Showing papers by "Xidian University published in 2004"

Elementary siphons of Petri nets and their application to deadlock prevention in flexible manufacturing systems

Abstract: A variety of important Petri net-based methods to prevent deadlocks arising in flexible manufacturing systems (FMS) are to add some control places and related arcs to strict minimal siphons (SMS) such that no siphon can be emptied. Since the number of minimal siphons grows in general exponentially with respect to a Petri net size, their disadvantages lie in that they often add too many additional places to the net, thereby making the resulting net model much more complex than the original one. This paper explores ways to minimize the new additions of places while achieving the same control purpose. It proposes for the first time the concept of elementary siphons that are a special class of siphons. The set of elementary siphons in a Petri net is generally a proper subset of the set of all SMS. Its smaller cardinality becomes evident in large Petri net models. This paper proves that by adding a control place for each elementary siphon to make sure that it is marked, deadlock can be successfully prevented. Compared with the existing methods, the new method requires a much smaller number of control places and, therefore, is suitable for large-scale Petri nets. An FMS example is used to illustrate the proposed concepts and policy, and show the significant advantage over the previous methods.

Wavelet support vector machine

Abstract: An admissible support vector (SV) kernel (the wavelet kernel), by which we can construct a wavelet support vector machine (SVM), is presented. The wavelet kernel is a kind of multidimensional wavelet function that can approximate arbitrary nonlinear functions. The existence of wavelet kernels is proven by results of theoretic analysis. Computer simulations show the feasibility and validity of wavelet support vector machines (WSVMs) in regression and pattern recognition.

A multiagent genetic algorithm for global numerical optimization

Abstract: In this paper, multiagent systems and genetic algorithms are integrated to form a new algorithm, multiagent genetic algorithm (MAGA), for solving the global numerical optimization problem. An agent in MAGA represents a candidate solution to the optimization problem in hand. All agents live in a latticelike environment, with each agent fixed on a lattice-point. In order to increase energies, they compete or cooperate with their neighbors, and they can also use knowledge. Making use of these agent-agent interactions, MAGA realizes the purpose of minimizing the objective function value. Theoretical analyzes show that MAGA converges to the global optimum. In the first part of the experiments, ten benchmark functions are used to test the performance of MAGA, and the scalability of MAGA along the problem dimension is studied with great care. The results show that MAGA achieves a good performance when the dimensions are increased from 20-10,000. Moreover, even when the dimensions are increased to as high as 10,000, MAGA still can find high quality solutions at a low computational cost. Therefore, MAGA has good scalability and is a competent algorithm for solving high dimensional optimization problems. To the best of our knowledge, no researchers have ever optimized the functions with 10,000 dimensions by means of evolution. In the second part of the experiments, MAGA is applied to a practical case, the approximation of linear systems, with a satisfactory result.

A new authentication scheme with anonymity for wireless environments

Abstract: Wireless network is susceptible to security attacks because its openness of transmission media. Wireless network security is somewhat more concentrated and complex than that of wired network. Authentication is the most essential procedure to ensure that the service is properly used. But its limited resource, such as weak power supplies and limited bandwidth, must be taken into account in the design of security schemes. In this paper, we present a new and efficient wireless authentication protocol providing user anonymity. Our scheme is based on the hash function and smart cards, and mobile users only do symmetric encryption and decryption. In our protocol, it takes only one round of message exchange between the mobile user and the visited network, and one round of message exchange between the visited network and the corresponding home network. The most significant feature is one-time use of key between mobile user and visited network. Finally, the performance of our scheme is analyzed.

A quantum particle swarm optimization

Abstract: The particle swarm optimization algorithm is a new methodology in evolutionary computation. It has been found to be extremely effective is solving a wide range of engineering problems, however, it is of low efficiency in dealing with the discrete problems. In this paper, a new discrete particle swarm optimization algorithm based on quantum individual is proposed. It is simpler and more powerful than the algorithms available. The simulation experiments and its application in the CDMA also prove its high efficiency.

