Non-line-of-sight ultraviolet single-scatter path loss model

A novel non-line-of-sight ultraviolet single-scatter path loss model for coplanar geometries is proposed on the basis of spherical coordinate system. In comparison with the classical single-scatter analytical model based on the prolate-spheroidal coordinate system, it is of a simple integral form which only depends on the variables of the zenith and receiver elevation angles. Additionally, analytical approximation for the proposed single-scatter path loss model is presented. Numerical examples on path loss are presented for various system geometries. Correspondingly, the results are verified with the classical single-scatter analytical model, which demonstrates the validity of our path loss model and the reasonability of the analytical approximation.     

Constructing Analytical Energy Functions for Network-Preserving Power System Models

This paper presents a general procedure for constructing analytical energy functions for network-preserving power system stability models. Canonical representations of network-preserving power system models are presented first. It is demonstrated that such canonical representations can cover existing stability models. Theoretical results regarding the existence of analytical energy functions for the canonical representation are derived. In addition, a new network-preserving model with detailed generator and hybrid load representations is developed. The corresponding analytical energy function for the proposed model is studied. Physical explanations of each term in the energy function are also investigated.     

受光阑限制离轴高斯光束的解析传输

激光束的传输特性在激光技术应用中有着重要的意义。光束的解析传输问题是激光光学中的难点之一。从Collins公式出发，详细研究了离轴高斯光束(OAGB)通过有光阑近轴ABCD光学系统的传输特性，推导出了受硬边光阑、高斯光阑或余弦光阑限制的离轴高斯光束通过近轴ABCD光学系统的解析传输公式，并讨论了硬边光阑、高斯光阑或余弦光阑之间的关系。数值计算证明了所得公式的正确性和优点。分析了求解受多光阑限制的激光束通过近轴ABCD光学系统的解析传输公式的困难性，结果表明，其困难性在于受单光阑限制激光束的解析传输公式中含有误差函数。     

抛物反射镜对高斯束变换特性的研究

在准光技术的研究和应用中,利用解析公式设计准光系统具有方便快捷的优点。采用解析公式设计透镜和椭球反射镜组成的准光系统都得到与实际吻合的良好结果。但在使用解析公式计算抛物反射面对高斯束的变换特性时存在较大误差,不满足设计抛物面组成的准光系统的要求。为解决此问题,在Ka波段利用CST 全波分析软件对高斯束经抛物面镜的变换特性进行大量仿真并进行相关的数据处理,对经典解析公式进行了校正。校正后的公式对于在Ka波段和W波段的高斯束斜入射抛物面镜问题上的计算结果与全波仿真结果有较好吻合,可以用于设计相关准光系统,同时也消除了使用全波仿真软件带来的耗时长及占用计算机空间大等问题。     

Queuing Analysis of Power Management in the IEEE 802.11 Based Wireless LANs

Energy efficiency is an important aspect in wireless networks and power management is a technique that can save energy. We investigate the power management in the IEEE 802.11 based infrastructure mode wireless LANs and seek the optimal power management parameters that can achieve good energy efficiency without degrading other performances. We propose two models for the power management scheme: the M/G/1 queue with bulk service model and the D/G/1 queue model. From the models, we obtain the analytical results for the energy efficiency and the response time performance metrics, which are controlled by a listen interval. Our simulation results are in good agreement with the analysis. Based on the analytical models and simulation, we propose to select the largest listen interval with the satisfaction of response time requirement. The analytical models can be used to predict system performance if system configurations are given. This can help system deployment and system optimization     

Virtual partitioning resource allocation for multiclass traffic in cellular systems with QoS constraints

Resource allocation is a vital component of call-admission control that determines the amount of resource to assign to new and handoff connections for quality-of-service (QoS) satisfaction. In this paper, we present approximate analytical formulations of virtual partitioning resource-allocation schemes for handling multiclass services with guard channels in a cellular system. Resource-allocation models for best effort and guarantee access with preemption for best effort traffic and virtual partition with preemption for all classes are investigated. The analytical models, derived using a K-dimensional Markov chain, are solved using preemption rules for these schemes. Call-level grade of service, such as new-call-blocking probability, handoff-call-blocking probability, and system utilization, and packet-level QoS, such as packet-loss probability, are used as performance metrics. The performances of fast and slow mobile users are evaluated analytically and by simulation. The analytical and simulation results show excellent agreement. A method to maximize system utilization through joint optimization of call-/packet-level parameters is proposed. Numerical results indicate that significant gain in system utilization is achieved.     

