I-Tai Lu - Academia.edu (original) (raw)
Papers by I-Tai Lu
A multi layered approach is proposed to provide energy and spectrum efficient designs of Cognitiv... more A multi layered approach is proposed to provide energy and spectrum efficient designs of Cognitive Radio Based Wireless Sensor Networks (CR-WSN) at the smart grid utility. CR-WSNs consume higher power and involve complex design procedure. Since smart grid wireless applications being used currently are meant to save power, we model the CR-WSN based home area networks by keeping minimum power
Analytical modeling of acoustic detection of flaws in composite laminates poses a difficult probl... more Analytical modeling of acoustic detection of flaws in composite laminates poses a difficult problem in wave propagation and scattering. Wave excitation and propagation in the laminate itself is complicated by the layering and by the generally multiwave character (due to anisotropy, elasticity, etc.) of each layer. Scattering from a flaw, even if it is understood in an unbounded material, is complicated by the presence of the layered environment. Dealing with the overall problem requires a self-consistent combination of phenomena due to layering and scattering. In this context, attention is here being called to self-consistent hybrid ray-mode and wavefront-resonance techniques — originally introduced in electromagnetics and underwater acoustics, and more recently in seismology — which incorporate a new approach to the multiwave, multilayer problem and the scattering problem, respectively. For the layered environment, a hybrid ray-mode Green’s function seeks to remove the disadvantages of separate ray propagation and mode propagation models. Ray fields alone may be inconvenient due to the multiwave character (caused by elasticity, anisotropy, etc.) of the layers, which results in wave species coupling at boundaries, and consequent ray proliferation after a few multiple reflections. Mode fields alone may be inconvenient at high frequencies because many normal modes are then required. Thus, for general conditions encompassing a broad range of observables, neither rays nor modes alone provide an efficient algorithm for numerical implementation. For scattering of wide-band signals by targets modeling flaws or inclusions in the unlayered environment, a self-contained wavefront-resonance description seeks to reconcile the spiked wavefront-like responses observed at early times with the more smoothly oscillatory resonance-like responses observed at later times. These hybrid formulations are reviewed and illustrated by examples which clearly reveal the phenomenology noted above. Emphasis is placed on the implications of these concepts for NDE.
A robust kernel-based machine learning localization scheme using time of arrival (TOA) or time di... more A robust kernel-based machine learning localization scheme using time of arrival (TOA) or time difference of arrival (TDOA) in none-line-of-sight (NLOS) environments is proposed. The scheme can provide accurate position estimation while the reference nodes are coarsely and randomly distributed in the area of interests. Moreover, the scheme is insensitive with respect to random TOA synchronization and measurement errors.
Elsevier eBooks, 1989
Location and identification of faults in multilayer elastic materials by ultrasound is aided by a... more Location and identification of faults in multilayer elastic materials by ultrasound is aided by a physically based parametrization of the input, scattered and detected fields. When the transducer input is beam-shaped, the beam-to-mode conversion in the unflawed layered environment suggests a “good” parametrization in terms of a self-consistent hybrid beam-mode format. The scattered field produced by interaction of this beam-mode field with a fault zone should then be parametrized in a similar manner. This strategy guides the present investigation of a weak bonding flaw in a multilayer aluminum plate. The horizontal and vertical displacements excited by a high frequency two-dimensional dilatational (P) Gaussian input beam have previously been tracked through successive cross sections in the perfectly bonded material. The resulting displacement profiles reveal clearly the beam-like character near the source, the deterioration of the successively reflected beam due to P-SV coupling at the boundaries, and the eventual evolution of oscillatory mode-like patterns. This input is now allowed to interact with an elongated weak bond zone. The induced equivalent forcing terms are modeled in the Born approximation, and the scattered field is evaluated accordingly. Depending on the flaw size, its location relative to the input and output transducers, and other variables, the detected response at the plate surface may contain beam-like or mode-like features. The beam-like phenomena are explored here with a view toward finding conditions through which the physical observables that should facilitate flaw location and identification are enhanced. Although, for convenience, the numerical data have been generated by normal mode summation, the results reveal clearly that the hybrid beam-mode format, to be developed next, furnishes the proper parametrization.
