Adaptive synchronization of Chen chaotic system with uncertain parameters

By the control method independent of system parameters, synchronization of two Chen chaotic systems with identical, but uncertain parameters is discussed in this article. Based on Lyapunov’s theorem, an adaptive controller and the parameters estimate update law are derived to make the solution of the error dynamical equation converge at the point E(0, 0, 0) with a quick speed, that is, the states of two Chen chaotic systems can be asymptotically synchronized. Numerical simulations verify the effectiveness and the adaptivity to the variation of Chen system parameters.     

中国数字电视OFDM的时频同步及其仿真

文中分析了中国数字电视标准GB20600-2006中的多载波调制的时频同步方法，提出了一种改进的时间同步算法，用安捷伦公司的ADS（Advanced Design System2006A）计算机仿真平台仿真分析了该方法在高斯白噪声信道下的性能，表明了该同步方法的有效性．     

一种基于超混沌M-G系统的图像加密算法

针对低维混沌序列加密图像保密性差,而复合混沌序列又使得混沌系统结构复杂,同步性差,本文研究了一种基于参数辨识的超混沌时滞模型的图像加密算法,引入位图像加密的思想,并对待加密图像信息进行加密前处理,使得图像信息能够应用M-G超混沌模型进行加解密。此系统结构简单,实用性强,不需要混沌同步。试验和理论分析表明加密效果是令人满意的。     

Maximum Likelihood (ML) Symbol Timing Recovery (STR) Techniques for Reconfigurable PAM and QAM Modems

A fast symbol timing recovery (STR) scheme suitable for flexible-symbol-rate, burst-mode M-ary QAM (M-QAM) and PAM (M-PAM) demodulators used in broadband communications is proposed. The maximum- likelihood (ML) estimation is used to derive a feed-forward STR strategy to achieve fast and accurate derivation of the optimum timing instant with a very short training preamble for applications requiring short packet transmission. In addition, the signal sample at the optimum timing instant is reproduced by interpolation. Analysis to derive the ML-based timing estimation algorithm and STR structure is presented. Analytical models are developed to evaluate the effects of imperfect interpolation and channel additive white Gaussian noise (AWGN) on the timing estimation performance. The derived expressions can be used for optimum interpolation filter design and selection of key parameters to achieve the required mean squared timing error. Simulation results are in good agreement with the analytical prediction.     

量子细胞神经网络超混沌系统同步及在保密通信中的应用

研究了六阶量子细胞神经网络超混沌系统的同步方法,提出了一种基于量子细胞神经网络超混沌同步系统的保密通信系统,应用MATLAB对六阶量子细胞神经网络超混沌系统进行了数值模拟,结果证明利用线性反馈法可实现该高维系统的混沌同步,利用混沌掩盖可实现保密通信.     

锁相环在SDH网络中的应用

在同步数字网络中,同步是数据流正确传输的基础,因此同步技术是数字传输领域的关键技术。为了实现网络的同步,业界普遍采用锁相技术,因为锁相环的性能优越,尤其是数字锁相环的可调范围更宽而且更容易实现。文中以SDH(同步数字系列)技术为例,介绍了以锁相环为基础的同步技术的原理和特点,根据SDH网络中的同步结构和方式,提供了锁相环在SDH网络同步中的具体应用方案,着重分析了这种结构的特性。这种方案在实际应用中有较好的稳定性,对各种网络的同步是一种很好的参考。     

一种可外同步应用的CMOS弛张振荡器

设计了一种输出频率稳定,调频范围宽,且可外同步应用的弛张振荡器电路。针对传统弛张振荡器线性控制能力和频率抖动间的矛盾,对二者合理折中,通过对幅值控制电路电平检测速度的调整,在实现较高控制线性度的同时,抑制了频率失真。给出了整体设计电路和外同步原理。HSPICE仿真结果显示,振荡器输出频率稳定,且有较宽的外同步频率范围。     

Passive control and synchronization of hyperchaotic Chen system

This paper investigates the control and synchronization of hyperchaotic Chen system based on the passive theory. By using two outputs, novel passive controllers are respectively designed to realize the globally asymptotical stability of the hyperchaotic Chen system and the error dynamical system, which avoids mistakes in Ref.[11], where function W（z） cannot guarantee that fo（z） is globally asymptotically stable via only one output and W（z） is the Lyapunov function of f0（z）. Furthermore, numerical simulations are given to show the effectiveness of our method.     

Improving performance of optical fibre chaotic communication by dispersion compensation techniques

This paper numerically investigates the effects of dispersion on optical fibre chaotic communication, and proposes a dispersion compensation scheme to improve the performance of optical fibre chaotic communication system. The obtained results show that the transmitter-receiver synchronization progressively degrades and the signal-to-noise ratio of the recovered message deteriorates as the fibre length increases due to the dispersion accumulation. Two segments of 2.5-km dispersion-compensating fibres are symmetrically placed at both ends of a segment of 245-km nonzero dispersionshifted fibre with low dispersion in one compensation period. The numerical results show that the signal-to-noise ratio of the extracted 1 GHz sinusoidal message is improved from -2.92 dB to 15.38 dB by this dispersion compensation for the transmission distance of 500 km.     

Exponential synchronization of stochastic impulsive perturbed chaotic Lur''e systems with time-varying delay and parametric uncertainty

This paper is devoted to investigating the scheme of exponential synchronization for uncertain stochastic impulsive perturbed chaotic Lur＇e systems. The parametric uncertainty is assumed to be norm bounded. Based on the Lyapunov function method, time-varying delay feedback control technique and a modified Halanay inequality for stochastic differential equations, several sufficient conditions are presented to guarantee the exponential synchronization in mean square between two identical uncertain chaotic Lur＇e systems with stochastic and impulsive perturbations. These conditions are expressed in terms of linear matrix inequalities （LMIs）, which can easily be checked by utilizing the numerically efficient Matlab LMI toolbox. It is worth pointing out that the approach developed in this paper can provide a more general framework for the synchronization of multi-perturbation chaotic Lur＇e systems, which reflects a more realistic dynamics. Finally, a numerical example is provided to demonstrate the effectiveness of the proposed method.