一种异构分布式存储再生码变换原理

再生码是一类分布式存储编码,由于在节点存储和修复带宽两方面均有效而被广泛研究。基于乘积矩阵(PM)理论的最小存储再生(PM-MSR)码是一类同构分布式存储再生码,具有最小的节点存储。提出一种再生码变换原理,能够根据PM-MSR码产生新的再生码,新的再生码用于异构分布式存储系统。严格证明了新再生码结构的数据重构和数据修复性质,并提供了编码实例。新的再生码与PM-MSR码具有相同的存储消耗和带宽消耗,但新的再生码具有更小的平均节点故障率,这对实际应用具有吸引力。     

RS纠删码在云存储中的应用

云存储作为一种旨在为用户提供高效、廉价、安全、可扩展、可定制的存储服务的存储模式,已然成为存储服务的发展趋势.但是因为其云端存储节点的不可控性,云存储在如何保障数据安全性的问题上面临着挑战.通过将RS纠删码引入云存储中,采用分片聚合机制,为云存储的数据安全性保障提供了一种新的解决方案.     

空间信息网络中基于LT码的分布式存储策略

针对空间信息网络(Space Information Network, SIN)节点存储资源严重受限及存储可靠性问题,该文提出一种基于LT(Luby Transform)码的分布式存储策略(Distributed Storage Strategy based on LT codes, DSSLT)。采用定向随机漫步机制,使得源数据包能够更快地遍历整个网络。在信息估计阶段利用基于ID的估计方法进行网络全局信息估计,使所有节点快速获得网络全局信息。合理的数据包选择机制使得最终编码度分布趋于期望的度分布。分析和仿真结果表明,与具有代表性的分布式存储策略相比,该方法大幅度减少了数据包传输时的随机漫步步长,同时提高了译码性能,简单易行。     

几类near MDS码和最优局部修复码的构造

局部修复码是一种通过局部修复提高存储节点修复效率的重要编码方法,在分布式存储和云存储中有重要应用.本文首先构造了几类维数为4或5的near MDS (near Maximum Distance Separable)码,精确计算出了它们的参数和重量分布.特别地,得到了一些参数相同但重量分布不同的near MDS码.此外,通过确定near MDS码的局部度,得到了几类距离最优和维数最优的局部修复码.这些局部修复码的参数和文献中已知最优局部修复码的参数不同.     

分布式存储系统中容错技术综述

互联网、5G及其相关产业的飞速发展使我们迈入了大数据时代,存储海量数据将面临着巨大挑战。大规模分布式存储系统以其海量存储能力、高吞吐量、高可用性和低成本的突出优势取代了集中式存储系统成为主流系统。由于分布式存储系统中节点数量庞大,经常会产生各种类型故障,从而导致节点失效情况频发。因此,必须采用容错技术来保证在部分存储节点失效的情况下,数据仍然能够被正常读取和下载,具有容错能力且节约存储资源的分布式存储编码成为大数据时代重点研究的核心技术之一。讨论了大数据背景下存储与可靠性的问题,从而引出数据容错对分布式存储的重要性。阐述了传统的2种数据存储容错技术,即多副本机制和MDS码。重点分析了3种主要的分布式存储编码,即再生码(RGC)、局部可修复码(LRC)和Piggybacking编码的基本原理、优缺点以及发展现状。总结对比了这5种数据容错技术的性能差异。面向数据的容错存储,针对存储中的节点修复问题,为大数据和移动数据的分布式存储编码提供理论基础,为海量数据的高效、可靠存储提供技术支撑。     

异构个人域网络中的分布式目录信息存储

移动技术和泛在计算的融合在推动移动业务发展的同时也带来了移动性方面的挑战。分析了移动泛在条件下个人域网络的异构性、短距离性与组移动性的特征,针对这些特征给出了一种无中心化目录存储机制,用于个人域网络的自主维护与组织。在大量设备成组加入的情况下,消耗的带宽资源不会随之大幅增加,有效节约了带宽,维护了系统工作的稳定性。     