In frequency division duplex (FDD) wireless MIMO communications, the channel state information (C... more In frequency division duplex (FDD) wireless MIMO communications, the channel state information (CSI) of the forward link needs to be fed back to the transmitter for precoder design. In practice, the inevitable CSI feedback delay results in system performance degradation. In this paper, to mitigate the CSI feedback delay, an efficient adaptive double codebook based CSI prediction scheme is proposed by exploiting the LTE Release 10 double codebook framework. Simulation results demonstrate that the proposed scheme is effective in mitigating the CSI feedback delay in single-and multiuser (SU/MU) MIMO-OFDM systems.
A novel receiver I/Q imbalance estimation and compensation strategy is proposed for the 3GPP Long... more A novel receiver I/Q imbalance estimation and compensation strategy is proposed for the 3GPP Long Term Evolution (LTE) system using the proposed synchronization signals available in each frame. System architecture and algorithm design for the receiver I/Q imbalance estimation and compensation are described in detail. Algorithm optimization is also discussed for further enhancement of the design. Simulation results indicate that the proposed approach can effectively compensate the receiver I/Q imbalance. Index Terms-In-phase and quadrature-phase (I/Q) imbalance, orthogonal frequency division multiplexing (OFDM), Long Term Evolution (LTE).
IEEE Communications Letters, Oct 1, 2014
ABSTRACT
Electronics Letters, Nov 1, 2014
The channel bonding proposed in IEEE 802.11ac has the potential to multiply the data rate. Howeve... more The channel bonding proposed in IEEE 802.11ac has the potential to multiply the data rate. However, the backward compatibility with legacy 802.11 stations (STAs) and the overlapping basic service set (OBSS) problem make the available frequency resource severely under-utilised. The downlink (DL) approach (where the access point (AP) uses the available non-primary channels to transmit DL data to other 802.11ac STAs) and the relay (RL) approach (where the AP instructs some 802.11ac OBSS STAs to use the available non-primary channels to transmit uplink data to a pre-designated RL) are proposed to improve the performance of 802.11ac by efficiently using the under-utilised spectrum. The simulation results show that the proposed scheme can mitigate the OBSS problem and obtain significantly better performance than the current media access control (MAC) protocol in the 801.11ac draft. In addition, the proposed approaches can work seamlessly with the 802.11ac protocol.
ABSTRACT Orthogonal Frequency Division Multiplexing (OFDM) systems suffer from large out-of-band ... more ABSTRACT Orthogonal Frequency Division Multiplexing (OFDM) systems suffer from large out-of-band emission (OOBE). As one of the approaches to suppress the OOBE, the precoding technique is able to achieve significant OOBE suppression with a small spectral efficiency loss and does not depend on the input data. In this paper, a low-complexity individual precoded OFDM (I-P-OFDM) by precoding each contiguous frequency band independently is presented. Furthermore, two resource block (RB) based precoding schemes, namely, the U-RB-P-OFDM and NU-RB-P-OFDM are presented. The RB structures utilized in these two schemes enables mitigation of the precoding matrix dependency on the spectrum allocation. Numerical results show that all three schemes can achieve satisfying spectrum containment without any degradation in BER performance, and provide various tradeoffs between spectral efficiency, computational complexity, and PAPR performance.
Journal of Computational Acoustics, Jun 1, 1997
This paper presents a new ray travel-time inversion scheme not only for localizing the source and... more This paper presents a new ray travel-time inversion scheme not only for localizing the source and calibrating the array position, but also for characterizing environmental parameters such as sound speed profiles (in both water column and sediment), bathymetry, etc. Special attention is given to link the unknowns to good physical observables in order to enhance robustness and efficiency. Numerical studies show the algorithm is indeed extremely efficient. The algorithm is also shown to be insensitive to model mismatch and to yield quite accurate results. This paper also focuses on specific Lincoln-Sea application and analysis of a specific data set from Iceshelf-89.
