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Wireless Communications, IEEE Transactions on

Issue 5 • Date Sept. 2005

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Displaying Results 1 - 25 of 74
  • Table of contents

    Publication Year: 2005 , Page(s): c1 - 1962
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    Freely Available from IEEE
  • IEEE Transactions on Wireless Communications publication information

    Publication Year: 2005 , Page(s): c2
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    Freely Available from IEEE
  • Low-complexity iterative equalization for EDGE with bidirectional processing

    Publication Year: 2005 , Page(s): 1963 - 1968
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (176 KB) |  | HTML iconHTML  

    We present a new and simple iterative equalization scheme for the enhanced data rates for global evolution (EDGE) wireless system. This scheme can significantly reduce the number of trellis states in a maximum a posteriori probability (MAP) equalizer via delayed decision-feedback (DDF) approach. Relying on the mechanism of decision feedback in the DDF trellis, bidirectional processing can be applied to exploit the time diversity of the received signal bursts for a more reliable equalizer output. With mild increase in computational complexity over the more traditional single-directional (Si) DDF turbo equalizer, the bidirectional turbo equalizer can achieve a significant performance gain. View full abstract»

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  • Wideband adaptive beamforming array with improved radiation characteristics

    Publication Year: 2005 , Page(s): 1969 - 1973
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (128 KB) |  | HTML iconHTML  

    An efficient subband adaptive beamforming array (ABA) using a quadrature mirror filter (QMF) bank is presented. For wideband beamforming, taps have to be added to the full-band ABA for efficient suppression of the interference. However, the introduction of multiple taps results in the addition of uncorrelated noise to the ABA. This results in power loss in the direction perpendicular to the ABA. In order to compensate for the loss introduced by the addition of taps, the proposed concept is investigated. This configuration shows improved signal gain and deep suppression of the interference in the direction perpendicular to the ABA. View full abstract»

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  • Full-rate full-diversity space-time code for four-transmit-antenna systems

    Publication Year: 2005 , Page(s): 1974 - 1979
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (216 KB) |  | HTML iconHTML  

    This paper introduces a low-complexity full-rate full-diversity space-time (ST) code for wireless communication systems with four transmit antennas. This novel code is designed by combining delay-diversity transmission with Alamouti's orthogonal ST block code. Analytical and computer simulation results show that this code yields significant frame-error-rate (FER) performance gains over some previously reported full-rate full-diversity codes for four transmit antennas. View full abstract»

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  • Joint estimation of carrier offset and code timing for DS-CDMA with performance analysis

    Publication Year: 2005 , Page(s): 1980 - 1987
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (272 KB) |  | HTML iconHTML  

    This paper considers the problem of joint carrier offset and code timing estimation for code-division multiple-access (CDMA) systems. In contrast to existing schemes that require nonlinear iterative searches over the multidimensional parameter space, this paper proposes a blind estimator that provides an algebraic solution to the joint parameter estimation problem. By exploiting the subspace structure of the observed signal, the multiuser estimation is first decoupled into a series of single-user estimation problems, and then analytical tools of polynomial matrices are invoked for joint carrier and code timing estimation of a single user. The proposed estimator is near-far resistant. It can deal with frequency-selective and time-varying channels. The performance of the proposed scheme is examined analytically by a first-order perturbation analysis. The authors also derive an unconditional Crame´r-Rao bound (CRB) that is conditioned neither on fading coefficients nor information symbols; as such, the CRB is considered a suitable lower bound for blind methods. Numerical examples are presented to evaluate and compare the proposed and a multidimensional search (MD-search)-based scheme. View full abstract»

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  • Turbo processing for an OFDM-based MIMO system

    Publication Year: 2005 , Page(s): 1988 - 1993
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (216 KB) |  | HTML iconHTML  

