基于差集矩阵的部分重复码构造

针对最小带宽再生码的有效修复问题，该文提出一种基于差集矩阵的部分重复(FR)码的构造算法。利用差集矩阵和克罗内克(Kronecker)和来构造正交排列，根据正交排列每一列取相同元素所在行作为节点的编码块，得到相应的FR码。构造的FR码可以划分成多个平行类，同时还能调整数据块的重复度和节点的存储容量。仿真结果表明，与传统的里德-所罗门(RS)码和简单再生码(SRC)相比，构造的FR码在修复复杂度、修复带宽开销和修复局部性方面具有更好的性能，修复选择度上虽然是基于表格的修复方案，但选择度依旧可以达到很高。     

异构分布式存储系统中部分重复码的构造

部分重复(FR)码因对故障节点提供精确无编码修复,能够提高分布式存储系统的修复效率和可靠性。异构分布式存储系统中FR码的构造更接近于存储数据的实际应用,即每个节点的存储容量和数据块的重复度不同。考虑到用户访问数据的不均衡性,基于数据热度不同重复度不同的思想,文章提出了基于循环置换矩阵(CPMs)与映射置换矩阵(APMs)的异构分布式存储系统中部分重复码的构造。性能分析表明,异构分布式存储系统中的部分重复码可实现存储系统中故障节点的快速修复,具有较低的修复局部性;相对于RS编码以及简单再生码,部分重复码具有更优的修复带宽开销和修复复杂度。     

数据中心中路由编码的可行性研究

修复带宽最优并不代表修复通信量也是最优的,后者与物理网络拓扑有着密切联系.本文基于路由编码的思想减少修复通信量.首先,基于信息流图对物理网络中数据的传递过程进行建模,证明得出了满足路由编码可行的充要条件,并发现路由编码可以基于再生码实现.然后,针对数据中心网络设计的特点,为Fat-tree设计了一个工作在应用层的协议来生成修复树,为CamCube设计了一个启发式算法来生成修复树.关于最小存储再生码的数据修复过程的仿真实验表明,路由编码可以有效地降低修复通信量,2种修复树生成方案在各自适合的网络中均有较好性能：在帮助节点数较小时,Fat-tree和CamCube中的修复通信量分别降低了大约50%和30%.     

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。     

基于层修复技术的DVC鲁棒传输框架

针对分布式视频编码(DVC)系统鲁棒传输问题,设计了一种基于层修复的DVC系统传输框架。该传输框架首先对关键帧(K帧)同时采用高效视频编码(HEVC)帧内编码和Wyner-Ziv编码,并将校验信息(Wyner-Ziv码流)作为修复层码流存入缓存中。若当前关键帧有丢失,则向编码端请求该帧对应的层修复码流,在解码端对错误块进行修复,获得关键帧解码质量的提升。同时,研究了层修复码率估计算法,利用已成功解码的位平面辅助完成算法重建。实验结果表明,该传输框架利用关键帧的层修复码流对关键帧失真部分进行了修复,提高了关键帧质量,改善了边信息质量,实现了DVC的鲁棒传输。     

基于再生码的云存储系统——Ustor

摘 要：Ustor是一个构建在多个商业云存储服务之上的云存储系统,它旨在保证数据可靠性的同时减少单点失效时占用的修复带宽。不同于将所有数据存储在单个云中,Ustor将数据编码后分布在多个云存储系统中保证可靠性。Ustor的编码模块部署了包括Reed-Solomon码和功能性修复再生码（FRC）在内的多种纠删码,是第一个将功能性修复再生码应用于多个异构的、真实的云存储系统中的应用。与传统的冗余编码比较,FRC显著地减少了单个云存储发生数据丢失时需要从网络上传输的数据量。实验表明：与不编码比较,冗余编码给系统增加了5%~10%的响应时间开销,但可保障节点失效;FRC码编、解码和修复速度与Reed-Solomon码基本相当,256 MB大小文件编码时间差距在0.5 s以内;FRC码修复时与传统的Reed-Solomon码相比减少了25%以上需要下载的数据量。     

一种云存储中基于干扰对齐的多节点精确修复方法

本文提出了一种基于干扰对齐的满足MDS性质的多节点精确修复码(MMSR).首先利用柯西矩阵构造MMSR码的生成矩阵,使其适用干扰对齐技术,并同时修复多个节点.然后讨论了MMSR码同步修复和异步修复方案的优缺点.最后证明了MMSR码的MDS性质,并通过一个(7,3,5)-MMSR码的数据重建方案验证了MMSR码的MDS性质和可行性.     

