Showing papers by "Xidian University published in 2001"
TL;DR: The objective is to apply methods of experimental design to enhance the genetic algorithm, so that the resulting algorithm can be more robust and statistically sound and a quantization technique is proposed to complement an experimental design method called orthogonal design.
Abstract: We design a genetic algorithm called the orthogonal genetic algorithm with quantization for global numerical optimization with continuous variables. Our objective is to apply methods of experimental design to enhance the genetic algorithm, so that the resulting algorithm can be more robust and statistically sound. A quantization technique is proposed to complement an experimental design method called orthogonal design. We apply the resulting methodology to generate an initial population of points that are scattered uniformly over the feasible solution space, so that the algorithm can evenly scan the feasible solution space once to locate good points for further exploration in subsequent iterations. In addition, we apply the quantization technique and orthogonal design to tailor a new crossover operator, such that this crossover operator can generate a small, but representative sample of points as the potential offspring. We execute the proposed algorithm to solve 15 benchmark problems with 30 or 100 dimensions and very large numbers of local minima. The results show that the proposed algorithm can find optimal or close-to-optimal solutions.
783 citations
TL;DR: Since the selected bispectra of range profiles are translation invariant and can avoid redundant and baneful bispecta as features, they are especially suitable for radar target recognition, which is shown by experiments.
Abstract: Radially integrated bispectra (RIB), axially integrated bispectra (AIB), and circularly integrated bispectra (CIB) were used as feature vectors of signals, but many bispectra on integration paths may be redundant, and some bispectra are even baneful for signal classification. To avoid these problems, this paper proposes using selected bispectra with the maximum interclass separability as feature vectors of signals. In radar target recognition, range profiles are suitable feature vectors, but they have two main shortcomings: sensitivity to time shift and aspect dependence. Since the selected bispectra of range profiles are translation invariant and can avoid redundant and baneful bispectra as features, they are thus especially suitable for radar target recognition, which is shown by experiments.
135 citations
TL;DR: A solution to the problem of scattering of a Gaussianbeam by a homogeneous prolate (or oblate) spheroidal particle is obtained and the numerical values of the expansion coefficients and the scattered intensity distribution for incidence of an on-axis Gaussian beam are given.
Abstract: An approach to expanding a Gaussian beam in terms of the spheroidal wave functions in spheroidal coordinates is presented. The beam-shape coefficients of the Gaussian beam in spheroidal coordinates can be computed conveniently by use of the known expression for beam-shape coefficients, gn, in spherical coordinates. The unknown expansion coefficients of scattered and internal electromagnetic fields are determined by a system of equations derived from the boundary conditions for continuity of the tangential components of the electric and magnetic vectors across the surface of the spheroid. A solution to the problem of scattering of a Gaussian beam by a homogeneous prolate (or oblate) spheroidal particle is obtained. The numerical values of the expansion coefficients and the scattered intensity distribution for incidence of an on-axis Gaussian beam are given.
102 citations
TL;DR: This correspondence investigates the principles of ISAR imaging of maneuvering targets, and proposes an algorithm for application in situations where the maneuverability is not too severe and the Doppler variation of subechoes from scatterers can be approximated as a first-order polynomial.
Abstract: Inverse synthetic aperture radar (ISAR) imaging of the noncooperative maneuvering target is a challenging task because of its time variant orientation and rotation velocity which cannot be measured accurately. This correspondence investigates the principles of ISAR imaging of maneuvering targets, and proposes an algorithm for application in situations where the maneuverability is not too severe and the Doppler variation of subechoes from scatterers can be approximated as a first-order polynomial. The imaging results obtained by using real data show the effectiveness of the new method.
91 citations
TL;DR: This paper is concerned with a family of concatenated tree (CT) codes, which are special low-density parity check codes consisting of several trees with large spans and decodable by the belief-propagation algorithm.
Abstract: This paper is concerned with a family of concatenated tree (CT) codes. CT codes are special low-density parity check (LDPC) codes consisting of several trees with large spans. They can also be regarded as special turbo codes with hybrid recursive/nonrecursive parts and multiple constituent codes. CT codes are decodable by the belief-propagation algorithm. They combine many advantages of LDPC and turbo codes, such as low decoding cost, fast convergence speed, and good performance.
