On Partial Downloading for Wireless Distributed Storage Networks

Characterizing the exact repair storage-vs-repair bandwidth tradeoff for distributed storage systems remains an open problem for more than four storage nodes. Motivated by the prevalence and practical applicability of linear codes, the exact repair problem when restricted to linear codes is considered. The main result of this paper is a new approach to develop bounds for exact repair distributed storage systems with linear codes (LDSS). Using this approach, the exact repair region for the (k + 1, k, k) LDSS is completely characterized. The new approach utilizes the properties of linear codes together with the exact repair constraints. These constraints are formally captured through an optimization problem with a recursive structure, and its solution finally yields the new bounds for the LDSS. These bounds together with recent code constructions characterize the exact repair region for (k + 1, k, k) LDSS.

We propose to construct a joint channel-network coding (knosswn as Random Linear Coding) scheme based on improved turbo codes for the distributed storage in wireless communication network with k data nodes, s storage nodes (k<s) and a data collector. This framework extends the classical distributed storage with erasure channel to AWGN and fading channel scenario. We investigate the throughput performance of the Joint Channel-Network Coding (JCNC) system benefits from network coding, compared with that of system without network coding based only on store and forward (S-F) approach. Another helpful parameter: node degree (L) indicates how many storage nodes one data packet should fall onto. L characterizes the en/decoding complexity of the system. Moreover, this proposed framework can be extended to ad-hoc and sensor network easily.

Storage allocation, meaning the way that a chunk of data is stored over a set of storage nodes, affects different performance measures of a distributed storage system (DSS). In this work, we study the storage allocation problem for a DSS where nodes have different storage capacities. To this end, we first introduce the notion of k-guaranteed allocations referring to allocations where the data can be recovered by accessing any arbitrary set of k storage nodes. We then find the necessary conditions for an allocation to be k-guaranteed considering the limit on the individual node capacities and the overall storage budget. Using these conditions, an iterative algorithm is developed to find k-guaranteed allocations, if feasible.

This paper presents a novel downlink resource allocation scheme for OFDMA-based next generation wireless networks subject to inter-cell interference (ICI). The scheme consists of radio resource and power allocations, which are implemented separately. Low-complexity heuristic algorithms are first proposed to achieve the radio resource allocation, where graph-based framework and fine physical resource block (PRB) assignment are performed to mitigate major ICI and hence improve the network performance. Given the solution of radio resource allocation, a novel distributed power allocation is then performed to optimize the performance of cell-edge users under the condition that desirable performance for cell-center users must be maintained. The power optimization is formulated as an iterative barrier-constrained water-filling problem and solved by using the Lagrange method. Simulation results indicate that our proposed scheme can achieve significantly balanced performance improvement between cell-edge and cell-center users in multi-cell networks compared with other schemes, and therefore realize the goal of future wireless networks in terms of providing high performance to anyone from anywhere.

We had proposed a distributed storage system which relocates data blocks autonomously among the storage nodes. Generally, owing to requirement of exchanging the management information frequently, such autonomous block migration tends to increase network traffic. Our previous work has presented a scheme to reduce network traffic by appending the management information onto an iSCSI short packet. In this paper, we present a scheme to propagate the management information by utilizing internode communications more aggressively. Our scheme utilizes iSCSI read/write packets which are exchanged more frequently to transmit the management information, and appends also the management information which is collected from the other nodes. This indirect propagation helps to reduce broadcast packets on the network. We have investigated the traffic behavior in the iSCSI environment, and show that our scheme can effectively reduce extra Ethernet frames for exchanging the management information.

We have proposed a distributed storage system which aims to utilize storage fragments distributed in network nodes without administrators' maintenance cost. Even the performance of storage devices are not uniform, autonomously data block migration helps to achieve enhancing the whole I/O performance of the storage system. However, we have considered all the storage devices to be reliable equally. On this assumption, migration of an important data block to unstable storage might cause degradation of the availability of the data block. In this paper, we propose a scheme to choose the destination of data block migration by evaluating the nodes' reliability along with the performance of storage devices. This scheme aims to improve system stability by preventing to locate a critical data onto an unstable storage device. The storage nodes which lack stability are also utilized for storing a data block which can be easily regenerated or duplicated. The results of the preliminary investigation show that a large number of warning logs from Machine Check Architecture may suggest a sign of unexpected system shutdown.