Disturbance-rejection high-precision motion control of a Stewart platform

Abstract: A simple robust autodisturbance rejection controller (ADRC) in linkspace is proposed to realize high precision tracking control of a general 6 degrees of freedom (DOF) Stewart platform in this paper. In practice, the performance of the controlled system is limited by how to select the high-quality differential signal in the presence of disturbances and measurement noise. Moreover, unmodeled nonlinear friction provides degradation on the motion precision. So, a nonlinear tracking differentiator in the feedforward path and an extended states observer in the feedback path are designed to obtain high quality differential signal and the real action component of unknown disturbance signals including nonlinear friction without a precise mathematical model. The nonlinear PD (proportional derivative) controller is used to synthesize the control action to give a superior performance. Extensive simulations and experimental results are presented to verify the effectiveness and ease of engineering implementation of the proposed method. The developed ADRC controller is simple and directly intuitive to the practitioners.

Migration through resolution cell compensation in ISAR imaging

Abstract: Range-Doppler (RD) processing is widely used in conventional inverse synthetic aperture radar (ISAR) imaging. The unwanted translational motion of moving targets is compensated by envelope alignment and autofocus. For existing ISAR imaging algorithms, the scatterers' migration through resolution cells (MTRC) caused by the rotational motion is usually ignored. With the improvement of resolution or the increase of target size, MTRC cannot be neglected. In this letter, the keystone formatting algorithm developed in SAR is used for the MTRC compensation in ISAR. Before the keystone formatting, coherent processing must be performed on the raw phase history data. An effective approach is proposed for this kind of coherent processing. Numerical examples are provided to demonstrate the performance of the proposed approach.

A survey of ionospheric effects on space-based radar

Abstract: In this survey, we fully review almost all potential ionospheric effects on the performance of space-based radar systems (SBRs), which operate in the ambient ionosphere environment; in particular, we review the use of space-based synthetic aperture radar systems (SARs) for imaging. There are two families of effects involved. One is the effects of the background ionosphere (non-turbulent ionosphere), such as dispersion, group delay, refraction, Faraday rotation, and phase shift. The other is the effects due to ionospheric irregularities, such as refractive index fluctuation, phase perturbation, angle-of-arrival fluctuation, pulse broadening, clutter, and amplitude scintillation. These effects adversely affect SAR imaging in several respects, such as by causing image shift in the range, and degradations of the range resolution, azimuthal resolution, and/or the resolution in height (elevation). We also review ionospheric irregularity characteristics and descriptions, propagation channel statistics, ...

Nonlinear PID control of a six-DOF parallel manipulator

Abstract: A nonlinear proportional integral derivative (N-PID) algorithm in linkspace is proposed to realise high precision tracking control of a general six-DOF parallel manipulator. In practice, the performance of the controlled system is limited by how to pick out the differential signals of the noncontinuous measured signals with stochastic noise. Therefore, the developed N-PID controller uses two nonlinear tracking differentiators to yield high quality differential signals in the presence of disturbances and measurement noise. A nonlinear combination of proportional, integral and derivative action on the control error is used to synthesise the control law for enhanced performance in areas such as increased damping and reduced tracking error. Experimental results indicate that the nonlinear control method is easy for the engineer to implemente and achieves a superior performance.

Microscopic spin-Hamiltonian parameters and crystal field energy levels for the low C3 symmetry Ni2+ centre in LiNbO3 crystals

Abstract: The microscopic spin-Hamiltonian (MSH) parameters and the crystal field (CF) energy levels for Ni2+ ions in LiNbO3 crystals have been investigated using the crystal field analysis/microscopic spin-Hamiltonian package recently developed. The investigations considered for the first time the spin–spin (SS) and spin-other-orbit (SOO) interactions. The low-symmetry effects (LSE) arising from the additional terms (Im(B43)≠0) induced at the C3 symmetry sites by the distortion angle ϕ, which have been omitted in earlier works, have also been dealt with. This study shows that for LiNbO 3 : Ni 2+ the contributions arising from SS and SOO interactions to the zero-field splitting parameter D are appreciable, whereas those to g|| and g⊥ are quite small. Since the distortion angle ϕ (≅0.68°) for LiNbO 3 : Ni 2+ is rather small, the contributions to the spin-Hamiltonian (SH) parameters arising from LSE are also small. Feasibility of application of the superposition model is also discussed. A good overall agreement between the theoretical and experimental results for the SH parameters and the CF energy levels has been obtained.