DICOM全方向M型心动图系统DICOM图像解析方法研究

DICOM全方向M型心动图系统是福州大学生物医学工程研究所的国家发明专利＂全方向M型心动图方法及其系统ZL98125713.5＂和国外的DICOM标准结合生成的新系统。为了实现无损且适应性更好的DICOM图像解析,使用改进的DICOM遍历解析与组织嵌套数据集的方法。在基于对应DCIOM编码的嵌套数据结构的基础上,使用几个递归过程互相调用,实现了无损的DICOM编码,为新系统平稳接入PACS系统奠定了基础。     

一个新系统的Hopf分岔与混沌运动

利用解析方法和数值方法研究了一新三维系统Hopf分岔解的稳定性。利用Si’lnikov方法研究了该系统的混沌运动,严格地给出了系统产生混沌的机理与相应的参数条件。数值模拟验证了理论分析的结果。     

用行波解法研究集总放大光纤孤子系统的稳定性问题

本文采用行波解法求解了集总放大光纤孤子系统脉宽为皮秒量级含放大器增益的非线性薛定谔方程，得到了近似形式的解析解，并得到了孤子振幅、中心位置、相位的演化方程，在此基础上统一地研究了孤子传输的稳定性问题，得到了在集总放大光纤孤子系统中孤子能稳定传输的结论。     

Uplink user capacity in a CDMA system with hotspot microcells: effects of finite transmit power and dispersion

This paper examines the uplink user capacity in a two-tier code division multiple access (CDMA) system with hotspot microcells when user terminal power is limited and the wireless channel is finitely-dispersive. A finitely-dispersive channel causes variable fading of the signal power at the output of the RAKE receiver. First, a two-cell system composed. of one macrocell and one embedded microcell is studied and analytical methods are developed to estimate the user capacity as a function of a dimensionless parameter that depends on the transmit power constraint and cell radius. Next, novel analytical methods are developed to study the effect of variable fading, both with and without transmit power constraints. Finally, the analytical methods are extended to estimate uplink user capacity for multicell CDMA systems, composed of multiple macrocells and multiple embedded microcells. In all cases, the analysis-based estimates are compared with and confirmed by simulation results.     

A UNIFYING QUEUEING MODEL FOR ATM AND ITS ANALYSIS

This paper considers a discrete-time single-server queueing system with infinite buffer size and a finite number of independent Markov-modulated Bernoulli processes (MMBPs). A simple analytical approach is presented to analyse the asymptotic behaviour of such a queueing system. An explicit expression for the tail distribution of the buffer contents is given, from which two upper bounds for the tail distribution are derived. These two upper bounds are good and even tight in many cases, as shown by the numerical results. Compared to a previously reported general solution technique, our approximate analytical approach is very easy to use and is not limited by the system size and the traffic parameters. The CPU time required to calculate the upper bounds of the tail distribution is quite acceptable for practical use; especially for a single traffic type, the calculation costs nearly no CPU time on a normal PC. This analytical method is also suitable for more general Markov-modulated arrival processes.     

System performance analysis of cooperative multihop relaying network applying approximation to dual‐hop relaying network

In this paper, the closed‐form expressions for outage probability, channel capacity, and average symbol error probability are derived for amplify‐and‐forward multihop relay network. Based on approximation of multihop relay by dual‐hop relay systems, the analytical expressions are obtained for the case when maximal ratio combining technique is employed at each relay while destination node uses selection combining technique. The impact of system and channel parameters on the system performances is investigated, and numerical results are graphically presented. The derived analytical expressions are verified by numerical simulation.     

System level design and optimization of single-loop CT sigma-delta modulators for high resolution wideband applications

In this paper, the main resolution limitations in single-stage continuous-time sigma-delta modulators (CT ΣΔMs) are analytically estimated as the function of system level parameters for wideband applications. The analytical results are supported by simulation results. The power consumption of CT ΣΔMs is also analytically estimated as the function of system level parameters, and then, it is validated by the reported power consumption of several state-of-the-art fabricated prototypes. Based on analytical results, for a targeted resolution and bandwidth, an algorithm is proposed to design the system level parameters of CT ΣΔMs for the minimum power consumption. The estimation of power consumption and the designed parameters match well with the design of best state-of-the-art fabricated modulators.     

