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Communications, IEEE Transactions on

Issue 8 • Date Aug. 1999

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Displaying Results 1 - 21 of 21
  • A discrete-time method of demodulating large deviation FM signals

    Page(s): 1194 - 1200
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (573 KB)  

    A method of enhancing the performance of a numerical FM discriminator in specific receive signal conditions, using frequency feedback techniques, is developed and evaluated. The receive signal conditions of interest are: (1) frequency deviations that are large relative to the bandwidth of the message signal; (2) a low-uniform (complex) sample rate commensurate with the bandwidth; and (3) noise strengths that yield values of input carrier-to-noise ratio of the order of 10 dB or more. Through computer simulation, observed phase cycle-slip counts and phase noise variance estimation are used to compare the enhanced demodulator to the performance of a numerical FM discriminator baseline. Based upon the theoretical analyses and simulation results, the presented method of numerical FM demodulation is shown to be a viable technique for enhancing the performance of numerical FM discriminators under the given modulation conditions. View full abstract»

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  • Capacity enhancement of band-limited DS-CDMA system using weighted despreading function

    Page(s): 1218 - 1226
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (268 KB)  

    This paper addresses capacity enhancement of a band-limited direct-sequence code-division multiple-access system by using a weighted despreading function (WDF) in the receiver. An ideal Gaussian channel with perfect power control is assumed. The system performance is measured by the signal-to-interference-plus-noise ratio of the decision variable derived in the frequency domain, the bandwidth efficiency factor, the capacity enhancement factor, and the bit-error rate. It is shown that tuning a parameter of the WDF employed helps to partially flatten the in-band cross-spectrum of a pair of spreading and despreading functions. Numerical results show that the capacity of the proposed system improves over the conventional system using rectangular despreading function. To assess practical implications of the WDF receiver, the sensitivity to timing error is also analyzed View full abstract»

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  • Two simple stopping criteria for turbo decoding

    Page(s): 1117 - 1120
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (108 KB)  

    This paper presents two simple and effective criteria for stopping the iteration process in turbo decoding with a negligible degradation of the error performance. Both criteria are devised based on the cross-entropy (CE) concept. They are as efficient as the CE criterion, but require much less and simpler computations View full abstract»

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  • Modified dilated Benes networks for photonic switching

    Page(s): 1253 - 1259
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (212 KB)  

    A modified dilated Benes (1965) network composed of directional couplers is proposed. This structure is introduced to improve the signal-to-noise ratio (SNR) characteristics of dilated Benes networks. A new estimation of the SNR for dilated Benes networks is derived, and it is shown that this SNR is much worse than that previously known. The SNR for modified dilated Benes networks is estimated and compared to dilated Benes and other network architectures. Some other properties including the number of switching elements required, number of crossovers, and system attenuation are also derived and analyzed. Most of the characteristics are shown to be similar to dilated Benes networks and better than those of other well-known networks fabricated in Ti:LiNbO 3 View full abstract»

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  • Adaptive MLSDE using the EM algorithm

    Page(s): 1181 - 1193
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (388 KB)  

    The theory of adaptive sequence detection incorporating estimation of channel and related parameters is studied in the context of maximum-likelihood (ML) principles in a general framework based on the expectation and maximization (EM) algorithm. A generalized ML sequence detection and estimation (GMLSDE) criterion is derived based on the EM approach, and it is shown how the per-survivor processing and per-branch processing methods emerge naturally from GMLSDE. GMLSDE is developed into a real time detection/estimation algorithm using the online EM algorithm with coupling between estimation and detection. By utilizing Titterington's (1984) stochastic approximation approach, different adaptive ML sequence detection and estimation (MLSDE) algorithms are formulated in a unified manner for different channel models and for different amounts of channel knowledge available at the receiver. Computer simulation results are presented for differentially encoded quadrature phase-shift keying in frequency flat and selective fading channels, and comparisons are made among the performances of the various adaptive MLSDE algorithms derived earlier View full abstract»

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  • Improving differential detection of MDPSK by nonlinear noise prediction and sequence estimation

