基于非参数平滑的OFDM系统信道估计算法

研究了双衰落信道下正交频分复用(Orthogonal Frequency Division Multiplexing,OFDM)系统中信道估计的非参数方法.提出的方案首先利用梳状导频或散布导频和最小二乘算法估计出导频处的信道频率响应并进行简单的分段线性插值,然后用基于非参数统计方法的Savitzky-Golay平滑滤波器对插值后的信道估计值进行非参数平滑.与传统信道估计算法相比,算法大大降低了信道估计的均方误差、系统的误符号率和计算复杂度,运算量仅正比于有效子载波数,且对多普勒频移具有很强的鲁棒性.数值仿真结果证明了上述结论的正确性.统计检验结果表明,该算法在最小二乘意义下是最优的.     

无人机OFDM数据链路中信道估计算法研究

针对无人机信道的特点,以及采用正交频分复用技术进行无人机数据链路传输的优点.在对OFDM关键技术信道估计进行研究时,要确保接收端能够准确的检测出由于无线信道变化造成的码间干扰,准确的解调出原信号.根据系统需要设计了梳状导频和块状导频联合的导频插入方式,该方式可以在数据传输和信道估计性能上做到折中,并对常用的信道估计算法进行分析研究提出了改进的最小均方误差信道估计算法,最后建立频率选择性信道模型对不同的信道估计算法进行仿真,分析仿真结果可以看出该导频插入方式和信道估计算法具有较低的复杂度,而且又具有良好的信道估计性能,适合在实际系统中应用.     

基于平滑l0范数的OFDM系统稀疏信道估计

信道估计是无线通信系统的关键技术.为了提高信道估计的精确性,针对现有压缩传感的信道估计算法需预先知道信道稀疏度的问题,提出了一种新的基于压缩传感理论的正交频分复用系统信道估计平滑l0范数(Smoothed l0 Norm,SLO)算法,并引入双曲正切函数对SL0算法进行改进.仿真结果表明,在相同条件下,与传统最小二乘(LS)以及匹配追踪(MP)和压缩采样匹配追踪(CoSaMP)算法比较,改进算法收敛速度快,估计值均方误差小,降低了系统复杂度.     

基于块自适应滤波的核最小均方算法

核最小均方(KLMS)算法在非线性系统中收敛性能较好,但其使用瞬时梯度估计均方误差梯度,导致随机性较大。而块自适应滤波理论利用多个输入-输出的误差来估计均方误差梯度,可降低KLMS算法稳态误差。为此,将块自适应滤波理论运用到KLMS算法中,提出核块最小均方(KBLMS)算法,根据最陡下降法原理推导出KBLM S权矢量更新公式,使用核方法计算得到滤波器输出表达式,并通过并行处理减小算法计算复杂度。仿真结果表明,KBLMS算法可有效提高KLMS算法的稳态性能,并且相比块最小均方算法具有更低的误码率。     

基于压缩感知的多小区MASSIVE MIMO信道估计

针对多小区多用户大规模多输入多输出（MASSIVE MIMO）系统信道估计在低信噪比情况下估计精度较差的问题,提出了一种基于群智能搜索的果蝇分段正交匹配追踪（FF-StOMP）压缩感知算法。该算法在分段正交匹配追踪（StOMP）求解不同阈值下的信道矩阵参数与归一化最小均方误差的基础上,采用果蝇优化算法动态搜索出最小归一化均方误差与其对应的阈值,达到自适应参数设定的目的。仿真结果表明,与StOMP算法相比,信噪比在0~10 dB情况下,所提出的FF-StOMP算法信道估计性能能够提升0.5~1 dB;信噪比在11~20 dB时,信道估计性能能够提升0.2~0.3 dB。当小区用户数发生变化时,所提出的算法能实现自适应信道估计,能够有效提升MASSIVE MIMO系统低信噪比情况下的信道估计精度。     

基于正交频分复用的线性最小均方误差信道估计改进算法

传统的线性最小均方误差(LMMSE)信道估计要求已知信道的统计特性,而实际应用中无线信道的统计特性往往是不可知的.针对无线信道的不确定性,根据时域信道上能量分布的稀疏性特点,在最小二乘(LS)算法的基础上提出了一种改进的LMMSE信道估计算法.该算法从当前信道置信度较高的频率响应出发,把相邻子载波信道估计误差的比值作为信道响应的加权系数,然后通过加权平均的方法计算出多径信道下的信道响应.该算法避免了繁琐的矩阵求逆与分解运算,能够有效降低算法复杂度.实验结果表明,所提算法总体性能优于LS算法及经过奇异值分解的线性最小均方误差(SVD-LMMSE)估计算法,且其误码率接近于传统的LMMSE算法.     