Analysis and simulation of interrupt overhead impact on OS throughput in high‐speed networks

The paper presents analytical and simulation models to study the impact of interrupt overhead on operating system throughput of network elements such as PC‐based routers, servers, and hosts when subjected to high‐speed network traffic. Under such high network traffic, the system throughput will be negatively affected due to interrupt overhead caused by the incoming traffic. We first present an analytical model for the ideal system when interrupt overhead is ignored. We then present two models which describe the impact of high interrupt rate on system throughput. One model is for employing PIO in which network adapters are not equipped with DMA engines, and the other model is for employing DMA in which network adapters are equipped with DMA engines. The paper also describes detailed discrete‐event simulation models for the ideal system and for systems with DMA and PIO. Simulations results as well as reported experimental measurements show that our analytical models are valid and give a good approximation. Our analysis and simulation work can be valuable in providing insight to understand and predict system behaviour, as well as improving and maintaining good host performance. The paper identifies analytically critical design operation points such as that of overload condition. The paper also proposes solutions and recommendations for improving performance. Copyright © 2005 John Wiley & Sons, Ltd.     

Nonlinearity modelling of an on-board microwave photonics system based on Mach-Zehnder modulator

For the nonlinearity distortion problem of Mach-Zehnder modulator(MZM)applied in the on-board microwave photonics system,the situation for two input radio frequency(RF)signals with different frequencies and phases is discussed,and an exact analytical solution is derived with the method of expanding Bessel series and Graf addition theory.According to the analytical expression,the nonlinearity characteristics of the modulator can be precisely predicted,and the system performance can be optimized.The correctness of the analytical solution is approved by simulation results.Analytical results indicate that the nonlinearity distortion is suppressed as the decrease of modulation index,the increase of direct current bias phase shift and phase difference between two input RF signals.When the phase difference equals zero orπand the direct current bias phase shift isπ/2,there are only odd-order distortion terms.When the phase difference equals zero orπand the direct current bias phase shift isπ,there are only even-order distortion terms.     

Performance of coherent MQAM schemes in the presence of frequency‐selective Rayleigh fading and CCI

Performance of a coherent MQAM system in the presence of frequency-selective Rayleigh fading, co-channel interference (CCI) and additive white Gaussian noise (AWGN) is presented. Square-root raised-cosine filters are used in both the transmitter and receiver for an optimum performance in a band-limited AWGN channel. Frequency-selective Rayleigh fading channel is modeled as a two-ray model. Based on the characteristic functions of the received signals and a discrete Fourier transform (DFT) method, an analytical procedure to compute the error probability is derived. Numerical results for an illustrative example of a 16QAM system are given. Effects of CCI and frequency-selective fading on the system performance are examined. Accuracy of the proposed method is discussed in comparison with other simulation and analytical techniques. This revised version was published online in June 2006 with corrections to the Cover Date.     

Development and control of a single-wheel robot: Practical Mechatronics approach

This article presents a Mechatronics approach to make the complex dynamical system satisfy the specification as desired. The Mechatronics approach has several phases: analytical design, system integration, sensing & control, and evaluation. The Mechatronics approach means that cycles of design, implementation, sensing, and control are repeated until the system satisfies the goal through evaluation. A single-wheel robot system called GYROBO after a robot that uses gyroscopic effect is developed and controlled by the Mechatronics approach. The goal of GYROBO is to navigate its terrain while maintaining the stable balance. However, successful balancing and navigation of a single-wheel robot are quite difficult and challenging since one point contact may fall down in lateral direction with ease. To have a successful balancing performance, many problems have to be solved a priori before applying any advanced control algorithms. Among several phases of analytical design, integration, sensing & control, and evaluation, the most important phase is the analytical design. However, the analytical design cannot guarantee successful performances due to the complexity of the system. Practical Mechatronic approach is to repeat cycles of system integration, sensing & control, and evaluation. After several modifications of mechanical assembly and relocation of components inside the wheel housing, simple linear controllers enable GYROBO to perform successful balancing and navigation. GYROBO is able to follow the specified trajectory given by a remote operator. Experimental studies of control of balancing, driving forward and backward, turning, and climbing over an obstacle of GYROBO are conducted to demonstrate and evaluate its functionality and support the concept of the Mechatronics approach to control complex systems.     

通信抗干扰技术的激活与决策分析

介绍了通信抗干扰技术的分析方法,讨论了通信抗干扰技术的激活过程和控制策略,提出了通信抗干扰技术决策系统的设计思想,对决策系统的组成进行了分析,最后指出了通信抗干扰技术研究的核心问题所在。