采用低秩稀疏建模的盲频谱检测算法

频谱检测技术是认知无线电的一项关键技术,传统的频谱检测方法或依赖于相关的先验信息,或受限于低信噪比和运算复杂度的影响,在实际应用中均有一定的缺陷。针对此问题,本文基于协方差矩阵的检测算法,结合低秩稀疏建模理论,建立了频谱检测的低秩稀疏模型,提出了一种改进的频谱检测新方法。所提方法不需要事先获取主用户信号和噪声功率等先验信息,对信号样本的协方差矩阵进行低秩稀疏分解,以低秩矩阵之间的特征差异来判决当前是否存在主用户信号。仿真实验验证了所提方法具有较好的检测性能和鲁棒性。      

Built-in Self Test of RF Subsystems with Integrated Detectors

This paper describes a built-in self test technique for RF subsystems, using low-overhead on-chip detectors to calculate circuit specifications. A novel on-chip amplitude detector has been designed and optimized for RF circuit specification test. The detector has small area overhead with a low-frequency output. A test chip was fabricated in a commercial 0.18 μm CMOS process. By using on-chip detectors in a loopback setup, both the system performance and specifications of the individual components can be accurately measured. Measurements show accurate prediction of system and component specifications.     

A Parametric Approach to Suboptimal Signal Detection in α-Stable Noise

This paper deals with the detection of a known deterministic signal embedded in alpha-stable noise. The implementation of the optimal receiver requires the explicit expression of the probability density function (pdf) of the noise. Unfortunately, since there exists no closed-form for the pdf of alpha-stable distributed random variables, numerical integrations are required. To avoid such numerical approximations, we suggest a low-complexity parametric suboptimal detector well matched to essential properties of alpha-stable noises. This receiver does not require the explicit expression of the noise pdf. In addition, parameter optimization is fast for several optimization criteria and the selected receiver allows retrieval of the optimal Gaussian detector (matched filter) as well as the locally optimal detector in the Cauchy context. The performance of the detector is studied and a comparison with the optimal solution along with a variety of classical detectors is given. The robustness of the detector against the signal amplitude and the stability index alpha of the noise is discussed     

Anomaly detection from hyperspectral imagery

We develop anomaly detectors, i.e., detectors that do not presuppose a signature model of one or more dimensions, for three clutter models: the local normal model, the global normal mixture model, and the global linear mixture model. The local normal model treats the neighborhood of a pixel as having a normal probability distribution. The normal mixture model considers the observation from each pixel as arising from one of several possible classes such that each class has a normal probability distribution. The linear mixture model considers each observation to be a linear combination of fixed spectra, known as endmembers, that are, or may be, associated with materials in the scene, and the coefficients, interpreted as fractional abundance, are constrained to be nonnegative and sum to one. We show how the generalized likelihood ratio test (GLRT) may be used to derive anomaly detectors for the local normal and global normal mixture models. The anomaly detector applied with the linear mixture approach proceeds by identifying target like endmembers based on properties of the histogram of the abundance estimates and employing a matched filter in the space of abundance estimates. To overcome the limitations of the individual models, we develop a joint decision logic, based on a maximum entropy probability model and the GLRT, that utilizes multiple decision statistics, and we apply this approach using the detection statistics derived from the three clutter models. Examples demonstrate that the joint decision logic can improve detection performance in comparison with the individual anomaly detectors. We also describe the application of linear prediction filters to repeated images of the same area to detect changes that occur within the scene over time     

带虚警抑制的基于归一化残差的野值检测方法

野值检测,或称异常值检测是模式识别和知识发现中一个重要的问题。以往的野值检测方法难以有效地抑制虚警概率,针对这一问题,该文提出一种带监督情形下基于归一化残差(Normalized Residual, NR)的野值检测方法。首先利用训练样本计算待考查模式的NR值,其次比较NR值与野值检测门限的相对大小,从而判断待考查模式是否为野值。该文理论上推导了野值门限与虚警概率之间的关系表达式,以此为依据设置检测门限,可实现在少量训练样本情况下仍能抑制虚警率的目的。计算机仿真和实测数据测试验证了所提方法在野值检测和虚警抑制方面的优越性能。     

一种混合模型的时序数据异常检测方法

对设备性能指标、用户数据指标的异常检测能有效地发现系统潜在故障,本文提出了一种混合异常检测方法。该方法利用k-means将历史数据按照时间进行划分,使用grubbs算法剔除历史数据中的噪音,并计算各时间段的阈值形成动态阈值,同时利用曲线拟合和ARIMA算法对预处理后的历史数据进行训练,得到对应的模型,作为判断异常的依据。该方法结合了统计学的高效、机器学习的准确,无需对数据进行标注,该方法能自动发现单指标和多指标异常。通过在几个系统的实际运维的检验,本文提出的方法能有效地发现缺数异常和系统异常,提高告警准确率,单指标的查全率达到100%,平均查准率为95.7%,算法的效率满足生产环境中的性能要求。     

