基于小波的变换域通信系统抗干扰性能研究

变换域通信系统通过信道估计在变换域设计信号波形避开干扰,它没有采用载波调制,而是用一个类似噪声的基函数进行信息调制。对高斯白噪声信道下的取不同门限值的基于小波的变换域通信系统与DSSS的抗干扰性能作了比较分析,仿真结果表明基于小波的变换域通信系统相比于DSSS在单音、多音、线性调频、10%部分带宽干扰下误码率平均改进约10dB,在70%部分带宽干扰下误码率平均改进约5dB,并对基于小波的变换域通信系统门限值的选取给出了建议。     

模拟与数字调制方式的非线性变换识别方法的研究

随着我国经济发展水平的不断提高,通信技术得到了快速发展与进步,通信信号的调制分为数字与模拟两个方面,依据数字调制的方法与特点以及模拟的特征,应用非线性变换与小波变换结合的方法能够得到变化信息与包络,进而将变换以后的频域特征提取出来,可以省去其他操作,直接实现这种调制方法。本文通过实验仿真与分析,对该算法有效性进行分析,对几种常见信号进行仿真结果分析。     

基于小波变换的雪崩光电二极管信号检测方法

空间激光通信中的常用调制方式是脉冲位置调制(PPM)．雪崩光电二极管(APD)具有高增益、高灵敏度和响应速度快的特点，因而成为空间激光通信中的首选信号探测器件。针对空间激光通信的脉冲位置调制信道．分析了空间光通信系统中雪崩光电二极管探测噪声的特点和类别．根据小波变换具有提取信号局部特征的能力，提出了一种基于小波变换的雪崩光电二极管信号检洲方法。采用四种不同的阈值选择算法选取小波系数以恢复信号．并进行了初步的仿真实验和分析。结果表明，自适应阈值选择算法取得的信号恢复结果最佳．可有效减弱强背景噪声的影响．提高雪崩光电二极管信号检测系统的性能。     

小波变换技术及其在信号调制方式识别中的应用

小波变换（ＷＴ）理论正被广泛地应用于各种通信领域,既可以用作非稳态数据谱分析的短时傅里叶变换（ＦＴ）处理,亦可以用作联系时域分析和频域分析的新工具。应用哈尔小波变换分析法对Ｍ元ＦＳＫ和ＰＳＫ信号的分类识别进行了描述,讨论了可供实际使用的相关统计分析法,最后给出了对１０种ＦＳＫ和ＰＳＫ信号的分类识别模拟结果。     

小波包变换和加权分数阶傅里叶变换的通信应用对比分析

针对小波包变换和加权分数阶傅里叶变换在通信中表现出的不同性能,在对2种变换进行介绍的基础上,分别对2种变换直接应用于通信以及结合变换域通信技术后的性能进行了仿真对比分析。仿真结果表明,当直接用于通信时,小波包变换的性能要优于加权分数阶傅里叶变换;而当与变换域通信结合以及考虑通信安全性时,加权分数阶傅里叶变换要优于小波包变换,二者在通信中的性能各有优劣,具体取决于应用的方式和目标。     

基于小波变换的可见光通信系统码间干扰抑制技术

码间干扰直接影响可见光通信系统的通信性能,当前的应对方法存在一定的不足,为了实现系统信号稳定传输,文章采用基于小波变换的可见光通信系统码间干扰抑制技术,在分析可见光通信系统信道模型和信号多径特征基础上,利用小波变换将系统回波数据频谱变换到小波域,在小波域内通过恒虚警概率方法识别码间干扰小波系数,构建码间干扰小波系数的恒虚警检测器,将小波系数大于检测门限的码间干扰去除,实现对可见光通信系统码间干扰的抑制。实验结果表明,该方法的信号干扰抑制比和信号失真比均较低,可提高可见光通信系统的输出信噪比,有效抑制码间干扰对系统信号频谱的影响,保证系统信号传输稳定性。     