70 citations
TL;DR: The theoretical analyses show that the multiwavelet network converges more rapidly than the wavelet network, especially for smooth functions, and that at the jump discontinuities, the approximation performance of the two networks are about the same.
Abstract: A model of multiwavelet-based neural networks is proposed. Its universal and L/sup 2/ approximation properties, together with its consistency are proved, and the convergence rates associated with these properties are estimated. The structure of this network is similar to that of the wavelet network, except that the orthonormal scaling functions are replaced by orthonormal multiscaling functions. The theoretical analyses show that the multiwavelet network converges more rapidly than the wavelet network, especially for smooth functions. To make a comparison between both networks, experiments are carried out with the Lemarie-Meyer wavelet network, the Daubechies2 wavelet network and the GHM multiwavelet network, and the results support the theoretical analysis well. In addition, the results also illustrate that at the jump discontinuities, the approximation performance of the two networks are about the same.
68 citations
TL;DR: In this article, a new sufficient condition related to the global asymptotic stability for cellular neural networks with delay (DCNNs) is derived, which is less restrictive than that given in the literature.
Abstract: The problem of stability for cellular neural networks with delay (DCNNs) is studied. A new sufficient condition related to the global asymptotic stability for DCNNs is derived. This condition is less restrictive than that given in the literature.
57 citations
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TL;DR: In this article, the authors present experiments designed to convince the aerospace industry that microelectromechanical systems (MEMS) could open the door to low-cost, high-reliability, mass-produced satellites.
Abstract: The satellite industry could experience its biggest revolution since it joined the ranks of commerce, thanks to some of the smallest machines in existence. Researchers are performing experiments designed to convince the aerospace industry that microelectromechanical systems (MEMS) could open the door to low-cost, high-reliability, mass-produced satellites. MEMS combine conventional semiconductor electronics with beams, gears, levers, switches, accelerometers, diaphragms, microfluidic thrusters, and heat controllers, all of them microscopic in size. Some of the advantages of using MEMS-based satellites are low launch costs and high resistance to radiation and vibration. MEMS-based satellites also promise to be cheaper to develop and fabricate than conventional spacecraft.
51 citations
TL;DR: In this article, the authors presented a methodology for the design of optimal kinematical characteristics of Stewart platform using genetic algorithms (GAs), where the minimum of condition numbers of Jacobian matrix in the whole trajectory tracing workspace is used as the objective function, and the constrained optimal design problem is transformed to unrestrained optimal one which is suitable to GAs by penalizing strategy.
50 citations
TL;DR: It is proved that the proposed criterion has a unique global minimum at the minor subspace and that all other equilibrium points are saddle points.
Abstract: An information criterion for adaptively estimating multiple minor eigencomponents of a covariance matrix is proposed It is proved that the proposed criterion has a unique global minimum at the minor subspace and that all other equilibrium points are saddle points Based on the gradient search approach of the proposed information criterion, an adaptive algorithm called adaptive minor component extraction (AMEX) is developed The proposed algorithm automatically performs the multiple minor component extraction in parallel without the inflation procedure Similar to the adaptive lattice filter structure, the AMEX algorithm also has the flexibility wherein increasing the number of the desired minor component does not affect the previously extracted minor components The AMEX algorithm has a highly modular structure and the various modules operate completely in parallel without any delay Simulation results are given to demonstrate the effectiveness of the AMEX algorithm for both the minor component analysis (MCA) and the minor subspace analysis (MSA)
49 citations
TL;DR: A theory on incoherently coupled soliton pairs for photorefractive screening solitons is developed that gives rise to incoherencely coupled steady-statesoliton pairs and multicomponent spatial soliton in biased photoreFractive-photovoltaic materials, which result from both the bulk photvoltaic effect and the spatially nonuniform screening of the external bias field.
