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Communications, IEEE Transactions on

Issue 12 • Date Dec. 2004

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Displaying Results 1 - 25 of 36
  • Table of contents

    Page(s): c1 - c4
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    Freely Available from IEEE
  • IEEE Transactions on Communications publication information

    Page(s): c2
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  • On soft-input soft-output decoding using "box and match" techniques

    Page(s): 2033 - 2037
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (256 KB) |  | HTML iconHTML  

    The box and match decoding algorithm (BMA) significantly reduces the computational complexity of the ordered statistic decoding algorithm at the expense of increased memory requirements. A soft-input/soft-output version of the BMA is developed. Additional complexity-reduction techniques are also described. View full abstract»

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  • Reliability-based schedule for bit-flipping decoding of low-density Parity-check codes

    Page(s): 2038 - 2040
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (224 KB) |  | HTML iconHTML  

    A reliability-based message-passing schedule for iterative decoding of low-density parity-check codes is proposed. Simulation results for bit-flipping algorithms (with binary messages) show that a reliability-based schedule can provide considerable improvement in performance and decoding speed over the so-called flooding (parallel) schedule, as well as the existing graph-based schedules. The cost associated with this improvement is negligible and is equivalent to having a two-bit representation for initial messages, instead of the standard one bit for hard-decision algorithms, only at the first iteration (all the exchanged messages are still binary). View full abstract»

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  • An efficient algorithm to compute the Euclidean distance spectrum of a general intersymbol interference channel and its applications

    Page(s): 2041 - 2046
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (352 KB) |  | HTML iconHTML  

    We present an efficient algorithm to compute the distance spectrum of a general finite intersymbol interference (ISI) channel, whose complexity is lower than those of existing methods. Closed-form expressions are derived for both input-output Euclidean distance enumerators and asymptotic distance spectrum shapes for 2-tap and 3-tap ISI channels. Coded and/or precoded ISI channels are also discussed. View full abstract»

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  • Reduced-complexity error-State diagrams in TCM and ISI channel performance evaluation

    Page(s): 2047 - 2051
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (256 KB) |  | HTML iconHTML  

    The performance evaluation of trellis-coded modulation (TCM) schemes and intersymbol interference (ISI) channels via union bounds involves a transfer function computation of an error-state diagram which enumerates all possible error events. This letter presents a new method for obtaining equivalent error-state diagrams with a reduced number of states. View full abstract»

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  • A modified Blahut algorithm for decoding Reed-Solomon codes beyond half the minimum distance

    Page(s): 2052 - 2056
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (224 KB) |  | HTML iconHTML  

    A modification of the Blahut algorithm is proposed for decoding of Reed-Solomon codes beyond half the minimum distance. An effective method is offered for the searching of unknown discrepancies needed for analytical continuation of the Berlekamp-Massey algorithm through two additional iterations. This reduces the search time by 2(q-1)n/((n+t+1)(n-t)) times, compared with the Blahut algorithm. An architecture of a searcher for unknown discrepancies is given. The coding gain of the proposed algorithm is shown for some practical codes. View full abstract»

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  • Lattice-reduction-aided broadcast precoding

    Page(s): 2057 - 2060
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (272 KB) |  | HTML iconHTML  

    A precoding scheme for multiuser broadcast communications is described, which fills the gap between the low-complexity Tomlinson-Harashima precoding and the sphere decoder-based system of Peel et al. Simulation results show that, replacing the closest-point search with the Babai approximation, the full diversity order supported by the channel is available to each user, as in the system of Peel et al., and unlike Tomlinson-Harashima precoding, which suffers some diversity penalty. The complexity of the scheme is similar to that of Tomlinson-Harashima precoding. View full abstract»

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  • Bit-interleaved turbo equalization over static frequency-selective channels: constellation mapping impact

    Page(s): 2061 - 2065
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (288 KB) |  | HTML iconHTML  

    The purpose is to assess the performance of bit-interleaved turbo equalization (TE) over static frequency-selective channels. The asymptotic performance is therefore first pointed out, emphasizing the fundamental role played by the constellation mapping. This specific feature is then further analyzed using the extrinsic information-transfer chart technique, leading to an efficient optimization tool. This finally enables showing that bit-interleaved TE can outperform its symbol-interleaved counterpart. View full abstract»

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  • Mobile speed estimation based on average fade slope duration

    Page(s): 2066 - 2069
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (184 KB) |  | HTML iconHTML  

    Based on the zero crossing rate of the slope (first derivative) of the underlying fading process, a mobile speed-estimation scheme, constructed by counting the average number of sampling steps in a positive-going (and/or negative-going) fade envelope slope, is proposed. The proposed speed-estimation approach requires neither knowledge of the average fade power nor a variable temporal observation window. The computational complexity and the required memory storage are negligibly small. Simulation results show that the proposed speed estimator yields good estimation accuracy, with relatively small estimation error. View full abstract»

