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Communications, IEEE Transactions on

Issue 234  Part 1 • Date Feb-Apr 1994

 This issue contains several parts.Go to:  Part 2  | Part 3 

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Displaying Results 1 - 25 of 73
  • Construction of trellis codes with a good distance profile

    Publication Year: 1994 , Page(s): 290 - 298
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1016 KB)  

    Systematic feedforward trellis codes for 8-PSK and 16-QAM modulation are constructed using a nested step by step algorithm which guarantees a good distance profile. This makes the codes suitable for use with sequential decoding, where a rapidly growing distance profile is needed to reduce the average number of computations. In addition to having a good distance profile, the new codes achieve asymptotic coding gains of up to 6.53 dB. A procedure based upon the Fano (1963) algorithm (FA) is used to calculate the free distance of the new codes. This procedure is very effective for finding the free distances of long trellis codes because of the computational and storage efficiency of the FA. From a comparison of the new systematic feedforward codes with Ungerboeck's (1982, 1987) systematic feedback codes, the authors conjecture that a systematic feedforward code of constraint length 2/spl nu/ can achieve the same free distance as a systematic feedback code of constraint length /spl nu/.<> View full abstract»

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  • Disparity-based segmentation of stereoscopic foreground/background image sequences

    Publication Year: 1994 , Page(s): 673 - 679
    Cited by:  Papers (4)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1440 KB)  

    Describes a method for displacement estimation in stereoscopic images, which is closely coupled with a segmentation of the pictures into homogeneously displaced regions. The technique is driven by a statistical optimization criterion which assesses the quality of the disparity estimate and of the segmentation, thus improving both of these simultaneously. In addition, the optimization criterion explicitly takes occluded areas into consideration. With the additional help of two constraints, this enables the algorithm to locate regions corresponding to occlusions accurately View full abstract»

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  • On optimal AGC structure for direct sequence spread spectrum PN-code tracking

    Publication Year: 1994 , Page(s): 680 - 688
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (740 KB)  

    The performance of various AGC configurations, namely presync, postsync and an adaptive (optimal) AGC are analyzed at and above the threshold for a coherent pseudonoise (PN) second-order code tracking loop (delay lock loop, DLL) used in direct sequence spread spectrum systems. At and near the threshold the criterion of performance is chosen to be the mean time to lose lock (MTLL). Applying a recently presented method, analytic expressions for the loop performance are given, and the threshold degradation caused by Doppler rate is derived. Above the threshold, the “worst case” steady state tracking error is chosen as the loop index of performance. The performance and structure of the “globally-optimal“ AGC (at and above the threshold region) is derived, and a simplified, practical and still close to optimum adaptive AGC is presented. This configuration can easily be realized by digitally controlling the AGC parameters View full abstract»

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  • An improvement on codebook search for vector quantization

    Publication Year: 1994 , Page(s): 208 - 210
    Cited by:  Papers (20)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB)  

    Presents a simple but effective algorithm to speed up the codebook search in a vector quantization scheme when a MSE criterion is used. A considerable reduction in the number of operations is achieved. This algorithm was originally designed for image vector quantization in which the samples of the image signal (pixels) are positive, although it can be used with any positive-negative signal with only minor modifications View full abstract»

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  • A unified approach to network survivability for teletraffic networks: models, algorithms and analysis

    Publication Year: 1994 , Page(s): 534 - 548
    Cited by:  Papers (24)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1420 KB)  

    Addresses the problem of network survivability by presenting a unified approach where the wide-area circuit-switched teletraffic network and the underlying transmission facility network are considered simultaneously. The author assumes the backbone circuit-switched teletraffic network to be nonhierarchical with dynamic call routing capabilities. The transmission facility network is considered to be sparse (as is observed for emerging fiber optic networks) and is assumed to be two-arc connected. The approach addresses the network survivability objective by considering two grade-of-service parameters: one for the traffic network under normal operating condition and the other for affected part of the network under a network failure. The author presents unified mathematical models and develops heuristic algorithms. The author then presents computational results to demonstrate the effectiveness of the unified approach View full abstract»

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  • Multiple symbol partially coherent detection of MPSK

    Publication Year: 1994 , Page(s): 430 - 439
    Cited by:  Papers (14)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (628 KB)  

