Browsing by Author "LEE, TS"

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BEAMSPACE ML BEARING ESTIMATION INCORPORATING LOW-ANGLE GEOMETRY
(1991-05-01)
ZOLTOWSKI, MD
;
LEE, TS
;
電信工程研究所
;
Institute of Communications Engineering
A problem of interest in low-angle radar tracking is that of bearing estimation in the presence of a strong specular multipath component that arrives within a beamwidth of the direct path signal. Three-dimensional beamspace domain maximum likelihood (3D-BDML) is a computationally simple ML bearing estimation algorithm applicable in this scenario which operates in a 3-D beamspace. A variation of 3D-BDML incorporating the multipath geometry as a priori information is presented. In symmetric 3D-BDML the pointing angle of the center beam is equal to the bisector angle between the direct path ray and the image ray, which may be estimated a priori given only the radar height and the target range. The effect of the inclusion of a priori information on the performance of 3D-BDML is analyzed in terms of the dependence on the relative phase difference between the direct and specular path signals, the sensitivity to error in the bisector angle estimate, and the results of operation when no specular multipath component is present in the data. In addition, computationally simple schemes for coherently incorporating multifrequency data into 3D-BDML are investigated as well.
BISECTOR ANGLE ESTIMATION IN A NONSYMMETRIC MULTIPATH RADAR SCENARIO
(1991-12-01)
ZOLTOWSKI, MD
;
LEE, TS
;
電信工程研究所
;
Institute of Communications Engineering
In the classical problem of low-angle radar tracking, echoes return to the array via a specular path as well as by a direct path, with the angular separation between the two ray paths a fraction of a beamwidth. The performance of any bearing estimation scheme in this scenario is dependent on the phase difference between the direct and specular path signals at the centre of the array. The beamspace domain maximum likelihood (BDML) bearing estimator is a recently developed three-beam extension of the sum and difference beam technique employed in conventional radar. Nonsymmetric BDML breaks down when the phase difference is either 0-degrees or 180-degrees. In contrast, symmetric BDML, in which the point angle of the centre beam is the bisector angle between the two ray paths, can theoretically handle any phase difference, with the 0-degrees case giving rise to the best performance. A simple, closed-form bisector angle estimator is developed based on characteristic features of the 3 x 3 forward-backward averaged beamspace correlation matrix when the centre pointing angle is the true bisector angle. In this way, a 2-D parameter estimation problem is decomposed into two successive 1-D parameter estimation problems: estimation of the bisector angle, followed by estimation of the target bearing. Simulations are presented assessing the performance of the new bisector angle estimator and comparing the performance of symmetric BDML employing the new estimator with other ML based bearing estimation schemes in a simulated low-angle radar tracking environment.
EFFICIENT WIDE-BAND SOURCE LOCALIZATION USING BEAMFORMING INVARIANCE TECHNIQUE
(1994-06-01)
LEE, TS
;
交大名義發表
;
電信工程研究所
;
National Chiao Tung University
;
Institute of Communications Engineering
A novel scheme for wideband direction-of-arrival (DOA) estimation is proposed. The technique performs coherent signal subspace transformation by a set of judiciously constructed beamforming matrices. The beamformers are chosen to transform each of the narrowband array manifold vectors into the one corresponding to the reference frequency, regardless of the actual spatial distribution of the sources. The focused data correlation matrix can thus be obtained without any preliminary DOA estimation or iteration. A simplified version of the beamspace Root-MUSIC algorithm is developed and used in conjunction with the proposed method to efficiently localize multiple wideband sources with a linear, equally spaced array. Numerical simulations are conducted to demonstrate the efficacy of the new scheme.
FAST IMPLEMENTATION OF ROOT-FORM EIGEN-BASED METHODS FOR DETECTING CLOSELY SPACED SOURCES
(1992-08-01)
LEE, TS
;
交大名義發表
;
電信工程研究所
;
National Chiao Tung University
;
Institute of Communications Engineering
Root-form eigen-based methods for direction-of-arrival (DOA) estimation represent a class of estimators that exhibit a higher resolution capability relative to spectral-form estimators in detecting closely spaced sources with a linear, equally spaced (LES) array. These methods require an eigenvalue decomposition (EVD) and a polynomial rooting. Although the numerical complexity associated with the EVD is greatly reduced with the use of beamspace transformation, large-order polynomial rooting still raises practical difficulties. As a remedy, the author proposes a novel iterative implementation of beamspace root-form methods without the need for large-order polynomial rooting. The new method exploits the banded structure of the augmented noise eigen-vector matrix associated with an LES array. It requires only rooting in parallel several small-order polynomials and some minor matrix manipulations at each iteration. It is shown that the proposed method offers the performance of beamspace root-MUSIC.
