Performance of receivers with linear detectors

The false-alarm and detection probabilities of a receiver summing M independent outputs of a linear detector are calculated by numerical saddlepoint integration. The saddlepoint approximation is also considered. Both constant-amplitude and Rayleigh-fading signals are treated, and the relative efficiency of the quadratic and the linear detectors for these is calculated for a broad range of values of M . The numerical integration method is the more efficient, the smaller the false-alarm probability or the false-dismissal probability, that is, under just those conditions for which the terms in the Gram-Charlier series oscillate most violently and the series becomes least reliable. The simpler saddlepoint approximation yields values that in those same regions have been found close enough to the exact probabilities to be adequate for most engineering purposes. The larger the number M of samples, the more efficient methods are     

Estimation techniques for GMSK using linear detectors in satellite communications

This paper describes data-aided signal level and noise variance estimators for Gaussian minimum shift keying (GMSK) when the observations are limited to the output of a filter matched to the first pulse-amplitude modulation (PAM) pulse in the equivalent PAM representation. The estimators are based on the maximum likelihood (ML) principle and assume burst-mode transmission with known timing and a block of L₀ known bits. While it is well known that ML estimators are asymptotically unbiased and efficient, the analysis quantifies the rate at which the estimators approach these asymptotic properties. It is shown that the carrier phase, amplitude, and noise variance estimators are unbiased and can achieve their corresponding Cramer-Rao bounds with modest combinations of signal-to-noise ratio and observation length. The estimates are used to estimate the signal-to-noise ratio. It is shown that the mean squared error performance of the ratio increases with signal-to-noise ratio while the mean squared error performance of the ratio in decibels decreases with signal-to-noise ratio. Simulation results are provided to confirm the accuracy of the analytic results.     

Cycle slip performance of digitally implemented phase detectors onAWGN channel

Cycle slip performance of digitally implemented phase detectors on additive white Gaussian noise (AWGN) channel is investigated. The performance measure evaluated is the mean cycle slip time of a first-order phase-locked loop. An equivalent phase detector model with state-dependent loop noise is employed. It is shown that this working basis is vital to arrive at correct results. Numerical results for triangular and saw-tooth type phase detectors are reported and compared with those for the multiplier phase detector     

Automatic generation of binary feature detectors

The authors discuss the automatic generation of feature detectors, which is the major task in the design of classical pattern recognition systems. They present a software environment that, in place of human intuition, utilizes learning strategies and stochastic search procedures to guide the generation process. The environment allows the exploration of evolutionary learning processes and adaptive control mechanisms. A preliminary experiment with a two-class recognition system is described, and initial observations are discussed. The recognition task requires the classification of upper case English letters into two categories: target and nontarget     

凸曲线的求长问题

本文给出并证明了凸函数的一个新的性质（文中引理及其证明）,依此证明了凸曲线是可以求出长度的曲线（文中定理及其证明）及凸函数是可以积分的函数。     

Performance of MAX family of order-statistic CFAR detectors

The MAX family of constant-false-alarm-rate (CFAR) detectors is introduced as a generalization of the greatest of CFAR (GO-CFAR) or MX mean-level detector (MX-MLD). Members of the MAX family use local estimators based on order statistics and generate both a near-range and a far-range noise-level estimate. Local estimates are always combined through a maximum operation; this insures false-alarm control at clutter edges. At the same time, order-statistic-based estimators result in a high-resolution detector. A complete detection analysis is provided for SWII targets and a reference channel contaminated by large outliers. Results are presented for the MX censored MLD (MX-CMLD) operating in clutter. The MX order statistic detector (MX-OSD) based on only a single-order statistic per window, is analyzed, and curves showing the required threshold, CFAR loss, optimum censoring point, and signal-to-noise ratio (SNR) loss in the presence of outliers are given. Simulations are used to compare the dynamic responses of various MX-OSD detectors in a clutter and a multiple-target environment     

表面微观形貌的MOTIF参数计算

对MOTIF参数的基本概念、意义及算法作了介绍,并在精密加工试件上进行了实验。     

Effect of initial microstructure on performance and corrosion behavior of GH4169 superalloy joint produced by linear friction welding

The pre-weld heat treatment was carried out to obtain different initial microstructures of the GH4169 superalloy, and then Linear Friction Welding（LFW） was performed. The effect of the pre-weld heat treatment on the microstructure evolution and mechanical properties of the joint was analyzed, and the joint electrochemical corrosion behavior as well as the hot corrosion behavior was studied. The results show that the joint hardness of Base Metal（BM） increases after pre-weld heat treatment, and the strengthening phases γ'and γ'further precipitate. However, the precipitation phases dissolve significantly in the Weld Zone（WZ） due to the thermal process of LFW. The corrosion resistance in BM is reduced after the pre-weld heat treatment, while it is similar in WZ with a slight decrease. The surface morphology of the BM and WZ can be generally divided into a loose and porous matrix and a scattered oxide particle layer after hot corrosion. The joint cross section exhibits a Cr-depleted zone with the diffusion of Cr to form an oxide film. The corrosion product mainly consists of Fe₂O₃/Fe₃O₄ as the outer layer and Cr₂O₃ as the inner layer.     

