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Communications, IEEE Transactions on

Issue 7 • Date July 1996

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Displaying Results 1 - 20 of 20
  • Comments on "A tabulation of Hilbert transforms for electrical engineers"

    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (46 KB)  

    A new table of Hilbert transforms was prepared and published by Alavi-Sereshki and Prabhakar (see ibid., vol.COM-20, no.6, p.1194, 1972). During preparation, it was found that some formulas in the above paper were in error. Therefore, the tables in that should be used with great care. Correct Hilbert transform pairs are presented by Hahn (1996). The Hilbert transform of an amplitude-modulated signal, given in the above paper, as the infinite sum of quotients of integrals, is derived in compact form. View full abstract»

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  • Robustly good trellis codes

    Page(s): 791 - 798
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (876 KB)  

    The relationship between the distance properties of trellis codes and the computational effort and error performance of sequential decoding is studied and optimum distance profile (ODP) and optimum free distance (OFD) trellis codes are constructed for 8-PSK and 16 QAM modulation. A comparison of the performance of both the ODP and the OFD trellis codes reveals that neither class of codes results in the best trade-off between error performance and computational effort when sequential decoding is used. A new algorithm is then proposed to construct robustly good trellis codes for use with sequential decoding. New trellis codes with asymptotic coding gains up to 6.66 dB are obtained using this algorithm, and the new codes achieve nearly the same free distances as the OFD codes and nearly the same distance profiles as the ODP codes. View full abstract»

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  • Discrete multitone echo cancelation

    Page(s): 817 - 825
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (804 KB)  

    Multicarrier transmission methods have long been known to optimize the performance of data transceivers on bandlimited communication channels. One form of multicarrier transmission, known as discrete multitone modulation (DMT), is particularly attractive for its ability to be implemented using efficient digital signal processing techniques. Given a basic DMT system, it is possible to increase the aggregate data rate with full-duplex transmission using echo cancelation. However, DMT echo cancelation at first appears difficult because of the computational complexity required in a straightforward implementation to cancel the cross-echoes produced by each carrier into every carrier. This paper presents high-speed echo cancelation techniques for full-duplex data transmission using DMT systems. The techniques estimate the echo with a method of fast convolution that combines a complex multiply per tone with a short convolution in the time domain. In addition, the frequency-domain update of the echo parameters consists of one complex multiply per tap. As a result, these techniques can achieve much lower complexity than that required by traditional single-carrier technique, such as the least mean square (LMS) algorithm. This approach has been implemented for asymmetric digital subscriber line (ADSL) applications View full abstract»

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  • Bayesian techniques for blind deconvolution

    Page(s): 826 - 835
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (816 KB)  

    This paper introduces extended Bayesian filters (EBFs), a new family of blind deconvolution filters for digital communications. The blind deconvolution problem is formulated as a nonlinear and non-Gaussian fixed-lag minimum mean square error filtering problem, and the EBF is derived as a suboptimal recursive estimator. The model-based setting makes extensive use of the transmitted symbol and noise distributions. A key feature of the EBF is that the filter lag can be chosen to be larger than the channel length, while the complexity is exponential in a parameter which is typically chosen to be smaller than both the channel length and the filter lag. Extensive simulations characterizing the performance of EBFs in severe intersymbol interference channels are presented. The fast convergence and robust equalization of the EBFs are demonstrated for uncoded linearly modulated signals [e.g., differentially encoded quaternary phase shift keying (QPSK)] transmitted over unknown channels. Comparisons are made to other blind symbol-by-symbol demodulation algorithms. The results show that the EBF provides much better performance (at increased complexity) compared to the constant modulus algorithm and the extended Kalman filter, and achieves a better performance-complexity trade-off than other Bayesian demodulation algorithms. The simulations also show that the EBF is applicable with large constellations and shaped modulations View full abstract»

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  • A new lattice polynomial perceptron and its applications to frequency-selective fading channel equalization and ACI suppression

    Page(s): 761 - 767
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    It is expected that the available spectrum for the proposed personal communication networks will soon be at a premium as the user population increases, and using multilevel quadrature amplitude modulation (MQAM), an bandwidth efficient transmission method for digital signals, may significantly ease the problem. A new lattice polynomial perceptron (LPP), with faster and less input signal-dependent convergence behavior, is presented and applied to frequency-selective slow fading channel equalization and adjacent-channel interference (ACI) suppression in a 16-QAM system. Computer simulation results are given, which shows that, in a 16-QAM system, the performance of LPP is clearly superior to that of the other structures View full abstract»

