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Communications, IEEE Transactions on

Issue 3 • Date March 1983

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Displaying Results 1 - 25 of 26
  • [Front cover and table of contents]

    Publication Year: 1983 , Page(s): 0
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    Freely Available from IEEE
  • Comments on "Discrete-Time Queueing Systems and Their Networks"

    Publication Year: 1983 , Page(s): 461 - 463
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (282 KB)  

    In the paper Bharath-Kumar presented an analysis of a discrete buffered system of infinite capacity, where the length of the packets is drawn from a geometric distribution and the packets leaving the resource have to be retransmitted with some probability. In this correspondence an analysis of the same system is given which applies for a general packet length distribution, and where the length of a packet remains the same each time it is retransmitted, as opposed to Bharath-Kumar's model where the retransmission packet lengths are independently chosen. View full abstract»

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  • Comments on "Real-Time Speech Coding"

    Publication Year: 1983 , Page(s): 466 - 468
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    First Page of the Article
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  • [Back cover]

    Publication Year: 1983 , Page(s): 0
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    Freely Available from IEEE
  • Time Diversity with Adaptive Error Detection to Combat Rayleigh Fading in Digital Mobile Radio

    Publication Year: 1983 , Page(s): 378 - 387
    Cited by:  Papers (5)  |  Patents (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1024 KB)  

    A new diversity technique is proposed to combat Rayleigh fading in digital mobile radio systems transmitting speech signals. The speech signals are μ-law PCM encoded ( \mu = 255 , 8 kHz sampling, 8 bits/code word, 64 kbit/s data rate), and alternate data words are used to form two streams called "odd" and "even." The even stream is delayed by τ seconds and the streams are interleaved prior to radio transmission using two-level PSK modulation. At the receiver the odd data stream is delayed by τ and interleaved with the even stream. Consequently, if an error burst occurs, the effect of the reshuffling of the data stream is, in general, to place words with bit errors in juxtaposition to those correctly received. After μ-law PCM decoding of the words, a statistical error detection strategy is evoked to identify the erroneous samples. These samples are replaced by adjacent sample interpolation to give the recovered speech sequence. No recourse to channel protection coding is made. In our experiments a Rayleigh fading envelope was generated from a hardware simulator and stored in a computer, along with four sentences of speech. The system was then simulated and the recovered speech perceived. The objective performance measures were segmental SNR for the audio signal, and BER. Different error detection strategies were examined and restrictions on τ investigated. For a mobile speed of 30 mph, SNR values of 32, 21, and 16 dB were obtained for BER values of 0.1, 1, and 2 percent, corresponding to SNR gains over an uncorrected system of 3, 9, and 11 dB, respectively. View full abstract»

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  • A Comparison of Two Types of Symbol Synchronizers for Which Self-Noise Is Absent

    Publication Year: 1983 , Page(s): 329 - 334
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (528 KB)  

    For most symbol synchronizers operating on a PAM waveform corrupted by noise, the timing error consists of a noisedependent term and a data-dependent term. When the signal-to-noise ratio (SNR) is high, the data-dependent term, which is often called self-noise, dominates, and the timing error variance becomes independent of SNR. In this paper we present two types of symbol synchronizers for which self-noise is absent: the modified maximum-likelihood (MML) synchronizer and the minimum mean-square error (MMSE) synchronizer. As a consequence of the absence of self-noise, their timing error variances at high SNR are inversely proportional to the SNR. The performances of these synchronizers are evaluated and compared with the Cramér-Rao bound. View full abstract»

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  • On Binary DPSK Error Rates Due to Noise and Intersymbol Interference

    Publication Year: 1983 , Page(s): 463 - 466
    Cited by:  Papers (8)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (344 KB)  

    This paper presents a new series for evaluating the conditional bit error rate (BER) of a given transmitted data sequence in a band-limited binary differential-phase-shift-keyed system. This series involves modified Struve functions and it was found to have converged quickly. The conditional BER can then be averaged over all possible bit sequences to yield the system BER. The results obtained are close to those reported by G. J. Marshall. In our analysis the noise samples a bit period apart were assumed to be uncorrelated. View full abstract»

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  • Routing to Multiple Destinations in Computer Networks

    Publication Year: 1983 , Page(s): 343 - 351
    Cited by:  Papers (105)  |  Patents (15)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (872 KB)  