Mutual and conditional mutual informations for optimizingdistributed Bayes detectors

This paper considers optimization of distributed detectors under the Bayes criterion. A distributed detector consists of multiple local detectors and a fusion center that combines the local decision results to obtain a final decision. Introduced first are distributional distance measures, the mutual information (MI) and the conditional mutual information (CMI), that are obtained by applying information theoretic concepts to detection problems. Error bound analyses show that these distance measures approximate the Bayesian probability of error better than the conventional ones regardless of the operational environments. Then, a new optimization technique is proposed for distributed Bayes detectors. The method uses the distributional distances instead of the original Bayes criterion to avoid the complexity barrier of the optimization problem. Numerical examples show that the proposed distance measures yield solutions far better than the existing ones     

备件配置方法研究

针对电路板件故障数据记录的实际,运用可靠性理论,提出了没有故障数据板件的备件数量计算方法;对有故障统计数据的板件引用了经验模型来确定备件配置。     

飞机重心位置的计算分析方法

飞机重心位置对飞机的安定性和操纵性影响很大.不在飞机重心允许范围内装货或载客时,会使飞机操纵性和安定性变差,影响飞行安全.飞机重心位置计算分析是新型飞机研制、现役飞机加改(换)装设计等工程中必不可少的一个重要环节.以某型现役飞机进口短波单边带电台换装国产短波自适应/跳频电台工程作为研究对象,研究了基于力矩平衡法的飞机重心位置计算方法,计算了该型飞机换装短波电台后空机重心位置.计算结果表明,该型飞机进口短波电台换装国产短波电台后,空机状态下的重心位置满足重心允许范围要求.     

Family of constrained signal detectors for hyperspectral imagery

Generalized likelihood ratio tests (GLRTs) are derived for the problem of detecting targets in hyperspectral images. These detectors are derived under the assumptions that the signals from the materials in the image mix linearly and that the noise in the system is Gaussian. It is also assumed that the abundances of the signals from the various materials in a pixel must sum to one. This constraint models the fact that the material abundances in a pixel are just the fraction of the pixel that they occupy. Under these assumptions, detectors are derived which outperform the detectors derived without the sum-to-one constraint.     

直升机的RCS计算

RCS（Radar Cross Section）是反映目标雷达散射特性的一个重要参数。一般把雷达目标除质心平动之外的转动,小幅振动和其它高阶运动统称为微动。主要研究旋翼转动情况下的直升机RCS计算。通过对直升机模型进行可视化计算即一种将目标建模与散射特性计算合为一体的交互式计算,使用图形算法（GRECO）和三维造型软件UG相结合的方法,这种方法与传统的RCS计算方法相比具有实时性好,效率高的优点,计算出直升机主体的RCS,再通过其加入调制的方法,计算得到直升机在旋翼转动条件下的RCS。最后给出了微动直升机的在具体入射情况下的单站RCS值。     

CFAR behavior of adaptive detectors: an experimental analysis

We conduct an experimental analysis for assessing the constant false alarm rate (CFAR) behavior of four coherent adaptive radar detectors in the presence of experimentally measured clutter data. To this end we exploit several data files containing both land, lake, and mixed land and sea clutter, collected by two radar systems (the MIT Lincoln Laboratory Phase-One radar and the McMaster IPIX radar) at different polarizations, range resolutions, and frequency bands. The results show that all the receivers, in the presence of real data, don't respect their nominal probability of false alarm (P/sub fa/), namely they exhibit a false alarm rate higher than the value preassigned at the design stage. Nevertheless one of them, the recursive persymmetric adaptive normalized matched filter (RP-ANMF) is very robust, in the sense that it presents an acceptable displacement from the nominal P/sub fa/, in correspondence of all the analyzed scenarios.     

Electrostatic field detectors, the seaside, and the desert wind?[PERIFELD-M security fence]

In the early 1960s, the first ideas were developed by leading companies in Germany to design an intrusion detection system following a capacitance measurement principle. In 1982, Siemens AG was the first company in this market which analysed all outdoor influences and recognised the essential problems which cause any classic capacitive or electrostatic detector to suffer from high unwanted false alarm rates. The result was that, already in 1984, a complete new peripheral hardware design, with a very high electrical and capacitive stability, was created by Siemens AG which remains state-of-the-art. Nevertheless, even if this high-grade material is installed, it can happen in certain cases that apparently invisible peripheral influences are the cause of important electrical effects. This paper describes a practical case experienced in 1999 where a coincidental combination of seaside conditions and a local desert wind strongly interfered in the physics of a capacitive electrostatic field detector     

Development of the Technique for Calculating the Ejectors with Low Entrainment Ratios

This paper presents the results of an investigation of ejectors with the low entrainment ratio. A technique for calculating the ejectors with a curvilinear axis has been developed. Comparative studies of the performance characteristics of ejectors with the rectilinear axis of the mixing chamber and the curvilinear initial section of the mixing chamber are carried out.     

AHP在企业货币资金占有率计算中的应用

持有一定数额的货币资金是企业维持正常生产经营的保证，文章利用层次分析法对企业货币资金的占有率计算问题进行了研究，为企业持有合理数量的货币资金提供一种有效的计算方法。     

目标运动要素解算方法的探讨

提出了适用于水下目标运动要素估算数据融合、最小二乘估计和Kalman滤波估计模型,本模型被用于航空反潜作战中目标运动要素估算,具有良好的效果。     

基于阻力气动特性计算的飞艇艇身外形研究

采用SIMPLE算法、S-A湍流模型求解了三维不可压雷诺平均N-S方程,数值模拟了绕飞艇的低速不可压粘性流动,计算了不同艇身外形的阻力特性.本文方法计算结果与实验结果或其他文献的计算结果符合良好,可以用于飞艇的气动特性计算.通过对6个不同外形的相同体积飞艇阻力特性计算,得到了最佳艇身外形,表明本文方法可以用于艇身外形的选型设计.