An effective dynamic coarse model for optimization design of LTCC RF circuits with aggressive space mapping

Abstract: A new concept called the dynamic coarse model is proposed and is applied to the optimization design of low-temperature co-fired ceramic (LTCC) multilayer RF circuits with the aggressive space mapping (ASM) technique. The dynamic coarse model is a combination of an evolutionary equivalent-circuit model and an efficient quasi-static numerical electromagnetic (EM) model-partial-element equivalent-circuit model. Namely, there are two forms of coarse models jointly in use: the coarse schematic model and the coarse EM model. The coarse schematic model evolutionarily incorporates parasitic effects that can be extracted from its accompanying coarse EM model. This process can greatly facilitate the original ASM process by easily determining a "high-quality" optimized coarse model. Two LTCC frequency-selective passive modules, i.e., a bandpass filter and a diplexer, are designed using the proposed scheme and ASM. No nonuniqueness in parameter extraction is encountered. Good convergence performance is achieved for the designs of both modules.

A soft decision decoding scheme for wireless COFDM with application to DVB-T

Abstract: This paper investigates the soft decision decoding techniques for wireless COFDM systems. A new method to estimate the channel state information (CSI) for the Viterbi decoder is proposed, which overcomes the problem of reliability metric of transmitted signals in wireless as well as mobile channels. The CSI for each subcarrier is calculated as a properly defined squared Euclidean distance. On the basis of which, a soft decision decoding scheme to improve reception performance under multipath fading interference and co-channel interference (CCI) from existing analog broadcasting signals is also proposed. The simulation results show that the scheme can provide a compatible improvement to the terrestrial digital video broadcasting (DVB-T) system. The proposed scheme is also suitable for other wireless COFDM transmission systems.

A novel wideband coplanar-fed monopole antenna

Abstract: A new T-shaped monopole antenna with a CPW feed line is presented. The theoretical analysis is based on the finite-difference time-domain (FDTD) method. The novel antenna is designed, fabricated, and then measured. The measured results, which agree with the numerical calculations very well, are given. The measured bandwidth of the antenna is approximately 116% for VSWR ≤ 2.0. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 43: 50–52, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.20372

Theoretical investigations of the microscopic spin Hamiltonian parameters including the spin–spin and spin–other-orbit interactions for Ni2+(3d8) ions in trigonal crystal fields

Abstract: The microscopic origin of the spin Hamiltonian (SH) parameters for Ni2+(3d8) ions in a trigonal type I symmetry (C3v,D3d,D3) crystal field (CF) is studied. In addition to the spin–orbit (SO) interaction, we consider also the spin–spin (SS) and spin–other-orbit (SOO) interactions. The relative importance of the four (SO, SS, SOO, and combined SO–SS–SOO) contributions to the SH parameters is investigated using the CFA/MSH package and the complete diagonalization method (CDM). The SO mechanism is dominant for all CF parameter (CFP) ranges studied, except where the contributions DSO to the zero-field splitting (ZFS) parameter D change sign. For the trigonal CFP, due to the other three mechanisms exceeds DSO. Although |DSOO| is quite small, the combined |DSO−SOO| is appreciable. The SO-based perturbation theory (PT) works generally well for the g-factors: and , while it fails for D in the vicinity of vc and for large and v>0. The high percentage discrepancy ratio δD = 2020% for vc indicates unreliability of DSO (in PT). Applications to Ni2+ ions at trigonal symmetry sites in LiNbO3, α-LiIO3, and Al2O3, are provided. The theoretical SH parameters are in good agreement with the experimental data. The low symmetry (C3) effects induced by the angle are tentatively studied, but appear to be quite small.

Generalized self-shrinking generator

Abstract: In this correspondence, we present a simple bit-stream generator. It is a specialization of shrinking generator and a generalization of self-shrinking generator. We call it "generalized self-shrinking generator." The family of such generated sequences has a group structure. The correlation between the sequences is quite good and the sequences themselves are balanced. For each k, 0

A fast recursive total least squares algorithm for adaptive FIR filtering

Abstract: This paper proposes a new fast recursive total least squares (N-RTLS) algorithm to recursively compute the TLS solution for adaptive finite impulse response (FIR) filtering. The N-RTLS algorithm is based on the minimization of the constrained Rayleigh quotient (c-RQ) in which the last entry of the parameter vector is constrained to the negative one. As analysis results on the convergence of the proposed algorithm, we study the properties of the stationary points of the c-RQ. The high computational efficiency of the new algorithm depends on the efficient computation of the fast gain vector (FGV) and the adaptation of the c-RQ. Since the last entry of the parameter vector in the c-RQ has been fixed as the negative one, a minimum point of the c-RQ is searched only along the input data vector, and a more efficient N-RTLS algorithm is obtained by using the FGV. As compared with Davila's RTLS algorithms, the N-RTLS algorithm saves the 6M number of multiplies, divides, and square roots (MADs). The global convergence of the new algorithm is studied by LaSalle's invariance principle. The performances of the relevant algorithms are compared via simulations, and the long-term numerical stability of the N-RTLS algorithm is verified.

