The Experts below are selected from a list of 171 Experts worldwide ranked by ideXlab platform

G.f. Boudreaux-bartels - One of the best experts on this subject based on the ideXlab platform.

  • Wideband Weyl symbols for Dispersive Time-varying processing of systems and random signals
    IEEE Transactions on Signal Processing, 2002
    Co-Authors: Byeong-gwan Iem, Antonia Papandreou-suppappola, G.f. Boudreaux-bartels
    Abstract:

    We extend the narrowband Weyl symbol (WS) and the wideband P/sub O/-Weyl symbol (PoWS) for Dispersive Time-frequency (TF) analysis of nonstationary random processes and Time-varying systems. We obtain the new TF symbols using unitary transformations on the WS and the P/sub O/WS. For example, whereas the WS is matched to systems with constant or linear TF characteristics, the new symbols are better matched to systems with Dispersive (nonlinear) TF structures. This results from matching the geometry of the unitary transformation to the specific TF characteristics of a system. We also develop new classes of smoothed Weyl symbols that are covariant to TF shifts or Time shift and scaling system transformations. These classes of symbols are also extended via unitary warpings to obtain classes of TF symbols covariant to Dispersive shifts. We provide examples of the new symbols and symbol classes, and we list some of their desirable properties. Using simulation examples, we demonstrate the advantage of using TF symbols that are matched to the changes in the TF characteristics of a system or random process. We also provide new TF formulations for matched detection applications.

  • The power classes-quadratic Time-frequency representations with scale covariance and Dispersive Time-shift covariance
    IEEE Transactions on Signal Processing, 1999
    Co-Authors: Franz Hlawatsch, Antonia Papandreou-suppappola, G.f. Boudreaux-bartels
    Abstract:

    We consider scale-covariant quadratic Time-frequency representations (QTFRs) specifically suited for the analysis of signals passing through Dispersive systems. These QTFRs satisfy a scale covariance property that is equal to the scale covariance property satisfied by the continuous wavelet transform and a covariance property with respect to generalized Time shifts. We derive an existence/representation theorem that shows the exceptional role of Time shifts corresponding to group delay functions that are proportional to powers of frequency. This motivates the definition of the power classes (PCs) of QTFR's. The PCs contain the affine QTFR class as a special case, and thus, they extend the affine class. We show that the PCs can be defined axiomatically by the two covariance properties they satisfy, or they can be obtained from the affine class through a warping transformation. We discuss signal transformations related to the PCs, the description of the PCs by kernel functions, desirable properties and kernel constraints, and specific PC members. Furthermore, we consider three important PC subclasses, one of which contains the Bertrand (1992) P/sub k/ distributions. Finally, we comment on the discrete-Time implementation of PC QTFRs, and we present simulation results that demonstrate the potential advantage of PC QTFRs.

  • A wideband Time-frequency Weyl symbol and its generalization
    Proceedings of the IEEE-SP International Symposium on Time-Frequency and Time-Scale Analysis (Cat. No.98TH8380), 1
    Co-Authors: B.-g. Iem, A. Papandreou-suppappola, G.f. Boudreaux-bartels
    Abstract:

    We extend the work of Shenoy and Parks (1994) on the wideband Weyl correspondence. We define a wideband Weyl symbol (P/sub 0/WS) in the Time-frequency plane based on the Bertrand (1988) P/sub 0/-distribution, and we study its properties, examples and possible applications. Using warping relations, we generalize the P/sub 0/WS and the wideband spreading function (WSF) to analyze systems producing Dispersive Time shifts. We provide properties and special cases (e.g. power and exponential) to demonstrate the importance of our generalization. The new generalized WSF provides a new interpretation of a system output as a weighted superposition of Dispersive Time-shifted versions of the signal. We provide application examples in analysis and detection to demonstrate the advantages of our new results for linear systems with group delay characteristics matched to the specific warping used.

Antonia Papandreou-suppappola - One of the best experts on this subject based on the ideXlab platform.

  • Wideband Weyl symbols for Dispersive Time-varying processing of systems and random signals
    IEEE Transactions on Signal Processing, 2002
    Co-Authors: Byeong-gwan Iem, Antonia Papandreou-suppappola, G.f. Boudreaux-bartels
    Abstract:

    We extend the narrowband Weyl symbol (WS) and the wideband P/sub O/-Weyl symbol (PoWS) for Dispersive Time-frequency (TF) analysis of nonstationary random processes and Time-varying systems. We obtain the new TF symbols using unitary transformations on the WS and the P/sub O/WS. For example, whereas the WS is matched to systems with constant or linear TF characteristics, the new symbols are better matched to systems with Dispersive (nonlinear) TF structures. This results from matching the geometry of the unitary transformation to the specific TF characteristics of a system. We also develop new classes of smoothed Weyl symbols that are covariant to TF shifts or Time shift and scaling system transformations. These classes of symbols are also extended via unitary warpings to obtain classes of TF symbols covariant to Dispersive shifts. We provide examples of the new symbols and symbol classes, and we list some of their desirable properties. Using simulation examples, we demonstrate the advantage of using TF symbols that are matched to the changes in the TF characteristics of a system or random process. We also provide new TF formulations for matched detection applications.

