Synchronization of general chaotic systems using neural controllers with application to secure communication

The main contribution of this paper is to propose a nonlinear robust controller to synchronize general chaotic systems, such that the controller does not need the information of the chaotic system’s model. Following this purpose, in this paper, two methods are proposed to synchronize general forms of chaotic systems with application in secure communication. The first method uses radial basis function neural network (RBFNN) as a controller. All the parameters of the RBFNN are derived and optimized via particle swarm optimization (PSO) algorithm and genetic algorithm (GA). In order to increase the robustness of the controller, in the second method, an integral term is added to the RBF neural network gives an integral RBFNN (IRBFNN). The coefficients of the integral term and the parameters of IRBFNN are also derived and optimized via PSO and GA. The proposed methods are applied to the famous Lorenz chaotic system for secure communication. The performance and control effort of the proposed methods are compared with the recently proposed PID controller optimized via GA. Simulation results show the superiority of the proposed methods in comparison to the recent one in improving synchronization while using smaller control effort.     

Identification and modeling of nonlinear dynamical systems using a novel self-organizing RBF-based approach

In this paper, a novel self-organizing radial basis function (SORBF) neural network is proposed for nonlinear identification and modeling. The proposed SORBF consists of simultaneous network construction and parameter optimization. It offers two important advantages. First, the hidden neurons in the SORBF neural network can be added or removed, based on the neuron activity and mutual information (MI), to achieve the appropriate network complexity and maintain overall computational efficiency for identification and modeling. Second, the model performance can be significantly improved through the parameter optimization. The proposed parameter-adjustment-based optimization algorithm, utilizing the forward-only computation (FOC) algorithm instead of the traditionally forward-and-backward computation, simplifies neural network training, and thereby significantly reduces computational complexity. Additionally, the convergence of the SORBF is analyzed in both the structure organizing process phase and the phase following the modification. Lastly, the proposed approach is applied to model and identify the nonlinear dynamical systems. Simulation results demonstrate its effectiveness.     

Optimal controllers for spatially invariant systems with delayed communication requirements

We consider the problem of optimal design of semi-decentralized controllers for a special class of spatially distributed systems. This class includes spatially invariant and distributed discrete-time systems with an inherent temporal delay in the interaction of neighboring sites. We consider the problem of optimal design of distributed controllers that have the same information passing delay structure as the plant. We show how for stable plants, the YJBK parameterization of such stabilizing controllers yields a convex parameterization for this class. We then show how the optimal problem can be solved.     

A watermarking technique to improve the security level in face recognition systems

Multimedia Tools and Applications - This paper presents a proposal for a suitable and viable combination of a face recognition system and a watermarking system, namely a PCA—DCT combination,...     

Four ways to improve security

How can you tell if an IT security product (or a product that includes security components) can secure your application? How can you be certain that a product will fully deliver on its claims that it will protect against malice in a deployed environment? Unfortunately, few vendors - and even fewer customers - can make these judgments. The article won't make you a security wizard, but it will give you a feel for what to look for in, and when to be concerned about, a vendor's claims. To ensure that a product has a chance of being secure; customers should check that vendors use adequate approaches in four primary areas. In order of importance (and maturity and availability), they are: quality-control (QC) mechanisms; cryptographic primitives; hardware assist mechanisms; and separation mechanisms.     

Fail-safe stability for dynamic systems using neural-network controllers

The small gain theorem is used to consider the stability of a neural network controlled system under the condition that some of the neurons may fail with attenuated outputs and possibly with the addition of a constant output bias. Sufficient conditions based on the small gain theorem and the circle criterion are obtained for fail-safe stability. A loop-transformation technique is used to overcome the conservative nature of the small gain approach.     

Fixed modes in multivariable systems using constrained controllers

A general expression is derived relating an arbitrary output feedback controller to the resulting closed-loop characteristic polynomial in terms of suitably defined zero polynomials of the system. This expression is then used to characterize the fixed modes of a multivariable system with respect to controllers of any desired structure.     

Design of optimal controllers for spatially invariant systems with finite communication speed

We consider the problem of designing optimal distributed controllers whose impulse response has limited propagation speed. We introduce a state-space framework in which all spatially invariant systems with this property can be characterized. After establishing the closure of such systems under linear fractional transformations, we formulate the H₂ optimal control problem using the model-matching framework. We demonstrate that, even though the optimal control problem is non-convex with respect to some state-space design parameters, a variety of numerical optimization algorithms can be employed to relax the original problem, thereby rendering suboptimal controllers. In particular, for the case in which every subsystem has scalar input disturbance, scalar measurement, and scalar actuation signal, we investigate the application of the Steiglitz–McBride, Gauss–Newton, and Newton iterative schemes to the optimal distributed controller design problem. We apply this framework to examples previously considered in the literature to demonstrate that, by designing structured controllers with infinite impulse response, superior performance can be achieved compared to finite impulse response structured controllers of the same temporal degree.     

