基于预测法的超声波测距研究

提出了一种基于预测法的超声波测距方法,采用预测法实现超声波回波信号时间的检测,有效抑制了干扰回波信号和回波信号噪音的影响,显著提高了回波信号检测的可靠性和测量精度;采用ATmega8微处理器实现了预测法回波信号检测,并实现高精度的温度补偿的超声波测距装置,文中详细介绍了电路框图和软件流程图;实践证明具有测量精度高、对干扰回波的抑制能力强,满足了工业测距的要求。     

基于相关法的高精度超声波流量计的设计

基于相关法的超声波流量检测方法,能有效利用超声波脉冲的整体信息进行时差测量,具有精度高,抗干扰能力强等优点.同时相关法对测量过程中计算量需求大,对超声波脉冲的可配置性要求高,所需的硬件平台设计具有一定难度.作者设计并实现了一款基于相关法的超声波流量检测系统,利用高精度浮点DSP为数字核心,配合相应的模拟电路,实现高速计算、可配置、高频采样率的超声波流量检测过程,对小口径小流量的管道液体检测达到了纳秒级的精度.     

超声波测距系统的设计

该系统是基于单片机的超声波测距系统,由STC89C52RC型SCM、按键模块、警报模块、超声波收发模块、显示模块及环境温度采集模块电路组成.采用计数脉冲的方法测出超声波自发射至接收的往返时间,进而计算出测量距离,同时在数据处理中采用了温度补偿以提高测距精度.此系统适用智能避障、倒车雷达、测量井深、测量水库水位和高精度测距等.     

基于最小二乘法的超声波传感器拟合与测距实现研究

本文主要针对超声波传感器测距的电路设计和超声波传感器使用前的拟合做了深入的描述.利用大量的实验测试数据,作者通过最小二乘法对超声波传感器进行了拟合,建立了超声波传感器的测距方程,为超声波传感器的使用提供了较好的数学模型.     

基于小波变换的机器人超声波测距误差补偿

本文论述了超声波在井下钻孔机器人避障系统中的局限性,讨论了超声波声速随复杂环境的变化给避障系统所带来的误差,提出了基于小波变换的广义自相关渡越时间估计方法.本方法采用小波变换对输入信号进行了白化滤波,实现了在复杂的强干扰环境下实时测量超声传播速度的目的,提高了超声测距的精度.实测结果表明:在5 m测距范围内测距相对误差被控制在1%以内.     

一种利用自相关法和三点法检测信号频率的方法

电力系统的频率测量在工业和生活中有很重要的作用,提高频率的测量精度至关重要。生活中常见的信号都带有很多噪声,测量时因为噪声影响结果往往存在很大的误差,所以测量频率的关键就是减少噪声带来的误差影响。采用自相关法可以有效地去噪声,再通过改进的三点法进一步测量信号频率,可大大提高信号测量的精度。     

基于ARM的超声波测距系统设计

介绍了基于ARM处理器的超声波测距系统的组成,给出工作原理和程序设计方法。分析了嵌入式Linux系统下超声波测距模块驱动程序的结构。设计了发射,接收电路。本系统可用于需要测量距离参数的各种应用场合。     

运用运动矢量的中心偏向性改进三步搜索算法

在视频图像压缩算法中,运动估计的目的在于在参考帧中寻找最相似的匹配块,使匹配后的残差最小。由于目前的运动估计算法仅适用于平移运动,小残差的运动匹配往往发生在搜索窗口的中心位置附近,快速的三步搜索算法没有考虑到这些情况,文章就此对其改进,提出了改进的三步搜索算法,实验结果证明了改进的合理性和有效性。     

New approach to WLAN security with synchronized pseudo random

Wireless transmission is becoming increasing ubiquitous, but there is a big black hole in the security of this kind of network. Although IEEE 802.11 provides an optional Wired Equivalent Privacy (WEP) to implement the authentication and confidentiality, it leaves a lot of vulnerabilities and threats. This paper proposes a protocol called SPRNG for wireless data-link layer security. SPRNG is based on the sender and receiver who generate in a synchronized way a pseudo-random number sequence. In each transmission, the sender and receiver use a pair of random numbers, one for data frame authentication, and the other for encryption key. The random numbers are used as "one-time passwords" for sender authentication and as fresh encryption keys for each frame. SPRNG is designed to be compatible with the existing 802.11 products. Like WEP, the current 802.11 security protocol, SPRNG uses a symmetric key as its seed. SPRNG has already been simulated and tested in experiment, it shows that SPRNG has stronger secur     

超声测距中的伪随机码渡越时间的捕获

采用数字相关的方法确定超声波测距中的渡越时间.借助于一个经过适当选择的伪随机序列信号作为超声波的发射信号,可以通过数字相关方法求出发射序列和接收序列的相位差,即渡越时间.本文在计算自相关函数时放弃了快速傅立叶变换(FFT)算法,省去了乘法运算,取而代之的是只用异或和加法的并行数字相关技术,它显著地减少了数据处理时间和FPGA资源.系统以Altera公司的quartusⅡ为开发平台,经逻辑综合、布局布线后,适配到FPGA芯片中,给出了仿真结果.     

