A general solution technique for discrete queueing analysis ofmultimedia traffic on ATM

The author presents a general solution using a generating function approach. The queue has multiple deterministic servers with infinite buffer size. Each server represents a time slot on an ATM link for the transmission of one cell. The arrival process is modeled by a number of independent Markov chains and each characterizes the stochastic properties of a different traffic type. By decomposing the generating function of the queue, the evaluation of the characteristic roots is separated. To characterize the great diversity of time scales of variation in multimedia traffic, the overall traffic arrivals are decomposed into multiple independent types. Each type is constructed by a number of i.i.d. two-state Markov chains and represents a different time scale of variation. Simple Kronecker product properties are then used to separate the evaluation of each individual root, so that the complexity involved to solve such a root is basically independent of the system size     

一种直线同步电机的控制方法

针对直线同步电机(LSM)控制系统,提出一种基于观测器的鲁棒控制方法。该方法首先建立了LSM矢量控制模型。然后利用李亚普诺夫方法,给出基于状态观测器的闭环控制系统鲁棒渐近稳定的充分条件,利用线性矩阵不等式处理方法,获得观测器和反馈控制器的参数。最后通过数值仿真,实验结果优于传统的控制方法,验证了该方法的正确性。     

A queueing analysis of the performance of DQDB

A queueing model for the DQDB protocol with a single priority level is presented and analyzed. The state of a node is defined by the number of requests in the distributed queue prior to, and post generation of a segment. It is shown that the number of states that a node can be in, is finite and position dependent. Moreover, it is shown that the request rate and the network traffic that a node perceives at any particular moment are highly dependent on its state. An iterative technique is presented to calculate the request rate and network traffic for all the nodes in a DQDB network by carefully modeling the relationship between adjacent nodes. The node average waiting time and average throughput are analyzed as functions of the node position and state in the network. Our results illustrate the effect of the various parameters on the waiting time and throughput. Comparisons with simulation and existing analytical results are presented     

Semi-discrete finite element method analysis of arbitrarymicrostrip elements-static solution

The semi-discrete finite-element method (FEM) is applied to solve the Poisson equation for a class of microstrip structures. This numerical technique is a variant of the conventional FEM. Its name stems from the fact that finite-element approximation is implemented only along two of the Cartesian coordinates, while the solution dependence on the third is handled analytically. When applicable, this method is simpler and more economical than the conventional fully-discrete version. Convergence properties of the solution are examined, and its validity tested for a number of geometries through comparison with other solutions and published data     

A queueing model for analysis of a bursty multiple-access communication channel

A bursty multiple-access communication channel with constrained total system bandwidth, total average power, and message error rates is considered. A stochastic model for the number of active transmitters is developed. Four schemes for the dynamic assignment of power and coding rate to active transmitters are considered and compared under the expected burst system time criterion. Necessary and sufficient conditions for system operation are given, and all schemes are shown to have the same saturation behavior. Adaptive coding rates are shown to enjoy substantial advantages over fixed coding; adaptive power assignment does not offer advantages over fixed power assignment.     

超宽带系统中同步和信道参数的闭式估计算法

提出超宽带系统中同步和信道参数的新型估计算法。首先对接收信号进行傅立叶变换,由傅立叶变换系数构造两个矩阵,把信道时延估计转化成矩阵束的特征值求解问题。在求解出时延后再进一步求解信道参数。算法的最大特点是能得到多径时延和多径增益的闭式解,避免现有算法普遍存在的搜索和迭代求解。     

A queueing theoretic approach to the delay analysis for the FCFS0.487 conflict resolution algorithm

The authors apply their queuing-theoretic delay analysis methodology to several variations of the FCFS 0.487 conflict resolution algorithm. In this approach, the main component of the packet delay is viewed as a queuing problem in which each window selected by the channel access algorithm is a customer requiring conflict resolution as its service. The authors' methodology is extended to handle all the features of the full FCFS 0.487 algorithm, including variable-size windows, arrival-time addressing (and hence true FCFS scheduling), and biased interval splitting. Some of these extensions involve approximations, but they make it possible to obtain the Laplace transform and moments of the packet delay. The authors also present an exact analysis for the three-cell algorithm, which is the 0.487 algorithm with a few modifications to satisfy the separability condition that reduces its capacity to 0.48. Comparisons made with other analyses (which provide bounds on the mean delay) and with extensive simulations show that the present results for both the mean and the variance of the packet delay are extremely accurate     