    We consider improving the overall system performance of an orthogonal frequency-division multiplexing-based multiple-input multiple-output (MIMO) wireless local area network system. We use a combined iterative detection/decoding and channel updating method, referred to herein as turbo processing, to improve performance. First, we improve a recently proposed list sphere decoder-based iterative MIMO soft-detector by constraining the value of the a priori information from a soft-in soft-out channel decoder. Second, we propose a channel updating scheme using the decoded packet data to improve the channel estimation accuracy. Simulation results show that turbo processing can be used to significantly improve the performance of the system considered. View full abstract»

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  • Invertible bounds for M-QAM in Rayleigh fading

    Publication Year: 2005 , Page(s): 1994 - 2000
    Cited by:  Papers (21)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (296 KB) |  | HTML iconHTML  

    In this letter, we derive tight invertible bounds on the bit-error probability (BEP) for the coherent detection of M-ary quadrature amplitude modulation with Gray code bit mapping in Rayleigh fading channels. These bounds enable us to easily obtain tight lower and upper bounds on the bit-error outage (BEO), i.e., BEP-based outage probability, in a log-normal shadowing environment. As examples of applications, these bounds are used to investigate the BEO and mean spectral efficiency for slow adaptive modulation. View full abstract»

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  • Accurate computation of bit error probabilities of band-limited asynchronous DS-CDMA systems using higher order moments

    Publication Year: 2005 , Page(s): 2001 - 2005
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (144 KB) |  | HTML iconHTML  

    An existing method called the simplified improved Gaussian approximation (SIGA) was previously applied to compute the bit error probabilities (BEPs) of band-limited asynchronous direct sequence code division multiple access (DS-CDMA) systems employing general pulse shaping (IEEE Trans. Commun., vol. 50, p. 656, 2002). The SIGA method uses moments up to the second order and is more accurate than the standard Gaussian approximation (SGA) (IEEE Trans. Commun., vol. 50, p. 656, 2002). In this paper, a new method that uses moments up to the fourth order is proposed for computing the BEP. The method is derived from a five-point Chebyshev interpolation formula and is inherently more accurate than the SIGA. Like the SIGA, the new method requires the evaluation of only closed-form expressions and the error function. The new method achieves higher accuracy with a modest increase in computational complexity. View full abstract»

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  • SLM and PTS peak-power reduction of OFDM signals without side information

    Publication Year: 2005 , Page(s): 2006 - 2013
    Cited by:  Papers (78)  |  Patents (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (224 KB) |  | HTML iconHTML  

    Selected mapping (SLM) and partial transmit sequence (PTS) are well-known techniques for peak-power reduction in orthogonal frequency-division multiplexing (OFDM). We derive a simplified maximum likelihood (ML) decoder for SLM and PTS that operates without side information. This decoder exploits the fact that the modulation symbols belong to a given constellation and that the multiple signals generated by the PTS or SLM processes are widely different in a Hamming distance sense. Pairwise error probability (PEP) analysis suggests how SLM and PTS vectors should be chosen. The decoder performs well over additive white Gaussian noise (AWGN) channels, fading channels, and amplifier nonlinearities. View full abstract»

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  • The impact of fading correlation on the error performance of MIMO systems over Rayleigh fading channels

    Publication Year: 2005 , Page(s): 2014 - 2019
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (216 KB) |  | HTML iconHTML  

    This paper analyzes the impact of receive fading correlation on the error performance of a multiple-input multiple-output (MIMO) system that employs a zero-forcing detection scheme over frequency-nonselective Rayleigh fading channels. Error rate expressions as a function of the eigenvalues of the fading correlation matrix and the number of transmit and receive antennas are derived. Numerical results indicate that MIMO systems are resistant to receive fading correlation. View full abstract»

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  • Performance of symbol-sampled receivers over unknown continuous-time Rayleigh channels

    Publication Year: 2005 , Page(s): 2020 - 2026
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (208 KB) |  | HTML iconHTML  

    The performance of symbol-sampled receivers is usually evaluated via Forney's finite impulse response (FIR) model for the equivalent channel [discrete-time transversal filter (DTTF)]. This model contains a matched filter, and, thus, requires prior knowledge of the continuous-time channel-impulse response. Therefore, if the channel is continuous and unknown, it is unrealistic to use the DTTF model, which leads to an upper bound on the system performance. Using an alternative model for the equivalent discrete-time channel, where the matched filter is replaced by a receive filter matched to the symbol waveform, we propose a framework to quantitatively investigate the performance loss from a theoretical perspective. The theoretical results are corroborated using a practical system. View full abstract»

