Evaluating the Detectability of Gaussian Stochastic Signals by Steepest Descent Integration

It is shown how to compute the detection probability of certain signals by numerical integration of the Laplace inversion integral involving the characteristic function or the moment-generating function of the detection statistic. The contour of integration is taken as the path of steepest descent of the integrand and is determined numerically as the integration proceeds. The method is applied to calculating the performance of the optimum detector of a Gaussian stochastic signal in white noise when the signals actually present have a different average s.n.r. from that assumed in the design. Results are presented for narrowband signals with Lorentz and rectangular spectral densities. The detectability of the former is shown to be more sensitive than that of the latter to the value of the design s.n.r. The relative disadvantage of the threshold detector, also assessed by this method, is smaller for signals with a rectangular than for those with a Lorentz spectral density.     

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     

Geometric aspects of long-term noncoherent integration

Long-term integration is defined as integration, perhaps interrupted, over time periods long enough for targets to move through volumes in space resolvable by the radar. Because the motion of the target is unknown prior to detection, long-term integration must be performed along multiple paths representing plausible target paths. The geometry of such a set of integration paths affects detection performance in several ways. The simplest implementation of long-term integration, using constant radial velocity paths, is investigated. The effects of path geometry on detection is quantified and optimized for a target whose motion is nearly radial but otherwise unknown     

喷管跨声速流场计算

本文用时间相关法求解定常跨声速喷管流场。对守恒型和非守恒型方程采用全场统一时间步长、当地时间步长和修正超阻尼法进行了计算。计算表明:采用当地时间步长可大大提高收敛速度,采用全场统一时间步长时,数值解非守恒型方程收敛较快;采用修正超阻尼法也能提高收敛速度,但与阻尼系数和时间间隔有关。     

Detectability of signals in Laplace noise

Closed-form expressions for the false-alarm and detection probabilities attained by the optimum and the linear detectors of a positive signal in n independent samples of noise having a bilateral exponential or Laplace distribution require lengthy computation when n is large, and those for the optimum detector suffer from round-off error because their terms alternate in sign. It is shown how the method of saddlepoint integration can be conveniently applied to compute these probabilities, and numerical comparisons of the accuracies of the methods are presented. The relative efficiency of the two detectors is calculated as a function of n and found to approach the asymptotic value of 2 very slowly     

Mean-Level Detection of Nonfluctuating Signals

Analysis of the performance of a mean-level threshold in the detection of nonfluctuating signals is performed. Formulas for the probability of detection are derived and a simple recursive method that can be used for computations is described. Binary integration is discussed, and it is shown that the loss in sensitivity due to the use of an adaptive threshold followed by binary integration is only a fraction of a decibel when compared with optimum binary integration. Binary integration results are given for both fluctuating and nonfluctuating signals.     

Hybrid integration method for highly maneuvering radar target detection based on a Markov motion model

To detect highly maneuvering radar targets in low signal-to-noise ratio conditions, a hybrid long-time integration method is proposed, which combines Radon-Fourier Transform (RFT), Dynamic Programming (DP), and Binary Integration (BI), named RFT-DP-BI. A Markov model with unified range-velocity quantification is formulated to describe the maneuvering target’s motion. Based on this model, long-time hybrid integration is performed. Firstly, the whole integration time is divided into multiple time segments and coherent integration is performed in each segment via RFT. Secondly, non-coherent integration is performed in all segments via DP. Thirdly, 2/4 binary integration is performed to further improve the detection performance. Finally, the detection results are exported together with target range and velocity trajectories. The proposed method can perform the long-time integration of highly maneuvering targets with arbitrary forms of motion. Additionally, it has a low computational cost that is linear to the integration time. Both simulated and real radar data demonstrate that it offers good detection and estimation performances.     

