Volterra series transfer function of single-mode fibers

A nonrecursive Volterra series transfer function (VSTF) approach for solving the nonlinear Schrodinger (NLS) wave equation for a single-mode optical fiber is presented. The derivation of the VSTF is based on expressing the NLS equation In the frequency domain and retaining the most significant terms (Volterra kernels) in the resulting transfer function. Due to its nonrecursive property and closed-form analytic solution, this method can excel as a tool for designing optimal optical communication systems and lumped optical equalizers to compensate for effects such as linear dispersion, fiber nonlinearities and amplified spontaneous emission (ASE) noise from optical amplifiers. We demonstrate that a third-order approximation to the VSTF model compares favorably with the split-step Fourier (recursive) method in accuracy for power levels used in current optical communication systems. For higher power levels, there is a potential for improving the accuracy by including higher-order Volterra kernels at the cost of increased computations. Single-pulse propagation and the interaction between two pulses propagating at two different frequencies are also analyzed with the Volterra method to verify the ability to accurately model nonlinear effects. The analysis can be easily extended to include inter-channel interference in multi-user systems like wavelength-division multiple-access (WDM), time-division multiplexed (TDM), or code-division multiplexed (CDM) systems     

An Efficient Approach for Large-Signal Modeling and Analysis of the GaAs MESFET

A nonlinear circuit model of the GaAs MESFET is developed by extracting circuit parameters from dc and small-signal RF measurements in a systematic manner. The circuit model is then analyzed by an efficient algorithm called the modified multiple-reflection method. For the first time, this method is applied to MESFET circuit analysis. Compared with the original multiple-reflection method, the modified multiple-reflection method shows a dramatic increase in convergence speed. The validity of the nonlinear MESFET model is confirmed by comparing the simulation results with experimental data.     

Minimax design of two-dimensional parallelogram filter banks

The authors present a technique for the minimax design of two-dimensional (2-D) parallelogram filter bank (PFB) systems with linear-phase analysis/synthesis filters. To achieve perfect reconstruction, the required analysis filters must have parallelogram-shaped frequency responses. In general, the original design problem is found to be an optimisation problem with nonlinear constraints. The authors present a linearisation approach to reformulate the design problem. As a result, updating the filter coefficient vector at each iteration for the original design problem can be accomplished by searching the gradient of the linearised optimisation problem. They further present an efficient method based on a modified Karmarkar's algorithm for computing the required gradient vector and finding the required step size analytically. Therefore the filter coefficients can easily be computed by solving only linear equations at each iteration during the design process. The effectiveness of the proposed technique is shown by computer simulations     

Stabilizing unstable equilibria of chaotic systems from a State observer approach

In this paper, a simple control method is proposed for stabilizing unstable equilibria of two typical classes of chaotic systems. For piecewise-linear chaotic systems, such as Chua's circuit, the control parameters can be selected via the pole placement technique from the linear control theory. For general nonlinear chaotic systems with continuously differentiable nonlinearities, particularly polynomial chaotic systems such as the Ro/spl uml/ssler system, Lorenz system, Chen's system, and the modified Chua's circuit with cubic nonlinearity, the control parameters can be chosen according to the pole placement technique and some additional theories of nonlinear ordinary differential equations. The criteria for the design of the control parameters are also investigated. This method is demonstrated to be highly robust against system parametric variations. To verify the effectiveness of the method, it is applied to both the original and the modified chaotic Chua's circuits, where satisfactory control performance is observed in simulations.     

Reliability optimization of systems by a surrogate-constraintsalgorithm

A method for solving the problem of optimizing both, redundancy (number of redundant components) and component reliability in each stage of a system under multiple constraints is presented. A mixed-integer nonlinear programming formulation and the surrogate dual method are used. The solution of the surrogate dual problem is not always feasible in the original problem, that is, a `surrogate gap' exists. Two countermeasures to surrogate gaps are considered: (1) modifying the original problem to tighten the constraints, with the modification being continued until the solution of the surrogate dual problem of the modified problem becomes feasible in the original problem, and (2) decreasing component reliabilities in the vertical direction to the tangential plane of the objective function. The method applies to reliability optimization problems for general systems, enabling complex systems such as communication networks to be treated. Some computational results are shown and compared with other approaches; they show the efficiency of the method     

A control method for a nonlinear multivariable system: applicationto interstitial laser hyperthermia

An original adaptive control method is presented for controlling a nonlinear multivariable system. The method, which could be described as a modified quasi-linear approach, involves dividing the source excitation into a series of pulsing rounds and is implemented as a control algorithm on a computer. The theory underlying the method is developed with reference to an application involving temperature control in interstitial laser hyperthermia. In this application, the method is both successful and necessary to achieve optimally uniform elevated temperatures in a ground beef phantom. Apart from variable and parameter definitions, the method is otherwise general and might be useful for controlling a nonlinear system in which no prior exact characterization of the system is possible. Simulations were conducted to assess the effectiveness of the method in systems for which the unit excitation response changes by factors ranging from zero to three over the total period of excitation. In each case the method has proven stable.     

