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超宽带的频谱受两个因素影响：一个是它的调制方式,另一个就是它的脉冲信号的波形。超宽带系统采用的波形有多种,本文重点讨论了最常使用的高斯波形,并根据高斯导函数的特点,组合其一阶和二阶导数,提出了一种符合要求的超宽带发射脉冲的波形。 相似文献
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研究了目前超宽带系统中脉冲波形的几种设计方法,分析了各种方法的优点和缺点,对超宽带系统脉冲的设计和优化有一定参考价值. 相似文献
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首先对雷电放电电流的波形进行分析,提出用脉冲函数作为雷电放电电流的波形函数,然后得出雷电放电电流的频谱和幅频特性。结果对避雷方案的设计、避雷器件的选取和雷害的评估具有一定的指导意义。 相似文献
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文章首先分析了UWB脉冲波形设计原则,然后结合这些要求,对基于不同包络的调制脉冲进行频谱分析,并用MATLAB进行了仿真.结果表明,性能比较理想的是高斯型包络的调制脉冲和升余弦包络的调制脉冲.前者的频谱能量绝大部分集中在主峰;后者的矩形系数比较好,能更好地匹配FCC的频谱模板. 相似文献
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基于超宽带脉冲的脉冲锁相环接收机的研究 总被引：1，自引：0，他引：1
根据超宽带脉冲信号波形及特征,为了在超宽带定位系统中简单、准确的定位。文章采用脉冲锁相环接收机,用脉冲锁相环对标签发射的窄脉冲信号进行相位跟踪,利用相位信息来进行定位。最后通过计算机仿真和实测,验证了此接收机方案能提取较好的定位信息,可以准确定位,同时也降低了接收机的复杂度和设备成本,还避免了传统定位接收机在复杂环境下定位精度不够的缺点。 相似文献
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Chaotic waveforms are natural information carriers since a correspondence can be established between the symbolic dynamics of a chaotic oscillator and the symbols of a message. Message symbols can be efficiently encoded in a chaotic waveform by applying vanishingly small perturbations to an oscillator to guide its symbolic dynamics to follow a desired course. Recently, two chaotic hybrid dynamical systems were shown to have matched filters enabling robust reception of chaotic communication waveforms in the presence of noise. The first of these, the exact shift oscillator, produces waveforms with desirable properties similar to antipodal signaling, but a physical implementation may be difficult to control using small perturbations. The second oscillator, the exact folded-band oscillator, produces less optimal waveforms but is more easily controlled. Here we introduce a method for generating waveforms of the exact shift oscillator by summing waveforms from a bank of easily controlled exact folded-band oscillators. We show that any solution of the exact shift oscillator can be so constructed using only three folded-band oscillators. Thus, this scheme allows us to realize the advantages of both chaotic systems while overcoming their individual disadvantages, thereby enabling practical chaos communications. 相似文献
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提出一种应用于脉冲超宽带相关接收机的新型门控积分方法,它利用简单的线性时不变系统实现带清除的积分．这种门控积分方法简化了系统结构,易于实现．论文引入误差函数和干扰函数评价等效积分性能,还以二阶低通滤波器为例,给出了等效积分应用在模拟匹配相关时的性能计算结果,表明等效方法完全适用于脉冲超宽带模拟相关接收机． 相似文献
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Load voltage waveforms corresponding to symmetrical phase-angle triggering and integral-cycle triggering in single-phase thyristor circuits, and also the waveform due to half-wave rectification, are all discrete forms of amplitude modulation. In each case the modulated output voltage is obtained from a sinusoidal (supply) carrier signal by use of a rectangular modulating function, dependent on thyristor switching.The use of amplitude modulation (AM) techniques for frequency conversion in high power applications is subject to certain severe restrictions of performance. These restrictions can be largely overcome by the use of phase modulation (PM) methods which involve two channels of AM in each electrical supply line.Appropriate waveforms may be realised by the use of controlled switching of thyristors. These are arranged in combinations of inverse-parallel connected pairs forming subtractor modulators. Certain thyristor commutation problems arise in PM systems at high power levels. These problems can be overcome by producing so-called AM/PM waveforms that combine the separate advantages of AM and PM systems. 相似文献
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提出一种基于游程统计和Walsh谱能量分布的调色板图像隐写分析方法,利用调色板颜色的奇偶值(parity value,P值)构造P值图像,通过游程统计和Walsh变换提取出46维特征,并用校准技术削弱载体图像差异对分析统计量的干扰.实验表明,该方法适用于EzStego、分量和以及最佳奇偶隐写等调色板图像隐写算法,比奇异颜色分析准确. 相似文献
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Huifeng Zhang Xinjiang Wei Lingyan Zhang Meiqin Tang 《Journal of The Franklin Institute》2017,354(11):4404-4424
A disturbance rejection approach based on disturbance observer is proposed for a class of nonlinear systems subject to mismatched disturbances. The mismatched disturbances are described by exogenous systems and satisfy partially-known information, which enter the system in the different channels with the control input. The disturbance observer is designed to estimate the mismatched disturbances, which can be introduced separately from the controller design. By integrating disturbance observer with back-stepping method, the disturbance observer plus back-stepping (DOPBS) controller can be constructed to reject the mismatched disturbances. And the asymptotically stability for the closed-loop system can be achieved. Finally, simulation examples are given to demonstrate the feasibility and effectiveness of the proposed scheme compared with existing methods. 相似文献
