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Communications, IEEE Transactions on

Issue 7 • Date July 2005

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Displaying Results 1 - 25 of 35
  • Table of contents

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

    Page(s): c2
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  • Robust source decoding of variable-length encoded video data taking into account source constraints

    Page(s): 1077 - 1084
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (768 KB) |  | HTML iconHTML  

    We first provide an analysis of available redundancy remaining in compressed video data. This residual redundancy has two origins: the variable-length code (VLC) syntax and the source constraints. We compute the two in terms of equivalent redundancy bits. Then, a VLC decoding algorithm able to exploit both VLC syntax and source constraints for improving the decoding performance is outlined. Finally, it is shown that by taking this redundancy into account, video decoding over additive white Gaussian noise channels is substantially improved. View full abstract»

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  • A closed-form expression for the symbol-error rate of M-ary DPSK in fast Rayleigh fading

    Page(s): 1085 - 1087
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (144 KB) |  | HTML iconHTML  

    The error performance of M-ary differential phase-shift keying on Rayleigh fading channels is widely analyzed in the framework originated by Pawula, and the results usually take the form of an integral. In this letter, we formulate the same problem in a different framework, and solve it by using a linear prediction-based technique resulting in a simple solution in closed form. View full abstract»

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  • SEP performance of coherent MPSK over fading channels in the presence of phase/quadrature error and I-Q gain mismatch

    Page(s): 1088 - 1091
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (160 KB) |  | HTML iconHTML  

    This letter presents a joint approach to the symbol-error probability (SEP) of coherent M-ary phase-shift keying in a situation where the phase error, quadrature error, and in-phase-quadrature (I-Q) gain mismatch problems take place all concurrently over an additive white Gaussian noise and arbitrary fading channel. A set of equations that characterizes the conditional SEP on an instantaneous fading signal-to-noise ratio is derived in the form of the Craig representation. View full abstract»

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  • Closed-form expressions for the outage and ergodic Shannon capacity of MIMO MRC systems

    Page(s): 1092 - 1095
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (272 KB) |  | HTML iconHTML  

    Transmit-beamforming (TB) over multiple-input multiple-output (MIMO) fading channels steers the transmit power in the receiver's direction, so as to maximize the output signal-to-noise ratio (SNR) after maximal ratio combining (MRC) at the receiver. This letter proposes a simple algorithm that allows evaluating an exact and tractable expression for the probability density function of the SNR at the output of the TB receiver, subject to Rayleigh fading. The latter enables the derivation of closed-form expressions for the outage and ergodic capacity of MIMO MRC systems under Rayleigh fading, thereby avoiding the need for time-consuming numerical integrations or Monte Carlo simulations. View full abstract»

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  • Effect of imperfect phase and timing synchronization on the bit-error rate performance of PSK modulations

    Page(s): 1096 - 1099
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (272 KB) |  | HTML iconHTML  

    A great deal of attention has been devoted in the recent literature to the study of the bit-error rate (BER) performance of phase-shift keyed (PSK) constellations, due to their high spectral efficiency. It is well known that an error in phase or timing synchronization affects the probability of correct decisions at the receiver. This problem becomes much more significant as data rates increase, and the corresponding symbol durations decrease. In this letter, we look into this problem and analyze the exact BER performance of generalized hierarchical PSK constellations under imperfect phase or timing synchronization over additive white Gaussian noise channels. View full abstract»

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  • Simple CPM receivers based on a switched linear modulation model

    Page(s): 1100 - 1103
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (232 KB) |  | HTML iconHTML  

    Based on a switched linear modulation model recently developed for continuous-phase modulated (CPM) signal representation and approximation, and incorporated with new phase state symbol definitions, three simple CPM receivers are proposed in this letter. Their performance simulation results and complexity comparison are given using a quaternary 2RC (raised cosine frequency pulse) CPM scheme. View full abstract»

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  • Sphere decoding algorithms with improved radius search

    Page(s): 1104 - 1109
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (336 KB) |  | HTML iconHTML  

    We start by identifying a relatively efficient version of sphere decoding algorithm (SDA) that performs exact maximum-likelihood (ML) decoding. We develop novel algorithms based on an improved increasing radius search (IIRS), which offer error performance and decoding complexity between two extremes: the ML receiver and the ing-canceling (NC) receiver with detection ordering. With appropriate choices of parameters, our IIRS offers the flexibility to trade error performance for complexity. We provide design intuitions and guidelines, analytical parameter specifications, and a semianalytical error-performance analysis. Simulations illustrate that IIRS achieves considerable complexity reduction, while maintaining performance close to ML. View full abstract»

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  • Adaptive signal detection over fast frequency-selective fading channels under class-A impulsive noise

