Consensus-based linear distributed filtering

We address the consensus-based distributed linear filtering problem, where a discrete time, linear stochastic process is observed by a network of sensors. We assume that the consensus weights are known and we first provide sufficient conditions under which the stochastic process is detectable, i.e. for a specific choice of consensus weights there exists a set of filtering gains such that the dynamics of the estimation errors (without noise) is asymptotically stable. Next, we develop a distributed, sub-optimal filtering scheme based on minimizing an upper bound on a quadratic filtering cost. In the stationary case, we provide sufficient conditions under which this scheme converges; conditions expressed in terms of the convergence properties of a set of coupled Riccati equations.     

基于一致性的并联虚拟同步发电机分布式协同控制

虚拟同步发电机(virtual synchronous generator,VSG)可模拟同步发电机运行机制,并为系统提供惯性和阻尼支撑.在孤岛模式下,VSG并联运行多采用分散下垂控制,不具备频率恢复以及有功出力合理分配等功能,为此,本文提出了一种基于一致性的并联VSG分布式控制方法,可改善系统频率与有功功率特性.本文首先介绍了传统VSG控制的数学模型,并在此基础上设计了VSG并联系统频率恢复及有功出力合理分配的整体方案.在分布式控制模式下,相邻VSG只需少量信息交互即可控制频率恢复到额定值,并可实现功率的按需分配,满足了不同用户的定制需求.仿真结果验证了所提方法的正确性和有效性.     

Consensus-based evaluation framework for distributed information retrieval systems

Multi-agent systems have been attacking the challenges of information retrieval tasks on distributed environment. In this paper, we propose a consensus choice selection method based framework to evaluate the performance of cooperative information retrieval tasks of the multiple agents. Thereby, two well-known measurements, precision and recall, are extended to handle consensual closeness (i.e., local and global consensus) between the sets of retrieved results. We show that in a motivating example the proposed criteria are prone to solve the rigidity problem of classical precision and recall. More importantly, the retrieved results can be ranked with respect to the consensual score, and the ranking mechanism has been verified to be more reasonable.

传感器网络一致性分布式滤波算法

为了改善分布式传感器网络的估计性能,提出了一种基于状态预测一致的滤波算法.在对局部估计值进行一致化处理的基础上,重点研究了利用邻居节点前一时刻的估计值对当前局部状态预测值进行修正来提高估计精度.给出了一种一致性增益的选择方法,利用李雅普诺夫方法得到了算法收敛的充分条件,并讨论了影响算法收敛速度的因素.仿真结果表明了算法的有效性,并发现节点度较大的传感器在网络估计中发挥着重要作用,可通过调整这类节点的一致性系数来改善算法性能.     

带宽受限下的基于一致性的分布式融合估计器

研究带宽受限下的基于一致性的分布式融合估计问题. 建立以一致性滤波增益为决策变量, 以所有传感器有限时域下融合估计误差协方差矩阵的迹的和为代价函数的优化问题. 在给定一致性权重的前提下, 给出使得系统融合估计误差在无噪声时渐近稳定的一致性滤波增益存在的充分条件, 并通过最小化代价函数的上界得到一组次优的一致性滤波增益. 最后通过算例仿真验证了所提出方法的有效性.     

Adaptive data replication strategy in cloud computing for performance improvement

Cloud computing is becoming a very popular word in industry and is receiving a large amount of attention from the research community. Replica management is one of the most important issues in the cloud, which can offer fast data access time, high data availability and reliability. By keeping all replicas active, the replicas may enhance system task successful execution rate if the replicas and requests are reasonably distributed. However, appropriate replica placement in a large-scale, dynamically scalable and totally virtualized data centers is much more complicated. To provide cost-effective availability, minimize the response time of applications and make load balancing for cloud storage, a new replica placement is proposed. The replica placement is based on five important parameters: mean service time, failure probability, load variance, latency and storage usage. However, replication should be used wisely because the storage size of each site is limited. Thus, the site must keep only the important replicas.We also present a new replica replacement strategy based on the availability of the file, the last time the replica was requested, number of access, and size of replica. We evaluate our algorithm using the CloudSim simulator and find that it offers better performance in comparison with other algorithms in terms of mean response time, effective network usage, load balancing, replication frequency, and storage usage.     

基于一致性的小型四旋翼机群自主编队分布式运动规划

设计一种小型四旋翼无人机群起飞后自主形成正多边形编队的分布式运动规划方法.在四旋翼无人机的串级控制系统框架下,分布式编队控制器以简化agent模型为基础,同时采用平均一致性算法和有领导一致性算法,共同产生各无人机位置与偏航角的期望轨迹.讨论了达成最终协调目标队形的拓扑条件,并给出一种基于有向Hamilton环的通信拓扑设计方案.最后通过数值仿真验证了所提出算法的有效性.     