INTERFERENCE CANCELLATION MATRIX BEAMFORMING FOR 3-D BEAMSPACE ML/MUSIC BEARING ESTIMATION
(1991-08-01)
ZOLTOWSKI, MD
;
LEE, TS
;
電信工程研究所
;
Institute of Communications Engineering
In conventional monopulse radar, the bearing of a single target within the mainlobe of the transmitted beam is estimated via a ML procedure based in a 2-D beamspace defined by sum and difference beams. For the case of two closely spaced targets angularly located within the mainlobe of the transmitted beam, 3D-BDML is a computationally simple ML bearing estimation scheme which operates in a 3-D beamspace generated by three orthogonal, classical beamformers. The presence of strong interferers angularly located outside the mainlobe encompassing the two targets of interest necessitates the use of adaptively formed left, center, and right beams. Let M denote the number of elements comprising the array. Novel procedures are developed for the construction of an M x 3 interference cancellation matrix beamformer which retains those properties of the M x 3 classical matrix beamformer critical to the computational simplicity of 3D-BDML. The most important of these is commonality of M - 3 nulls among the left, center, and right beams. Simulations are presented demonstrating the excellent performance of both single frequency and multifrequency 3D-BDML incorporating interference cancellation in a simulated low-angle radar tracking environment.
NOVEL BEAMSPACE NEURAL NETWORK APPROACH TO MOBILE UNIT LOCALIZATION
(1994)
DAI, TY
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LEE, TS
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HWANG, CR
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電信工程研究所
;
Institute of Communications Engineering
OPTIMUM 2-DIMENSIONAL BEAMFORMING EMPLOYING SUM-AND-DIFFERENCE TECHNIQUE
(1995-05-01)
LEE, TS
;
LIN, TT
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交大名義發表
;
電信工程研究所
;
National Chiao Tung University
OPTIMUM BEAMFORMERS FOR MONOPULSE ANGLE ESTIMATION USING OVERLAPPING SUBARRAYS
(1994-05-01)
LEE, TS
;
DAI, TY
;
交大名義發表
;
電信工程研究所
;
National Chiao Tung University
We here derive the optimum sum and difference beamformers for monopulse target localization using a linear array. The beamformers are constructed, treating as superelements two overlapping subarrays. Removing the common factor associated with the superelement pattern from the angle error function leads to a closed-form target angle estimator independent of any adaptive nulling performed. Performance analysis of the angle estimator is conducted, and a procedure is developed to construct the beamformers, which achieve the minimum estimation variance under Gaussian noise. It is shown that the optimum angle estimator using the maximum overlapping subarrays is efficient for a moderately high signal-noise ratio (SNR) and a small off-boresight angle. The proposed method can be easily modified to incorporate interference cancellation.
SIMULTANEOUS NULLING FOR MONOPULSE ARRAY WITH PARTIALLY ADAPTIVE WEIGHTS
(1994-07-01)
LEE, TS
;
交大名義發表
;
電信工程研究所
;
National Chiao Tung University
;
Institute of Communications Engineering
A new simple method is described for synthesizing low-sidelobe sum and difference patterns with partially adaptive weights. By partially adaptive, we mean that only part of the weights are adapted for simultaneous nulling. These adaptive weights are shared by the sum and difference channels, leading to a significant reduction in the number of variable attenuators/phase shifters used, as compared to the fully adaptive implementation. An objective function is derived that yields different configurations of the shared adaptive weights. Numerical examples are presented to ascertain the efficacy of the new method for both point and extended interference.
SOURCE LOCALIZATION IN A MULTIPATH ENVIRONMENT VIA BEAMSPACE CUMULANT-BASED NEURAL PROCESSING
(1995)
DAI, TY
;
LEE, TS
;
電信工程研究所
;
Institute of Communications Engineering
SUBARRAY-SYNTHESIZED LOW-SIDE-LOBE SUM AND DIFFERENCE PATTERNS WITH PARTIAL COMMON WEIGHTS
(1993-06-01)
LEE, TS
;
TSENG, TK
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交大名義發表
;
電信工程研究所
;
National Chiao Tung University
New methods of synthesizing low-side-lobe sum and difference patterns for linear arrays are described. By subarray beam forming, the sum and difference patterns exhibit a common factor, leading to a simple monopulse estimator. A procedure is proposed for the synthesis of the subarray-based sum and difference patterns which approximate a set of reference patterns in least-squares sense. Supervised nulling is incorporated as a means of suppression of strong interference. To further reduce system complexity, we impose the constraint that parts of the beam-forming weights are shared by the sum and difference channels. The relationship between the maximum number of common weights allowable and the number of subarrays used is discussed. Numerical results are presented to demonstrate the efficacy of the proposed methods.
TRANSIENT NATURAL-CONVECTION HEAT-TRANSFER BETWEEN CONCENTRIC SPHERES
(1993-09-01)
CHU, HS
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LEE, TS
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交大名義發表
;
機械工程學系
;
National Chiao Tung University
The transient laminar natural convection heat transfer of fluids between two concentric isothermal spheres is investigated theoretically. The fluid is initially at rest and then the inner wall is subjected to a step change of temperature. The stream function/vorticity formulation is employed for the analysis because of the symmetry of the problem. The transient behavior of the flow field and its subsequent effect on the temperature distribution for different Rayleigh numbers and radius ratios are analyzed by finite difference methods. Forward differences are used for the time derivatives and second-order central differences for the space derivatives. The alternating direction implicit method is used for solution of the discretization equations. The results show that the Rayleigh number and radius ratio have a profound influence on the temperature and flow fields. The results of average Nusselt numbers are also compared with those of previous experimental and numerical investigations. Excellent agreement is obtained.