一种分布容错系统中的检查点设置技术

本文提出一种在分布处理环境中,消除向后恢复过程中多米诺效应的检查点设置技术,其优点是功能强,代价小、适用面广而且实现简单.在理论分析的基础上,本文提供了该技术的实现方案,检查点存储管理方法及其评价技术.     

多米诺效应的解决策略研究

定义了备查点间隔之间的先于关系，并对分布式系统执行的语义正确性进行了约束，证明了逆时先于现象是产生多米诺效应的本质，提出了多米诺避免、多米诺检测与消除、多米诺容忍三大解决策略.     

图像的运动模糊复原技术研究

由于成像系统与地面目标的相对运动,在目标图像上产生运动模糊,图像复原技术可以消除图像模糊.介绍两种模糊图像的恢复方法,根据匀速直线运动造成的图像模糊的特点,建立原始图像与模糊图像间的关系,在此基础上分析匀速模糊图像的退化及恢复过程,山此推出相关的数学模型,试验结果证明了方法的有效性.     

一种基于组通信的复制数据库在线恢复策略研究

数据复制是提高数据库系统性能和可用性的重要技术.近年来出现的基于组通信技术的数据库复制协议较之传统的数据库复制协议因其实现简单灵活、性能较优,在构建实用复制数据库系统时得到广泛应用.维持各节点副本一致性是数据复制技术研究的核心问题.讨论了当故障节点恢复后重新加入系统或增加新节点后如何恢复、维护系统节点副本间的一致性的问题.提出了一个针对分布复制数据库系统的在线恢复策略,该策略结合基于组通信技术的复制协议,可在不影响系统正常事务处理的情况下,实现故障恢复后节点或全新节点重新加入系统时的系统正确恢复,并给出了理论证明.同时还证明,该策略对于分布在不可靠网络上的复制数据库的在线恢复同样适用.     

用于高速运算单元的时钟延迟动态多米诺逻辑电路的设计

时钟延迟多米诺逻辑是一种自定时的动态逻辑。时钟延迟多米诺逻辑门的输出信号是单向跳变的，但它可以提供倒相和非倒相的输出。使用这种动态逻辑可以大大提高运算电路的速度。本文通过一个64位的快速并行加法器的实现说明时钟延迟多米诺的特性及其设计方法。这个快速并行加法器用于高性能的64位微处理器的运算单元中。采用0.25μm CMOS工艺设计了这个加法器。加法器在最坏情况下的运算时间是700ps。这个时钟延迟多米诺加法器比使用相同单元库和技术的静态逻辑加法器快2.3倍。     

基于代表点与K近邻的密度峰值聚类算法

密度峰值聚类(density peaks clustering, DPC)是一种基于密度的聚类算法,该算法可以直观地确定类簇数量,识别任意形状的类簇,并且自动检测、排除异常点.然而, DPC仍存在些许不足:一方面, DPC算法仅考虑全局分布,在类簇密度差距较大的数据集聚类效果较差;另一方面, DPC中点的分配策略容易导致“多米诺效应”.为此,基于代表点(representative points)与K近邻(K-nearest neighbors, KNN)提出了RKNN-DPC算法.首先,构造了K近邻密度,再引入代表点刻画样本的全局分布,提出了新的局部密度;然后,利用样本的K近邻信息,提出一种加权的K近邻分配策略以缓解“多米诺效应”;最后,在人工数据集和真实数据集上与5种聚类算法进行了对比实验,实验结果表明,所提出的RKNN-DPC可以更准确地识别类簇中心并且获得更好的聚类结果.     

E波段微波传输系统中频域交叠均衡技术

为了提高传输效率,E波段微波传输系统采用了不加循环前缀的单载波块传输方式,针对多径信道中传输时引入的块间干扰,采用频域交叠均衡技术有效消除了前后数据块之间的混叠干扰。通过MATLAB仿真评估,该技术可以在中低信噪比时以较低的系统复杂度实现系统传输速率的提升以及多径效应的消除。     

医学图像DCT变换压缩中方块效应的消除

针对基于分块的医学图像DCT变换压缩中恢复图像的方块效应,提出了一种自适应DCT变换域修正方法.通过模拟实验表明,该方法能在消除方块效应的同时保留图像的高频部分信息,并且不需要复杂的计算,在满足适合实时性的应用需求下,可以很好消除恢复图像中的方块效应,给医生良好的视觉效果.     

STC-OFDM系统改进的消除串行干扰算法

STC-OFDM系统有效弥补了正交频分复用多址系统中符号间干扰和频率选择性衰落等不足,但存在如何有效抑制因多天线传输产生的相互干扰问题.为此,提出了一种结合信道频率响应恢复和串行干扰消除来抑制干扰的改进算法,该算法在串行干扰消除之前先对导频进行信道频率响应恢复,减小估计对信道频率响应的影响.仿真实验表明,该算法能进一步改善STC-OFDM系统比特误码率并进而抑制相互干扰.     