  • The power classes-quadratic Time-frequency representations with scale covariance and Dispersive Time-shift covariance
    IEEE Transactions on Signal Processing, 1999
    Co-Authors: Franz Hlawatsch, Antonia Papandreou-suppappola, G.f. Boudreaux-bartels
    Abstract:

    We consider scale-covariant quadratic Time-frequency representations (QTFRs) specifically suited for the analysis of signals passing through Dispersive systems. These QTFRs satisfy a scale covariance property that is equal to the scale covariance property satisfied by the continuous wavelet transform and a covariance property with respect to generalized Time shifts. We derive an existence/representation theorem that shows the exceptional role of Time shifts corresponding to group delay functions that are proportional to powers of frequency. This motivates the definition of the power classes (PCs) of QTFR's. The PCs contain the affine QTFR class as a special case, and thus, they extend the affine class. We show that the PCs can be defined axiomatically by the two covariance properties they satisfy, or they can be obtained from the affine class through a warping transformation. We discuss signal transformations related to the PCs, the description of the PCs by kernel functions, desirable properties and kernel constraints, and specific PC members. Furthermore, we consider three important PC subclasses, one of which contains the Bertrand (1992) P/sub k/ distributions. Finally, we comment on the discrete-Time implementation of PC QTFRs, and we present simulation results that demonstrate the potential advantage of PC QTFRs.

  • ICASSP (3) - Discrete Time-Frequency Models of Generalized Dispersive Systems
    2006 IEEE International Conference on Acoustics Speed and Signal Processing Proceedings, 1
    Co-Authors: Ye Jiang, Antonia Papandreou-suppappola
    Abstract:

    Ih this paper, we propose a discrete characterization of Dispersive Time-varying systems. Based on a unitary warping relation with the narrowband system model, we formulate a representation that decomposes the system output as a weighted superposition of sampled signal transformations that reflect the Dispersive system characteristics. Such discrete representations can be important in designing wave-forms for transmission through Dispersive systems with improved processing performance. We demonstrate the usefulness of our proposed model by applying it to a shallow water acoustic environment characterized by nonlinear frequency dispersions

Lawrence Carin - One of the best experts on this subject based on the ideXlab platform.

  • Wave-oriented signal processing of Dispersive Time-domain scattering data
    IEEE Transactions on Antennas and Propagation, 1997
    Co-Authors: Lawrence Carin, Leopold B. Felsen, D. Kralj, Won Cheol Lee, S. Unnikrishna Pillai
    Abstract:

    Phase-space data processing is receiving increased attention because or its potential for furnishing new discriminants relating to classification and identification of targets and other scattering environments. Primary emphasis has been on Time-frequency processing because of its impact on transient, especially wideband, short-pulse excitations. Here, we investigate the windowed Fourier transform, the wavelet transform, and model based superresolution algorithms within the context of a fully quantified and calibrated test problem investigated by us previously: two-dimensional (2-D) short-pulse plane wave scattering by a finite periodic array of perfectly conducting coplanar flat strips. Because the forward problem has been fully calibrated and parametrized, some quantitative measures can be assigned with respect to the tradeoffs of these Time-frequency algorithms, yielding tentative performance assessments of the tested processing algorithms.

  • Dispersive modes in the Time domain: analysis and Time-frequency representation
    IEEE Microwave and Guided Wave Letters, 1994
    Co-Authors: Lawrence Carin, Leopold B. Felsen, D. Kralj, S.u. Pillai, Won Cheol Lee
    Abstract:

    Four algorithms for Time-frequency (TF) distributions are considered for the processing and interpretation of Dispersive Time-domain (TD) data: the short-Time Fourier transform, frequency and Time-domain wavelets, and a new ARMA-based representation. The TF resolutions of the various distributions are discussed and compared with reference to results for the scattered fields from a chirped finite grating excited by a pulsed plane wave. The processing in the TF phase space extracts TD phenomenology, in particular the instantaneous dispersion relation /spl minus/ with its associated Time-dependent frequencies-descriptive of the local TD Floquet modes on the chirped truncated grating. >

Johan Paul Marie Gerard Linnartz - One of the best experts on this subject based on the ideXlab platform.