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  • MLSE for an unknown channel .I. Optimality considerations

    Page(s): 836 - 846
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (928 KB)  

    The problem of performing joint maximum-likelihood (ML) estimation of a digital sequence and unknown dispersive channel impulse response is considered starting from a continuous-time (CT) model. Previous investigations of this problem have not considered the front-end (FE) processing in detail; rather, a discrete-time signal model has been assumed. We show that a fractionally-spaced whitened matched filter, matched to the known data pulse, provides a set of sufficient statistics when a tapped delay line channel model is assumed, and that the problem is ill-posed when the channel impulse response is generalized to a CT, finite-length model. Practical approximations are considered that circumvent this ill-posed condition. Recursive computation of the joint-ML metric is developed. Together, the FE processing and metric recursion provide a receiver structure which may be interpreted as the theoretical foundation for the previously introduced technique of per-survivor processing, and they lead directly to generalizations. Several FE processors representative of those suggested in the literature are developed and related to the practically optimal FE View full abstract»

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  • New suboptimal multiuser detectors for synchronous CDMA systems

    Page(s): 782 - 785
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (320 KB)  

    In code-division multiple access (CDMA) systems, the optimal multiuser detection is equivalent to an unconstrained quadratic bivalent optimization problem, and its computational complexity increases exponentially with the number of users. In this paper, we propose several new suboptimal detectors with a greatly reduced computational complexity based on a local minimization algorithm for a synchronous CDMA system. The performances of these detectors are compared with those of the conventional, optimal, and several other suboptimal detectors View full abstract»

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  • Multiple tone interference of frequency-hopped noncoherent MFSK signals transmitted over Ricean fading channels

    Page(s): 867 - 875
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (780 KB)  

    This paper investigates the performance degradation resulting from multitone interference of orthogonal, frequency-hopped, noncoherent M-ary frequency-shift keyed receivers (FH/MFSK) where the effect of thermal and other wideband noise is not neglected. The multiple, equal power jamming tones are assumed to correspond to some or all of the possible FH M-ary orthogonal signaling tones. Furthermore, the channel is modeled as a Ricean fading channel; and both the signaling tones and the multiple interference tones are assumed to be affected by channel fading. It is also assumed that channel fading need not necessarily affect the signaling tones and the interference tones in the same-way. When the information signal power exceeds the power of the individual interference tones, poorer overall system performance is obtained when the multiple interfering tones experience fading. This trend is accentuated as M increases. When the information signal experiences fading, the effect of fading multiple interference tones on overall system performance lessens, and for a Rayleigh-faded information signal, fading of the multiple interference tones has no effect on overall system performance regardless of M View full abstract»

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  • Computing upper bounds to error probability of coded modulation schemes

    Page(s): 786 - 790
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (528 KB)  

    To evaluate an upper bound on error probabilities of signal constellations used for transmission over the additive white Gaussian noise (AWGN) channel, enumeration of all the constellation intradistances is required. These may be infinite in number, for example, when convolutional codes are used and the constellations are lattices. Truncation of the series does not necessarily provide a bound anymore, and must be done with care. Yet the union bound is very simple, as it does not require any further knowledge about the signal constellation than the distance enumerator. In this paper, we describe some methods that can be used to evaluate error probabilities of infinite signal constellations, and that require only a finite number of terms. These methods are applicable, for example, to convolutional codes decoded with a finite-depth Viterbi algorithm and to signal constellations carved from lattices. Coded modulations based on lattices and convolutional or block codes can also be dealt with. As an example of application, we analyze a variable-rate 3-stage coded modulation encoder/decoder, which has been built and is based on a combination of convolutional codes with a single-parity-check block code View full abstract»

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  • Results of optimal discrete pulse shaping for MSK-type signals

    Page(s): 769 - 771
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (244 KB)  

