分层软小区无线接入网及其性能分析

基于分布式天线系统的概念,提出了一种新型的无线接入网络结构--分层软小区(HSC)无线网络.该网络采用集中统一的资源管理策略,由软件控制多个天线端口形成软小区服务于移动终端,同时,按照资源的正交划分形成地域上重叠的多层不同大小和形状的软小区,以适应不同的用户场景.分析表明,分层软小区无线网络的系统容量、干扰、阻塞率等性能都比传统蜂窝网络有较大的提高.     

Fuzzy-logic-based network for complex systems risk assessment: Application to ship performance analysis

In this paper, a new interpretation of intuitionistic fuzzy sets in the advanced framework of the Dempster–Shafer theory of evidence is extended to monitor safety-critical systems’ performance. Not only is the proposed approach more effective, but it also takes into account the fuzzy rules that deal with imperfect knowledge/information and, therefore, is different from the classical Takagi–Sugeno fuzzy system, which assumes that the rule (the knowledge) is perfect. We provide an analytical solution to the practical and important problem of the conceptual probabilistic approach for formal ship safety assessment using the fuzzy set theory that involves uncertainties associated with the reliability input data. Thus, the overall safety of the ship engine is investigated as an object of risk analysis using the fuzzy mapping structure, which considers uncertainty and partial truth in the input–output mapping. The proposed method integrates direct evidence of the frame of discernment and is demonstrated through references to examples where fuzzy set models are informative. These simple applications illustrate how to assess the conflict of sensor information fusion for a sufficient cooling power system of vessels under extreme operation conditions. It was found that propulsion engine safety systems are not only a function of many environmental and operation profiles but are also dynamic and complex.     

Comparative performance analysis of versions of TCP in a local network with a mobile radio link

The scenario is that a bulk data transfer is being performed over a TCP connection, from a host on a local area network (LAN) to a mobile host attached to the LAN by a radio link. In an earlier work we had assumed that packet losses in a TCP connection over a radio link are statistically independent. In this paper, we extend this analysis to a Rayleigh fading link, which we model by a two-state Markov model. The bulk throughputs of TCP-OldTahoe and TCP-Tahoe are compared with and without fading, for various average signal-to-noise ratios. We also study the performance with a link protocol on the wireless link, and study the effect of varying the link packet size, the number of link packet attempts, and the vehicle speed. For the parameters of the BSD UNIX implementation, over a 1.5 Mbps wireless link, we find that, with fading, a signal-to-noise ratio of at least 30 dB is required to get reasonable throughput with TCP Tahoe or OldTahoe; this corresponds to at least 100 times more power than is needed without fading. For fixed signal-to-noise ratio, as the vehicle speed varies there are roughly 3 regions of performance: at very low speeds (pedestrian speeds) the throughput is very good; at low vehicular speeds the throughput deteriorates, and again becomes very good at higher vehicle speeds. The speeds corresponding to the various regions depend on the parameters of the link protocol. This work was done while the first author was on Sabbatical at WINLAB, Rutgers University     

Sustainability performance analysis of environment innovation systems using a two-stage network DEA model with shared resources

The term environmental innovation system refers to an innovation network composed of enterprises, universities, and research institutions involved in the development and diffusion of environmental technology, with the participation of a government. An environmental innovation system not only exerts important impact on the achievement of carbon neutrality but also affects social and economic activities. Investigations on environmental innovation system performance constantly assume a single-stage independent system while ignoring its internal structure. However, such systems are composed of environmental innovation research and development (R&D) and environmental innovation conversion subsystems. A two-stage data envelopment analysis (DEA) model is developed in this study to analyze the efficiency of Chinese regional environmental innovation system by opening the “black box” and considering shared resources. Empirical results indicated that China presents high overall environmental innovation efficiency although some regions need to improve. Regions with low efficiencies in both environmental innovation R&D (EIR) and environmental innovation conversion (EIC) subsystems should expand their investment in and strengthen the management of environmental innovation resources. Regions with low EIR efficiency should improve the absorption and transformation of environmental innovation achievements. Regions with low EIC efficiency should increase investment in the commercialization of environmental innovation achievements and encourage green economy industries, such as new energy, art, tourism, and environmental protection.     