    Page(s): 1110 - 1113
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB) |  | HTML iconHTML  

    The problem of adaptive detection of signals contaminated with Middleton's class-A impulsive noise and transmitted over a fast time-varying frequency-selective fading channel is addressed. Adaptive algorithms are derived to update the estimate of the channel parameters to the detector. A theoretical performance evaluation of the detector is provided. Computer simulations are performed to validate the theoretical developments. View full abstract»

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  • Joint network-centric and user-centric radio resource management in a multicell system

    Page(s): 1114 - 1118
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (208 KB) |  | HTML iconHTML  

    A pricing mechanism to mediate (and allocate resources) between conflicting user and network objectives has been recently proposed by the authors in a single-cell system. Here, we extend the results to a multicell system, where the autonomous base station assignment and power control are formulated as a noncooperative game among users. The network prices the resources using two strategies: global pricing that maximizes the revenue, and minimax pricing that trades off the revenue for a more even resource allocation. View full abstract»

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  • Experimental evaluation of capacity statistics for short VDSL loops

    Page(s): 1119 - 1122
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (264 KB) |  | HTML iconHTML  

    We assess the capacity potential of very short very-high data-rate digital subscriber line loops using full-binder channel measurements collected by France Telecom R&D. Key statistics are provided for both uncoordinated and vectored systems employing coordinated transmitters and coordinated receivers. The vectoring benefit is evaluated under the assumption of transmit precompensation for the elimination of self-far-end crosstalk, and echo cancellation of self-near-end crosstalk. The results provide useful bounds for developers and providers alike. View full abstract»

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  • Propagation models for short-range wireless channels with predictable path geometries

    Page(s): 1123 - 1126
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (536 KB) |  | HTML iconHTML  

    We consider wireless data services characterized by short distances, no shadowing, low power, and low antenna heights, deployed in places where a high frequency of potential users is expected, e.g., toll booths, parking lots, intersections, etc. Within such a system, we expect to see a well-defined geometry of base-to-user radio paths, as well as a predictable user trajectory, neither of which can be assumed for the wide-area cellular case. This offers the promise of a strong deterministic component of the channel response, in addition to a weaker stochastic component. Here, we combine analysis of the former with measurements and modeling of the latter for three typical outdoor scenarios. Comparisons between predicted and measured behavior show excellent agreement. View full abstract»

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  • Single-carrier frequency-domain equalization with decision-feedback processing for time-reversal space-time block-coded systems

    Page(s): 1127 - 1131
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (192 KB) |  | HTML iconHTML  

    In this letter, we propose to introduce frequency-domain equalization with decision-feedback processing (FD-DFE) for time-reversal space-time block-coded (TR-STBC) systems with multiple transmit antennas to effectively achieve both spatial diversity and multipath diversity over frequency-selective channels. This letter will also present a theoretical performance analysis result that relates the minimum mean-squared error (MMSE) to a new tight upper bound for the probability of error. It is shown that the new bound is not only valid for the TR-STBC systems, but also valid for single-input single-output, single-input multiple-output, and multiple-input multiple-output systems with MMSE equalization. View full abstract»

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  • Generalized switch-and-examine combining (GSEC) over fading paths with unequal average SNR

    Page(s): 1132 - 1135
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (200 KB) |  | HTML iconHTML  

    A generalized switch-and-examine combining (GSEC) scheme was previously proposed by the authors as a low-complexity diversity technique for diversity-rich environments. In this letter, we extend the study of GSEC to independent and nonidentically distributed (i.n.d.) fading environments. In particular, after presenting the mode of operation of the GSEC scheme over i.n.d. fading paths, we analyze its error performance based on the moment generating function of combined signal-to-noise ratios. We then study its complexity in terms of the average number of path estimations. We finally investigate the effect of path examination order on the performance and complexity of GSEC over i.n.d. paths. View full abstract»

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  • Joint synchronization and SNR estimation for turbo codes in AWGN channels

    Page(s): 1136 - 1144
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (432 KB) |  | HTML iconHTML  

    Turbo codes are sensitive to both (timing) synchronization errors and signal-to-noise ratio (SNR) mismatch. Since turbo codes are intended to work in environments with very low SNR, conventional synchronization methods often fail. This paper investigates blind symbol-timing synchronization and SNR estimation based on oversampled data frames. The technique is particularly suitable for low-rate turbo codes operating in additive white Gaussian noise at low SNR and modest data-transfer rates, as in deep space, satellite, fixed wireless, or wireline communications. In accordance with the turbo principle, intermediate decoding results are fed back to the estimator, thereby facilitating decision-directed estimation. The analytical and simulated results show that with three or more samples per symbol and raised cosine-rolloff pulse shaping, performance approaches that of systems with perfect timing and SNR knowledge at the receiver. View full abstract»