Journal of the Acoustical Society of America, Jul 1, 1989
Thin elastic plates form the building blocks in whole, or in part, for many structures of current... more Thin elastic plates form the building blocks in whole, or in part, for many structures of current interest. The acoustic response of such plates can be found from thin plate or shell equations. It has recently been shown (A. D. Pierce, IUTAM Meeting, Galway, Ireland, 1988) how time-harmonic point force excitation of a thin circular cylindrical elastic tube of uniform thickness and composition in vacuum can be modeled equivalently as line source excitation in a homogeneous anisotropic medium, and how the exact Fourier spectral integral representation of the field in the radiation zone can be reduced by asymptotics to distinct ray contributions that account for the anisotropy. For the cylindrical geometry, the thin shell equations yield three fundamental wave types established, at high frequencies, by compression, bending, and shear. By appealing to concepts of spectral localization, these results are extended here to allow for weak deviations brought about by variable radius of curvature, variations in thickness and(or) material properties, and edge truncations or joints. The treatment is approximate, based on localization of wave phenomena that occur at sufficiently high frequencies. Modifications for fluid loading have also been considered. The tools are adiabatic spectral transforms as well as uniform and nonuniform asymptotics with their ray or mode interpretations, as performed within the context of an equivalent inhomogeneous anisotropic medium with boundaries or interfaces. In essence, the aim of this study is to formulate for the acoustic response of a class of curved sections of thin plates a geometrical theory of diffraction.
JOURNAL OF KIEE, Mar 1, 1990
![Research paper thumbnail of Erratum: “Three-dimensional Green’s function for fluid-loaded thin elastic cylindrical shell: Alternative representations and ray acoustic forms” [J. Acoust. Soc. Am. <b>87</b>, 554–569 (1990)]](https://attachments.academia-assets.com/109250469/thumbnails/1.jpg)
](Journal of the Acoustical Society of America, Mar 1, 1991
The following corrections should be made to the article entitled "Three-dimensional Green's funct... more The following corrections should be made to the article entitled "Three-dimensional Green's function for fluidloaded thin elastic cylindrical shell: Formulation and solution," by L. B. Felsen, J. M. Ho, and I. T. Lu, which appeared on pp. 543-553 in the February 1990 issue of JASA. (1) • in the second equation of (9c) should be replaced by •'. (2) oe • oo in the second equation of (11 c) should be replaced by oe• =. (3) The minus sign in the first equation of (B7b) should be replaced by a plus sign, and the plus and minus signs should be interchanged in the sentence that follows.
2017 IEEE Long Island Systems, Applications and Technology Conference (LISAT), 2017
This paper presents an extension of the ITU-R P.1411-8 urban low antenna path loss models to high... more This paper presents an extension of the ITU-R P.1411-8 urban low antenna path loss models to higher antennas. The Line-of-Sight (LOS) and non-Line-of-Sight (NLOS) urban canyon models presented in the paper are typically used for street level peer-to peer or cellular communications, but can be more generally used to account for radio waves propagating through urban street canyons. It is shown through comparisons with measurements of varying transmit antenna height and large variations of height difference between transmit and receive antennas, that the presented urban street canyon models are applicable to taller microcellular antennas. The measurements that are used in the comparisons and analysis were obtained in an urban high-rise environment in San Francisco at 850 and 1920 MHz frequencies.
Propagation of low frequency acoustic signals in an ocean environment with weak lateral variation... more Propagation of low frequency acoustic signals in an ocean environment with weak lateral variation in the sound speed and (or) bottom profile can be modeled effectively in terms of local intrinsic modes (Arnold and Felsen, to be published in Wave Motion). At any lateral location (x,y), these local modes have a depth (z) variation like a normal mode in a laterally homogeneous ocean defined by conditions at (x,y), and they propagate in the (x,y)-plane along lateral ray trajectories. Local intrinsic modes differ from adiabatic modes, first, by incorporating some adiabatic mode coupling effects and, second, by uniformly accommodating the transition through cutoff from trapped to radiating during upslope propagation. It has previously been shown that local intrinsic modes become exact for the prototype problem of a homogeneous water column separated from a homogeneous fluid bottom by a plane slanted interface. The model is now generalized to allow for stratification of the slanted bottom ...
