混沌噪声产生器及其FPGA实现

为实时产生混沌噪声,设计了一种基于Tent映射双向耦合映象格子和"接收-拒绝"法的混沌噪声产生器,将其由浮点运算转换为定点运算后在FPGA上实现.所实现的混沌噪声产生器具有结构简单、运算复杂度低、资源占用少且易于控制等优点.性能测试结果表明:混沌噪声产生器能够产生具有任意分布和平坦功率谱的混沌噪声,且随机性较好.     

高精度数字式高斯白噪声发生器的FPGA实现

高斯随机白噪声是一种常用的信号形式,在信号分析和信号处理中具有重要价值.文中介绍了一种基于混沌映射法的高精度数字式高斯白噪声发生器的设计方案,它改进了传统的蒙特卡洛方法,利用映射函数方法实现均匀分布噪声到高斯分布噪声的快速转换,最大限度地降低运算量,是一种较理想的噪声信号产生方法.该噪声发生器可以快速产生周期长、性能稳定、噪声统计特性好的高斯宽带白噪声,具有很大的实用价值.文中给出了原理分析、系统设计及实际应用结果.     

多用户相干CSK数字通信系统的误码性能分析

基于离散混沌信号,提出一种在AWGN环境中双基函数相干CSK系统多用户噪声性能的分析方法。用Logistic映射作为混沌发生器,导出了用信噪比、用户数及比特序列长度表示的误码率(BER)表达式,理论计算与仿真结果相符。单用户情况下的BER和已提出的噪声性能上界是笔者所得结果的特例。     

基于三维Wigner分布的混沌信号判定方法

提出了基于Wigner分布(WD)的判定混沌信号的改进方法.利用混沌信号的窄带特性和三维时频谱图的峰值波动情况判定混沌信号.该方法经洛伦兹系统验证是可行的.计算了混沌信号与高斯噪声的Wigner分布,结果表明可以从三维时频谱直接将两者区分开.计算基于半导体光放大器(SOA)的环形激光器输出光实验数据的三维时频谱,结果与洛伦兹系统的非常相似,从而可判定该实验装置产生信号确为混沌信号.Wigner分布三维时频谱准确地反映了信号的谱特性,能够将系统的不稳状态与混沌状态以及噪声区分开.无论是由动力学方程产生的混沌还是实验上产生的混沌信号都可直观、有效地进行判定.     

保密通信中数字流混沌产生器的同步

由于混沌保密通信系统研究中传统的连续流混沌同步理论存在一些难于解决的问题,本文提出了基于数字流混沌的混沌保密通信理论,在实验室中实现了一类语音保密通信方案,建立了数字流混沌产生器的时钟间隔脉冲驱动同步原理和实现方法,同步通信实验表明,该方法是可行的.     

改进的Tent映射混沌调频雷达信号抗多径性能

最近几年,许多研究人员利用基于混沌的频率调制信号应用于距离和多普勒成像,在研究中发现,基于Tent映射的调频雷达信号性能有待进一步改善。文中提出了改进途径,对Tent映射进行多段线性分段处理,给出了数学定义式及其性能,如最大Lyapunov指数、宽带噪声特性、优异的自相关和图钉状的模糊函数。通过分析计算和仿真结果表明,基于多段线性分段Tent映射混沌调频雷达信号在多径传播环境下的抗多径性能得到明显改善,在高分辨成像雷达中有良好的应用前景。     

超混沌调相信号抗干扰技术研究

该文根据超混沌映射初值敏感性、内随机性和高维超混沌等特点,提出了一种新的脉内混沌调相-脉间随机编码的SAR信号。文中详细比较了4种超混沌映射调相信号的特点,并在此基础上选择了超混沌Logistic映射调相信号作为SAR发射信号,仿真实验表明,这种信号的确具有高保密性和较强的抗干扰性能。     

一种脉间混沌频率步进/退雷达信号设计与分析

文章结合混沌的类随机性、低截获性特点和脉间线性频率步进信号易于处理等优势,设计提出了一种基于混沌映射控制频率步进/退方式的新的雷达信号形式。详细阐述了信号设计原理,并进一步分析了回波信号处理方法,以Bernoulli混沌映射为例比较分析了脉间线性频率步进信号和脉间混沌步进/退信号的自相关函数、模糊函数和频谱特点,最后设计了一种基于该信号的雷达系统。研究表明,脉间混沌频率步进/退信号在理论上具有良好的性能,在工程上具有可实现性,是一种有潜力的雷达信号形式。     