A novel quantum evolutionary algorithm and its application

Abstract: In this paper, an algorithm - the quantum evolutionary algorithm (QEA) is introduced. It is characterized by a representation of quantum chromosomes, quantum mutation and quantum crossover. Its advantages lies on better diversity of individuals, effective guidance of mutation and the avoidance of prematurity by crossover. Some simulations are given to illustrate its efficiency and better performance than its counterpart. Finally, we applied it to the multi-user detection in DS-CDMA, and good results are attained.

A framed temporal logic programming language

Abstract: We discuss the projection temporal logic (PTL), based on a primitive projection operator, prj. A framing technique is also presented, using which a synchronization operator, await, is defined within the underlying logic. A framed temporal logic programming language (FTLL) is presented. To illustrate how to use both the language and framing technique, some examples are given.

Symbol synchronization technique in COFDM systems

Abstract: In this paper we focus our research on the symbol timing synchronization technique in COFDM systems. A new method utilizing pilots to do coarse symbol timing is proposed. It overcomes the problem of fluctuation of the estimated symbol start position with cyclic prefix correlation method. The symbol timing error with the proposed method is within only /spl plusmn/10 samples. Different from previous algorithms in , we utilize the known pilot information to estimate the residual symbol timing offset with low system complexity. This paper also proposes a new control model for the sampling clock adjustment, different from the phase-locked loop (PLL), or delay-locked loop (DLL) method. The simulation and correspondent Field Programmable Gate Array (FPGA) circuit through test in HDTV prototype in Team of Engineering Expert Group (TEEG) proves its feasibility and availability. The proposed method is also suitable for burst mode transmission systems such as Wireless Local Area Network (WLAN) and Fixed-Broadband Wireless Access (F-BWA).

Automatic parameters selection for SVM based on GA

Abstract: Motivated by the fact that automatic parameter selection for support vector machines (SVM) is an important issue in order to make the SVM practically useful against the commonly used leave-one-out (loo) method, which has complex calculation and time consuming An effective strategy for automatic parameter selection for SVM is proposed by using the genetic algorithm (GA) in this paper Simulation results of the practice data model demonstrate the effectiveness and high efficiency of the proposed approach

Hidden space support vector machines

Abstract: Hidden space support vector machines (HSSVMs) are presented in this paper. The input patterns are mapped into a high-dimensional hidden space by a set of hidden nonlinear functions and then the structural risk is introduced into the hidden space to construct HSSVMs. Moreover, the conditions for the nonlinear kernel function in HSSVMs are more relaxed, and even differentiability is not required. Compared with support vector machines (SVMs), HSSVMs can adopt more kinds of kernel functions because the positive definite property of the kernel function is not a necessary condition. The performance of HSSVMs for pattern recognition and regression estimation is also analyzed. Experiments on artificial and real-world domains confirm the feasibility and the validity of our algorithms.

Study of modulation recognition based on HOCs and SVM

Abstract: The paper presents a new algorithm for modulation recognition of digital communication signals based on higher order cumulants (HOCs) and support vector machines (SVM). The fourth and sixth order cumulants of the received signal are used as the input classification feature vector to the SVM. The SVM maps the input vectors nonlinearly into a high dimensional feature space, constructs the optimum separating hyperplane in that space and makes the non-separable data separable. This method is robust to Gaussian noise and constellation rotation due to the initial phase of the signal and avoids the overfitting and local minimum in a neural network. The high performance and robustness of the algorithms are proved by computer simulation.

Adaptive blind separation with an unknown number of sources

Abstract: The blind source separation (BSS) problem with an unknown number of sources is an important practical issue that is usually skipped by assuming that the source number n is known and equal to the number m of sensors. This letter studies the general BSS problem satisfying m ≥ n. First, it is shown that the mutual information of outputs of the separation network is a cost function for BSS, provided that the mixing matrix is of full column rank and the m × m separating matrix is nonsingular. The mutual information reaches its local minima at the separation points, where the m outputs consist of n desired source signals and m-n redundant signals. Second, it is proved that the natural gradient algorithm proposed primarily for complete BSS (m=n) can be generalized to deal with the overdetermined BSS problem (m>n), but it would diverge inevitably due to lack of a stationary point. To overcome this shortcoming, we present a modified algorithm, which can perform BSS steadily and provide the desired source signals at specified channels if some matrix is designed properly. Finally, the validity of the proposed algorithm is confirmed by computer simulations on artificially synthesized data.