化工园区危险品仓储智能管理系统软件设计

针对化工园区规模大、化工工艺复杂、危险源数量多、密度大,以及化学品控制和监管效率低等问题,设计并实现了一种化工园区危险品仓储智能管理系统.系统采用C#编程语言,综合利用虹膜身份识别门禁、RFID物品识别、环境感知、无线传感网络、多米诺效应风险管理和评估等技术,实现化工危险品仓储的智能监控和追踪、风险评估和预警.经过应用测试,整个系统性能良好,操作方便,提升了化工危险品仓储的安全性,以及管理的精细化和智能化.     

一种优化的分布式系统的失效恢复策略

本文对确定性进程组的分布式系统的失效恢复策略做了深入的研究,独到地提出了应用数据流分析来静态地计算进程的最小备查点数据集的方法。     

The Effects of an ARMOR-based SIFT environment on the performance and dependability of user applications

Few, distributed software-implemented fault tolerance (SIFT) environments have been experimentally evaluated using substantial applications to show that they protect both themselves and the applications from errors. We present an experimental evaluation of a SIFT environment used to oversee spaceborne applications as part of the Remote Exploration and Experimentation (REE) program at the Jet Propulsion Laboratory. The SIFT environment is built around a set of self-checking ARMOR processes running on different machines that provide error detection and recovery services to themselves and to the REE applications. An evaluation methodology is presented in which over 28,000 errors were injected into both the SIFT processes and two representative REE applications. The experiments were split into three groups of error injections, with each group successively stressing the SIFT error detection and recovery more than the previous group. The results show that the SIFT environment added negligible overhead to the application's execution time during failure-free runs. Correlated failures affecting a SIFT process and application process are possible, but the division of detection and recovery responsibilities in the SIFT environment allows it to recover from these multiple failure scenarios. Only 28 cases were observed in which either the application failed to start or the SIFT environment failed to recognize that the application had completed. Further investigations showed that assertions within the SIFT processes-coupled with object-based incremental checkpointing-were effective in preventing system failures by protecting dynamic data within the SIFT processes.     

交替互补定位器及其用于双模比较冗余结构的差错定位

双模比较冗余结构是一种广泛应用的低成本容错结构。当两个冗余模块之一发生故障时,比较器将给出差错检测指示输出,该输出既可以按中断信号形式通知系统作出相应的差错处理,也可以按硬件信号形式直接用于终止系统工作或启动重构,目的是防止故障冗余结构给出错误输出,或者确保系统能够提供连续的服务。这种冗余结构的缺点是比较器不能确切指明故障模块,并因此而需要较大的时间开销来完成系统重构和恢复操作。为解决这一问题,提出了一种具有并发输出差错定位功能的双重比较冗余结构。其中单个冗余模块的输出是一个交替矢量,两个冗余模块的输出形成了一个交替互补矢量,该矢量送入一个交替互补定位器。在正常输入情况下,根据定位器的输出就可以确定冗余系统是无差错的、还是冗余模块或定位顺本身存在故障。交替互补定位器由D型触发器和通用门电路构成,它被证明为是一个完全故障定位的定位器。由于所提出的双模比较冗余结构是基于时间冗余原理工作的,因此它适用于对速度要求并不是非常苛刻的容错系统。     

Hierarchical error detection in a software implemented faulttolerance (SIFT) environment

Proposes a hierarchical error detection framework for a software-implemented fault tolerance (SIFT) layer of a distributed system. A four-level error detection hierarchy is proposed in the context of Chameleon, a software environment for providing adaptive fault tolerance in an environment of commercial off-the-shelf (COTS) system components and software. The design and implementation of a software-based distributed signature monitoring scheme, which is central to the proposed four-level hierarchy, is described. Both intra-level and inter-level optimizations that minimize the overhead of detection and are capable of adapting to runtime requirements are proposed. The paper presents results from a prototype implementation of two levels of the error detection hierarchy and results of a detailed simulation of the overall environment. The results indicate a substantial increase in availability due to the detection framework and help in understanding the tradeoffs between overhead and coverage for different combinations of techniques     

自控天车定位精度的研究与实现

基于误差补偿方式提高天车系统的定位精度。从误差源分析入手,分析了引起天车运行定位精度的原因及其对天车定位精度的影响,采用软件方式进行针对性补偿。根据研究的误差补偿算法设计了铝型材氧化着色及电泳生产线的天车系统,经过几个月的生产实践验证,该自动天车在运行过程中,实际运行位置与理想定位点的最大偏差不超过2.6 cm。实践证明采用该方法设计的天车系统运行稳定,能够满足生产实际对天车系统的行程精度要求。     