TTCAN通讯网络实时性分析

在自主研发的CAN总线实时仿真系统上,通过软件编程,分别实现了CAN协议通讯和TTCAN(Time-Triggered CAN)协议时间触发通讯.通过对两种不同通讯协议下的网络实时性进行比较,分析了TTCAN通讯网络的实时性.研究结果表明,引入TTCAN协议的时间触发功能能解决CAN协议中的总线冲突问题,有效提高了实时性要求较高的周期型消息的实时性.     

基于企鹅过冬行为的提高网络寿命算法性能分析

由于传感节点能量供应受限,为延长无线传感网络(wireless sensor networks,WSNs)寿命,提出基于能量消耗率的节点位置对调(energy consumption ratio-based node rotation,ECRNR)方案。ECRNR方案将能量消耗率高的传感节点位置由多个传感节点轮流驻守,即由多个传感节点一起分担任务,避免由单一传感节点独自承担繁重任务而能量过早耗尽。仿真结果表明:提出的ECRNR方案能够有效提高网络寿命,与传统的方案相比,网络寿命得到有效提高。     

Investigation of road network features and safety performance

The analysis of road network designs can provide useful information to transportation planners as they seek to improve the safety of road networks. The objectives of this study were to compare and define the effective road network indices and to analyze the relationship between road network structure and traffic safety at the level of the Traffic Analysis Zone (TAZ). One problem in comparing different road networks is establishing criteria that can be used to scale networks in terms of their structures. Based on data from Orange and Hillsborough Counties in Florida, road network structural properties within TAZs were scaled using 3 indices: Closeness Centrality, Betweenness Centrality, and Meshedness Coefficient. The Meshedness Coefficient performed best in capturing the structural features of the road network. Bayesian Conditional Autoregressive (CAR) models were developed to assess the safety of various network configurations as measured by total crashes, crashes on state roads, and crashes on local roads. The models’ results showed that crash frequencies on local roads were closely related to factors within the TAZs (e.g., zonal network structure, TAZ population), while crash frequencies on state roads were closely related to the road and traffic features of state roads. For the safety effects of different networks, the Grid type was associated with the highest frequency of crashes, followed by the Mixed type, the Loops & Lollipops type, and the Sparse type. This study shows that it is possible to develop a quantitative scale for structural properties of a road network, and to use that scale to calculate the relationships between network structural properties and safety.     

Improving performance in the OpMiGua hybrid network employing the network layer packet redundancy scheme

The optical migration-capable network with service guarantees hybrid network is a time-divided packet/circuit hybrid network offering absolute performance guarantees and high resource utilisation. Guaranteed service traffic (GST) follows lightpaths receiving absolute priority over statistically multiplexed (SM) traffic. Transmission resources are fully shared by interleaving SM and GST packets, but packet-switched SM packets experience contention, resulting in a packet loss that should be minimised. This article explores a novel bufferless network approach where the performance of the SM class is satisfied by applying packet-level forward error correction (FEC). Two implementation strategies are proposed: RedSM transmitting redundancy packets as SM traffic and RedGST transmitting redundancy packets as low-priority GST traffic. The performance of the schemes is explored analytically and by simulation. For uniform traffic loads, the RedGST scheme shows the best performance of the two, but even at 60% load the RedSM scheme shows packet loss rates (PLRs)close to 1025. Simulations with non-uniform traffic loads illustrate the importance of selecting the optimal redundancy ratio; the failure to do so results in up to two orders of magnitude increase in PLR for the RedGST scheme. A much higher tolerance for traffic variations is the main benefit for the RedSM scheme. In view of the results, both schemes are attractive alternatives to buffered contention resolution techniques.     

