Showing papers by "Xidian University published in 1996"
TL;DR: In this paper, the generalized marginal integration along straight lines with varying slopes is calculated over the time-frequency plane, instead of the traditional uniformly rotating model, which produces smeared images.
Abstract: Range-Doppler imaging is the basic method of inverse syn- thetic aperture radar, which is based on the uniform rotation of targets. Nonuniform rotation can occur to maneuvering targets, which produces smeared images. A constantly acceleratively rotating model is used here instead of the traditional uniformly rotating model. The generalized mar- ginal integration along straight lines with varying slopes is calculated over the time-frequency plane. The imaging quality is improved by using the new method. © 1996 Society of Photo-Optical Instrumentation Engineers. Subject terms: inverse synthetic aperture radar; time-frequency distribution.
39 citations
TL;DR: A silicon-on insulator (SOI) zero-gap directional coupler switch is studied based on the large-cross-section singlemode rib waveguide condition, the dual-mode interference principle, and the free-carrier plasma dispersion effect.
Abstract: A silicon-on insulator (SOI) zero-gap directional coupler switch is studied based on the large-cross-section singlemode rib waveguide condition, the dual-mode interference principle, and the free-carrier plasma dispersion effect, in which the SOI technique uses silicon and silicon dioxide thermal bonding and backpolishing. The SOI is fabricated by potassium hydroxide anisotropic etching. Its insertion loss and cross talk are measured to be less than 4.81 dB and 218.6 dB, respectively, at a wavelength of 1.3 microm and a switching voltage of 0.91 V. Response time is ~210 ns.
39 citations
TL;DR: It is shown from theoretical analysis and experimental results which were obtained with data acquired in a microwave anechoic chamber that the method proposed in this paper offers promise for target recognition.
35 citations
TL;DR: A wavelet transform based analogue speech scrambling scheme is presented and analyses and simulation results indicate that scrambled speech is highly secure in both the time and frequency domains.
Abstract: A wavelet transform based analogue speech scrambling scheme is presented. The proposed scheme offers 2-D scrambling. Related analyses and simulation results indicate that scrambled speech is highly secure in both the time and frequency domains.
34 citations
TL;DR: In this paper, a method is proposed to precisely control the peak (rather than average) sidelobe level of adaptive array patterns, which is also generalized to adaptive array antennas with moderate bandwidth and large random amplitude and phase errors.
Abstract: Adaptive beamforming techniques are now widely used to reject interference (jammer/clutter) signals in radar, communication, and sonar applications. In adaptive arrays using the sample matrix inversion (SMI) algorithm, inadequate estimation of the covariance matrix results in adaptive antenna patterns with high sidelobes and distorted mainbeams. In this paper, a method is proposed to precisely control the peak (rather than average) sidelobe level of adaptive array patterns. The proposed method is also generalized to adaptive array antennas with moderate bandwidth and large random amplitude and phase errors. Theoretical analysis and simulation results are provided to illustrate the performance of the method proposed.
33 citations
TL;DR: In this paper, an atmospheric pressure chemical vapor deposition (APCVD) technique is used to prepare gas-sensing α-Fe 2 O 3 thin films, which are then deposited successfully onto alumina substrates.
Abstract: There has been considerable interest in recent years in thin film gas-sensing materials. In comparison with conventional sintered bulk gas sensors, thin film gas-sensing materials have good sensitivity, optimum operating temperature and selectivity. Therefore, it is attractive to prepare thin film gas sensors so as to improve the characteristics of commercialized sintered body gas sensors. In addition, sensors based on thin film gas-sensing materials are essential to the development and fabrication of ‘integrated gas sensors’. Up to now, there seem to have been very few papers on the preparation and gas-sensing properties of α-Fe 2 O 3 thin films. In this paper, an atmospheric pressure chemical vapor deposition (APCVD) technique is used to prepare gas-sensing α-Fe 2 O 3 thin films. The ultrafine particle α-Fe 2 O 3 films are deposited successfully onto alumina substrates. The films are characterized by X-ray diffraction and scanning electron microscopies (SEM), and the effects of process conditions on the average grain size are also investigated. Experiments show that the ultrafine particle α-Fe 2 O 3 films made by APCVD exhibit a high sensitivity of 96% at 250°C to grade 12 smoke and a good selectivity for detecting smoke in the presence of alcohol (C 2 H 5 OH), liquified petroleum gas (LPG), methane (CH 4 ), and hydrogen (H 2 ).
