Distributed Time Synchronization in Wireless Sensor Networks via Second-Order Consensus Algorithms

This paper proposes a distributed second-order consensus time synchronization, which incorporates the second-order consensus algorithm into wireless sensor networks. Since local clocks may have different skews and offsets, the algorithm is designed to include offset compensation and skew compensation. The local clocks are not directly modified, thus the virtual clocks are built according to the local clocks via the compensation parameters. Each node achieves a virtual consensus clock by periodically updated compensation parameters. Finally, the effectiveness of the proposed algorithm is verified through a number of simulations in a mesh network. It is proved that the proposed algorithm has the advantage of being distributed, asymptotic convergence, and robust to new node joining.

Research on Time Synchronization Method Under Arbitrary Network Delay in Wireless Sensor Networks

To cope with the arbitrariness of the network delays,a novel method,referred to as the composite particle filter approach based on variational Bayesian(VB-CPF),is proposed herein to estimate the clock skew and clock offset in wireless sensor networks.VB-CPF is an improvement of the Gaussian mixture kalman particle filter(GMKPF)algorithm.In GMKPF,Expectation-Maximization(EM)algorithm needs to determine the number of mixture components in advance,and it is easy to generate overfitting and underfitting.Variational Bayesian EM(VB-EM)algorithm is introduced in this paper to determine the number of mixture components adaptively according to the observations.Moreover,to solve the problem of data packet loss caused by unreliable links,we propose a robust time synchronization(RTS)method in this paper.RTS establishes an autoregressive model for clock skew,and calculates the clock parameters based on the established autoregressive model in case of packet loss.The final simulation results illustrate that VB-CPF yields much more accurate results relative to GMKPF when the network delays are modeled in terms of an asymmetric Gaussian distribution.Moreover,RTS shows good robustness to the continuous and random dropout of time messages.

Linear Pulse-Coupled Oscillators Model¬—A New Approach for Time Synchronization in Wireless Sensor Networks

Mutual synchronization is a ubiquitous phenomenon that exists in various natural systems. The individual participants in this process can be modeled as oscillators, which interact by discrete pulses. In this paper, we analyze the synchronization condition of two- and multi-oscillators system, and propose a linear pulse-coupled oscillators model. We prove that the proposed model can achieve synchronization for almost all conditions. Numerical simulations are also included to investigate how different model parameters affect the synchronization. We also discuss the implementation of the model as a new approach for time synchronization in wireless sensor networks.

On the Trade-off between Power Consumption and Time Synchronization Quality for Moving Targets under Large-Scale Fading Effects in Wireless Sensor Networks

In this work we find a lower bound on the energy required for synchronizing moving sensor nodes in a Wireless Sensor Network (WSN) affected by large-scale fading, based on clock estimation techniques. The energy required for synchronizing a WSN within a desired estimation error level is specified by both the transmit power and the required number of messages. In this paper we extend our previous work introducing nodes’ movement and the average message delay in the total energy, including a comprehensive analysis on how the distance between nodes impacts on the energy and synchronization quality trade-off under large-scale fading effects.

Network-Wide Time Synchronization in Multi-Channel Wireless Sensor Networks

Recent advances in wireless sensor technology have enabled simultaneous exploitation of multiple channels in wireless sensor systems. In this paper, a novel time synchronization algorithm is proposed for multi- channel Wireless Sensor Networks (WSNs) called Multi-Channel Time Synchronization (MCTS) protocol. Time synchronization is critical for many WSN applications and enables efficient communications between sensor nodes along with intelligent spectrum access. Contrary to many existing protocols that do not exploit multi-channel communications, the protocol takes advantage of potential multiple channels and distributes the synchronization of different nodes to distinct channels and thus, reduces the convergence time of synchronization processes significantly.

TDOA Localization Algorithm with Compensation of Clock Offset for Wireless Sensor Networks

This paper presents a source localization algorithm based on the source signal's time-difference-of-arrival(TDOA) for asynchronous wireless sensor network.To obtain synchronization among anchors,all anchors broadcast signals periodically,the clock offsets and skews of anchor pairs can be estimated using broadcasting signal's time-of-arrivals(TOA) at anchors.A kalman filter is adopted to improve the accuracy of clock offsets and track the clock drifts due to random fluctuations.Once the source transmits signal,the TOAs at anchors are stamped respectively and source's TDOA error due to clock offset and skew of anchor pair can be mitigated by a compensation operation.Based on a Gaussian noise model,maximum likelihood estimation(MLE) for the source position is obtained.Performance issues are addressed by evaluating the Cramer-Rao lower bound and the selection of broadcasting period.The proposed algorithm is simple and effective,which has close performance with synchronous TDOA algorithm.

