partial response continuous phase modulation (CPM) schemes have a high spectrum utilization and also a high immunity to nonlinear distortion, since they have a constant envelope. Schemes with high power efficiency can also be designed when they are coherently detected with a Viterbi detector. These schemes are sometimes complex, however. In this paper two minimum-shift-keyed (MSK)type receivers are studied. The MSK-type receiver can be implemented as a serial receiver and as a parallel receiver. Both receivers are useful for binary modulation schemes with modulation index h = 1/2 . Only coherent detection of signals transmitted over an additive white Gaussian noise channel is considered. The serial receiver can be implemented with only two filters and simple decision logic. The decisions are made serially in one decision eye pattern. Two types of receiver filters are considered. Error probability results are presented for the receiver, both with and without phase and timing errors present in the receiver. It is shown that, assuming perfect phase and time synchronization, the serial and parallel receivers have equal performances. The advantages of the serial receiver over the parallel receiver are the same for partial response continuous phase modulation as for classical MSK; i.e., both in implementation aspects and in the reduced sensitivity to phase errors. View full abstract»

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  • On The Equivalence of Time-Division and Frequency-Division Multiplexing

    Publication Year: 1985 , Page(s): 97 - 99
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    On the basis of a general sampling formula it is shown that, for a system of n band-limited signals, FDM and band-limited TDM are equivalent in the sense that one can be derived from the other by a simple linear transformation. The transformation matrix is the same as for expanding an arbitrary polyphase system with n phases into its symmetric components. It is further shown that this equivalence also holds for nonideal sampling waveforms as they appear in certain multiplexing and demultiplexing systems used in practice. View full abstract»

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  • Individual Traffic Characteristics Queueing Systems with Multiple Poisson and Overflow Inputs

    Publication Year: 1985 , Page(s): 1 - 9
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (760 KB)  

    A theoretical method for analyzing overflow problems in queueing systems is presented. An interrupted Poisson process (IPP) approximation of overflow traffic is employed. An overflow stream is replaced by an IPP using the three-moment matching method. For a three-input model, to which one Poisson and two IPP streams are offered simultaneously, explicit and iterative formulas are derived to calculate the mean waiting time, overflow probability, and moments of overflow traffic intensity from the system for each of the three input streams. This three-input model is a general one, and can be used for analyzing complex problems such as multistage overflow models and individual traffic characteristics for a model with more than three inputs. By setting the capacity of the waiting room of the three-input model to 0, this method can cover loss systems. For both queueing and loss systems, several numerical examples of typical traffic models are shown. Comparisons are made between theoretical values and experimental values by computer simulations, and it is demonstrated that the accuracy of the method is excellent. View full abstract»

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  • An Algorithm for the Design of Labeled-Transition Finite-State Vector Quantizers

    Publication Year: 1985 , Page(s): 83 - 89
    Cited by:  Papers (66)
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    A finite-state vector quantizer (FSVQ) is a switched vector quantizer where the sequence of quantizers selected by the encoder can be tracked by the decoder. It can be viewed as an adaptive vector quantizer with backward estimation, a vector generalization of an AQB system. Recently a family of algorithms for the design of FSVQ's for waveform coding application has been introduced. These algorithms first design an initial set of vector quantizers together with a next-state function giving the rule by which the next quantizer is selected. The codebooks of this initial FSVQ are then iteratively improved by a natural extension of the usual memoryless vector quantizer design algorithm. The next-state function, however, is not modified from its initial form. In this paper we present two extensions of the FSVQ design algorithms. First, the algorithm for FSVQ design for waveform coders is extended to FSVQ design of linear predictive coded (LPC) speech parameter vectors using an Itakura-Saito distortion measure. Second, we introduce a new technique for the iterative improvement of the next-state function based on an algorithm from adaptive stochastic automata theory. The design algorithms are simulated for an LPC FSVQ and the results are compared with each other and to ordinary memoryless vector quantization. Several open problems suggested by the simulation results are presented. 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