30 citations
TL;DR: In this paper, a technique for the synthesis of fractal radiation patterns from concentric-ring arrays has been developed for the first time, using a family of functions known as generalised Weierstrass functions.
Abstract: A technique has been developed for the synthesis of fractal radiation patterns from concentric-ring arrays. A family of functions known as generalised Weierstrass functions, have been shown to play a key role in the theory of fractal radiation pattern synthesis. The authors examine the self-similarity relation of the array patterns.
20 citations
08 Oct 1996
TL;DR: The clutter rejection performance of the HSTAP method is superior to conventional cascaded space-time processing (CST), which is verified by computer simulations.
Abstract: This paper overviews reduced rank space-time adaptive processing (STAP) for clutter suppression in airborne early warning (AEW) radars. A new hybrid low dimensional STAP (HSTAP) approach without high implementation cost is also discussed by assigning reasonably the number of system degrees of freedom (DOFs) between the spatial and temporal domains. The clutter rejection performance of the HSTAP method is superior to conventional cascaded space-time processing (CST), which is verified by computer simulations.
12 citations
TL;DR: A silicon-on-insulator (SOI) optical intensity modulator has been proposed and fabricated, and is based on the large cross-section singlemode rib waveguide condition, the waveguide vanishing effect and the free-carrier plasma dispersion effect as mentioned in this paper.
Abstract: A silicon-on-insulator (SOI) optical intensity modulator has been proposed and fabricated, and is based on the large cross-section singlemode rib waveguide condition, the waveguide-vanishing effect and the free-carrier plasma dispersion effect. In the modulator the SOI technique uses silicon and silicon dioxide thermal bonding and back-polishing. The insertion loss of the device is measured to be 3.65 dB at a wavelength of 1.3 µm. The modulation depth is 96% at an injection current of 45 mA. Response time is ~160 ns.
11 citations
14 Oct 1996
TL;DR: A novel image coding method using the visual entropy (VE)-based classification of image blocks and classified bath fractal transform (CBFT) algorithm, VECBFT, is proposed, which allows the decoded images to keep a good subjective quality with some improvements of the compression performance.
Abstract: A novel image coding method using the visual entropy (VE)-based classification of image blocks and classified bath fractal transform (CBFT) algorithm, VECBFT, is proposed. At first the VE is introduced conceptually and the implementation of VE-based classification of image blocks is presented. Secondly, the CBFT is described generally. Finally, a combination of the VE and CBFT generates a new algorithm-VECBFT, which allows the decoded images to keep a good subjective quality with some improvements of the compression performance. The VECBFT can be an attempt to integrate human visual system (HVS) into an adaptive algorithm for image compression.
9 citations
18 Nov 1996
TL;DR: A new decision-directed (NDD) algorithm based on a new cost function is proposed for equalization of QAM channels that can accomplish blind equalization and carrier phase recovery simultaneously and can achieve faster convergence speed and small residual ISI.
Abstract: A new decision-directed (NDD) algorithm based on a new cost function is proposed for equalization of QAM channels. It can be seen as a variable step-size algorithm of the conventional DD algorithm, whose adaption step-size is changed according to the region in which the equalized signal lies in the constellation plane. The reasonableness of the new decision-directed algorithm is illustrated from the DD algorithm. The new algorithm can accomplish blind equalization and carrier phase recovery simultaneously and can achieve faster convergence speed and small residual ISI. Simulation results confirm the effectiveness of the proposed algorithm.
08 Oct 1996
TL;DR: In this paper, a multilayer feed-forward neural network (MFNN) based classification scheme is presented for radar target identification (RTID) using range profiles offered by the HRR radar.
Abstract: In this paper range profiles offered by the high range resolution (HRR) radar are used as features and a multilayer feedforward neural network (MFNN) based classification scheme is presented for radar target identification (RTID). Typical experimental examples for identifying aircraft-type targets have shown that the range profiles can provide stable feature available for RTID, even in the situation where the change range of observing aspect angle is large. In addition, with a low ratio of learning patterns to test patterns, the trained network has good generalization capability.
TL;DR: In this article, the dynamic reliability of antenna reflector accuracy under wind excitation is studied based on the assumptions that the wind vibration responses of structures are mutually independent Gaussian stationary processes and the cross points of responses with the boundary are approximately submitted to Poisson process.