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  • Sharing of ARQ slots in Gilbert-Elliot channels

    Page(s): 2070 - 2072
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (128 KB) |  | HTML iconHTML  

    This letter treats the problem of m transmission slots sharing a pool of n automatic repeat request slots. Two cases are treated. In one, these m slots belong to the same base station-terminal pair, i.e., a frequency-division multiplexing channel. In the other, they are used by m different base station-terminal pairs, i.e., a time-division multiplexing channel. The smallest n to satisfy loss and delay requirement is determined. View full abstract»

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  • Doppler-channel blind identification for noncircular transmissions in multiple-access systems

    Page(s): 2073 - 2078
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (240 KB) |  | HTML iconHTML  

    The problem of blindly estimating the parameters of a Doppler channel for noncircular transmissions in multiple-access communication systems is addressed. A nondata-aided algorithm based on the cyclostationarity features of the received signal is proposed to estimate amplitude, phase, time delay, and frequency shift of each user. Under mild assumptions on the disturbance and user signals, the proposed method provides estimates of the unknown parameters that are mean-square consistent. Moreover, the proposed algorithm is asymptotically near-far resistant, and is not based on the usual assumption of white and/or Gaussian noise. View full abstract»

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  • An alternative expression for the symbol-error probability of MPSK in the presence of I/Q unbalance

    Page(s): 2079 - 2081
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (200 KB) |  | HTML iconHTML  

    This letter provides a new expression for the probability of the phase angle between two vectors perturbed by Gaussian noise with in-phase/quadrature-phase (I/Q) unbalance, in order to simplify the analysis of the error probabilities of M-ary phase-shift keying (MPSK). The error probabilities, symbol-error rates, or bit-error rates for MPSK with I/Q balance or unbalance, can be presented straightforwardly from the derived expression. Because the newly derived result is provided in terms of the conventional first-order Gaussian Q-function and the joint Gaussian Q-function with a correlation coefficient dependent on M, it readily allows rapid evaluation for various cases of practical interest. View full abstract»

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  • Matched-filter bound for binary signaling over dispersive fading channels with receive diversity

    Page(s): 2082 - 2086
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (352 KB) |  | HTML iconHTML  

    The matched-filter bound (MFB) for continuously dispersive Rayleigh fading channels with receive diversity is derived. The treatment is quite general, as the case of discrete multipath channels with correlated fading is included in our model as a special case, and we impose no constraints with regard to the selectivity of the channel. It is assumed that a statistical characterization of the channel is available through its direction-delay-Doppler power spectral density. The Karhunen-Loe`ve expansion for vector processes is used to describe the received signal. The MFB is analyzed with respect to several parameters characterizing the mobile radio channel, the waveform, and the antenna configuration. View full abstract»

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  • Threshold values and convergence properties of majority-based algorithms for decoding regular low-density parity-check codes

    Page(s): 2087 - 2097
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (560 KB) |  | HTML iconHTML  

    This work presents a detailed study of a family of binary message-passing decoding algorithms for low-density parity-check (LDPC) codes, referred to as "majority-based algorithms." Both Gallager's algorithm A (GA) and the standard majority decoding algorithm belong to this family. These algorithms, which are, in fact, the building blocks of Gallager's algorithm B (GB), work based on a generalized majority-decision rule and are particularly attractive for their remarkably simple implementation. We investigate the dynamics of these algorithms using density evolution and compute their (noise) threshold values for regular LDPC codes over the binary symmetric channel. For certain ensembles of codes and certain orders of majority-based algorithms, we show that the threshold value can be characterized as the smallest positive root of a polynomial, and thus can be determined analytically. We also study the convergence properties of majority-based algorithms, including their (convergence) speed. Our analysis shows that the stand-alone version of some of these algorithms provides significantly better performance and/or convergence speed compared with GA. In particular, it is shown that for channel parameters below threshold, while for GA the error probability converges to zero exponentially with iteration number, this convergence for other majority-based algorithms is super-exponential. View full abstract»

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  • Graph-based message-passing schedules for decoding LDPC codes

    Page(s): 2098 - 2105
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (584 KB) |  | HTML iconHTML  

    We study a wide range of graph-based message-passing schedules for iterative decoding of low-density parity-check (LDPC) codes. Using the Tanner graph (TG) of the code and for different nodes and edges of the graph, we relate the first iteration in which the corresponding messages deviate from their optimal value (corresponding to a cycle-free graph) to the girths and the lengths of the shortest closed walks in the graph. Using this result, we propose schedules, which are designed based on the distribution of girths and closed walks in the TG of the code, and categorize them as node based versus edge based, unidirectional versus bidirectional, and deterministic versus probabilistic. These schedules, in some cases, outperform the previously known schedules, and in other cases, provide less complex alternatives with more or less the same performance. The performance/complexity tradeoff and the best choice of schedule appear to depend not only on the girth and closed-walk distributions of the TG, but also on the iterative decoding algorithm and channel characteristics. We examine the application of schedules to belief propagation (sum-product) over additive white Gaussian noise (AWGN) and Rayleigh fading channels, min-sum (max-sum) over an AWGN channel, and Gallager's algorithm A over a binary symmetric channel. View full abstract»