Estimating the impact of abnormal loads on network performance

The English Highways Agency is required to improve network performance including journey time reliability measured by average delay on the 10% slowest journeys along a specified set of primary routes in the strategic road network. Abnormal indivisible loads, which behave as moving bottlenecks, can cause significant delay, but the factors involved are complex, so methods have been developed to model their effect. These methods have been extended to estimate their impact through the Average Vehicle Delay (formerly PSA1 delay) measure, allowing mitigations through intelligent transportation system or policy options to be evaluated. Environmental impacts are also considered.     

Road safety performance indicators for the interurban road network

Various road safety performance indicators (SPIs) have been proposed for different road safety research areas, mainly as regards driver behaviour (e.g. seat belt use, alcohol, drugs, etc.) and vehicles (e.g. passive safety); however, no SPIs for the road network and design have been developed. The objective of this research is the development of an SPI for the road network, to be used as a benchmark for cross-region comparisons. The developed SPI essentially makes a comparison of the existing road network to the theoretically required one, defined as one which meets some minimum requirements with respect to road safety. This paper presents a theoretical concept for the determination of this SPI as well as a translation of this theory into a practical method. Also, the method is applied in a number of pilot countries namely the Netherlands, Portugal, Greece and Israel. The results show that the SPI could be efficiently calculated in all countries, despite some differences in the data sources. In general, the calculated overall SPI scores were realistic and ranged from 81 to 94%, with the exception of Greece where the SPI was relatively lower (67%). However, the SPI should be considered as a first attempt to determine the safety level of the road network. The proposed method has some limitations and could be further improved. The paper presents directions for further research to further develop the SPI.     

Reliability analysis of shuffle-exchange network systems

Shuffle-exchange networks (SENs) have been widely considered as practical interconnection systems due to their size of its switching elements (SEs) and uncomplicated configuration. SEN is a network among a large class of topologically equivalent multistage interconnection networks (MINs) that includes omega, indirect binary n-cube, baseline, and generalized cube. In this paper, SEN with additional stages that provide more redundant paths are analyzed. A common network topology with a 2×2 basic building block in a SEN and its variants in terms of extra-stages is investigated. As an illustration, three types of SENs are compared: SEN, SEN with an additional stage (SEN+), and SEN with two additional stages (SEN+2). Finally, three measures of reliability: terminal, broadcast, and network reliability for the three SEN systems are analyzed.     

Recent developments in lightwave network analysis

The widespread use of photonic systems having microwave modulation bandwidths, coupled with the inclusion of photonic components in microwave and millimetre-wave systems, is creating a demand for efficient characterization techniques. In particular, new tools will be required for the measurement of fundamental quantities such as the microwave frequency response, bandwidth, gain and return loss of microwave photonic components. However, existing lightwave measurement techniques are primitive when compared with conventional RF and microwave network analysis. This paper provides a review of the theory and techniques used for the small-signal characterization of microwave photonic components. State-of-the-art architectures for lightwave network analysers and the two-port calibration techniques are described     

基于SNMP协议的分布式网络性能测试与分析

针对网络性能优化对提高网络运行效率的重要作用,采用基于网络性能评测的方法寻找影响网络运行效率的瓶颈,以及进行相关优化的方式,在具体实现上采用基于简单网络管理协议(SNMP)、RFC 2544协议和分布式软件测评体系结构相结合方式进行网络性能测评。最终通过测试结果来进一步说明分布式网络性能测试解决方案。     