Abstract: A theory on incoherently coupled soliton pairs for photorefractive screening solitons is developed that gives rise to incoherently coupled steady-state soliton pairs and multicomponent spatial solitons in biased photorefractive-photovoltaic materials, which result from both the bulk photovoltaic effect and the spatially nonuniform screening of the external bias field. When the bulk photovoltaic effect is neglectable, these soliton pairs are the previously studied soliton pairs for screening solitons, these multicomponent spatial solitons predict incoherently coupled multicomponent spatial solitons for screening solitons, and their space-charge field is the space-charge field of screening solitons. When the external field is absent, these soliton pairs and multicomponent spatial solitons predict incoherently coupled soliton pairs and multicomponent spatial solitons for photovoltaic solitons, and their space-charge field is the space-charge field of photovoltaic solitons. The stability of these soliton pairs and multicomponent spatial solitons is also discussed using the modulation instability theory.
TL;DR: A large parallel-cable manipulator for the feed-supporting system of a next-generation large radio telescope is presented and the rationality of this approximation is validated by a kinematics accuracy analysis.
Abstract: A large parallel-cable manipulator for the feed-supporting system of a next-generation large radio telescope is presented in this paper. The approximate kinematics model of the system is developed to improve real-time controllability, and the rationality of this approximation is validated by a kinematics accuracy analysis. In order to guarantee the effectiveness of control, the singularity of the large parallel-cable manipulator is analyzed (including kinematics and force singularities). The control strategy of the parallel-cable feed-supporting system is also proposed. © 2001 John Wiley & Sons, Inc.
TL;DR: In this article, the expansion of the Gaussian beam in terms of the prolate spheroidal vector wave function was studied and the expansion coefficients were determined, and the numerical values of the sphroidal eigenvalues and expansion coefficients have been computed.
Abstract: We study the expansion of the Gaussian beam in terms of the prolate spheroidal vector wavefunction. The expansion coefficients are determined. The numerical values of the spheroidal eigenvalues and expansion coefficients have been computed.
TL;DR: It is shown through extensive comparisons with other candidate handoff strategies that if the total traffic load of the system is not very heavy, this scheme has the best bandwidth efficiency and can provide better quality of service for mobile subscribers without bringing too much processing expense to the system.
Abstract: In this paper, a bandwidth-efficient handoff strategy is proposed and analyzed for hierarchical cellular systems. Mobile subscribers are divided into two classes, i.e., low- and high-mobility subscribers. In our bandwidth-efficient handoff strategy, each of the originating and handoff calls of both slow and fast mobile subscribers first tries to get a channel in a microcell. Macrocells are overlaid over the microcells to handle overflowed calls. A call overflowed into a macrocell requests a take-back to the new microcell at each border crossing of the microcells. The request will be accommodated by the target microcell if there is any idle traffic channel in the cell. An analytical model is developed, and the most important performance measures such as the blocking probability of originating calls and the forced termination probability of calls are evaluated. It is shown through extensive comparisons with other candidate handoff strategies that if the total traffic load of the system is not very heavy, our scheme has the best bandwidth efficiency and can provide better quality of service for mobile subscribers without bringing too much processing expense to the system.
TL;DR: In this paper, the molar ratio of LaCuO4 to SnO2 was chosen as 1:10 (sample 1), 1:8 (sample 2, 1:4 (sample 3), and 2:1 (sample 4), respectively.
Abstract: The preparation of SnO2 and La2CuO4 powders, and the manufacture of La2CuO4–SnO2 gas sensors are described in some details. The molar ratio of LaCuO4 to SnO2 was chosen as 1:10 (sample 1), 1:8 (sample 2), 1:4 (sample 3), and 2:1 (sample 4), respectively. All samples were measured in the temperature range 20–300°C and under different concentrations of alcohol vapor, H2, and H2S, respectively. The results show that the resistance of La2CuO4–SnO2 sample increases with an increase of La2CuO4 content at given temperature when the La2CuO4 content in sample is lower than 50 mol%. Except sample 4, samples 1, 2, and 3 are sensitive to alcohol vapor, H2, and H2S. As compared with CuO–SnO2 sensor, sample 1 has faster response property and lower operating temperature in the case of same H2S–air mixture concentration.
15 Oct 2001
TL;DR: The principle of the SIAR is introduced, some questions are discussed, and some questions (including optimization of the frequency coding of the transmitting signal) are discussed and some experiment results are given, with strong agreement observed on both experiment and theoretical results.
