A frequency domain approach to state estimation

A novel input-to-state approach to the problem of robust state estimation in the presence of model uncertainty as well as plant disturbance and sensor noise is considered. A new observer structure is introduced and shown to have certain advantages over the classical Luenberger observer when studying robustness issues. This structure is then used to solve the robust estimation problem in the H_∞ framework.     

A polynomial-rooting algorithm for CFO estimation in slow fading OFDM

This study proposes a polynomial-rooting algorithm to estimate the carrier-frequency-offset (CFO) of a slow fading orthogonal frequency division multiplexing (OFDM) system. The proposed algorithm uses an inter-carrier-interference self-cancellation (ICI-SC) scheme to precode data symbols at the transmitter. This study derives the time coherency of the precoded OFDM signal, which enables the proposed algorithm to estimate the CFO through array signal processing techniques. The proposed algorithm first constructs snapshot vectors using the receive time samples at specific positions. This snapshot vector is CFO-directed because of the coherent property of the precoded signal. Using the second order statistics of the snapshot vector, the proposed approach estimates the CFO through a polynomial-rooting algorithm.     

Blind estimation of carrier frequency offset for OFDM systems with time-varying DC offset

Orthogonal frequency division multiplexing (OFDM) has been widely adopted in radar and communication systems. High sensitivity to carrier frequency offset (CFO) is one of the major drawbacks of OFDM. CFO estimation for OFDM systems had been extensively studied and various algorithms had been proposed. However, the established algorithms may be compromised by the adoption of direct-conversion architecture and multi-mode low noise amplifier in the OFDM receiver, which introduces time-varying direct current offset (TV-DCO) into the system. In our previous study, we developed an eigen-decomposition based estimation algorithm, which is robust to TV-DCO but suffers from performance degradation under low to medium signal-to-noise ratio and requires high computation efforts. To address those issues, we in this paper propose a novel blind CFO estimation algorithm. By making use of the second order differential filtering and subspace method, the proposed algorithm achieves great performance improvement with reduced complexity. The performance of the proposed algorithm is demonstrated by simulations.     

无线局域网中OFDM系统的频偏估计技术研究

正交频分复用（OFDM）是一种正交多载波技术，目前在很多领域得到广泛的应用。其主要缺点之一就是对于发送接收之间的载波频偏（CFO）很敏感。如果在接受机中CFO没有得到补偿，子载波间就会失去正交性，这会导致严重的信道间干扰（ICI）。本文分析了目前无线局域网中OFDM频偏估计常用的两种算法，提出一种针对IEEE802．11aOFDM系统频偏的解决方案，该方案将目前无线局域网中的解决OFDM系统的频偏纠正算法的优点和802．11a的帧结构充分结合起来，最后通过计算机的仿真证明了我们方案的正确性。     

无线局域网中OFDM系统的频偏估计技术研究

正交频分复用(OFDM)是一种正交多载波技术,目前在很多领域得到广泛的应用.其主要缺点之一就是对于发送接收之间的载波频偏(CFO)很敏感.如果在接受机中CFO没有得到补偿,子载波间就会失去正交性,这会导致严重的信道间干扰(ICI).本文分析了目前无线局域网中OFDM频偏估计常用的两种算法,提出一种针对IEEE802.11aOFDM系统频偏的解决方案,该方案将目前无线局域网中的解决OFDM系统的频偏纠正算法的优点和802.11a的帧结构充分结合起来,最后通过计算机的仿真证明了我们方案的正确性.     

A combined time and frequency domain method for model reduction of discrete systems

A new combined time and frequency domain method for the model reduction of discrete systems in z-transfer function is presented. First, the z-transfer functions are transformed into the w-domain by the bilinear transformation, z = (1+w)/(1?w). Then, four model reduction methods—Routh approximation, Hurwitz polynomial approxima- tion, stability equation, and retaining dominant poles—are used respectively to reduce the order of the denominator polynomials in the w-domain. Least squares estimate is then used to find the optimal coefficients in the numerator polynomials of the reduced models so that the unit step response errors are reduced to a minimum. The advantages of the proposed method are that both frequency domain and time domain characteristics of the original systems can be preserved in the reduced models, and the reduced models are always stable provided the original models are stable.     

