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Communications, IEEE Transactions on

Issue 234 • Date Feb-Apr 1994

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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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  • A new artificial speech signal for objective quality evaluation of speech coding systems

    Publication Year: 1994 , Page(s): 664 - 672
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (844 KB)  

    Describes a new artificial speech signal (ASVQ: artificial speech by vector quantization technique) which reflects the average characteristics of the human voice. The ASVQ is intended for use as a test signal in the objective evaluation of speech coding system quality. To obtain the average characteristics, a very large speech data base is analysed, The ASVQ generation method which reflects the extracted average characteristics of the human voice is formulated. This method applies vector quantizing analysis to the speech data base. The LPC speech synthesis circuit is used to reproduce the average characteristics. Finally, the new artificial speech signal is compared with a human voice and the estimation accuracy of the subjective quality of speech coding systems and nonlinear distortions is evaluated 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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  • Signal and interference statistics of a CDMA system with feedback power control. II

    Publication Year: 1994 , Page(s): 597 - 605
    Cited by:  Papers (79)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (964 KB)  

    For pt.I see ibid., vol 41, p.1626-34 (1993). Power control is essential in the use of direct-sequence code division multiple-access (CDMA) techniques. Early system-level performance analyses of a CDMA approach to wireless mobile and personal communications have assumed the ability of power control to equalize the absolute signal powers of CDMA users received at each base station. The present paper studies a more practical, although analytically more complicated, uplink power control technique that uses measurements of the received signal-to-interference ratio (SIR) instead. A combination of discrete-event link simulation and analysis of the obtained SIR statistics is used to explore the previously little-known behavior of a CDMA system using SIR-based power control and to obtain performance estimates for such a system under various operating assumptions. The overall results indicate that power control based on SIR has the potential for somewhat higher system performance than power control based on absolute signal strength assumed in the early analyses View full abstract»

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  • Distributed power control in cellular radio systems

    Publication Year: 1994 , Page(s): 226 - 228
    Cited by:  Papers (121)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (252 KB)  

    The capacity of cellular mobile radio systems can be increased by controlling the transmitter powers so as to balance the carrier to interference ratios at the receivers. A distributed algorithm for implementing such power control was proposed earlier for satellite systems by Meyerhoff (1974). The authors tighten the mathematical arguments and apply this scheme to cellular systems. The mobile units adjust their transmitter powers at discrete time instants. Specifically at each time instant the mobile multiplies its current power by a factor equal to a constant over its current carrier to interference ratio (CIR). So power is increased or decreased based on the value of the current CIR. After a number of such power adjustments all the mobiles converge to a common CIR. They also present numerical results which show that the above scheme has the potential to converge faster than the scheme proposed by J. Zander (see IEEE Transactions on Vehicular Technology, vol.41, no.3, August 1992) for high CIR values 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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  • Universal source coding with codebook transmission

    Publication Year: 1994 , Page(s): 336 - 346
    Cited by:  Papers (17)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1128 KB)  

    A universal source coding system with vector quantizer codebook transmissions is studied using high resolution quantization theory. Conditions are derived for the optimal tradeoff between quantizer resolution and the information rate used to transmit codebooks. A formula that tightly bounds the mean squared error of the universal coding system as a function of the time between codebook transmissions is experimentally verified and found to be tight, and a new and simpler derivation is given. Other research in the literature has proposed vector quantizing the transmitted codebooks; one conclusion we prove here is that under some reasonable conditions uniform scalar quantization of the transmitted codebooks performs as well as vector quantizing them. Experimental results are given that support the analytic derivations 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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  • Impact of a non-fading Gaussian characterization of interference on portable radio link analysis

    Publication Year: 1994 , Page(s): 396 - 402
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (552 KB)  