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  • On low-complexity joint-detection techniques for TD-CDMA

    Publication Year: 2005 , Page(s): 2027 - 2034
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (272 KB) |  | HTML iconHTML  

    This paper is focused on low-complexity joint-detection (JD) algorithms, where the computational complexity is reduced using banks of discrete Fourier transformations. Mainly, we have developed a fast hybrid zero-forcing block decision-feedback equalizer (H-ZF-BDFE) combining the Fourier-based JD scheme (IEEE J. Sel. Areas Commun., vol. 19, p. 1461, 2001) with the fast decision-feedback structure (F-ZF-BDFE) IEEE J. Sel. Areas Commun., vol. 19, p. 245, 2001. In a Rayleigh frequency-selective fading channel, the new structure yields an improvement in Eb/N0 of almost 2 dB against the fast block linear equalizer (BLE) (IEEE J. Sel. Areas Commun., vol. 19, p. 1461, 2001) at a bit error rate (BER)=10-3. Moreover, it has the same performance as the F-ZF-BDFE, but the computational complexity for the signal processing is reduced by almost 50%. View full abstract»

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  • Space-time Chase decoding

    Publication Year: 2005 , Page(s): 2035 - 2039
    Cited by:  Papers (14)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (176 KB) |  | HTML iconHTML  

    Multiple-antenna wireless systems are of interest because they provide increased capacity over single-antenna systems. Several space-time signaling schemes have been proposed to make use of this increased capacity. Space-time techniques, such as space-time block coding and spatial multiplexing, can all be viewed as signaling with a multidimensional constellation. Because of the large capacity of multiple-input multiple-output (MIMO) channels, these multidimensional constellations often have large cardinalities. For this reason, it is impractical to perform optimal maximum-likelihood (ML) decoding for space-time systems, even for a moderate number of transmit antennas. In this paper, we propose a modified version of the classic Chase decoder for multiple-antenna systems. The decoder applies successive detection to yield an initial estimate of the transmitted bit sequence, constructs a list of candidate symbol vectors using this initial estimate, and then computes bit likelihood information over this list. Three algorithms are presented for constructing the candidate vector list. This decoder can be adjusted to have a fixed or variable complexity, while maintaining performance close to that of an ML decoder. View full abstract»

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  • The geometry of the capacity region for CDMA systems with general power constraints

    Publication Year: 2005 , Page(s): 2040 - 2044
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (128 KB) |  | HTML iconHTML  

    Access-control strategies and rational pricing in code-division multiple-access (CDMA) systems need exact knowledge of the available transmission capacity and its limiting boundaries. We use the term "capacity region" to specify the set of user-transmission demands that can be supported at the desired quality of service (QoS). In this paper, we investigate the geometrical properties of the capacity region for a fixed number of users in a CDMA radio network under general QoS characteristics and general power constraints. It turns out that, under very mild assumptions, the capacity region is convex, and has an appealing monotonicity property. As a side result, we develop an elementary theory for characterizing the existence of solutions to systems of linear equations with nonnegative elements, analogous to Perron-Frobenius' theory, but bypassing irreducibility. View full abstract»

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  • Space-frequency coding reduces the collision rate in FH-OFDMA

    Publication Year: 2005 , Page(s): 2045 - 2050
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (184 KB) |  | HTML iconHTML  

    A frequency-hopping (FH) space-frequency (SF)-coded clustered orthogonal frequency division multiple access (OFDMA) system is considered. It is shown that SF coding reduces the number of collisions in OFDMA with FH provided that the subcarrier clusters are formed randomly at each hopping instant. Analytical expressions for the collision rate, which is defined as the expected number of collisions per symbol, are derived. Bit error rate (BER) computations via simulations in a frequency-selective fading channel corroborate the theoretical findings for SF-coded FH-OFDMA. View full abstract»