A CSO-based approach for secure data replication in cloud computing environment

The Journal of Supercomputing - Cloud computing has a significant impact on information technology solutions for both organizations and researchers. Different users share critical data over the...     

Consensus-based modeling using distributed feature construction with ILP

A particularly successful role for Inductive Logic Programming (ILP) is as a tool for discovering useful relational features for subsequent use in a predictive model. Conceptually, the case for using ILP to construct relational features rests on treating these features as functions, the automated discovery of which necessarily requires some form of first-order learning. Practically, there are now several reports in the literature that suggest that augmenting any existing feature with ILP-discovered relational features can substantially improve the predictive power of a model. While the approach is straightforward enough, much still needs to be done to scale it up to explore more fully the space of possible features that can be constructed by an ILP system. This is in principle, infinite and in practice, extremely large. Applications have been confined to heuristic or random selections from this space. In this paper, we address this computational difficulty by allowing features and models to be constructed in a distributed manner. That is, there is a network of computational units, each of which employs an ILP engine to construct some small number of features and then builds a (local) model. We then employ an asynchronous consensus-based algorithm, in which neighboring nodes share information and update local models. This gossip-based information exchange results in the formation of non-stationary Markov chains. For a category of models (those with convex loss functions), it can be shown (using the Supermartingale Convergence Theorem) that the algorithm will result in all nodes converging to a consensus model. In practice, it may be slow to achieve this convergence. Nevertheless, our results on synthetic and real datasets suggest that in relatively short time the “best” node in the network reaches a model whose predictive accuracy is comparable to that obtained using more computational effort in a non-distributed setting (the best node is identified as the one whose weights converge first).     

An efficient multipath routing for distributed computing systems with data replication

In distributed computing environments, executing a program often requires the access of remote data files. An efficient data routing scheme is thus important for time-critical applications. To ensure a prior desired communication quality, we present a connection-oriented routing scheme, the multipath routing, which allows multiple routes to be established between the source and the destination. Based on the multipath routing scheme, the problem of finding a collection of routing paths for an application to minimize its data transmission time is addressed. Such a problem becomes a complex combinatorial one when the application accesses multiple replicated data sources. Since finding an optimal solution is computationally infeasible in practice, we thus propose a heuristic method to get a sub-optimal solution.     

Locality-aware process placement for parallel and distributed simulation in cloud data centers

The Journal of Supercomputing - Cloud is a multi-tenant paradigm providing resources as a service. With its easily available computing infrastructure, researchers are adopting cloud for...     

分布式系统数据复制协议的研究

数据复制正在并行信息系统的设计中起着越来越重要的作用.特别地,为了提高性能和可用性,对集群体系结构的广泛使用经常要求复制数据.然而,维持不同拷贝的一致性带来严重的可伸缩性问题.为了克服这个局限性,基于表决的协议经常被作为一种缩减复制的总开销的方法.为了更好理解它们在实际中的性能,分析了几种表决算法,结果是基于表决的复制协议表现出不错的性能.测试表明ROWA-A(read-one/write-all-available)协议对于需要大量数据复制的应用是最好的选择.     

Static and adaptive distributed data replication using genetic algorithms

Fast dissemination and access of information in large distributed systems, such as the Internet, has become a norm of our daily life. However, undesired long delays experienced by end-users, especially during the peak hours, continue to be a common problem. Replicating some of the objects at multiple sites is one possible solution in decreasing network traffic. The decision of what to replicate where, requires solving a constraint optimization problem which is NP-complete in general. Such problems are known to stretch the capacity of a Genetic Algorithm (GA) to its limits. Nevertheless, we propose a GA to solve the problem when the read/write demands remain static and experimentally prove the superior solution quality obtained compared to an intuitive greedy method. Unfortunately, the static GA approach involves high running time and may not be useful when read/write demands continuously change, as is the case with breaking news. To tackle such case we propose a hybrid GA that takes as input the current replica distribution and computes a new one using knowledge about the network attributes and the changes occurred. Keeping in view more pragmatic scenarios in today's distributed information environments, we evaluate these algorithms with respect to the storage capacity constraint of each site as well as variations in the popularity of objects, and also examine the trade-off between running time and solution quality.     

