共查询到19条相似文献,搜索用时 125 毫秒
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GPS接收机输入信号的功率随时间而变化,如果采用固定门限判决是否完成捕获会出现检测概率降低或虚警概率提高的问题.鉴于此,提出了采用自适应捕获门限判决策略完成信号捕获.采用最大似然估计原理,根据判决统计量的样本值得到了噪声方差的最大似然估计,进而求得恒虚警率下的自适应捕获门限.同时,信号的平均捕获时间是GPS接收机性能的重要指标之一,研究了载波频率与伪码相位均为不确定值时的平均捕获时间的计算方法,推导了平均捕获时间与信噪比及门限值之间的约束关系.分析结果表明,自适应门限捕获方法能减小平均捕获时间,实现信号的快速捕获. 相似文献
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介绍了谱差法的原理,导出了自动检测门限,讨论了实际应用中存在的问题。仿真结果表明谱差法可提高信噪比,降低虚警率,增强检测可靠性。 相似文献
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针对次声监测研究领域广泛使用的短时间与长时间信号功率比检测方法性能不能满足要求,渐进多通道互相关检测算法虚警率较高的缺点,利用信号的时、频、波数域特性和次声台阵各子台信号的互相关性特性,提出了一种基于次声台阵信号慢度估计的自动检测算法。次声信号慢度估计结果的合理性、一致性是该检测算法的依据。考虑到该检测算法计算量较大,在具体应用中加入其他计算量较小的传统算法,进行逐次检测,最后应用的慢度估计方法既是一种检测方法,也是对其他检测算法结果的最终审核,一方面可以降低单项检测方法对检测参数的敏感性,另一方面也可提高检测的正确率(虚警率和漏警率同时降低)。该复合检测算法应用于某实验次声台站信号的检测(信噪比大于1.1),结果虚警率为4.0%,漏警率为5.0%,表明了该方法的优良性能。从检测应用处理结果还可以推测,结合一个区域现有密集的地震台站数据和2~3个次声台阵的数据,可以方便地识别、监控爆破方式日益复杂的人工爆破事件和真正的地震(余震)事件,为地震灾害减灾防灾、采矿监控等多领域服务,具有重大推广价值。 相似文献
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一、引 言 声纳信号处理的基本目的是尽量增大声纳信号的输出信噪比,提高信号检测概率,同时减小虚警率,提高检测信号的可信度。声纳信号接收机通常利用干扰信号与有用信号在频谱和能量上的差别,采用滤波和设置门限判决电路的方法来抑制干扰信号,检测出有用信号。 相似文献
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基于分层动态规划的红外弱小目标检测 总被引:2,自引:0,他引:2
为了检测低信噪比下的红外弱小目标,本文将方向中值滤波与分层动态规划算法相结合进行检测前跟踪。利用背景杂波在局部空间上的相关性,提取目标在四个方向的中值进行自适应加权滤波,抑制结构性杂波分量,改善信噪比。针对分割后的备选目标点,为了减少跟踪检测的计算量,根据真实目标运动轨迹的连续性与光滑性,利用分层动态规划算法进行多帧检测,进而对多层检测结果进行配准并做出决策。仿真实验表明方向中值滤波有效的提高了信噪比,分层动态规划算法进一步降低了虚警概率,同时大大提升了计算速度。 相似文献
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Built-in tests (BITs) are widely used in manufacturing and production systems to find whether system failures occur, whereas the problem of BIT false alarms caused by intermittent failures adds to much trouble for the precise failure detection and diagnosis. Fighting with false alarms caused by intermittent failures is an urgent issue. However, the nature and temporal regularity of intermittent failures are not fully exploited, as well as the relationship between intermittent failure and BIT false alarms. The present paper introduces the method of constructing failure test profile for false alarm assessments. Probabilistic models are proposed of the failure evolution process, as well as the interactions between intermittent failures and false alarms. The false alarm time expectation is derived with the given model, serving as the foundation for the optimisation problem to find the best test threshold to enable the highest BIT capability. A numerical analysis is made to illustrate the proposed model and examine the threshold determination method. An application study is also carried out to show how the model can be applicable in real engineering practices. 相似文献
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An improved probabilistic neural network (IPNN) algorithm for use in chemical sensor array pattern recognition applications is described. The IPNN is based on a modified probabilistic neural network (PNN) with three innovations designed to reduce the computational and memory requirements, to speed training, and to decrease the false alarm rate. The utility of this new approach is illustrated with the use of four data sets extracted from simulated and laboratory-collected surface acoustic wave sensor array data. A competitive learning strategy, based on a learning vector quantization neural network, is shown to reduce the storage and computation requirements. The IPNN hidden layer requires only a fraction of the storage space of a conventional PNN. A simple distance-based calculation is reported to approximate the optimal kernel width of a PNN. This calculation is found to decrease the training time and requires no user input. A general procedure for selecting the optimal rejection threshold for a PNN-based algorithm using Monte Carlo simulations is also demonstrated. This outlier rejection strategy is implemented for an IPNN classifier and found to reject ambiguous patterns, thereby decreasing the potential for false alarms. 相似文献
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Nassim Sahki Anne Gégout-Petit Sophie Wantz-Mézières 《Quality and Reliability Engineering International》2020,36(8):2699-2719
Sequential detection is based on a recursive statistic and a threshold it must reach to report a change. In this paper, we consider the score-based cumulative sum statistic and propose to evaluate the detection performance of some thresholds on simulated data. Three thresholds come from the literature: the Wald constant, the empirical constant, and the conditional empirical instantaneous threshold (the latter two are built by a simulation-based procedure). Two new thresholds are built by a simulation-based procedure: the first one is instantaneous, the second is a dynamical version of the previous one. The thresholds' performance measured by an estimation of the mean time between false alarm (MTBFA) and the average detection delay (ADD) are evaluated on independent and autocorrelated data for several scenario, according to the detection objective and the real change in the data. The simulations allow us to compare the difference between the thresholds' results and to see that their performances prove to be robust when a parameter of the prechange regime is misestimated or when the data independence assumption is violated. We found also that the conditional empirical threshold is the best at minimizing the detection delay while maintaining the given false alarm rate. However, on real data, we suggest to use the dynamic instantaneous threshold because it is the easiest to build for practical implementation. 相似文献
