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Marc Moonen - One of the best experts on this subject based on the ideXlab platform.

  • Estimation and direct equalization of doubly Selective Channels
    EURASIP Journal on Advances in Signal Processing, 2006
    Co-Authors: Imad Barhumi, Geert Leus, Marc Moonen
    Abstract:

    We propose Channel estimation and direct equalization techniques for transmission over doubly Selective Channels. The doubly Selective Channel is approximated using the basis expansion model (BEM). Linear and decision feedback equalizers implemented by time-varying finite impulse response (FIR) filtersmay then be used to equalize the doubly Selective Channel, where the time-varying FIR filters are designed according to the BEM. In this sense, the equalizer BEM coefficients are obtained either based on Channel estimation or directly. The proposed Channel estimation and direct equalization techniques range from pilot-symbol-assisted-modulation- (PSAM-) based techniques to blind and semiblind techniques. In PSAM techniques, pilot symbols are utilized to estimate the Channel or directly obtain the equalizer coefficients. The training overhead can be completely eliminated by using blind techniques or reduced by combining training-based techniques with blind techniques resulting in semiblind techniques. Numerical results are conducted to verify the different proposed Channel estimation and direct equalization techniques.

  • Time-varying FIR equalization for doubly Selective Channels
    IEEE Transactions on Wireless Communications, 2005
    Co-Authors: Imad Barhumi, Geert Leus, Marc Moonen
    Abstract:

    We propose a time-varying (TV) finite impulse response (FIR) equalizer for doubly Selective (time- and frequency-Selective) Channels. We use a basis expansion model (BEM) to approximate the doubly Selective Channel and to design the TV FIR equalizer. This allows us to turn a complicated equalization problem into an equivalent simpler equalization problem, containing only the BEM coefficients of both the doubly Selective Channel and the TV FIR equalizer. The minimum mean-square error (MMSE) as well as the zero-forcing (ZF) solutions are considered. Comparisons with the block linear equalizer (BLE) are made. The TV FIR equalization we propose here unifies and extends many previously proposed serial equalization approaches. In contrast to the BLE, the proposed TV FIR equalizer allows a flexible tradeoff between complexity and performance. Moreover, through computer simulations, we show that the performance of the proposed MMSE TV FIR equalizer comes close to the performance of the ZF and MMSE BLE, at a point where the design as well as the implementation complexity are much lower.

  • ICC - Direct semi-blind design of serial linear equalizers for doubly-Selective Channels
    2004 IEEE International Conference on Communications (IEEE Cat. No.04CH37577), 2004
    Co-Authors: Geert Leus, Imad Barhumi, O. Rousseaux, Marc Moonen
    Abstract:

    Recently, serial linear equalizers (SLEs) and serial decision feedback equalizers (SDFEs) have been proposed to mitigate the doubly-Selective Channel effects. To design the SLE/SDFE and to model the doubly-Selective Channel, a so-called finite impulse response basis expansion model (FIR-BEM) is used. Initially, the FIR-BEM coefficients of the SLE/SDFE were designed based on the exact knowledge of the FIR-BEM coefficients of the doubly-Selective Channel. In practice, we can use a direct SLE/SDFE design procedure, which avoids an intermediate Channel estimation step. In this paper, we describe this idea for the SLE and focus on direct semi-blind design of the FIR- BEM coefficients of the SLE. Simulation results demonstrate the validity of the proposed approach.

  • Time-domain and frequency-domain per-tone equalization for OFDM over doubly Selective Channels
    Signal Processing, 2004
    Co-Authors: Imad Barhumi, Geert Leus, Marc Moonen
    Abstract:

    In this paper, we propose new time- and frequency-domain per-tone equalization techniques for orthogonal frequency division multiplexing (OFDM) transmission over time- and frequency-Selective Channels. We present one mixed time- and frequency-domain equalizer (MTFEQ) and one frequency-domain per-tone equalizer. The MTFEQ consists of a one-tap time-varying (TV) time-domain equalizer (TEQ), which converts the doubly Selective Channel into a purely frequency-Selective Channel, followed by a one-tap frequency-domain equalizer (FEQ), which then equalizes the resulting frequency-Selective Channel in the frequency-domain. The frequency-domain per-tone equalizer (PTEQ) is then obtained by transferring the TEQ operation to the frequency-domain. While the one-tap TEQ of the MTFEQ optimizes the performance on all subcarriers in a joint fashion, the PTEQ optimizes the performance on each subcarrier separately. This results into a significant performance improvement of the PTEQ over the MTFEQ, at the cost of a slight increase in complexity. Through computer simulations we show that the MTFEQ suffers from an early and high error floor, while the PTEQ outperforms the MMSE equalizer for OFDM over purely frequency-Selective Channels, it can approach the performance of the block MMSE equalizer. An important feature of the proposed techniques is that no bandwidth expansion or redundancy insertion is required except for the cyclic prefix.