Recently, a graph-theoretic model for a single-failure-recoverable distributed storage system was proposed. Unlike the usual local recovery model of codes for distributed storage, this model accounts for the fact that each server or storage node in a network is connectible to only some, and not all other, nodes. Here we provide bounds and constructive schemes for data storage in such networks. We also impose an additional requirement on the codes for such model — a minimum distance guarantee. The model is further generalized for multiple node failures and cooperative repairs.

In this paper, we study the problem of distributed multi-user secret sharing, including a trusted master node, $N\in \mathbb{N}$ storage nodes, and $K$ users, where each user has access to the contents of a subset of storage nodes. Each user has an independent secret message with certain rate, defined as the size of the message normalized by the size of a storage node. Having access to the secret messages, the trusted master node places encoded shares in the storage nodes, such that (i) each user can recover its own message from the content of the storage nodes that it has access to, (ii) each user cannot gain any information about the message of any other user. We characterize the capacity region of the distributed multi-user secret sharing, defined as the set of all achievable rate tuples, subject to the correctness and privacy constraints. In the achievable scheme, for each user, the master node forms a polynomial with the degree equal to the number of its accessible storage nodes minus one, where the value of this polynomial at certain points are stored as the encoded shares. The message of that user is embedded in some of the coefficients of the polynomial. The remaining coefficients are determined such that the content of each storage node serves as the encoded shares for all users that have access to that storage node.

Radio resource allocation is always a central and complex computational task in state-of-the-art wireless networks. Computationally efficient implementation of radio resource allocation is certainly desirable in wireless networks, and can be generalized to many resource allocation/management problems in C4ISR systems. Quantum optimization, an emerging quantum computation technology, suggests a new avenue toward (radio) resource allocation particularly potential to reduce computing latency in systems. Quantum approximation optimization algorithm (QAOA) was recently shown to possibly achieve resource allocation (RRA) in limited scope, while the generalization of QAOA for RRA remains an active research subject. Considering OFDMA resource allocation, this paper extends QAOA to multiple radio blocks by quantum state preparation, and takes the interference between adjacent radio resource units into account by introducing the conflict graphs to formulate quantum optimization. Computational experiments successfully verify proposed quantum optimization to RRA.

Big data becomes the key for ubiquitous computing and intelligence, and Distributed Storage Systems (DSS) are widely used in large-scale data centers or in the cloud for efficient data management. However, the data on stored are likely to be unavailable due to hardware failures and cyberattacks, e.g. DDoS. Maximum Distance Separable (MDS) codes are commonly used for the recovery of faulty storage nodes or unavailable data. However, the recovery of data nodes usually involves access to multiple nodes, which introduces significant communication overheads to the DSS. In this paper, a new DSS based on the Redundant Residue Number System (RRNS) is proposed, where efficient recovery is enabled by applying the second version of Chinese Remainder Theorem (CRT-II). The complexity and network traffic of the proposed data protection scheme is analyzed theoretically and compared with that of traditional MDS based DSSs. Experimental results show that the proposed DSS achieves lower encoding complexity, lower recovery complexity and lower network traffic than the MDS based schemes. Although the proposed data protection scheme introduces computation overheads for the case on which there are no failing nodes, its complexity is still lower for scenarios with frequent data updates. In addition, the proposed scheme introduces additional advantages in terms of security and storage flexibility.

It is significant to repair (or rebuilt) the damaged storage node in the distributed storage system (DSS). Recently, the network coding technique is applied to DSS to decrease the repair bandwidth. In practice, in addition to repair bandwidth, repair time is usually one of the key concerns in the DSS, which has not been investigated in the existing DSSs in which network coding is applied. In this paper, we propose the minimum-time repair (MTR) scheme, which is able to achieve the lower bound of repair time while considerably decreasing repair bandwidth. Numerical results show that MTR outperforms some available node recovery approaches in terms of repair time.

