An Optimal Stability Matching Algorithm for DAG Blockchain Based on Matching Theory

IOTA is a typical blockchain designed for IoT applications. The Markov chain monte carlo algorithm (MCMC) used in IOTA may lead to a large number of unverified blocks, which increases transaction delay to a certain extent. We propose a Stable matching algorithm (SMA) based on matching theory to stimulate nodes to verify blocks, thereby reducing the number of unverified blocks and the consensus delay. The structure of our IoT blockchain uses the Directed acyc1ic graph (DAG) to improve the transaction processing capability. The nodes in the network are abstracted as transaction issuers and transaction verifiers. A verification service scheduling system is used to assign transactions to the verifiers and achieve the optimal matching. We designed a trust evaluation mechanism which offers verifiers references and awards to check transactions. The simulation results show that SMA can significantly reduce the number of orphan blocks and improve the transaction throughput, which helps to improve the reliability of the IoT blockchain.     

Multi-level sharded blockchain system for edge computing

Blockchain technology is used in edge computing ( EC) systems to solve the security problems caused by single point of failure ( SPOF) due to data loss, task execution failure, or control by malicious nodes. However, the disadvantage of blockchain is high latency, which contradicts the strict latency requirements of EC services. The existing single-level sharded blockchain system ( SLSBS) cannot provide different quality of service for different tasks. To solve these problems, a multi-level sharded blockchain system ( MLSBS) based on genetic algorithm ( GA) is proposed. The shards are classified according to the delay of the service, and the parameters such as the shard size of different shards are different. Using the GA, the MLSBS obtains the optimal resource allocation strategy that achieves maximum security. Simulation results show that the proposed scheme outperforms SLSBS.     

面向车联网异构节点的区块链高效一致性共识算法研究

车联网异构节点由于其性能差异大、具有移动性等原因会造成区块链共识算法交易吞吐率低、交易时延较大等问题,该文提出面向车联网异构节点的区块链高效一致性共识算法(ECCA).首先,在ECCA中,考虑由验证节点、一般节点和恶意节点组成的车联网异构节点,提出一种信用等级机制,实现信用等级划分和3类异构节点的划分.其次,提出一种跨...     

FastFabric: Scaling hyperledger fabric to 20 000 transactions per second

Blockchain technologies are expected to make a significant impact on a variety of industries. However, one issue holding them back is their limited transaction throughput, especially compared to established solutions such as distributed database systems. In this paper, we rearchitect a modern permissioned blockchain system, Hyperledger Fabric, to increase transaction throughput from 3000 to 20 000 transactions per second. We focus on performance bottlenecks beyond the consensus mechanism, and we propose architectural changes that reduce computation and I/O overhead during transaction ordering and validation to greatly improve throughput. Notably, our optimizations are fully plug‐and‐play and do not require any interface changes to Hyperledger Fabric.     

An efficient channel assignment algorithm for multicast wireless mesh networks

Multicast can enhance the performance of wireless mesh networks (WMNs) effectively, which has attracted great attentions in recent years. However, multicast communication in WMNs requires efficient channel assignment strategy to reduce the total network interference and maximize the network throughput. In this paper, the concept of local multicast is proposed to measure interference and solve hidden channel problem in multicast communication. Basing on the concept, we propose a channel assignment algorithm considering the interference of local multicast and forwarding weight of each node (LMFW). The algorithm fully considers partially overlapped channels and orthogonal channels to improve the network performance. Simulations show that the proposed algorithm can reduce interference and improve network capacity of WMNs.     

一种基于信誉值拍卖的区块链下的感知收益分配机制

实现频谱共享,需要以实时准确地掌握主用户的频谱占用情况以及频谱交易信息为前提.为此,在利用群智感知以及区块链的前提下,提出了三层式的基于区块链的认知无线电系统,即物理层、传输层以及应用层.其中区块链网络位于传输层,用以记录交易信息,并利用区块链的去中心化以及去信任化特性以保证交易的安全性与可靠性.特别地,为了激励系统中...     