    Page(s): 1161 - 1172
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB)  

    A new technique is proposed to improve the performance of differential detection (DD) of M-ary differential phase-shift keying (MDPSK) significantly, applying sequence estimation. In order to obtain an appropriate representation of the received signal, a nonlinear time-variant finite impulse response or infinite impulse response prediction-error filter is used. For both filter structures the optimum coefficients are derived, assuming transmission over an additive white Gaussian noise (AWGN) channel. Delayed decision-feedback sequence estimation (DDFSE) is employed to estimate the transmitted symbol sequence. It is shown by simulations that even for decision-feedback equalization, which is a simple special case of DDFSE, a significant performance improvement of conventional DD under AWGN conditions results. In contrast to other noncoherent low-complexity receivers proposed in literature, this receiver is very robust under flat fading (Rayleigh and Ricean) conditions View full abstract»

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  • The probability of multiple correct packet reception in coded synchronous frequency-hopped spread-spectrum networks

    Page(s): 1227 - 1232
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (172 KB)  

    We present a computationally efficient method of evaluating the probability of multiple correct packet reception in coded synchronous frequency-hopped spread-spectrum (FHSS) networks. We show that the approximation using the independent receiver operation assumption (IROA), which has been frequently employed in the literature without rigorous validation, produces reasonable results in most network load conditions when compared to the exact computations derived from our proposed method. Specifically, the expected value of the absolute error was in the range of 0.0055%-18.21% in the investigated scenarios View full abstract»

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  • Orthogonal-transformed variable-gain least mean squares (OVLMS) algorithm for fractional tap-spaced adaptive MLSE equalizers

    Page(s): 1151 - 1160
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (228 KB)  

    A fast channel-estimation scheme for adaptive maximum-likelihood sequence-estimation (MLSE) equalizers called the orthogonal-transformed variable-gain least mean squares (OVLMS) algorithm is proposed. This algorithm requires only as many operations as the least mean squares algorithm in spite of its excellent performance. Furthermore, an operational complexity reduction method is proposed in which the orthogonal matrix is reconfigured as eigenvectors with valid eigenvalues. The OVLMS algorithm is theoretically analyzed and is shown to have both a fast acquisition and a good tracking performance. An equalizer using OVLMS (OVLMS-MLSE) experimentally attains a 5-dB improvement in bit-error rate (BER) performance at BER of 1.0×10 -4 over coherent detection. The OVLMS-MLSE is found to be free of the degradation caused by sampling phase error. Finally, the OVLMS-MLSE equalizer is experimentally verified to synchronize within five symbols View full abstract»

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  • Optical CDMA communication systems with multiuser and blind detection

    Page(s): 1211 - 1217
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (144 KB)  

    We study the use of multiuser detection and blind detection techniques to improve the performance of optical code division multiple access (OCDMA) systems. First, a new multiuser receiver known as the interference suppression receiver is proposed. Second, we study the use of blind detection by proposing a blind receiver for OCDMA systems. While previous studies on multiuser detection are limited to systems with p-i-n detectors, avalanche photodiode detectors are also included here View full abstract»

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  • Bit-error rate of M-QAM signal and its analysis model for composite distortions in AM/QAM hybrid transmission

    Page(s): 1173 - 1180
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (188 KB)  

    In cable television (CATV) systems that deliver digital video services by employing a hybrid fiber and coaxial network, it is important to consider digital channel deterioration due to composite distortions, as well as the amplitude-modulation vestigial-sideband channel. Furthermore, it is essential to clearly estimate a digital channel's quality in designing CATV transmission systems. However, there have been few studies on statistical models and an analysis method to estimate the bit-error rate (BER) of M-ary quadrature amplitude-modulation signals for composite distortions. This paper shows statistical properties of composite distortions and a new BER analysis method to handle them. In the evaluations, the amplitude distributions of composite distortions are given by Weibull distributions with skewness levels of 2.3 for composite second-order distortion and 1.5 for composite triple-beat distortion. We propose a new BER analysis method that uses the Weibull distributions for the composite distortion statistical features and demonstrate the effectiveness of the new BER analysis method in estimating BER by comparing its measurement results to calculation results View full abstract»

