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Communications, IEEE Transactions on

Issue 2 • Date Feb. 2005

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  • Table of contents

    Publication Year: 2005 , Page(s): c1 - c4
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  • IEEE Transactions on Communications publication information

    Publication Year: 2005 , Page(s): c2
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  • Shuffled iterative decoding

    Publication Year: 2005 , Page(s): 209 - 213
    Cited by:  Papers (111)  |  Patents (23)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (240 KB) |  | HTML iconHTML  

    Shuffled versions of iterative decoding of low-density parity-check codes and turbo codes are presented. The proposed schemes have about the same computational complexity as the standard versions, and converge faster. Simulations show that the new schedules offer better performance/complexity tradeoffs, especially when the maximum number of iterations has to remain small. View full abstract»

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  • BAD: bidirectional arbitrated decision-feedback equalization

    Publication Year: 2005 , Page(s): 214 - 218
    Cited by:  Papers (31)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (312 KB) |  | HTML iconHTML  

    The bidirectional arbitrated decision-feedback equalizer (BAD), which has bit-error rate performance between a decision-feedback equalizer (DFE) and maximum a posteriori (MAP) detection, is presented. The computational complexity of the BAD algorithm is linear in the channel length, which is the same as that of the DFE, and significantly lower than the exponential complexity of the MAP detector. While the relative performance of BAD to those of the DFE and the MAP detector depends on the specific channel model, for an error probability of 10-2, the performance of BAD is typically 1-2 dB better than that of the DFE, and within 1 dB of the performance of MAP detection. View full abstract»

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  • Parameter estimation and equalization techniques for communication channels with multipath and multiple frequency offsets

    Publication Year: 2005 , Page(s): 219 - 223
    Cited by:  Papers (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB) |  | HTML iconHTML  

    We consider estimation of frequency offset (FO) and equalization of a wireless communication channel, within a general framework which allows for different frequency offsets for various multipaths. Such a scenario may arise due to different Doppler shifts associated with various multipaths, or in situations where multiple basestations are used to transmit identical information. For this general framework, we propose an approximative maximum-likelihood estimator exploiting the correlation property of the transmitted pilot signal. We further show that the conventional minimum mean-square error equalizer is computationally cumbersome, as the effective channel-convolution matrix changes deterministically between symbols, due to the multiple FOs. Exploiting the structural property of these variations, we propose a computationally efficient recursive algorithm for the equalizer design. Simulation results show that the proposed estimator is statistically efficient, as the mean-square estimation error attains the Crame´r-Rao lower bound. Further, we show via extensive simulations that our proposed scheme significantly outperforms equalizers not employing FO estimation. View full abstract»

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  • A new choice of penalty function for robust multiuser detection based on M-estimation

    Publication Year: 2005 , Page(s): 224 - 227
    Cited by:  Papers (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (232 KB) |  | HTML iconHTML  

    In this letter, we propose a new robust MUD, called α detector, for non-Gaussian noise. We consider the Gaussian-mixture model for non-Gaussian or impulsive noise. Our technique outperforms the decorrelator and the minimax detectors in highly impulsive noise. The proposed method uses a parametric cost function, where the parameter α is selected using the difference between the asymptotic variance of estimation error of the α detector and that of the minimax detector. View full abstract»

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  • Sum capacity of equal-power users in overloaded channels

    Publication Year: 2005 , Page(s): 228 - 233
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (232 KB) |  | HTML iconHTML  

    We consider the sum capacity of code-division multiple-access (CDMA) signature-sequence sets in overloaded channels that contain an orthogonal subset of dimension N. We introduce a family of signature-sequence sets that consists of a hierarchy of orthogonal subsets (HOS), and show that various signature-sequence sets designed for channel overloading belong to this family. Assuming an equal average energy (EAE) constraint on the user signals, an expression for the sum capacity of the HOS family is derived. We point out that the maximum sum capacity over the HOS family is achieved by the multiple-orthogonal (m-O) CDMA sequence sets. The sum capacity of m-O is only slightly less than the upper bound imposed by the Gaussian multiple-access channel. Moreover, m-O is superior to a system with N orthogonal sequences and (K-N) pseudonoise (PN) sequences (PN/O), which, in turn, outperforms a system with K PN sequences. Both for PN/O and sequence sets over HOS, there is no additional loss in sum capacity if we require the sequences to consist of chips that are binary or quaternary valued. View full abstract»

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  • Supplementary proof for "Exact and approximate construction of digital phase modulations by superposition of AMP" by P. A. Laurent

    Publication Year: 2005 , Page(s): 234 - 237
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (136 KB) |  | HTML iconHTML  