Robust throughput and routing for mobile ad hoc wireless networks

Flows transported across mobile ad hoc wireless networks suffer from route breakups caused by nodal mobility. In a network that aims to support critical interactive real-time data transactions, to provide for the uninterrupted execution of a transaction, or for the rapid transport of a high value file, it is essential to identify robust routes across which such transactions are transported. Noting that route failures can induce long re-routing delays that may be highly interruptive for many applications and message/stream transactions, it is beneficial to configure the routing scheme to send a flow across a route whose lifetime is longer, with sufficiently high probability, than the estimated duration of the activity that it is selected to carry. We evaluate the ability of a mobile ad hoc wireless network to distribute flows across robust routes by introducing the robust throughput measure as a performance metric. The utility gained by the delivery of flow messages is based on the level of interruption experienced by the underlying transaction. As a special case, for certain applications only transactions that are completed without being prematurely interrupted may convey data to their intended users that is of acceptable utility. We describe the mathematical calculation of a network’s robust throughput measure, as well as its robust throughput capacity. We introduce the robust flow admission and routing algorithm (RFAR) to provide for the timely and robust transport of flow transactions across mobile ad hoc wireless network systems.     

Efficient allocation of LTE downlink spectral resource to improve fairness and throughput

For the current generation of cellular communication systems, long‐term evolution (LTE) has been the major protocol to support high‐speed data transmission. It is critical to allocate downlink spectral resource in LTE, namely, resource blocks (RBs), but the issue is not well addressed in the standard. Therefore, the paper develops an efficient RB allocation algorithm with 4 mechanisms to improve both fairness and throughput in LTE. For fairness concern, our RB allocation algorithm uses a resource‐reservation mechanism to prevent cell‐edge user equipments from starvation, and a credit‐driven mechanism to keep track of the amount of resource given to each user equipment. For throughput concern, it adopts both weight‐assignment and RB‐matching mechanisms to allocate each RB to a packet according to its flow type and length. Through simulations, we demonstrate that the proposed RB allocation algorithm can significantly increase both throughput and fairness while reducing packet dropping and delays of real‐time flows, as compared with previous methods.     

Imp Raft: a consensus algorithm based on Raft and storage compression consensus for IoT scenario

In order to meet various challenges in the Internet of things (IoT), such as identity authentication, privacy preservation of distributed data and network security, the integration of blockchain and IoT became a new trend in recent years. As the key supporting technology of blockchain, the consensus algorithm is a hotspot of distributed system research. At present, the research direction of the consensus algorithm is mainly focused on improving throughput and reducing delay. However, when blockchain is applied to IoT scenario, the storage capacity of lightweight IoT devices is limited, and the normal operations of blockchain system cannot be guaranteed. To solve this problem, an improved version of Raft (Imp Raft) based on Raft and the storage compression consensus (SCC) algorithm is proposed, where initialization process and compression process are added into the flow of Raft. Moreover, the data validation process aims to ensure that blockchain data cannot be tampered with. It is obtained from experiments and analysis that the new proposed algorithm can effectively reduce the size of the blockchain and the storage burden of lightweight IoT devices.     

SCMA mMTC系统中基于联盟区块链的无线电资源交易的信用支付

无线电资源交易发生在MTC网关（MTC Gateway MTCG）和LTE用户之间.根据基于联盟区块链的空闲无线电资源交易来建立MTCG之间的信用度.在多个授权的本地基站（Base Station BS）上建立了一个联盟区块链,用于公开审计和共享交易记录.资源交易记录在加密后上传到BS.在交易记录通过审查和共识过程之后,新区块被存储在BS上,并且可以由MTCG,LTE用户和连接到联盟区块链的BS进行公开访问.为了最大化系统的利益,支持频繁的资源交易,提出了一种基于信用贷款的支付方案,并给出了相应的最优定价策略.     

Determining the Order of Processor Transactions in Statically Scheduled Multiprocessors

This paper addresses embedded multiprocessor implementation of iterative, real-time applications, such as digital signal and image processing, that are specified as dataflow graphs. Scheduling dataflow graphs on multiple processors involves assigning tasks to processors (processor assignment), ordering the execution of tasks within each processor (task ordering), and determining when each task must commence execution. We consider three scheduling strategies: fully-static, self-timed and ordered transactions, all of which perform the assignment and ordering steps at compile time. Run time costs are small for the fully-static strategy; however it is not robust with respect to changes or uncertainty in task execution times. The self-timed approach is tolerant of variations in task execution times, but pays the penalty of high run time costs, because processors need to explicitly synchronize whenever they communicate. The ordered transactions approach lies between the fully-static and self-timed strategies; in this approach the order in which processors communicate is determined at compile time and enforced at run time. The ordered transactions strategy retains some of the flexibility of self-timed schedules and at the same time has lower run time costs than the self-timed approach.In this paper we determine an order of processor transactions that is nearly optimal given information about task execution times at compile time, and for a given processor assignment and task ordering. The criterion for optimality is the average throughput achieved by the schedule. Our main result is that it is possible to choose a transaction order such that the resulting ordered transactions schedule incurs no performance penalty compared to the more flexible self-timed strategy, even when the higher run time costs implied by the self-timed strategy are ignored.     