A linear well-posed solution to recover high-frequency information for super resolution image reconstruction

Multiview super resolution image reconstruction (SRIR) is often cast as a resampling problem by merging non-redundant data from multiple images on a finer grid, while inverting the effect of the camera point spread function (PSF). One main problem with multiview methods is that resampling from nonuniform samples (provided by multiple images) and the inversion of the PSF are highly nonlinear and ill-posed problems. Non-linearity and ill-posedness are typically overcome by linearization and regularization, often through an iterative optimization process, which essentially trade off the very same information (i.e. high frequency) that we want to recover. We propose a different point of view for multiview SRIR that is very much like single-image methods which extrapolate the spectrum of one image selected as reference from among all views. However, for this, the proposed method relies on information provided by all other views, rather than prior constraints as in single-image methods which may not be an accurate source of information. This is made possible by deriving explicit closed-form expressions that define how the local high frequency information that we aim to recover for the reference high resolution image is related to the local low frequency information in the sequence of views. The locality of these expressions due to modeling using wavelets reduces the problem to an exact and linear set of equations that are well-posed and solved algebraically without requiring regularization or interpolation. Results and comparisons with recently published state-of-the-art methods show the superiority of the proposed solution.     

A modified finite element method for analysis of finite periodicstructures

A modified finite element method with new solving algorithm is proposed to analyze electromagnetic problems of finite periodic structures. Dielectric-loaded parallel-plate waveguides with rectangular and triangular dielectric gratings are tackled as an example of the present approach. Numerical results are checked by the self-convergence test and by comparing with those obtained by other methods. Finally, the dependence of the scattering parameters on the frequency, the period number, and the grating height is analyzed and compared     

Experimental queueing analysis with long-range dependent packettraffic

Traffic measurement studies from a wide range of working packet networks have convincingly established the presence of significant statistical features that are characteristic of fractal traffic processes, in the sense that these features span many time scales. Of particular interest in packet traffic modeling is a property called long-range dependence (LRD), which is marked by the presence of correlations that can extend over many time scales. We demonstrate empirically that, beyond its statistical significance in traffic measurements, long-range dependence has considerable impact on queueing performance, and is a dominant characteristic for a number of packet traffic engineering problems. In addition, we give conditions under which the use of compact and simple traffic models that incorporate long-range dependence in a parsimonious manner (e.g., fractional Brownian motion) is justified and can lead to new insights into the traffic management of high speed networks     

Improved queueing analysis of shared buffer switching networks

The authors describe several methods for analyzing the queueing behavior of switching networks with flow control and shared buffer switches. They compare the various methods on the basis of accuracy and computation speed, where the performance metric of most concern is the maximum throughput. The best of the methods accurately predicts throughput for multistage networks constructed from large switches (⩾8 ports)     

Note on the solution of a queueing model by Sharda and Garg

In this note, some more results of the queueing model of Sharda and Garg (Microelectron. Reliab.25, 651–653) are derived.     

A single-server M/G/1 queueing system subject to breakdowns—some reliability and queueing problems

We consider a single-server M/G/1 queueing system. While the server is up and working it is subject to breakdowns according to a Poisson process with rate δ(>0); while the server is up but idle it is subject to brekdowns according to a renewal process with distribution Y(t). When the server breaks down, we need to repair the broken server immediately with two repair models as types 1 and 2, corresponding to whether the breakdowns occur in the server's working or idle period. Under some mild conditions on the repair time and service time distributions, we study not only some queueing problems of the system, but also some reliability problems of the server, and obtain some satisfactory results.     