    The authors show that by using the known (or estimated) value of carrier tracking loop SNR in the decision metric, it is possible to improve the error probability performance of a partially coherent MPSK system relative to that corresponding to the commonly used ideal coherent decision rule. Using a maximum-likelihood approach, an optimum decision metric is derived and shown to take the form of a weighted sum of the ideal coherent decision metric (i.e., correlation) and the noncoherent decision metric which is optimum for differential detection of MPSK. The performance of a receiver based on this optimum decision rule is derived and shown to provide continued improvement with increasing length of observation interval (data symbol sequence length). Unfortunately increasing the observation length does not eliminate the error floor associated with the finite loop SNR. Nevertheless, in the limit of infinite observation length, the average error probability performance approaches the algebraic sum of the error floor and the performance of ideal coherent detection, i.e., at any error probability above the error floor, there is no degradation due to the partial coherence. While the above is strictly speaking only true in the limit of infinite observation length, it is shown that one can virtually achieve this limiting behavior with practical size observation lengths. Furthermore, the performance is quite insensitive to mismatch between the estimate of loop SNR (e.g., obtained from measurement) fed to the decision metric relative and its true value View full abstract»

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  • Noise performance of two frequency-error detectors derived from maximum likelihood estimation methods

    Publication Year: 1994 , Page(s): 793 - 802
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (912 KB)  

    Frequency tracking loops are used in digital links to control the carrier frequency of the received signals. A basic component in these loops is the frequency difference detector. This paper concentrates on two detectors that have previously been derived from maximum likelihood estimation criteria. Noise spectra of the detector outputs are computed and the results are used to assess the performance of frequency control loops operating in the tracking mode. Computer simulations are used to validate the theory. The detector implementation in digital form is also addressed and design criteria are provided that lead to structures with a limited computing complexity. Comparisons are made with other frequency detection schemes available in literature View full abstract»

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  • Combined source-channel vector quantization using deterministic annealing

    Publication Year: 1994 , Page(s): 347 - 356
    Cited by:  Papers (22)  |  Patents (26)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1172 KB)  

    The authors present a new approach to combined source-channel vector quantization. The method, derived within information theory and probability theory, utilizes deterministic annealing to avoid some local minima that trap conventional descent algorithms such as the generalized Lloyd algorithm. The resulting vector quantizers satisfy the necessary conditions for local optimality for the noisy channel case. They tested the method against several versions of the noisy channel generalized Lloyd algorithm on stationary, first order Gauss-Markov sources with a binary symmetric channel. The method outperformed other methods under all test conditions, with the gains over noisy channel GLA growing with the codebook size. The quantizers designed using deterministic annealing are also shown to behave robustly under channel mismatch conditions. As a comparison with a separate source-channel system, over a large range of test channel conditions, the method outperformed a bandwidth-equivalent system incorporating a Hamming code. Also, for severe channel conditions, the method produces solutions with explicit error control coding View full abstract»

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  • Efficient hybrid ARQ protocols with adaptive forward error correction

    Publication Year: 1994 , Page(s): 281 - 289
    Cited by:  Papers (20)  |  Patents (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (812 KB)  

    In this paper, efficient stop-and-wait, go-back-N and selective-repeat hybrid ARQ protocols with adaptive forward error correction (AFEC) using convolutional coding are proposed and analyzed. The basic idea is to vary the coding rate for error correction according to system parameters, such as the signal-to-noise ratio, the round trip delay and the buffer size at the receiver, so as to maximize the throughput efficiency. The performances of the proposed ARQ protocols are evaluated for two channel models: a non-fading and an ideally-interleaved Rayleigh-fading additive white Gaussian noise channel. In all cases it is found that the hybrid ARQ protocols with AFEC yield a comparatively high throughput under all channel conditions View full abstract»

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  • A simple evaluation of DPSK error probability performance in the presence of bit timing error

    Publication Year: 1994 , Page(s): 263 - 267
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (272 KB)  

    This paper presents a simple closed form expression for the conditional (on the timing error) bit error probability of an otherwise ideal DPSK receiver. Numerical results are given for average bit error probability obtained by averaging the conditional error probability over a Tikhonov PDF which is a typical characterization of the timing error in practical bit synchronizers View full abstract»

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  • A comparison of fixed and variable-rate signaling for meteor burst communications

    Publication Year: 1994 , Page(s): 211 - 215
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (456 KB)  