Rotorcraft flight endurance estimation based on a new battery discharge model

To avoid the numerical complexities of the battery discharge law of electric-powered rotorcrafts,this study uses the Kriging method to model the discharge characteristics of Li-Po batteries under standard conditions.A linear current compensation term and an ambient temperature compensation term based on radial basis functions are then applied to the trained Kriging model,leading to the complete discharged capacity-terminal voltage model.Using an orthogonal experimental design and a sequential method,the coefficients of the current and ambient temperature compensation terms are determined through robust optimization.An endurance calculation model for electric-powered rotorcrafts is then established,based on the battery discharge model,through numerical integration.Laboratory tests show that the maximum relative error of the proposed discharged capacity-terminal voltage model at detection points is 0.0086,and that of the rotorcraft endurance calculation model is 0.0195,thus verifying their accuracy.A flight test further demonstrates the applicability of the proposed endurance model to general electric-powered rotorcrafts.     

Efficient numerical algorithm for steady-state Kalman covariance

A stable, quadratically convergent numerical algorithm is presented for computing the steady-state covariance and gain matrices of the Kalman filter. The method is more rapidly convergent than standard Riccati integration techniques and is easier to implement than existing eigenvalue-eigenvector algorithms. The quadratic convergence is proved analytically and illustrated by a numerical example     

Loss in Single-Channel MTI with Post-Detection Integration

The detection performance of a single-channel MTI receiver with post-detection integration, for a Swerling I target, has been evaluated by a Monte Carlo simulation. It is shown that a fairly good approximation is obtained by applying the ?effective number of independent integrated samples? to the standard detection curves. The ?I-only? loss is about 2 dB for integration of more than 20 pulses; thus this receiver is acceptable if implementation constraints dictate it.     

Calculating the performance of linear and square-law detectors

A method is presented for calculating the performance of linear and square-law detectors in detection schemes that employ noncoherent integration. The method consists of transforming the coherent characteristic function, which is usually easy to obtain to a noncoherent moment generating function describing the test statistic of a linear or square-law detector. The method provides a single mathematical framework for many signal models (both classical and new) and can be implemented using standard numerical routines. Although the method is not always optimum in terms of computing speed for specific classical models, its common approach for all signal models makes it very efficient in term of learning and implementation times. Classical results as well as results for an extended set of target models consisting of an arbitrary number of constant amplitude random phase returns are presented to demonstrate the technique. It is shown for the signal parameters considered that the performance difference between the linear and square-law detectors is relatively insignificant     

基于多载频MIMO雷达的Radon-Fourier变换盲速旁瓣抑制

 长时间相干积累方法Radon-Fourier变换(RFT)中盲速旁瓣(BSSL)现象会导致雷达虚警增加、目标检测性能降低。针对BSSL问题,给出了一种基于多输入多输出(MIMO)雷达多载频设计的BSSL抑制方法。首先根据载频与BSSL分布的关系,详细推导了BSSL不交叠的约束条件;然后基于该约束条件给出了具体的载频设计公式。利用设计的载频可得到具有不交叠BSSL的两个RFT输出,通过联合处理这两个RFT输出,可实现BSSL抑制。给出了BSSL抑制性能的评价方法。理论分析和数值实验结果表明,本文算法能够在不降低RFT相干积累性能的同时,有效实现BSSL抑制。     

一种无条件稳定的时域推进法与有限元混合分析瞬态热传导问题

本文将一种新的无条件稳定的时域推进法与有限元结合,用于分析瞬态热传导问题。根据微-积分型热传导控制方程,对时间变量在小区闻内插值积分,变初-边值问题为一系列离散时刻的边界值问题,再应用有限元法求解之。由于推进中的每一时刻的解,都严格满足原给定的初始条件,就消除了累积误差的影响。此外,这种时域推进法对时间变量的数值积分也优于数值微分。因而,与现行的基于微分型控制方程,采用时-空有限元模型同时离散,再逐步求解的直接积分算法相比,计算精度可大大提高。不难预料,当求解较长时间后的瞬态值时,本算法的优越性会更加明显。     

压气机叶片流固耦合数值计算

采用流固耦合方法对压气机单排跨声叶片进行气动弹性数值模拟.首先对压气机流场进行三维定常求解,并与试验结果进行比对.在定常流场分析的基础上,进行流固耦合计算,采用非定常方法分别求解流体域Navier-Stokes(N-S)方程和固体域结构动力学方程.耦合过程中,流体域和固体域在物理边界上进行能量传递.计算结果表明:所采用的流固耦合数值方法用于判断叶轮机械叶片气弹稳定性是可行的,可以得到叶片的瞬态响应,从而判断叶片是否发生颤振.      