基于小波变换的信号去噪

小波分析是现代数字信号处理的重要分支。为实现基于小波变换的图像去噪,以小波变换为基础,对一维信号及二维图像信号进行去噪。实验结果表明,基于小波变换的图像处理可以有效地去除噪声,与传统的信号分析技术相比,小波变换能在对信号进行消噪的同时,更好地保留原始信号。     

调制信号小波变换的尺度特征

本文根据小波变换的定义和通信调制信号的一般表示形式,分析了典型调制信号的小波系数在时间-尺度平面上的特征,详细推导了小波系数达到最大时所对应的最佳尺度因子与调制类型的关系,并给出了仿真结果.理论分析和实验结果均表明,不同调制信号的小波系数有着不同特征,最佳尺度因子的变化规律与调制类型一一对应,并且与被调制的基带信号存在确定关系.最佳尺度因子的这种特征可用来构造基于小波变换的调制信号分类器和解调器.     

基于小波变换的非平稳信号瞬时频率分析方法

利用小波变换的优越时频分辨特性,对非平稳信号的瞬时频率进行了分析,给出了模拟仿真结果,并与短时傅立叶变换作比较,得出了两者对信号瞬时频率分析的适用范围及各自的优缺点。     

基于小波变换/小波包变换的多载波调制技术

小波/小波包在通信系统中的应用是近年来一个新的研究领域,而基于小波/小波包变换的多载波调制技术是其中一大研究热点。由于小波/小波包基函数具有良好的正交性与时频局域性等特点,基于小波/小波包变换的多载波调制技术,能够有效地提高通信系统性能。本文介绍了当前几种主要的基于小波/小波包变换的多载波调制方案,分析了这些方案的性能特点及发展趋势,并与其他方案进行了比较。     

Fiber-optic interferometric strain gauge producing asymmetricfringes by using nonlinear feedback

Source wavelength modulation by feedback of the interference signal of an unbalanced fiber-optic Michelson interferometer to the driver of the semiconductor laser source gives rise to sawtooth shaped fringes under fiber strain. The dependence of the theoretically predicted fringe asymmetry on feedback gain is verified experimentally. Elimination of the fringe counting directional ambiguity via differentiation of the asymmetric closed loop interference signal is demonstrated for the first time     

一种新的FBG传感信号解调技术研究

在基于当前FBG传感信号解调技术的基础上,提出了基于可调谐法布里一珀罗(F-P)滤波法和非平衡马赫一曾德尔(M-z)滤波法的FBG解调方法,并进行了系统仿真模型的设计,对其仿真结果与单独的可调谐F-P滤波法和非平衡M-z滤波法的仿真结果进行了比较.结果表明这种方法的性能得到了明显的提高,适用于FBG传感信号的静态和动态解调.     

用Multisim仿真分析数据选择器的工作过程

介绍用Multisim仿真软件分析数据选择器工作过程的方法,即用Multisim仿真软件中的字组产生器产生数据选择器的各个数据输入信号,字组产生器的字组内容反映数据选择器不同数据输入端的输入情况,用Multisim中逻辑分析仪多踪同步显示数据选择器的各个数据输入信号及输出信号波形,可直观描述数据选择器的数据选择的工作过程。所述方法的创新点是解决了数据选择器的工作波形无法用电子实验仪器进行分析验证的问题。     

A Distributed RC Network Broadband FM Discriminator in Thin-Film Technique

The paper describes a frequency discriminator using two distributed RC null networks with different null frequencies, which can be realized in thin- or thick-film technology. The null networks with their null frequencies situated on either side of the carrier frequency use a common input. Their output signals are rectified and subtracted. The demodulated output signal is available either balanced or unbalanced. The analysis covers exponentially tapered and uniformly distributed networks, their difference in sensitivity, and harmonic disitortion due to nonlinearity of the response. The circuit can handle wide frequency deviations of up to /spl plusmn/ 20 percent and delivers an unbalanced output signal of approximately 0.46 volt rms using exponentially tapered networks and an input signal of 1 volt rms with /spl plusmn/ 10 percent frequency deviation. The harmonic distortion in this case is 3.3 percent. Calculated results are compared with measurements of an experimental 1O-MHz discriminator.     