超宽带通信中的伪混沌脉冲位置调制

提出了一种新的适于超宽带脉冲通信的伪混沌脉冲位置调制方式(PCPPM),该方式采用符号动力学对混沌脉冲位置调制方式(CPPM)进行了改进,作为载波的脉冲串的相邻脉冲之间的间隔由混沌映射的符号动力学特性确定,采用脉冲位置调制方式对二进制符号进行调制.系统可以在无辅助握手的情况下获得同步.与CPPM相比,其降低了对脉冲间距的测量精度要求,适合数字方式实现.由丁系统输出的脉冲间隔是随机分布的,具有近似噪声的频谱特性,最后对系统的性能进行了分析和仿真.     

基于混沌码的PPM-TH超宽带信号功率谱分析

为了减小超宽带通信对其它通信系统造成干扰,依据混沌码元丰富、良好的相关特性和白噪声统计特性,将混沌码引入TH-UWB系统,推导了TH-PPM超宽带信号的功率谱密度,采用matlab仿真工具分析了基于logistic混沌映射跳时码的PPM-TH超宽带信号功率谱密度.结果表明混沌跳时码可以有效平滑功率谱且增长码周期、增大码...     

基于信号集合势和连续性的认知无线电宽带频谱感知

针对传统感知算法依赖主用户信号与噪声先验信息,以及易受噪声功率估计不确定性影响的缺点,提出了一种基于信号集合势和连续性的宽带频谱感知方案。该方案将宽带频谱感知分为主用户占子带集合势的估计和子带位置判决两步。在两次不同感知结果中利用主用户连续占用子带的特性,有效地实现最终感知性能的提升。理论分析和仿真结果表明,该方案不仅能够解决传统感知方法依赖噪声和主用户信号先验信息的问题,而且对抗噪声功率不确定性具有鲁棒性。特别地,与传统的能量检测频谱感知算法相比,该算法能有效地实现宽带频谱盲感知。     

脉冲噪声下基于中值离差相关熵的DOA估计方法

作为阵列信号处理的一个基本问题,波达方向估计在现代通信领域有着广泛的应用。常规估计方法通常基于高斯噪声假设。 而当阵列接收数据包含 Alpha 稳定分布脉冲噪声时算法将完全失效。针对 Alpha 稳定分布噪声下的波达方向估计问题,本文定义了一种改进的相关熵算子——中值离差相关熵,并从理论上证明了它的有界性。 以此为基础结合 MUSIC 算法提出了一种波达方向估计新方法。该方法不需要噪声先验知识,且在脉冲噪声环境中具有鲁棒性。仿真实验表明, 即使在短快拍、强脉冲噪声的恶劣环境下,本文方法依然具有良好的性能。      

多用户直扩超宽带信号的码片宽度估计

针对低信噪比多用户直扩超宽带(DS-UWB)信号码片宽度估计的问题,提出了利用循环谱的谱冗余估计该信号码片宽度的方法。首先推导了单用户DS-UWB信号的循环谱密度函数,进一步利用循环谱的叠加特性推导出了多用户DS-UWB信号的循环谱密度函数,最后得出了利用信号循环谱的谱冗余特性估计其码片宽度的方法。计算机仿真实验表明:多用户DS-UWB信号具有循环平稳性,其码片宽度参数可以在低信噪比时完全准确地估计出来,并且优于分段相关累积法的估计性能。     

Antenna subset selection at multi‐antenna relay with adaptive modulation

In this paper, we proposed several antenna selection schemes for cooperative diversity systems with adaptive transmission. The proposed schemes were based on dual‐hop relaying where a relay with multiple‐antenna capabilities at reception and transmission is deployed between the source and the destination nodes. We analyzed the performance of the proposed schemes by quantifying the average spectral efficiency and the outage probability. We also investigated the trade‐off of performance and complexity by comparing the average number of active antennas, path estimations, and signal‐to‐noise ratio comparisons of the different proposed schemes. Copyright © 2011 John Wiley & Sons, Ltd.     