Pyroelectric detection properties of gadolinium molybdate (gmo)

The pyroelectric detection properties of gadolinium molybdate (GMO) crystals have been studied near and at its 159°C ferroelectric transition temperature. Responsivity and detectivity figures of merit are calculated from measurements of pyroelectric currents induced by white light irradiation and are compared with room temperature figures of merit for TGS and SBN detectors. Since GMO does not exhibit a dielectric anomaly, it can be used as a threshold detector by heating through the transition temperature from a pre-selected temperature increment below the transition. Voltage-sensitive pyroelectric currents at the transition, found previously, permit voltage control of the threshold.     

Dark noise of Ga0.47 In0.53As photoconductive detectors

We have studied the dark noise of planar, interdigitated Ga0.47In0.53As photoconductive detectors by measuring the statistical distribution of the dark current under DC bias. The measurements reveal two interesting results: (i) the probability distribution of the dark current around its DC level is Gaussian and (ii) the standard deviation of the probability distribution grows exponentially with increasing bias voltage. Utilising these data an optimum bias level was calculated to maximise the receiver sensitivity of the detector.     

基于特征检测器的能量采集认知无线电系统优化研究

将特征检测器频谱感知方案引入能量采集的认知无线电系统中, 分析比较了不同检测器背景下感知阈值和感知时间对系统性能的影响,且在能量约束和碰撞限制条件下,以最大化系统次级用户的吞吐量为目标计算出最优的感知时间。计算机仿真结果表明,在合适的感知阈值条件下,三种检测器的感知时间最优解有所差异,能量检测器同时依赖于能量约束和碰撞限制,最大特征值检测器仅受限于能量,而最大最小特征值检测器则无法找到最优的感知时间。     

Experimental Results for Self-Dual Multi-Output Combinational Circuits

In this short note, the possibilities and the limitations for the application of self-dual circuits with alternating inputs are experimentally investigated. The original circuit is assumed to be given as a netlist of gates. The necessary area overhead, the fault coverage for single stuck-at faults in test mode and the error detection probability in on-line mode due to internal stuck-at faults and stuck-at faults at the input lines are determined for MCNC benchmark circuits.     

Threshold learning and Brownian motion (Corresp.)

An approach to the analysis of threshold learning suggested by the classical theory of Brownian motion is presented. In particular, it is shown how a nonlinear Langevin equation represents the motion of the threshold of a trainable signal detector, and how a Fokker-Planck diffusion equation yields an estimate of the shape of the probability density of the threshold. Our results are applicable to all trainable signal detectors in which the training procedure 1) raises the threshold in response to a false alarm, lowers the threshold in response to a false rest, and keeps the threshold unchanged in response to a correct decision, and 2) adjusts the size of the threshold increment by an amount that depends only on the trial number, and such that the threshold can eventually reach any real number.     

Performance of positron imaging systems as a function of energy threshold and shielding depth

The effect of energy discrimination and shielding on positron imaging data quality was investigated using a detector pair to simulate a ring positron emission tomograph. Formulas are presented relating the sensitivity, random fraction, and scatter fraction for a detector pair to the same parameters for a ring system. Data were fitted to detector pair expressions for the variation of the above parameters with shielding depth in order to obtain information on the effect of energy threshold level. These fitted curves were used to determine the sensitivity, random fraction, and scatter fraction, as well as an overall data quality factor as a function of energy threshold level and shielding depth. Data were obtained for both NaI(T1) and BGO detector types using activity levels in the range of 1.5 muCi/cm3. Results show that for NaI(T1) detectors, the lowest possible energy threshold level is optimal, with the corresponding optimal shielding depth determined by the level of activity to be imaged. For BGO detectors, a tradeoff exists between energy thresholds of 100-400 keV and shielding depths of 15-30 cm with smaller shielding depths requiring higher energy thresholds.     

Light Emission to Time Resolved Emission For IC Debug and Failure Analysis

Light emission is routinely used to locate abnormal areas in failed ICs. Localization is done while the device is activated by a test pattern in a loop. Time Resolved Emission (TRE) has the potential to analyse faults by studying the emission of one area as a function of time. For failure analysis both techniques are valuable to identify where and when abnormal emission events have occurred. At low VDD, using only one or the other emission technique has shown some limitations. A solution, presented here, is to add a NIR PMT detector on an existing light emission microscope. Choice of detectors, performances and implementation are detailed on 120 and 90 nm structures.     