    In this letter, we supplement the derivation in Laurent's paper by mathematically proving that combining binary continuous phase modulation (CPM) signals in different bit durations results in the decomposed CPM expression consisting of a set of continuous amplitude-modulated pulse functions. View full abstract»

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  • A wideband crosstalk canceller for xDSL using common-mode information

    Publication Year: 2005 , Page(s): 238 - 242
    Cited by:  Papers (7)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (192 KB) |  | HTML iconHTML  

    This letter uses the twisted-pair common-mode signal as the input of an adaptive canceller to remove some wideband crosstalk in a digital subscriber line (xDSL) differential signal. Simulations using simple crosstalk and line balance models show the potential benefits of the canceller to improve the signal-to-noise ratio of an xDSL channel. View full abstract»

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  • Construction of low-density parity-check codes by superposition

    Publication Year: 2005 , Page(s): 243 - 251
    Cited by:  Papers (31)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (552 KB) |  | HTML iconHTML  

    This paper presents a superposition method for constructing low-density parity-check (LDPC) codes. Several classes of structured LDPC codes are constructed. Codes in these classes perform well with iterative decoding, and their Tanner graphs have girth at least six. View full abstract»

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  • Serial concatenated TCM with an inner accumulate code - part II: density-evolution analysis

    Publication Year: 2005 , Page(s): 252 - 262
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (504 KB) |  | HTML iconHTML  

    In a companion paper, we showed the existence of decoding thresholds for maximum-likelihood (ML) decoding of a serial concatenated trellis-coded modulation (SCTCM) system with one or more inner accumulate codes. In this paper, we compute the decoding thresholds for an iterative, non-ML decoder by density evolution (DE), assuming infinite blocklengths. We also derive a stability condition for the particular case of an outer parity-check code and a single inner accumulate code. We show that, for equiprobable signaling, the bit-wise log-likelihood ratio densities for higher order constellations are symmetric. Furthermore, when used in DE, these densities can be averaged without significantly affecting the resulting threshold values. For an outer single parity-check code, the lowest decoding thresholds are achieved with two inner accumulate codes. For an outer repeat code, a single inner accumulate code gives the lowest thresholds. At code rates rc>2/3, the decoding thresholds for the SCTCM system are within 1 dB of the constellation-constrained channel capacity for additive white Gaussian noise channels, and within 1.5 dB for independent, identically distributed Rayleigh channels. Simulation results verify the computed thresholds. View full abstract»

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  • Redundancy allocation in turbo-equalizer design

    Publication Year: 2005 , Page(s): 263 - 268
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (328 KB) |  | HTML iconHTML  

    This paper considers properties of the extrinsic information transfer (EXIT) functions of turbo equalized intersymbol interference channels and finite-impulse response precoders. An analytic expression is derived for the maximum value of the EXIT function of the equalizer. Using this parameter, a design strategy is proposed for allocating redundancy between the equalizer and the decoder. The key quantities are pilot-symbol rate and code puncturing, for fixed overall data and symbol rates. View full abstract»

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  • Split soft-decision equalization for wireless channels with large delay spread

    Publication Year: 2005 , Page(s): 269 - 277
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (504 KB) |  | HTML iconHTML  

    A novel split soft-decision equalizer (SSE) with near-optimum performance is proposed for wireless multipath channels with large delay spread. The concept of SSE is significantly different from the traditional notions of the Viterbi algorithm and decision-feedback equalizer. Instead of dealing with received sequence as a combined sequence, it splits the received sequence into its constituent paths. Using an iterative soft-decision algorithm, reliability of the soft decisions on each decomposed element is improved iteratively. The major advantage of SSE is the independence of computation complexity on channel time dispersion. Joint design of SSE with a soft-decision decoder is also considered in this paper. Performance analysis and simulation results show that performance of the proposed algorithm comes very close to that of the logarithmic maximum a posteriori decoder. View full abstract»

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  • Sampling-based soft equalization for frequency-selective MIMO channels

    Publication Year: 2005 , Page(s): 278 - 288
    Cited by:  Papers (17)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (576 KB) |  | HTML iconHTML  

    We consider the problem of channel equalization in broadband wireless multiple-input multiple-output (MIMO) systems over frequency-selective fading channels, based on the sequential Monte Carlo (SMC) sampling techniques for Bayesian inference. Built on the technique of importance sampling, the stochastic sampler generates weighted random MIMO symbol samples and uses resampling to rejuvenate the sample streams; whereas the deterministic sampler, a heuristic modification of the stochastic counterpart, recursively performs exploration and selection steps in a greedy manner in both space and time domains. Such a space-time sampling scheme is very effective in combating both intersymbol interference and cochannel interference caused by frequency-selective channel and multiple transmit and receiver antennas. The proposed sampling-based MIMO equalizers significantly outperform the decision-feedback MIMO equalizers with comparable computational complexity. More importantly, being soft-input soft-output in nature, these sampling-based MIMO equalizers can be employed as the first-stage soft demodulator in a turbo receiver for coded broadband MIMO systems. Such a turbo receiver successively improves the receiver performance through iterative equalization, channel re-estimation, and channel decoding. Finally, computer simulation results are provided to demonstrate the performance of the proposed sampling-based soft MIMO equalizers in both uncoded and turbo coded systems. View full abstract»