A novel LMI-based optimization algorithm for the guaranteed estimation of the domain of attraction using rational Lyapunov functions

In this article we deal with the classical problem of estimating the domain of attraction (DOA) of autonomous dynamical systems. We propose a new LMI estimation method based on recent results from the mathematical theory of moments. In contrast to previous works we exploit the advantages of rational Lyapunov functions to enhance the estimates. Several examples illustrate the estimation method.     

Scholarly research and information practices: a domain analytic approach

This paper deals with information needs, seeking, searching, and uses within scholarly communities by introducing theory from the field of science and technology studies. In particular it contributes to the domain-analytic approach in information science by showing that Whitley’s theory of ‘mutual dependence’ and ‘task uncertainty’ can be used as an explanatory framework in understanding similarity and difference in information practices across intellectual fields. Based on qualitative case studies of three specialist scholarly communities across the physical sciences, applied sciences, social sciences and arts and humanities, this paper extends Whitley’s theory into the realm of information communication technologies. The paper adopts a holistic approach to information practices by recognising the interrelationship between the traditions of informal and formal scientific communication and how it shapes digital outcomes across intellectual fields. The findings show that communities inhabiting fields with a high degree of ‘mutual dependence’ coupled with a low degree of ‘task uncertainty’ are adept at coordinating and controlling channels of communication and will readily co-produce field-based digital information resources, whereas communities that inhabit fields characterised by the opposite cultural configuration, a low degree of ‘mutual dependence’ coupled with a high degree of ‘task uncertainty’, are less successful in commanding control over channels of communication and are less concerned with co-producing field-based digital resources and integrating them into their epistemic and social structures. These findings have implications for the culturally sensitive development and provision of academic digital resources such as digital libraries and web-based subject portals.     

Document indexing: a concept-based approach to term weight estimation

Traditional index weighting approaches for information retrieval from texts depend on the term frequency based analysis of the text contents. A shortcoming of these indexing schemes, which consider only the occurrences of the terms in a document, is that they have some limitations in extracting semantically exact indexes that represent the semantic content of a document. To address this issue, we developed a new indexing formalism that considers not only the terms in a document, but also the concepts. In this approach, concept clusters are defined and a concept vector space model is proposed to represent the semantic importance degrees of lexical items and concepts within a document. Through an experiment on the TREC collection of Wall Street Journal documents, we show that the proposed method outperforms an indexing method based on term frequency (TF), especially in regard to the few highest-ranked documents. Moreover, the index term dimension was 80% lower for the proposed method than for the TF-based method, which is expected to significantly reduce the document search time in a real environment.     

On non-fragility of controllers for time delay systems: A numerical approach

In this paper an explicit numerical procedure is proposed to determine the non-fragility of parameters of controllers used to stabilize a class of time delay systems. The proposed procedure finds the largest possible circle inscribed in a stability subregion delimited by a simple closed curve in the plane of the controller parameters. The center of this circle is declared to be the controller’s least fragile parameters. The obtained theoretical results are applied and compared with some of the most relevant examples found in the literature. This illustrates that the proposed procedure improves previous results found in the literature so far.     

基于改进小波脊提取算法的数字信号瞬时频率估计方法

在深入分析小波脊原理的基础上,针对数字信号瞬时频率提取精度要求,利用小波脊提取数字信号的瞬时频率,并对方法的初始值设置、解析小波参数设置和估计精度设置等关键问题进行了分析并改进.实际信号实验表明,改进算法鲁棒性明显增强,实用价值较大.     