15 Oct 1996
TL;DR: A user authentication scheme is proposed according to the database structure in the intelligent layer of the PCS that has the following properties: The authentication of mobile users in the visited network is not controlled by its home network, and the traffic load of location update and interrogation is greatly reduced.
Abstract: The logical structure of a personal communication system (PCS) is divided into three layers: intelligent layer, transmission layer and access layer. The authentication of mobile users is realized in the intelligent layer. The database structure of the PCS, different from the existing systems such as GSM and IS-41 etc., is centralized. Therefore the authentication schemes used in existing systems cannot meet the requirement of the PCS. In this paper, a user authentication scheme is proposed according to the database structure in the intelligent layer of the PCS. Compared with the existing authentication schemes, it has the following properties: (1) The authentication of mobile users in the visited network is not controlled by its home network. The traffic load of location update and interrogation is greatly reduced. (2) The authentication protocol adopts a public key/secret key hybrid algorithm. (3) When the data transmission network adopts PSPDN or common channel signaling network, the scheme still has very high security.
14 Oct 1996
TL;DR: A template based fuzzy c-shells (TBFCS) clustering algorithm is proposed that can obtain better clustering performance for any-shell type clusters, so that it is used more widely than the existing FCS algorithms.
Abstract: The fuzzy c-shells (FCS) clustering algorithms are widely applied in pattern recognition and computer vision. However, the available FCS algorithms are valid only for detecting the hyper-spherical-shell or hyper-ellipsoidal-shell type clusters, which limits their applications. In this paper, a template based fuzzy c-shells (TBFCS) clustering algorithm is proposed. Its fast implementation is also given. This approach can obtain better clustering performance for any-shell type clusters, so that it is used more widely than the existing FCS algorithms. The effectiveness of the proposed algorithm is illustrated with experimental results.
08 Oct 1996
TL;DR: A newly 2-D (two dimension) space-time adaptive processing is presented, which is segmented in the range and a recursive algorithm of adaptive weight is presented with considering the real-time implementation and the performance of the processor simultaneously.
Abstract: The non-stationary characteristic of clutter echoes is analyzed in the clutter circumstance of airborne early warning (AEW) radar. A newly 2-D (two dimension) space-time adaptive processing is presented, which is segmented in the range. The segmentation method is determined by analyzing the range of neighboring clutter subspaces. A recursive algorithm of adaptive weight is presented with considering the real-time implementation and the performance of the processor simultaneously. Theoretical analysis and computer simulation results show that the proposed approach is effective.
08 Oct 1996
TL;DR: In this paper, a method of dividing a uniform linear array with identical elements into unequally sized subarrays is proposed based on the principle of designing a density tapering array, where noise power at every subarray output is normalized for partially adaptive processing to obtain near-optimum interference suppression performance with low sidelobe level and distortionless mainlobe in the adapted antenna pattern.
Abstract: A method of dividing a uniform linear array with identical elements into unequally sized subarrays is proposed based on the principle of designing a density tapering array. Noise power at every subarray output is normalized for partially adaptive processing to obtain near-optimum interference suppression performance with low sidelobe level and distortionless mainlobe in the adapted antenna pattern. Unlike regular subarray architectures, irregular subarray architectures may not have a problem with grating lobes. An example of space-time adaptive processing (STAP) for airborne radar systems based on irregular subarrays is given.
05 Jun 1996
TL;DR: In this article, a temperature compensated crystal oscillator (ASCXO) is used to obtain the voltage-time characteristics of sine waveform, which can be translated into V-V relationship.
Abstract: Analog storage (function storage) temperature compensated crystal oscillator (ASCXO) is low in price, simple in structure and high in precision. According to the similarity between cubic curve of crystal oscillator frequency control voltage-temperature sensing voltage and the voltage-time characteristics of sine waveform, the control voltage can be obtained through translating V T characteristics of sine waveform into V-V relationship. With compensation and increment regulation, the temperature compensated curve can be obtained. The test and regulation of the voltage curve are also described. ASCXO has a low demand on the accuracy of the temperature chamber, as is the case in MCXO. In the test process, we utilize measurement instead of control to simplify the equipment. When the temperature of chamber changes slowly the temperature sensing voltage and the frequency modification voltage of the oscillator are measured cyclically. Using a computer some special voltages are recorded and the reference temperature curve is obtained. After a temperature cycle experiment, the storage curve adjustment is done at room temperature. Using coincidence process of the curves the adjustment is completed by computer. One can also find out the accuracy of the oscillator at room temperature. This paper also describes some special demands upon the components. It is easy to obtain 10/sup -7/ or better frequency-temperature stability with ASCXO.