Technological advances and rapid development of handheld wireless terminals have facilitated the rapid growth of wireless communications and mobile computing. Essentially we have a limited resource transmission spectrum, which must be shared by several users. Since the available frequency spectrum is limited the channels must be reused as much as possible in order to increase the system capacity. This requires a proper channel allocation scheme. The role of a channel allocation scheme is to allocate channels to cells or mobiles in such a way as to minimize call blocking or call dropping probabilities. The process of channel allocation must satisfy the electromagnetic compatibility constraints known as hard constraints and the demand of channels in a cell for new calls as well as existing calls. The proposed scheme presents new Hybrid Channel Allocation (HCA) scheme that allocate a channel to an incoming call from pool of available channel such as basic constraints are satisfied. The proposed scheme presents an efficient Integer Linear Program (ILP) formulation that helps to allocate channel to a new call. This formulation does not allow channel reassignment of existing calls. We have simulated the formulation on a standard ideal network model of 70 channels and 49 cells. We have done our experiments using MATLAB 7.9.0 R2009b.

Distributed storage systems have been receiving increasing attention lately due to the developments in cloud and grid computing. Furthermore, a major part of the stored information comprises of multimedia, whose content can be communicated even with a lossy (non-perfect) reconstruction. In this context, Multiple Description Lattice Quantizers (MDLQ) can be employed to encode such sources for distributed storage and store them across distributed nodes. Their inherent properties yield that having access to all nodes gives perfect reconstruction of the source, while the reconstruction quality decreases gracefully with fewer available nodes. If a set of nodes fails, lossy repair techniques could be applied to reconstruct the failed nodes from the available ones. This problem has mostly been studied with the lossless (perfect) reconstruction assumption. In this work, a general model, Multiple Description Lattice Quantizer with Repairs (MDLQR), is introduced that encompasses the lossy repair problem for distributed storage applications. New performance measures and repair techniques are introduced for MDLQR, and a non-trivial identity is derived, which is related to other results in the literature. This enables us to find the optimal encoder for a certain repair technique used in the MDLQR. Furthermore, simulation results are used to evaluate the performance of the different repair techniques.

We address the problem of securing distributed storage systems against passive eavesdroppers that can observe a limited number of storage nodes. An important aspect of these systems is node failures over time, which demand a repair mechanism aimed at maintaining a targeted high level of system reliability. If an eavesdropper observes a node that is added to the system to replace a failed node, it will have access to all the data downloaded during repair, which can potentially compromise the entire information in the system. We are interested in determining the secrecy capacity of distributed storage systems under repair dynamics, i.e., the maximum amount of data that can be securely stored and made available to a legitimate user without revealing any information to any eavesdropper. We derive a general upper bound on the secrecy capacity and show that this bound is tight for the bandwidth-limited regime which is of importance in scenarios such as peer-to-peer distributed storage systems. We also provide a simple explicit code construction that achieves the capacity for this regime.

SUMMARYCo‐channel interference seriously influences the throughput of a wireless mesh network. This study proposes an end‐to‐end channel allocation scheme (EECAS) that extends the radio‐frequency‐slot method to minimize co‐channel interference. The EECAS first separates the transmission and reception of packets into two channels. This scheme can then classify the state of each radio‐frequency‐slot as transmitting, receiving, interfered, free, or parity. A node that initiates a communication session with a quality of service requirement can propagate a channel allocation request along the communication path to the destination. By checking the channel state, the EECAS can determine feasible radio‐frequency‐slot allocations for the end‐to‐end path. The simulation results in this study demonstrate that the proposed approach performs well in intra‐mesh and inter‐mesh communications, and it outperforms previous channel allocation schemes in end‐to‐end throughput. Copyright © 2013 John Wiley &amp; Sons, Ltd.