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  • Sample rejection for efficient simulation of binary coding schemes over quantized additive white Gaussian noise channels

    Page(s): 1145 - 1154
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (608 KB) |  | HTML iconHTML  

    We re-examine sample rejection (SR), introduced previously as an easy-to-implement efficient simulation technique. Since the decoding operation often represents a major part of the required simulation time, SR can be used to avoid decoding of the received sequences that are known beforehand to be decoded error-free. Previous work seems to indicate that SR may be effective only for simulations having small dimensionality, less than 10. We assume estimation of decoded bit-error probabilities for a general coding scheme of finite block length transmitted over an additive white Gaussian noise channel with quantized output using binary antipodal signaling and maximum-likelihood sequence decoding. We show that knowledge of the minimum Hamming distance of the code and conditioning on the transmitted sequence can be exploited to form the rejection regions. In particular, we investigate hypersphere, hypercube, and hyperquadrant rejection regions. Our analysis shows that SR can be effective for some systems with dimensionality on the order of hundreds with soft-decision decoding, and some systems with dimensionality more than a thousand with hard-decision decoding if the rejection regions are properly chosen. View full abstract»

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  • An interference-cancellation scheme for carrier frequency offsets correction in OFDMA systems

    Page(s): 1155 - 1165
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (528 KB) |  | HTML iconHTML  

    Recently, orthogonal frequency-division multiplexing (OFDM), with clusters of subcarriers allocated to different subscribers (often referred to as OFDMA), has gained much attention for its ability in enabling multiple-access wireless multimedia communications. In such systems, carrier frequency offsets (CFOs) can destroy the orthogonality among subcarriers. As a result, multiuser interference (MUI) along with significant performance degradation can be induced. In this paper, we present a scheme to compensate for the CFOs at the base station of an OFDMA system. In the proposed scheme, circular convolutions are employed to generate the interference after the discrete Fourier transform processing, which is then removed from the original received signal to increase the signal-to-interference power ratio (SIR). Both SIR analysis and simulation results will show that the proposed scheme can significantly improve system performance. View full abstract»

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  • MMSE-optimal approximation of continuous-phase modulated signal as superposition of linearly modulated pulses

    Page(s): 1166 - 1177
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (624 KB) |  | HTML iconHTML  

    The optimal linear modulation approximation of any M-ary continuous-phase modulated (CPM) signal under the minimum mean-square error (MMSE) criterion is presented in this paper. With the introduction of the MMSE signal component, an M-ary CPM signal is exactly represented as the superposition of a finite number of MMSE incremental pulses, resulting in the novel switched linear modulation CPM signal models. Then, the MMSE incremental pulse is further decomposed into a finite number of MMSE pulse-amplitude modulated (PAM) pulses, so that an M-ary CPM signal is alternatively expressed as the superposition of a finite number of MMSE PAM components, similar to the Laurent representation. Advantageously, these MMSE PAM components are mutually independent for any modulation index. The optimal CPM signal approximation using lower order MMSE incremental pulses, or alternatively, using a small number of MMSE PAM pulses, is also made possible, since the approximation error is minimized in the MMSE sense. Finally, examples of the MMSE-optimal CPM signal approximation and its comparison with the Laurent approximation approach are given using raised-cosine frequency-pulse CPM schemes. View full abstract»

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  • Optimal diversity-multiplexing tradeoff with group detection for MIMO systems

    Page(s): 1178 - 1190
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (624 KB) |  | HTML iconHTML  

    It is well known that multiple-input multiple-output (MIMO) systems provide two types of gains: diversity gains and spatial multiplexing gains. Recently, a tradeoff function of these two gains has been derived for a point-to-point MIMO system when optimal detection is used. In this paper, we extend the previous work to a more general MIMO system, where the transmitted data is coded in groups. Group detection is applied at the receiver to retrieve the data. It consists of a zero-forcing decorrelation that separates the groups, followed by a joint detection for each of the groups. Two receiver structures are considered in this paper; namely, group zero forcing (GZF) and group successive interference cancellation (GSIC). We assess the diversity-multiplexing tradeoff function of each of these receivers over a richly scattered Rayleigh fading channel. Three rate-allocation algorithms will be considered here; namely, equal rate, group-size proportional rate, and optimal-rate allocation. An explicit expression of the system tradeoff will be derived for both receivers with these three rate allocations. The obtained results will first be optimized over all possible group partitions for a given number of groups. Next, the number of groups will be varied to further optimize the system-tradeoff performance. An overall optimum tradeoff for a general MIMO system with group detection will then be obtained. Numerical results will indicate that optimum performance can be approached with very-low-complexity schemes for a wide range of data rates. It will be also demonstrated that group detection bridges the gap between the traditional decorrelator and the optimal receiver tradeoff performances. View full abstract»