TL;DR: To reduce the dimension of the required networks, as well as to achieve invariancy, six distortion-invariant feature are extracted from each image and are used as inputs to the neural networks.
Abstract: In this paper, a neural networks based approach for distortion invariant image recognition is presented. To reduce the dimension of the required networks, as well as to achieve invariancy, six distortion-invariant feature are extracted from each image and are used as inputs to the neural networks. These six features are derived from the modified geometrical moments of the image, which are calculated through a corrected discrete formula for computing moments more accurately. A multilayer perceptron network trained by the back-propagation algorithm can carry out the classification based on the above features. Experimental results on industrial tools and character recognition are to be given.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
14 Oct 1996
TL;DR: In this article, a modified adaptive wavelet analysis (group-normalized wavelet packet transform (GNWPT)) is presented to correct the drawback that the magnitude of the transform coefficients cannot exactly indicate the strength of the signal components.
Abstract: Through the analysis, remarks on the time-frequency characteristics of wavelets and wavelet packets, and a modified adaptive wavelet analysis (group-normalized wavelet packet transform (GNWPT)) are presented to correct the drawback that the magnitude of the transform coefficients cannot exactly indicate the strength of the signal components. With the time-frequency masking technique, signal extraction and detection from formidable clutter or noises can be carried out well by GNWPT. Besides the choice of linear phased nonorthogonal FIR subband filter banks, the extended l/sup p/-norm entropy presented here improves the performance of GNWPT. A similar method can be applied in image enhancement, clutter and noise suppression, optimal detection and radar imaging.
14 Oct 1996
TL;DR: The main idea of the proposed method accords with procedure of a human's partition process in pattern recognition and experimental results show S2FCM clustering method's effectiveness and advantage.
Abstract: A new effective soft clustering method-sectional set fuzzy C-means (S2FCM) clustering is presented, in which the ideas of traditional "hard" clustering (HCM) and "fuzzy" clustering (FCM) are united and generalized. A effective /spl lambda/ value (/spl lambda//spl isin/~0,1\ is a factor of fuzzy sectional set) of S2FCM is /spl lambda/=0.5+1/2c (c is the total number of clusters). The main idea of the proposed method accords with procedure of a human's partition process in pattern recognition. Experimental results show S2FCM clustering method's effectiveness and advantage.
22 Apr 1996
TL;DR: The authors address the problem of deadlock avoidance by introducing a Petri net controller and prove a necessary and sufficient liveness condition on a PetRI net model.
Abstract: A Petri net model for a class of manufacturing systems is presented. The authors address the problem of deadlock avoidance by introducing a Petri net controller and prove a necessary and sufficient liveness condition on a Petri net model. The authors then present their deadlock avoidance controller and prove that the controlled system with their controller is live. The proposed controller can be realized by a Petri net and the final model of the controlled system is a live Petri net.
07 May 1996
TL;DR: An algorithm for direction finding and array calibration based on the maximal set of nonredundant cumulants (MSNC) is presented, which is insensitive to additive Gaussian noise and superior to conventional covariance-based DOA algorithms with reduced estimation variances and enhanced resolvability.
Abstract: An algorithm for direction finding and array calibration based on the maximal set of nonredundant cumulants (MSNC) is presented in this paper. The algorithm utilizes all nonredundant information of the spatial fourth-order cumulants. It has been shown that the algorithm is insensitive to additive Gaussian noise and superior to conventional covariance-based DOA algorithms with reduced estimation variances and enhanced resolvability. The algorithm also circumvents the iteration between direction finding and array calibration, without the problem of convergence and with improved robustness. Simulation experiments demonstrate the potential performance of the proposed algorithm.
08 Oct 1996
TL;DR: This paper evaluates the performance of partial adaptive space-time adaptive processing approaches based on Doppler prefiltering for inclined sideways looking array (ISLA) airborne radar, in which the angle between the axis of a linear antenna array with that of platform flight is not zero.
