基于低阶近似分布源的目标方位估计

广义阵列流型描述的分布源模型,利用了一阶Taylor级数展开,使得模型与分布源空间能量分布形式无关,能够更加广泛地在实际中得到应用,称之为一阶近似分布源模型。研究表明,此种模型忽略高次Taylor级数项后带来的模型误差以及后续方位估计算法的性能损失,因此提出了二阶近似分布源模型,即利用二阶Taylor级数展开。新模型能够进一步减小模型误差,并且对相应的方位估计算法带来较大的性能提升。将分布源的一阶近似模型和二阶近似模型统称为低阶近似分布源模型。随后分析了低阶近似分布源模型在方位估计中的应用,提出了广义SMVDR算法。通过计算机仿真,验证了低阶近似分布源模型方位估计算法的性能,并且研究了分布源的低阶近似模型、空间频率模型和低阶Jacobi-Anger(JA)级数展开模型的模型误差。     

复合高斯海杂波环境下雷达虚警概率分析

针对在服从复合高斯分布的海杂波条件下,进行脉冲积累检测的非相干处理雷达,推导出了其检测变量因子的概率密度函数。由于复合高斯海杂波的分布形式较为复杂,导致直接求解其概率密度困难。为了在数学上获得上述条件下雷达系统的理论性能,文中借助一种基于矩生成函数的近似方法,得到了检测变量因子概率密度的高精度解析结果。经过仿真分析,结果表明该近似方法的精确性很高,并且可以方便地推导出雷达虚警概率等性能的解析结论。     

Accurate evaluation of bit-error rates of optical communication systems using the Gram-Charlier series

The probability densities and cumulative distribution functions of decision statistics of optical communications systems are expanded as a Gram-Charlier (G-C) series, leading to arbitrarily accurate systematic evaluation of bit-error rates (BERs) and optimal decision thresholds of optical communication systems. The method displays negligible computational complexity and is applicable whenever the moment or cumulant generating functions of the decision statistics are analytically available. We applied the technique to a birth-and-death Markovian model of a direct-detection receiver with optical preamplifier in a two-level amplitude-shift keying system. The modal expansion series rapidly converged, whereas the alternative saddlepoint approximation method predicted a BER which deviated by 7% from the G-C result.     

Bayes credibility estimation of an exponential parameter for randomcensoring and incomplete information

A Bayes interval estimation for an exponential parameter Θ in a model of random censoring with incomplete information is investigated. The instant of item failure is observed if it occurs before a randomly chosen inspection time and the failure was signaled; otherwise, the experiment is terminated at the instant of inspection. An explicit expression for the posterior PDF (probability distribution function) of the parameter is derived, and a normal approximation to it based on Taylor expansion near the maximum likelihood estimate is suggested. The results of an extension simulation showed that the reparametrization Θ₁=log Θ appreciably increases the accuracy of the normal approximation. Highly accurate highest posterior density intervals for Θ₁ are derived in a closed form for a normal prior for Θ₁ or, equivalently, for the lognormal prior on Θ     

Accurate Evaluation of Bit-Error Rates of Optical Communication Systems Using the Gram–Charlier Series

Accurate Evaluation of Bit-Error Rates of Optical Communication Systems Using the Gram–Charlier Series The probability densities and cumulative distribution functions of decision statistics of optical communications systems are expanded as a Gram–Charlier series, leading to arbitrarily accurate systematic evaluation of bit-error rates and optimal decision thresholds of optical communication systems. The method displays negligible computational complexity, and is applicable whenever the moment or cumulant generating function of the decision statistics are analytically available. We applied the technique to a birth-and-death Markoffian model of a direct-detection receiver with optical preamplifier in a two-level amplitude-shift keying system. The modal expansion series rapidly converged, whereas the alternative saddlepoint approximation method predicted a bit-error rate which deviated by 7% from the Gram–Charlier result.     

Robust estimation using the Robbins-Monro stochastic approximation algorithm

The problem of minmax estimation of a location parameter introduced by Huber is considered. It is shown that under general conditions there exists a solution which is a form of the Robbins-Monro stochastic approximation algorithm. This generalizes earlier work by Martin and Masreliez who have given stochastic approximation (SA)-estimate solutions for two particular cases. As with theM-estimate solutions given by Huber, the SA solutions are completely determined by the probability distribution function with least Fisher information in the distribution set used to model the observation errors.     

A novel receiver architecture for single-carrier transmission over time-varying channels

In this paper, we present a single-carrier transceiver for rapidly time-varying channels, where the equalization step is implemented in the frequency domain. When the channel abides with both fast fading and severe inter-block interference, our equalizer relies on a band approximation of the frequency-domain channel matrix to maintain low complexity. We will show that the band approximation error can be associated in the time domain to a critically-sampled complex exponential basis expansion modeling error. Based on this property, we propose a novel receiver architecture that extends the original data model by inserting zeros at the receiver. The resulting effective channel can be characterized by an oversampled complex exponential basis expansion model, which has a considerably reduced modeling error compared to the critically-sampled one. In other words, the band assumption that is essential to the equalizer will be made more accurate and thus the equalization performance can be improved.     