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  • A more accurate one-dimensional analysis and design of irregular LDPC codes

    Page(s): 2106 - 2114
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (512 KB) |  | HTML iconHTML  

    We introduce a new one-dimensional (1-D) analysis of low-density parity-check (LDPC) codes on additive white Gaussian noise channels which is significantly more accurate than similar 1-D methods. Our method assumes a Gaussian distribution in message-passing decoding only for messages from variable nodes to check nodes. Compared to existing work, which makes a Gaussian assumption both for messages from check nodes and from variable nodes, our method offers a significantly more accurate estimate of convergence behavior and threshold of convergence. Similar to previous work, the problem of designing irregular LDPC codes reduces to a linear programming problem. However, our method allows irregular code design in a wider range of rates without any limit on the maximum variable-node degree. We use our method to design irregular LDPC codes with rates greater than 1/4 that perform within a few hundredths of a decibel from the Shannon limit. The designed codes perform almost as well as codes designed by density evolution. View full abstract»

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  • Subspace algorithms for error localization with quantized DFT codes

    Page(s): 2115 - 2124
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (472 KB) |  | HTML iconHTML  

    Recently, a class of real-number Bose-Chaudhuri-Hocquengem codes known as discrete Fourier transform (DFT) codes have been considered as joint source and channel codes for providing robustness to erasures and errors over wireless networks. We propose three subspace algorithms for error localization with quantized DFT codes. The algorithms are similar to the MUSIC, the minimum-norm, and the ESPRIT algorithms used in array signal processing for direction-of-arrival estimation. They provide different but related formulations of the error localizations by first partitioning a vector space into the channel error subspace and its orthogonal complement, the noise subspace. The locations of the errors are determined from either the error subspace eigenvectors or the noise subspace eigenvectors. We also present a brief performance analysis of the localization error in terms of the perturbation of the error subspace due to quantization. Simulation results show that their localization performances are similar, and they perform better than the coding-theoretic approach over a broad range of channel-error-to-quantization-noise ratios. View full abstract»

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  • On finite-state vector quantization for noisy channels

    Page(s): 2125 - 2133
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (472 KB) |  | HTML iconHTML  

    Finite-state vector quantization (FSVQ) over a noisy channel is studied. A major drawback of a finite-state decoder is its inability to track the encoder in the presence of channel noise. In order to overcome this problem, we propose a nontracking decoder which directly estimates the code vectors used by a finite-state encoder. The design of channel-matched finite-state vector quantizers for noisy channels, using an iterative scheme resembling the generalized Lloyd algorithm, is also investigated. Simulation results based on encoding a Gauss-Markov source over a memoryless Gaussian channel show that the proposed decoder exhibits graceful degradation of performance with increasing channel noise, as compared with a finite-state decoder. Also, the channel-matched finite-state vector quantizers are shown to outperform channel-optimized vector quantizers having the same vector dimension and rate. However, the nontracking decoder used in the channel-matched finite-state quantizer has a higher computational complexity, compared with a channel-optimized vector-quantizer decoder. Thus, if they are allowed to have the same overall complexity (encoding and decoding), the channel-optimized vector quantizer can use a longer encoding delay and achieve similar or better performance. Finally, an example of using the channel-matched finite-state quantizer as a backward-adaptive quantizer for nonstationary signals is also presented. View full abstract»

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  • Parametric construction of Nyquist-I pulses

    Page(s): 2134 - 2142
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (488 KB) |  | HTML iconHTML  

    A novel parametric approach for constructing families of intersymbol-interference (ISI)-free pulses is presented and examined. Some new pulses so constructed have smaller maximum distortion, a more open receiver eye, and a smaller probability of error in the presence of symbol-timing error than the Nyquist raised-cosine pulse for the same excess bandwidth. The parametric approach gives more degrees of freedom in the design of ISI-free pulses, and subsumes previous ISI-free pulses as special cases. A number of theorems that relate time-domain behaviors of a pulse to the pulse's frequency spectrum are proved. A previously known result relating pulse tail-time decay to discontinuity of the pulse-frequency spectrum is corrected and clarified. View full abstract»

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  • SER and outage of threshold-based hybrid selection/maximal-ratio combining over generalized fading channels

    Page(s): 2143 - 2153
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (720 KB) |  | HTML iconHTML  