  • ISSPA (1) - Time-varying multiuser detection for DS-CDMA in doubly-Selective Channels
    Seventh International Symposium on Signal Processing and Its Applications 2003. Proceedings., 2003
    Co-Authors: Geert Leus, Marc Moonen
    Abstract:

    The problem of multiuser detection for DS-CDMA in doubly-Selective (timeand frequency-Selective) Channels is considered, and a time-varying multiuser detector (TV-MUD) to solve this problem is proposed. Using a basis expansion model (BEM) to model the doubly-Selective Channel and the TV-MUD, we derive a closed-form expression for the BEM coefficients of the TV-MUD as a function of the BEM coefficients of the doubly-Selective Channel. The criterion we use is the symbol mean-square error.

Imad Barhumi - One of the best experts on this subject based on the ideXlab platform.

  • Estimation and direct equalization of doubly Selective Channels
    EURASIP Journal on Advances in Signal Processing, 2006
    Co-Authors: Imad Barhumi, Geert Leus, Marc Moonen
    Abstract:

    We propose Channel estimation and direct equalization techniques for transmission over doubly Selective Channels. The doubly Selective Channel is approximated using the basis expansion model (BEM). Linear and decision feedback equalizers implemented by time-varying finite impulse response (FIR) filtersmay then be used to equalize the doubly Selective Channel, where the time-varying FIR filters are designed according to the BEM. In this sense, the equalizer BEM coefficients are obtained either based on Channel estimation or directly. The proposed Channel estimation and direct equalization techniques range from pilot-symbol-assisted-modulation- (PSAM-) based techniques to blind and semiblind techniques. In PSAM techniques, pilot symbols are utilized to estimate the Channel or directly obtain the equalizer coefficients. The training overhead can be completely eliminated by using blind techniques or reduced by combining training-based techniques with blind techniques resulting in semiblind techniques. Numerical results are conducted to verify the different proposed Channel estimation and direct equalization techniques.

  • Time-varying FIR equalization for doubly Selective Channels
    IEEE Transactions on Wireless Communications, 2005
    Co-Authors: Imad Barhumi, Geert Leus, Marc Moonen
    Abstract:

    We propose a time-varying (TV) finite impulse response (FIR) equalizer for doubly Selective (time- and frequency-Selective) Channels. We use a basis expansion model (BEM) to approximate the doubly Selective Channel and to design the TV FIR equalizer. This allows us to turn a complicated equalization problem into an equivalent simpler equalization problem, containing only the BEM coefficients of both the doubly Selective Channel and the TV FIR equalizer. The minimum mean-square error (MMSE) as well as the zero-forcing (ZF) solutions are considered. Comparisons with the block linear equalizer (BLE) are made. The TV FIR equalization we propose here unifies and extends many previously proposed serial equalization approaches. In contrast to the BLE, the proposed TV FIR equalizer allows a flexible tradeoff between complexity and performance. Moreover, through computer simulations, we show that the performance of the proposed MMSE TV FIR equalizer comes close to the performance of the ZF and MMSE BLE, at a point where the design as well as the implementation complexity are much lower.

  • ICC - Direct semi-blind design of serial linear equalizers for doubly-Selective Channels
    2004 IEEE International Conference on Communications (IEEE Cat. No.04CH37577), 2004
    Co-Authors: Geert Leus, Imad Barhumi, O. Rousseaux, Marc Moonen
    Abstract:

    Recently, serial linear equalizers (SLEs) and serial decision feedback equalizers (SDFEs) have been proposed to mitigate the doubly-Selective Channel effects. To design the SLE/SDFE and to model the doubly-Selective Channel, a so-called finite impulse response basis expansion model (FIR-BEM) is used. Initially, the FIR-BEM coefficients of the SLE/SDFE were designed based on the exact knowledge of the FIR-BEM coefficients of the doubly-Selective Channel. In practice, we can use a direct SLE/SDFE design procedure, which avoids an intermediate Channel estimation step. In this paper, we describe this idea for the SLE and focus on direct semi-blind design of the FIR- BEM coefficients of the SLE. Simulation results demonstrate the validity of the proposed approach.