A multi layered approach is proposed to provide energy and spectrum efficient designs of Cognitiv... more A multi layered approach is proposed to provide energy and spectrum efficient designs of Cognitive Radio Based Wireless Sensor Networks (CR-WSN) at the smart grid utility. CR-WSNs consume higher power and involve complex design procedure. Since smart grid wireless applications being used currently are meant to save power, we model the CR-WSN based home area networks by keeping minimum power
Analytical modeling of acoustic detection of flaws in composite laminates poses a difficult probl... more Analytical modeling of acoustic detection of flaws in composite laminates poses a difficult problem in wave propagation and scattering. Wave excitation and propagation in the laminate itself is complicated by the layering and by the generally multiwave character (due to anisotropy, elasticity, etc.) of each layer. Scattering from a flaw, even if it is understood in an unbounded material, is complicated by the presence of the layered environment. Dealing with the overall problem requires a self-consistent combination of phenomena due to layering and scattering. In this context, attention is here being called to self-consistent hybrid ray-mode and wavefront-resonance techniques — originally introduced in electromagnetics and underwater acoustics, and more recently in seismology — which incorporate a new approach to the multiwave, multilayer problem and the scattering problem, respectively. For the layered environment, a hybrid ray-mode Green’s function seeks to remove the disadvantages of separate ray propagation and mode propagation models. Ray fields alone may be inconvenient due to the multiwave character (caused by elasticity, anisotropy, etc.) of the layers, which results in wave species coupling at boundaries, and consequent ray proliferation after a few multiple reflections. Mode fields alone may be inconvenient at high frequencies because many normal modes are then required. Thus, for general conditions encompassing a broad range of observables, neither rays nor modes alone provide an efficient algorithm for numerical implementation. For scattering of wide-band signals by targets modeling flaws or inclusions in the unlayered environment, a self-contained wavefront-resonance description seeks to reconcile the spiked wavefront-like responses observed at early times with the more smoothly oscillatory resonance-like responses observed at later times. These hybrid formulations are reviewed and illustrated by examples which clearly reveal the phenomenology noted above. Emphasis is placed on the implications of these concepts for NDE.
A robust kernel-based machine learning localization scheme using time of arrival (TOA) or time di... more A robust kernel-based machine learning localization scheme using time of arrival (TOA) or time difference of arrival (TDOA) in none-line-of-sight (NLOS) environments is proposed. The scheme can provide accurate position estimation while the reference nodes are coarsely and randomly distributed in the area of interests. Moreover, the scheme is insensitive with respect to random TOA synchronization and measurement errors.
Elsevier eBooks, 1989
Location and identification of faults in multilayer elastic materials by ultrasound is aided by a... more Location and identification of faults in multilayer elastic materials by ultrasound is aided by a physically based parametrization of the input, scattered and detected fields. When the transducer input is beam-shaped, the beam-to-mode conversion in the unflawed layered environment suggests a “good” parametrization in terms of a self-consistent hybrid beam-mode format. The scattered field produced by interaction of this beam-mode field with a fault zone should then be parametrized in a similar manner. This strategy guides the present investigation of a weak bonding flaw in a multilayer aluminum plate. The horizontal and vertical displacements excited by a high frequency two-dimensional dilatational (P) Gaussian input beam have previously been tracked through successive cross sections in the perfectly bonded material. The resulting displacement profiles reveal clearly the beam-like character near the source, the deterioration of the successively reflected beam due to P-SV coupling at the boundaries, and the eventual evolution of oscillatory mode-like patterns. This input is now allowed to interact with an elongated weak bond zone. The induced equivalent forcing terms are modeled in the Born approximation, and the scattered field is evaluated accordingly. Depending on the flaw size, its location relative to the input and output transducers, and other variables, the detected response at the plate surface may contain beam-like or mode-like features. The beam-like phenomena are explored here with a view toward finding conditions through which the physical observables that should facilitate flaw location and identification are enhanced. Although, for convenience, the numerical data have been generated by normal mode summation, the results reveal clearly that the hybrid beam-mode format, to be developed next, furnishes the proper parametrization.