Cascaded Bayesian inferencing for switching activity estimation with correlated inputs

In this paper, we investigate the estimation of switching activity in VLSI circuits using a graphical probabilistic model based on cascaded Bayesian networks (CBNs). First, we develop a theoretical analysis for Bayesian inferencing of switching activity and then derive upper bounds for certain circuit parameters which, in turn, are useful in establishing the cascade structure of the CBN model. We formulate an elegant framework for maintaining probabilistic consistency in the interfacing boundaries across the CBNs during the inference process using a tree-dependent (TD) probability distribution function. A TD distribution is an approximation of the true joint probability function over the switching variables, with the constraint that the underlying BN representation is a tree. The tree approximation of the true joint probability function can be arrived at by using a maximum weight spanning tree (MWST) built using pairwise mutual information about the switching occurring at pairs of signal lines on the boundary. Further, we show that the proposed TD distribution function can be used to model correlations among the primary inputs which is critical for accuracy in modeling of switching activity. Experimental results for ISCAS circuits are presented to illustrate the efficacy of the proposed CBN models.     

复合衰落信道下分布式MIMO系统中断概率及信道容量分析

针对分布式MIMO系统中断概率和信道容量这2大性能指标,在复合衰落信道模型下,当上行链路采用最大比发送—选择合并,下行链路采用选择发送—最大比合并时,利用Lognormal分布对复杂Gamma-Lognormal分布的近似,推导得到当移动台位置给定时,系统中断概率和信道容量的闭合表达式,证明了系统性能指标与移动台分布之间存在密切的联系;随后依照实际通信环境,提出一种考虑存在小区热点的移动台非均匀分布模型,然后推导得到考虑该分布模型后的系统平均中断概率和平均信道容量闭合表达式;最后通过计算机仿真,证明了所提近似处理的精确性以及各项理论分析的合理性。     

Regression on the basis of nonstationary Gaussian processes with Bayesian regularization

We consider the regression problem, i.e. prediction of a real valued function. A Gaussian process prior is imposed on the function, and is combined with the training data to obtain predictions for new points. We introduce a Bayesian regularization on parameters of a covariance function of the process, which increases quality of approximation and robustness of the estimation. Also an approach to modeling nonstationary covariance function of a Gaussian process on basis of linear expansion in parametric functional dictionary is proposed. Introducing such a covariance function allows to model functions, which have non-homogeneous behaviour. Combining above features with careful optimization of covariance function parameters results in unified approach, which can be easily implemented and applied. The resulting algorithm is an out of the box solution to regression problems, with no need to tune parameters manually. The effectiveness of the method is demonstrated on various datasets.     

Microwave coherent propagation in cylindrical-shaped forestcomponents: interpretation of attenuation observations

A theory of the coherent field propagation is presented to explain attenuation observations previously obtained at X-band through various forest components. On the basis of the Foldy-Lax approximation, a polarimetric loss factor model for a sparse medium is developed. This model accounts for both observation parameters and vegetation characteristics, including the scatterer orientation distributions. The model is valid for any scatterer shape, but for comparison purposes only the cylindrical shape is considered. The forest components, such as bare twigs and leafy coniferous branches are represented as dielectric, homogeneous, infinite-circular cylinders characterized by their dielectric properties, dimensions, number density, and orientation probability density functions. For the model-experiment comparison, the infinite-circular cylinder scattering function is incorporated into the model     

Si+自注入Si晶体中缺陷分布的计算模拟

在两体近似碰撞模型基础上,采用SRIM程序对自注入硅离子及其造成的损伤在样品的分布进行了研究,模拟了Si<'+>自注入si晶体的Si<'+>深度分布几率和注入时的能量传递.计算结果表明:在相同注入能量的情况下,注入Si<'+>的分布概率是恒定的,在注入过程中电离能是阻止Si<'+>进一步深入的主导因素.论文还初步讨论了注入剂量和退火温度对发光强度的影响,以及W缺陷的可能形成原因.     