一种多径信道直扩信号伪码序列盲估计方法

针对多径信道下直接序列扩频信号伪码序列盲估计的难题,拓展了基于加性高斯白噪声信道提出的子空间法,提出了一种基于子空间法和三阶相关函数法相结合的多径信道直扩信号伪码序列盲估计的新算法,进行了理论推导。该算法对接收到的多径直扩信号按照伪码周期的两倍进行分段形成数据向量,构造自相关矩阵并进行特征值分解得到不同增益伪码序列的延迟叠加,运用m序列的三阶相关特性估计生成多项式进而估计伪码序列。计算机仿真结果验证了该算法的有效性。     

云存储威胁模型的伪随机双线性映射完整性检查

在云存储应用中,用户文件不在本地存储,因此文件安全性、数据机密性和鲁棒性是关键问题。首先,针对现有文献提出的多个密钥服务器的安全擦除码存储系统未考虑数据鲁棒性导致数据恢复存在缺陷的问题,利用伪随机双线性映射构建云存储完整性检查策略威胁模型;其次,编制接口文件块结构,并参照相关文献算法进行完整性检查方案设计,实现多密钥服务器安全擦除码存储系统算法功能补充,并给出算法计算复杂度分析;最后,实验结果显示,所提出的完整性检查方案可实现较大的数据成功检索概率。     

Study on the distribution law of random code structure of irregular LDPC codes and its application in eliminating short cycles

The distribution law of the random code structure of randomly constructed irregu- lar low-density parity-check (LDPC) codes is studied. Based on the Progressive Edge-Growth (PEG) algorithm, a new algorithm which can both eliminate short cy- cles and keep the distribution of the random code structure is presented. The ex- perimental results show that the performance of the irregular LDPC codes con- structed by the new algorithm is superior to that of the PEG algorithm.     

Optimal linear filter design for systems with correlation in the measurement matrices and noises: recursive algorithm and applications

This paper addresses the optimal least-squares linear estimation problem for a class of discrete-time stochastic systems with random parameter matrices and correlated additive noises. The system presents the following main features: (1) one-step correlated and cross-correlated random parameter matrices in the observation equation are assumed; (2) the process and measurement noises are one-step autocorrelated and two-step cross-correlated. Using an innovation approach and these correlation assumptions, a recursive algorithm with a simple computational procedure is derived for the optimal linear filter. As a significant application of the proposed results, the optimal recursive filtering problem in multi-sensor systems with missing measurements and random delays can be addressed. Numerical simulation examples are used to demonstrate the feasibility of the proposed filtering algorithm, which is also compared with other filters that have been proposed.     

超声弹性模量测量中声时测量精度的提高方法

超声脉冲回波法是一种高精度的弹性模量声速测量法。实验测定由声耦合界面引起声时测量相对误差达0. 3%,延时相对误差在0. 2%左右。为减小声时测量误差,提高超声脉冲回波法弹性模量的测量精度,采用了台阶轴试样,避免了由声耦合界面引起的声时测量相对误差;利用试样后端面的二次回波,变相的改变声程,消除了由各种延时引起的声时测量误差。     

A counterexample to the uniqueness of the asymptotic estimate in ARMAX model identification via the correlation approach

This paper deals with the identifiability of an ARMAX system when the correlation approach is adopted. In general, identifiability depends on both the parametrization of the model class and on the informativeness of the data. Here, we focus on the latter aspect and, therefore, a full-order model class is considered. The main goal is to provide a counterexample to the uniqueness of the asymptotic estimate when a persistently exciting input is adopted. This shows the somehow counterintuitive fact that the identifiability of ARMAX systems within the correlation approach is related to the “color” of the input.     

Determination of correlation factor and NMR diffusion parameters from the computer-simulated random motion of vacancies in cubic crystals

Title of adaptations: CORRELATION FACTOR AND NMR Adaptation number: 0001 Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland (see application form in this issue) Reference to original program: Catalogue number: ACKO; Title: RANDOM VACANCY MIGRATION; Ref. in CPC: preceding paper Authors of original program: D. Wolf and K. Differt Peripherals used: Card reader, line printer, card punch, extended core storage (31000₈ words) No. of cards required to effect adaptation: 169     

Testing for random effects in panel data under cross sectional error correlation—A bootstrap approach to the Breusch Pagan test

When testing the pooled regression via the Breusch Pagan test model disturbances are often assumed to be i.i.d. over both the time and the cross section dimension. A bootstrap approach to generate critical values for the Breusch Pagan statistic is provided which is valid under heteroskedasticity and cross sectional correlation as typically formalized in the framework of seemingly unrelated regressions. Moreover, asymptotic results are derived for a finite cross section and infinite time dimension. Finite sample simulations show that ignoring cross sectional correlation may lead to large size distortions in practice. Conditional versions of the test statistic designed to cope with random time effects or spatial error correlation show empirical size distortions in case the source of contemporaneous error correlation is misspecified. Moreover, the bootstrap is robust if contemporaneous error correlation is induced by random time effects or in case of spatial error correlation.