信息安全风险评估中权重优化方法研究

论文提出了一种新的提高层次分析法(AHP)判断矩阵一致性的新方法,即通过逐步修改判断矩阵中的一对元素,并利用通用的一致性检验方法,使一致性得到不断改进,并将此方法用于信息安全风险评估中,使评估结果更科学、合理。最后辅以实例说明。     

一种基于混沌系统的数字水印方法

文中提出了一种基于混沌系统的数字水印方法,该方法在水印嵌入时将原始图像的中频系数与混沌序列相加,并将取模后的结果用于混沌动力学的迭代。在水印嵌入过程中引入的取模非线性变换使得所产生的水印信号与原来的混沌信号大不相同,同时原始混沌水印序列的周期加长,可以克服有限字长效应的影响,从而进一步技术安全性。理论分析及仿真结果表明,该方法在水印提取过程中不需要原始图像,简单易行,具有较好的鲁棒性。     

用改进的非线性电流源法分析微波振荡器的稳态响应

本文提出用改进的非线性电流源法和振荡器的振荡条件相结合,进行微波FET振荡器非线性分析的方法.非线性电流源法已经被证明为分析微波振荡器的一种行之有效的方法.但是,当电路中含有多维非线性元件时(例如FET中的I_(d5)(V_(g5),V_(d5)),以往的非线性电流源法就显得无能为力.在此,我们将对非线性电流源法进行改进,并将它运用到微波FET振荡器的非线性分析中.改进的非线性电流源法能够有效地处理含有多维非线性元件电路的分析问题,从而大大提高了非线性电流源法的分析能力和实用性,扩大了其应用范围.     

流体不稳定性实验中条纹相机像场畸变的影响

针对激光惯性约束聚变研究中的流体力学不稳定性问题,分析了X光条纹相机固有的像场畸变对惯性约束聚变研究中瑞利-泰勒不稳定性面向背光实验结果的大范围影响,利用非线性插值、非线性坐标变换及代数方法提出了针对该问题的专门的数据处理方法,并给出了一个在实际实验数据处理中的应用例子。实验表明,该方法能有效消除瑞利-泰勒不稳定性面向背光实验结果中的全局像场畸变影响。该方法结合傅里叶分析技术,较好地还原了扰动界面的真实频谱分布。     

A nonlinear and dispersive APML ABC for the FD-TD methods

We have developed a modified anisotropic perfectly matched layer (APML) absorbing boundary condition (ABC) for the finite-difference time-domain (FD-TD) analysis of nonlinear and dispersive media. The formulation is a simple modification to the original nonsplit APML, and retains the robustness and the simple implementation in the FD-TD and the higher-order schemes. The proposed ABC has a broad area of application, and is especially suitable for the analysis of nonlinear optical waveguide problems.     

Modified nonlinear least square approaches to carrier frequency offset estimation in OFDM systems

Two modified nonlinear least square (NLS) estimators for carrier frequency offset (CFO) in orthogonal frequency-division multiplexing (OFDM) systems are proposed. In the modified NLS CFO estimators, slot elements in an OFDM block symbol are weighted in terms of their received energies. Simulation results show that the proposed new estimators outperform the original one especially in a low signal-to-noise ratio range.     

New modified saleh models for memoryless nonlinear power amplifier behavioural modelling

A new generic modified Saleh (MS) model for use in memoryless nonlinear power amplifier (PA) behavioural modelling is proposed. The model was evolved primarily to overcome some particular weaknesses in the original Saleh model when handling the polar AM-PM envelope modelling. From it new twoparameter MS polar models are derived. By modelling a nearmemoryless LDMOS PA amplifying a WCDMA signal, evidence of the improvement in modelling accuracy and performance of the MS over the original Saleh for both polar and quadrature models is provided.     

