ACC: using active networking to enhance feedback congestion controlmechanisms

Active congestion control (ACC) uses active networking (AN) technology to make feedback congestion control more responsive to network congestion. Current end-to-end feedback congestion control systems detect and relieve congestion only at endpoints. ACC includes programs in each data packet that tell routers how to react to congestion without incurring the round-trip delay that reduces feedback effectiveness in wide area networks. The congested router also sends the new state of the congestion control algorithm to the endpoints to ensure that the distributed state becomes consistent. We present a model for extending feedback congestion control into an active network, apply that model to TCP congestion control, and present simulations that show that the resulting system exhibits up to 18 percent better throughput than TCP under bursty traffic. In simulations without bursty traffic, the systems behaved comparably     

Sliding window protocol with selective-repeat ARQ: performance modeling and analysis

A sliding window mechanism is well known to be a convenient way to integrate cumulative acknowledgement and flow control functions in a simple manner. Hence, widely used reliable data-transfer protocols such as TCP-SACK and RLC utilize this sliding window mechanism in conjunction with a selective-repeat ARQ (automatic repeat request) function, namely, the selective-repeat sliding window protocol (SR-SWP). We demonstrate that SR-SWP yields a throughput restraint effect (TORE) in particular situations when packet losses occur. We propose an analytical performance model to represent the TORE in the case of heavy traffic. Using this model, we derive explicit forms of goodput and mean resequencing delay, which are fundamental qualities of service parameters. From numerical results, we demonstrate that the impact of TORE on the performance is not negligible for high packet-loss probabilities. Furthermore, we show that the SR-SWP model exhibits the lower goodput and the smaller mean resequencing delay than those obtained from the traditional SR-ARQ protocol model.     

Markov-modulated flow model for the output queues of a packetswitch

The output queues of an M×N packet switch are studied using a Markov-modulated flow model. The switching element is a central server which sequentially routes packets from the inputs to the outputs. The focus is on systems in which the server speed is such that the bulk of the queuing takes place in the output queues. The conventional point process approach neglects the impact of switching and transmission time. An attempt is made to account for these finite system speeds by using a Markov-modulated continuous flow to approximate the arrival process to an output queue. This model captures the dependency between arrivals at different outputs and reflects the fact that packet arrivals and departures are not instantaneous. The output queue content distribution is obtained, for both infinite and finite buffer systems, from the spectral expansion of the solution of a system of differential equations. Numerical examples and comparisons with the results of an M/M/1 approximation are presented     

Fairness in window flow controlled computer networks

A measure is proposed that is based on two key concepts: (1) the congestion caused by a virtual circuit (VC) on the others; and (2) the penalty inflicted by the network on a VC. These two concepts are then combined to define a fairness criterion that uses the principle that a virtual circuit should not be able to congest the network more than it is being penalized by the same network. A suboptimal algorithm to select window sizes according to this fairness criterion was devised and applied to several networks; results are presented for two of these networks. The examples show that the window set produced by the algorithm does not cause any significant degradation in the net overall performance and is superior, in terms of fairness, to other window assignments methods discussed in the literature     

Accurate analysis and modeling of laminated multilayered 3-D optical waveguides

The theoretical investigation of waveguides having nonuniform cross-sections is an attractive and challenging problem which deserves serious interest. In this paper, we present a novel analysis of laminated multilayered three-dimensional waveguide, based on two modes: 1) a new coupled transmission line approach that considers the sloping of the layers along the longitudinal direction and 2) a transmission line matrix integral equation (TLMIE) modeling that complete and extends the investigation of the field propagation. In method 1), we neglect radiation modes and their EM coupling. All physical effects instead are accounted for by the full-wave TLMIE method. By using TLMIE, we validate the EM analysis and calculate TE/TM losses, arising from radiation modes.     

Hybrid analytical modeling method for split power bus in multilayered package

As multiple chips are being integrated into a single package with increased operating frequency, switching noise coupling on power buses has become an important design issue. To reduce the noise coupling, a split power bus structure has been generally used in package substrates having multilayered power and ground planes. Consequently, there is an increasing need for an efficient method to analyze a split power bus in a multilayered package. This paper introduces a hybrid analytical modeling method for characterizing a split power bus in a multilayered package. The proposed method uses a resonant cavity model combined with a segmentation method. Furthermore, a port assignment technique and an associated calculation method for the equivalent circuit model parameter of the split gap are proposed. The proposed port assignment technique and the analytical equation make it possible to analyze a split power bus, especially in a multilayered package. To verify the proposed method, multilayered test packages are fabricated and tested by means of frequency-domain measurements. In addition, an optimal power bus design method was successfully demonstrated for suppressing noise coupling between chips on a single package. Finally, the proposed method and optimal power bus design method was verified using a series of frequency-domain and time-domain measurements.     