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Burcu Aytaçoğlu William H. Woodall 《Quality and Reliability Engineering International》2020,36(2):592-603
We consider the problem of monitoring a proportion with time-varying sample sizes. Control charts are generally designed by assuming a fixed sample size or a priori knowledge of a sample size probability distribution. Sometimes, it is not possible to know, or accurately estimate, a sample size distribution or the distribution may change over time. An improper assumption for the sample size distribution could lead to undesirable performance of the control chart. To handle this problem, we propose the use of dynamic probability control limits (DPCLs) which are determined successively as the sample sizes become known. The method is based on keeping the conditional probability of a false alarm at a predetermined level given that there has not been any earlier false alarm. The control limits dynamically change, and the in-control performance of the chart can be controlled at the desired level for any sequence of sample sizes. The simulation results support this result showing that there is no need for any assumption of a sample size distribution with the use of this proposed approach. 相似文献
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AbstractThe frequency histogram of connected elements (FHCE) is a recently proposed algorithm that has successfully been applied in various medical image segmentation tasks. The FHCE is based on the idea that most pixels belong to the same class as their neighbouring pixels. However, the FHCE performance relies to a great extent on the optimal selection of a threshold parameter. Since evaluating segmentation results is a highly subjective process, a collection of threshold values must typically be examined. No algorithm has been proposed to automate the determination of the threshold parameter value of the FHCE. This study presents a method based on the fuzzy C-means clustering algorithm, designed to automatically generate optimal threshold values for the FHCE. This new approach was applied as a part of a structured sequence of image processing steps in order to facilitate segmentation of microcalcifications in digitized mammograms. A unique threshold value was generated for each mammogram, taking into account the different grey-level patterns based on different compositions of various breast tissues in it. The segmentation algorithm was tested on 100 mammograms (50 collected from the Mammographic Image Analysis Society and 50 normal mammograms onto which a number of simulated microcalcifications were generated). The algorithm was able to detect subtle microcalcifications with sensitivity ranging from 93 to 98%, False alarm ratio from 3 to 5% and false negatives variability from 2 to 3%. 相似文献
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针对现有缺陷管道的磁记忆信号降噪效果不佳及信号完整性鲜有考虑等问题,提出了基于总体平均经验模态分解(ensemble empirical mode decomposition,EEMD)和分层阈值的磁记忆信号降噪方法。首先,设计了以STM32F407为控制核心的金属磁记忆检测系统,用于采集缺陷管道的磁信号;然后,对磁信号进行EEMD预处理,得到其本征模函数(intrinsic mode function, IMF)分量,并根据频谱分析和相似度计算选择最佳分解层数;最后,利用分层阈值降噪算法重构在最佳分解层数下的IMF分量,得到降噪后的信号。通过仿真分析和实验测试,对EEMD分层阈值降噪方法进行定量评价。结果表明:该方法适用于信噪比较小的含噪信号;与小波阈值降噪方法相比,其降噪后信号的信噪比和平滑度较高,均方根误差较小,缺陷特征信号完整,可更直观地显示缺陷位置。研究结果为金属管道磁信号降噪提供了一种切实可行的方法,为管道缺陷的在线检测奠定了基础。 相似文献
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The exclusive use of the time domain analysis in the design tuning to lower the probability of false alarms is caused by the output signal binary nature prevailing in the optical smoke detector designs. However, the characteristic of a standard detector circuit is fairly linear up to the output comparator. On the basis of the generalized functional block scheme, for this linear dependence the Laplace transform is derived in this paper. The transfer function obtained is optimized with respect to false alarm probability minimization, for the second and the fourth order cases. Exploiting the optimization results presented, the improvement of the detector design to obtain lower probability of false alarm reduces to the calculation of element parameters from the coefficients of the optimized transfer function. If the requests for detector time response behavior are different from those adopted here, this paper presents a systematic set of design steps that have to be performed to obtain the optimal performance 相似文献
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Cumulative pulses detection with appropriate cumulative pulses number and threshold has the ability to improve the detection performance of the pulsed laser ranging system with GM-APD. In this paper, based on Poisson statistics and multi-pulses cumulative process, the cumulative detection probabilities and their influence factors are investigated. With the normalized probability distribution of each time bin, the theoretical model of the range accuracy and precision is established, and the factors limiting the range accuracy and precision are discussed. The results show that the cumulative pulses detection can produce higher target detection probability and lower false alarm probability. However, for a heavy noise level and extremely weak echo intensity, the false alarm suppression performance of the cumulative pulses detection deteriorates quickly. The range accuracy and precision is another important parameter evaluating the detection performance, the echo intensity and pulse width are main influence factors on the range accuracy and precision, and higher range accuracy and precision is acquired with stronger echo intensity and narrower echo pulse width, for 5-ns echo pulse width, when the echo intensity is larger than 10, the range accuracy and precision lower than 7.5 cm can be achieved. 相似文献