Design of two-dimensional spatially coupled LDPC codes for combating burst erasures

Spatially-coupled low-density parity-check(SC-LDPC)codes are prominent candidates for fu-ture communication standards due to their‘threshold saturation’properties.However,when facing burst erasures,the decoding process will stop and the decoding performances will dramatically de-grade.To improve the ability of burst erasure corrections,this paper proposes a two-dimensional SC-LDPC(2D-SC-LDPC)codes constructed by parallelly connecting two asymmetric SC-LDPC coupled chains for resistance to burst erasures.Density evolution algorithm is presented to evaluate the as-ymptotic performances against burst erasures,by which the maximum correctable burst erasure length can be computed.The analysis results show that the maximum correctable burst erasure lengths of the proposed 2D-SC-LDPC codes are much larger than the SC-LDPC codes and the asym-metric SC-LDPC codes.Finite-length performance simulation results of the 2D-SC-LDPC codes over the burst erasure channel confirm the excellent asymptotic performances.

一种基于Erasure Code的分布式文件系统模型

提出了一种基于Erasure code容错理论的分布式文件系统模型并对其关键技术进行了深入的研究和探讨。介绍了文件系统和分布式文件系统的概念,基于Erasure code理论提出了具有适度容错机制的分布式文件系统架构。详细讨论和分析了该系统实现中涉及的一系列关键技术,最后简短描述了本模型的实现,并给出了其性能评价。

基于Erasure Code的分割文件P2P存储结构设计

在充分考虑P2P存储特点的前提下,设计了一种新颖的基于Erasure Code的分割文件P2P存储方案,构建Chord协议上的P2P文件存储结构。通过设计有效的文件存储、访问和更新功能,克服传统Erasure Code冗余文件存储方案的不足,使存储文件具有一定的数据修改能力和结构伸缩能力。理论分析和实验仿真验证了设计方案在P2P存储系统中的可行性和有效性。

SegEra:一种Erasure Code与分割相结合的P2P存储结构

基于Erasure Code编码冗余存储技术,结合传统的文件分割存储思想,提出称为SegEra的Erasure Code与分割相结合的P2P存储结构.研究了SegEra的文件构成方式和存储结构特性,讨论其所适合的索引化离散数据存储分布架构;然后,从理论上研究了SegEra的P2P存储节点选择的优化方案,并针对P2P存储环境特点设计了与之相适应的简化算法;并通过仿真实验表明SegEra采用简化节点选择算法能够有效的提高存储文件的可用性水平.

一种基于Erasure码的数据安全体制研究

在利用可信计算技术的基础上,结合分布式门限存储思想,提出一种容灾系统的安全增强体制。该体制采用基于Erasure码的分布式门限存储的安全增强技术,不仅能解决海量数据的存储问题,而且可以较好地防止单点失效、减轻在容灾过程中网络负载以及解决联合欺骗等安全问题,通过应用这些安全增强技术,可以为容灾系统中的海量数据提供全面的安全保护。

基于Erasure Code的分布式文件存储系统

在局域网环境下,实现一种基于Erasure Code的分布式文件存储系统。该系统由元数据服务器和多个文件存储节点组成,通过对元数据与文件数据分离存储以提高文件访问效率,将Erasure Code有效冗余存储技术应用于文件编解码以增强可靠性,采用MD5消息摘要技术保证文件完整性。对30 MB^600 MB大小的文件测试结果表明,该系统具有更高的可靠性、安全性以及资源利用率。

The Erasure of Signifiers and Refusal of Signification in Philip Larkin's Poem“High Window”

This paper tries to analyze Philip Larkin's poem"High Window"from a deconstructive perspective. It is to show that in the poem the key words/signifiers are always under erasure, and thus the chain of signification is endless since the poem is self-deconstructing. Then, the paper argues that the linguistic features of the poem paradoxically meaningful in the sense that it reflects the poet's skepticism and anxiety.

基于Erasure code的实时流媒体传输系统

传统的流媒体传输系统需要一定规模的服务器群和集中式的带宽,在丢包问题中大部分采用丢包重传,即带ACK回执和重传的数据报文。提出一种新的容忍丢包和边缘服务器的传输方式,基于Erasure code的可恢复性,实现容忍丢包的发送接收模型。采用边缘计算的思想,将集中式的服务器群分散到任意主机上,通过动态地获取服务端地址,将实时数据流分成多块,经由不连续的边缘服务器进行转发,以降低对边缘服务器的带宽要求。可以根据边缘服务器的服务能力的不同分配传输数据量,达到动态的负载均衡。同时该系统具备隐私保护的功能。实验结果表明,该系统即使在较高丢包率和较差的网络环境下,仍然可以保证较低延迟的正常使用。

Frame erasure concealment in wideband speech coding based on large hidden Markov model

Frame erasure concealment is studied to solve the problem of rapid speech quality reduction due to the loss of speech parameters during speech transmission. A large hidden Markov model is applied to model the immittance spectral frequency （ISF） parameters in AMR-WB codec to optimally estimate the lost ISFs based on the minimum mean square error （MMSE） rule. The estimated ISFs are weighted with the ones of their previous neighbors to smooth the speech, resulting in the actual concealed ISF vectors. They are used instead of the lost ISFs in the speech synthesis on the receiver. Comparison is made between the speech concealed by this algorithm and by Annex I of G. 722. 2 specification, and simulation shows that the proposed concealment algorithm can lead to better performance in terms of frequency-weighted spectral distortion and signal-to-noise ratio compared to the baseline method, with an increase of 2.41 dB in signal-to-noise ratio （SNR） and a reduction of 0. 885 dB in frequency-weighted spectral distortion.