    In order to make the analytical evaluation of portable radio link performance tractable while avoiding lengthy simulations, intersymbol interference and cochannel interference are often modelled as non-fading, Gaussian noise. This paper investigates the viability of such an approach for wideband channels where equalization and space diversity are used to combat interference and signal fading. Comparisons of results obtained using such an assumption of interference with those of a simulation-based approach indicate that as long as the number of cochannel interferers is smaller than the space diversity order, the variance of the Gaussian interfering symbols can be adjusted to provide a reasonable estimate of performance over error rates of interest 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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  • Nlog N dual shuffle-exchange network with error-correcting routing

    Publication Year: 1994 , Page(s): 754 - 766
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1332 KB)  

    Describes a dual shuffle-exchange switching network (DSN) that makes use of the principle of error-correcting routing. For motivation, parallels are drawn between error-correcting routing in switching and error-correcting coding in transmission. Based on a novel error-correcting and self-routing algorithm, the authors show by analysis and simulation that the DSN can achieve the Shannon's lower bound Nlog N on switch complexity while satisfying four desirable criteria: 1) self-routing property; 2) no queueing of packets at the inputs or inside the switch; 3) arbitrarily small packet-loss probability; 4) close-to-100% throughput. Different implementations of the basic DSN concept and their trade-offs are discussed View full abstract»

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  • An exact performance analysis of the clipped diversity combining receiver for FH/MFSK systems against a band multitone jammer

    Publication Year: 1994 , Page(s): 700 - 710
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1088 KB)  

    This paper applies the clipper receiver with diversity combining techniques to the frequency hopping (FH) M-ary frequency shift keying (MFSK) systems against a destructive band multitone jammer, and presents an exact error probability performance evaluation with further discussions. A noise free channel is first assumed for analysis, and this assumption is then verified by computer simulation. Both optimal jamming tone power from the jammer's view and the choice of the clipping level from the communicator's view are investigated. The worst case performance of the FH/MFSK system against an optimum jammer is discussed in detail with extensive numerical results. It is also found that the clipper receiver provides the most attractive performance as compared to several other diversity combining receivers previously proposed View full abstract»

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  • Calculation of message delays and message waiting times in switching elements with slow access lines

    Publication Year: 1994 , Page(s): 255 - 259
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (440 KB)  

    In this paper we study the delay performance of an ATDM switching element, to which messages composed of a variable number of fixed-length packets arrive via “low-speed” access lines, at the rate of one packet per time slot. More specifically, we analyse the message waiting times and the message delays encountered in this switching element, and compare the results with the case of “fast” access lines, in which all the packets of a message arrive in the same slot. The study is an extension/continuation of previous work, which was mainly concerned with the derivation of buffer occupancies and packet delays View full abstract»

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  • Performance analysis of a multilevel coded modulation system

    Publication Year: 1994 , Page(s): 299 - 312
    Cited by:  Papers (32)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1444 KB)  

    A modified version of the multilevel coded modulation scheme of Imai and Hirakawa (1977) is presented and analyzed. In the transmitter, the outputs of the component codes are bit interleaved prior to mapping into 8-PSK channel signals. A multistage receiver is considered, in which the output amplitudes of the Gaussian channel are soft limited before entering the second and third stage decoders. Upper bounds and Gaussian approximations for the bit error probability of every component code, which take into account errors in previously decoded stages, are presented. Aided by a comprehensive computer simulation, it is demonstrated in a specific example that the addition of the interleaver and soft limiter in the third stage improves its performance by 1.1 dB at a bit error probability of 10-5, and that the multilevel scheme improves on an Ungerboeck's code with the same decoding complexity. The rate selection of the component codes is also considered and a simple selection rule, based on information theoretic arguments, is provided View full abstract»

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  • Modeling and analysis of a tandem link connection under the burst-error condition

    Publication Year: 1994 , Page(s): 360 - 366
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (740 KB)  