多用户分布式MIMO-OFDM系统中天线与子载波分配算法研究

本文针对多用户分布式MIMO-OFDM系统中的资源联合分配问题,提出了一种基于端口选择的天线与子载波分配算法。该算法依据计算复杂度容限设定用户通信静态端口数,以此为每个用户选取信道状况最好的通信端口进行通信,进而通过天线端口与下属用户的相互配合,并行地完成天线与子载波的分配。仿真结果表明,该算法在系统天线数大于用户数的情况下容量性能优于MASA算法,且其端口并行处理机制可以有效提高资源分配效率。     

Contention-conscious transaction ordering in multiprocessor DSP systems

This paper explores the problem of efficiently ordering interprocessor communication (IPC) operations in statically scheduled multiprocessors for iterative dataflow graphs. In most digital signal processing (DSP) applications, the throughput of the system is significantly affected by communication costs. By explicitly modeling these costs within an effective graph-theoretic analysis framework, we show that ordered transaction schedules can significantly outperform self-timed schedules even when synchronization costs are low. However, we also show that when communication latencies are nonnegligible, finding an optimal transaction order given a static schedule is an NP-complete problem, and that this intractability holds both under iterative and noniterative execution. We develop new heuristics for finding efficient transaction orders, and perform an extensive experimental comparison to gauge the performance of these heuristics.     

Multi-input address incremental clustering for the Bitcoin blockchain based on Petri net model analysis

Bitcoin is a cryptocurrency based on blockchain. All historical Bitcoin transactions are stored in the Bitcoin blockchain, but Bitcoin owners are generally unknown. This is the reason for Bitcoin's pseudo-anonymity, therefore it is often used for illegal transactions. Bitcoin addresses are related to Bitcoin users' identities. Some Bitcoin addresses have the potential to be analyzed due to the behavior patterns of Bitcoin transactions. However, existing Bitcoin analysis methods do not consider the fusion of new blocks' data, resulting in low efficiency of Bitcoin address analysis. In order to address this problem, this paper proposes an incremental Bitcoin address cluster method to avoid re-clustering when new block data is added. Besides, a heuristic Bitcoin address clustering algorithm is developed to improve clustering accuracy for the Bitcoin Blockchain. Experimental results show that the proposed method increases Bitcoin address cluster efficiency and accuracy.     

多射频无线mesh网中的联合协作路由与信道分配算法

现有的协作路由算法没有考虑多射频无线mesh网中的信道分配问题.为了给多并发业务流提供更优质的网络服务,本文结合多射频多信道技术和协作通信技术来降低同信道干扰并获得协作分集增益.基于协作通信模块虚拟化的方法,本文将联合协作路由和信道分配问题简化为联合直接路由和信道分配问题,将其建模为一个混合整数线性规划问题,并证明该问题为NP-hard问题.为了解决该问题,提出了一种宽松的联合协作路由选择和信道分配算法(Loose Joint Cooperative Routing and Channel Assignment algorithm,L-JCRCA).仿真实验结果表明,L-JCRCA可以有效提升网络整体吞吐量.     

Fog-Sec: Secure end-to-end communication in fog-enabled IoT network using permissioned blockchain system