On acknowledgement schemes of sliding window flow control

An investigation is conducted of two acknowledgment schemes for sliding window flow control in packet communications: the delayed acknowledgment (D-ACK) scheme and the window acknowledgment (W-ACK) scheme. It is shown that the acknowledgment scheme of the link layer of the X.25 protocol can be modeled by the D-ACK scheme and that of the packet layer by the W-ACK scheme. The efficiencies of these acknowledgment schemes are shown by the mean number of acknowledgment control frames generated for the transmission of a single information frame, the transmission blocking probability, and the mean transmission time of data frames. Numerical and simulation results showing that the D-ACK scheme with an appropriately selected value of predetermined waiting time is better than the W-ACK scheme are presented     

Hybrid modeling techniques for multilayered printed circuit board in power electronics: association of electromagnetic methods

With the fast development of power electronics circuits at increasing switching frequency (over 10 MHz), the multilayered printed circuits boards (PCBs) are being used more and more in the field of power electronics. In this paper, two main computational methods are presented to simulate the dynamic behavior of power electronics interconnection systems. Our aim is to present a methodology to analyze the electromagnetic (EM) behavior of power PCB regarding parasitic effects ( EM couplings) or dynamic effects (impedance): a general procedure is given to calculate EM couplings between strip conductors in multilayered configurations based on the principle of hybrid methods. Finally, we propose a new method to limit computation time based on matrix sparsification.     

Application of flow graph analysis to noise calculations in multilayered structures

Studies in fields as dissimilar as remote sensing and radio astronomy often require calculation of noise generation and propagation through a multilayered structure. Signal flow graphs are very powerful in the handling of multiple reflections, and in this article is derived the flow graph equivalent source for noise emission in a lossy transmission medium.     

Characterization and modeling of a new via structure in multilayered printed circuit boards

We demonstrate that structure engineering of the transmission line near the via can reduce the amount of reflection of the RF signal. We have fabricated two types of vias with different transmission line geometries and have measured the reflection. The measured results show that the shape of the transmission line near the via hole is important in determining the total reflection of the via structure. The amount of reflection obtained from full three-dimensional (3-D) electromagnetic simulations can reproduce the measured results with reasonable accuracy, which suggests that efficient design of the via structure could be possible without resorting to hardware fabrication and characterization.     

A computer analysis of Ga1-xAlxAs-GaAs solar cells with multilayered window structure

Numerical calculations have been made of the spectral response and conversion efficiency of Ga1-xAlxAs-GaAs solar cells with multilayered window structures. Maximum conversion efficiencies of about 20 percent are predicted, equaling those achieved with graded band-gap solar cells, for the case of three-layered window structures.     

Errors-in-variables modeling in optical flow estimation

Gradient-based optical flow estimation methods typically do not take into account errors in the spatial derivative estimates. The presence of these errors causes an errors-in-variables (EIV) problem. Moreover, the use of finite difference methods to calculate these derivatives ensures that the errors are strongly correlated between pixels. Total least squares (TLS) has often been used to address this EIV problem. However, its application in this context is flawed as TLS implicitly assumes that the errors between neighborhood pixels are independent. In this paper, a new optical flow estimation method (EIVM) is formulated to properly treat the EIV problem in optical flow. EIVM is based on Sprent's (1966) procedure which allows the incorporation of a general EIV model in the estimation process. In EIVM, the neighborhood size acts as a smoothing parameter. Due to the weights in the EIVM objective function, the effect of changing the neighborhood size is more complex than in other local model methods such as Lucas and Kanade (1981). These weights, which are functions of the flow estimate, can alter the effective size and orientation of the neighborhood. In this paper, we also present a data-driven method for choosing the neighborhood size based on Stein's unbiased risk estimators (SURE).     

Analysis of multilayered dielectric waveguides: variationaltreatment

A fast and near exact modal analysis is presented to obtain the propagation constants and electric field profiles for dielectric multilayered channel (rib) waveguides. Calculations are performed for a particular channel configuration and found to be in excellent agreement with those obtained using the finite difference method     

Integral equation modeling of multilayered doubly-periodic lossy structures using periodic boundary condition and a connection scheme

This paper presents a boundary integral formulation to analyze multilayered doubly-periodic lossy structures with arbitrary geometry. The formulation is based on the moment method using first-order triangular patch basis functions. Each individual layer is analyzed separately using the simple free-space Green's function. After discretization, periodic boundary conditions are imposed on each region and a connection scheme is used to connect the regions. Metallic patches between layers or on the periodic boundary are also included in the model. Several examples are presented showing both the flexibility and the accuracy of the method.     

