Research on resolution between multi-component LFM signals in the fractional Fourier domain

When the initial frequencies and chirp rates of multi-component linear frequency modulation (LFM or chirp) signals are close,the signals may not be distinguished in the fractional Fourier domain (FRFD).Consequently,some signals cannot be detected.In this paper,first,the spectral distribution characteristics of a continuous LFM signal in the FRFD are analyzed,and then the spectral distribution characteristics of a LFM signal in the discrete FRFD are analyzed.Second,the critical resolution distance between the peaks of two LFM signals in the FRFD is deduced,and the relationship between the dimensional normalization parameter and the distance between two LFM signals in the FRFD is also deduced.It is discovered that selecting a proper dimensional normalization parameter can increase the distance.Finally,a method to select the parameter is proposed,which can improve the resolution ability of the fractional Fourier transform (FRFT).Its effectiveness is verified by simulation results.     

Negative effects of sufficiently small initial weights on back-propagation neural networks

In the training of feedforward neural networks,it is usually suggested that the initial weights should be small in magnitude in order to prevent premature saturation.The aim of this paper is to point out the other side of the story:In some cases,the gradient of the error functions is zero not only for infinitely large weights but also for zero weights.Slow convergence in the beginning of the training procedure is often the result of sufficiently small initial weights.Therefore,we suggest that,in these cases,the initial values of the weights should be neither too large,nor too small.For instance,a typical range of choices of the initial weights might be something like(0.4,0.1) ∪(0.1,0.4),rather than(0.1,0.1) as suggested by the usual strategy.Our theory that medium size weights should be used has also been extended to a few commonly used transfer functions and error functions.Numerical experiments are carried out to support our theoretical findings.     

基于森林火灾平台的红外图像识别技术研究

森林火灾探测一直是森林资源保护工作中的老大难问题。早期的火灾探测技术多是基于火灾的烟雾和温度特征的,但其判别标准过于单一,误报率较高。随着计算机技术的发展和红外探测器的发明,出现了基于红外图像处理的森林火灾防护技术,该技术主要对红外探测器获得的森林现场的红外图像进行一定的处理后识别图像中是否有火灾出现。本文的主要工作是进行红外图像增强算法的研究,通过对各种算法的描述和仿真实验结果分析,提出一种相对较适合森林背景红外图像的处理算法一将基于频域处理的提升小波变换与直方图修正结合起来的红外图像增强算法。     

Transit smart card data mining for passenger origin information extraction

The automated fare collection(AFC) system,also known as the transit smart card(SC) system,has gained more and more popularity among transit agencies worldwide.Compared with the conventional manual fare collection system,an AFC system has its inherent advantages in low labor cost and high efficiency for fare collection and transaction data archival.Although it is possible to collect highly valuable data from transit SC transactions,substantial efforts and methodologies are needed for extracting such data because most AFC systems are not initially designed for data collection.This is true especially for the Beijing AFC system,where a passenger’s boarding stop(origin) on a flat-rate bus is not recorded on the check-in scan.To extract passengers’ origin data from recorded SC transaction information,a Markov chain based Bayesian decision tree algorithm is developed in this study.Using the time invariance property of the Markov chain,the algorithm is further optimized and simplified to have a linear computational complexity.This algorithm is verified with transit vehicles equipped with global positioning system(GPS) data loggers.Our verification results demonstrated that the proposed algorithm is effective in extracting transit passengers’ origin information from SC transactions with a relatively high accuracy.Such transit origin data are highly valuable for transit system planning and route optimization.     

物联网与国际陆港发展研究

物联网方兴未艾,正在世界各地掀起发展的热潮,这种发展更多的是和相关领域的应用结合在一起的。国际陆港作为典型现代物流服务产业集聚平台,成为近年来内陆地区发展外向型经济的重要模式。物联网与国际陆港发展的结合不仅是先进信息技术与物流业的融合,更为国际陆港这一现代服务业代表的发展提升注入了强大的动力,也为陆港的"智慧"发展带来了新的契机。     

基于Profibus-DP的西门子S7—300 PLC与ABB 800XA数据通信的实现

本文介绍基于Profibus—DP通信协议的西门子S7—300PLC与ABB 800XA系统之间的数据通信。详细描述了分别通过S7—300 PLC CPU的DP接口和CP342—5通信模块与ABB 800XA系统通信两种不同条件下的有关通信配置及实现数据通信的过程。     

基于MSP430的低功耗近距无线图像传输系统设计与实现

近距无线图像传输系统主要用于无线传感器网络中的图像采集、传输、处理和显示,本文设计并实现了一种具有较强实用性的近距无线图像传输系统。采用OV7670图像传感器作为图像数据采集器,高速低功耗的nRF24L01射频模块作为无线收发器,采用MSP430F14916位超低功耗单片机作为微处理器,所构成的系统具有功耗低、图像传输速度快等优点。作者详细阐述了该系统的硬件结构和软件设计。     

直升机发动机超转实验系统的测频设计

本文采用FPGA技术测量直升机发动机转速,介绍了双通道等精度测频的原理,设计了信号调理电路,并在FPGA上设计了Verilog代码,在实际应用中测量直升机发动机转速表现了良好的系统实时性能。     

基于减聚类优化算法的无线传感网络分簇路由协议研究

无线传感网络是当前无线网络研究的热点领域,分簇路由协议作为降低网络能耗、提高网络生存时间的核心技术而备受关注。在深入分析已有算法存在诸多不足的基础上,本文提出了一种基于减聚类优化的分簇路由算法。本文首先建立一阶能耗模型,确定网络最优簇首数量;然后建立减聚类优化数学模型,确定可供选择的分簇方案;最后以最小化最大簇内距离方差作为评价指标,确定最优的分簇结果。仿真结果表明:相比经典的LEACH分簇路由协议,该算法划分的网络能够有效地降低网络能耗、提高网络生存时间,弥补已有算法的不足之处。     

数字磁通门传感器的自动相位对准

三轴数字磁通门传感器信号处理电路的延时(相位延迟)及各轴延时不一致,影响数字滤波器的输出性能。提出了基于加权最小二乘法的互功率谱相位法计算延时的方法,针对该数字滤波器的特性,选择传感器的不同谐波信号对比分析相位延迟计算的精度,并设计了传感器的自动相位对准方法。实验结果表明:该计算方法精确有效,自动相位对准使滤波器输出性能提高25.89%。