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  • An evolutionary approach to designing complex spreading codes for DS-CDMA

    Publication Year: 2005 , Page(s): 2051 - 2056
    Cited by:  Papers (7)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (168 KB) |  | HTML iconHTML  

    This paper proposes a novel evolutionary approach to spreading code design in direct sequence code division multiple access (DS-CDMA). Specifically, a multiobjective evolutionary algorithm (EA) is used to generate complex spreading sequences that are optimized with respect to the average mean-square cross- and/or autocorrelation (CC and/or AC) properties. A theoretical model is developed in order to demonstrate the optimality of the generated codes. The proposed algorithm enables spreading code design with no constraints on the code length. Furthermore, it is possible to generate K≥N codes of length N with very little cost in correlation properties. This results in significant capacity enhancement in DS-CDMA systems. View full abstract»

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  • Generalized performance analysis of a delay diversity receiver in asynchronous CDMA channels

    Publication Year: 2005 , Page(s): 2057 - 2063
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (272 KB) |  | HTML iconHTML  

    In this letter, the performance for the delay diversity receiver is analyzed in asynchronous code division multiple access (CDMA) channels. The outage probability and the bit error probability of the delay diversity receiver are accurately derived and compared with those of the conventional diversity receiver. From the analytical and numerical results, it is confirmed that the delay diversity receiver achieves a remarkable diversity gain with reasonable cost and complexity in asynchronous CDMA channels. Specifically, for roughly the same hardware complexity, the delay diversity receiver achieves nearly twice the diversity order of the conventional receiver. View full abstract»

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  • A novel prefiltering technique for downlink transmissions in TDD MC-CDMA systems

    Publication Year: 2005 , Page(s): 2064 - 2069
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (168 KB) |  | HTML iconHTML  

    We discuss a prefiltering technique for interference mitigation in the downlink of a time division duplex (TDD) multicarrier code-division multiple access (MC-CDMA) system. The base station (BS) is equipped with multiple transmit antennas, and channel state information (CSI) is obtained at the transmitter side by exploiting the channel reciprocity between uplink and downlink transmissions. The prefiltering coefficients are designed so as to minimize a proper cost function that depends on the signal-to-interference-plus-noise ratios (SINRs) at the mobile terminals (MTs). The resulting scheme allows using a simple despreading receiver, thereby eliminating the need for channel estimation and equalization. Numerical results show the advantages of the proposed scheme over some existing solutions. View full abstract»

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  • Transmission of multiple description codes over wireless channels using channel balancing

    Publication Year: 2005 , Page(s): 2070 - 2075
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (192 KB) |  | HTML iconHTML  

    Multiple description coding (MDC) is an error-resilient scheme for transmission over packet erasure channels. In this paper, we propose a channel-balancing scheme for the transmission of an MDC source over time-varying channels, such as wireless links. We consider a system in which there are more subchannels than the number of descriptions and the transmission rate is adapted to the channel variation. The proposed balancing scheme is based on the polynomial-time set-partitioning algorithm using the differencing method. It is shown that the proposed scheme results in a low-delay and high-throughput transmission, which is desirable for real-time multimedia content delivery over wireless channels. View full abstract»

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  • Pilot-symbol-assisted LDPC coded BICM over correlated Rayleigh fading channels

    Publication Year: 2005 , Page(s): 2076 - 2082
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB) |  | HTML iconHTML  

    Pilot-symbol-assisted low-density parity-check (LDPC)-coded bit-interleaved coded modulation (BICM) is analyzed using the density evolution (DE) and the extrinsic information-transfer (EXIT) chart for correlated Rayleigh fading channels. The key parameter (the power correlation coefficient) is identified, and the threshold degradation is quantified. The optimal tradeoff of energy allocation between pilots and coded symbols is found to be sensitive to the normalized Doppler spread of the channel, the interpolation filter, the modulation scheme, and the pilot selection. In addition, a simple upper bound on the performance of any receiver that performs joint iterative decoding and channel estimation is derived. Extension to irregular code design is also discussed. View full abstract»