In frequency division duplex (FDD) wireless MIMO communications, the channel state information (C... more In frequency division duplex (FDD) wireless MIMO communications, the channel state information (CSI) of the forward link needs to be fed back to the transmitter for precoder design. In practice, the inevitable CSI feedback delay results in system performance degradation. In this paper, to mitigate the CSI feedback delay, an efficient adaptive double codebook based CSI prediction scheme is proposed by exploiting the LTE Release 10 double codebook framework. Simulation results demonstrate that the proposed scheme is effective in mitigating the CSI feedback delay in single-and multiuser (SU/MU) MIMO-OFDM systems.
A novel receiver I/Q imbalance estimation and compensation strategy is proposed for the 3GPP Long... more A novel receiver I/Q imbalance estimation and compensation strategy is proposed for the 3GPP Long Term Evolution (LTE) system using the proposed synchronization signals available in each frame. System architecture and algorithm design for the receiver I/Q imbalance estimation and compensation are described in detail. Algorithm optimization is also discussed for further enhancement of the design. Simulation results indicate that the proposed approach can effectively compensate the receiver I/Q imbalance. Index Terms-In-phase and quadrature-phase (I/Q) imbalance, orthogonal frequency division multiplexing (OFDM), Long Term Evolution (LTE).
IEEE Communications Letters, Oct 1, 2014
ABSTRACT
Electronics Letters, Nov 1, 2014
The channel bonding proposed in IEEE 802.11ac has the potential to multiply the data rate. Howeve... more The channel bonding proposed in IEEE 802.11ac has the potential to multiply the data rate. However, the backward compatibility with legacy 802.11 stations (STAs) and the overlapping basic service set (OBSS) problem make the available frequency resource severely under-utilised. The downlink (DL) approach (where the access point (AP) uses the available non-primary channels to transmit DL data to other 802.11ac STAs) and the relay (RL) approach (where the AP instructs some 802.11ac OBSS STAs to use the available non-primary channels to transmit uplink data to a pre-designated RL) are proposed to improve the performance of 802.11ac by efficiently using the under-utilised spectrum. The simulation results show that the proposed scheme can mitigate the OBSS problem and obtain significantly better performance than the current media access control (MAC) protocol in the 801.11ac draft. In addition, the proposed approaches can work seamlessly with the 802.11ac protocol.
ABSTRACT Orthogonal Frequency Division Multiplexing (OFDM) systems suffer from large out-of-band ... more ABSTRACT Orthogonal Frequency Division Multiplexing (OFDM) systems suffer from large out-of-band emission (OOBE). As one of the approaches to suppress the OOBE, the precoding technique is able to achieve significant OOBE suppression with a small spectral efficiency loss and does not depend on the input data. In this paper, a low-complexity individual precoded OFDM (I-P-OFDM) by precoding each contiguous frequency band independently is presented. Furthermore, two resource block (RB) based precoding schemes, namely, the U-RB-P-OFDM and NU-RB-P-OFDM are presented. The RB structures utilized in these two schemes enables mitigation of the precoding matrix dependency on the spectrum allocation. Numerical results show that all three schemes can achieve satisfying spectrum containment without any degradation in BER performance, and provide various tradeoffs between spectral efficiency, computational complexity, and PAPR performance.
Journal of Computational Acoustics, Jun 1, 1997
This paper presents a new ray travel-time inversion scheme not only for localizing the source and... more This paper presents a new ray travel-time inversion scheme not only for localizing the source and calibrating the array position, but also for characterizing environmental parameters such as sound speed profiles (in both water column and sediment), bathymetry, etc. Special attention is given to link the unknowns to good physical observables in order to enhance robustness and efficiency. Numerical studies show the algorithm is indeed extremely efficient. The algorithm is also shown to be insensitive to model mismatch and to yield quite accurate results. This paper also focuses on specific Lincoln-Sea application and analysis of a specific data set from Iceshelf-89.