The technological integration of the Internet of Things (IoT)-Cloud paradigm has enabled intelligent linkages of things, data, processes, and people for efficient decision making without human intervention. However, it poses various challenges for IoT networks that cannot handle large amounts of operation technology (OT) data due to physical storage shortages, excessive latency, higher transfer costs, a lack of context awareness, impractical resiliency, and so on. As a result, the fog network emerged as a new computing model for providing computing capacity closer to IoT edge devices. The IoT-Fog-Cloud network, on the other hand, is more vulnerable to multiple security flaws, such as missing key management problems, inappropriate access control, inadequate software update mechanism, insecure configuration files and default passwords, missing communication security, and secure key exchange algorithms over unsecured channels. Therefore, these networks cannot make good security decisions, which are significantly easier to hack than to defend the fog-enabled IoT environment. This paper proposes the cooperative flow for securing edge devices in fog-enabled IoT networks using a permissioned blockchain system (pBCS). The proposed fog-enabled IoT network provides efficient security solutions for key management issues, communication security, and secure key exchange mechanism using a blockchain system. To secure the fog-based IoT network, we proposed a mechanism for identification and authentication among fog, gateway, and edge nodes that should register with the blockchain network. The fog nodes maintain the blockchain system and hold a shared smart contract for validating edge devices. The participating fog nodes serve as validators and maintain a distributed ledger/blockchain to authenticate and validate the request of the edge nodes. The network services can only be accessed by nodes that have been authenticated against the blockchain system. We implemented the proposed pBCS network using the private Ethereum 2.0 that enables secure device-to-device communication and demonstrated performance metrics such as throughput, transaction delay, block creation response time, communication, and computation overhead using state-of-the-art techniques. Finally, we conducted a security analysis of the communication network to protect the IoT edge devices from unauthorized malicious nodes without data loss.     

Joint Channel Assignment and Routing for Throughput Optimization in Multiradio Wireless Mesh Networks

Multihop infrastructure wireless mesh networks offer increased reliability, coverage, and reduced equipment costs over their single-hop counterpart, wireless local area networks. Equipping wireless routers with multiple radios further improves the capacity by transmitting over multiple radios simultaneously using orthogonal channels. Efficient channel assignment and routing is essential for throughput optimization of mesh clients. Efficient channel assignment schemes can greatly relieve the interference effect of close-by transmissions; effective routing schemes can alleviate potential congestion on any gateways to the Internet, thereby improving per-client throughput. Unlike previous heuristic approaches, we mathematically formulate the joint channel assignment and routing problem, taking into account the interference constraints, the number of channels in the network, and the number of radios available at each mesh router. We then use this formulation to develop a solution for our problem that optimizes the overall network throughput subject to fairness constraints on allocation of scarce wireless capacity among mobile clients. We show that the performance of our algorithms is within a constant factor of that of any optimal algorithm for the joint channel assignment and routing problem. Our evaluation demonstrates that our algorithm can effectively exploit the increased number of channels and radios, and it performs much better than the theoretical worst case bounds     

基于Fisco-Bcos平台的区块链系统性能精确分析模型

为了解决区块链系统实际部署面临的性能难以估计、所需的硬件设施性能难以确定等问题，建立了不同网络结构下基于模型和数据融合的区块链网络吞吐量精确表达模型。通过分析实用拜占庭容错（practical Byzantine fault tolerance,PBFT）算法区块链系统的交易流程，综合考虑网络拓扑结构、采用的共识算法、节点的通信方式等状况，基于大量实际数据建立了Fisco-Bcos区块链平台的交易吞吐量（transaction per second,TPS）精确表达模型。实际的区块链系统测试结果表明，本文建立的TPS预测模型可以在不同的网络结构下保持较高的预测精确度。     

信息优先级保护的动态频谱分配算法

为提高海上无人艇编队无线网络频谱利用率,同时满足不同优先级信息的传输需求,提出了一种信息优先级保护的动态频谱分配算法。算法采用完全信息动态博弈模型,引入异步分布式定价（Asynchronous Distributed Pricing,ADP）算法设计效用函数。鉴于传统ADP算法在有较多通信余量时干扰价格定价过高,改进干扰价格定义。为体现优先级对分配的影响,在效用函数中加入信息权重。对效用函数成本部分进一步更改,可在实现高优先级信息优先传输的同时,依据通信速率需求合理分配信道通信容量。经过仿真验证,所提算法在吞吐量和可靠性方面优于基于节点优先级的分配算法。     

Theoretical aspects in the analysis and synthesis of packet communication networks

With the intention of outlining some of the theoretical studies on the design of packet communication networks the present paper introduces the models and the basic relations underlying the analysis as well as the method for evaluating packet delay. Then the multicommodity flow problem as applied to the route assignment is described with particular reference to static and quasi-static routing schemes. Following this topological design methods are described in terms of capacity assignment, flow assignment, capacity and flow assignment, and topology, capacity and flow assignment. Theoritical studies on such factors as flow control and error control that affect the network throughput are also outlined together with the theoretical aspects on packet radio, satellite, and radio systems.