基于连通性检测的视频监控运动目标提取

针对背景相对静止、主要检测对象为行人的视频监控序列,提出了一种基于连通性检测的目标提取算法,它把形态学滤波与连通性检测相结合,对分割后的二值化图像进行噪声干扰去除,在获得若干连通区域后,利用面积、外界矩形及其特征对连通区域进行识别,通过区域重心标注目标在各帧位置,实现目标提取.实验结果表明,该算法简单可靠,具有实时性,易于硬件实现,可应用于实际系统.     

Analytical Model for Connectivity in Vehicular Ad Hoc Networks

We investigate connectivity in the ad hoc network formed between vehicles that move on a typical highway. We use a common model in vehicular traffic theory in which a fixed point on the highway sees cars passing it that are separated by times with an exponentially distributed duration. We obtain the distribution of the distances between the cars, which allows us to use techniques from queuing theory to study connectivity. We obtain the Laplace transform of the probability distribution of the connectivity distance, explicit expressions for the expected connectivity distance, and the probability distribution and expectation of the number of cars in a platoon. Then, we conduct extensive simulation studies to evaluate the obtained results. The analytical model that we present is able to describe the effects of various system parameters, including road traffic parameters (i.e., speed distribution and traffic flow) and the transmission range of vehicles, on the connectivity. To more precisely study the effect of speed on connectivity, we provide bounds obtained using stochastic ordering techniques. Our approach is based on the work of Miorandi and Altman, which transformed the problem of connectivity distance distribution into that of the distribution of the busy period of an equivalent infinite server queue. We use our analytical results, along with common road traffic statistical data, to understand connectivity in vehicular ad hoc networks.      

面向拒止环境的无人机集群数据链网络拓扑优化策略研究

针对现有无人机集群在卫导和通信拒止环境下，由于网络连通性降效导致任务遂行能力严重降级的问题，分析了国内外基于数据链网络降低拒止环境影响的最新研究现状，提出了一种基于任务优先级的动态优化连接度拓扑自适应位置选择策略，实现多个无人机集群在拒止环境下通过大区域拓扑连接获取拒止区域外信息，从而降低或抵消拒止影响，有效提升了无人机集群生存能力和任务遂行能力。     

Fuzzy VA-Files for multi-label image annotation based on visual content of regions

In this work, we propose an efficient image annotation approach based on visual content of regions. We assume that regions can be described using low-level features as well as high-level ones. Indeed, given a labeled dataset, we adopt a probabilistic semantic model to capture relationships between low-level features and semantic clusters of regions. Moreover, since most previous works on image annotation do not deal with the curse of dimensionality, we solve this problem by introducing a fuzzy version of the Vector Approximation Files (VA-Files). Indeed, the main contribution of this work resides in the association of the generative model with fuzzy VA-Files, which offer an accurate multi-dimensional indexing, to estimate relationships between low-level features and semantic concepts. In fact, the proposed approach reduces the computation complexity while optimizing the annotation quality. Preliminary experiments highlight that the suggested approach outperforms other state-of-the-art approaches.     

Cooperative Caching for Efficient Data Search in Mobile P2P Networks

Wireless Personal Communications - In this paper, we propose a cooperative caching scheme for structured data via clusters based on peer connectivity in mobile P2P networks. In the...     

A DTI-Derived Measure of Cortico-Cortical Connectivity

We arm researchers with a simple method to chart a macroscopic cortico-cortical connectivity network in living human subjects. The researcher provides a diffusion-magnetic resonance imaging (MRI) data set and $N$ cortical regions of interest. In return, we provide an $N times N$ structural adjacency matrix (SAM) quantifying the relative connectivity between all cortical region pairs. We also return a connectivity map for each pair to enable visualization of interconnecting fiber bundles. The measure of connectivity we devise is: 1) free of length bias, 2) proportional to fiber bundle cross-sectional area, and 3) invariant to an exchange of seed and target. We construct a 3-D lattice scaffolding (graph) for white-matter by drawing a link between each pair of voxels in a 26-voxel neighborhood for which their two respective principal eigenvectors form a sufficiently small angle. The connectivity between a cortical region pair is then measured as the maximum number of link-disjoint paths that can be established between them in the white-matter graph. We devise an efficient Edmonds–Karp-like algorithm to compute a conservative bound on the maximum number of link-disjoint paths. Using both simulated and authentic diffusion-tensor imaging data, we demonstrate that the number of link-disjoint paths as a measure of connectivity satisfies properties 1)–3), unlike the fraction of intersecting streamlines—the measure intrinsic to most existing probabilistic tracking algorithms. Finally, we present connectivity maps of some notoriously difficult to track longitudinal and contralateral fasciculi.      