Abstract: Sparse-array synthetic impulse and aperture radar (SIAR) is a new concept of 4D radar, based on the use of a transmit array, simultaneously radiating a set of orthogonal waveforms, and of a reception array, delivering sampled signals to a processing equipment, dedicated to Doppler filtering, time-space beamforming (including a transmitting beam and a receiving beam by calculation), and target extraction, thus, it can isotropically radiate. This radar adopt sparse arrays to improve its angle resolution. This paper introduces the principle of the SIAR, discusses some questions (including optimization of the frequency coding of the transmitting signal. to eliminate the coupling effects between distance and angles, a low-range-sidelobe technique based on frequency-coding agility among these frequencies and application of large time-bandwidth signals) and presents a description of the experiment system. Finally, some experiment results are given. Moreover, the strong agreement observed on both experiment and theoretical results.
TL;DR: A method is proposed for extracting a useful signal hidden in a deterministic chaotic signal using a wavelet multiscale decomposition algorithm that can separate two signals with different wavelet ...
Abstract: A method is proposed for extracting a useful signal hidden in a deterministic chaotic signal using a wavelet multiscale decomposition algorithm that can separate two signals with different wavelet ...
TL;DR: A novel approach to designing regular orthogonal symmetric interpolating scaling filters for wavelets with compact support, orthogonality, linear-phase, regularity, and interpolation is proposed.
Abstract: In many applications, wavelets are usually expected to have the following properties: compact support, orthogonality, linear-phase, regularity, and interpolation. To construct such wavelets, it is crucial designing scaling functions with the above properties. In two- and three-band cases, except for the Haar functions, there exists no scaling function with the above five properties. In M-band case (M/spl ges/4), more free degrees available in design enable us to construct such scaling functions. A novel approach to designing such scaling functions is proposed. First, we extend the two-band Dubuc (1986) filters to the M-band case. Next, the M-band FIR regular symmetric interpolating scaling filters are parameterized, and then, M-band FIR regular orthogonal symmetric interpolating scaling filters (OSISFs) are designed via optimal selection of parameters. Finally, two family of four-band and five-band OSISFs and scaling functions are developed, and their smoothness are estimated.
TL;DR: In this paper, a two-dimensional fractional Brown motion (fBm) fractal model is presented, which is suitable for describing the natural rough surface, and the expressions of the electromagnetic scattering field and the normalized radar cross section from this fractal surface are obtained.
Abstract: A two-dimensional fractional Brown motion (fBm) fractal model is presented, which is suitable for describing the natural rough surface. Using the Kirchhoff approximation, the expressions of the electromagnetic scattering field and the normalized radar cross section from this fractal surface are obtained. Numerical results of the normalized radar cross section as a function of the fractal dimension, characteristic length and incidence frequency are given. Our fBm model is also compared with classical models of Gaussian and exponential correlation.
TL;DR: A mapping relationship from P_QoS to buffer which is used to compensate for delay variations is given based on delay jitter statistics, and its theoretical analysis is shown so the buffer size of a multimedia synchronization system can be determined.
Abstract: In multimedia systems end to end delay jitter has a great impact on the continuity of information playback. Therefore, it is necessary to compensate for delay variations to preserve the intramedia and intermedia temporal relationships. A buffer at the destination site is often adopted to compensate for the delay jitter. In this paper, a mapping relationship from P_QoS to buffer which is used to compensate for delay variations is given based on delay jitter statistics, and its theoretical analysis is also shown. So the buffer size of a multimedia synchronization system can be determined.
TL;DR: Three novel models of threshold estimator are presented, which are polynomial interpolatingresholding method, compromising method of hard- and soft-thresholding and modulus square thresholding method respectively, which overcome the disadvantages of the hard-and-soft-th thresholds method.
Abstract: The soft-thresholding and the hard-thresholding method to estimate wavelet coefficients in wavelet threshold denoising are firstly discussed. To avoid the discontinuity in the hard-thresholding and biased estimation in the soft-thresholding, three novel models of threshold estimator are presented, which are polynomial interpolating thresholding method, compromising method of hard- and soft-thresholding and modulus square thresholding method respectively. They all overcome the disadvantages of the hard- and soft-thresholding method. Finally, an example is given and the experimental results show that the improved techniques presented in this paper are efficient.