OFDM系统中一种低复杂度的信道估计算法

提出一种适用于正交频分复用(Orthogonal frequency division multiplexing,OFDM)系统的低复杂度信道时域响应估计算法.在发送端,算法基于最小均方误差(Mean-square error,MSE)准则以及给定的导频分布对导频功率及相位进行设计;在接收端,算法直接对接收到的导频符号进行求和,通过对求和结果进行简单加权后得到信道时域响应的估计.由于该算法在估计信道时只需进行很少量的复数乘法运算,因此接收端的计算复杂度非常低.理论分析与仿真结果表明,当信道时不变或慢时变时,该算法具有较小的估计均方误差.     

基于相位差分算法的参数估计研究

在数字信道化接收机后续精测频结构的基础上,讨论了相位差分算法在信号参数估计中的应用.首先从最小二乘估计模型人手分析了相对无模糊的相位差分算法,然后根据算法分别对加性高斯白噪声中的复正弦信号的频率估计方法和线性调频信号参数的联合估计方法进行了研究,最后给出了方法的最小均方误差分析及其数值结果.实验结果证明,方法能够有效、准确地估计出信号的参数,而且在较高信噪比条件下,其估计均方误差能达到Cramer-Rao下限.同时方法不含复杂运算,非常易于硬件实现.     

毫米波通信的低复杂度时变信道估计算法

当毫米波通信系统工作于时变信道场景中时,为解决通信用户快速位移导致的方位角计算误差和信道估计算法精度下降等问题,通常要消耗大量计算资源。因此,基于用户在快时变信道场景下的信号传输特征,首先在确定毫米波传输信号方位时采用对角加载方法,根据高斯白噪声先验信息得到对角加载方法的参数;然后采用对角带矩阵分解方法对所得到的信道干扰矩阵模型进行处理,从而降低信道估计与均衡算法的复杂度。仿真结果表明,所提算法能够使工作在时变信道条件下的通信系统以低于常规算法的运算复杂度处理系统中的干扰,且不降低传输性能。     

LTE-A系统中改进的信道估计算法的研究及实现

先进的长期演进(LTE-A)系统接收端需要对多径信道进行动态估计和跟踪,以满足相干解调的目的,准确而有效的信道估计方法可以提高数据传输速率。针对线性最小均方误差(LMMSE)信道估计矩阵求逆运算复杂度大的问题,提出一种基于GaussSeidel算法的低复杂度的LMMSE算法。通过对基于导频的几种常用的信道估计算法进行对比分析和研究,得到的LMMSE算法具有较低的误比特率和算法复杂度。最后基于Gauss-Seidel算法,分别设计了低复杂度LMMSE算法的各个子模块的DSP实现方案。     

Only connect: teaching, technology and telesis

Abstract This paper describes an approach to the design of interactive multimedia materials being developed in a European Community project. The developmental process is seen as a dialogue between technologists and teachers. This dialogue is often problematic because of the differences in training, experience and culture between them. Conditions needed for fruitful dialogue are described and the generic model for learning design used in the project is explained.     

European Community policy and the market

Abstract This paper starts with some reflections on the policy considerations and priorities which are shaping European Commission (EC) research programmes. Then it attempts to position the current projects which seek to capitalise on information and communications technologies for learning in relation to these priorities and the apparent realities of the marketplace. It concludes that while there are grounds to be optimistic about the contribution EC programmes can make to the efficiency and standard of education and training, they are still too technology driven.     

一种自适应子融合集成多分类器方法

融合集成方法已经广泛应用在模式识别领域,然而一些基分类器实时性能稳定性较差,导致多分类器融合性能差,针对上述问题本文提出了一种新的基于多分类器的子融合集成分类器系统。该方法考虑在度量层融合层次之上通过对各类基多分类器进行动态选择,票数最多的类别作为融合系统中对特征向量识别的类别,构成一种新的自适应子融合集成分类器方法。实验表明,该方法比传统的分类器以及分类融合方法识别准确率明显更高,具有更好的鲁棒性。     

Avoiding semantic and temporal gaps in developing software intensive systems

Development of software intensive systems (systems) in practice involves a series of self-contained phases for the lifecycle of a system. Semantic and temporal gaps, which occur among phases and among developer disciplines within and across phases, hinder the ongoing development of a system because of the interdependencies among phases and among disciplines. Such gaps are magnified among systems that are developed at different times by different development teams, which may limit reuse of artifacts of systems development and interoperability among the systems. This article discusses such gaps and a systems development process for avoiding them.     