    Algorithms for effectively routing messages from a source to multiple destination nodes in a store-and-forward computer network are studied. The focus is on minimizing the network cost (NC), which is the sum of weights of the links in the routing path. Several heuristic algorithms are studied for finding the NC minimum path (which is an NP-complete problem). Among them are variations of a minimum spanning tree (MST) heuristic and heuristics for the traveling salesman problem, both of which use global network information. Another set of heuristics examined are based on using only the shortest paths to the destinations. While the MST algorithm has the best worst case performance among all algorithms, a detailed, empirical study of the "average" performance of the algorithms on typical, randomly chosen networks reveals that simpler heuristics are almost as effective. The NC cost measure is also compared to the destination cost (DC), which is the sum of weights of the shortest path distances to all destinations. A scheme of algorithms is given which trades off between NC and DC. View full abstract»

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  • Redundancy, the Discrete Fourier Transform, and Impulse Noise Cancellation

    Publication Year: 1983 , Page(s): 458 - 461
    Cited by:  Papers (75)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (440 KB)  

    The relationship between the discrete Fourier transform and error-control codes is examined. Under certain conditions we show that discrete-time sequences carry redundant information which then allow for the detection and correction of errors. An application of this technique to impulse noise cancellation for pulse amplitude modulation transmission is described. View full abstract»

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  • A Hybrid Multichannel Hardware Simulator for Frequency-Selective Mobile Radio Paths

    Publication Year: 1983 , Page(s): 370 - 377
    Cited by:  Papers (20)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (968 KB)  

    We present the analysis and design of an efficient hybrid digital/analog multichannel hardware simulator for frequencyselective Rayleigh-fading mobile radio paths. The simulator has eight RF outputs and is linear and reciprocal. All outputs exhibit mutually independent Rayleigh fading over a 45 dB range and have identical time delay spreads. Analog RF techniques are combined with a digital signal processor (DSP) to generate random path modulation. Frequency selectivity from time delay spread is created using several RF path delay elements. Simulated vehicle velocity is continuously variable from 6 to 60 mph. The simulator is thus a flexible tool for the study of mobile radio transmission techniques. View full abstract»

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  • Diversity ALOHA--A Random Access Scheme for Satellite Communications

    Publication Year: 1983 , Page(s): 450 - 457
    Cited by:  Papers (40)  |  Patents (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (664 KB)  

    A generalization of the slotted ALOHA random access scheme is considered in which a user transmits multiple copies of the same packet. The multiple copies can be either transmitted simultaneously on different frequency channels (frequency diversity) or they may be transmitted on a single high-speed channel but spaced apart by random time intervals (time diversity). In frequency diversity, two schemes employing channel selections with and without replacements have been considered. In time diversity, two schemes employing a fixed number of copies or a random number of copies for each packet have been considered. In frequency diversity, activity factor-throughput tradeoffs and in time diversity, delay-throughput tradeoffs for various diversity orders have been compared. It is found that under light traffic, multiple transmission gives better delay performance. If the probability that a packet fails a certain number or more times is specified not to exceed some time limit (realistic requirement for satellite systems having large round trip propagation delay), then usually multiple transmission gives higher throughput. View full abstract»

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  • A Class of Two-Symbol-Interval Modems for Nonlinear Radio Systems

    Publication Year: 1983 , Page(s): 433 - 441
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (624 KB)  

    Based on Feher's nonlinear filter (NLF) invention, we developed a class of intersymbol-interference and jitter-free (IJF) baseband signals and JJF-OQPSK systems. In [14] and [18] we demonstrated the performance advantages of these systems over QPSK, OQPSK, and MSK systems. In this paper a new class of IJF two-symbol-interval (TSI) baseband pulse shapes is introduced. The spectral properties and the Peperformance of these TSI-OQPSK modulated systems is investigated. We show that in a hard-limited radio system the main lobe of the n \geq 2 , TSI-OQPSK is narrower and that the sidelobes, in the critical |(f-f_{c})T_{s}| < 2 region, are lower than that of QPSK, OQPSK, MSK, and N = 1 , IJF-OQPSK systems. A new filtering strategy, the sum of approximate eye (SAE), is also introduced. It is shown that SAE filters may reduce the E_{b}/N_{0} requirements of band-limited and hard-limited TSI-OQPSK modems. View full abstract»

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  • An Analytical Formulation for Grade of Service Determination in Telephone Networks

    Publication Year: 1983 , Page(s): 420 - 424
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (400 KB)  

    The paper provides a simple method for point-to-point blocking estimation in telephone networks. A one-moment model is developed which incorporates the definition of fictitious offered traffic that enables one to take into account the deviation of smooth and peaked traffics from the Poisson. Numerical results illustrate the accuracy of the method. View full abstract»

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  • The Stability of Adaptive Minimum Mean Square Error Equalizers Using Delayed Adjustment