    This paper compares fixed-rate signaling (FRS) with variable-rate signaling (VRS) when used in conjunction with forward error-correction coding for meteor burst communications. VRS refers to the reduction of bandwidth to compensate for the signal decay, which occurs as a meteor trail diffuses. The performance is quantified by calculating the cutoff channel model which assumes that signal amplitude decays exponentially. It is that VRS achieves the limiting performance constant-amplitude channel if the signaling rate is adjusted to maintain a constant received energy per bit. It is also shown that the improvement of VRS over FRS is moderate to high. Small if the code rate is low and the decoder is provided with side information on the received signal level. Therefore, the use of low-rate coding and PRS is viable alternative to VRS for achieving good performance View full abstract»

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  • Folding algorithm: a computational method for finite QBD processes with level-dependent transitions

    Publication Year: 1994 , Page(s): 625 - 639
    Cited by:  Papers (34)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1492 KB)  

    This paper presents a new computational method for steady state analysis of finite quasi-birth-death (QBD) processes with level-dependent transitions. The QBD state space is defined in two-dimension with N phases and K levels. Instead of formulating solutions in matrix-geometric form, the Folding-algorithm provides a technique for direct computation of πP=0, where P is the QBD generator which is an (NK)×(NK) matrix. Taking a finite sequence of fixed-cost binary reduction steps, the K-level matrix P is eventually reduced to a single-level matrix, from which a boundary vector is obtained. Each step halves the matrix size but keeps the QBD form. The solution π is expressed as a product of the boundary vector and a finite sequence of expansion factors. The time and space complexity for solving πP=0 is therefore reduced from O(N3K) and O(N2K) to O(N3 log2 K) and O(N2 log2 K), respectively. The Folding-algorithm has a number of highly desirable advantages when it is applied to queueing analysis. First, the algorithm handles the multilevel control problem in finite buffer systems. Second, its total independence of the phase structure allows the algorithm to apply to more elaborate, multiple-state Markovian sources. Its computational efficiency, numerical stability and superior error performance are also distinctive advantages View full abstract»

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  • Blind equalization based on joint minimum MSE criterion

    Publication Year: 1994 , Page(s): 648 - 654
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (596 KB)  

    A joint minimum mean square error (MSE) criterion is presented for blind adaptive channel equalization of QAM signals. By jointly estimating the transmitted sequence and the equalizer parameters through the minimization of MSE, the equalizer parameters can be optimized and the channel input sequence can be restored at the equalizer output. To improve computational efficiency, a reduced constellation recursive least squares (RLS) algorithm is introduced for blind equalisation. Simulation results show the success of both the least square and the reduced constellation RLS algorithms View full abstract»

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  • The performance of focused error control codes

    Publication Year: 1994 , Page(s): 272 - 280
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (824 KB)  

    Consider an additive noise channel with inputs and outputs in the field GF(q) where q>2; every time a symbol is transmitted over such a channel, there are q-1 different errors that can occur, corresponding to the q-1 non-zero elements that the channel can add to the transmitted symbol. In many data communication/storage systems, there are some errors that occur much more frequently than others; however, traditional error correcting codes-designed with respect to the Hamming metric-treat each of these q-1 errors the same. Fuja and Heegard (1990) have designed a class of codes, called focused error control codes, that offer different levels of protection against “common” and “uncommon” errors; the idea is to define the level of protection in a way based not only on the number of errors, but the kind as well. In this paper, the performance of these codes is analyzed with respect to idealized “skewed” channels as well as realistic non-binary modulation schemes. It is shown that focused codes, used is conjunction with PSK and QAM signaling, can provide more than 1.0 dB of additional coding gain when compared with Reed-Solomon codes for small blocklengths View full abstract»

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  • Laurent's representation of binary digital continuous phase modulated signals with modulation index 1/2 revisited

    Publication Year: 1994 , Page(s): 221 - 224
    Cited by:  Papers (46)  |  Patents (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (288 KB)  

    In order to simplify modulator and demodulator structures, the composition of binary continuous phase modulations (CPMs) by the linear superposition of impulses as developed by Laurent (1986) is advantageous. Based on differential encoding of the binary data sequence, a novel CPM modulator concept for modulation index 1/2 is presented View full abstract»

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  • Performance analysis of an ARQ transmission scheme for meteor burst communications

    Publication Year: 1994 , Page(s): 268 - 271
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (316 KB)  

    Packet error probability is the key parameter in evaluating the performance of ARQ schemes, in terms of waiting time to receive a data packet, and system throughput. The authors present an analysis of the packet error probability for two modulation schemes, BFSK and BPSK, when uncoded packets are transmitted over the meteor burst channel using a fixed data rate. They show that the optimum transmission rate, minimizing the waiting time to receive a packet correctly, is independent of the initial SNR of the trail and the modulation used. The results were derived analytically, and are in excellent agreement with exact numerical calculations. They also present simple approximations to the exact calculations, and lower bounds on the packet error rate which are tight in the neighborhood of the optimum transmission rate View full abstract»