分布式系统中数据复制的研究与应用

维持数据的一致性是复制数据库并发执行的关键。介绍分析了MS SQL Server 2000中内置的数据复制构件以及MS SQL Server 2000的事务模型,最后结合实际的应用软件开发对数据复制的并发控制原理与措施进行了相关实现。     

On construction of a distributed data storage system in cloud

In the past, people have focused on cluster computing and grid computing. Now, however, this focus has shifted to cloud computing. Irrespective of what techniques are used, there are always storage requirements. The challenge people face in this area is the huge amount of data to be stored, and its complexity. People are now using many cloud applications. As a result, service providers must serve increasingly more people, causing more and more connections involving substantially more data. These problems could have been solved in the past, but in the age of cloud computing, they have become more complex. This paper focuses on cloud computing infrastructure, and especially data services. The goal of this paper is to implement a high performance and load balancing, and able-to-be-replicated system that provides data storage for private cloud users through a virtualization system. This system extends and enhances the functionality of the Hadoop distributed system. The proposed approach also implements a resource monitor of machine status factors such as CPU, memory, and network usage to help optimize the virtualization system and data storage system. To prove and extend the usability of this design, a synchronize app was also developed running on Android based on our distributed data storage.     

能量和带宽受限下的分布式一致性融合估计器

针对网络化多传感器分布式估计中传感器能量和通信网络带宽约束问题,提出一种基于降低发送频率和数据压缩降维的分布式一致性融合估计算法.为了满足通信网络带宽要求,各传感器节点直接选取局部估计信号的部分分量进行传输;与此同时,各节点随机间歇式发送数据包到其他节点来节省能量.在给定一致性权重下,建立以一致性估计器增益为决策变量,以所有传感器节点有限时域下状态融合估计误差协方差矩阵的迹的和为代价函数的优化问题,基于Lyapunov稳定性理论给出使得融合估计误差在无噪声时渐近稳定的一致性估计器增益存在的充分条件,并通过最小化代价函数的上界得到一组次优的一致性估计器增益值.最后,通过算例仿真验证算法的有效性.     

Hierarchical data replication strategy to improve performance in cloud computing

Cloud computing environment is getting more interesting as a new trend of data management. Data replication has been widely applied to improve data access in distributed systems such as Grid and Cloud. However, due to the finite storage capacity of each site, copies that are useful for future jobs can be wastefully deleted and replaced with less valuable ones. Therefore, it is considerable to have appropriate replication strategy that can dynamically store the replicas while satisfying quality of service (QoS) requirements and storage capacity constraints. In this paper, we present a dynamic replication algorithm, named hierarchical data replication strategy (HDRS). HDRS consists of the replica creation that can adaptively increase replicas based on exponential growth or decay rate, the replica placement according to the access load and labeling technique, and finally the replica replacement based on the value of file in the future. We evaluate different dynamic data replication methods using CloudSim simulation. Experiments demonstrate that HDRS can reduce response time and bandwidth usage compared with other algorithms. It means that the HDRS can determine a popular file and replicates it to the best site. This method avoids useless replications and decreases access latency by balancing the load of sites.     

云存储系统中基于分簇的数据复制策略

云存储技术已经成为当前互联网中共享存储和数据服务的基础技术,云存储系统普遍利用数据复制来提高数据可用性,增强系统容错能力和改善系统性能。提出了一种云存储系统中基于分簇的数据复制策略,该策略包括产生数据复制的时机判断、复制副本数量的决定以及如何放置复制所产生的数据副本。在放置数据副本时,设计了一种基于分簇的负载均衡副本放置方法。相关的仿真实验表明,提出的基于分簇的负载均衡副本放置方法是可行的,并且具有良好的性能。     

Improved security of a dynamic remote data possession checking protocol for cloud storage

Cloud storage offers the users with high quality and on-demand data storage services and frees them from the burden of maintenance. However, the cloud servers are not fully trusted. Whether the data stored on cloud are intact or not becomes a major concern of the users. Recently, Chen et al. proposed a remote data possession checking protocol to address this issue. One distinctive feature of their protocol support data dynamics, meaning that users are allowed to modify, insert and delete their outsourced data without the need to re-run the whole protocol. Unfortunately, in this paper, we find that this protocol fails to achieve its purpose since it is vulnerable to forgery attack and replace attack launched by a malicious server. Specifically, we show how a malicious cloud server can deceive the user to believe that the entire file is well-maintained by using the meta-data related to the file alone, or with only part of the file and its meta-data. Then, we propose an improved protocol to fix the security flaws and formally proved that our proposal is secure under a well-known security model. In addition, our improvement keeps all the desirable features of the original protocol.