    This paper presents the results of discrete bandwidth optimizations used on minimum shift keying (MSK)-type signals. Bandwidth-optimal pulse shaping achieves maximum spectral confinement with respect to given confinement frequencies and given levels of allowable modulated signal envelope nonuniformity. This paper presents a family of design curves defining optimal confinement with respect to confinement frequency and the level of modulated signal amplitude modulation (AM) View full abstract»

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  • Performance analysis of CDMA with imperfect power control

    Page(s): 777 - 781
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (412 KB)  

    The standard correlation receiver for code-division multiple access (CDMA) systems is susceptible to the near-far problem. Power control techniques attempt to overcome near-far effects by varying transmitted power levels to ensure that all signals are received with equal power levels. Since these algorithms cannot perfectly compensate for power fluctuations in a mobile communications channel, the capacity of the system is reduced for a given bit-error rate (BER). This paper examines the performance of a CDMA system using imperfect power control by extending analytical techniques that account for multiple access interference. Single cell capacity is compared with systems employing perfect power control View full abstract»

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  • Adaptive combined DFE/MLSE techniques for ISI channels

    Page(s): 847 - 857
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (720 KB)  

    By embedding a decision-feedback equalizer (DFE) into the structure of a maximum-likelihood sequence estimator (MLSE), an adaptive combined DFE/MLSE scheme is proposed. In this combined DFE/MLSE, the embedded DFE has three functions: (i) prefiltering the received signals and truncating the equivalent channel response into the desired one, (ii) compensating for channel distortions, and (iii) providing the MLSE detector with predicted values of input signals. Since the embedded MLSE detector operates on the predicted signals the detected symbols at the output of the DFE/MLSE do not suffer any delay and can be directly fed back into the embedded DFE so that the error propagation, which usually takes place in a conventional DFE, can be greatly reduced. Analytical and simulation results indicate that the performance is significantly improved by the DFE/MLSE compared to the conventional DFE while its computation complexity is much less than that of the conventional MLSE receiver. The combined DFE/MLSE can use different adaptive structures (block-updating, sliding window updating or symbol-by-symbol updating) to meet different performance objectives. Moreover, the proposed DFE/MLSE provides a trade-off between performance and complexity with a parameter m representing the MLSE detection depth as well as the number of predicting steps of the embedded DFE. For some particular values of m, this scheme is capable of emulating the conventional DFE, MLSE-VA, adaptive LE-MLSE equalizer, adaptive DDFSE, and adaptive BDFE without detection delay View full abstract»

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  • Differential service in high-speed interconnection systems: an algorithm for prioritized access

    Page(s): 858 - 866
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (944 KB)  

    The requirement to connect high-performance components of supercomputer systems has caused an increasing demand for connection-oriented, high-speed communication in a peer-to-peer environment. The importance of this type of communication is underscored by the advent of the high-performance parallel interface (HIPPI) standard, designed to support the commercial development of interconnection systems for this environment. For such interconnection systems, we present a connection management algorithm that supports priorities to provide preferential access for important classes of traffic, and that assures equitable access for all connections within the same priority class. At the same time, the algorithm utilizes the connection resources efficiently and assures low overhead at the nodes. We demonstrate the algorithm's applicability by outlining a centralized as well as a distributed implementation in an HIPPI-based interconnection system. Furthermore, we introduce an analytic priority model that can be used to evaluate an interconnection system's performance under the algorithm. Using this model, we analyze the efficacy of the nonpreemptive priority discipline and show the load/throughput behavior of a typical system View full abstract»

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  • Optimization for crosstalk suppression with noncoordinating users

    Page(s): 894 - 905
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (824 KB)  

    A joint transmitter/receiver optimization problem for multiuser communications in a symmetric crosstalk environment based on the minimum mean squared error (MMSE) criterion is addressed. It is assumed that each user employs an identical transmit pulse shaping filter and sees identical direct and crosstalk channel responses. All the channels are assumed to be bandlimited with identical support that, in general, extends beyond the basic Nyquist zone [-(1/2T), 1/2T], corresponding to the common symbol period T. Necessary conditions for the optimum transmitter and receiver are derived and several useful insights generated. In particular, the performance advantage obtained by exploitation of the cyclostationary nature of the interference is demonstrated, corroborating earlier results. An algorithmic procedure to solve for the jointly optimal transmit-receive pair is outlined and used for numerical evaluation of the system performance as a function of several parameters of interest such as system bandwidth, the number of users and the number of points at which the transmitter is nonzero in the set (f: f0+k/T) where T is the symbol period, and f0 ∈[-(1/2T),1/2T] View full abstract»