  • Robust OFDM receivers for Dispersive Time-varying channels: equalization and channel acquisition
    IEEE Transactions on Communications, 2004
    Co-Authors: A. Gorokhov, Johan Paul Marie Gerard Linnartz
    Abstract:

    In orthogonal frequency-division multiplexing, Time variations of a multipath channel lead to a loss of orthogonality between the subcarriers, and thereby limit the achievable throughput. This paper proposes a general framework for a controlled removal of intercarrier interference (ICI) and channel acquisition. The core idea behind our method is to use a finite power series expansion for the Time-varying frequency response, along with the known statistical properties of mobile radio channels. Channel acquisition and ICI removal are accomplished in the frequency domain and allow for any desired tradeoff between the residual ICI level, the required training for channel acquisition, and processing complexity. The proposed approach enables a high spectral efficiency (64-quadrature amplitude modulation mode) of digital video broadcasting-terrestrial in highly mobile environments.

  • ICC - Robust OFDM receivers for Dispersive Time varying channels: equalisation and channel acquisition
    2002 IEEE International Conference on Communications. Conference Proceedings. ICC 2002 (Cat. No.02CH37333), 1
    Co-Authors: A. Gorokhov, Johan Paul Marie Gerard Linnartz
    Abstract:

    In orthogonal frequency division multiplexing (OFDM), Time variations of a fading multipath environment lead to a loss of orthogonality between the subcarriers and thereby limit the achievable throughput. This paper suggests a general framework for a controlled removal of intercarrier interference (ICI) and channel acquisition. The core idea behind our method is to use a finite Taylor expansion for the Time-varying frequency response along with the known statistical properties of mobile radio channels. Channel acquisition and ICI removal are accomplished in the frequency domain and allow for any desired tradeoff between the residual ICI level, the required training for channel acquisition and processing complexity.

Norman C. Beaulieu - One of the best experts on this subject based on the ideXlab platform.

  • Maximum Likelihood Based Channel Estimation for Macrocellular OFDM Uplinks in Dispersive Time-Varying Channels
    IEEE Transactions on Wireless Communications, 2011
    Co-Authors: Xuegui Song, Julian Cheng, Norman C. Beaulieu
    Abstract:

    Coherent modulation is more effective than differential modulation for orthogonal frequency division multiplexing (OFDM) systems requiring high data rate and spectral efficiency. Channel estimation is therefore an integral part of the receiver design. Two iterative maximum likelihood (ML) based channel estimation algorithms are proposed for OFDM uplinks in Dispersive Time-varying channels. The uplink multipath fading channel is modeled such that the channel state can be determined by estimating the unknown channel parameters. A second-order Taylor series expansion is adopted to simplify the channel estimation problem. Based on the system model, an iterative ML-based algorithm is first proposed to estimate the discrete-Time channel parameters. The mean square error performance of the proposed algorithm is analyzed using a small perturbation technique. Based on a convergence rate analysis, an improved iterative ML channel estimation algorithm is presented using a successive overrelaxation method. Numerical experiments are performed to confirm the theoretical analyses and show the improvement in convergence rate of the improved algorithm.

  • A channel estimation technique for OFDM systems in Dispersive Time-varying channels
    2009 11th Canadian Workshop on Information Theory, 2009
    Co-Authors: Xuegui Song, Julian Cheng, Norman C. Beaulieu
    Abstract:

    Coherent modulation is more appropriate than differential modulation for orthogonal frequency division multiplexing (OFDM) systems requiring high data rate and spectral efficiency. Channel estimation is therefore required as an integral part of the receiver design. An iterative maximum likelihood-based channel estimation algorithm for an OFDM system in Dispersive Time-varying channels is proposed. The multipath fading channel is modeled such that the channel state can be determined by estimating the unknown channel parameters. A second-order Taylor series expansion is adopted to simplify the channel estimation problem. The performance of the proposed algorithm is analyzed and numerical experiments are performed to confirm the theoretical analysis.

  • WCNC - A Convergence Study of Iterative Channel Estimation Algorithms for OFDM Systems in Dispersive Time-Varying Channels
    2009 IEEE Wireless Communications and Networking Conference, 2009
    Co-Authors: Xuegui Song, Julian Cheng, Norman C. Beaulieu
    Abstract:

    Maximum-likelihood based channel estimation is considered for orthogonal frequency division multiplexing systems in Dispersive Time-varying channels. A successive overrelaxation approach is adopted to analyze the convergence rate of an iterative channel estimation algorithm. Based on the analysis, an improved fast converging iterative channel estimation algorithm is proposed. Numerical tests are performed to show the improvement of the proposed algorithm over a recently proposed channel estimation algorithm.