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  • Analysis of an all-digital maximum likelihood carrier phase and clock timing synchronizer for eight phase-shift keying modulation

    Publication Year: 1994 , Page(s): 773 - 782
    Cited by:  Papers (6)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (884 KB)  

    An all-digital trellis-coded 8PSK (TC-8PSK) demodulator well suited for VLSI implementation, including maximum likelihood estimation decision-directed (MLE-DD) carrier phase and clock timing recovery, is introduced and analysed. By simply removing the trellis decoder the demodulator can efficiently cope with uncoded 8PSK signals. The proposed MLE-DD synchronisation algorithm requires one sample for the phase and two samples per symbol for the timing loop. The joint phase and timing discriminator characteristics are analytically derived and numerical results checked by means of computer simulations. An approximated expression for steady-state carrier phase and clock timing mean square error has been derived and successfully checked with simulation findings. Synchronizer deviation from the Cramer Rao bound is also discussed. Mean acquisition time for the digital synchronizer has also been computed and checked, using the Monte Carlo simulation technique. Finally TC-8PSK digital demodulator performance in terms of bit error rate and mean time to lose lock, including digital interpolators and synchronization loops, is presented View full abstract»

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  • Complexity reduction of CELP speech coders through the use of phase information

    Publication Year: 1994 , Page(s): 248 - 251
    Cited by:  Papers (1)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (412 KB)  

    An efficient search procedure for CELP coders is described. Based on the phase spectra of the codevectors and the ideal excitation vector, a subset of the codebook is preselected. This subset is then exhaustively searched to find the best, perhaps optimum, codevector. Computational savings of the order of 30-40 are achieved while still maintaining good output speech quality View full abstract»

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  • Broadband packet switches based on dilated interconnection networks

    Publication Year: 1994 , Page(s): 732 - 744
    Cited by:  Papers (20)  |  Patents (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1288 KB)  

    A theoretical foundation for the evaluation and comparison of a very broad spectrum of fast packet-switching techniques is developed. Based on this framework, the authors investigate the complexity of various packet switch designs, and demonstrate the advantage of dilation as a switch-design technique. Packet switches are classified either as loss systems or waiting systems, according to whether packets losing contention are dropped or queued. In a loss system, the packet loss probability can be made arbitrary small by providing enough paths between inputs and outputs. The authors focus on the question: how does the switch complexity grow as a function of switch size for a given loss probability requirement? A uniform approach to this problem is developed. It is shown that for an N×N switch, the required number of switch elements for both the parallel-banyan network and the tandem-banyan network is of order N(log N)2, whereas the complexity of a dilated-banyan network is of order N log N(log log N). Within the class of waiting systems, it is shown that the parallel banyan networks in a Batcher-parallel-banyan network can be replaced by a dilated-banyan network without sacrificing the nonblocking property. Thus, as with parallelization, dilation can also be used to increase the throughput of a waiting system. In addition, the authors also explore the application of dilation in a large modular switch design which is realized by an interconnection structure consisting of Batcher-dilated-banyan networks and statistical multiplexers View full abstract»

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  • Channel assignment under a conflict-free allocation policy

    Publication Year: 1994 , Page(s): 466 - 476
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1104 KB)  

    A random, conflict-free slot assignment policy is adopted for the allocation of a common channel between two (non-communicating) stations. Although this policy is inferior to the optimal periodic, fixed slot assignment policy, it is shown than it achieves the performance of that optimal policy as the variance of the packet arrival process increases. The main advantage of the random, conflict-free slot assignment policy is that it is simple and always feasible unlike the optimal, periodic, fixed slot assignment policy. Furthermore, the proposed policy is easily implemented in a dynamically changing environment; the optimal such policy is derived and a simple strategy based on a threshold test is developed for the identification of the optimal such policy, when estimates of the traffic parameters are available. No such strategy is known for the adaptation of the parameters of the optimal periodic, fixed slot assignment policy. The developed analysis approach can be applied, to a great extent, to a system with more than two stations View full abstract»

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  • Four-dimensional signaling for bandlimited channels

    Publication Year: 1994 , Page(s): 403 - 409
    Cited by:  Papers (8)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (600 KB)  