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  • A unified analysis for coded DS-CDMA with equal-gain chip combining in the downlink of OFDM systems

    Publication Year: 2005 , Page(s): 289 - 298
    Cited by:  Papers (2)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (520 KB) |  | HTML iconHTML  

    This paper presents a novel unified analysis for the bit-error rate in the downlink of convolutionally coded and single-user detected multicarrier code-division multiple access (CDMA), multicarrier direct-sequence CDMA, time and frequency-domain spreading CDMA, and orthogonal frequency-division multiple access. Performance is analyzed under the assumption of Hadamard spreading codes, equal-gain chip combining, and a highly correlated frequency-selective Rayleigh-fading channel. Closed-form expressions are presented for the cumulative distribution function, probability distribution function, and moment-generating function for the signal-to-noise plus interference ratio after despreading. The presented results assume error-free channel estimates, a perfectly synchronized receiver, and are found to reasonably well agree with simulation results. View full abstract»

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  • On the optimality of bit detection of certain digital modulations

    Publication Year: 2005 , Page(s): 299 - 307
    Cited by:  Papers (27)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (464 KB) |  | HTML iconHTML  

    In this paper, we study the optimality of bit detection for coherent M-ary phase-shift keying (PSK) and M-ary quadrature amplitude modulation (QAM), and noncoherent M-ary frequency-shift keying (FSK) signal sets. For M-PSK and M-QAM signal constellations, we employ Gray mapping, consider 8-PSK and 16-QAM signal sets as representative of the general results, and derive the log-likelihood ratio (LLR) for each bit forming the symbol. Using the LLRs, we derive the average bit-error probability (BEP) for the individual bits, and show that the decision regions and the corresponding average BEP for the case of M-PSK coincide with those obtained with the optimal symbol-based detector, whereas, in general, this is not the case for both M-QAM and M-FSK. View full abstract»

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  • Performance analysis of k-fold multicast networks

    Publication Year: 2005 , Page(s): 308 - 314
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (352 KB) |  | HTML iconHTML  

    Multicast involves transmitting information from a single source to multiple destinations, and is an important operation in high-performance networks. A k-fold multicast network was recently proposed as a cost-effective solution to providing better quality-of-service functions in supporting real-world multicast applications. To give a quantitative basis for network designers to determine the suitable value of system parameter k under different traffic loads, in this paper, we propose an analytical model for the performance of k-fold multicast networks under Poisson traffic. We first give the stationary distribution of network states, and then derive the throughput and blocking probability of the network. We also conduct extensive simulations to validate the analytical model, and the results show that the analytical model is very accurate under the assumptions made. The analytical and simulation results reveal that by increasing the fold of the network, network throughput increases very fast when the fanouts of multicast connections are relatively small, compared with the network size. View full abstract»

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  • Optimality of the users strength in optical PPM-CDMA channels

    Publication Year: 2005 , Page(s): 315 - 322
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (312 KB) |  | HTML iconHTML  

    An upper bound on the users strength in direct-detection optical code-division multiple-access communication systems, which employ pulse-position modulation techniques, is developed. This upper bound is consistent with the lower bound derived previously, as long as the transmitted information per photon is less than some positive threshold. The concept of users strength was introduced by the author in a previous paper, where it provides a measure to the maximum number of simultaneous users that can communicate simultaneously with arbitrary small probability of error. View full abstract»

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  • On the cutoff rates of a multiclass OFFH-CDMA system

    Publication Year: 2005 , Page(s): 323 - 334
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (512 KB) |  | HTML iconHTML  

    We consider an optical code-division multiple-access (OCDMA) network that supports multiple traffic classes. Each class has different processing gain and performance requirements. In this paper, a new method is proposed to analyze the cutoff rates for a multiclass, multirate optical frequency-hopping code-division multiple-access system using fiber Bragg gratings and direct detection. This approach exploits the linear structure of passive OCDMA systems and the nominal time required to accomplish the encoding-decoding operations in such systems. A system model is presented and analyzed, based on a newly introduced bit-overlap procedure. An expression for the cutoff rate of a single-class system is derived. In addition, for a multiclass system, an expression that relates the cutoff rates of the offered classes is introduced, and it is called the service curve. It is shown that for a required quality of service guarantee, a number of active users, and a given probability of hit, the system's data rate can be increased beyond the nominal limit imposed by the physical constraint of the encoder-decoder set. View full abstract»

