多径衰落信道下混沌直扩通信的可破解性

本文在文献[1]的基础上,研究多径衰落信道条件下采用无先导卡尔曼滤波混沌拟合对混沌直扩通信的可破解性.由针对混沌直扩信号的无先导卡尔曼滤波混沌拟合的状态空间方程出发,分析了多径衰落信道对于无先导卡尔曼滤波混沌拟合过程中的跟踪误差的影响,得到了信息码状态估计的值域范围,从而提出了多径衰落信道下混沌直扩信号可被破解的充分条件定理.仿真结果表明,在满足充分条件下,混沌直扩信号无论是通过时不变信道还是时变信道,都可以被成功破解,并且具有良好的误码率性能. 关键词： 混沌通信 破解 多径衰落信道 无先导卡尔曼滤波     

一种破译混沌直接序列扩频保密通信的方法

提出了一种新型的混沌保密通信破译方法,并破译了混沌直接序列扩频保密通信(简称混沌直扩).针对混沌直扩信号中只有一个混沌吸引子的特点,基于混沌系统广义同步的思想,提出了混沌拟合方法;针对混沌直扩中混沌实值序列和数字信号相乘的特点,充分利用混沌直扩的基本原理和信息码是慢变信号的特性,提出了用无先导卡尔曼滤波混沌拟合的方法估计信息码的破译方法;进一步针对无先导卡尔曼滤波的过程噪声和混沌拟合的拟合误差共同导致的跟踪误差,提出了跟踪误差控制因子的方法,从而将跟踪误差转变成有利因素并加以利用,根据跟踪误差的值域范围破     

混沌直接序列扩频信号盲解调的硬件电路实现

提出了基于现场可编程门阵列 (FPGA) 技术的混沌直接序列扩频信号盲解调的硬件电路实现方法. 设计了混沌直接序列扩频信号发射机与接收机. 发射机可产生10种不同的混沌直接序列扩频信号. 为方便接收机的硬件电路实现, 对无先导卡尔曼滤波混沌拟合盲解调算法进行了简化, 在简化模型的基础上设计了接收机硬件结构. 提出了一种动态调整偏移因子的新方法, 使接收机能实时适应混沌映射的变化. 通过高斯白噪声信道及多径信道条件下的盲解调实验, 验证了盲解调算法硬件实现的抗噪声与抗多径性能, 以及对10种不同的混沌直接序列扩频信号的自适应破译效果. 关键词： FPGA 混沌直接序列扩频通信 盲解调     

基于状态估计的混沌直扩信号联合均衡与解调

针对混沌直接序列扩频信号(以下称混沌直扩信号)通过非理想信道,利用信道和混沌直扩信号的状态方程及其均衡和解调的关联性,提出一种基于状态估计的联合均衡与解调算法.算法采用多扩展卡尔曼滤波(extended kalman filter,EKF)结构,一边对信道均衡,一边估计二进制信息码,二者互为因果,同时进行,不仅可以有效克服非理想信道所带来的多径信道畸变、加性噪声等对信号的影响,还可将掩藏在混沌直扩信号中的原始二进制信息码解调出来,比均衡和解调分离的做法更有效地利用信息,有更好的实时性.仿真结果表明,所提出的算法收敛速度快,能在信道特性未知情况下较好地抵御多径效应和噪声影响,实现了混沌直扩信号在非理想信道条件下的有效可靠传输. 关键词： 混沌直扩通信 非理想信道 联合均衡与解调算法 扩展卡尔曼滤波     

基于高斯混合概率假设滤波的水下目标跟踪算法

为了解决传统水下目标跟踪中目标数目估计不准确、状态估计误差增长过快的问题,提出了一种基于高斯混合概率假设滤波的水下目标跟踪算法。该算法基于双基地观测模型,采用高斯混合概率假设滤波算法处理方位和时延信息,利用粒子群算法处理多普勒频率获得矢量速度,进一步提升算法的跟踪精度。结果表明,该算法能完成在杂波环境下对目标的跟踪,相比传统的关联算法,能够有效地实现目标个数估计和抑制状态误差增长的目的。     