级连码在卫星通信中的应用与RS码的译码

讨论卫星通信中的编码技术。根据卫星通信的特点与编码技术的主要作用,选用卷积码与RS码级连的方法来提高数据传输的质量与降低通信设备的成本。着重讨论RS码的编译码技术,在分析非系统RS码的过程中采用Blahut定理,获得一些新的结果。对有限域上的乘法,采用对偶基的概念使乘法器硬件实现非常容易,文中给出了求对偶基的算法。提出对著名的Berlekamp—Massey算法的改进。最后比较了系统RS码与非系统RS码译码的复杂性及其各自适用的场合。     

MATLAB在RS码实现中的应用

介绍如何利用MATLAB中的rsenc函数和rsdec函数等来帮助实现RS码的编码和译码程序,以及如何利用MATLAB强大的数值计算能力对RS码的性能测试结果进行数据分析.该方法具有编程简单灵活,计算速度快等特点.     

一种分布式编码算法在云存储中的应用

在云存储中为保证数据的完整可靠,必须采用冗余备份的方式存储数据.为了更好的发挥存储节点的作用,在分析现有的冗余方式基础上提出了一种分布式编码算法.在新的冗余方案中编解码操作在各存储节点并行完成,而不需要将整个数据文件集中进行编解码,充分发挥了分布式系统优势.通过实验仿真验证了方法的可行性,大大提高了数据存储速率,提高了数据可用性,改善了系统性能.     

Turbo码在短波通信中的应用

针对短波信道存在干扰严重的问题,提出一种高效的信道编码用于短波电台的编码模块。描述了短波电台RS码和卷积码的信道编码基本原理,对接近Shannon限的高效信道编码——Turbo码做了介绍,并对其进行计算机仿真和性能比较。仿真结果表明,Turbo码在低信噪比条件下具有较强的纠错能力,将其应用到短波通信系统中,有效地提高短...     

VMesh: Distributed Segment Storage for Peer-to-Peer Interactive Video Streaming

Provisioning random access functions in peer-to-peer on-demand video streaming is challenging, due to not only the asynchronous user interactivity but also the unpredictability of group dynamics. In this paper, we propose VMesh, a distributed peer-to-peer video-on-demand (VoD) streaming scheme which efficiently supports random seeking functionality. In VMesh, videos are divided into segments and stored at peers' local storage in a distributed manner. An overlay mesh is built upon peers to support random forward/backward seek, pause and restart during playback. Our scheme takes advantage of the large aggregate storage capacity of peers to improve the segment supply so as to support efficient interactive commands in a scalable manner. Unlike previous work based on "cache-and-relay" mechanism, in our scheme, user interactivity such as random seeking performed by a peer does not break the connections between it and its children, and hence our scheme achieves better playback continuity. Through simulation, we show that our system achieves low startup and seeking latency under random user interactivity and peer join/leave which is a crucial requirement in an interactive VoD system.     

Existence and Construction of Capacity-Achieving Network Codes for Distributed Storage

In a distributed storage system based on erasure coding, when a storage node fails, repairing the erasure code incurs some network traffic. Previous work has characterized the fundamental tradeoff between storage efficiency and repair network bandwidth. This was done via a cut-based analysis on a graph that models the evolution of information flow in the storage system subject to arbitrary sequences of node failures/repairs. This paper presents techniques for constructing network codes that achieve the optimal tradeoff between storage efficiency and repair network bandwidth. The challenge here is that network coding is applied over an unbounded graph with an unbounded number of receivers. It is shown in this paper that optimal codes can be constructed over a finite field whose size depends only on the maximum number of nodes at any instant, but independent of how many failures/repairs can happen. Key to the code construction is a "path-weaving" procedure that leads to inductive existence proof and code construction.     

LT Codes and the Minimum Spanning Tree Based Distributed Storage in Wireless Sensor Networks

Mobile Networks and Applications - In wireless sensor networks, sensor nodes are vulnerable due to the challenging environment and limited energy. Once a sensor node fails, the stored sensed data...     

