一种基于功率谱估计的盲载频估计新算法

信号载波频率估计是通信、雷达、声纳以及电子对抗等领域信号处理中的一个重要问题,将经典的载频估计算法——频率居中法与Welch功率谱估计算法相结合,提出一种改进的盲载频估计新算法。该算法无须信号的调制类别和定时信息即可实现信号的盲载频估计,在短波信道的仿真环境下,其低信噪比下的估计性能要优于频率居中法。即使在恶劣的短波信道环境下,该算法仍可实现对载频较为精确的估计,在短波通信中有着良好的应用前景。     

一种DSSS信号载频与码片速率的估计方法

在军事通信领域中,为解决抗干扰问题,直接序列扩频(Direct Sequence Spread Spectrum,DSSS)信号具有较低的功率谱密度,信号淹没在背景噪声中,侦查难度较大.针对低信噪比DSSS信号载频与码片速率检测的难题,为提高通信系统的性能,消除噪声,利用循环统计量的循环特性可以体现出循环平稳信号的频率参数,高阶循环累积量可以有效地抑制任何平稳噪声与非平稳高斯有色噪声的特点,提出了一种可同时对DSSS信号的载频与码片速率进行盲估计的方法.通过对不同延时切片的选择可以实现低信噪比DSSS信号载频与码片速率的检测,不需要任何的先验信息,在低信噪比的情况下有较好的估测效果.仿真实验验证了估计方法有效性.     

基于循环谱的MPSK信号盲检测

针对MPSK信号在低信噪比、非合作条件下存在检测概率低的问题,提出了基于循环谱分析器的检测方法。方法根据MPSK信号循环平稳特性,通过在频率和循环频率双频率平面内的循环谱峰值特征搜索完成检测,不需要知道信号的编码序列、载频、码元宽度等先验参数,采用时域平滑实现循环谱估计,减小了计算量。仿真结果表明方法对MPSK信号具有较高的检测概率,而且证明数据长度的增加能够显著提高检测性能。     

基于SC-FDE循环自相关的盲参数估计算法

分析单载波频域均衡(SC-FDE)信号循环自相关截面的性质,研究循环自相关与有用信号长度和循环前缀长度的关系,提出一种在没有先验信息的情况下,对其有用信号长度和循环前缀长度进行盲估计的算法。根据循环截面关于零点对称的性质以及循环前缀长度与截面谱线的关系限制谱峰搜索的区域,从而估计循环前缀长度和循环前缀符号个数。仿真结果表明,该算法可提高估计精度,在低信噪比时也能有较好的估计性能。     

基于循环谱的猝发信号解调

针对传统解调方法应用于猝发信号解调的缺点,提出了一种运用循环谱解调猝发信号算法,采用循环谱快速估计猝发信号的载波频率,根据载波频率进行猝发信号的解调,对以BPSK和QPSK调制方式的猝发信号进行了仿真。仿真结果显示：在满足一定约束条件下,该方法可以快速地捕获猝发信号的载波频率,从而实现了在较短的时间内解调出猝发信号,并且采用此算法对猝发信号进行解调的结果和理论分析一致。     

一种低信噪比条件下QPSK信号盲处理方法

提出了一种用于盲估计四相编码(Quaternary phase shift key,QPSK)载波频率的改进MAT(M-MAT)算法,并给出了一种新型QPSK信号码元估计方法。在没有接收信号先验知识的情况下,首先对QPSK信号粗估计出其载频重心和3dB带宽,并适度滤除带外噪声,之后利用MAT方法估计载频。在此基础上,利用每个码元带宽内相位幅度不变的特性,通过相邻码元的相位差值来估计码元变化。仿真结果表明,该载频估计方法估计精度高于传统的MAT方法,解码方法可以在低信噪比条件下,达到较高的解码精度。     

低信噪比下高精度通信信号载频盲估计算法

未知制式的通信信号的载频估计是台站监测与频谱管理中的一个重要问题,针对现有载频估计算法的估计精度和复杂度不能兼得的不足,在分析信号功率谱特性的基础上,结合线性调制信号的功率谱的对称性,在频谱重心法的基础上提出了以一种改进的估计算法,首先对信号的功率谱进行平滑和高斯拟合的预处理,然后通过迭代搜索的方法估计载频大小,该算法无需知道信号的制式以及其他信息即可实现载频的盲估计,仿真结果表明,在高斯信道环境下,该算法可以实现对载频的快速估计,并且其在低信噪比下的估计较为精确,在台站监测方面有着良好的应用前景。     

低信噪比OFDM信号符号周期盲估计

针对认知无线电系统中正交频分复用(OFDM)信号参数估计这一重要问题,利用OFDM信号的循环谱实现了符号周期的盲估计。首先证明了加循环前缀矩形脉冲成型的OFDM信号具有循环平稳性,然后分别在无噪声和低信噪比条件下,以单载波信号的循环谱为基础,利用OFDM信号各子载波的正交性,从理论上推导出了OFDM信号的循环谱表达式。最后通过对连续信号和离散信号进行仿真,得到了相同的循环谱图,并且在低信噪比条件下,利用循环谱实现了OFDM信号符号周期的盲估计。     

MIMO-OFDM信号参数盲估计方法

为解决非协作通信中多输入多输出-正交频分复用(MIMO-OFDM)信号的参数盲估计问题,提出基于循环自相关结合四阶循环累积量的多参数估计方法。求MIMO-OFDM信号的自相关函数,对其傅里叶变换后得到循环自相关函数,通过对循环自相关三维图不同切面的分析估计出符号周期、有用符号时间、循环前缀时间;求MIMO-OFDM信号的四阶循环累积量,通过检测峰值的数目及其对应的循环频率估计出子载波数及子载波频率。仿真结果表明,在较低信噪比下,所提算法可准确估计出MIMO-OFDM信号的多个参数。     

基于二阶循环累积量的载波频率估计

针对单信道中时频重叠双信号的载波频率估计问题,提出一种基于二阶循环累积量的载波频率估计方法。该方法通过检测信号二阶循环累积量的峰值进行载波频率估计,不需要对信号进行分离,可以直接估计双信号的载波频率。仿真结果表明,对于BPSK、QPSK、8QAM、16QAM任意组合的时频重叠双信号,在信噪比不低于－5 dB的情况下,该方法的载波频率估计准确率高于95%。     

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     

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。     

How do children do mathematics with LOGO?

Abstract  This paper considers some results of a study designed to investigate the kinds of mathematical activity undertaken by children (aged between 8 and 11) as they learned to program in LOGO. A model of learning modes is proposed, which attempts to describe the ways in which children used and acquired understanding of the programming/mathematical concepts involved. The remainder of the paper is concerned with discussing the validity and limitations of the model, and its implications for further research and curriculum development.