A Quorum-based Mechanism as an Enhancement to Clock Synchronization Protocols for IEEE 802.11 MANETs

In wireless mobile ad hoc networks (MANETs), it is essential that all mobile hosts (MHs) are synchronized to a common clock to support the power-saving (PS) mechanism. Many protocols have been proposed for clock synchronization in IEEE 802.11 MANETs. However, it is practically impossible for any protocol to completely solve the asynchronism problem especially when connectivity is achieved by multi-hop communication or when a network could be temporarily disconnected. In this work, we propose a quorum-based mechanism, which includes a new structure of beacon intervals for MHs to detect potential asynchronous neighbors and an enhanced beacon transmission rule to assist clock synchronization protocols to discover asynchronous neighbors within bounded time. The proposed mechanism should be regarded as an enhancement to existing clock synchronization protocols. Our simulation results show that the mechanism can effectively relieve the clock asynchronism problem for IEEE 802.11 MANETs     

A Novel Artificial Intelligence Based Timing Synchronization Scheme for Smart Grid Applications

The smart grid control applications necessitate real-time communication systems with time efficiency for real-time monitoring, measurement, and control. Time-efficient communication systems should have the ability to function in severe propagation conditions in smart grid applications. The data/packet communications need to be maintained by synchronized timing and reliability through equally considering the signal deterioration occurrences, which are propagation delay, phase errors and channel conditions. Phase synchronization plays a vital part in the digital smart grid to get precise and real-time control measurement information. IEEE C37.118 and IEC 61850 had implemented for the synchronization communication to measure as well as control the smart grid applications. Both IEEE C37.118 and IEC 61850 experienced a huge propagation and packet delays due to synchronization precision issues. Because of these delays and errors, measurement and monitoring of the smart grid application in real-time is not accurate. Therefore, it has been investigated that the time synchronization in real-time is a critical challenge in smart grid applications, and for this issue, other errors raised consequently. The existing communication systems are designed with the phasor measurement unit (PMU) along with communication protocol IEEE C37.118 and uses the GPS timestamps as the reference clock stamps. The absence of GPS increases the clock offsets, which surely can hamper the synchronization process and the full control measurement system that can be imprecise. Therefore, to reduce this clock offsets, a new algorithm is needed which may consider any alternative reference timestamps rather than GPS. The revolutionary Artificial Intelligence (AI) enables the industrial revolution to provide a significant performance to engineering solutions. Therefore, this article proposed the AI-based Synchronization scheme to mitigate smart grid timing issues. The backpropagation neural network is applied as the AI method that employs the timing estimations and error corrections for the precise performances. The novel AIFS scheme is considered the radio communication functionalities in order to connect the external timing server. The performance of the proposed AIFS scheme is evaluated using a MATLAB-based simulation approach. Simulation results show that the proposed scheme performs better than the existing system.

     

ZigBee信标同步算法设计与仿真

由于受到时钟准确性和精度要求的影响,传统网络中的时间同步算法已经不能满足无线传感器网络的要求.根据ZigBee郊术的特点,研究了基于CSMA-CA机制的具有针对性的信标同步算法.给出了相应的算法分析、算法流程,以及在NS2平台中的仿真结果与性能分析,同时给出了在信标网络与非信标网络中的效果对比.     

基于工业网络的分布式时钟同步算法研究

为了实现工业控制过程中的时钟同步,基于以太网的网络通信协议IEEE1588标准,作为以太网中使用最广的时钟同步算法,已经具有十分精确的同步性。IEEE1588使用集中式同步方法,导致如果有一个发送给主时钟的结点发生故障时,将会影响到网络中其余结点的同步性能,某些结点的时钟出现不同步会引起同步控制系统的瘫痪。采用把IEEE1588与FlexRay同步算法结合的分布式同步方法实现时钟同步的机制,结果证明该算法更加适合于工业通信协议的时钟同步。     

无线传感器网络分布式一致时间同步协议的收敛分析及加速设计

该文研究了基于分布式一致的无线传感器网络时间同步协议的收敛和加速问题。通过将其同步迭代过程映射到马尔可夫链的状态转移过程,推导出了分布式一致时间同步协议在循环网中的收敛速度与节点邻居数和网络规模有关。Matlab仿真实验表明该结论对类均匀规则网和类均匀网也是正确的。此外,对于类均匀网,邻居数分布也会影响协议的收敛速度。因此该文提出了基于改变网络邻居数分布的加速算法来提高分布式一致时间同步协议的收敛速度。规模为100个节点的类均匀网络实验结果表明,该文提出的加速算法在没有显著改变节点平均传输半径的情况下可使分布式一致时间同步协议的收敛迭代次数降低约25%。     