云存储中一种抗窃听攻击的弱安全再生码

纠删码和再生码是保证云存储可靠性的有效机制,但是它们并不能提供节点被窃听情况下存储数据的机密性。该文设计了两类抗窃听攻击的弱安全再生码方案,方案结合All-or-Nothing变换与精确修复再生码策略,保证了攻击者在窃听能力有限的情况下无法获取关于原始数据符号的任何有意义信息,同时具有较小的数据修复带宽。该文给出了通用编码构造方法,证明了其安全性,并通过实验进行了对比分析,结果表明与其它安全再生码相比该方案的编解码时间更短,且具有更好的秘密数据存储能力。     

基于Fano图的局部循环码构造

为了提高分布式存储系统中数据的可靠性及修复故障节点的可靠性,提出一种基于Fano图的局部循环码。该编码采用了局部性编码的思想,并在局部组内采用基于Fano图的循环码,可以在局部修复组内对故障节点进行快速修复,计算复杂度低。实验结果表明,该编码单节点故障的修复局部性为2,小于现有的RS码与SRC码,且修复带宽开销,与现有的RS码和简单再生码相比具有更低的修复局部性、修复复杂度与修复带宽开销,且修复效率高。     

“双码”架构下的云存储多节点修复协作编码

针对云存储中现有多节点失效修复模型的不足,给出了一种可以对多个系统节点或冗余节点同时修复的多节点协作的精确修复码,证明了其存在性,并且将此修复码与具有健康节点协作的MDS双码架构模型相结合,以达到对多节点修复的同时,降低修复带宽、修复链路数和单个中间节点需要处理的数据量。通过数值仿真结果表明,本模型与修复方案在以上3个方面具有较大改进,尤其削弱了修复时中间节点的负荷,且随着云存储中节点数量的增多,本方案的优势更加明显。     

Optimal Heterogeneous Distributed Storage Regenerating Code at Minimum Remote‐Repair Bandwidth Regenerating Point

Recently, a product‐matrix (PM) framework was proposed to construct optimal regenerating codes for homogeneous distributed storage systems (DSSs). In this paper, we propose an extended PM (EPM) framework for coding of heterogeneous DSSs having different repair bandwidths but identical storage capacities. Based on the EPM framework, an explicit construction of minimum remote‐repair bandwidth regenerating (MRBR) codes is presented for a specific heterogeneous DSS, where two geographically different datacenters with associated storage nodes are deployed. The data reconstruction and regeneration properties of the MRBR code are proved strictly. For the purpose of demonstration, an example implementation of MRBR code is provided. The presented MRBR code is the first optimal strict‐regenerating code for heterogeneous DSSs. In addition, our proposed EPM framework can be applied to homogeneous systems also.     

Design of exact regenerating hierarchical code for distributed storage system

Erasure code is widely used as the redundancy scheme in distributed storage system. When a storage node fails, the repair process often requires to transfer a large amount of data. Regenerating code and hierarchical code are two classes of codes proposed to reduce the repair bandwidth cost. Regenerating codes reduce the amount of data transferred by each helping node, while hierarchical codes reduce the number of nodes participating in the repair process. In this paper, we propose a "sub-code nesting framework" to combine them together. The resulting regenerating hierarchical code has low repair degree as hierarchical code and lower repair cost than hierarchical code. Our code can achieve exact regeneration of the failed node, and has the additional property of low updating complexity.     

Block error-correcting codes for systems with a very high BER: Theoretical analysis and application to the protection of watermarks

This paper addresses the problem of error-correction for extremely noisy channels (BER from 0.1 to 0.5), such as those obtained for image or video watermarking. Minimum distance arguments are used to identify a region for which no other code is as efficient as repetition codes, whatever the rate, at least when bounded decoding is considered. However, in order to obtain a reasonable and sufficiently low BER, repetition codes are not very efficient. We present a coding scheme concatenating a repetition code with another one, and design rules in order to select these codes for a given watermarking application are developed. The repetition code lowers the huge channel BER, as no other code can do this part of the job. Then, the second more powerful code working at a lower BER achieves a larger BER reduction. In this paper, this role is devoted to BCH codes, as members of a classical family. Thanks to their moderate decoding complexity, they turn out to be an interesting cost versus performance trade-off, while more efficient coding schemes based on soft decoding are far more complex. However, we also provide an idea of the solutions to consider for watermarking applications with fewer complexity limitations, for which more powerful decoding techniques can be implemented.     

A secure regenerating code‐based cloud storage with efficient integrity verification

Cloud storage is gaining popularity as it relieves the data owners from the burden of data storage and maintenance cost. However, outsourcing data to third‐party cloud servers raise several concerns such as data availability, confidentiality, and integrity. Recently, regenerating codes have gained popularity because of their low repair bandwidth while ensuring data availability. In this paper, we propose a secure regenerating code‐based cloud storage (SRCCS) scheme, which utilizes the verifiable computation property of homomorphic encryption scheme to check the integrity of outsourced data. In this work, an error‐correcting code (ECC)–based homomorphic encryption scheme (HES) is employed to simultaneously provide data privacy as well as error correction while supporting efficient integrity verification. In SRCCS, server regeneration process is initiated on detection of data corruption events in order to ensure data availability. The ECC‐based HES significantly reduces the probability of server regeneration and minimizes the repair cost. Extensive theoretical analysis and simulation results validate the security, efficiency, and practicability of the proposed scheme.     

Rate-adaptive indoor infrared wireless communication systems usingrepeated and punctured convolutional codes

We propose a rate-adaptive transmission scheme using repeated and punctured convolutional codes for indoor infrared wireless communications. The proposed system uses a coding scheme consisting of an outer punctured convolutional code and an inner repetition code, and varies code rate, i.e., bit rate adaptively depending on channel conditions. We show that the proposed system can realize communications in worse channel conditions at the expense of bit rate, while maximizing the throughput available to a user on his position