QoS Adaptive Topology Configuration in Synchronous Wireless Sensor Networks

By using hyper-graph theory,this paper proposes a QoS adaptive topology configuration(QATC) algorithm to effectively control large-scale topology and achieve robust data transmitting in synchronous wireless sensor networks.Firstly,a concise hyper-graph model is abstracted to analyze the large-scale and high-connectivity network.Secondly,based on the control theory of biologic "Cell Mergence",a novel self-adaptive topology configuration algorithm is used to build homologous perceptive data logic sub-network for data aggregation.Compared with Flooding,Directed Diffusion,and Energy Aware Directed Diffusion protocols,the simulation proved that QATC algorithm can save more energy,e.g.,about 23.7% in a large size network,and has less delay than the other algorithms.In dynamic experiments,QATC keeps a robust transmitting quality with 10%,20% and 30% random failure nodes.

A Secure Clock Synchronization Scheme for Wireless Sensor Networks Against Malicious Attacks

This paper studies the secure and accurate clock synchronization problem for sensor networks with time-varying delays and malicious attacks.A novel clock synchronization scheme based on the attack detection mechanism,attack compensation,and maximum consensus protocol is proposed.The proposed scheme starts with the detection of the malicious attacks and the clock data under attacks is eliminated.On the basis,software clock parameters are updated so that all the nodes in the network can have the same software skew and offset,so the clock synchronization can be achieved.Furthermore,it is theoretically proved that the proposed scheme can achieve the attack detection correctly,and further can guarantee a secure and accurate clock synchronization.In addition,extensive simulations are also conducted to validate the effectiveness of the proposed scheme.

A consensus time synchronization protocol in wireless sensor network

Time synchronization is one of the base techniques in wireless sensor networks(WSNs).This paper proposes a novel time synchronization protocol which is a robust consensusbased algorithm in the existence of transmission delay and packet loss.It compensates for transmission delay and packet loss firstly,and then,estimates clock skew and clock offset in two steps.Simulation and experiment results show that the proposed protocol can keep synchronization error below 2μs in the grid network of 10 nodes or the random network of 90 nodes.Moreover,the synchronization accuracy in the proposed protocol can keep constant when the WSN works up to a month.

Clapping and Broadcasting Synchronization in Wireless Sensor Networks

The Clapping and Broadcasting Synchronization （CBS） algorithm, which is specifically designed for large-scale sensor networks with low communication overhead and high synchronization accuracy, is introduced. The CBS protocol uses broadcasting rather than pairwise communication to accomplish synchronization. In the CBS scheme, the initial offset of local clocks can be successfully eliminated by the operation of clapping nodes, which leads to significant improvement in synchronization accuracy. The CBS protocol was implemented on the TelosB platform and its performance was evaluated in a variety of experiments. The results demonstrate that the CBS protocol outperforms the current state-of-the-art approach, the Flooding Time Synchronization Protocol （FTSP）, in both single-hop and multi-hop scenarios in terms of synchronous precision and energy consumption. In multi-hop scenarios, the CBS algorithm keeps about 50% of its synchronization errors within 1 ms. In comparison, the FTSP keeps less than 7% of its synchronization errors within this range. In both single-hop and multi-hop scenarios, the CBS protocol is over 3.2 times more energy-efficient than the FTSP.

A Reliable and Efficient Time Synchronization Protocol for Heterogeneous Wireless Sensor Network

L-SYNC is a synchronization protocol for Wireless Sensor Networks which is based on larger degree clustering providing efficiency in homogeneous topologies. In L-SYNC, the effectiveness of the routing algorithm for the synchronization precision of two remote nodes was considered. Clustering in L-SYNC is according to larger degree techniques. These techniques reduce cluster overlapping, resulting in the routing algorithm requiring fewer hops to move from one cluster to another remote cluster. Even though L-SYNC offers higher precision compared to other algorithms, it does not support heterogeneous topologies and its synchronization algorithm can be influenced by unreliable data. In this paper, we present the L-SYNCng (L-SYNC next generation) protocol, working in heterogeneous topologies. Our proposed protocol is scalable in unreliable and noisy environments. Simulation results illustrate that L-SYNCng has better precision in synchronization and scalability.

A Survey on Clock Synchronization in the Industrial Internet

Clock synchronization is one of the most fundamental and crucial network communication strategies.With the expansion of the Industrial Internet in numerous industrial applications,a new requirement for the precision,security,complexity,and other features of the clock synchronization mechanism has emerged in various industrial situations.This paper presents a study of standardized clock synchronization protocols and techniques for various types of networks,and a discussion of how these protocols and techniques might be classified.Following that is a description of how certain clock synchronization protocols and technologies,such as PROFINET,Time-Sensitive Networking(TSN),and other well-known industrial networking protocols,can be applied in a number of industrial situations.This study also investigates the possible future development of clock synchronization techniques and technologies.

