共查询到20条相似文献，搜索用时 31 毫秒
1.
In many phase-locked loop (PLL) applications, the natural pull-in mechanism is too slow and unreliable, and it must be accelerated. By adding an externally-generated ramp to its control voltage input, the PLL voltage controlled oscillator (VCO) frequency can be swept towards the input reference frequency in an attempt to speed up the pull-in process. This popular acquisition aid has a significant limitation when it is used in a second-order, Type II PLL. If the applied ramp voltage has a slope magnitude greater than (alternatively, less than) some value Rm, the PLL state can (alternatively, cannot) sweep past the desired lock point, resulting in a phase lock failure (alternatively, success). In general, the maximum sweep rate magnitude Rm can be computed by using a numerical integration-and-search procedure that is described in the PLL literature. A special case exists for a second-order, Type II PLL that incorporates a triangular-characteristic phase detector (with logic-level binary input signals). For this case, it is possible to develop an exact, closed-form expression for Rm, the main result of this paper. For a range of loop parameters most often used in applications, Rm values are computed by using the exact formula, and these are used in two ways. First, they are used to validate the previously-mentioned numerical integration-and-search procedure. Second, they are compared to maximum sweep rate values computed for a PLL that utilizes a sinusoidal phase detector to show that the triangular-phase-detector PLL can be swept significantly faster than the sinusoidal-phase-detector loop. 相似文献
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3.
John Stensby 《Journal of The Franklin Institute》2011,348(4):671-684
A second-order phase-lock loop (PLL) that is based on a triangular-characteristic phase detector and imperfect-integrator loop filter is found in many applications where simplicity and economics are major considerations. For many of these applications, digital-logic-compatible reference and VCO signals are used, an exclusive-OR gate implements the phase detector, and the loop filter is constructed from passive components. When designing these loops, the half-plane pull-in range Ω2 is of interest. Until now, this important loop parameter could only be calculated by using a computer-based technique that numerically integrated the nonlinear differential equation that describes the PLL model. This requirement/limitation is removed here by the development of an exact closed-form formula for Ω2, the main contribution of this paper. More generally, the value of Ω2 is dependent on the PLL phase detector characteristic that is used, be it triangular, sinusoidal, or something else. With regard to the value of Ω2 produced, a comparison is given of two PLLs, both described by the same linear model so that the comparison is meaningful. The first PLL is based on a triangular-characteristic phase detector; the second loop is based on a sinusoidal phase detector. 相似文献
4.
《Journal of The Franklin Institute》1986,322(2):79-92
The detection of a sequence of echo pulses with random carrier phase is an important problem in radar. It is well known that, to a first approximation, the optimum receiver is a quadratic detector for small signal-to-noise ratios and is a linear detector for large signal-to-noise ratios. In this paper, a detector based on scaling and rounding envelope samples into digital words of only a few bits is presented and analyzed. This detector is essentially a generalization of a suboptimum detector known as a binary detector which performs postdetection integration by digital counting and is particularly useful in automatic detection systems. The asymptotic relative efficiencies of this detector relative to the quadratic detector and the linear detector are obtained. Also, non-asymptotic performance comparisons based on relative efficiency and on probability of detection are made. It is shown that this detector is more efficient than the other two detectors in most signal-to-noise ratio ranges. In addition, this detector is applicable when the noise environment is somewhat different from Gaussian. 相似文献
5.