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  • Optimum pilot pattern for channel estimation in OFDM systems

    Publication Year: 2005 , Page(s): 2083 - 2088
    Cited by:  Papers (39)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB) |  | HTML iconHTML  

    The performance of channel estimation in orthogonal frequency division multiplexing (OFDM) systems significantly depends on the pilot signal, which is usually scattered in time and frequency domains. For a given pilot density, the authors optimally design the pilot pattern so as to minimize the mean squared error (MSE) of the channel estimate with the use of a general interpolator. The analytic results are verified by computer simulation. View full abstract»

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  • Quasi-orthogonal STBC with minimum decoding complexity

    Publication Year: 2005 , Page(s): 2089 - 2094
    Cited by:  Papers (119)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (280 KB) |  | HTML iconHTML  

    In this paper, we consider a quasi-orthogonal (QO) space-time block code (STBC) with minimum decoding complexity (MDC-QO-STBC). We formulate its algebraic structure and propose a systematic method for its construction. We show that a maximum-likelihood (ML) decoder for this MDC-QO-STBC, for any number of transmit antennas, only requires the joint detection of two real symbols. Assuming the use of a square or rectangular quadratic-amplitude modulation (QAM) or multiple phase-shift keying (MPSK) modulation for this MDC-QO-STBC, we also obtain the optimum constellation rotation angle, in order to achieve full diversity and optimum coding gain. We show that the maximum achievable code rate of these MDC-QO-STBC is 1 for three and four antennas and 3/4 for five to eight antennas. We also show that the proposed MDC-QO-STBC has several desirable properties, such as a more even power distribution among antennas and better scalability in adjusting the number of transmit antennas, compared with the coordinate interleaved orthogonal design (CIOD) and asymmetric CIOD (ACIOD) codes. For the case of an odd number of transmit antennas, MDC-QO-STBC also has better decoding performance than CIOD. View full abstract»

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  • Dynamic channel partitioning with flexible channel combination for TDMA-based cellular systems

    Publication Year: 2005 , Page(s): 2095 - 2099
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (176 KB) |  | HTML iconHTML  

    In this paper, we propose flexible dynamic channel partitioning (FDCP) with a flexible channel-combination scheme to support multiple services. CP is based on the idea that different services may require different signal-to-interference ratios (SIRs), and thus, different reuse factors. In FDCP, different services are allocated to the channels depending on the reuse factors they require. FDCP tries to minimize the effect of the assigned channels on the channel availability to the interfering cells and to reduce the overall reuse distances of the systems. View full abstract»

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  • ICI cancellation for OFDM communication systems in time-varying multipath fading channels

    Publication Year: 2005 , Page(s): 2100 - 2110
    Cited by:  Papers (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (280 KB) |  | HTML iconHTML  

    In orthogonal frequency division multiplexing (OFDM) systems, time-varying multipath fading leads to the loss of subcarrier orthogonality and the occurrence of intercarrier interference (ICI). In this study, an efficient ICI suppression with less noise enhancement for multicarrier equalization is presented by using a parallel canceling scheme via frequency-domain equalization techniques, with the assumption that the channel impulse response (CIR) varies linearly during a block period. In order to avoid performance deterioration due to unreliable initial estimations in the parallel cancellation scheme, a cost function with proper weighting factor is introduced to improve the performance of the proposed equalizer. The proposed equalizer consists of a set of prefilters and a set of ICI cancellation filters, with two stages to perform different functions to achieve minimum mean square error (MMSE) equalization. The prefilters compensate for the multiplicative distortion at the first stage, and the ICI cancellation filters remove the effects of ICI by a parallel cancellation scheme at the second stage. Finally, the performance of the proposed equalizer is analyzed and compared with that of other equalizers, indicating significant performance improvement. View full abstract»

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The IEEE Transactions on Wireless Communications publishes high-quality manuscripts on advances in the state-of-the-art of wireless communications.

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Editor-in-Chief
Jeff Andrews
Cullen Trust for Higher Education Endowed Professor of Engineering