一种2D—RAKE接收机

在DS—CDMA无线移动环境中，存在严重的多址干扰和多径衰落。本文利用自适应天线阵列分离出多径信号，利用RAKE消除多径衰落。导频位符号辅助(PSA)信道估计用来对BAKE的输入端进行加权，天线阵列的加权系数的自适应更新是采用RLS算法而得。结果表明，该方案具有很强的抗多径干扰和多址干扰的能力。     

一种基于强跟踪滤波的混沌保密通信方法

提出了一种基于强跟踪滤波器的混沌保密通信方法. 在发送端, 混沌映射和信息符号被建模成非线性状态空间模型, 信息符号被加性混沌掩盖或乘性混沌掩盖调制, 然后通过信道输出. 在接收端, 驱动信号被接收, 使用带有贝叶斯分类器(信息符号估计)的强跟踪滤波器算法动态地恢复信息符号. Logistic混沌映射的仿真表明, 当信息符号为二进制编码时, 不管是加性混沌掩盖调制还是乘性混沌掩盖调制, 强跟踪滤波器均能较好地从混沌信号中恢复信息符号. 与扩展卡尔曼滤波器相比, 由于卡尔曼滤波器对于离散的信息符号跟踪能力差, 混沌映射中信息符号难以恢复, 比特误码率高. 因此, 这种基于强跟踪滤波器的混沌保密通信方法是有效的.     

一种多用户上行放大转发中继系统中快速收敛的信道估计方法

针对传统交替最小二乘算法存在的收敛缓慢问题,本文在多用户上行放大转发中继系统中基于Levenberg Marquardt(LM)算法,提出了一种能够快速收敛的信道估计方法,实现了用户-中继信道和中继-基站信道的独立估计.在基站,通过对中继多次放大转发的信号进行建模,构造出具有平行因子结构的三维信号张量模型,并采用LM算法对该模型进行拟合,从而得到系统中两跳链路的信道状态信息.理论分析与仿真结果表明,与已有二线性交替最小二乘方法相比,所提方法具有近乎相同的估计精度;当中继放大因子矩阵为随机矩阵或者包含近似共线性相关列时,所提方法具有更快的收敛速度.     

激光捷联惯导系统高程通道滤波模型设计

针对传统航位推算算法中里程计俯仰安装误差角难以精确辨识,以及高程通道定位精度较差等问题,提出利用高度计作为辅助手段的激光捷联惯导／航位推算／高度计组合导航算法,并设计了高程通道的滤波模型。该算法基于Kalman滤波最优估计理论,利用气压高度计量测信息对SINS／DR组合系统高程通道进行估计补偿,以达到高程通道精确定位的目的。试验表明,经高度阻尼后系统高程定位精度达到3m。     

区间衍生粒子滤波器

针对非线性、非高斯环境下具有不确定动态模型参数的系统状态估计问题,提出了一种新颖的区间衍生粒子滤波算法.该算法利用区间滤波生成的重要性密度函数,在系统状态转移概率密度的基础上,融入最新的系统观测数据,从而提高了对系统状态后验概率的逼近程度.为了进一步提高算法的实时性,提出一种类似光子衍射的粒子衍生过程,进而缓解了滤波精度与运算量之间的矛盾.通过陀螺/星敏感器组合定姿问题验证了该算法的有效性和鲁棒性.     

Synchronization between fractional-order chaotic systems and integer orders chaotic systems (fractional-order chaotic systems)

Based on the idea of tracking control and stability theory of fractional-order systems, a controller is designed to synchronize the fractional-order chaotic system with chaotic systems of integer orders, and synchronize the different fractional-order chaotic systems. The proposed synchronization approach in this paper shows that the synchronization between fractional-order chaotic systems and chaotic systems of integer orders can be achieved, and the synchronization between different fractional-order chaotic systems can also be realized. Numerical experiments show that the present method works very well.     

Digital chaotic sequence generator based on coupled chaotic systems

Chaotic systems perform well as a new rich source of cryptography and pseudo-random coding. Unfortunately their digital dynamical properties would degrade due to the finite computing precision. Proposed in this paper is a modified digital chaotic sequence generator based on chaotic logistic systems with a coupling structure where one chaotic subsystem generates perturbation signals to disturb the control parameter of the other one. The numerical simulations show that the length of chaotic orbits, the output distribution of chaotic system, and the security of chaotic sequences have been greatly improved. Moreover the chaotic sequence period can be extended at least by one order of magnitude longer than that of the uncoupled logistic system and the difficulty in decrypting increases 2¹²⁸*2¹²⁸ times indicating that the dynamical degradation of digital chaos is effectively improved. A field programmable gate array (FPGA) implementation of an algorithm is given and the corresponding experiment shows that the output speed of the generated chaotic sequences can reach 571.4~Mbps indicating that the designed generator can be applied to the real-time video image encryption.     