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  • Analysis of a multicarrier DS-CDMA code-acquisition system

    Page(s): 1233 - 1244
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (364 KB)  

    We present two code-acquisition schemes for a multicarrier direct-sequence code-division multiple-access system, one that uses equal gain combining and the other that uses selection combining. The code-acquisition performance of the two multicarrier systems, as well as that of a single-carrier system, are analyzed in both nonfading and Rayleigh fading channels under the assumption that the receiver is chip-synchronized; the effect of partial-band interference (PBI) on the performance is also included. It is demonstrated that in an additive white Gaussian noise channel, the single-carrier system has a better code-acquisition performance than both multicarrier systems. However, in a Rayleigh fading channel, the code-acquisition performance of a multicarrier system with equal gain combining is better than that of the single-carrier system, while a multicarrier system with selection combining has the same performance as the single-carrier system. Further, the presence of PBI more severely affects the code-acquisition performance of the single-carrier system than those of both multicarrier systems. Finally, the code-acquisition performance of a multicarrier system with equal gain combining is always better than that of the selection combining system View full abstract»

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  • Blind estimation of multipath channel parameters: a modal analysis approach

    Page(s): 1140 - 1150
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (264 KB)  

    We propose a novel approach to efficiently estimate multipath channel parameters, which is particularly useful in sparse multipath channels. Conventional methods do not fully exploit the inherent structure present in the combined channel response; the excess number of parameters to be estimated by conventional methods makes the identification difficult. By utilizing a priori knowledge of the transmission data pulse, the channel identification problem is transformed into the mode estimation problem. Then, the parameters directly related to the multipath propagation are extracted in the the modal analysis framework, and hence, the number of estimation parameters are significantly reduced. Finally, the multipath channel parameters are obtained by inverse-transforming the mode parameters. Simulation results show significant improvement in the normalized mean square error over existing approaches View full abstract»

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  • Zipper: a duplex method for VDSL based on DMT

    Page(s): 1245 - 1252
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (312 KB)  

    We present a new duplex scheme, called Zipper, for discrete multitone (DMT)-based very high bit-rate digital subscriber line (VDSL) systems on copper wires. This scheme divides the available bandwidth by assigning different subcarriers for the upstream and downstream directions. It has high flexibility to divide the capacity between the up and downstream, as well as good coexistence possibilities with other systems such as ADSL. Simulation results show the high bit-rate performance in different environments such as mixed ADSL and VDSL traffic under radio frequency interference and with different background noise sources View full abstract»

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  • Achieving 100% throughput in an input-queued switch

    Page(s): 1260 - 1267
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB)  

    It is well known that head-of-line blocking limits the throughput of an input-queued switch with first-in-first-out (FIFO) queues. Under certain conditions, the throughput can be shown to be limited to approximately 58.6%. It is also known that if non-FIFO queueing policies are used, the throughput can be increased. However, it has not been previously shown that if a suitable queueing policy and scheduling algorithm are used, then it is possible to achieve 100% throughput for all independent arrival processes. In this paper we prove this to be the case using a simple linear programming argument and quadratic Lyapunov function. In particular, we assume that each input maintains a separate FIFO queue for each output and that the switch is scheduled using a maximum weight bipartite matching algorithm. We introduce two maximum weight matching algorithms: longest queue first (LQF) and oldest cell first (OCF). Both algorithms achieve 100% throughput for all independent arrival processes. LQF favors queues with larger occupancy, ensuring that larger queues will eventually be served. However, we find that LQF can lead to the permanent starvation of short queues. OCF overcomes this limitation by favoring cells with large waiting times View full abstract»

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  • Frequency-offset estimation for HIPERLAN

    Page(s): 1137 - 1139
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (84 KB)  