Efficient sign based normalized adaptive filtering techniques for cancelation of artifacts in ECG signals: Application to wireless biotelemetry

In this paper, several simple and efficient sign based normalized adaptive filters, which are computationally superior having multiplier free weight update loops are used for cancelation of noise in electrocardiographic (ECG) signals. The proposed implementation is suitable for applications such as biotelemetry, where large signal to noise ratios with less computational complexity are required. These schemes mostly employ simple addition, shift operations and achieve considerable speed up over the other least mean square (LMS) based realizations. Simulation studies shows that the proposed realization gives better performance compared to existing realizations in terms of signal to noise ratio and computational complexity.     

基于人工噪声辅助的D2D异构蜂窝安全通信方法

A secure communication scheme based on artificial noise assisted from base station(BS)was proposed to improve the system secrecy rate of the D2D underlaying cellular.Firstly,the system secrecy rate was modeled.Then the BS with multi-antennas added artificial noise(AN)in cellular user’s signal as well as designed beam vectors of the desired signal and artificial noise to maximize system secrecy rate.In the end,a joint optimization scheme based on the fairness constraint was introduced to optimize beam vectors of the desired signal,the power allocation for BS’s information signal and AN and the D2D power control.Simulation results show that the system ergodic secrecy rate can be improved 2.7 bit·s^?1·Hz^?1more than the schemes based on SVD and zero-forcing at most.     

Performance evaluation of multilevel polarisation shift keying modulation schemes

The performance of coherent optical transmission systems using multilevel polarisation modulation is derived in terms of the symbol error probability. Four new multilevel modulation schemes based on equipower signal constellations at the vertices of regular polyhedra inscribed into the Poincare sphere are proposed. For an increasing number of signals in the constellation, the shot noise performance of these systems show a remarkably less rapid degradation with respect to standard multilevel schemes with an equal number of signals.<>     

基于LFM-OTDR的超长跨距光纤电力通信链路监测

为了降低电力通信系统中白噪声和随机多径噪声,提出了2种基于线性调频-光时域反射仪(LFM-0TDR)技术的监测方案,即单频LFM-0TDR方案和频分复用LFM-0TDR(FDM-LFM-0TDR)方案.该监测方案采用LFM光脉冲信号作为探测信号,利用分数阶傅里叶变换将后向散射回来的探测信号变换到分数阶傅里叶域进行信号处...     

Efficient hybrid watermarking schemes for robust and secure 3D‐MVC communication

Digital watermarking is a promising and efficient methodology for protecting the copyright of the transmitted multimedia data. Three‐dimensional videos (3DVs) are transmitted and stored in the form of compressed information. Thus, there is a great need for compressed 3DV watermarking. This paper presents 2 proposed hybrid watermarking schemes for securing the 3DV transmission. The first watermarking scheme is the homomorphic transform–based singular value decomposition in discrete wavelet transform domain. The second scheme is the 3‐level discrete stationary wavelet transform in discrete cosine transform domain. The objective of the 2 proposed hybrid watermarking schemes is to increase the immunity of the watermarked 3DV to attacks and achieve adequate perceptual quality. The performances of the 2 proposed hybrid watermarking schemes are compared with those of the state‐of‐the‐art watermarking schemes. The comparisons depend on both of the subjective visual results and the objective results; the peak signal‐to‐noise ratios of the watermarked frames and the normalized correlation of the extracted watermark frames. Extensive simulation results on standard 3DV sequences have been conducted in the presence of attacks. The obtained results confirm that the 2 suggested hybrid watermarking schemes are robust in the presence of attacks. They achieve not only very good perceptual quality with appreciated peak signal‐to‐noise ratio values but also high correlation coefficient values in the presence of attacks.     

基于遗传算法的UWB信号非相干捕获方法

 本文针对动态信噪比环境超宽带（UWB, Ultra WideBand）信号的非相干捕获,提出了一种基于遗传算法的信号捕获方案.以遗传算法结合在线估计接收信噪比,搜索积分窗口长度与定时位置的参数组合,实现系统要求的比特错误概率.该方法解决了传统捕获方案在未知信噪比条件下积分长度无法择优选取以及捕获门限难于设定的问题.仿真结果表明,基于遗传算法的二维参数捕获方法与传统Look and Jump by K steps算法相比有效的提高了未知信噪比条件下的系统捕获性能,拓展了UWB非相干系统的应用范围.