基于TDMA的工业无线网时间同步算法改进与实现

基于TDMA机制的MAC层接入协议在工业控制网络的实时性保证方面具有极大的优势.然而要保证该机制微秒级的时隙调度,网络中所有的节点必须保持时间同步的高精度.针对现有的一些同步算法并不能完全满足这种高精度时间同步要求的问题,在传统的时间同步算法基础上,添加时钟漂移预测与补偿机制,改进得到一种具有同步精度高、能量消耗低等优点的同步算法——ITR(Improved Wireless Sensor Networks Time Synchronization Algorithm Based OnTPSN andRBS),并在RouterBOARD493G路由节点上进行实验测试.实验结果表明ITR同步算法的平均同步误差比传统同步算法降低了约52％.     

DTMB标准LDPC码译码算法研究

本文主要研究了DTMB标准的LDPC码译码算法,并对LDPC译码算法中不同消息传递机制及其不同核心运算单元（校验节点更新）算法进行了组合仿真。仿真结果表明基于串行消息传递机制的改进型最小和算法在降低了译码复杂度的同时,它在BER=3e-6处译码性能比基于溢出消息传递机制的BP算法劣化不到0．1dB,而译码的平均迭代次数要减少50％以上,是一种能较好兼顾性能与实现复杂度的译码方法。     

LDPC码串行解码算法建模

消息传递机制是影响LDPC码解码性能的重要因素。简要介绍了Gallager提出的LDPC码和基于洪水消息传递机制的和积解码算法。在此基础上引入基于校验节点的串行消息传递机制并提出具体可实现的解码算法模型。该串行解码算法按照校验节点一定的顺序进行消息处理和传递,保证更新的消息能够马上进入迭代过程,从而改善消息传递的收敛特性;同时充分利用消息间相互关联的特点,融合消息传递步骤,可以降低所需的存储容量,简化解码复杂度。分别应用洪水解码算法和串行解码算法在AWGN信道下进行性能仿真。仿真结果表明串行解码算法使解码性能得到明显提高。     

分簇型无线传感器网络时间同步机制的研究

提出了一种基于分簇型网络结构的时间同步算法。算法的主要思想是通过在簇建立阶段利用LEACH优化算法优化网络拓扑结构,降低网络的跳数,从而降低了时间同步精度由于跳数增加而导致的误差积累,为时间同步算法提供一个良好的网络结构。在LEACH优化算法中,簇首选取机制融入簇首节点的剩余能量和密度因子,并且提出了助理簇首节点用以均衡簇首节点的能量消耗。同时在时间同步阶段,采用双向时间同步机制和单向广播时间机制。实验仿真证明,提出的时间同步算法降低了网路的跳数,提高了时间同步精度,降低了节点的能量消耗,提高了网路的运行时间,具有一定的实用价值。     

分簇式无线传感器网络睡眠调度机制研究

提出了一个容忍节点失效和时间同步误差的簇内睡眠调度算法JCSS(Intra-Cluster Sleeping scheduling),该算法不需要外部的精确时间同步机制,对不同类型的节点采用不同的调度机制,在对时间同步的估计中考虑了误差和更新.仿真实验显示在密集部署的网络环境中,该睡眠调度算法在满足网络传输性能的情况下,相对于无同步的固定时间间隔调度和有同步的固定时间间隔调度,网络生存周期分别提高了16.7%和10.5%.     

基于TDMA机制的工业无线网时间同步算法的改进与实现

基于TDMA机制的MAC层接入协议在工业控制网络的实时性保证方面具有极大的优势。然而要保证该机制微秒级的时隙调度,网络中所有的节点必须保持时间同步的高精度。针对现有的一些同步算法并不能完全满足这种高精度时间同步要求的问题,在传统的时间同步算法基础上,添加时钟漂移预测与补偿机制,改进得到一种具有同步精度高、能量消耗低等优点的同步算法--ITR(Improved Wireless Sensor Networks Time Synchronization Algorithm Based On TPSN and RBS),并在RouterBOARD493G路由节点上进行实验测试。实验结果表明ITR同步算法的平均同步误差比传统同步算法降低了约52%。     

时间触发总线时钟同步技术研究

时间触发协议(TTP)总线,或称时间触发总线,是一种用于安全关键实时控制系统的总线,采用基于全局时间基的时间触发通信机制。针对时钟同步高精度、容错的要求,研究了时间触发总线时钟同步算法,在OMNe T++仿真环境下建立了节点机模型和时钟同步算法模型,构建了时间触发总线系统模型,对时钟同步算法进行仿真,验证了同步算法。在同步周期足够的情况下,可以达到1μs以内的同步精度。     

一种基于交错行列消息传递的LDPC码改进译码算法

为进一步改善低密度奇偶校验(LDPC)码译码算法的纠错性能,并加快其译码的收敛速度,提出一种基于交错行列消息传递的改进译码算法.该算法通过将动态调度策略译码算法中的残差值思想引入到串行调度译码算法中,使得串行调度译码算法在每次迭代进行消息更新前都会进行一次残差值排序的计算,并对其节点消息原有的固定更新顺序进行重新排序.仿真结果表明:在误码率为10-4时,该改进的译码算法相比于行消息传递算法和列消息传递算法有0.25和0.24 dB的增益;在误码率为10-5时,相比于交错行列消息传递算法有0.13 dB的增益.     