25 Sep 2001
TL;DR: A new autofocus algorithm based on coherent integration to solve the imaging problem of maneuvering target and proposes a instantaneous ISAR imaging method based on multicomponent amplitude modulation and linear frequency modulation (AM-LFM) signal's parameter estimation.
Abstract: Inverse Synthetic Aperture Radar (ISAR) imaging of maneuvering target has received much attention in recent years. In the paper, we first discuss translational motion compensation (TMC), which can be decomposed into two step: envelope alignment and autofocus. There are many effective algorithms for these two step, but most of algorithms are only suitable to steadily flying targets. The analysis of the paper shows that the envelope alignment algorithms for steadily flying targets are still effective for maneuvering targets, but most of autofocus algorithms are not work very well, especially when the maneuverability is great, so this paper also presents a new autofocus algorithm based on coherent integration to solve this problem. Then after TMC, we discuss imaging problem of maneuvering target, in fact, it is a instantaneous spectrum estimation problem, most of instantaneous ISAR imaging methods of maneuvering target are based on time-frequency distribution, and suppose scatterer echo has constant amplitude and linear frequency modulation. In fact, when target has dihedrals and trihedrals component, or scatterer' migration through resolution cells (MTRC) exists, these situation all will cause the amplitude is not a constant. For maneuvering target, scatterer echo's Doppler is time varying, usually, its time-frequency distribution can be regard as linear or part linear. So we propose a instantaneous ISAR imaging method based on multicomponent amplitude modulation and linear frequency modulation(AM-LFM) signal's parameter estimation, this method first estimates the chirp rate of one component by dechirping, then demodulates this component to a sinusoidal signal, separates and cleans this component in Fourier domain, and estimates instantaneous amplitude, then for next component, finally we get all the scattterers instantaneous amplitudes and frequencies, and the instantaneous ISAR images are obtained now.
TL;DR: In this paper, a theory on spatial solitons in photovoltaic (PV)-photorefractive (PR) crystals for short circuits is developed that gives rise to spatial nonuniform screening of the external field.
Abstract: A theory on spatial solitons in photovoltaic (PV)-photorefractive (PR) crystals for short circuits is developed that gives rise to spatial solitons due to both a bulk PV effect and spatial nonuniform screening of the external field. When the PV effect is neglected these solitons are screening solitons. When the external field is absent these solitons are PV solitons in short and open circuits and it is predicted that grey solitons exist in PV-PR crystals for short circuits. We also show theoretically that PV nonlinearity can be switched from self-defocusing to self-focusing (or vice versa) by adding the external field.
15 Oct 2001
TL;DR: Through theoretical analysis and simulation results it is shown that the proposed approach has improved adaptation to non-stationary noise and the echos of the large target has a smaller negative effect on the adjacent range cell.
Abstract: The projection of the conventional radar waveform in wavelet space is comparatively complex, which complicated the wavelet decomposition of the radar waveform. A novel radar waveform design method is proposed. The proposed approach uses the wavelet function of a specific scale as the waveform and thus the inter-dependency of the wavelet coefficients in different subspaces is reduced. Better detection performance is achieved when only two wavelet decomposition coefficients are used. Through theoretical analysis and simulation results it is shown that the proposed approach has improved adaptation to non-stationary noise and the echos of the large target has a smaller negative effect on the adjacent range cell.
TL;DR: A cross-associative neural network for singular value decomposition (SVD) of a non-squared data matrix in signal processing, in order to improve the convergence speed and avoid the potential instability of the deterministic networks associated with the cross-correlation neural-network models.
Abstract: This paper proposes a cross-associative neural network (CANN) for singular value decomposition (SVD) of a non-squared data matrix in signal processing, in order to improve the convergence speed and avoid the potential instability of the deterministic networks associated with the cross-correlation neural-network models. We study the global asymptotic stability of the network for tracking all the singular components, and show that the selection of its learning rate in the iterative algorithm is independent of the singular value distribution of a non-squared matrix. The performances of CANN are shown via simulations.
06 May 2001
TL;DR: This paper describes medium access protocols and proposes a CDMA-based CSMA protocol to solve the collision problems well with the help of multi-channel scheme and results show that the proposed protocol offers high throughput.