  • Time-domain and frequency-domain per-tone equalization for OFDM over doubly Selective Channels
    Signal Processing, 2004
    Co-Authors: Imad Barhumi, Geert Leus, Marc Moonen
    Abstract:

    In this paper, we propose new time- and frequency-domain per-tone equalization techniques for orthogonal frequency division multiplexing (OFDM) transmission over time- and frequency-Selective Channels. We present one mixed time- and frequency-domain equalizer (MTFEQ) and one frequency-domain per-tone equalizer. The MTFEQ consists of a one-tap time-varying (TV) time-domain equalizer (TEQ), which converts the doubly Selective Channel into a purely frequency-Selective Channel, followed by a one-tap frequency-domain equalizer (FEQ), which then equalizes the resulting frequency-Selective Channel in the frequency-domain. The frequency-domain per-tone equalizer (PTEQ) is then obtained by transferring the TEQ operation to the frequency-domain. While the one-tap TEQ of the MTFEQ optimizes the performance on all subcarriers in a joint fashion, the PTEQ optimizes the performance on each subcarrier separately. This results into a significant performance improvement of the PTEQ over the MTFEQ, at the cost of a slight increase in complexity. Through computer simulations we show that the MTFEQ suffers from an early and high error floor, while the PTEQ outperforms the MMSE equalizer for OFDM over purely frequency-Selective Channels, it can approach the performance of the block MMSE equalizer. An important feature of the proposed techniques is that no bandwidth expansion or redundancy insertion is required except for the cyclic prefix.

  • ICASSP (3) - Time-domain Channel shortening and equalization of OFDM over doubly-Selective Channels
    2004 IEEE International Conference on Acoustics Speech and Signal Processing, 1
    Co-Authors: Imad Barhumi, Geert Leus, Marc Moonen
    Abstract:

    We discuss time-domain equalization of OFDM over doubly-Selective Channels. We consider the most general case, where the Channel delay spread is larger than the cyclic prefix (CP), which results in inter-block interference (IBI). IBI, in conjunction with the Doppler effect, destroys the orthogonality between subcarriers and, hence, results in intercarrier interference (ICI). The time-domain equalizer (TEQ) is assumed to be a time-varying finite impulse response (TV FIR). The purpose of the TEQ is to convert the doubly-Selective Channel into a purely frequency-Selective Channel whose delay spread fits within the CP. In other words, the purpose of the TEQ is to restore orthogonality between subcarriers in the OFDM system.

Geert Leus - One of the best experts on this subject based on the ideXlab platform.

  • Estimation and direct equalization of doubly Selective Channels
    EURASIP Journal on Advances in Signal Processing, 2006
    Co-Authors: Imad Barhumi, Geert Leus, Marc Moonen
    Abstract:

    We propose Channel estimation and direct equalization techniques for transmission over doubly Selective Channels. The doubly Selective Channel is approximated using the basis expansion model (BEM). Linear and decision feedback equalizers implemented by time-varying finite impulse response (FIR) filtersmay then be used to equalize the doubly Selective Channel, where the time-varying FIR filters are designed according to the BEM. In this sense, the equalizer BEM coefficients are obtained either based on Channel estimation or directly. The proposed Channel estimation and direct equalization techniques range from pilot-symbol-assisted-modulation- (PSAM-) based techniques to blind and semiblind techniques. In PSAM techniques, pilot symbols are utilized to estimate the Channel or directly obtain the equalizer coefficients. The training overhead can be completely eliminated by using blind techniques or reduced by combining training-based techniques with blind techniques resulting in semiblind techniques. Numerical results are conducted to verify the different proposed Channel estimation and direct equalization techniques.

  • Time-varying FIR equalization for doubly Selective Channels
    IEEE Transactions on Wireless Communications, 2005
    Co-Authors: Imad Barhumi, Geert Leus, Marc Moonen
    Abstract:

    We propose a time-varying (TV) finite impulse response (FIR) equalizer for doubly Selective (time- and frequency-Selective) Channels. We use a basis expansion model (BEM) to approximate the doubly Selective Channel and to design the TV FIR equalizer. This allows us to turn a complicated equalization problem into an equivalent simpler equalization problem, containing only the BEM coefficients of both the doubly Selective Channel and the TV FIR equalizer. The minimum mean-square error (MMSE) as well as the zero-forcing (ZF) solutions are considered. Comparisons with the block linear equalizer (BLE) are made. The TV FIR equalization we propose here unifies and extends many previously proposed serial equalization approaches. In contrast to the BLE, the proposed TV FIR equalizer allows a flexible tradeoff between complexity and performance. Moreover, through computer simulations, we show that the performance of the proposed MMSE TV FIR equalizer comes close to the performance of the ZF and MMSE BLE, at a point where the design as well as the implementation complexity are much lower.