    Transmission errors are known to be bursty in nature. In block-oriented data communication, this bursty error behavior should be treated assuming that there are non-renewal correlations between the transmission conditions of data block. In this paper, using the stochastic sequential machine method the authors suggest a block-level burst error model of a digital tandem connection that consists of a set of segmented channels, and then investigate several end-to-end error performance characteristics under the burst-error condition. Also, they derive expressions that approximate the tandem connection model parameters by combining individual segment channel models into an equivalent combined error model. They show the proposed method is very useful in describing the error performance of tandem link connections View full abstract»

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  • Application of generalized minimum distance decoding to hybrid-ARQ error control

    Publication Year: 1994 , Page(s): 640 - 647
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (760 KB)  

    Generalized minimum distance (GMD) decoding is modified to allow simultaneous error detection and error correction. The soft-decision information retained by the generalized minimum distance concept is used as a source of reliability information which determines when a retransmission of the received packet should be requested. The performance of hybrid-ARQ GMD decoding is shown to be comparable to the ideal reliability metrics proposed by Loeliger (1990) and superior to the performance of hard-decision decoders. Performance expressions are derived for low to moderate signal-to-noise ratios and bounds are derived for high signal-to-noise ratios which are loose by 0.5 to 1.0 dB View full abstract»

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  • Design of transmit and receive digital filters for data communications

    Publication Year: 1994 , Page(s): 357 - 359
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (288 KB)  

    This paper describes a design method for the synthesis of digital filters in data communication systems. The coefficients in the transmit and receive filters are optimized to meet specified requirements on (i) out-of-band emission, (ii) intersymbol interference, (iii) adjacent channel interference and (iv) thermal noise immunity 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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  • Error states and synchronization recovery for variable length codes

    Publication Year: 1994 , Page(s): 783 - 792
    Cited by:  Papers (18)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (752 KB)  

    An efficient technique for obtaining a variable length code (VLC) resistant to synchronization loss due to channel errors is proposed. Bit errors in the channel lead to incorrect decoding of a VLC and result in error states for continuous codewords. In this paper first a precise value is found for assessing the ability of a VLC to recover synchronization from the error states. Next a new transformation for converting a code into another of the same efficiency (equivalent transformation) is introduced, and several VLCs with an identical efficiency are compared through estimation of synchronization recovery in order to find an error-resistant VLC. Based on the equivalent transformation, an efficient method for finding an error-resistant VLC with high recovery performance from among multiple VLCs is described View full abstract»

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  • Perfect three-level and three-phase sequences and arrays

    Publication Year: 1994 , Page(s): 767 - 772
    Cited by:  Papers (8)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (572 KB)  

    Introduces construction methods for synthesizing new classes of perfect sequences and arrays. Time discrete sequences and arrays are perfect, if their periodic autocorrelation function sidelobes are zero. The construction of perfect three-level and three-phase sequences is performed in two steps. In the first step, a maximal length shift-register sequence with elements in GF(q) is built for a length of gm-1, where q is a prime power and m is a positive integer. In the second step, a sequence is constructed by mapping the elements of the shift-register sequence to 1, b1 or b2. Two real numbers b1 and b2 are determined such that the sequence becomes perfect and has high energy efficiency. The phase values for complex numbers b1 and b2 with magnitude 1 are given for perfect three-phase sequences. It is shown that the phase values of b1 and b2 tend for growing lengths to 2π/3 and 4π/3. A different similar synthesizing method starts with Legendre sequences. The construction of perfect three-level and three-phase arrays is performed by several methods, which make use of the new respective sequences 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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  • Packet speech transmission on ATM networks using a variable rate embedded ADPCM coding scheme

    Publication Year: 1994 , Page(s): 243 - 247
    Cited by:  Papers (8)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (504 KB)  

    The authors propose a packet speech coding scheme to vary the code bits of an embedded ADPCM coder between 6 bits per sample, for high prediction gain speech blocks, to 2 bits for blocks representing silence. Subjective quality of 3.2 MOS on a scale of 1 to 5 at an enhancement-bit loss rate of 30% was obtained 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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Meet Our Editors

Editor-in-Chief
Robert Schober
University of British Columbia