The structure of an Al3Pd-based modulated structure studied by atomic-scale electron microscopy observations

A modulated structure based on an Al3Pd structure in an Al70Co25Pd5 alloy has been studied by atomic-scale observations with high-resolution transmission electron microscopy (HREM) and high-angle annular detector dark-field (HAADF) technique using a scanning transmission electron microscope. From the electron microscopy observations, we can reveal an arrangement of atom columnar clusters, which produces peculiar shifts of diffraction spots in an electron diffraction pattern. Arrangements of transition-metal atoms in defect regions in the modulated structure are proposed from the observed HAADF image.     

基于RankClus算法的机场流程日志活动挖掘

流程挖掘技术可以提取机场流程日志中的有用信息用于流程分析。但机场流程日志处于细节化的低抽象层次,不符合分析者的预期。对机场流程日志挖掘得到的流程模型呈现意面状的复杂结构,流程模型的含义难于理解。解决该问题的一种方法是通过活动挖掘,将低抽象层次活动聚类为流程模型中表征高抽象层次活动的活动类簇。为此提出了一种基于RankClus算法的活动挖掘方法,将机场流程日志的活动聚类与活动排序评分计算相结合,从而构建更易理解的活动聚类流程模型。实验结果表明,RankClus活动聚类流程模型的日志回放一致性与原生日志流程模型大致相当,但在结构复杂度上要显著低于原生日志流程模型。     

The COST259 Directional Channel Model?Part I: Overview and Methodology

This paper describes a model for mobile radio channels that includes consideration of directions of arrival and is thus suitable for simulations of the performance of wireless systems that use smart antennas. The model is specified for 13 different types of environments, covering macro- micro- and picocells. In this paper, a hierarchy of modeling concepts is described, as well as implementation aspects that are valid for all environments. The model is based on the specification of directional channel impulse response functions, from which the impulse response functions at all antenna elements can be obtained. A layered approach, which distinguishes between external (fixed), large-scale-, and small-scale- parameters allows an efficient parameterization. Different implementation methods, based on either a tapped-delay line or a geometrical model, are described. The paper also derives the transformation between those two approaches. Finally, the concepts of clusters and visibility regions are used to account for large delay and angular spreads that have been measured. In two companion papers, the environment-specific values of the model parameters are explained and justified     

Managing Layer 1 VPN services

Control Plane architectures enhance transport networks with distributed signaling and routing mechanisms which allow dynamic connection control. As a result, layer 1 switching networks enabled with a distributed control plane can support the provisioning of advanced connectivity services like Virtual Private Networks (VPNs). Such Layer 1 VPN (L1VPN) service allows multiple customer networks to share a single transport network in a cost-effective way. However, L1VPN deployment still faces many challenges.In this work, we are concerned on configuration management and interdomain provisioning of L1VPN services. We propose an L1VPN management architecture based on the Policy-Based Management (PBM) approach. First, we describe the architecture and how it allows a single service provider to support multiple L1VPNs while providing customers with some level of control over their respective service. Then we explain how the architecture was extended to support interdomain L1VPNs by using the Virtual Topology approach. We also discuss the prototype implementation and evaluation of the proposed architecture. Moreover, this work is a tentative note before raising a more deep discussion related to interdomain provisioning of L1VPN services and implications of a policy-based approach for L1VPN configuration management.     