VCO sweep-rate limit for a phase-lock loop 总被引：1，自引：0，他引：1
John Stensby 《Journal of The Franklin Institute》2009,346(3):223-236
Phase-lock loops (PLLs) serve important roles in phase-lock receivers, coherent transponders, and similar applications. For many of these uses, the bandwidth of the loop must be kept small to limit the detrimental influence of noise, and this requirement makes the natural PLL pull-in phenomenon too slow and/or unreliable. For each such case, the phase-lock acquisition process can be aided by the application of an external sweep voltage to the loop voltage controlled oscillators (VCOs). The goal is to have the applied sweep voltage rapidly decrease the closed-loop frequency error to a point where phase lock occurs quickly. For a second-order loop containing a perfect integrator loop filter, there is a maximum VCO sweep-rate magnitude, denoted here as Rm rad/s2, for which phase lock is guaranteed. If the applied VCO sweep rate is less than Rm, the loop cannot sweep past a stable phase-lock point, and it will phase lock. On the other hand, for an applied sweep-rate magnitude that is greater than Rm, the PLL may sweep past a lock point and fail to phase lock. In the existing PLL literature, only a trial-and-error approach has been described for estimating Rm, given values of loop damping factor ζ and natural frequency ωn. Furthermore, no plots exist of computed versus ζ and versus ζ (BL denotes loop-noise bandwidth). These deficiencies are dealt with in this paper. A new iterative numerical technique is given that converges to the maximum sweep-rate magnitude Rm. It is used to generate data for plots of and versus ζ, the likes of which have never appeared before in the PLL literature. 相似文献
6.
The definite integral is generally interpreted geometrically as an “area”. An alternate interpretation as a steady-state “flux” through a unit slab is derived, which leads to a new method of numerical integration. The usual sum of a large number of approximate areas is replaced by the flux through a “single” increment.The method involves the solution of a system of linear finite difference equations. The coefficient matrix is tri-diagonal and is solved efficiently by the Thomas algorithm. During the iterative process the coefficients are determined by simple quadrature schemes applied to each increment.Error analysis revealed that an expression could be derived for the roundoff error associated with the final Thomas iteration. It is shown that the roundoff error is smallest when the matrix coefficients ak\S>1. The method is shown to be superior to the classical methods due to its simplicity and tolerance for variable increment size. In addition, a new function is determined which is useful in diffusion studies. Numerical data are presented confirming these results. 相似文献
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分析了中高分辨率SAR海洋图像的目标和海杂波特点. 利用舰船目标的灰度相关性和形状特性与背景杂波的差异,提出了一种基于独立联合K-分布CFAR的舰船检测算法. 算法建立了海杂波的二维独立联合K-分布概率模型,通过给定的虚警率得到检测阈值以对图像进行检测. 该算法能够极大地抑制斑点噪声和背景局部不均匀对检测带来的影响,有效地降低了虚警数,检测效果得到了明显改善. 相似文献
8.
Emad S. Hassan 《Journal of The Franklin Institute》2019,356(3):1640-1657
The multi-taper spectrum (MTS) estimator enjoys a relatively low computational complexity and high estimation accuracy making it an attractive method for spectrum sensing in cognitive radio (CR) networks. However, it is difficult to guarantee both detection and false alarm probabilities when its design is based on fixed threshold, especially when the noise power fluctuates due to channel conditions. In this paper, a new adaptive threshold method to guarantee both detection and false alarm probabilities for MTS based spectrum sensing is proposed. By means of estimating noise power and signal power, the decision of adaptive threshold is able to adapt the noise fluctuation and achieve efficient trade-off between detection and false alarm probabilities. A closed form expression for the adaptive threshold is derived for both additive white Gaussian noise (AWGN) channel and multipath fading channel. Several metrics are employed to compare the performance of the proposed adaptive threshold method with that of the fixed threshold methods such as: error decision probability, detection probability, false alarm probability and throughput. The obtained results show that the proposed method achieves better spectrum efficiency and high throughput in comparison with the conventional fixed and adaptive threshold methods presented in the literature. 相似文献
9.
有记忆信号的观测值是相互关联的,传统检测方法不能达到最佳效果。本文提出一种基于维特比算法的最大似然序列检测器,Viterbi算法将ML序列检测器执行的网格路径搜索的数量减到最小,采用全并行方案,用FPGA作为硬件载体,从而获得更快的速度和更小的电路规模。 相似文献
10.
直接射频采样的L波段星载SAR数字接收机设计 总被引：1，自引：0，他引：1
设计了一种直接射频采样的L波段星载合成孔径雷达(SAR)数字接收机.适当选取射频采样频率,优化了数字正交解调结构.为减轻数据存储和传输的压力,实现了压缩比可变的分块自适应量化模块.直接射频采样简化了电路设计,提高了SAR系统的精确性和灵活性,仿真结果证明该设计技术可行、有效. 相似文献
11.