  • ICC - Direct semi-blind design of serial linear equalizers for doubly-Selective Channels
    2004 IEEE International Conference on Communications (IEEE Cat. No.04CH37577), 2004
    Co-Authors: Geert Leus, Imad Barhumi, O. Rousseaux, Marc Moonen
    Abstract:

    Recently, serial linear equalizers (SLEs) and serial decision feedback equalizers (SDFEs) have been proposed to mitigate the doubly-Selective Channel effects. To design the SLE/SDFE and to model the doubly-Selective Channel, a so-called finite impulse response basis expansion model (FIR-BEM) is used. Initially, the FIR-BEM coefficients of the SLE/SDFE were designed based on the exact knowledge of the FIR-BEM coefficients of the doubly-Selective Channel. In practice, we can use a direct SLE/SDFE design procedure, which avoids an intermediate Channel estimation step. In this paper, we describe this idea for the SLE and focus on direct semi-blind design of the FIR- BEM coefficients of the SLE. Simulation results demonstrate the validity of the proposed approach.

  • Time-domain and frequency-domain per-tone equalization for OFDM over doubly Selective Channels
    Signal Processing, 2004
    Co-Authors: Imad Barhumi, Geert Leus, Marc Moonen
    Abstract:

    In this paper, we propose new time- and frequency-domain per-tone equalization techniques for orthogonal frequency division multiplexing (OFDM) transmission over time- and frequency-Selective Channels. We present one mixed time- and frequency-domain equalizer (MTFEQ) and one frequency-domain per-tone equalizer. The MTFEQ consists of a one-tap time-varying (TV) time-domain equalizer (TEQ), which converts the doubly Selective Channel into a purely frequency-Selective Channel, followed by a one-tap frequency-domain equalizer (FEQ), which then equalizes the resulting frequency-Selective Channel in the frequency-domain. The frequency-domain per-tone equalizer (PTEQ) is then obtained by transferring the TEQ operation to the frequency-domain. While the one-tap TEQ of the MTFEQ optimizes the performance on all subcarriers in a joint fashion, the PTEQ optimizes the performance on each subcarrier separately. This results into a significant performance improvement of the PTEQ over the MTFEQ, at the cost of a slight increase in complexity. Through computer simulations we show that the MTFEQ suffers from an early and high error floor, while the PTEQ outperforms the MMSE equalizer for OFDM over purely frequency-Selective Channels, it can approach the performance of the block MMSE equalizer. An important feature of the proposed techniques is that no bandwidth expansion or redundancy insertion is required except for the cyclic prefix.

  • ISSPA (1) - Time-varying multiuser detection for DS-CDMA in doubly-Selective Channels
    Seventh International Symposium on Signal Processing and Its Applications 2003. Proceedings., 2003
    Co-Authors: Geert Leus, Marc Moonen
    Abstract:

    The problem of multiuser detection for DS-CDMA in doubly-Selective (timeand frequency-Selective) Channels is considered, and a time-varying multiuser detector (TV-MUD) to solve this problem is proposed. Using a basis expansion model (BEM) to model the doubly-Selective Channel and the TV-MUD, we derive a closed-form expression for the BEM coefficients of the TV-MUD as a function of the BEM coefficients of the doubly-Selective Channel. The criterion we use is the symbol mean-square error.

Vito De Pinto - One of the best experts on this subject based on the ideXlab platform.

  • the voltage dependent anion Selective Channel 1 vdac1 topography in the mitochondrial outer membrane as detected in intact cell
    PLOS ONE, 2013
    Co-Authors: Marianna Flora Tomasello, Angela Messina, Simona Reina, Francesca Guarino, Vito De Pinto
    Abstract:

    Voltage-Dependent Anion Selective Channel maintains the permeability of the outer mitochondrial membrane and is relevant in bioenergetic metabolism and apoptosis. The structure of the protein was shown to be a β-barrel formed by 19 strands. The topology or sideness of the pore has been predicted with various approaches but a general consensus was never reached. This is an important issue since VDAC is considered receptor of Hexokinase and Bcl-2. We fused at VDAC1 C-terminus two tags separated by a caspase cleavage site. Activation in cellulo of caspases was used to eventually separate the two reporters. This experiment did not require the isolation of mitochondria and limited the possibility of outer membrane rupture due to similar procedures. Our results show that the C-terminus end of VDAC faces the mitochondrial inter-membrane space.