分布式声探测无线网络时间同步算法研究

分布式声探测无线网络是一种基于声达时间差(TDOA)进行目标定位的无线传感器网络;而基于TDOA算法的分布式定位需要节点之间严格时间同步,本文正是对节点之间严格时间同步进行了重点研究.文中系统分析了分布式声探测无线网络的应用环境、工作机制和硬件平台,在此基础上提出节点之间的采样同步和全网同步问题,并基于后同步思想和分级同步机制,设计了分布式声探测无线网络节点同步的整体解决方案.该方案已经进行了组网测试,有效解决了分布式身探测的时间同步问题.本文对相关工程实践具有一定的指导意义.     

基于重加权近似消息传递算法的稀疏信道估计

基于近似消息传递(AMP)算法,提出了一种重加权近似消息传递(Rw AMP)算法用于稀疏信道估计,该算法增加了重加权过程与衰减机制。在信号重构时加入权重更新过程,待重构信号中较大的元素几乎不变,较小元素迅速降低为零,从而提高正确重构概率。其次,当稀疏信道估计的观测矩阵为Toeplitz矩阵时,为了提高AMP类算法收敛性,文中加入衰减机制。仿真结果表明,在相同复杂度的条件下,Rw AMP算法的信号重构性能优于基追踪(BP)算法和AMP算法。     

一种基于松弛循环差集的高性能分布式互斥算法

基于竞争的分布式互斥算法以请求集为基础.对称的请求集才能产生对称、公平的分布式互斥算法.本文首先证明了循环请求集与松弛循环差集具有等价性,并在此基础上提出了一种基于松弛循环差集的对称请求集生成算法.在提出动态令牌和请求集重构概念的基础上,本文将Maekawa类分布式互斥的同步时间降为T,节点容错能力达到N-1,一次临界区执行所需交换的消息数降为2m-3m,m是请求集大小.     

Accelerometer-based fall detection using optimized ZigBee data streaming

Wireless body-area sensor networks (WBSNs) are key components of e-health solutions. Wearable wireless sensors can monitor and collect many different physiological parameters accurately, economically and efficiently. In this work we focus on WBSN for fall detection applications, where the real-time nature of I/O data streams is of critical importance. Additionally, this generation of alarms promises to maximize system life. Throughput and energy efficiency of the communication protocol must also be carefully optimized. In this article we investigate ZigBee’s ability to meet WBSN requirements, with higher communication efficiency and lower power consumption than a Bluetooth serial port profile (SPP) based solution. As a case study we implemented an accelerometer-based fall detection algorithm, able to detect eight different fall typologies by means of a single sensor worn on the subjects’ waist. This algorithm has a low computational complexity and can be processed on an embedded platform. Fall simulations were performed by three voluntary subjects. Preliminary results are promising and show excellent values for both sensitivity and specificity. This case study showed how a ZigBee-based network can be used for high throughput WBSN scenarios.     

STS_4e: Secure Time Synchronization in IEEE802.15.4e Networks

IEEE802.15.4e networks adopt time-synchronized medium access control protocols which enables highly reliable and ultra-low power industrial wireless networks. In these networks, nodes use timeslot to communicate which need a high-precision time synchronization. In hostile environments, the time synchronization protocol may be destroyed by external, compromise or pulse-delay attacks. In this paper, we present a secure time synchronization for IEEE802.15.4e networks called STS_4e which includes a secure single-hop pair-wise time synchronization and a secure cluster-wise time synchronization. The secure pair-wise time synchronization adopts message integrity authentication mechanism to defend against external attacks and threshold filter algorithm to defend against compromise and pulse-delay attacks. The secure cluster-wise time synchronization adopts packet-based key chain to improve µTESLA broadcast authentication mechanism which can well balance the delay of disclosed keys and the length of key chain. Finally, we implement the STS_4e scheme on OpenMoteSTM node running OpenWSN. The results show that the proposed scheme can successfully defend against time synchronization attacks as well as the low energy consumption.     