    The average symbol-error rate and outage probability of threshold-based hybrid selection/maximal-ratio combining (T-HS/MRC) in generalized fading environments are analyzed. A T-HS/MRC combiner chooses the combined branches according to a predetermined normalized threshold and the strength of the instantaneous signal-to-noise ratio (SNR) of each branch. Therefore, the number of combined branches is a random variable, rather than a fixed number, as in conventional hybrid selection/maximal-ratio combining (H-S/MRC). Using the moment generating function method, a unified analysis of T-HS/MRC over various slow and frequency-nonselective fading channels is presented. Both independent, identically distributed and independent, nonidentically distributed diversity branches are considered. The derivation allows different M-ary linear modulation schemes. The theory is illustrated using coherent M-ary phase-shift keying in Nakagami-m fading as an example. It is shown that previous published results are incorrect. View full abstract»

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  • An NS frequency-domain approach for continuous-time design of CAP/ICOM waveform

    Page(s): 2154 - 2164
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (800 KB) |  | HTML iconHTML  

    The carrierless amplitude and phase (CAP) waveforms belong to a class of intersymbol interference ( ISI)-free and cross-channel interference (CCI)-free orthogonally multiplexed (ICOM) waveforms, and are considered as several modulation techniques for high-speed digital subscriber loops. This paper contributes a new set of frequency-domain constraints which are necessary and sufficient (NS) for the most general m-dimensional CAP or ICOM transceiver structure to be free of ISI and CCI in the continuous-time domain. The minimum bandwidth required for the most general m-dimensional ICOM transceiver structure is also theoretically proven using the new constraints. A new set of continuous-time two-dimensional (2-D) ICOM pulses, designed using the new NS constraints, is also included to demonstrate the usefulness of the frequency-domain NS constraints. The new 2-D ICOM pulses lead to transceiver eye patterns that are larger than the conventional 2-D CAP eye patterns. View full abstract»

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  • OCDMA-coded free-space optical links for wireless optical-mesh networks

    Page(s): 2165 - 2174
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (448 KB) |  | HTML iconHTML  

    We propose a wireless optical-mesh network based on optical code-division multiple-access (OCDMA)-coded free-space optical links. The performance of the proposed network under intermediate and strong turbulence channel conditions is investigated for synchronous and asynchronous OCDMA. We show that synchronous OCDMA using complementary Walsh-Hadamard codes operating at a raw bit rate of 622 Mb/s per user can achieve a bit-error rate of 10-9. This is achievable in channels with strong turbulence and high temporal correlation, or in channels with intermediate turbulence conditions; reasonable conditions based on channel characteristics inferred from the refractive index spectrum. For asynchronous OCDMA using optical orthogonal codes (OOCs), using a lower bound, we show that asynchronous OCDMA using OOCs cannot achieve acceptable performance for the same channel conditions, due to interference limitations. View full abstract»

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  • Performance modeling of optical-burst switching with fiber delay lines

    Page(s): 2175 - 2183
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (352 KB) |  | HTML iconHTML  

    We develop analytical models to evaluate the performance of optical-burst switch (OBS) architectures employing fiber delay lines (FDLs) as optical buffers to reduce burst-loss probability. The performance of such architectures cannot be captured accurately using traditional queueing models, since FDLs behave fundamentally differently from conventional electronic buffers. We formulate a Markovian model to evaluate the system performance when the burst-arrival process is Poisson and the burst lengths are exponentially distributed under an idealized model of FDL behavior. The model accurately captures both the balking and deterministic delay properties of FDLs, but the complexity of the model makes it infeasible for solving problems of practical interest. By considering approximations of the model in the regimes of short and long FDLs, we develop relatively simple closed-form expressions that can be used for dimensioning OBS architectures. We also extend the approximate model to include the impact of FDL delay granularity. We present numerical results that validate our modeling approach and demonstrate that significant performance gains in optical-burst switching are achievable when FDLs are employed as optical buffers. View full abstract»

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  • Bandwidth-efficient WDM channel allocation for four-wave mixing-effect minimization

    Page(s): 2184 - 2189
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (432 KB) |  | HTML iconHTML  

    A novel channel-allocation method that allows reduction of the four-wave mixing (FWM) effect while maintaining bandwidth efficiency is presented. It is composed of a fractional bandwidth-allocation algorithm, taking into consideration the use of parameters with distinct differences. This proposed technique allows the computation of an optimal channel-allocation set, where degradation caused by interchannel interference and FWM is minimal. Simulation is carried out to show significant performance improvement, such as an average bit-error rate improvement factor of 1.336 for an eight-channel wavelength-division multiplexing system, without the requirement of increased bandwidth, unlike existing channel-allocation 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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Meet Our Editors

Editor-in-Chief
Robert Schober
University of British Columbia