    Publication Year: 1983 , Page(s): 430 - 432
    Cited by:  Papers (28)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (280 KB)  

    The necessary and sufficient conditions for the stability and convergence of adaptive minimum mean square error equalizers are developed. The analysis includes the effect of delays in the adjustment path, as occur, for instance, when the decoder in a data transmission system delays its output decisions. View full abstract»

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  • Anisotropic Nonstationary Image Estimation and Its Applications: Part II--Predictive Image Coding

    Publication Year: 1983 , Page(s): 398 - 406
    Cited by:  Papers (13)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1736 KB)  

    A new predictive coder, based on an estimation method which adapts to line and edge features in images, is described. Quantization of the prediction error is performed by a two-level adaptive scheme: an adaptive transform coder, and threshold coding in both transform and spatial domains. Control information, which determines the behavior of the predictor, is quantized using a simple variable rate technique. The results are improved by pre- and postfiltering using a related noncausal form of the estimator. Acceptable images have been produced in this way at bit rates of less than 0.5 bit/pixel. View full abstract»

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  • Anisotropic Nonstationary Image Estimation and Its Applications: Part I--Restoration of Noisy Images

    Publication Year: 1983 , Page(s): 388 - 397
    Cited by:  Papers (42)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2072 KB)  

    A new form of image estimator, which takes account of linear features, is derived using a signal equivalent formulation. The estimator is shown to be a nonstationary linear combination of three stationary estimators. The relation of the estimator to human visual physiology is discussed. A method for estimating the nonstationary control information is described and shown to be effective when the estimation is made from noisy data. A suboptimal approach which is computationally less demanding is presented and used in the restoration of a variety of images corrupted by additive white noise. The results show that the method can improve the quality of noisy images even when the signal-to-noise ratio is very low. View full abstract»

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  • Two-Dimensional DPCM Image Transmission Over Fading Channels

    Publication Year: 1983 , Page(s): 315 - 328
    Cited by:  Papers (13)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1528 KB)  

    A combined source-channel coding approach is described for the encoding, transmission, and remote reconstruction of image data. The transmission medium considered is that of a fading dispersive communications channel. Both the Rician fading and Rayleigh fading channel models are considered. The image source encoder employs two-dimensional (2-D) differential pulse code modulation (DPCM). This is a relatively efficient encoding scheme in the absence of channel errors. In the presence of fading, however, the performance degrades rapidly. By providing error control protection to those encoded bits which contribute most significantly to image reconstruction, it is possible to minimize this degradation without sacrificing transmission bandwidth. Several modulation techniques are employed in evaluation of system performance including noncoherent multiple frequency shift-keyed (MFSK) modulation. Analytical results are provided for assumed 2-D autoregressive image models, while simulation results are described for real-world images. View full abstract»

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  • Sharing Memory Optimally

    Publication Year: 1983 , Page(s): 352 - 360
    Cited by:  Papers (50)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (848 KB)  

    Efficient design of service facilities, such as data or computer networks that meet random demands, often leads to the sharing of resources among users. Contention for the use of a resource results in queueing. The waiting room is a part of any such service facility. The number of accepted service requests per unit of time (throughput), or the fraction of the time the servers are busy (utilization), are often used as performance measures to compare designs. Most common models in queueing theory consider the design of the waiting rooms with the assumption that, although individual requests may differ from one another, they are statistically indistinguishable. However, there are several instances where available information allows us to classify the requests for service into different types. In such cases the design of the service facility not only involves the determination of an optimum size for the waiting room but also the rules of sharing it among the different types. Even with a fixed set of resources, the rules of sharing them can influence performance. In data networks (or computer networks) the "waiting room" consists of memory of one kind or another. Messages (jobs) destined for different locations (processors) sharing common storage is an important example of shared use of memory. Recently, Kleinrock and Kamoun have modeled such use of memory and computed the performance of various policies for managing the allocation of memory to several types of users. Decisions to accept or reject a demand for service were based on the number of waiting requests of each type. However, the optimal policy was not determined even in the case where there were only two types of users. We determine the structure of optimal policies for the model considered with three types of users. The optimal policy consists of limiting the number of waiting requests of each type, and reserving a part of the memory to each type. View full abstract»

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  • A Class of High Rate Codes for Byte-Oriented Information Systems

    Publication Year: 1983 , Page(s): 334 - 342
    Cited by:  Papers (6)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (816 KB)  