On novel trajectory tracking control of quadrotor UAV: A finite-time guaranteed performance approach

In this work, aiming at the trajectory tracking control of the quadrotor UAV subject to external disturbances and model uncertainties, a finite-time approach with preassigned performance guaranteed is proposed. First, the control system is decoupled into translational and rotational subsystems. Then, in both two subsystems, the performance bounds constructed by the newly established appointed-time performance functions are devised for guaranteeing the tracking performance, and the controllers are designed via applying the dynamic surface control technique with integral barrier Lyapunov functions involved. Moreover, finite-time tracking differentiators and finite-time multivariable disturbance observers are exploited to estimate the target signals and the lumped disturbances, respectively. Finally, two examples of simulation are carried out to validate the effectiveness and superiority of the proposed control method.     

On the estimation of the covariance of the continuous multiplicative systems

This paper addresses the estimation problem for the steady state and error covariances of continuous systems subjected to additive and multiplicative noise. Several upper and lower matrix bounds of these covariances are developed. Comparing to existing results, these obtained bounds are more general. Furthermore, it is also shown that they are sharper for some case(s).     

关于C—D生产函数的参数估计

C-D生产函数的应用中，最关键和最困难的环节是参数的估计，尽管有多种方法可供选择，但若对方法本身没有透彻的了解，对所考察对象没有深刻的认识，生搬硬套就可能得出错误的结论。对该生产函数的常用参数估计方法，作了归纳比较，指出各种方法的特点和局限，以便于应用时参考、选择。     

非均质渗透介质纵向弥散度数值模拟 估算法适宜性探析

介绍了地下水溶质迁移转化模拟软件MT3DMS中的数值解法MOC、MMOC、HMOC和高阶TVD等的基本原理,分析比较了不同解法所获得的地下水污染时空分布模拟结果的质量误差以及纵向弥散度模拟计算结果异同,并进一步探讨了网格大小与污染源质量浓度对模拟结果的影响等.展现了通过数值模拟估算纵向弥散度的基本过程及其适宜性,重点探析了不同数值解法模拟估算弥散度的适用性.     

农业发展的新思路:第二农业

随着中国加入世界贸易组织,农业生产部门在面临着前所未有的挑战的同时,也存在一些难得的发展机遇。如果能在农业发展思路上更新观念,做到扬长避短,则我国的农业生产水平有可能迈上一个新台阶。笔者认为发展第二农业是提高我国农业生产水平、保障农业可持续发展的     

On frequency distribution of impulsive feedback control times

The present work considers an impulsive feedback control problem governed by a system of ODEs defined on a class of isolated time scales. The control is activated once the unique solution’s trajectory leaves a bounded connected domain. A periodicity of the controlled system’s solution in the context of shift-invariant time scales are discussed. Making use of the Δ-measure theory, a cumulative distribution of the control times is introduced. Then with the help of dynamic inequalities on time scales such as Opial-type inequality, upper estimations for the occurrence frequency of the control times are obtained. A uniform distribution of the control times mod 1 is studied and a necessary condition for the uniformity of distribution of control times in terms of critical dynamic of the controlled system is obtained.     

A unified approach to the realization of canonic RC-active,single as well as variable,frequency oscillators using operational amplifiers

A general, unified and systematic approach is employed to study realization of operational amplifier (OA) based sinusoidal RC-active oscillators. Both single frequency and variable frequency operations are investigated. A set of circuits is found for each case. The sets consist of 12 and 16 circuits respectively. The circuits are canonic, that is, they require the minimum number of active and passive components. For each circuit, the single frequency set requires one OA, two capacitors and four resistors, while the variable frequency set needs one OA, two capacitors and five resistors. Both sets are shown to be complete in that generation of any additional canonic circuit is not possible. Variable frequency oscillators are all single resistor controlled. They are classified into four groups according to the nature of their dependence on the variable resistor. All the circuits are laboratory tested. Experimental results agree closely with the theoretical analysis. Representative test results are included.