Modeling and evaluating the time overhead induced by BER in COMA multiprocessors

Designing multiprocessors based on distributed shared memory (DSM) architecture considerably increases their scalability. But as the number of nodes in a multiprocessor increases, the probability of encountering failures in one or more nodes of the system raises as a serious problem. Thus, every large-scale multiprocessor should be equipped with mechanisms that tolerate node failures. Backward error recovery (BER) is one of the most feasible strategies to build fault tolerant multiprocessors and it can be shown that among various DSM-based architectures, cache only memory architecture (COMA) is the most suitable for implementing BER. The main reason is the existence of built-in mechanisms for data replication in COMA memory system. BER is applicable to COMA multiprocessors with minor hardware redundancy, but it will obviously cause some other kinds of overheads. The most important overhead induced by BER is the time required to produce and store recovery data. This paper introduces an analytical model for predicting the amount of this time overhead and then verifies the correctness of the model through comparing the results predicted from this model with the previously published simulation results. Both the analytical model and simulation results show that the overhead is nearly independent of the number of nodes. The immediate result is that BER is a cost-effective strategy for tolerating node failures in large-scale COMA multiprocessors with large numbers of nodes.     

一种基于多层次校验的低恢复成本纠删码

随着纠删码在分布式存储系统中的实际应用,纠删码为存储系统提供了更加优秀的存储效率,但当节点丢失时,相较于传统副本技术更多的网络传输带宽开销成为了造成系统性能瓶颈的关键因素。为了解决MDS编码高带宽开销对系统性能的影响,一类新型编码方案——分组码被应用在分布式存储系统中,相较于传统MDS编码能够有效地降低节点修复时的数据传输量,从而减少网络带宽需求。在Pyramid分组码的基础上进行层次扩展,提出一种HLRC（hierarchical local repair codes）纠删码。HLRC相较于LRC引入了层次编码模型,将原始数据块构建为编码矩阵,根据层次进行分别编码,生成包含数据块范围不同的局部校验块;每个层次包含的数据块数量不同,可以保证修复节点时的低修复成本,同时还拥有较高的存储效率。HLRC相较于Pyramid拥有额外的校验块冗余,能够降低校验块出错和多节点出错时的恢复开销。在基于Ceph的分布式存储系统中的实验结果表明,HLRC与Pyramid等分组码相比,单节点修复开销最高可降低48.56%,多节点修复开销最高可降低25%。     

一种低单盘故障恢复开销的局部修复码

如今随着存储系统规模的扩大和廉价磁盘的大量使用,单一磁盘故障在存储系统中发生故障的概率也不断上升。而在基于RDP编码的阵列存储系统中,恢复单个故障磁盘,需要读取全部的剩余数据磁盘,读取开销大,故障恢复时间长。而故障时间长就会导致系统在恢复过程中出错的概率增大,影响系统整体的稳定性。为进一步降低单个磁盘故障恢复的读取开销,减少恢复时间,提升存储系统可靠性,提出一种局部修复RDP码,通过增加一个局部冗余列来减少故障恢复时需要读取的数据量。实验结果表明改进方法在降低读取开销和减少恢复时间方面相对于传统的RDP单盘故障恢复方法有明显提高,并且能够恢复75%的三盘故障情况。     

Trading off logging overhead and coordinating overhead to achieve efficient rollback recovery

In the rollback recovery of large‐scale long‐running applications in a distributed environment, pessimistic message logging protocols enable failed processes to recover independently, though at the expense of logging every message synchronously during fault‐free execution. In contrast, coordinated checkpointing protocols avoid message logging, but they are poor in scalability with a sharply increased coordinating overhead as the system grows. With the aim of achieving efficient rollback recovery by trading off logging overhead and coordinating overhead, this paper suggests a partitioning of the system into clusters, and then presents a scheme to implement the conversion between these overheads. Using the proposed conversion, coordination can be introduced to reduce the unbearable logging overhead found in some systems, whereas proper logging can be employed to alleviate the unacceptable coordinating overhead in others. Furthermore, heuristics are introduced to address the issue of how to partition the system into clusters in order to speed up the recovery process and to improve recovery efficiency. Performance evaluation results indicate that our scheme can lower the overall system overhead effectively. Copyright © 2008 John Wiley & Sons, Ltd.     

基于概率传输的无线传感网数据汇聚方案

针对传统无线传感网数据汇聚中通信开销较大的问题,提出了基于概率传输的无线传感网数据汇聚方案。由于簇内节点有限,汇聚误差难以避免,在可容忍汇聚误差下,簇内节点按概率进行数据发送,可有效减少簇内消息传输量,降低通信开销。同时,采取狄克逊准则对小样本中的粗大误差进行剔除提供高的簇内汇聚可靠性。实验结果表明,在可容忍误差下进行概率发送可有效降低簇内消息传输量,所提方案的簇内数据汇聚通信开销约为传统方案的27.5%;概率发送的汇聚误差与所有节点进行数据发送的汇聚误差基本在同一水平,都是传感器网络可接受的。