A stochastic model to study the impact of the transmission frequency of hello messages on the connectivity of ad hoc networks

In this paper, we exploit the utility of Hello messages in the Ad hoc networks to study the impact of their transmission frequencies on the connectivity of the network. Assuming that the Hello messages arrive at a given node according to a Poisson process, we model a cluster-head motion (respectively an ordinary node motion) using a random process. This model allows us to find the critical value of the transmission frequency of Hello messages. We also have investigate a fundamental property of an Ad hoc network: its connectivity. We then analyze the number of neighbors of a given node, the isolation probability, the handoff probability and the probability that the considered network is connected, i.e. each node can communicate with an other node via the network.     

Cluster‐based mobility management algorithms for wireless mesh networks

Wireless mesh networks (WMNs) have been the recent advancements and attracting more academicians and industrialists for their seamless connectivity to the internet. Radio resource is one among the prime resources in wireless networks, which is expected to use in an efficient way especially when the mobile nodes are on move. However, providing guaranteed quality of service to the mobile nodes in the network is a challenging issue. To accomplish this, we propose 2 clustering algorithms, namely, static clustering algorithm for WMNs and dynamic clustering algorithm for WMNs. In these algorithms, we propose a new weight‐based cluster head and cluster member selection process for the formation of clusters. The weight of the nodes in WMN is computed considering the parameters include the bandwidth of the node, the degree of node connectivity, and node cooperation factor. Further, we also propose enhanced quality of service enabled routing protocol for WMNs considering the delay, bandwidth, hopcount, and expected transmission count are the routing metrics. The performance of the proposed clustering algorithms and routing protocol are analyzed, and results show high throughput, high packet delivery ratio, and low communication cost compared with the existing baseline mobility management algorithms and routing protocols.     

Exact probability of connectivity one-dimensional ad hoc wireless networks

The probability that a one-dimensional stationary ad hoc wireless network is composed of at most C clusters is presented. The probability of network connectivity, i.e. the case of C=1, can be derived as a special case. A very simple approximate formula is also presented for the probability of network connectivity. We also explain our approximation heuristically, which confirms the analytical result. The analysis is validated by computing the probability of network connectivity and comparing it with the Monte Carlo simulation results.     

Dense cluster gateway based routing protocol for multi-hop mobile ad hoc networks

In a multi-hop mobile ad hoc network dynamic clusterization of nodes can be quite effective for better management of routing problems. In a cluster based protocol inter cluster data transfer takes place through the cluster gateways. Therefore, it is important to maintain information about the gateways as a part of the routing tables in order that the inter cluster routing proceeds smoothly even as the nodes move about. In this paper we propose a randomized approach for inter cluster routing over dense cluster gateways (DCG). A group of large number of gateway edges between two adjacent clusters offering inter cluster connectivity between the two is referred to as a DCG. The minimum number of gateway edges that define a DCG is dependent on the characteristics of particular ad hoc network. A DCG is expected to offer robust inter cluster connectivity as it typically has a large number of gateway edges. Our protocol is an improvement over the cluster based routing using k-tree core backbone proposed in [Information Processing Letters 88 (2003) 187–194]. It distributes the routing load on the cluster gateways without adding the extra overhead of maintaining information about dense cluster gateways. We also propose a heuristic which reduces the load on the cluster-heads. The heuristic elects some nodes to act as sub-cluster-heads which share a part of the workload of the respective cluster-heads. The protocol has been implemented on ns-2 simulator. An analysis of the result of the experiments has been presented.     

Using Local Geometry for Tunable Topology Control in Sensor Networks

Neighbor-Every-Theta (NET) graphs are such that each node has at least one neighbor in every theta angle sector of its communication range. We show that for thetas < pi, NET graphs are guaranteed to have an edge-connectivity of at least floor (2pi)/thetas, even with an irregular communication range. Our main contribution is to show how this family of graphs can achieve tunable topology control based on a single parameter thetas. Since the required condition is purely local and geometric, it allows for distributed topology control. For a static network scenario, a power control algorithm based on the NET condition is developed for obtaining k-connected topologies and shown to be significantly efficient compared to existing schemes. In controlled deployment of a mobile network, control over positions of nodes can be leveraged for constructing NET graphs with desired levels of network connectivity and sensing coverage. To establish this, we develop a potential fields based distributed controller and present simulation results for a large network of robots. Lastly, we extend NET graphs to 3D and provide an efficient algorithm to check for the NET condition at each node. This algorithm can be used for implementing generic topology control algorithms in 3D.     