Signal de-noising in wavelet domain based on a new kind of thresholding function

Abstract: A novel thresholding function is presented based on the wavelet shrinkage put forward by D.L.Donoho and I.M.Johnstone. This new thresholding function has many advantages over DJ's soft- and hard-thresholding function. It is simple in expression and as continuous as the soft-thresholding function, and has a high order derivative which makes convenient some kinds of mathematical disposals. It also overcomes the shortcoming that there is an invariable dispersion between the estimated wavelet coefficients and the decomposed wavelet coefficients of the soft-thresholding method. At the same time, the new thresholding function is more elastic than the soft- and hard-thresholding function. All these advantages make it possible to construct an adaptive denoising algorithm. Simulation results indicate that the de-noising method adopting the new thresholding function suppresses the Pseudo-Gibbs phenomena near the singularities of the signal effectively, and the numerical results also show the new method gives better MSE performance and SNR gains than DJ's hard- and soft-thresholding methods.

Enhancement of QoS differentiation over IEEE 802.11 WLAN

Abstract: IQD, a distributed coordination function (DCF) with integrated quality of service (QoS) differentiation, is proposed in this letter to enhance QoS over IEEE 802.11 WLAN. DCF does not support any QoS differentiation. Enhanced DCF (EDCF) only supports delay differentiation. IQD can achieve both delay and packet-loss-rate differentiation by differentiating the initial window size and the retry limit. Simulation results show that IQD performs better than DCF and EDCF in enhancing QoS, and the proposed analytical model is valid.

Convertible Nominative Signatures

Abstract: A feasible solution to prevent potential misuse of signatures is to put some restrictions on their verification Therefore SJKim, [4] SJPark and DHWon introduced the nominative signature, in which only the nominee can verify and prove the validity of given signatures, and proposed a nominative signature scheme (called KPW scheme) In this paper, we first show that KPW scheme is not nominative because the nominator can also verify and prove the validity of given signatures Then we extend the concept of nominative signature to the convertible nominative signature which has an additional property that the nominee can convert given nominative signatures into universally verifiable signatures We give a formal definition for it and propose a practical scheme that implements it The proposed scheme is secure, in which its unforgeability is the same as that of the Schnorr’s signature scheme and its untransferability relies on the hardness of the Decision-Diffie-Hellman Problem

T-matrix and its applications in image processing

Abstract: A T-matrix used for image scrambling is proposed and its periodicity is proved. The T-matrix has a simple conformation and a period twice as long as the Arnold matrix. It can be applied to image encryption and pre-processing in image processing such as image watermarking algorithms. Two examples of applications are given.

Signcryption based on elliptic curve and its multi-party schemes

Abstract: A new signcryption based on elliptic curve cryptosystems that combines ECDSA and PSCE-1 is presented. The signcryption scheme is a publicly verifiable scheme which can be verified by the third party after the specific recipient removes his key information. Analysis shows that the proposed scheme is secure against the adaptive chosen ciphertext attack. The signcryption saves the communication cost at least 1.25 times and enhances computation cost 1.19 times over ECDSA-then-PSCE-1. Compared with other signcryption schemes, such as Y. Zheng's ECSCS, the new signcryption uses a uniform elliptic curve cryptosystem platform instead of four kinds of cryptosystem components: hash function, keyed hash function, symmetric cipher and elliptic curve. While keeping high security and efficiency, the scheme can be implemented in software and hardware at low price because of above advantages. Based on the presented signcryption, a broadcast scheme for multiple recipients and a threshold scheme with Key Distributed Generation for multiple senders are also proposed.

Maximum likelihood method for integer frequency offset estimation of OFDM systems

Abstract: A novel method for integer frequency offset estimation of OFDM systems is derived, which is based on the maximum likelihood (ML) technique and exploits the differential information between two consecutive blocks of OFDM data symbols in the frequency domain. The reason why the proposed ML method has better performance than the conventional method is analysed.