为了提升VOIP的通话质量,提高回声抵消系统中双端通话检测的准确性,本文提出一种新的双门限双端通话检测算法。新算法首先利用小波阈值去噪算法对接收的各信号进行去噪处理;然后对去噪处理后的小波子带信号进行动态能量阈值比较,识别出静音帧、活跃帧和发声帧;再对活跃帧与静音帧进行基音周期比较,以判断活跃帧是处在近端发声阶段,还是回声路径的变化。仿真实验证明,新的双门限检测算法表现良好。 相似文献
12.
为了实现UPS快速、稳定和高精度锁相的要求,文章提出了一种基于TMS320F2812的数字锁相方法,建立了Simulink模型对锁相环进行仿真,给出了算法和程序流程。这种方法容易实现,稳定性、动态性能较好。锁相实验结果验证了该方法的可行性和有效性。 相似文献
13.
This research has investigated the feasibility of using a distance measure, called the Bayesian distance, for automatic sequential document classification. It has been shown that by observing the variation of this distance measure as keywords are extracted sequentially from a document, the occurrence of noisy keywords may be detected. This property of the distance measure has been utilized to design a sequential classification algorithm which works in two phases. In the first phase keywords extracted from a document are partitioned into two groups—the good keyword group and the noisy keyword group. In the second phase these two groups of keywords are analyzed separately to assign primary and secondary classes to a document. The algorithm has been applied to several data bases of documents and very encouraging results have been obtained. 相似文献
14.
Andreas M. Maras 《Journal of The Franklin Institute》2005,342(5):565-581
In this paper, a new approach to non-parametric signal detection with independent noise sampling is presented. The present approach is based on the locally asymptotically optimum (LAO) methodology, which is valid for vanishingly small signals and very large sample sizes, and on semi-parametric statistics. Its unique feature and essential difference from other techniques is that LAO non-parametric detectors are optimum according to the Neyman-Pearson criterion by being asymptotically uniformly most powerful at false alarm level α (AUMP (α)) and adaptive in the sense that no loss in Fisher's information number is incurred when the underlying noise process is no longer parametrically defined. Accordingly, they are robust against deviations from the postulated noise model and, unlike other non-parametric detectors, are distribution-free under both hypotheses H0 (“noise only present”) and H1 (“signal and noise present”). Non-parametric LAO detectors are derived from an asymptotic stochastic expansion of the log-likelihood ratio for coherent and narrowband incoherent “on-off” signals. Moreover, under the present framework it is shown that, in direct contrast to already known results, the non-parametric sign detector is AUMP (α) and adaptive even for non-constant signal samples. 相似文献
15.
提出一种对基于扩频信息隐藏图像进行隐写分析的方法.应用马尔科夫链模型,根据图像的相邻像素点之间的相关性,结合阈值判别方法和改进的模式识别方法,判断一幅图像中是否存在隐写信息.在Corel图像库上的实验表明,本方法降低了虚警率,且正检率的性能优于已有方法. 相似文献
16.
Felicitas Kraemer Kees van Overveld Martin Peterson 《Ethics and Information Technology》2011,13(3):251-260
We argue that some algorithms are value-laden, and that two or more persons who accept different value-judgments may have
a rational reason to design such algorithms differently. We exemplify our claim by discussing a set of algorithms used in
medical image analysis: In these algorithms it is often necessary to set certain thresholds for whether e.g. a cell should
count as diseased or not, and the chosen threshold will partly depend on the software designer’s preference between avoiding
false positives and false negatives. This preference ultimately depends on a number of value-judgments. In the last section
of the paper we discuss some general principles for dealing with ethical issues in algorithm-design. 相似文献
17.