    Frequency-offset correction is considered for a HIPERLAN (HIgh-PErformance Radio LAN) system over the indoor radio channel. Since the multipath channel response is not known a priori, a viable frequency-offset estimator should not depend on such knowledge. Such an estimator, using a single sample per symbol, is derived for HIPERLAN. The estimator is shown to approach the Cramer-Rao bound for frequency-offset estimation over a multipath channel. A HIPERLAN system simulation example shows that the performance with an offset of 150 kHz is within 0.5 dB of that of a system with zero frequency offset View full abstract»

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  • Performance of multiuser detection with adaptive channel estimation

    Page(s): 1129 - 1132
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (96 KB)  

    An adaptive multipath decorrelating multiuser receiver is considered for application in Rayleigh fading multipath channels with significant Doppler spread. Coherent diversity combining is performed using adaptively obtained channel estimates in a manner that minimizes the impact of estimation errors on data detection. The bit-error rate of the receiver is evaluated analytically, showing dependence on the fading rate of the channel and tracking capabilities of adaptive least mean square and recursive least square algorithms, in addition to the order of multipath diversity and the number of active code-division multiple-access users View full abstract»

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  • Outage probability of cellular radio systems using maximal ratio combining in the presence of multiple interferers

    Page(s): 1121 - 1124
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (108 KB)  

    In mobile radio systems, antenna diversity is used to combat fading and reduce the impact of cochannel interference. We derived a new expression for probability density functions of the signal-to-interference-plus-noise ratio and apply it to analyze the outage probability (OTP) for a maximal ratio combining diversity system when multiple cochannel interferers are present. Numerical results showing the impact of the number of antenna elements, the number of cochannel interferers, and signal-to-noise ratio on the OTP are presented. Simulation results validating the analytical results are also presented View full abstract»

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  • Differential pulse-position modulation for power-efficient optical communication

    Page(s): 1201 - 1210
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (244 KB)  

    We examine the use of differential pulse-position modulation (DPPM) for optical communication systems using intensity modulation with direct detection in the presence of additive white Gaussian noise. We present expressions for the error probability and power spectral density of DPPM. We show that for a given bandwidth, DPPM requires significantly less average power than pulse position modulation (PPM). We also examine the performance of DPPM in the presence of multipath intersymbol interference (ISI). We find that the ISI penalties incurred by PPM and DPPM exhibit very similar dependencies upon the channel RMS delay spread. We discuss the use of chip-rate and multichip-rate equalization to combat ISI. Finally, we describe potential problems caused by the nonuniform bit-rate characteristic of DPPM, and we propose several solutions View full abstract»

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  • Robust vector quantizer design by noisy channel relaxation

    Page(s): 1113 - 1116
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (88 KB)  

    This article proposes a method to design a vector quantizer (VQ) for robust performance under noisy channel conditions. By re-optimizing the quantizer at progressively lower levels of assumed channel noise, the design is less susceptible to poor local optima. The method is applied to: (1) channel-optimized VQ design; and (2) index assignment for a source-optimized VQ. For both problems, we demonstrate substantial performance improvements over commonly used techniques View full abstract»

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  • Computing the outage probability in mobile radio networks using the sampling theorem

    Page(s): 1125 - 1128
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (144 KB)  

    This article provides a novel, efficient numerical solution to evaluate the moment generating function of a Suzuki probability density function using the sampling theorem. Applications include outage probability calculations for mobile radio networks in Rayleigh fading and shadowing View full abstract»

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  • Automatic suppression of narrow-band interference in direct-sequence spread-spectrum systems

    Page(s): 1133 - 1136
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (116 KB)  

    This paper addresses the problem of narrow-band interference (NBI) cancellation in direct-sequence spread-spectrum systems. The proposed procedure amounts to a preliminary nonlinear processing, wherein, upon projection of the received signal onto a Fourier basis, a number of samples having the largest modula are excluded from further processing. The structure of the optimum detector operating on censored observations is obtained, showing that the optimum detector performs matched filtering on the censored data. The performance assessment demonstrates that this receiver is able to suppress narrow-band interferers, no matter what their structure, provided that the censoring depth is properly chosen. A blind version of such a receiver is presented also, and a comparative performance assessment demonstrates that, unlike other suppression procedures, the proposed system allows suppression of NBI with no prior knowledge on its structure 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