Generalized stochastic field model for reverberating chambers

In this paper, we present a new stochastic model to characterize the electromagnetic field in reverberating chambers. The model is physically based and is capable to embody as special cases the reference thermodynamic limit (perfectly stirred case) and the Rician case (presence of unstirred component). The stochastic field model is characterized by the generalized K distribution, i.e., a three parameters probability density function (pdf) that ensures a continuous and physically consistent transition among very different scattering scenarios. Theoretical modeling is supported by means of an experimental study based on measurements made at the Universita/spl grave/ di Napoli Parthenope, Naples, Italy, formerly Istituto Universitario Navale (IUN), mode-stirred reverberating chamber.     

A stochastic worm model

Internet worm infection continues to be one of top security threats and has been widely used by botnets to recruit newbots. In order to defend against future worms, it is important to understand how worms propagate and how different scanning strategies affect worm propagation dynamics. In our study, we present a (stochastic) continuous-time Markov chain model for characterizing the propagation of Internet worms. The model is developed for uniform scanning worms, and further for local preference scanning worms and flash worms. Specifically, for uniform and local preference scanning worms, we are able to (1) provide a precise condition that determines whether the worm spread would eventually stop and (2) obtain the distribution of the total number of infected hosts. By using the same modeling approach, we reveal the underlying similarity and relationship between uniform scanning and local preference scanning worms. Finally, we validate the model by simulating the propagation of worms.     

A multiscale stochastic image model for automated inspection

We develop a novel multiscale stochastic image model to describe the appearance of a complex three-dimensional object in a two-dimensional monochrome image. This formal image model is used in conjunction with Bayesian estimation techniques to perform automated inspection. The model is based on a stochastic tree structure in which each node is an important subassembly of the three-dimensional object. The data associated with each node or subassembly is modeled in a wavelet domain. We use a fast multiscale search technique to compute the sequential MAP (SMAP) estimate of the unknown position, scale factor, and 2-D rotation for each subassembly. The search is carried out in a manner similar to a sequential likelihood ratio test, where the process advances in scale rather than time. The results of this search determine whether or not the object passes inspection. A similar search is used in conjunction with the EM algorithm to estimate the model parameters for a given object from a set of training images. The performance of the algorithm is demonstrated on two different real assemblies.     

A stochastic model of the temporal and azimuthal dispersion seen atthe base station in outdoor propagation environments

A simple statistical model of azimuthal and temporal dispersion in mobile radio channels is proposed. The model includes the probability density function (PDF) of the delay and azimuth of the impinging waves as well as their expected power conditioned on the delay and azimuth. The statistical properties are extracted from macrocellular measurements conducted in a variety of urban environments. It is found that in typical urban environments the power azimuth spectrum (PAS) is accurately described by a Laplacian function, while a Gaussian PDF matches the azimuth PDF. Moreover, the power delay spectrum (PDS) and the delay PDF are accurately modeled by an exponential decaying function. In bad urban environments, channel dispersion is better characterized by a multicluster model, where the PAS and PDS are modeled as a sum of Laplacian functions and exponential decaying functions, respectively     

Reduced state Viterbi decoder for simple partial erasure model

A reduced state Viterbi decoder is introduced for a simple partial erasure model for magnetic recording systems. It is shown that the performance loss of an eight-state decoder is negligible compared to the original 16 state Viterbi decoder. The implementation issues of an eight-state decoder are also addressed     

基站建设及基站天线的设计与分析

移动基站建设是为人们提供良好通信基础的重要途径,在移动基站建设过程中必须要选择合适的位置,提高基站的维修和运行成本,同时提高运行可靠性和稳定性。文章对通信基站建设以及基站的天线分布进行设计,旨在提高基站的工作效率。     

MapReduce的随机Petri网模型研究

首次提出用随机Petri网为MapReduce逻辑模型建立Petri网模型的思想,目的在于采用随机Petri网工作流性质对其进行分析。因此,在研究MapReduce逻辑模型的基础上,为其建立了随机Petri网模型。该随机Petri网模型符合随机Petri网工作流系统的性质,本文利用随机Petri网的工作流系统的性能等价公式,分析了模型的性能,最终求出整个系统的性能参数。该性能参数能够很好地说明MapReduce处理大数据集的优势。     

A stochastic model for the interconnection topology of digitalcircuits

Rent's rule has been successfully applied to a priori estimation of wire length distributions. However, this approach is very restrictive: the circuits are assumed to be homogeneous. In this paper, recursive clustering is described as a more advanced model for the partitioning behavior of digital circuits. It is applied to predict the variance of the terminal count distribution. First, the impact of the block degree distribution is analyzed with a simple model. A more refined model incorporates the effect of stochastic self similarity. Finally, the model is further extended to describe the effects of heterogeneity. This model is a promising candidate for more accurate a priori estimation tools     

A base transport model for ultra-thin-base SiGe HBT

The characteristics of parameters such as carrier temperature and diffusion coefficient in ultra-thin-base SiGe heterojunction bipolar transistors (HBTs) are analysed according to the solution of the Boltzmann equation; a new model of base transport in SiGe HBTs, different from traditional ones is described.     