A chaotic masking scheme by using synchronized chaotic systems

We present a new chaotic masking scheme by using synchronized chaotic systems. In this method, synchronization and message transmission phases are separated, and while synchronization is achieved in the synchronization phases, the message is only sent in message transmission phases. We show that if synchronization is achieved exponentially fast, then under certain conditions any message of any length could be transmitted and successfully recovered provided that the synchronization length is sufficiently long. We also show that the proposed scheme is robust with respect to noise and parameter mismatch under some mild conditions.     

All-optical chaotic MQW laser repeater for long-haul chaotic communications

We present an all-optical chaotic multi-quantum-well (MQW) laser repeater system to be used in long-haul chaotic communications. Chaotic synchronization is achieved among transmitter, repeater, and receiver. Chaotic repeater communications with a sinusoidal signal of 0.2-GHz modulation frequency and a digital signal of 0.4-Gb/s bit rate are numerically simulated, respectively. Calculation results illustrate that the signals are well decoded by the chaotic repeaters. Its bandwidth and the characteristics at much high bit rate are also analyzed. Simulation shows that the repeater can improve decoding quality, especially in higher bit rate chaotic communications.     

Discrete chaotic cryptography

In the paper we propose a new method of constructing cryptosystems utilising a nonpredictability property of discrete chaotic systems. We formulate the requirements for such systems to assure their safety. We also give examples of practical realisation of chaotic cryptosystems, using a generalisation of the method presented in [7]. The proposed algorithm of encryption and decryption is based on multiple iteration of a certain dynamical chaotic system. We assume that some part of the initial condition is a plain message. As the secret key we assume the system parameter(s) and additionally another part of the initial condition.     

Synchronization of chaotic VCSELs by external chaotic signal parameter modulation

Synchronization of chaotic vertical-cavity surface-emitting lasers （VCSELs） is achieved by external chaotic signal modulation successfully. Simulation indicates that we can get chaos synchronization if the intensity of external chaotic signal is large enough. First of all, we use direct current modulation to achieve the chaos of VCSELs, and determine the laser＇s chaotic state by analyzing time series of the output and the corresponding power spectrum. And then we achieve synchronization of the two chaotic systems by external chaotic signal parameter modulation. We also find that the larger the modulation intensity is, the easier it is to achieve synchronization for chaotic VCSELs. This approach can also be applied to systems with a number of modulated lasers.     

Special chaotic systems

The European Physical Journal Special Topics - This topical issue collects contributions related to recent achievements and scientific progress in special chaotic systems. The individual papers...     

Noise-resistant chaotic maps

Synchronized chaotic systems are highly vulnerable to noise added to the synchronizing signal. It was previously shown that chaotic circuits could be built that were less sensitive to this type of noise. In this work, simple chaotic maps are demonstrated that are also less sensitive to added noise. These maps are based on coupling a shift map to a digital filter. These maps are simple enough that they should help lead to an understanding of how noise-robust chaotic systems work. (c) 2002 American Institute of Physics.     

一个新的混沌系统的动力学分析及混沌控制

提出了一个新的混沌系统,研究了其基本动力学特性.设计了实现该系统的混沌电路,电路实验结果验证了系统的混沌行为.根据Lyapunov稳定性理论,采用自适应backstepping控制方法,把系统控制到一个有界点.数值仿真证明了该方法的有效性和可行性.     

分数阶混沌系统与整数阶混沌系统之间的同步

基于追踪控制的思想,利用分数阶系统稳定性理论,实现了分数阶混沌系统与整数阶混沌系统之间的混沌同步,给出了补偿器和反馈控制器的选择方法.以三维分数阶Chen系统和三维整数阶Lorenz混沌系统之间的混沌同步为例进行了数值仿真和电路仿真.研究表明了该同步方法的有效性。