Energy saving with node sleep and power control mechanisms for wireless sensor networks

Energy efficiency sleep scheduling in wireless sensor networks is one of the most crucial technologies. In this paper, we propose a simple and feasible synchronous node sleeping and waking mechanisms for small scale wireless sensor networks. Sensor nodes are divided into forwarding nodes and listening nodes. Beacon frame containing sleep command from the coordinator can be forwarded to listening nodes via forwarding nodes. All the nodes in the network can enter sleep at about the same time. Through such network synchronization mechanisms, we can realize synchronous sleep and wake of the entire network. Furthermore, a new power control scheme based on routing protocol （PCBRP） in the medium access control （MAC） layer is proposed. It operates with the help of routing protocol and calculates optimal transmission power according to the distance between neighbor nodes. A mapping table including optimal transmission power and node address is established during the route building procedure. The transmission power can be obtained by searching the table with the address of next-hop neighbor in subsequent data transmissions. The proposed mechanisms are implemented in sensor nodes and are evaluated in a test-bed. The analysis and evaluation based on the experimental results confirm that the proposed energy-saving mechanisms are feasible and effective.

On Energy-Efficient Time Synchronization for Wireless Sensors under Large-Scale and Small-Scale Fading Effects

In this work, the existing trade-off between time synchronization quality and energy is studied for both large-scale and small-scale fading wireless channels. We analyze the clock offset estimation problem using one-way, two-way and N-way message exchange mechanisms affected by Gaussian and exponentially distributed impairments. Our main contribution is a general relationship between the total energy required for synchronizing a wireless sensor network and the clock offset estimation error by means of the transmit power, number of transmitted messages and average message delay, deriving the energy optimal lower bound as a function of the time synchronization quality and the number of hops in a multi-hop network.

Fault-Tolerant WSN Time Synchronization

This paper proposes a new fault-tolerant time synchronization algorithm for wireless sensor networks that requires a short time for synchronization, achieves a guaranteed time synchronization level for all non-faulty nodes, accommodates nodes that enter suspended mode and then wake up, is computationally efficient, operates in a completely decentralized manner and tolerates up to f (out of 2 f + 1 total) faulty nodes. The performance of the proposed algorithm is analyzed, and an equation is derived for the resynchronization interval required for a specific level of synchronization precision. Results obtained from real runs on multi-hop networks are used to demonstrate the claimed features of the proposed algorithm.

Controlled Mobility Time Synchronization for WSNs

One of the important aspects in wireless sensor networks is time synchronization. Many applications such as military activity monitoring, environmental monitoring and forest fire monitoring require highly accurate time synchronization. Time synchronization assures that all the sensor nodes in wireless sensor network have the same clock time. It is not only essential for aforementioned applications but it is mandatory for TDMA scheduling and proper duty cycle coordination. Time synchronization is a challenging problem due to energy constraints. Most of the existing synchronization protocols use fixed nodes for synchronization, but in the proposed synchronization, algorithm mobile nodes are used to synchronize the stationary nodes in the sensing field. In this paper, we propose a new time synchronization algorithm, named controlled mobility time synchronization (CMTS) with the objective to achieve the higher accuracy while synchronizing the nodes. The proposed approach is used in this paper to synchronize the nodes externally by using the mobile nodes. Simulation results exhibit that proposed controlled mobility time synchronization increases the synchronization precision and reduces the energy consumption as well as synchronization error by reducing the collisions and retransmissions.

面向无线传感网络的同步时钟技术研究

考虑到传统的时钟同步技术在信息交互过程中产生的延迟具有不确定性,为了消除其对时钟同步的影响,提出了面向无线传感网络的同步时钟技术研究。通过对任意一个网络节点在真实物理时间的本地时间进行变换处理,构建无线传感网络的线性时钟模型,根据高斯分布所具有的加减特性,计算两个连续同步轮次的动态响应时间差值,在离散形式下,构建无线传感网络观测模型。通过计算无线传感网络时钟差值的均值,得到无线传感网络节点的时间戳,将无线传感网络节点数据交互误差补偿的目标函数转换成向量的形式,补偿无线传感网络节点数据交互误差,实现无线传感网络的时钟同步处理。实验结果表明,在微秒级延迟下,该技术的同步精度仍较高,可以有效消除网络信息延迟的不确定性对同步时钟的影响。

基于ZigBee无线传感网络的分簇时间同步算法

在无线传感网络中,时间同步技术在信道分配、数据收发、休眠调度中都有着关键作用。目前已有的时间同步算法,有些同步精度不高,有些需要进行频繁的数据交换导致功耗过大。因此设计出能同时满足高精度和低功耗两个要求的算法势在必行。提出的算法通过改变网络拓扑结构,构造分簇函数,选出簇头,进行分簇。在新的网络拓扑中,协调器与簇头之间通过频偏补偿来保证同步的精度,簇头与成员节点之间通过三次通信消除时延进行时间同步,从而实现全网时间同步。仿真结果表明,整个网络在较低功耗下也能有较高的同步精度。

机械振动无线传感器簇状网络路径感知同步触发方法

无线传感器可以实时监测机械振动情况,但如果同步触发问题解决不好,可能会直接影响监测效果,导致机械设备无法正常使用。为了从根源上解决这个问题,需要重新研究感知同步触发方法。文章以机械振动无线传感器数据采集为基础,提出了STBTC_P架构与实现,并探讨了簇状网络路径感知同步触发方式,谨供参考。