应用于跨声速旋翼气动声学计算的两种时域方法的比较

高速脉冲噪声(HSI)与流动非线性效应密切相关,是跨声速旋翼的主要声源之一。采用理论分析和数值实验相结合的方法,对预测HSI噪声的FfowcsWilliams-Hawkings方法(简称FW-H方法)和Kirchhoff方法进行了比较和分析。理论分析从两种方法的控制方程出发,采用广义函数方法对方程源项进行整理和比较,证实在线性区域Kirchhoff方程可视为FW-H方程的有效近似。数值实验以UH-1H悬停旋翼跨声速气动噪声计算为例,由三维Euler方程数值模拟提供近场气动数据,并在同一控制面上分别采用FW-H方法和Kirchhoff方法对远场噪声进行定量预测。计算结果表明,如果适当构造控制面,2种方法均能有效地预测跨声速旋翼非线性HSI噪声。进一步研究了控制面位置及控制面上物理参数时间导数计算精度对计算结果的影响,发现控制面位置对Kirchhoff方法计算结果具有决定性的影响,而控制面上物理参数时间导数的计算精度对FW-H方法计算结果具有重要影响。     

高阶精度间断Galerkin有限元方法研究

在二维非结构网格上,对高阶精度间断Galerkin有限元方法求解跨音速欧拉方程进行研究。运用间断有限元理论,采用施密特正交化多项式基函数对流场解进行近似描述,使用HLLC近似黎曼解方法计算网格单元边界处的数值通量,积分项通过高斯积分求解,时间推进采用经典四步Runge-Kutta方法,并引入斜率限制器,抑制数值振荡。对NACA0012翼型跨音速无粘流动进行数值模拟,数值结果表明：间断Galerkin有限元方法具有较高的精度,较小的数值耗散和较强的激波捕捉能力。     

Impedance Calculations for Elements of Sonar Arrays by Neural-Network-Based Integration

In this paper, a technique of neural network based integration is proposed to calculate the self-and mutual-impedances within arrays of sonar transducers. The multi-dimensional integrals appearing in self-and mutual-impedance formulations are transformed into neural-network-based integration and the final results can be found from look-up tables in mathematical handbooks. Initially, the integrand is modeled by a trained neural network. Integration on the integrand then becomes integration on the linear combination of weights and basis functions within the neural network. The results will become the linear combination of error functions which can be looked up in mathematical handbooks. Numerical simulation shows that the results calculated by the proposed method are consistent with those given in other existing studies. The proposed technique requires neither numerical nor artificial integration procedure. Due to the inherent learning and predicting property of neural network, only a small number of sampling points for the integrand are required in the proposed integration technique.     

C/C++软件的危险函数静态检查研究

C/C++软件开发过程中,源代码中若使用了危险函数,会造成内存缓冲区溢出,产生严重的安全漏洞和隐患,因此对源代码进行危险函数检查非常重要.对于大型软件模块需要将危险函数静态检查工具集成到持续集成工具上,对源代码进行危险函数检测.结合工作实践,介绍了危险函数检测工具,叙述了对源代码进行检查的流程;详细叙述了基于持续集成的危险函数检查过程;最后介绍了两个典型案例.工作实践表明,进行危险函数检查有助于及时发现和处理软件中的危险函数隐患,从而提高软件产品的质量和安全性.     

Filter Selection for Receivers Using Square-Law Detection

A numerical method is described for predicting the detection probability performance of a pulse receiver which uses square-law detection. The method is useful for receivers where the ratio of RF bandwidth to video bandwidth is in the range from 2 to 40; a range where numerical results have previously been hard to obtain. A key feature of the approach is that it takes into account the actual filter transfer functions, pulse envelope shape, and pulse frequency.