Tree-Structured Parallel Regeneration for Multiple Data Losses in Distributed Storage Systems Based on Erasure Codes

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 distributed over a large area and have few intersections. 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 band-width 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 optimizations: firstly, transferring the data through the bandwidth optimized-paths in a pipe-line 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.

A Fault Detection Mechanism in Erasure-Code Byzantine Fault-Tolerance Quorum

Fault-tolerance is increasingly significant for large-scale storage systems in which Byzantine failure of storage nodes may happen. Traditional Byzantine Quorum systems that tolerate Byzantine failures by using replication have two main limitations： low space-efficiency and static quorum variables. We propose an Erasure-code Byzantine Fault-tolerance Quorum that can provide high reliability with far lower storage overhead than replication by adopting erasure code as redundancy scheme. Through read/write operations of clients and diagnose operation of supervisor, our Quorum system can detect Byzantine nodes, and dynamically adjust system size and fault threshold. Simulation results show that our method improves performance for the Quorum with relatively small quorums.

Research of Methods for Lost Data Reconstruction in Erasure Codes over Binary Fields

In the process of encoding and decoding,erasure codes over binary fields,which just need AND operations and XOR operations and therefore have a high computational efficiency,are widely used in various fields of information technology.A matrix decoding method is proposed in this paper.The method is a universal data reconstruction scheme for erasure codes over binary fields.Besides a pre-judgment that whether errors can be recovered,the method can rebuild sectors of loss data on a fault-tolerant storage system constructed by erasure codes for disk errors.Data reconstruction process of the new method has simple and clear steps,so it is beneficial for implementation of computer codes.And more,it can be applied to other non-binary fields easily,so it is expected that the method has an extensive application in the future.

GFCache: A Greedy Failure Cache Considering Failure Recency and Failure Frequency for an Erasure-Coded Storage System

In the big data era,data unavailability,either temporary or permanent,becomes a normal occurrence on a daily basis.Unlike the permanent data failure,which is fixed through a background job,temporarily unavailable data is recovered on-the-fly to serve the ongoing read request.However,those newly revived data is discarded after serving the request,due to the assumption that data experiencing temporary failures could come back alive later.Such disposal of failure data prevents the sharing of failure information among clients,and leads to many unnecessary data recovery processes,(e.g.caused by either recurring unavailability of a data or multiple data failures in one stripe),thereby straining system performance.To this end,this paper proposes GFCache to cache corrupted data for the dual purposes of failure information sharing and eliminating unnecessary data recovery processes.GFCache employs a greedy caching approach of opportunism to promote not only the failed data,but also sequential failure-likely data in the same stripe.Additionally,GFCache includes a FARC(Failure ARC)catch replacement algorithm,which features a balanced consideration of failure recency,frequency to accommodate data corruption with good hit ratio.The stored data in GFCache is able to support fast read of the normal data access.Furthermore,since GFCache is a generic failure cache,it can be used anywhere erasure coding is deployed with any specific coding schemes and parameters.Evaluations show that GFCache achieves good hit ratio with our sophisticated caching algorithm and manages to significantly boost system performance by reducing unnecessary data recoveries with vulnerable data in the cache.

Priority-Based Real-Time Stream Coding over Multi-Channel with Packet Erasures

Multi-channel can be used to provide higher transmission ability to the bandwidth-intensive and delay-sensitive real-time streams. However, traditional channel capacity theories and coding schemes are seldom designed for the real-time streams with strict delay constraint, especially in multi-channel context. This paper considers a real-time stream system, where real-time messages with different importance should be transmitted through several packet erasure channels, and be decoded by the receiver within a fixed delay. Based on window erasure channels and i.i.d.(identically and independently distributed) erasure channels, we derive the Multi-channel Real-time Stream Transmission(MRST) capacity models for Symmetric Real-time(SR) streams and Asymmetric Real-time(AR) streams respectively. Moreover, for window erasures, a Maximum Equilibrium Intra-session Code(MEIC) is presented for SR and AR streams, and is shown able to asymptotically achieve the theoretical MRST capacity. For i.i.d. erasures, we propose an Adaptive Maximum Equilibrium Intra-session Code(AMEIC), and then prove AMEIC can closely approach the MRST transmission capacity. Finally, the performances of the proposed codes are verified by simulations.