Performance Analysis Over Unified Generalized Composite Fading Model

With the deep study of the Hamming distances of orthogonal arrays (OAs), the application of OAs has penetrated into many fields, one of which is to construct the key predistribution schemes (KPSs) for distributed sensor networks. In this paper, we define the Hamming distance distribution (HDD) of an OA and its uniqueness. Furthermore, we present some OAs with unique HDD. In KPSs based on these OAs, the calculations of metrics for evaluating connectivity and resilience can be simplified. We also illustrate that KPSs based on them have a wider application and better connectivity and resilience than the existing ones.

     

Selective avoidance of cycles in irregular LDPC code construction

This letter explains the effect of graph connectivity on error-floor performance of low-density parity-check (LDPC) codes under message-passing decoding. A new metric, called extrinsic message degree (EMD), measures cycle connectivity in bipartite graphs of LDPC codes. Using an easily computed estimate of EMD, we propose a Viterbi-like algorithm that selectively avoids small cycle clusters that are isolated from the rest of the graph. This algorithm is different from conventional girth conditioning by emphasizing the connectivity as well as the length of cycles. The algorithm yields codes with error floors that are orders of magnitude below those of random codes with very small degradation in capacity-approaching capability.     

Protocol for Dynamic Ad-Hoc Networks Using Distributed Spanning Trees

A dynamic ad-hoc network consists of a collection of mobile hosts with frequently changing network topology. We propose a distributed algorithm that adapts to the topology by utilizing spanning trees in the regions where the topology is stable, and resorting to an intelligent flooding-like approach in highly dynamic regions of the network. Routing is performed using the spanning trees based a hold-and-forward or shuttling mechanisms. We introduce the notion of connectivity-through-time and the parameter holding-time as new fundamental concepts that can be used by ad-hoc routing algorithms. For various network connectivity scenarios we evaluate the impact of these concepts on the performance of ad-hoc routing algorithms. Using simulation, we study the throughput, reachability and message–reachability ratio of the proposed schemes under various connection/disconnection rates and holding times.     

Efficient Placement and Dispatch of Sensors in a Wireless Sensor Network

Sensor deployment is a critical issue because it affects the cost and detection capability of a wireless sensor network. In this work, we consider two related deployment problems: sensor placement and sensor dispatch. The former asks how to place the least number of sensors in a field to achieve sensing coverage and network connectivity, and the latter asks how to determine from a set of mobile sensors a subset of sensors to be moved to an area of interest with certain objective functions such that the coverage and connectivity properties are satisfied. This work is targeted toward planned deployment. Our solution to the placement problem allows an arbitrary-shaped sensing field possibly with arbitrary-shaped obstacles and an arbitrary relationship between the communication distance and sensing distance of sensors and, thus, significantly relaxes the limitations of existing results. Our solutions to the dispatch problem include a centralized one and a distributed one. The centralized one is based on adopting the former placement results and converting the problem to the maximum-weight maximum-matching problem with the objective of minimizing the total energy consumption to move sensors or maximizing the average remaining energy of sensors after movement. Designed in a similar way, the distributed one allows sensors to determine their moving directions in an autonomous manner.     

Connectivity Probability of Wireless Ad Hoc Networks: Definition, Evaluation, Comparison

The paper presents a new approach investigating mobile ad hoc network connectivity. It is shown how to define and evaluate the connectivity probability of a mobile network where the position of the nodes and the link quality changes over time. The connectivity probability is a measure that can capture the impact of the node movement on the network connectivity. A number of mobility models is considered ranging from the classical Random Direction model to the Virtual World model based on the mobility measurements of a multi–player game. We introduce an Attractor model as a simple way to model non–homogeneous node distribution by incorporating viscosity regions in the simulation area. Methods of ergodic theory are used to show the correctness of the approach and to reduce the computational time. Simulation results show how the node density distribution affects the network connectivity.