    In this paper we discuss multidimensional signaling for transmission over the satellite channel, i.e., a bandlimited radio channel with nonlinearities. We derive a set of basis signals that are orthogonal and whose bandwidth occupancy is minimal, in the sense that they maximize the power inside a fixed frequency interval (-B, B). Since we remove the assumption that the signals be confined in one symbol interval, the concept of orthogonality must be revisited. We design basis signals that satisfy the following requirements: (a) When passed through their matched filter, the sample sequence has no intersymbol interference; (b) when passed through the filter matched to another basis signal, the sample sequence has no interchannel interference, and (c) their bandwidth occupancy is minimum. The performance of four-dimensional signals designed according to this criterion is evaluated in terms of bandwidth occupancy and error probability over nonlinear satellite channels. Comparisons with two-dimensional modulation schemes (in particular QPSK) are also made View full abstract»

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  • Differential detection of GMSK in Rician fading

    Publication Year: 1994 , Page(s): 216 - 220
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (392 KB)  

    The symbol error probability of Gaussian MSK using differential detection in a Rician fast fading channel is investigated. In the analysis, the effect of the infinite sequence of intersymbol interference inherent in this modulation is included exactly, and the performance can be evaluated at narrow shaping bandwidths where the intersymbol interference is extensive. Numerical results are presented for parameters typically encountered in the satellite-to-mobile channel View full abstract»

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  • Multiuser detectors for synchronous CDMA communication over non-selective Rician fading channels

    Publication Year: 1994 , Page(s): 711 - 722
    Cited by:  Papers (39)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1068 KB)  

    Synchronous code division multiple access (CDMA) data transmission over a non-selective Rician fading channel is considered, where the faded signal components arrive at the receiver in synchronism with the specular signal component. Under the assumption that the fading parameters are uncorrelated, this fading CDMA channel is shown to be equivalent to a Gaussian CDMA channel over which a modified signal set is employed. A fading counterpart of the multiuser asymptotic efficiency performance measure is defined. The asymptotic efficiencies of the optimum, decorrelating, and conventional detectors designed for the fading channel are derived. The conventional detector, which has low complexity, is shown to degrade rapidly in near-far environments. The optimal detector for the fading channel exhibits a significant improvement in performance but at the price of a computational complexity that increases exponentially with the number of users. The linear decorrelating detector for the fading case is optimally near-far resistant. The asymptotic efficiencies of multiuser detectors designed for the Gaussian channel when employed over the Rician fading channel are also obtained, thereby quantifying the loss in performance incurred by these mismatched detectors View full abstract»

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  • Video signal coding with DCT and vector quantization

    Publication Year: 1994 , Page(s): 200 - 207
    Cited by:  Papers (5)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2272 KB)  

    An image coding scheme using the discrete cosine transform is analyzed when the transform coefficients are vector quantized. The coding method is based on the known scheme proposed by Chen and Smith (1977) which sorts the picture blocks into classes according to the level of image activity. The coding scheme is modified to allow for vector quantization of the ac coefficients, in particular a pyramid vector quantizer (PVQ) is used. This is based on the statistical and geometric properties of a Laplacian source which, in fact, is the best model for the ac coefficients of the two-dimensional discrete cosine transform (2D-DCT) of an image. A method for forming almost statistically independent vectors is also suggested and improves quantization performance. Images are encoded with both the PVQ and standard scalar quantizer transform coders, demonstrating that the PVQ coder reduces the mean square encoding error and improves image quality. In particular, emphasis is given to how the use of fractional bit rates affects the objective and subjective gains obtained. The results presented (i.e. mean square error values and printed images) have been obtained experimentally, working with a statistical criterion in a group of images whose size was in accordance with the 50 Hz CCIR Recommendation 601 Standard View full abstract»

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  • Discrete time queues with phase dependent arrivals

    Publication Year: 1994 , Page(s): 606 - 614
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (948 KB)  

    The queueing behavior of many communication systems is well modeled by a queueing system in which time is slotted, and the number of entities that arrive during a slot is dependent upon the state of a discrete time, discrete state Markov chain. Techniques for analyzing such systems have appeared in the literature from time to time, but distributions have been presented in only rare instances In the paper, the authors present the probability generating function (PGF) for joint and marginal buffer occupancy distributions of statistical time division multiplexing systems in this class. They discuss inversion of the PGF using discrete Fourier transforms, and also discuss a simple technique for obtaining moments of the queue length distribution. Numerical results, including queue length distributions for some special cases, are presented View full abstract»

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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