Designing economic np control charts: A programmed simulation approach

This paper presents control charts models and the necessary simulation software for the location of economic values of the control parameters. The simulation program is written in FORTRAN, requires only 10K of main storage, and can run on most mini and micro computers. Two models are presented - one describes the process when it is operating at full capacity and the other when the process is operating under capacity. The models allow the product quality to deteriorate to a further level before an existing out-of-control state is detected, and they can also be used in situations where no prior knowledge exists of the out-of-control causes and the resulting proportion defectives.     

The development of robot art

Going through a few examples of robot artists who are recognized worldwide, we try to analyze the deepest meaning of what is called “robot art” and the related art field definition. We also try to highlight its well-marked borders, such as kinetic sculptures, kinetic art, cyber art, and cyberpunk. A brief excursion into the importance of the context, the message, and its semiotics is also provided, case by case, together with a few hints on the history of this discipline in the light of an artistic perspective. Therefore, the aim of this article is to try to summarize the main characteristics that might classify robot art as a unique and innovative discipline, and to track down some of the principles by which a robotic artifact can or cannot be considered an art piece in terms of social, cultural, and strictly artistic interest. This work was presented in part at the 13th International Symposium on Artificial Life and Robotics, Oita, Japan, January 31–February 2, 2008     

煤矿井下安全监控分站的设计及其仿真实现

为了设计一种具有低成本、低功耗、易操作、功能强且可靠性高的煤矿井下安全分站,针对煤矿安全生产实际,文章提出了采用MCS-51系列单片机为核心、具有CAN总线通信接口的煤矿井下安全监控分站的设计方案;首先给出煤矿井下安全监控分站的整体构架设计,然后着重阐述模拟量输入信号处理系统的设计过程,最后说明单片机最小系统及其键盘、显示、报警、通信等各个组成部分的设计;为验证设计方案的可行性与有效性,使用Proteus软件对设计内容进行仿真验证,设计的煤矿井下安全监控分站具有瓦斯、温度等模拟量参数超标报警功能和电机开停、风门开闭等开关量指示功能;仿真结果表明:设计的煤矿井下安全监控分站具有一定的实际应用价值.     

Explanation and prediction: an architecture for default and abductive reasoning

Although there are many arguments that logic is an appropriate tool for artificial intelligence, there has been a perceived problem with the monotonicity of classical logic. This paper elaborates on the idea that reasoning should be viewed as theory formation where logic tells us the consequences of our assumptions. The two activities of predicting what is expected to be true and explaining observations are considered in a simple theory formation framework. Properties of each activity are discussed, along with a number of proposals as to what should be predicted or accepted as reasonable explanations. An architecture is proposed to combine explanation and prediction into one coherent framework. Algorithms used to implement the system as well as examples from a running implementation are given.     

Three Process Perspectives: Organizations, Teams, and People

This paper provides the author's personal views and perspectives on software process improvement. Starting with his first work on technology assessment in IBM over 20 years ago, Watts Humphrey describes the process improvement work he has been directly involved in. This includes the development of the early process assessment methods, the original design of the CMM, and the introduction of the Personal Software Process (PSP)^SM and Team Software Process (TSP){^SM}. In addition to describing the original motivation for this work, the author also reviews many of the problems he and his associates encountered and why they solved them the way they did. He also comments on the outstanding issues and likely directions for future work. Finally, this work has built on the experiences and contributions of many people. Mr. Humphrey only describes work that he was personally involved in and he names many of the key contributors. However, so many people have been involved in this work that a full list of the important participants would be impractical.     

基于复小波噪声方差显著修正的SAR图像去噪

提出了一种基于复小波域统计建模与噪声方差估计显著性修正相结合的合成孔径雷达(Synthetic Aperture Radar,SAR)图像斑点噪声滤波方法。该方法首先通过对数变换将乘性噪声模型转化为加性噪声模型,然后对变换后的图像进行双树复小波变换(Dualtree Complex Wavelet Transform,DCWT),并对复数小波系数的统计分布进行建模。在此先验分布的基础上,通过运用贝叶斯估计方法从含噪系数中恢复原始系数,达到滤除噪声的目的。实验结果表明该方法在去除噪声的同时保留了图像的细节信息,取得了很好的降噪效果。