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  • On the capacity limits of HVAC duct channel for high-speed Internet access

    Publication Year: 2005 , Page(s): 335 - 342
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (792 KB) |  | HTML iconHTML  

    In this paper, we report theoretical and experimental channel-capacity estimates of heating, ventilation, and air conditioning (HVAC) ducts based on multicarrier transmission that uses M-ary quadrature amplitude modulation and measured channel responses at the 2.4-GHz industrial, scientific, and medical band. It is shown theoretically that data rates in excess of 1 Gb/s are possible over distances up to 500 m in straight ducts in which reflections have been suppressed. Our experimental results also show that even in the case of more complex HVAC duct networks (i.e., HVAC duct networks that include bends, tees, etc.) data rates over 2 Gb/s are possible. Our estimations in this case are valid for distances of up to 22 m, which was the maximum distance of our experimental setup. These experimental results, measured with a large-scale testbed set up at Carnegie Mellon University, Pittsburgh, PA, albeit limited in terms of transmitter-receiver separation distance, provide further evidence on the potential of HVAC systems as an attractive solution for providing communications in indoor wireless networks. View full abstract»

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  • An optimal training signal structure for frequency-offset estimation

    Publication Year: 2005 , Page(s): 343 - 355
    Cited by:  Papers (24)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (528 KB) |  | HTML iconHTML  

    This paper addresses an optimal training-signal design for frequency-offset estimation. Based on minimizing the Cramer-Rao lower bound for frequency-offset estimation with constraints on the peak and the total training signal energies, and the training block length, the optimal training-signal structure is developed. An approximate version of the optimal training-signal structure is proposed, which has practically the same performance as the optimal one, and provides convenience in training-signal generation and estimator derivation. Two robust reduced-complexity frequency-offset estimation methods for the proposed training structures are presented. In order to handle larger frequency offsets, modified training-signal structures are proposed. Frequency-offset estimation methods suitable for these training signals are also derived, based on the best linear unbiased estimation principle. Analytical and simulation results show that the proposed training-signal structures improve the estimation performance significantly. View full abstract»

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  • Directly estimated adaptive detectors for code-division multiple-access signals

    Publication Year: 2005 , Page(s): 356 - 365
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (512 KB) |  | HTML iconHTML  

    This paper presents adaptive multiuser detectors for code-division multiple-access (CDMA) signals in wireless communication systems. Directly estimated adaptive (DEA) detectors are developed by formulating CDMA detection as an inverse problem in the presence of channel-induced interference and noise. The detector parameters are computed by a fully sequential adaptive algorithm that requires no matrix inversion, and can be implemented online as the data arrive at the receiver. The proposed DEA detector is experimentally evaluated in terms of its robustness to noise, resistance to the near-far problem, and ability to handle multipath fading signals. This experimental study indicates that the proposed DEA detector requires shorter training sequences of bits to achieve the performance levels attained by existing adaptive implementations of the minimum mean-square error detector. View full abstract»

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  • Reduced-rank multistage receivers for DS-CDMA in frequency-selective fading channels

    Publication Year: 2005 , Page(s): 366 - 378
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (640 KB) |  | HTML iconHTML  

    Multistage (MS) implementation of the minimum mean-square error (MMSE), minimum output energy (MOE), best linear unbiased estimation (BLUE), and maximum-likelihood (ML) filter banks (FBs) is developed based on the concept of the MS Wiener filtering (MSWF) introduced by Goldstein et al. These FBs are shown to share a common MS structure for interference suppression, modulo a distinctive scaling matrix at each filter's output. Based on this finding, a framework is proposed for joint channel estimation and multiuser detection (MUD) in frequency-selective fading channels. Adaptive reduced-rank equal gain combining (EGC) schemes for this family of FBs (MMSE, MOE, BLUE, and ML) are proposed for noncoherent blind MUD of direct-sequence code-division multiple-access systems, and contrasted with the maximal ratio combining counterparts that are also formed with the proposed common structure under the assumption of known channel-state information. The bit-error rate, steady-state output signal-to-interference plus noise ratio (SINR), and convergence of the output SINRs are investigated via computer simulation. Simulation results indicate that the output SINRs attain full-rank performance with much lower rank for a highly loaded system, and that the adaptive reduced-rank EGC BLUE/ML FBs outperform the EGC MMSE/MOE FBs, due to the unbiased nature of the implicit BLUE channel estimators employed in the EGC BLUE/ML schemes. View full abstract»

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  • Erratum

    Publication Year: 2005 , Page(s): 379
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  • Erratum

    Publication Year: 2005 , Page(s): 379
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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