Dependency-aware unequal erasure protection codes

Classical unequal erasure protection schemes split data to be protected into classes which are encoded independently. The unequal protection scheme presented in this paper is based on an erasure code which encodes all the data together according to the existing dependencies. A simple algorithm generates dynamically the generator matrix of the erasure code according to the packets streams structure, i.e., the dependencies between the packets, and the rate of the code. This proposed erasure code was applied to a packetized MPEG4 stream transmitted over a packet erasure channel and compared with other classical protection schemes in terms of PSNR and MOS. It is shown that the proposed code allows keeping a high video quality-level in a larger packet loss rate range than the other protection schemes.

CLEC:Combination Locality Based Erasure Code for Permissioned Blockchain Storage

Building a new decentralized domain name system based on blockchain technology is helping to solve problems,such as load imbalance and over-dependence on the trust of the central node.However,in the existing blockchain storage system,the storage overhead is very high due to its fullreplication data storage mechanism.The total storage consumption for each block is up to O(n)with n nodes.Erasure code applied to blockchains can significantly reduce the storage overhead,but also greatly lower the read performance.In this study,we propose a novel coding scheme for blockchain storage,Combination Locality based Erasure Code for Permissioned blockchain storage(CLEC).CLEC uses erasure code,parity locality,and topology locality in blockchain storage,greatly reducing reading latency and repair time.In CLEC,the storage consumption per block can be reduced to O(1),and the repair penalty can also be lowered to O(1).Experiments in an open-source permissioned blockchain Tendermint show that CLEC has a maximum repair speed of 6 times and a read speed of nearly 1.7 times with storage overhead of only 1.17 times compared to the current work,a great improvement in reading performance and repair performance with slightly increased storage overhead via implementation.

OPPORTUNISTIC DECODING OF UNEQUAL ERASURE PROTECTED SCALABLE CODED SOURCE

In this paper,we propose an opportunistic decoding method to enhance the reconstruction of unequal erasure protected scalable coded source.This method explores some non-channel-decodable symbols of the received packets by opportunistically utilizing the structure information of joint source-channel coding scheme.As a result,a longer prefix of source coded stream may be obtained to enhance the reconstruction of scalable coded source.Experiment results indicate that opportunistic decoding at the receiver can improve the quality of the reconstructed source when channel decoding fails to recover all the source symbols.

A Hybrid ARQ System with Erasures Correction and Parity Retransmission

A modified type of Hybrid ARQ system with erasures correction and parity bits retransmission is considered. Performance of the system is analyzed under assumption that the forward channel suffers from Nakagami common fading and additive white Gaussian noise. A good agreement between theoretical results and simulation is achieved. The proposed ARQ protocol is compared with other known Hybrid ARQ algorithms. It demonstrates significantly higher throughput efficiency in a range of SNR.

On the Probability of Erasure for MIMO-OFDM

Detecting the presence of a valid signal is an important task of a telecommunication receiver.When the receiver is unable to detect the presence of a valid signal,due to noise and fading,it is referred to as an erasure.This work deals with the probability of erasure computation for orthogonal frequency division multiplexed(OFDM)signals used by multiple input multiple output(MIMO)systems.The theoretical results are validated by computer simulations.OFDM is widely used in present day wireless communication systems due to its ability to mitigate intersymbol interference(ISI)caused by frequency selective fading channels.MIMO systems offer the advantage of spatial multiplexing,resulting in increased bit-rate,which is the main requirement of the recent wireless standards like 5G and beyond.

DDUC:an erasure-coded system with decoupled data updating and coding

In distributed storage systems,replication and erasure code(EC)are common methods for data redundancy.Compared with replication,EC has better storage efficiency,but suffers higher overhead in update.Moreover,consistency and reliability problems caused by concurrent updates bring new challenges to applications of EC.Many works focus on optimizing the EC solution,including algorithm optimization,novel data update method,and so on,but lack the solutions for consistency and reliability problems.In this paper,we introduce a storage system that decouples data updating and EC encoding,namely,decoupled data updating and coding(DDUC),and propose a data placement policy that combines replication and parity blocks.For the(N,M)EC system,the data are placed as N groups of M+1 replicas,and redundant data blocks of the same stripe are placed in the parity nodes,so that the parity nodes can autonomously perform local EC encoding.Based on the above policy,a two-phase data update method is implemented in which data are updated in replica mode in phase 1,and the EC encoding is done independently by parity nodes in phase 2.This solves the problem of data reliability degradation caused by concurrent updates while ensuring high concurrency performance.It also uses persistent memory(PMem)hardware features of the byte addressing and eight-byte atomic write to implement a lightweight logging mechanism that improves performance while ensuring data consistency.Experimental results show that the concurrent access performance of the proposed storage system is 1.70–3.73 times that of the state-of-the-art storage system Ceph,and the latency is only 3.4%–5.9%that of Ceph.