RTEthernet中改进的FTA时钟同步算法研究

针对以太网存在节点时钟漂移、网络链路延迟、同步能力差等问题,文中基于RTEthernet协议的通信原理,构建了时钟同步系统的模型。文中研究了RTEthernet的组成、工作原理,考虑了影响实时以太网时钟同步精密度的三大因素：漂移率、网络传输延迟和时钟拜占庭故障,并基于此分析了原始的FTA时钟同步算法,发现它在拜占庭故障增多的情况下容错性能明显降低,进而引入“容错中值”的思想进行改进并提出了RTE-FTM算法。通过CANoe仿真平台,对系统(7个节点)中存在2个拜占庭故障与不存在拜占庭故障进行对比分析。结果表明系统的精密度损失率降低了3.1%,并由此验证了该算法的收敛性和有效性。     

A comprehensive survey of network coding in vehicular ad-hoc networks

Network coding is a data processing technique in which the flow of digital data is optimized in a network by transmitting a composite of two or more messages to make the network more robust. Network coding has been used in traditional and emerging wireless networks to overcome the communications issues of these networks. It also plays an important role in the area of vehicular ad-hoc networks (VANETs) to meet the challenges like high mobility, rapidly changing topology, and intermittent connectivity. VANETs consist of network of vehicles in which they communicate with each other to ensure road safety, free flow of traffic, and ease of journey for the passengers. It is now considered to be the most valuable concept for improving efficiency and safety of future transportation. However, this field has a lot of challenges to deal with. This paper presents a comprehensive survey of network coding schemes in VANETs. We have classified different applications like content distribution, multimedia streaming, cooperative downloading, data dissemination, and summarized other key areas of VANETs in which network coding schemes are implemented. This research work will provide a clear understanding to the readers about how network coding is implemented in these schemes in VANETs to improve performance, reduce delay, and make the network more efficient.     

Ratio-based time synchronization protocol in wireless sensor networks

Time synchronization plays a key role in the wireless sensor networks (WSNs). Time synchronization is realized by those messages that are time-stamped. But there are several delay times during transmission after time stamping. Most of them are uncertain and contribute directly to synchronization error. The uncertainties include send time, channel access time, transmission time, and receive time. In addition to the uncertainties, clock drift is also a main source of time synchronization error. In this paper, we present a time synchronization protocol that can be applied in the multi-hop WSNs. The proposed protocol estimates the clock drift between two nodes to keep them synchronized for duration after once synchronizing. It uses lower communication overhead and establishes more robust synchronization situations for all nodes in the network. By periodical re-synchronization, the un-synchronization conditions such as nodes failures or topology change can be easily overcome. We implement our protocol in the Berkeley MICAz platform. The experimenting scenarios are 5-node and 18-node multi-hop topologies, and the re-synchronization periods are 30-second and 300-second. The experiment results show that the average synchronization errors of all nodes run with our protocol are ranged within several micro-seconds which are better than the previous protocol.     

E2DTS: An energy efficiency distributed time synchronization algorithm for underwater acoustic mobile sensor networks

Time synchronization plays an important role in wireless sensor network applications and energy conservation. In this paper, we focus on the need of time synchronization in underwater acoustic mobile sensor networks (UAMSNs). Several time synchronization algorithms have been carried out in this issue. But most of them are proposed for RF-based wireless sensor networks, which assume that the propagation delay is negligible. In UAMSNs, the assumption about rapid communication is incorrect because the communication is primarily via acoustic channel, so the propagation speed is much slower than RF. Furthermore, the propagation delay in underwater environment is time-varying due to the nodes’ mobility. We present an energy efficiency distributed time synchronization algorithm (called “E²DTS”) for those underwater acoustic node mobility networks. In E²DTS, both clock skew and offset are estimated. We investigate the relationship between time-varying propagation delay and nodes mobility, and then estimate the clock skew. At last skew-corrected nodes send local timestamp to beacon node to estimate its clock offset. Through analysis and simulation, we show that it achieves high level time synchronization precision with minimal energy cost.     