Abstract: A wide variety of mobile computing devices have emerged, including portables, palmtops and personal digital assistants. Providing adequate network connectivity for these devices will require a new generation wireless technology. This paper describes medium access protocols and proposes a CDMA-based CSMA protocol to solve the collision problems well with the help of multi-channel scheme. New methods of code synchronization and assignment are presented. Our analysis results show that the proposed protocol offers high throughput.
TL;DR: The concept of local l/sup 2/ stability for a Volterra system is introduced, and the algorithmic formulae of a pth-order inverse equalizer via a multidimension z- transform are presented and it is shown that the approximation output error tends to zero as p tends to infinity for a finite range of input amplitude values.
Abstract: The pth-order inverse method is one of important approaches to Volterra equalization. However, when a pth-order Volterra equalizer instead of an exact Volterra equalizer is connected in cascade before (after) a nonlinear system, the existence of Volterra filter equalization and the approximation output error bound of the resulting system have yet to be reported. In this paper, the concept of local l/sup 2/ stability for a Volterra system is introduced, and the algorithmic formulae of a pth-order inverse equalizer via a multidimension z-transform are presented. The output error signal and the approximation output error bound of the resulting system are investigated as well. It is shown that the approximation output error tends to zero as p tends to infinity for a finite range of input amplitude values. Finally some simulation results are presented and discussed.
15 Oct 2001
TL;DR: An effective method for long-time coherent integration is presented, which includes a simply implemented motion compensation and time-frequency analysis, which shows that the novel method has good performance for weak target detection.
Abstract: Sparse-array synthetic impulse and aperture radar (SIAR) adopts the isotropic radiation scheme, thus can perform the long-time coherent integration. However, there are some problems in the process. In this paper, an effective method for long-time coherent integration is presented, which includes a simply implemented motion compensation and time-frequency analysis. The result shows that the novel method has good performance for weak target detection.
TL;DR: An efficient algorithm for determining the linear complexity and the minimal polynomial of a binary sequence with period 2npm is proposed and proved, where 2 is a primitive root modulop2.
Abstract: An efficient algorithm for determining the linear complexity and the minimal polynomial of a binary sequence with period 2 n p m is proposed and proved, where 2 is a primitive root modulo p 2 . The new algorithm generalizes the algorithm for computing the linear complexity of a binary sequence with period 2 n and the algorithm for computing the linear complexity of a binary sequence with period p n , where 2 is a primitive root modulo p 2 .
TL;DR: In this paper, the fine structure spectrum of the 14 July 2000 Bastille Day (14 July 2000) flare at 1.0-7.6 GHz globally appears as a U-shaped signature.
Abstract: 25 MHz–7.6 GHz global and detailed (fine structure – FS) radio spectra are presented, which were observed in the NOAA 9077 active region for the Bastille Day (14 July 2000) flare at 10:10–11:00 UT. Besides broadband radio bursts, high-resolution dynamic spectra reveal metric type II burst, decimetric type IV burst and various decimetric and microwave FSs, such as type III bursts, type U bursts, reverse-slope (RS)-drifting burst, fiber bursts, patch and drifting pulsation structure (DPS). The peak-flux-density spectrum of the radio bursts over the range 1.0–7.6 GHz globally appears as a U-shaped signature. Analyzing the features of backbone and herringbones of the type II burst, the speeds of shock and relevant energetic electron beams were estimated to be 1100 km s−1 and 58 500 km s−1, respectively. Also the time sequence of the radio emission is analyzed by comparing with the hard X-rays (HXRs) and the soft X-rays (SXRs) in this flare. After the maxima of the X-rays, the radio emission in the range 1.0–7.6 GHz reached maxima first at the higher frequency, then drifted to the lower frequency. This comparison suggested that the flare included three successive processes: firstly the X-rays rose and reached maxima at 10:10–10:23 UT, accompanied by fine structures only in the range 2.6–7.6 GHz; secondly the microwave radio emission reached maxima accompanied by many fine structures over the range 1.0–7.6 GHz at 10:23–10:34 UT; then a decimetric type IV burst and its associated FSs (fibers) in the range 1.0–2.0 GHz appeared after 10:40 UT.