RECONSTRUCTION OF ONE DIMENSIONAL MULTI-LAYERED MEDIA BY USING A TIME DOMAIN SIGNAL FLOW GRAPH TECHNIQUE

A novel inverse scattering method to reconstruct the permittivity profile of one-dimensional multi-layered media is proposed in this paper.Based on the equivalent network ofthe medium,a concept of time domain signal flow graph and its basic principles are introduced,from which the reflection coefficient of the medium in time domain can be shown to be a series ofDirac δ-functions(pulse responses).In terms of the pulse responses,we will reconstruct both thepermittivity and the thickness of each layer will accurately be reconstructed.Numerical examplesverify the applicability of this method     

Space-domain Green's function approach to the capacitancecalculation of multiconductor lines in multilayered dielectrics withimproved surface charge modeling

An integral equation method for the calculation of capacitance and inductance matrices is presented. The method is suitable for multiconductor transmission lines embedded in a multilayered dielectric medium on top of a ground plane. Conductors of arbitrary polygonal cross section can be handled, as well as infinitely thin conductors. The method is new in two respects. The kernel of the integral equation is the space-domain Green's function of the layered medium. The accuracy of the solution is enhanced by using basis functions that exactly model the singular behavior of the charge density in the neighborhood of a conductor edge. Numerical examples show the accuracy of the calculations and the complexity of the configurations that can be treated     

基于ARIMA的城市交叉路口交通流预测建模

传统城市交叉路口交通流预测方法受到交通流随机性影响,导致交通流预测精准度较低,为此提出基于ARIMA的城市交叉路口交通流预测建模.考虑时间的随机性,分析交通流预测建模原理.以路口主干道车流为研究对象,构建数据向量矩阵,计算该矩阵的平均相关系数,确定两个数据向量间的协方差.提取现场每天24h交通流数据,分析不同时间序列的...     

Automated onboard modeling of cartridge valve flow mapping

Proportional poppet-type cartridge valves are the key elements of the energy-saving programmable valves, which have been shown to be able to achieve good motion control performance while significantly saving energy usage in our previous studies. Unlike costly conventional four-way valves, the cartridge valve has a simple structure and is easy to manufacture, but the complicated mathematical model of its flow mapping makes the controller design and implementation rather difficult. Although off-line individually calibrated or manufacturer supplied flow mappings of the cartridge valves can be used, neither method is ideal for wide industrial applications. The former method is time-consuming and needs additional flow sensors while the latter may lead to significantly degraded control performance due to the inaccuracy of the manufacturer supplied flow mappings. Furthermore, due to inevitable system worn out and/or changing working conditions, actual cartridge valve flow mapping may change significantly over the life span of the system and need to be updated periodically in order to maintain the same level of control performance. Sometime, it may be even impractical to do off-line calibrations once the valve leaves the manufacturing plant. To solve this practically significant problem, this paper focuses on the automated onboard modeling of the cartridge valve flow mappings without using any extra sensors and removing the valves from the system. The estimation of flow mappings is based on the pressure dynamics of the hydraulic cylinder with the consideration of effects of some unknown system parameters such as the effective bulk modulus of the working fluid. Localized orthogonal basis functions are proposed to bypass the lack of persistent exciting identification data over the entire domain of the flow mapping during onboard experiments. Experimental results are obtained to illustrate the effectiveness and practicality of the proposed novel automated modeling method.     

光学头罩绕流流场气动光学效应数值模拟

以红外成像制导技术在高速拦截器上的应用需求为背景,进行了光学头罩绕流流场气动光学效应数值模拟.应用雷诺平均NS方程并选取了适当的湍流模型,对凹窗、凸窗和球头3种光学头罩的高速飞行器绕流流场进行了数值模拟,得到了绕流流场密度分布;研究了脉动流场引起的气动光学传输效应的计算方法,应用几何光学、物理光学和统计光学方法进行了光学传输效应计算,得到了点扩散函数,即像面光强分布.通过瞄视误差、Strehl比、含能半径等气动光学效应参数描述了流场引起的成像畸变,并分析了不同外形、飞行状态和光学系统参数对光学传输效应的影响.     

Neural networks in B-ISDN flow control: ATM traffic prediction ornetwork modeling?

The authors discuss a technique that offers the combination of shared bandwidth and rejection rate parameters, together with the quality of service predicted by neural networks in a novel strategy for connection admission control and call routing