Time Synchronization Protocol with Minimum Message Communication for High Latency Networks

Time synchronization is a critical component of the infrastructure of wireless sensor networks (WSN). In a high latency environment such as underwater, traditional approaches to time synchronization have limited accuracy. A new method is describe for time synchronization that takes into account clock skew, clock offset, and also propagation delay. Minimum message communication is used as a performance measure of the quality of this new time synchronization protocol.     

IP address allocation protocols in vehicular ad hoc networks

In vehicular ad hoc networks (VANETs), communication takes place between vehicles to vehicles, the vehicles to the road side units, and vice-versa. The basic purpose of these communications is to share and exchange tremendous amount of data and information. For efficient information sharing, a systematic and structured connection establishment algorithm is needed. In VANETs, each connected node of the network need to be assigned a unique address. Hence, an algorithm is needed for the proper assignment of unique address to all nodes in the network. This paper explains different types of IP address protocols in VANETs. We have also explained advantage and disadvantage of existing IP address allocation protocols in VANETs.     

Privacy Addressing-Based Anonymous Communication for Vehicular Ad Hoc Networks

Vehicle ad-hoc network (VANET) technology is a basic component of the future intelligent transportation system. With the advances in modern information society, privacy issues have become important considerations. However, most routing proposals for VANETs lack privacy support, namely anonymity or pseudonymity and unlinkability aspects. This paper presents a novel privacy addressing-based anonymous communication approach for VANETs, which prevents eavesdroppers from identifying a particular vehicle by its address. The proposed scheme is a kind of end-to-end solution, so it can potentially be extended to work with many traditional routing protocols. Finally, the simulation results show that the proposed scheme outperforms previous approaches with privacy support in terms of protocol overhead and packet latency.     

QoS‐aware broadcasting in VANETs based on fuzzy logic and enhanced kinetic multipoint relay

Vehicular ad hoc networks (VANETs) are emergent concepts in terms of infrastructure‐less communication. The data dissemination is usually done using broadcast schemes. Data broadcast in VANETs is a challenging issue due to the high mobility vehicles and the varying density. On one hand, these vehicles have to share and disseminate the safety‐critical information, in real time, to other intended vehicles. On the other hand, the existing broadcast solutions do not succeed, till now, to fulfill VANETs requirements especially in terms of performance and QoS. In this paper, we propose a new QoS‐aware broadcast method in order to face VANETs communications challenges. We choose to adapt a concept originally devoted to mobile ad hoc networks (MANETs) and join it to other specific VANET techniques to introduce a new broadcasting protocol in the aim of optimizing QoS fulfilment. The proposed solution is fundamentally based on enhanced kinetic strategy assisted with fuzzy logic for QoS‐aware multipoint relay (MPR). The protocol efficiency is eventually tested through an experimental study and compared with existing methods. The results prove the over‐performance of the proposed solution.     

Location- and delay-aware cross-layer communication in V2I multihop vehicular networks

Intelligent transportation systems are targeted to improve the traffic safety and driving experience of passengers. Vehicular ad hoc networks are wireless communication networks proposed to be used as parts of ITS. VANETs facilitate communication among vehicles, and between vehicles and roadside equipment. A key challenge in developing such systems is to design routing and MAC protocols that not only provide good end-to-end packet delay but can also quickly adapt to changes in the network topology due to vehicular mobility. In this article we outline a new framework for location- and delayaware cross-layer communication that addresses these challenges. Our framework provides an efficient V2I data delivery system that relays packets over low-delay paths to a fixed base station or access point. Furthermore, an instance of this framework is also presented as a protocol. Our preliminary evaluations show that our design approach is promising, and provides delay predictability, fairness, and a good packet delivery ratio.     