Approximate analysis of coupled queueing in ATM networks

We discuss a scheduling discipline for multiclass traffic in asynchronous transfer mode network nodes. The scheduler provides minimum bandwidth guarantees for each class of traffic and is well suited for high-speed implementation. The scheme is a modification of static head-of-line priority queueing, and was originally presented in a slightly different form by Huang and Wu (1993). We begin by considering a system with two queues which is analyzed by decoupling the system into separate M/G/1 queues. The analysis provides a very good estimate for the mean response time of customers in each queue. We also demonstrate the applicability of the analysis to a system with n⩾2 queues     

A generalization of intermediate transfer function analysis to arbitrary linear networks

This paper is concerned with the generalization of the intermediate transfer function analysis method, proposed in [1] for state-space filter circuits, to arbitrary continuous-time linear networks. This analysis technique involves the intermediate step of calculating a set of intermediate transfer functions (IFs) that can in turn be used to compute any desired transfer function, various sensitivity functions, output noise power spectral densities, harmonic and intermodulation distortion products (when the network contains quasilinear, or weakly nonlinear, elements), and various other linear network attributes. The salient feature of this approach is that all computations can be carried out in symbolic form, thus highlighting the interrelationship of the various network attributes.1. This work is not intended to compete with SPICE but rather help one better understand the behavior of circuits with the aid of a special set of transfer functions.2. No attempt to measure the input-referred noise current was made because its value is expected to be beyond our measuring capabilities.     

A critical analysis of linear inverse solutions to theneuroelectromagnetic inverse problem

This paper explores the possibilities of using linear inverse solutions to reconstruct arbitrary current distributions within the human brain. The authors formally prove that due to the underdetermined character of the problem, the only class of measurable current distributions that can be totally retrieved are those of minimal norm. The reconstruction of smooth or averaged versions of the currents is also explored. A solution that explicitly attempts to reconstruct averages of the current is proposed and compared with the minimum norm and the minimum Laplacian solution. In contrast to the majority of previous analysis carried out in the field, in the comparisons, the authors avoid the use of measures designed for the case of dipolar sources. To allow for the evaluation of distributed solutions in the case of arbitrary current distributions the authors use the concept of resolution kernels. Two summarizing measures, source identifiability and source visibility, are proposed and applied to the comparison. From this study can be concluded: (1) linear inverse solutions are unable to produce adequate estimates of arbitrary current distributions at many brain sites and (2) averages or smooth solutions are better than the minimum norm solution estimating the position of single point sources. However, they systematically underestimate their amplitude or strength especially for the deeper brain areas. Based on these result, it appears unlikely that a three-dimensional (3-D) tomography of the brain electromagnetic activity can be based on linear reconstruction methods without the use of a significant amount of a priori information     

基于推力磁链的永磁直线同步电机自适应观测器

永磁直线同步电机由于结构的特殊性使其直交轴电感不相等,数学模型变得较为复杂,传统的观测器不再适用于直线电机。同时直接推力控制依赖观测器观测结果的准确性,尤其在低速阶段,以线性模型为基础建立的观测器不能很好地适应电机参数变化。根据永磁直线同步电机的数学模型,采用了推力磁链等效的方法,简化了其数学模型,从而解决了交直轴电感不相等引起的推力观测误差。同时,在自适应观测器中引入定子电阻自适应律,减小了低速段由于电机参数变化引起的定子磁链观测误差,提高了直接推力控制的低速段性能。并建立了相关的仿真模型,对定子磁链和电磁推力的观测效果进行了分析,从而验证了基于推力磁链的自适应观测器的有效性。     

A novel two-degree-of-freedom controller design for a permanent magnet linear synchronous motor control system

This paper proposes a novel two-degree-of-freedom optimal controller design for a permanent magnet linear synchronous motor position-control system. The param-eters of the controller are obtained by using a frequency-domain optimization technique. A systematic design of the controller and the detailed implementation of the proposed system are discussed. The closed-loop control system possesses good transient responses and good load disturbance responses. In addition, the system has a good tracking ability. Several experimental results are provided to validate the theoretical analysis.     

A new finite element approach to stress analysis in microfabrication technology

It is well known that the standard displacement-based finite element approach to viscoelastic stress analysis in microfabrication technology is susceptible to the volumetric locking and highly oscillatory pressure solutions. As an effective remedy for these problems, a new finite element approach based on separate weak statements for the displacement and pressure is proposed in this paper. Apart from the various existing techniques, the proposed approach is inherently free from the constraints imposed on the selection of discrete approximation spaces and permits a robust and stable discretisation based on piecewise linear Galerkin elements. The accuracy and stability of the proposed methodology has been tested in numerical experiments involving stress analysis problems from microfabrication deposition and native film growing processes.     

Steady-state solution of linear time-invariant systems

The steady-state solution of the vector differential equation x=Ax+Bw(t) is determined in a compact form by using the solution for an input of a train of impulses.