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《Journal of The Franklin Institute》2022,359(15):7847-7865
The tracking control based on output feedback for a category of flexible-joint robot (FJR) systems is investigated in this brief. Control performance of the systems is inevitably bearing the brunt of various unknown time-varying disturbances, which can be categorized to be matched and mismatched and generally cover internal parameter uncertainties, couplings, unmodelled dynamics, and external load or changing operating environments. To cope with these disturbances, the mismatched disturbances are first transferred to the matched ones by a flatness method, which eliminates the computational cost of estimating mismatched disturbances. Then, a generalized proportional integral observer (GPIO) is constructed to estimate the unavailable states and disturbances. By integrating the estimated disturbance and states provided by the GPIO, a novel dynamic sliding surface is constructed. Finally, a continuous sliding mode control (CSMC)-based output feedback control framework is further designed. The presented control strategy only requires link position information and is continuous, which can effectively reduce the chattering driven by the high-frequency switching item in the traditional SMC method. Asymptotic convergence of output tracking error is guaranteed by theoretical analysis under some mild conditions. Comparative tests on a two-link FJR verify the claimed control performance. 相似文献
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引入矢量量化器码书的特征变量，提出基于结构化码书的两级波形矢量量化器设计新算法。算法包括：合理构造初始码书、快速训练码书、快速量化输入矢量。通过计算机对语音信号矢量量化的模拟，结果表明新算法明显地缩短了复杂度和提高了矢量量化的速度。 相似文献
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《Journal of The Franklin Institute》2019,356(16):9524-9544
This paper is concerned with the problem of discrete-time event-triggered H∞ control for networked cascade control systems (NCCSs) with time-varying network-induced delay. First of all, an event-triggered scheme is introduced to this system for reducing the unnecessary waste of limited network bandwidth resources. Considering the effect of time-varying delay, a new mathematical model for this system is constructed. In this paper, based on the model and Lyapunov functional method, the co-design method of event-triggered parameter, state feedback primary controller and secondary controller with H∞ performance is derived via linear matrix inequality technique. To illustrate the effectiveness of the proposed method, a simulation example considering a main steam temperature cascade control system is given. The proposed method emphasizes the application in the corresponding industrial control systems, it can be found that this method is superior to the one in some existing references, and the provided example demonstrates the effectiveness of the co-design method in the networked cascade control systems with event-triggered scheme. 相似文献
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《Information processing & management》2001,37(3):435-458
We are interested in how ideas from document clustering can be used to improve the retrieval accuracy of ranked lists in interactive systems. In particular, we are interested in ways to evaluate the effectiveness of such systems to decide how they might best be constructed. In this study, we construct and evaluate systems that present the user with ranked lists and a visualization of inter-document similarities. We first carry out a user study to evaluate the clustering/ranked list combination on instance-oriented retrieval, the task of the TREC-6 Interactive Track. We find that although users generally prefer the combination, they are not able to use it to improve effectiveness. In the second half of this study, we develop and evaluate an approach that more directly combines the ranked list with information from inter-document similarities. Using the TREC collections and relevance judgments, we show that it is possible to realize substantial improvements in effectiveness by doing so, and that although users can use the combined information effectively, the system can provide hints that substantially improve on the user's solo effort. The resulting approach shares much in common with an interactive application of incremental relevance feedback. Throughout this study, we illustrate our work using two prototype systems constructed for these evaluations. The first, AspInQuery, is a classic information retrieval system augmented with a specialized tool for recording information about instances of relevance. The other system, Lighthouse, is a Web-based application that combines a ranked list with a portrayal of inter-document similarity. Lighthouse can work with collections such as TREC, as well as the results of Web search engines. 相似文献