MQBV: multicast quality of service swarm bee routing for vehicular ad hoc networks

Vehicular ad hoc networks (VANETs) are witnessing in recent years a rapid development for road transmissions and are considered as one of the most important types of next generation networks, in which drivers can have access anywhere and anytime to information. However, vehicles have to deal with many challenges such as the links failures due to their frequent mobility as well as limited degrees of freedom in their mobility patterns. In this paper, we propose a new quality of service multicast and multipath routing protocol for VANETs, based on the paradigm of bee's communication, called multicast quality of service swarm bee routing for VANETs (MQBV). The MQBV finds and maintains robust routes between the source node and all multicast group members. Therefore, the average end‐to‐end delay and the normalized overhead load should be reduced, while at the same time increasing the average bandwidth and the packet delivery ratio. Extensive simulation results were obtained using ns‐2 simulator in a realistic VANET settings and demonstrated the efficiency of the proposed protocol. Copyright © 2013 John Wiley & Sons, Ltd.     

Routing protocols for vehicular Ad Hoc networks in rural areas

Research on vehicular ad hoc networks has focused mainly on efficient routing protocol design under conditions where there are relatively large numbers of closely spaced vehicles. These routing protocols are designed principally for urban areas with high node density and fully connected networks and are not suitable for packet delivery in a sparse, partially connected VANET. In this article, we examine the challenges of VANETs in sparse network conditions, review alternatives including epidemic routing, and propose a border node-based routing protocol for partially connected VANETs. The BBR protocol can tolerate network partition due to low node density and high node mobility. The performance of epidemic routing and BBR are evaluated with a geographic and traffic information- based mobility model that captures typical highway conditions. The simulation results show that under rural network conditions, a limited flooding protocol such as BBR performs well and offers the advantage of not relying on a location service required by other protocols proposed for VANETs.     

Efficient Privacy-Preserving Anonymous Authentication Protocol for Vehicular Ad-Hoc Networks

Vehicular ad-hoc network (VANET) has been considered as one of the most promising wireless sensor technologies, which could enhance driving convenience and traffic efficiency through real-time information interaction. Nevertheless, emerging security issues (e.g., confidentiality, integrity, identity privacy, message authentication) will hinder the widespread deployment of VANETs. To address these issues, in this paper, we propose an efficient privacy-preserving anonymous authentication protocol for VANETs. We first design an identity-based signature algorithm, and exploit it with an account information of a vehicle to propose our anonymous authentication protocol. The protocol enables each vehicle to anonymously send an authenticated message to nearby roadside units (RSUs) in a confidential way, and efficiently check the feedback information from nearby RSUs. Simultaneously, the protocol achieves key-exchange functionality, which could produce a session key for later secure communication between vehicles and RSUs. Finally, we give the security analysis of the proposed protocol and conduct a comprehensive performance evaluation, the results demonstrate its feasibility in the secure deployment of VANETs.

     

Self-correcting time synchronization using reference broadcast in wireless sensor network

Time synchronization is one of the most fundamental services for numerous wireless sensor network applications. In this article the definition and basic concepts of time synchronization are introduced, and the related work is summarized in brief. Through analyzing the characteristics of the existing typical synchronization protocols and making a comprehensive comparison of the performance of various algorithms, we present a common guideline for designing the time synchronization protocol in WSN. Following this guideline, we develop a new time synchronization protocol called Self-Correcting Time Synchronization (SCTS), which converts the time synchronization problem into an online dynamic self-adjusting optimizing process to make the offset compensation and drift compensation simultaneously. The time and space complexities of the algorithm implementation are very low. In addition, the SCTS protocol fully exploits the inherent broadcast property of wireless channel, so the communication overhead is rather low. Because the algorithm implementation is based on the phase locked loop principle, an equivalent digital PLL without an actual voltage controlled oscillator is also proposed to avoid introducing the extra hardware required by a traditional PLL circuit. Finally, we validate SCTS on the Berkeley Mica2 experimental platform, and the performance is evaluated and compared to the existing typical time synchronization protocol.     

水下传感器网络时间同步技术综述

 时间同步是传感器节点协同工作的基础.水下传感器网络由于采用水声通信方式,具有不同于陆地无线传感器网络的特点,为时间同步算法研究带来了新的挑战.论文首先说明同步问题与同步算法的形式化定义,然后讨论水下传感器网络不同于陆地传感器网络的特点,并指出相关特点对于同步问题的影响;接着综述陆地传感器网络同步算法的研究进展,分析相关算法用于水下环境的不足;进而介绍水下传感器网络同步算法的研究进展,并通过仿真实验完成了相关算法的性能对比;最后总结水下传感器网络时间同步的关键问题,指出进一步的研究方向.