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  • Intersymbol interference due to linear and nonlinear distortion

    Page(s): 809 - 816
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (728 KB)  

    The paper provides a recursion model for the calculation of the probability density function (pdf) of intersymbol interference (ISI) which is caused by the combined effect of linear channel dispersion and of nonlinear distortion. The nonlinearity introduces statistical interdependencies between the interfering symbols and these dependencies are implicitly taken into account in a trellis-structured recursion rule. The results were verified by time consuming Monte Carlo simulation and show, e.g., that the nonlinear characteristic of a high power amplifier (HPA) reduces in some cases the error probability caused by the linear dispersion. Surprisingly, the ISI due to the nonlinear amplifier is increased in the case of offset modulation View full abstract»

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  • The effect of timing jitter on the performance of a discrete multitone system

    Page(s): 799 - 808
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (848 KB)  

    The transmission of high-speed data over severely band-limited channels may be accomplished through the use of discrete multitone (DMT) modulation, a modulation technique that has been proposed for a number of new applications. While the performance of a DMT system has been analyzed by a number of authors, these analyses ignore the effect of timing jitter on system performance. Timing jitter becomes an increasingly important concern as higher data rates are supported and larger constellations are allowed on the DMT subchannels. Hence, in this paper, we assume that synchronization is maintained by using a digital phase-locked loop to track a pilot carrier, Given this model, we derive error rate expressions for an uncoded DMT system operating in the presence of timing jitter, and we derive an expression for the interchannel distortion that results from a varying timing offset across the DMT symbol. In addition, we investigate the performance of trellis-coded DMT modulation in the presence of timing jitter. Practical examples from the asymmetric digital subscriber line (ADSL) service are used to illustrate various results View full abstract»

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  • Power control in cellular networks subject to measurement error

    Page(s): 772 - 775
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    A distributed power control algorithm for cellular networks is proposed. This algorithm includes the distributive balancing (DB) algorithm (Zander 1992) and the distributed power control (DPC) algorithm (Grandhi et al. 1994) as special cases. We show that this algorithm converges much faster than the DB and DPC algorithms, is less sensitive to measurement error than the DPC algorithm, and its convergence rate and sensitivity to measurement error can be tuned by varying a design parameter View full abstract»

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  • Frequency-diversity spread-spectrum communication system to counter bandlimited Gaussian interference

    Page(s): 886 - 893
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (700 KB)  

    A spread spectrum system to counter bandlimited Gaussian interference is proposed. The optimum receiver for this system is easy to build. Frequency diversity which allows the receiver to distinguish unjammed signal replicas from their jammed versions is used. The system can also resist bandlimited partial-time jamming. The only choice left to a smart jammer to maximize the error probability is to spread its signal like the communicator. The optimum receiver, which jointly performs symbol detection and interference rejection, is derived. Side information needed by this receiver can easily be estimated. However, if the interference bandwidth is narrow compared to the signal bandwidth, side information on noise and interference levels is not needed by a simpler and near-optimum receiver. Bit-error probability is evaluated for quaternary phase shift keying (QPSK) modulation and compared to that of direct sequence spread spectrum. We also propose the use of polyphase filters for simple system implementation View full abstract»

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  • Error probabilities for generalized quadriphase DS/SSMA communication systems with random signature sequences

    Page(s): 876 - 885
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (716 KB)  

    Methods to determine the average error probabilities in quadriphase direct-sequence spread spectrum multiple-access (DS/SSMA) communication systems are proposed. The systems being considered employ random signature sequences and arbitrary chip waveforms that are time-limited to one chip interval. The methods range from an algorithm that determines upper and lower bounds with arbitrary accuracy, to simple formulas that provide accurate estimates efficiently. Each method will find applications in different areas. Numerical examples are provided to illustrate each of the methods View full abstract»

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Aims & Scope

IEEE Transactions on Communications focuses on all telecommunications including telephone, telegraphy, facsimile, and point-to-point television by electromagnetic propagation.

 

 

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Editor-in-Chief
Robert Schober
University of British Columbia