    In this paper we introduce a class of linear codes especially designed to provide additional error protection for data consisting of bytes all having even (or odd) parity (e.g., ASCII characters). The technique consists in adding an overall parity byte computed as a linear function of the information bytes. The linear function is designed such that the resulting codes can correct all single errors and all double errors occurring in distinct information bytes. It is shown that any code which can correct these latter mentioned error patterns has an overall length of at most 37 bytes, and a specific code of length 29 bytes is described. A practical decoding algorithm for the new class of codes is described. Finally, the performance of the codes, when used on the binary symmetric channel, is compared with that of the row-column codes for which the additional parity byte is simply the modulo-2 sum of the information bytes. View full abstract»

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  • Design Methodology for ΣΔM

    Publication Year: 1983 , Page(s): 360 - 370
    Cited by:  Papers (75)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1152 KB)  

    The paper presents a design methodology based on correspondence between performance requirements, mathematical parameters, and circuit parameters of a sigma-delta modulator. This methodology will guide a design engineer in selecting the circuit parameters based on system requirements, in translating paper design directly into LSI design, in predicting the effect of component sensitivity, and in analyzing the operations of the sigma-delta modulator. The sigma-delta modulator is viewed as a device which distributes the noise power, determined by peak SNR, over a much broader band, compared to signal bandwidth, shapes and amplifies it, and allows filtering of the out-of-band noise. The shaping and amplification are quantified by two parameters, F and P , whose product is analogous to the square of step size of a uniform coder. These two parameters are related, on one hand, to the time constants or location of zero and poles. On the other hand, inequalities are set up between performance parameters, like signal-to-noise ratio and dynamic range, and F and P . View full abstract»

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  • Line-Adaptive Hybrid Coding of Images

    Publication Year: 1983 , Page(s): 445 - 450
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (648 KB)  

    This paper describes novel adaptation strategy for hybrid transform/DPCM image coders. This strategy has yielded a 2-8 dB increase in signal-to-noise ratio in the transmission of a head and shoulders image at bit rates of 1-4 bits per pel and one-dimensional transform block sizes of 2-16. View full abstract»

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  • Performance of a Direct Sequence Spread-Spectrum System with Long Period and Short Period Code Sequences

    Publication Year: 1983 , Page(s): 412 - 419
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (616 KB)  

    In this paper, the performance of a direct sequence spread-spectrum system is analyzed with both a long period sequence and with a sequence whose period is one bit long. Bit error rates for both quadriphase and biphase chip spreading, in conjunction with both QPSK and BPSK data, are considered in the presence of noise and jamming. The frequency location of the jammer is arbitrary. View full abstract»

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  • Digital Image Compression by Outer Product Expansion

    Publication Year: 1983 , Page(s): 441 - 444
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (656 KB)  

    We approximate a digital image as a sum of outer products dxyTwhere d is a real number but the vectors x and y have elements +1, -1, or 0 only. The expansion gives a least squares approximation. Work is proportional to the number of pixels; reconstruction involves only additions. View full abstract»

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  • Bit Rate Reduction of Digitized Speech Using Entropy Techniques

    Publication Year: 1983 , Page(s): 424 - 430
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (616 KB)  

    We present the results of a study to reduce the bit rate of speech that has been digitized with a continuously variable slope delta modulator (CVSD) operating at 16, 24, and 32 kbits/s. The theoretical reduction is found from the bit stream entropy. The actual reduction, via Huffman coding, is within 1-2 Percent of the theoretical value. The conditional entropy indicates that additional bit rate reduction can be achieved if we use a set of Huffman codes, conditioned on the past CVSD bits. A third technique, tandem coding, using a maximum likelihood predictor in tandem with run length and Huffman coding, is also investigated. Using these entropy techniques, bit rate reductions of 11-25 percent are achieved for the CVSD rates considered. The paper concludes with a study of the buffer requirements needed to support these entropy coders. View full abstract»

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  • Error Rate Estimates in Digital Communication Over a Nonlinear Channel with Memory

    Publication Year: 1983 , Page(s): 407 - 412
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (528 KB)  

    The principal representations of Krein are known to provide very tight upper and lower bounds on the error probability in digital communication over a linear channel with intersymbol interference. These bounds depend on the signal-to-noise ratio, the amount of intersymbol interference, and the number of moments of the random interference variable. The same technique can be applied to a nonlinear channel with memory. However, it is difficult to calculate these moments when the channel is nonlinear and has memory. In this paper, we describe a method for computing the moments for the case of an arbitrary nonlinear channel with finite memory. The method of Krein is then used to evaluate the error probability from the moments obtained. We demonstrate the technique with two examples. The model of the nonlinear channel consists of a linear filter in cascade with a memoryless nonlinearity followed by another linear filter. If a sufficient number of moments are used, we obtain accurate estimates of the true error probability. 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