《Information processing & management》2005,41(4):745-758
Document filtering (DF) and document classification (DC) are often integrated together to classify suitable documents into suitable categories. A popular way to achieve integrated DF and DC is to associate each category with a threshold. A document d may be classified into a category c only if its degree of acceptance (DOA) with respect to c is higher than the threshold of c. Therefore, tuning a proper threshold for each category is essential. A threshold that is too high (low) may mislead the classifier to reject (accept) too many documents. Unfortunately, thresholding is often based on the classifier's DOA estimations, which cannot always be reliable, due to two common phenomena: (1) the DOA estimations made by the classifier cannot always be correct, and (2) not all documents may be classified without any controversy. Unreliable estimations are actually noises that may mislead the thresholding process. In this paper, we present an adaptive and parameter-free technique AS4T to sample reliable DOA estimations for thresholding. AS4T operates by adapting to the classifier's status, without needing to define any parameters. Experimental results show that, by helping to derive more proper thresholds, AS4T may guide various classifiers to achieve significantly better and more stable performances under different circumstances. The contributions are of practical significance for real-world integrated DF and DC. 相似文献
18.
Mohamed B. El Mashade 《Journal of The Franklin Institute》2005,342(5):521-550
The radar signals returning from the targets being illuminated are usually accompanied by thermal noise and clutter. Constant false alarm rate (CFAR) processors are useful for detecting these targets in a background for which the parameters of the statistical distribution are not known and may be nonstationary. The ordered-statistics (OS) CFAR technique has been proven to work satisfactorily in both multiple-target and nonuniform clutter cases. Unfortunately, the large processing time taken by this scheme limits its practical uses. The modified versions of the OS processor have been proposed to replace it in these applications. They can reduce the processing time of the single-window OS detector in half without changing its useful properties. Our goal in this paper is to provide a complete detection analysis for the OS processor along with ordered-statistic greatest-of (OSGO) and ordered-statistic smallest-of (OSSO) modified versions, for M postdetection integrated pulses when the operating environment is nonideal. Analytical results of performance are presented in both multiple-target situations and in regions of clutter power transitions. The primary and the secondary interfering targets are assumed to be fluctuating in accordance with the Swerling II target fluctuation model. As the number of noncoherently integrated pulses increases, lower threshold values and consequently better detection performances are obtained in both homogeneous and multiple-target background models. However, the false alarm rate performance of OSSO-CFAR scheme at clutter edges worsens with increasing the postdetection integrated pulses. As predicted, the OSGO-CFAR detector accommodates the presence of spurious targets in the reference window, given that their number is within its allowable range in each local window, and controls the rate of false alarm when the contents of the reference cells have clutter boundaries. The OSSO-CFAR scheme is useful in the situation where there is a cluster of radar targets amongst the estimation cells. 相似文献
19.
一种基于局部K-分布的新的SAR图像舰船检测算法 总被引：1，自引：0，他引：1
提出了一种基于局部K-分布的新的SAR图像舰船检测算法.取目标窗口和背景窗口,通过把泄露到背景窗口中的舰船部分去除,对背景窗口中的剩余部分统计均值和方差,最终得到杂波分布概率模型进行恒虚警检测.相对于K-分布CFAR检测算法和基于局部窗口的K-分布CFAR检测算法,该算法能够适应杂波的局部变化, 对距离很近的舰船不会产生漏检.仿真结果表明了方法的有效性. 相似文献
20.
《Information processing & management》2020,57(6):102302
With the increasing growth of video data, especially in cyberspace, video captioning or the representation of video data in the form of natural language has been receiving an increasing amount of interest in several applications like video retrieval, action recognition, and video understanding, to name a few. In recent years, deep neural networks have been successfully applied for the task of video captioning. However, most existing methods describe a video clip using only one sentence that may not correctly cover the semantic content of the video clip. In this paper, a new multi-sentence video captioning algorithm is proposed using a content-oriented beam search approach and a multi-stage refining method. We use a new content-oriented beam search algorithm to update the probabilities of words generated by the trained deep networks. The proposed beam search algorithm leverages the high-level semantic information of an input video using an object detector and the structural dictionary of sentences. We also use a multi-stage refining approach to remove structurally wrong sentences as well as sentences that are less related to the semantic content of the video. To this intent, a new two-branch deep neural network is proposed to measure the relevance score between a sentence and a video. We evaluated the performance of the proposed method with two popular video captioning databases and compared the results with the results of some state-of-the-art approaches. The experiments showed the superior performance of the proposed algorithm. For instance, in the MSVD database, the proposed method shows an enhancement of 6% for the best-1 sentences in comparison to the best state-of-the-art alternative. 相似文献