An efficient solution technique for discrete-time queues fed by heterogeneous traffic

During the past couple of years, a lot of effort has been put into solving all kinds of Markov modulated discrete-time queueing models, which occur, almost in a natural way, in the performance analysis of slotted systems, such as asynchronous transfer mode (ATM) multiplexers and switching elements. However, in most cases, the practical application of such solutions is limited, because of the large state space that is usually involved. In this paper we try to take a first step towards obtaining approximate solutions for a discrete-time multiserver queueing model with a general heterogeneous Markove modulated cell arrival process, which allows accurate predictions concerning the behaviour of the buffer occupancy in such a model and still remains tractable, both from an analytical and a computational point of view. We first introduce a solution technique which leads to a closed-form expression for the joint probability generating function of the buffer occupancy and the state of the arrival process, from which an expression for V(z), the probability generating function of the buffer occupancy is easily derived. On the basis of this result we propose an approximation for the boundary probabilities, which reduces all calculations to an absolute minimum. In addition, we show how accurate data for the distribution of the buffer occupancy can be obtained, by using multiple poles of V(z) in the geometric-tail approximation of the distribution. ©1997 by John Wiley & Sons, Ltd.     

Asymptotic distributions for the performance analysis of hypothesistesting of isolated-point-penalization point processes

The performance of the likelihood ratio test is considered for a many-point interaction point process featuring a reduced number of isolated points. Limit theorems are proved that establish the Poissonian asymptotic distribution of the log-likelihood function for point processes with the isolated-point-penalization joint probability density function. The asymptotic distribution is used to approximate the detection probability associated with the likelihood ratio test. The approximation is compared to empirical results generated using Markov-chain Monte Carlo simulation. The reported results provide an efficient alternative method to simulation in assessing the performance of hypothesis testing for the point-process model considered     

快时变OFDM系统中非采样间隔信道的信道估计

摘要：在快时变环境下的OFDM（orthogonal frequency division multiplexing,正交频分复用）系统中,针对非采样间隔信道CIR（channel impulse response,信道冲击响应）能量泄漏和ICI（inter-carrier interference,子载波间干扰）的问题,提出了一种基于分数抽头信道近似的复指数基扩展联合反馈离散傅里叶变换信道估计算法。该算法首先根据基于分数抽头信道近似的复指数基扩展模型计算信道参数,再根据该信道参数计算出快时变环境下OFDM系统的ICI系数,然后将初次消除ICI的信号作为反馈进行离散傅里叶变换,进一步消除噪声和ICI。该算法在一定程度上抑制了CIR能量泄漏,消除了ICI和噪声,有效地近似了实际信道。仿真结果表明,该算法在误比特率和信道均方误差方面均有明显提高。     

Scattering Properties of the Ocean Surface: The Miller–Brown–Vegh Model Revisited

We review the model of Miller-Brown-Vegh (MBV) that is commonly used to describe scattering from the ocean surface. The model has been built on two essential elements: the Kirchhoff approximation and an assumption regarding the probability distribution of the ocean surface elevations. A comparison with theoretical results preceeding the MBV model as well as with experimental data suggest that the MBV model is inconsistent with the predicted and observed probability distribution of sea waves. Here, a scattering model based on more rigorous statistics of the ocean surface is considered instead. The analysis we present offers an explanation as well as a remedy for the reported tendency of models describing propagation in evaporation ducts to overestimate the signal's intensity at the receiver.     

一种精确求解超薄栅NMOS器件隧穿电流的模型

提出了一种精确求解隧穿电流的模型。通过自洽求解一维薛定谔方程和泊松方程,得到NMOS器件的半导体表面电势分布、反型层二维电子气的量子化能级以及对应的载流子浓度分布。为计算隧穿电流,采用了多步势垒逼近方法计算栅氧化物势垒层的隧穿几率,从而避免了WKB方法在突变边界处波函数不连续带来的缺陷。通过考虑(100)Si衬底的导带多能谷效应和栅极多晶硅耗尽效应,讨论了不同栅氧化层厚度下隧穿电流与栅压的依赖关系。模拟结果与实验数据吻合。     

基于回归分析的研究及R语言实现

根据平顶山天安运销公司的实际情况,采用回归分析的数学方法,对该公司煤质密度与发热量的函数关系进行分析,并用最小二乘法进行函数逼近,最终得出煤质密度与发热量之间的函数关系。文中简述了线性拟合的模型及方法,以及如何运用线性回归的数学方法得出煤质密度与发热量的函数关系,进而更好地指导煤炭销售及提高公司利益。     

On the error probability of coded frequency-hopped spread-spectrummultiple-access systems

A simple, exact calculation is presented of the probability distribution of the number of hits in a block of n symbols in a frequency-hopped, spread-spectrum, multiple-access communication system. While the sequence of hits is not Markovian, there is an underlying Markovian structure that allows the probability distribution of the number of hits to be calculated in a recursive fashion. Knowing the probability distribution of the number of hits makes it possible to calculate the probability of error for a system employing error correcting codes for several different types of receivers, including receivers with both errors and erasures. The numerical results show that both the approximation obtained by assuming the actual sequence of hits is Markovian and the approximation obtained by assuming the hits are independent are very good. When the number of frequency slots is not too small (less than five), calculations show that assuming the independence of hits gives an error probability accurate to within 1% of the actual error probability. Assuming the hits are Markovian gives error probabilities which are accurate to within 0.001%