  • voltage dependent anion Selective Channel vdac in the plasma membrane
    FEBS Letters, 2010
    Co-Authors: Vito De Pinto, Angela Messina, Darius J R Lane, Alfons Lawen
    Abstract:

    Voltage-dependent anion Channels (VDACs) have originally been characterized as mitochondrial porins. Starting in the late 1980s, however, evidence began to accumulate that VDACs can also be expressed in plasma membranes. In this review, we briefly revisit the historical milestones in the discovery of plasma membrane-bound VDAC, and we critically analyze the evidence for VDAC plasma membrane localization obtained from various purification strategies and recently from plasma membrane proteomics studies. We discuss the possible biological function and relevance of VDAC in the plasma membrane and finally discuss a hypothetical model of how VDAC may be targeted to the plasma membrane.

  • voltage dependent anion Selective Channel 1 vdac1 a mitochondrial protein rediscovered as a novel enzyme in the plasma membrane
    The International Journal of Biochemistry & Cell Biology, 2005
    Co-Authors: Alfons Lawen, Angela Messina, Jennifer D Ly, Darius J R Lane, Kristof Zarschler, Vito De Pinto
    Abstract:

    Abstract The eukaryotic porin or voltage-dependent anion-Selective Channel (VDAC1) is a pore-forming protein discovered twenty five years ago in the mitochondrial outer membrane. Its gene in eukaryotes is known, but its tertiary structure has never been solved. Structure predictions highlight the presence of several amphipathic β-strands possibly organised in a β-barrel. VDAC1 has recently been described as being a NADH:ferricyanide reductase in the plasma membrane. There it affects the regulation of cell growth and death. Physiological cell death (apoptosis) has become a major research focus of biomedical research. Regulation of the enzyme will have impacts on cancer and autoimmune diseases (insufficient apoptosis) as well as neurodegenerative diseases (excessive apoptosis). VDAC1 in the plasma membrane establishes a novel level of apoptosis regulation putatively via its redox activity.

Ahmed Hesham Mehana - One of the best experts on this subject based on the ideXlab platform.

  • GLOBECOM - On the Performance of MIMO Receive Beamforming in Frequency-Selective Channels
    2015 IEEE Global Communications Conference (GLOBECOM), 2014
    Co-Authors: Ahmed Hesham Mehana
    Abstract:

    Linear transceivers prove efficiency and sometimes optimality under certain constraints. It is known that receive beamforming (matched filter) is diversity optimal in the case of SIMO Channel whereas the MMSE MIMO receiver is diversity optimal for only a small set of spectral efficiency $R$ b/s/Hz for an $M\times N$ MIMO Channel. In this paper we analyze the matched filter MIMO receiver over a frequency Selective Channel under cyclic-prefix transmission. It is shown that for a frequency Selective Channel with $\nu+1$ taps (where $\nu$ is the Channel memory) the matched filter has a rate-dependent diversity that switches between $(\nu+2)$ modes (with minimum of zero and a maximum of $MN(\nu+1)$) depending on the value of the operating $R$.

  • ISIT - Performance of MIMO single-carrier frequency domain zero-forcing equalizer
    2012 IEEE International Symposium on Information Theory Proceedings, 2012
    Co-Authors: Ahmed Hesham Mehana, Aria Nosratinia
    Abstract:

    Single-carrier frequency domain equalization (SC-FDE) has many advantages, but in the MIMO frequency Selective Channel its performance has not been fully characterized and several important open questions remain. This paper analyzes the diversity of zero-forcing MIMO SC-FDE. It is shown that the diversity of the ZF receiver over this Channel is the same as that of the ZF receiver in the frequency-flat Channel. To improve the performance, a lattice-reduction (LR) aided ZF equalization is proposed and analyzed. It is shown that the full spatial and temporal diversity is achieved by he LR-aided ZF receiver for the uncoded transmission. This is the first analytical proof for the LR-aided equalization for MIMO frequency Selective Channel.