激光辐照面阵CCD探测器系统局部的干扰效应

采用脉冲与连续激光实现了对面阵CCD探测器系统的干扰,研究了脉冲与连续激光辐照CCD探测器系统时,CCD探测器系统工作状态的变化,测量了CCD探测器系统的饱和阈值范围,并分析了造成饱和的原因.在实验中观察到了"光饱和串音"现象,采用脉冲激光实现了对面阵CCD探测器的硬破坏.     

Maximum likelihood detection and estimation of Bernoulli - Gaussian processes

A new detection algorithm, single most likely replacement (SMLR), for detecting randomly located impulsive events which have Gaussian-distributed amplitudes is presented. This detector is designed for the case of severely overlapping wavelets. Estimation of the probability of events also is consider. Experimental results and comparisons with other detectors, using synthetic data, are provided.     

A statistical and geometrical edge detector for SAR images

A constant-false-alarm-rate (CFAR) edge detector based on the ratio between pixel values is described. The probability distribution of the image obtained by applying the edge detector is derived. Hence, the decision threshold can be theoretically determined for a given probability of false alarm as a function of the number of looks of the image under study and the size of the processing neighborhood. For a better and finer detection, the edge detector operates along the four usual directions over windows of increasing sizes. A test performed, for a given direction, on a radar image of an agricultural scene shows good agreement with the theoretical study. The operator is compared with the CFAR edge detectors suitable for radar images     

Fault Coverage Analysis of Peak-Detector Based BIST for RF LNAs

Analog and mixed-signal testing is becoming an important issue that affects both the time-to-market and the product cost of many SoCs. In order to provide an efficient testing method for 865–870 MHz low noise amplifiers (LNAs), which constitute a mixed-signal circuit, a novel BIST method is developed. This BIST can be easily implemented with a RF peak detector and two comparators. The circuit used in the test and the LNA are designed using 0.35 μm CMOS technology. The simulation results show higher fault coverage than that of previous test methods. A total of twenty eight short and open (catastrophic) faults and eleven variation parameters have been introduced into the LNA, giving fault coverage of 100% for catastrophic faults and parametric variation. Thus, it provides an efficient structural test, which is suitable for a production test in terms of an area overhead, a test accessibility, and test time.     

多基地雷达中双门限CFAR检测算法

针对多基地雷达系统,该文为解决传统集中式检测算法数据传输率大的问题,根据广义似然比检测算法和自适应匹配滤波算法,提出两种双门限恒虚警率检测器:双门限广义似然比检测器和双门限自适应匹配滤波检测器。首先各个局部雷达站将超过第1门限的局部检验统计量传送到融合中心。然后融合中心根据局部雷达站传送的数据计算融合后的全局检验统计量,并与第2门限比较,得到最终的判决结果。在各空间分集通道的信杂噪比假设相同的条件下,给出了双门限自适应匹配滤波检测器的虚警概率和检测概率的解析表达式。仿真结果表明,两种双门限检测器在低数据率传输时能够保持较好的检测性能。     

采用多像素光子计数器的探测率与虚警率

为了完善多像素光子计数器（MPPC）在激光测距和激光雷达等方面应用的理论基础,对MPPC作为激光测距或激光雷达光探测器的探测率与虚警率进行了系统研究,运用泊松理论提出了基于MPPC的探测率与虚警率模型,推导了相应的解析表达式,并进行了数值分析,发现了一些传统探测器不存在的有趣特性。数值结果显示,利用多像素光子计数器作为激光测距的光接收器时,即使不使用门控（选通）技术,仅仅依靠等效光电子数探测阈值调节技术就可以达到实际应用中激光测距的系统要求。其灵敏度可达到光子量级,并能进行光子数分辨。该模型和结果对于促进MPPC在激光测距和激光雷达方面的应用,实现高灵敏度快速探测有一定的理论和实用价值。     

Detecting landmines with ground-penetrating radar using feature-based rules, order statistics, and adaptive whitening

An approach to detecting landmines using ground-penetrating radar (GPR) based on feature-based rules, order statistics, and adaptive whitening (FROSAW) is described. FROSAW relies on independent adaptation of whitening statistics in different depths and combining feature-based methods with anomaly detection using rules. Constant false alarm rate (CFAR) detectors are used for anomaly detection on the depth-dependent adaptively whitened data. A single CFAR confidence measure is computed via a function of order statistics. Anomalies are detected at locations with high CFAR confidence. Depth-dependent features are computed on regions containing anomalies. Rules based on the features are used to reject alarms that do not exhibit mine-like properties. The utility of combining the CFAR and feature-based methods is evaluated. The algorithms and analysis are applied to data acquired from tens of thousands of square meters from several outdoor test sites with a state-of-the-art array of GPR sensors.