Calculations on a method for measurement of capacitance changes

A method is described and analysed for measuring accurately small changes in capacitance. It employs a ramp signal applied to a bridge circuit and measures the unbalanced signal on an oscilloscope. The method lends itself to remote operation and operation in an intermittently electrically noisy environment. The feasibility of such measurements is confirmed experimentally.     

Impact of Mach-Zehnder Modulator Chirp on Radio over Fiber Links

The impact of Mach-Zehnder modulator (MZM) chirp on single sideband (SSB) and carrier suppressed double sideband (CS-DSB) modulation radio over fiber (RoF) links are investigated and simulated. Finite extinction ratio and drive signal unbalanced ratio of non-ideal MZM are considered, power variation of target microwave signal and harmonic suppression are calculated and evaluated. Our results suggest that unbalanced ratio could be optimized to minimized the power variation owing to the finite extinction ratio and improve the harmonic suppress ratio in the two kinds of RoF links. However, harmonic suppression ratio declined rapidly with the decrease of extinction ratio in the CS-DSB RoF link. For a non-ideal modulator with low extinction ratio, high quality microwave signal could be obtained in the SSB RoF link while an additional filter is required to suppress the unwanted harmonic components in the CS-DSB RoF link.     

广播节目传送中传输音频信号应注意的问题

为保证广播节目的传输质量,必须规范音频信号的传输标准。基于此结合实际工作,阐述了广播音频信号传输中常见的几个问题：平衡和不平衡的连接问题、阻抗匹配问题以及音频的接地问题,有利于提高音频信号的传输质量。通过实际运用经验的摸索和总结使大家对这些容易忽视的问题进行有效解决和防范,并使大家对这几个问题有一个理论联系实际的提高。     

On the Constrained Stochastic Gradient Algorithm: Model, Performance, and Improved Version

This paper discusses the constrained stochastic gradient (CSG) algorithm used for controlling antenna arrays, aiming to maximize the signal-to-interference-plus-noise ratio (SINR) in mobile communications. Firstly, analytical expressions for the first moment of the weight vector and the SINR characteristic of the standard CSG algorithm are derived for two interferer signals, considering small step-size conditions and assuming Gaussian signal, interference, and noise. From these model expressions, the CSG algorithm performance is assessed, which predicts undesired behavior (termed here unbalanced behavior, pertaining to an unbalance between maximizing signal power and minimizing interference power) when one or more interference angles-of-arrival are close to the signal angle-of-arrival and the angle-of-arrival spreads of the involved signals are small. Finally, by using the model expressions, an improved CSG (ICSG) algorithm is proposed to compensate the unbalanced behavior of the standard CSG algorithm. The accuracy of the proposed model and the effectiveness of the modified algorithm are assessed through numerical simulations.      

轨道电路抗不平衡牵引回流干扰的方法研究

轨道电路在铁路信号系统中属于故障率较高的设备,而钢轨中不平衡牵引回流的存在会对轨道电路产生干扰,大大增加了轨道电路的故障率。该文针对不平衡牵引电流对轨道电路的干扰,从轨道电路抗干扰角度入手,研究轨道电路抗不平衡牵引回流干扰的方法,从而减小轨道电路的故障率,提高轨道电路的可靠性。     

Multi-tap microwave photonic filter with positive and negative coefficients based on an unbalanced Mach-Zehnder modulator

A novel approach for the implementation of microwave photonic filter with positive and negative coefficients based on an unbalanced Mach-Zehnder modulator(MZM) is proposed.In the proposed filter,a microwave signal to be filtered is applied to an unbalanced MZM.Thanks to the unbalance between the two arms of the modulator,a π phase shift is obtained by adjusting the wavelength interval between the adjacent wavelengths,which leads to the generation of the positive and negative coefficients.The theoretical fundamentals of the design are described,which show that the required unbalanced MZM in the scheme can be well fabricated by the current technology,and the required other components,including the wavelength multiplexer,are also commercially available devices.An eight-tap microwave photonic filter with positive and negative coefficients is demonstrated.The tunability and reconfigurability of the eight-tap microwave photonic filter are also investigated to verify our approach.