Trend and efficiency analysis of co-authorship network

Although co-authorship in scientific research has a long history the analysis of co-authorship network to explore scientific collaboration among authors is a relatively new research area. Studies of current literature about co-authorship networks mostly give emphasis to understand patterns of scientific collaborations, to capture collaborative statistics, and to propose valid and reliable measures for identifying prominent author(s). However, there is no such study in the literature which conducts a longitudinal analysis of co-authorship networks. Using a dataset that spans over 20 years, this paper attempts to explore efficiency and trend of co-authorship networks. Two scientists are considered connected if they have co-authored a paper, and these types of connections between two scientists eventually constitute co-authorship networks. Co-authorship networks evolve among researchers over time in specific research domains as well as in interdisciplinary research areas. Scientists from diverse research areas and different geographical locations may participate in one specific co-authorship network whereas an individual scientist may belong to different co-authorship networks. In this paper, we study a longitudinal co-authorship network of a specific scientific research area. By applying approaches to analyze longitudinal network data, in addition to known methods and measures of current co-authorship literature, we explore a co-authorship network of a relatively young and emerging research discipline to understand its trend of evolution pattern and proximity of efficiency.     

基于神经网络趋势分析

文章在分析研究了国内外现状的基础上 ,利用神经网络的非线性处理特性 ,提出了通过神经网络预测常见机械零件剩余寿命的方法 ,用实例验证了其有效性     

大信号网络分析中的包络域

超越S参数的大信号网络分析是解决非线性问题的一个行之有效的方法,包络域是该分析法的一个重要概念,是指能同时表征载波基波和载波各高次谐波的包络的一种方法,它充分而形象地表征了系统的非线性特性.作者从基本原理出发详细分析了包络域的概念.     

Using social network analysis to combat counterfeiting

Counterfeiting undoubtedly produces great harm to companies and the society. This article presents a study on the application of social network analysis (SNA) to combating this problem. The supply chain can be viewed as a network of parties involved in delivering value to consumers. Normally, SNA is used to analyse relationships between people. In this study, it is utilised to analyse supply chains for the identification of parties that are likely to be involved in counterfeiting activities. After identifying the suspects in a supply chain, the company can deter and detect counterfeiting by tightening surveillance on these parties. The feasibility of using SNA as an anti-counterfeiting tool is investigated in a case study, the findings of which indicate that SNA can effectively help companies to prevent sources of counterfeit products from infiltrating into the supply chain. Problematic parties can be identified by characterising the following features: high degree of centrality, high closeness of centrality and high betweenness of centrality.     

Node Reordering algorithms for water network analysis

The node Admittance matrices for Water Networks are normally sparse and symmetrical. Advantage may be taken of these properties to reduce the amount of computational time and memory required to solve them. Two node reordering algorithms and an economic system of storing input data are described. The node reordering algorithms minimize the number of fill-ins which would occur in the solution of the node admittance matrix. Only non-zero elements are stored and operated on. Subroutines for the node reordering algorithms and storge of input data, written in FORTRAN IV are included.     

Bayesian network approach to change propagation analysis

The prediction of change propagation is one of the important issues in engineering change management. The aim of this article is to explore the capability of Bayesian network (BN), which is an emerging tool for a wide range of risk management, in modeling and analysis of change propagation. To this end, we compare the BN with change prediction method (CPM), which is the most established probabilistic methods for predicting change propagation. This paper shows that a CPM-based model can be converted into an equivalent BN, and the probabilistic inference technique on the latter results in the same change prediction result obtained from the former. Then, this paper shows that several improvements can be obtained at various levels using the BN. At the modeling level, complex relationship between components such as combined effect of simultaneous changes or multistate relationship can be naturally represented with the BN. At the analysis level, various change propagation scenarios can be analyzed using probabilistic inference on the BN. Finally, BN provides a robust framework for learning change propagation probabilities from empirical data. The case study is conducted to show the feasibility of the model.     

Accuracy analysis for six-port automated network analyzers

One of the assumptions made in six-port automated network analyzer (ANA) theory is that the reflection coefficient of the power detectors does not change with incident power level. This is not generally the case if diode detectors are used. Consequently, uncertainties in the measurement of the reflection coefficient of the unknown load appear because the calibration constants vary due to the variation of the detector reflection coefficients with power. Measurements of the variations of diode input impedance using commercial ANAs are used in a computer simulation to estimate their uncertainties