Journal of the Acoustical Society of America, Jul 1, 1989
Thin elastic plates form the building blocks in whole, or in part, for many structures of current... more Thin elastic plates form the building blocks in whole, or in part, for many structures of current interest. The acoustic response of such plates can be found from thin plate or shell equations. It has recently been shown (A. D. Pierce, IUTAM Meeting, Galway, Ireland, 1988) how time-harmonic point force excitation of a thin circular cylindrical elastic tube of uniform thickness and composition in vacuum can be modeled equivalently as line source excitation in a homogeneous anisotropic medium, and how the exact Fourier spectral integral representation of the field in the radiation zone can be reduced by asymptotics to distinct ray contributions that account for the anisotropy. For the cylindrical geometry, the thin shell equations yield three fundamental wave types established, at high frequencies, by compression, bending, and shear. By appealing to concepts of spectral localization, these results are extended here to allow for weak deviations brought about by variable radius of curvature, variations in thickness and(or) material properties, and edge truncations or joints. The treatment is approximate, based on localization of wave phenomena that occur at sufficiently high frequencies. Modifications for fluid loading have also been considered. The tools are adiabatic spectral transforms as well as uniform and nonuniform asymptotics with their ray or mode interpretations, as performed within the context of an equivalent inhomogeneous anisotropic medium with boundaries or interfaces. In essence, the aim of this study is to formulate for the acoustic response of a class of curved sections of thin plates a geometrical theory of diffraction.
JOURNAL OF KIEE, Mar 1, 1990
Journal of the Acoustical Society of America, Mar 1, 1991
The following corrections should be made to the article entitled "Three-dimensional Green's funct... more The following corrections should be made to the article entitled "Three-dimensional Green's function for fluidloaded thin elastic cylindrical shell: Formulation and solution," by L. B. Felsen, J. M. Ho, and I. T. Lu, which appeared on pp. 543-553 in the February 1990 issue of JASA. (1) • in the second equation of (9c) should be replaced by •'. (2) oe • oo in the second equation of (11 c) should be replaced by oe• =. (3) The minus sign in the first equation of (B7b) should be replaced by a plus sign, and the plus and minus signs should be interchanged in the sentence that follows.
2017 IEEE Long Island Systems, Applications and Technology Conference (LISAT), 2017
This paper presents an extension of the ITU-R P.1411-8 urban low antenna path loss models to high... more This paper presents an extension of the ITU-R P.1411-8 urban low antenna path loss models to higher antennas. The Line-of-Sight (LOS) and non-Line-of-Sight (NLOS) urban canyon models presented in the paper are typically used for street level peer-to peer or cellular communications, but can be more generally used to account for radio waves propagating through urban street canyons. It is shown through comparisons with measurements of varying transmit antenna height and large variations of height difference between transmit and receive antennas, that the presented urban street canyon models are applicable to taller microcellular antennas. The measurements that are used in the comparisons and analysis were obtained in an urban high-rise environment in San Francisco at 850 and 1920 MHz frequencies.
Propagation of low frequency acoustic signals in an ocean environment with weak lateral variation... more Propagation of low frequency acoustic signals in an ocean environment with weak lateral variation in the sound speed and (or) bottom profile can be modeled effectively in terms of local intrinsic modes (Arnold and Felsen, to be published in Wave Motion). At any lateral location (x,y), these local modes have a depth (z) variation like a normal mode in a laterally homogeneous ocean defined by conditions at (x,y), and they propagate in the (x,y)-plane along lateral ray trajectories. Local intrinsic modes differ from adiabatic modes, first, by incorporating some adiabatic mode coupling effects and, second, by uniformly accommodating the transition through cutoff from trapped to radiating during upslope propagation. It has previously been shown that local intrinsic modes become exact for the prototype problem of a homogeneous water column separated from a homogeneous fluid bottom by a plane slanted interface. The model is now generalized to allow for stratification of the slanted bottom ...