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  • Bit-interleaved time-frequency coded modulation for OFDM systems over time-varying channels

    Page(s): 1191 - 1199
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (408 KB) |  | HTML iconHTML  

    Orthogonal frequency-division multiplexing (OFDM) is a promising technology in broadband wireless communications, with its ability to transform a frequency-selective fading channel into multiple flat-fading channels. However, the time-varying characteristics of wireless channels induce the loss of orthogonality among OFDM subcarriers, which was generally considered harmful to system performance. In this paper, we propose a bit-interleaved time-frequency coded modulation (BITFCM) scheme for OFDM to achieve both the time and frequency diversity inherent in broadband time-varying channels. We will show that the time-varying characteristics of the channel are beneficial to system performance. Using the BITFCM scheme, and for relatively low maximum normalized Doppler frequency, a reduced-complexity maximum-likelihood decoding approach is proposed to achieve good performance with low complexity. For high maximum normalized Doppler frequency, the intercarrier interference (ICI) can be large, and an error floor will be induced. To solve this problem, we propose two ICI-mitigation schemes by taking advantage of the second-order channel statistics and the complete channel information, respectively. It will be shown that both schemes can reduce the ICI significantly. View full abstract»

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  • Simple rate control for fluctuating channels in ad hoc wireless networks

    Page(s): 1200 - 1209
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (656 KB) |  | HTML iconHTML  

    In the presence of channel fluctuation, rate adaptation is one way to maintain the quality of the link at a desired level. This is especially important in ad hoc wireless networks, where temporary channel fluctuations might create frequent needs for rerouting that would result in severe overhead and adversely affect the performance. We study an unusual method of passive rate adaptation in which some bits are dropped at the receiver end of a link. The symbol-error probability decreases as some bits are dropped. In terms of the distortion for a realtime analog signal, the tradeoff is between more reliable detection of fewer bits and less reliable detection of more bits. Our scheme achieves smaller distortion for a certain region of signal-to-noise ratio (SNR) values when compared with the original scheme without rate adaptation. Two examples, uniformly spaced, uncoded pulse amplitude modulation and quadrature amplitude modulation, are studied and compared for both a Gaussian channel and a Rayleigh fading channel. We conclude that our scheme is more suitable to use in a fading channel than in a Gaussian channel. We also verify that our scheme has a larger applicable region of SNR values when a nonuniform constellation is used, since the important bits are given additional protection. View full abstract»

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  • Optimum scheduling for smart antenna systems in Rayleigh fading channels

    Page(s): 1210 - 1219
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (576 KB) |  | HTML iconHTML  

    Optimum and suboptimum scheduling schemes are proposed in the uplink of array antenna systems. We assume that once a user is permitted to transmit the data, the user transmits the data using the maximum power, and adjusts the transmission bit rate so that the energy-per-bit-to-interference-plus-noise-density ratio should be equal or higher than a threshold. In this system model, we consider an optimization problem: How many and which users should be selected to transmit their data at a time in order to maximize the throughput? Based on the analysis on the complexity of the optimum scheme, we propose another optimum scheme having reduced complexity. To reduce the complexity further, we also propose three suboptimum scheduling schemes by limiting the number of users simultaneously transmitting, by choosing the users with higher channel gains, and by partitioning a cell into multiple parts. In circular and linear arrays, the performance results of all the proposed schemes are presented and compared. View full abstract»

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  • Trellis and convolutional precoding for transmitter-based interference presubtraction

    Page(s): 1220 - 1230
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (504 KB) |  | HTML iconHTML  

    This paper studies the combination of practical trellis and convolution codes with Tomlinson-Harashima precoding (THP) for the presubtraction of multiuser interference that is known at the transmitter but not known at the receiver. It is well known that a straightforward application of THP suffers power, modulo, and shaping losses. This paper proposes generalizations of THP that recover some of these losses. At a high signal-to-noise ratio (SNR), the precoding loss is dominated by the shaping loss, which is about 1.53 dB. To recover shaping loss, a trellis-shaping technique is developed that takes into account the knowledge of a noncausal interfering sequence, rather than just the instantaneous interference. At rates of 2 and 3 bits per transmission, trellis shaping is shown to be able to recover almost all of the 1.53-dB shaping loss. At a low SNR, the precoding loss is dominated by power and modulo losses, which can be as large as 3-4 dB. To recover these losses, a technique that incorporates partial interference presubtraction (PIP) within convolutional decoding is developed. At rates of 0.5 and 0.25 bits per transmission, PIP is able to recover 1-1.5 dB of the power loss. For intermediate SNR channels, a combination of the two schemes is shown to recover both power and shaping losses. 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