Simplified method for the construction of an orthonormal base forCPFSK signals

The authors present a simplified method to derive a 2M dimensional orthonormal base for M-ary CPFSK signals based on the well-known Gram-Schmidt procedure. On the basis of this method, the simulated bit error performance of 4, 8 and 16-ary CPFSK modulation in additive white Gaussian noise channels is presented     

Robust methods for model order estimation

Model order estimation is a subject in time series analysis that deals with fitting a parametric model to a vector of observations. This paper focuses on several model order estimators known in the literature and examines their performance under small deviations of the probability distribution of the noise with respect to a nominal distribution assumed in the model. It is demonstrated that the standard estimators suffer from high sensitivity to deviations from the nominal distribution, and a drastic performance degradation is experienced. To overcome this problem, robust estimators that are insensitive to small deviations from the nominal distribution are developed. These estimators are based on a composition between model order estimation methods and robust statistical inference techniques known in the literature. In addition, a new estimator based on a locally best test for weak signals is presented both in nonrobust and robust versions. The proposed robust model order estimators are developed on a heuristic basis, and there is no claim of optimality, but experimental results indicate that they provide significant improvement over the standard estimators     

A stochastic model for burst-correcting convolutional decoders (Corresp.)

A stochastic model is described for the decoder of an optimal burst-correcting convolutional code. From this model, an upper bound is obtained forbar{p}, the error probability per word after decoding.     

基于随机模型的可重构计算芯片互连资源估计

在可重构计算芯片设计初期,确定芯片的各种互连资源数目是一个关键问题.如果设计的互连资源过少,可能导致应用领域中的部分算法无法实现,而过多的互连资源会造成芯片面积的浪费.基于可重构计算的特点,分析了可重构计算的相邻连接、路由连接和近邻连接三种类型互连资源.通过建立互连资源估计的随机模型,提出了可重构计算芯片中各种互连资源数目的估计方法.仿真结果表明,该方法能够比较准确地估计各种互连资源的数目,从而指导可重构计算互连资源的设计,降低设计风险.     

A rework reduction model for construction projects

Rework is an endemic problem in building construction projects and is an area of research that has received limited attention. Recent research has shown that rework is the primary cause of time and schedule overruns in projects and that rework levels do not significantly differ between current procurement methods despite calls from government for the use of more integrated procurement approaches such as design-and-construct to improve project performance. To reduce the incidence of rework throughout the construction supply chain, data from 161 completed projects were gathered using a questionnaire survey. Stepwise multiple regression was used to determine the significant variables that contributed to rework in projects. In conjunction with previously reported research, these variables were used to develop an alternative procurement model for reducing rework in projects. It is suggested that the proposed model could be used to stimulate interorganizational relations and promote teambuilding during the formative stages of a project, which is essential for reducing design-related reworking.     

企业专网组建方式探讨

现在，越来越多的用户需要在企业专网上开通电子商务、电子办公、视频会议、IP电话等应用，对网络带宽和实时性要求大大提高，传统的组网技术已不能满足需要。目前主要有VLAN、VPN、MPLS VPN和LAN-ATM等几种企业组网新技术，各有其优势和适用范围，用户可根据需要各取所需。     

An accurate small-signal model for AlGaN-GaNHEMT suitable for scalable large-signal model construction

The validity of the proposed small-signal model (SSM) and the developed extraction method in for large GaN devices is investigated. Extraction of parasitic elements is performed for different size devices to show the scaling of these elements with the gate width. The model shows a very good result for describing the parasitic distributed effect, which is considerable for large devices.     

基站建设及基站天线的研究

为了能够满足基站易于选址、优质快速的建站要求和易维护、低成本、高可靠的运行要求,本文时以方舱来实现一体化结构基站做出一番探讨.从系统设计的观点阐述了移动通信高性能基站天线设计的几个关健问题,介绍了智能天线技术在基站中的应用,并且用HFSS软件仿真了一种新型的对称阵于天线,该天线驻波比小于2的带宽可以达到60%,真有良好的宽频带特性.     

Cauer continued fraction methods for model reduction

This letter surveys the recently published methods for deriving stable reduced-order models and justifies how sophisticated techniques had to be evolved to meet different problems which arise in the reduction of high-order systems.     

A stochastic multipath channel model including path directions for indoor environments

A novel stochastic channel model for the indoor propagation channel is presented. It is especially for, but not limited to future communication systems with multiple antennas like space division multiple access (SDMA), spatial filtering for interference reduction (SFIR), or multiple-input/multiple-output (MIMO). The model is designed for indoor scenarios, straight forward extendable to urban environments. It is based on physical wave propagation. The new approach describes the channel by multipath components, each characterized by its transfer matrix (including loss), delay, direction of arrival, and departure. The appearance and disappearance of multipath components over time is modeled as a birth and death process, a marked Poisson process. This enables first-time the correct modeling of spatial and temporal correlations. In each modeling step, path properties change according to the motion of transmitter and receiver. The changing delay times of propagation paths yield a realistic Doppler behavior of the channel. Deterministic ray tracing results are used to produce the huge data sets required for the statistical evaluation of the parameters of the proposed model. This method enables an automated parameter extraction for new environments or frequencies. The ray tracing tool has been verified by narrowband, wideband, and directional channel measurements. The novel stochastic spatial channel model allows the simulation of third-generation broadband radio systems including arbitrary antenna configurations and patterns. System simulations for the bit-error rate of radio links can be performed including intelligent antenna configurations like SDMA, SFIR, or MIMO. Furthermore, the capacity of complete systems can be investigated.