一种基于循环编码的高性能分布式互斥算法

公平、健壮和易于实现的分布式互斥算法对分布式系统保证数据一致性、逻辑一致性及时序一致性至关重要.除Lamport算法,RA算法和N^0.63算法外,以前提出的分布式互斥算法都只是在节点数目与请求集大小存在一定关系时才是公平和对称的,在大多数情况下是不对称的.这些算法的同步时间,容错性能与消息复杂度之间存在着不可调和的矛盾,不能三者兼顾.本文提出了一种基于循环编码的互斥请求集产生算法,并在此基础上改进了已有的基于请求集的分布式互斥算法,使该算法在系统节点数为任意值时都能公平和对称地产生请求集.其消息复杂度较低,同步时间为T,节点容错能力达到N-1.     

自适应高效无线传感器网络时间同步优化算法

针对无线传感器网络全网多跳自适应时间同步效率低的问题,在接收端与接收端同步模型基础上,该文提出一种自适应高效无线传感器网络时间同步优化算法(AEO)。首先,双节点同步时,从节点接收来自参考节点的同步消息并进行确认,在同步周期结束后通过拟合估计和数据更新完成时间修正,构建交互参数同步包,并与主节点进行信息交换完成同步过程。其次,全网同步时,建立Voronoi多边形拓扑结构,认定拓扑结构中参考节点和邻域节点身份(ID),参考节点覆盖区域间通过邻域节点交换同步信息,实现自适应多区域节点联合时间同步。仿真结果表明该算法在双节点时间同步中能够保证同步误差较小,网络能耗较低;同时,Voronoi拓扑相较于其他典型拓扑,在连通效率和收敛时间方面均有所改进。     

一种低功耗的多跳无线传感网时间同步算法

高精度低功耗的时间同步对于无线传感网络至关重要,文中重点分析了高精度时间同步算法,发现其在多跳网络时间同步过程中由于每跳范围内所有节点均要广播时间同步包,会产生大量的冗余信息。为降低同步功耗,提出了一种新方法,通过调节发射功率,筛选出每一跳范围内的周边节点,使其完成下一跳范围的时间同步,而非周边节点只接受却不发送时间同步包。最后,针对改进的算法在OMNet++上进行了仿真实验,仿真结果表明,改进后的算法能够有效地降低全网能量消耗。     

一种基于能量感知的延迟容忍移动无线传感器网络多拷贝路由协议(英文)

The two-phase replication-based routing has great prospects for Delay Tolerant Mobile Sensor Network (DTMSN) with its advantage of high message delivery ratio, but the blind spraying and the low efficiency forwarding algorithm directly influences the overall network performance. Considering the characteristic of the constrained energy and storage resources of sensors, we propose a novel two-phase multi-replica routing for DTMSN, called Energy-Aware Sociality-Based Spray and Search Routing (ESR), which imple...     

Performance evaluation of optical code division multiple access systems

In this paper, a new mechanism of faster routing known as message priority and fast routing (MPFR) mechanism in optical code division multiple access (OCDMA) is proposed for optimization of routing performance and to provide effective data transfer. In this proposed work, we have reduced the size of the header bits which are used in MPFR mechanism. In proposed algorithm, with accordance to packet header, the message size is being increased and priority bit is being added which leads to faster data transfer rate and effective data transfer in OCDMA. The transmitter sent the 2D codes to the MPFR which is then added priority bit. If the cover bit in any codes is enabling then the code is considered to be a priority packet and its superior bit then the code is considered to be routing. A modern novel approach which reduces the overhead for fast data transfer is proposed on name of MPFR. Thus the routing can be faster and the codes to be sent are being priorities and send. Thus the OCDMA can now become much faster to be used in critical areas. MPFR protocol, which prioritizes the code with high priority and also it reduces the header processing time of the codes with increase in message size. The prioritization of the code helped to process the particular code first and then rest of the codes and with increase in message size, help to reduce the transmission and processing time of the packet header.     

Research on Time Synchronization Algorithm of High Precision and Low Power Consumption Based on IRBRS WSNs

Based on the study of RBS algorithm in wireless sensor network, an improved algorithm named RBRS is presented, to solve the time synchronization problem of multi hop networks. On the basis of RBS, the broadcast group and least square linear regression methods were used to realize entire network time synchronization in the algorithm. Synchronization error and overhead with the existing improved BRS are compared in the article. The result shows that the algorithm has certain superiority in many algorithms, which is suitable for light and low power consumption network load. Through an emulation with the matlab software, the result indicates that error accumulation is lower in the optimized algorithm, the synchronization overhead is significantly reduced and can realize the time synchronization of the whole network. A time synchronization algorithm based on RBRS algorithm is proposed for multi-hop and the low power consumption. A variable period synchronization method is introduces in the algorithm: in line with Bias maximum a posterior estimation principle, the maximum phase offset is estimated to determine the synchronization period, which can reduce the number of node synchronization, and with the least square linear regression method, the periodic fitting clock offset. The Simulation in matlab indicate that RBRS algorithm can improve the synchronization accuracy and reduce energy consumption significantly, which is conducive to extend the life of the network.