Abstract: This paper evaluates the performance of partial adaptive space-time adaptive processing (STAP) approaches based on Doppler prefiltering for inclined sideways looking array (ISLA) airborne radar, in which the angle between the axis of a linear antenna array with that of platform flight is not zero. In ISLA the STAP is more complex than that in a sideways looking array (SLA), which is the particular case that these two axes are identical. After analyzing the characteristics of the clutter spectrum in ISLA, the principle of reduced rank STAP based on prefiltering is proposed and discussed. Also, several computer simulations are presented.
TL;DR: In this paper, a sequence of discrete time Markov decision processes with the criterion of discounted expected total rewards is discussed with the consideration of discounted moment optimality, and the authors transform them into discrete time decision processes.
08 Oct 1996
TL;DR: In this article, a phase-coded compression system with a hard limiter and an integrator possesses naturally of constant false alarm rate (CFAR), however, it is shown by theoretical analysis that the CFAR can not generally be guaranteed for the system.
Abstract: It is taken for granted in engineering that a phase-coded compression system with a hard limiter and an integrator possesses naturally of constant false alarm rate (CFAR). In this paper, however, it is shown by theoretical analysis that the CFAR can not generally be guaranteed for the system. In clutter environments, the CFAR feature of the system is violated due to the correlation of clutter residuals and can be recovered by additional decorrelating processing. The probability distribution of the sum of squares of a number of correlated Gaussian random variables is derived and a necessary and sufficient condition for the CFAR of the system is presented. This can serve as a guideline for radar engineering design. Simulation experiments support the analytical results.
TL;DR: In this paper, a variable-capacitance model for a GaAs MESFET three-terminal varactor applied to MMIC voltage-controlled runing frequency is presented.
Abstract: A variable-capacitance model for a GaAs MESFET three-terminal varactor applied to MMIC voltage-controlled runing frequency is presented. In this model, because the source is connected with the drain, the gate capacitance is only considered by analytical expressions, which are classified into three different regions for gate bias voltage: a before-pinch-off region, an after-pinch-off region, and a transition region. The model also includes the free-carrier movement in the active region, which is a very important contributor to the gate capacitance. The analytical results with the use of this model, compared with the experiment and other models, support the validity of the derived variable-capacitance model. © 1996 John Wiley & Sons, Inc.
TL;DR: In this article, a method to discriminate man-made objects from natural scenes was proposed based on the difference between the fractal properties of the objects and the natural scenes, and experiments were used to demonstrate the good efficiency of the developed technique.
Abstract: Fractional Brownian motion, continuous everywhere and differentiable nowhere, offers a convenient modeling for irregular nonstationary stochastic processes with long-term dependencies and power law behavior of spectrum over wide ranges of frequencies. It shows high correlation at coase scale and varies slightly at fine scale, which is suitable for and successful in describing and modeling natural scenes. On the other hand, man-made objects can be constructively well described by using a set of regular simple shape primitives such as line, cylinder, etc. and are free of fractal. Based on the difference, we provide a method to discriminate man-made objects from natural scenes. Experiments are used to demonstrated the good efficiency of the developed technique.
14 Oct 1996
TL;DR: This paper proposes a word dividing algorithm based on statistical language models and Markov chain theory, which find the optimal word dividing solution without making use of grammatical and semantic knowledge.
Abstract: In Chinese speech processing, word dividing still remains a challenging problem, but it is one of the key problems for Chinese speech understanding, text-to-speech (TTS) systems and vocoders based on speech recognition and synthesis (SRSB vocoders) This paper proposes a word dividing algorithm based on statistical language models and Markov chain theory, which find the optimal word dividing solution without making use of grammatical and semantic knowledge
08 Oct 1996
TL;DR: It is shown by the experimental results that the requirement of a high performance signal processing technique can be fully satisfied by the digital quadrature coherent detector.
Abstract: One of the key problems in high performance radar signal processing is the quadrature coherent detector. It is very difficult for the classical analog quadrature detector to satisfy the requirement of a high performance signal processing technique. The solution of this problem is to use the direct sampling of a low IF signal and generate quadrature samples by a digital filter. The performance of a quadrature IF sampling system based on a digital product detector is analyzed. The scheme is designed and the circuit is implemented by using the INMOS A100. The experimental results are tested. Several important problems about the realization are discussed and analyzed. It is shown by the experimental results that the requirement of a high performance signal processing technique can be fully satisfied by the digital quadrature coherent detector.