Improved Frey Chaotic Digital Encoder for Trellis-Coded Modulation

In this brief, nonlinear digital filters with finite precision are analyzed as recursive systematic convolutional (RSC) encoders. An infinite-impulse-response (IIR) digital filter with finite precision (wordlength of N bits) is a rate-1 RSC encoder over a Galois field GF(2N). The Frey chaotic filter is analyzed for different wordlengths N, and it is demonstrated that the trellis performances can be enhanced by proper filter design. Therefore, a modified definition for the encoding rate is provided, and a trellis design method is proposed for the Frey filter, which consists of reducing the encoding rate from 1 to 1/2. This trellis optimization partially follows Ungerboeck's rules, i.e., increasing the performances of the encoded chaotic transmission in the presence of noise. In fact, it is demonstrated that for the same spectral efficiency, the modified Frey encoder outperforms the original Frey encoder only for N = 2. To show the potential of these nonlinear encoders, it is demonstrated that a particular nonlinear digital filter over GF(4) is equivalent to a GF(2) conventional optimum RSC encoder. The symbol error rate (SER) is estimated for all the proposed schemes, and the results show the expected coding gains as compared to their equivalent nonencoded and linear versions.     

DV-Hop无线网络定位算法研究

针对无线传感器网络定位的DV-Hop定位算法定位精度不足,文中提出了一种改进后的DV-Hop算法。改进后的算法在原基础上引入了均匀量化模型来提高每段跳距的精度和最小二乘法以解决定位过程中造成的累积误差。仿真结果证明,改进后的算法显著的提高了未知节点的定位精度。     

An adaptive sliding-mode controller for discrete nonlinear systems

This paper presents a sliding-mode controller for a class of nonlinear discrete-time systems. The proposed controller uses a modified switching function that produces a low-chattering control signal. In order to improve the controller performance, an adaptive term is added to the original sliding-mode algorithm. This new feature uses an artificial neural network for online identification of the modeling error. Simulations and experimental results illustrate the main characteristics and performance of this approach,     

Some Properties of an Empirical Mode Type Signal Decomposition Algorithm

The empirical mode decomposition (EMD) has seen widespread use for analysis of nonlinear and nonstationary time-series. Despite some practical success, it lacks a firm theoretical foundation. This work addresses two important theoretical properties. The original EMD algorithm is slightly modified, in a way that facilitates this analysis. For periodic, band-limited, signals the convergence and time scale separation of the algorithm are proved.     

A weighted least squares approach to the design of FIR filters synthesized using the modified frequency response masking structure

This paper presents an application of the weighted least squares (WLS) method to the design of sharp linear phase finite-impulse response (FIR) digital filters synthesized using a modified frequency-response masking (FRM) structure. In our approach, the original minimax design problem is converted into a WLS problem. The WLS problem is highly nonlinear with respect to the coefficients of the filter. However, it can be decomposed into four linear least squares (LS) problems, each of which can be solved analytically. The design problem is then solved iteratively by using an alternating variable approach. The effectiveness of the method is demonstrated through solving a low-pass linear phase sharp FIR digital filter example.     

Harmonic Minimization in Multilevel Inverters Using Modified Species-Based Particle Swarm Optimization

Harmonic minimization in multilevel inverters is a complex optimization problem that involves nonlinear transcendental equations having multiple local minima. In this paper, a solution to the harmonic minimization problem using a novel particle swarm optimization (PSO) approach based on species-based PSO (SPSO) is presented. The original SPSO is modified, which increased the robustness of algorithm to find global optimum of the search space. The proposed method is able to find the optimum switching angles when their number is increased, while it is not possible to determine them using either conventional iterative techniques or resultant theory method. Theoretical results are verified by experiments and simulations for an 11-level H-bridge inverter. Results show that the proposed method effectively minimizes a large number of specific harmonics, and the output voltage results in very low total harmonic distortion and switching frequency.      

A reliability-driven placement procedure based on thermal-force model

This paper deals with placing chips on an MCM substrate in chip array style for minimizing the system failure rate. The placement procedure begins with constructing an initial placement based on cooling considerations. Then, a thermal-force model is presented to transform the reliability-driven placement problem to solve a set of simultaneous nonlinear equations to determine thermal-force-equilibrium locations of the chips. A modified Newton–Raphson method is used to solve this system of equations. Finally, a chip assignment procedure transforms the thermal-force-equilibrium placement into an array style placement for minimum thermal distortion. Two assignment methods are developed and compared each other. Experiments on three industrial MCMs designed by IBM show that the obtained placements have significant improvements to their original designs in system reliability. Additionally, a simulated annealing approach is presented for justifying the performance of the proposed method.