基于有色Petri 网的时钟同步协议安全性分析

随着工业以太网的发展,作为其实时性保障核心技术的时钟同步协议的安全性变得至关重要。针对时钟同步协议的安全性问题,首先提出一种基于有色Petri网的时钟同步协议安全性分析方法;然后通过建立协议的有色Petri网模型,利用状态方程等工具针对不安全状态的可达性进行判断分析,从而实现时钟同步协议的安全性分析;最后具体分析了一种基于精密时钟同步协议(PTP)的时钟同步协议以及针对该协议的主时钟欺骗攻击,验证了所提出方法的有效性。     

混沌Ikeda系统同步及其在保密通信中的应用

针对一类时滞Ikeda混沌系统,利用Lyapunov稳定和微分不等式,研究了其指数同步问题。基于线性矩阵不等式理论得到了指数同步的充分条件,给出了指数同步控制器的设计方法,利用混沌掩盖将该同步方法应用于保密通信。仿真表明,该方案具有同步速度快、鲁棒性良好等优良性能。     

Stabilizing controllers using observers for uncertain systems with delays

In this paper, we study the problem of designing stabilizing controllers using observers for a class of uncertain systems with state and input delays. The uncertainties are assumed to be norm bounded. By employing a Lyapunov-Krasovskii functional approach, it is proven that the closed-loop observer-based controlled system is asymptotically stable. The observer and state feedback controllers are determined by solving two linear matrix inequalities which are independent of the delay factors. A simulation example is given to illustrate the theoretical developments.     

Gain scheduled controllers for dynamic systems using sector nonlinearities

In this work we explore the use of gain scheduling for the control of nonlinear systems. The nonlinear system is represented locally by uncertain linear models using sector nonlinearities representation. The uncertain linear models are then used to design a family of robust controllers. We propose a gain scheduling procedure for the problem of guaranteed transition from an actual operating condition to a desired one by constructing a pre-specified path in the state space for the system operating points. As far as we know this problem has not been addressed before. The gain scheduling control procedure given is illustrated in the context of the regulator problem with state feedback.     

Computer-access security systems using keystroke dynamics

An approach to securing access to computer systems is described. By performing real-time measurements of the time durations between the keystrokes when a password is entered and using pattern-recognition algorithms, three online recognition systems were devised and tested. Two types of passwords were considered: phrases and individual names. A fixed phrase was used in the identification system. Individual names were used as a password in the verification system and in the overall recognition system. All three systems were tested and evaluated. The identification system used 10 volunteers and gave an indecision error of 1.2%. The verification system used 26 volunteers and gave an error of 8.1% in rejecting valid users and an error of 2.8% in accepting invalid users. The overall recognition system used 32 volunteers and gave an error of 3.1% in rejecting valid users and an error of 0.5% in accepting invalid users     

A Real-Time Interprocessor Synchronization Algorithm for Communication in Distributed Computer Systems

A real-time synchronization algorithm for interprncessor communication ispresented, which is based on the techniques of Reference 2, except that bufferedcommunication is used. The upper and lower bounds of the mean response time of thisalgorithm is derived.     

采用SPI接口实现双DSP双向通信和同步

为了实现两片TMS320F2812 DSP之间的双向数据通信和同步,给出了运用TMS320F2812DSP内部集成的串行SPI外设接口模块实现双DSP控制器双向数据通信和任务同步的硬件电路设计和软件协议实现方案,经过实验验证方案能满足两片DSP之间高效率、高可靠的双向数据通信和任务同步,最后提出了在通信过程中出现故障的解决方案.成功解决了两个DSP控制器的双向数据通信和任务同步的问题.     

Adaptive synchronization of leader-follower networked systems against communication attenuation and actuators faults

This paper addresses the adaptive asymptotic synchronization problem of a class of leader-follower large scale networked systems against communicated signal attenuation and actuator bias faults. Adaptive mechanisms are constructed to estimate each unknown faulty factor of communications and actuators on-line. Based on the estimations, an adaptive compensation controller is designed to automatically remove the unexpected impacts of communication and actuator faults. Through the adaptive adjustment parameters and Lyapunov functions, the achievement of asymptotic synchronization of the leader-follower large-scale networked system with the improper actuator and faulty transmitted signals is obtained. Finally, the synchronization results are validated by a multiple vehicle large-scale device.     

Training to improve virtual team communication

Abstract. Organizations are utilizing virtual teams, comprising workgroup members who communicate and collaborate with technology, to accomplish tasks. These teams are geographically distributed and communicate via computer-mediated communication systems (CMCS), and may never or rarely meet face-to-face. Relational links among team members have been found to be a significant contributor to the effectiveness of information exchange in the use of CMCS. In most cases, team members receive little or no training to improve the effectiveness of this form of communication. When training is used, it often focuses on software utilization skills, not on interpersonal communication dynamics. This paper discusses the effect of virtual team communication training on group interactions, especially for enhancing these relational links and thereby improving communication and information exchange in virtual teams. It was found that teams that were given appropriate training exhibited improved perceptions of the interaction process over time, specifically with regard to trust, commitment and frank expression between members. Discussion of the role of training on virtual team processes and outcomes is discussed and future research implications are presented.     

Designing stabilizing controllers for uncertain systems using theRiccati equation approach

A useful technique for determining a linear feedback control law stabilizes an uncertain system is the Riccati-equation approach of I.R. Petersen and C.V. Hollot (1986). They consider systems with time-varying uncertainty in the system matrix and obtain the constant feedback gains for the linear stabilizing controller in terms of the solutions of a Riccati equation. The technique is extended to include problems with time-varying uncertainty in the input connection matrix. Several examples are included to demonstrate the efficacy of this result