分布式分级保护LT码

LT码是喷泉码的一种,它是线型无速率码,在删除信道中性能优越。数据传输中有一些数据相对来说可能更重要,在这样的传输模型中,对于关键信息的保护显的尤为重要。基于此目的提出了一种分布式LT码多信源节点信息的保护措施,分级保护LT码是通过改进每个节点的度为1和2的数据包的原始数据包的选择以提高整个码字的性能,在此基础上引入分布式模型,使得得到的分布式分级保护码字结合了分布式LT码和分级保护LT码的双重优点。     

分布式无标度LT码

LT码是喷泉码的一种,在删除信道中性能优越,分布式喷泉码多信源多中继的特性适合用于深空通信中。无标度网络（SF network）具有平均路径（APL）长最小的特性,非常适合喷泉码的度分布设计需求。首先介绍了LT码的编译码算法,然后对无标度网络和基于无标度网络的SF-LT码度分布设计进行了详细分析和优化,最后在删除信道条件下,选取码长较短、删除概率较小的情形对分布式二信源SF-LT码进行仿真分析,仿真结果表明,与LT码相比,分布式SF-LT码具有更好的性能。     

基于纠删码的分布式存储系统中针对多数据失效的树型并行修复技术

To reduce the time required to complete the regeneration process of erasure codes, we propose a Tree-structured Parallel Regeneration (TPR) scheme for multiple data losses in distributed storage systems. Under the scheme, two algorithms are proposed for the construction of multiple regeneration trees, namely the edge-disjoint algorithm and edge- sharing algorithm. The edge-disjoint algorithm constructs multiple independent trees, and is simple and appropriate for environments where newcomers and their providers are dis-tributed over a large area and have few inter-sections. The edge-sharing algorithm constructs multiple trees that compete to utilize the bandwidth, and make a better utilization of the bandwidth, although it needs to measure the available bandwidth and deal with the bandwidth changes; it is therefore difficult to implement in practical systems. The parallel regeneration for multiple data losses of TPR primarily includes two op-timizations: firstly, transferring the data thr-ough the bandwidth optimized-paths in a pipeline manner; secondly, executing data regeneration over multiple trees in parallel. To evaluate the proposal, we implement an event- based simulator and make a detailed comparison with some popular regeneration methods. The quantitative comparison results show that the use of TPR employing either the edge-disjoint algorithm or edge-sharing algorithm reduces the regeneration time significantly.     

Segment Storage System:基于P2P的网络存储服务

Segment Storage System(S3)是一种基于P2P模型的网络存储服务,它具有高可用性、可靠性和持久性的特点。S3继承了P2P网络的优点并且摒弃了诸如文件时效性和不稳定性等缺点。S3的目标是提供一种高质量的网络存储服务。文章是对S3的设计架构的一个概览。     

Building Heterogeneous Peer-to-Peer Networks: Protocol and Analysis

In this paper, we propose a simple protocol for building heterogeneous unstructured peer-to-peer (P2P) networks. The protocol consists of two parts-the joining process and the rebuilding process. The basic idea for the joining process is to use a random walk to assist new incoming peers in selecting their suitable neighbors in terms of capacity and connectivity to achieve load-balancing. The rebuilding process specifies how the nodes should react when they lose links. In particular, we examine two representative schemes, namely the probabilistic-rebuilding scheme and the adaptive-rebuilding scheme. Furthermore, we provide a detailed analysis to investigate our proposed protocol under any heterogenous P2P environment. We prove that the topology structure of the P2P network depends heavily on the node heterogeneity. The analytical results are validated by the simulations. Our framework provides a guideline to engineer and optimize a P2P network in different respects under a heterogeneous environment. The ultimate goal of this paper is to stimulate further research to explore the fundamental issues in heterogeneous P2P networks.     

协同通信中的分布式线性疏散码

该文提出一种分布式线性疏散码解决无线网络中协同节点不能确定时的空时编码问题。参与协同的节点采用独立的疏散矢量进行编码,推导协同节点减少时分布式线性疏散码的互信息损失,并以此建立一种分布式疏散码的编码准则。仿真结果验证了这种分布式线性疏散码的误比特性能及编码准则的可行性。