Clock Synchronization Algorithm Research Articles

An Overview of a Class of Clock Synchronization Algorithms for Wireless Sensor Networks: A Statistical Signal Processing Perspective

Recently, wireless sensor networks (WSNs) have drawn great interest due to their outstanding monitoring and management potential in medical, environmental and industrial applications. Most of the applications that employ WSNs demand all of the sensor nodes to run on a common time scale, a requirement that highlights the importance of clock synchronization. The clock synchronization problem in WSNs is inherently related to parameter estimation. The accuracy of clock synchronization algorithms depends essentially on the statistical properties of the parameter estimation algorithms. Recently, studies dedicated to the estimation of synchronization parameters, such as clock offset and skew, have begun to emerge in the literature. The aim of this article is to provide an overview of the state-of-the-art clock synchronization algorithms for WSNs from a statistical signal processing point of view. This article focuses on describing the key features of the class of clock synchronization algorithms that exploit the traditional two-way message (signal) exchange mechanism. Upon introducing the two-way message exchange mechanism, the main clock offset estimation algorithms for pairwise synchronization of sensor nodes are first reviewed, and their performance is compared. The class of fully-distributed clock offset estimation algorithms for network-wide synchronization is then surveyed. The paper concludes with a list of open research problems pertaining to clock synchronization of WSNs.

Synchronization based on mixture alignment for sound source separation in wireless acoustic sensor networks

Desynchronization degrades the performance of many signal processing algorithms in Wireless Acoustic Sensor Networks. It is mainly caused by the different distances between the source and each node and by the clock phase offset and frequency skew. Classical solutions use clock synchronization protocols and algorithms in the communication layer, but these alternatives do not tackle the lack of synchronization caused by the distances between sources and nodes.In this paper, we present a novel study of the synchronization problem in acoustic sensor networks from a signal processing point of view. First, we propose a theoretical framework that allows us to study the effects of misalignment over any short-time based algorithm, focusing on the requirements of the effective length of the analysis time frame. From this framework, a theoretical synchronization delay is established aimed at reducing the required length of the time frame. Second, two novel alignment methods are developed and are tuned up to reduce the amount of synchronization information required for transmission. The results obtained demonstrate that our proposed methods represent a good solution in terms of performance over the quality of a standard Blind Source Separation algorithm, allowing us to reduce the transmission bandwidth required for synchronization data.

Clock Skew Estimation Using Kalman Filter and IEEE 1588v2 PTP for Telecom Networks

Accurate and precise frequency synchronization is an essential requirement for different areas in telecommunication industry. Emerging practise for frequency synchronization is to utilize packet networks since it is highly cost effective. One method of distributing frequency over a variety of packet networks is based on well known IEEE 1588v2 PTP standard that uses a master-slave architecture. Accuracy and precision of the frequency synchronization over IEEE 1588v2 PTP is mainly deteriorated by the Packet Delay Variations (PDVs) experienced on the transmission path. This problem can be overcome by deploying so-called timing aware routing elements, however slaves' frequency accuracy and precision still heavily relies on the quality of the slave's clock synchronization algorithm. Hence, this work introduces an improved Kalman filter based algorithm for frequency synchronization over IEEE 1588v2 protocol that outperforms other prior art techniques. The algorithm's performance is evaluated using simulation, yet the network impairments (PDVs) are based on experimentally measured data.

Epidemic Model based Security Analysis of Firefly Clock Synchronization in Wireless Sensor Networks

This paper discusses the security of the clock synchronization algorithm based on the biological example of Asian Fireflies in wireless sensor networks. Huge swarms of these fireflies use the principle of pulse coupled oscillators in order to synchronously emit light flashes to attract mating partners. When applying this algorithm to real sensor networks, the potential threat of hostile flashes may disturb this synchronization. An improved Reachback Firefly Algorithm is implemented in the MAC layer of wireless sensor networks (WSNs), which change coupling strength among oscillators to anti hostile attack in clock synchronization. Its security is analyzed through a Susceptible-InfectiveRecovered epidemic model. Numerical results and simulations are provided for further understanding of the analysis.

Random Broadcast Based Distributed Consensus Clock Synchronization for Mobile Networks

Clock synchronization is a crucial issue for mobile ad hoc networks due to the dynamic and distributed nature of these networks. In this paper, employing affine models for local clocks, a random broadcast based distributed consensus clock synchronization algorithm is proposed. In the absence of transmission delays, we theoretically prove the convergence of the proposed scheme, which is further illustrated by numerical results. In addition, it is concluded from simulations that the proposed scheme is scalable and robust to transmission delays as well as different accuracy requirements.

An evolutionary based topological optimization strategy for consensus based clock synchronization protocols in wireless sensor network

Recently, Consensus based Clock Synchronization (CCS) algorithms have gained much attention in wireless sensor networks due to its simplicity, distributed nature and robustness. But, most of the algorithms are “all node based”, i.e., every node iterates the consensus algorithm to reach the synchronized state. This increases the overall message complexity, imposes congestion and delay in the network and high consumption of energy. In an energy constraint environment, it is desirable that a subset of sensors along with a limited number of neighboring sensors should be selected a priori such that the message complexity will be minimized and energy can be saved. Further, the selection of “subset” sensors must ensure connectivity for consensus propagation to achieve network wide synchronization and the neighboring sensors must be assigned in such a way that the delay must be minimized and balanced for faster consensus convergence. The overall problem is formulated as a Connected Dominating Set based Delay Balanced Topology (CDSDBT) problem and is shown to be NP-complete. To make the problem tractable, a Random Weighted Genetic Algorithm (RWGA) based strategy is proposed to handle the trade-off between the objective functions and to select the Pareto optimal solution (topology). Simulation results show that using the proposed strategy, the performance of some state-of-the-art CCS protocols have been improved significantly over their “all node based” counterpart. A comparative analysis is also carried out with recent and state-of-the-art GA based Minimum Connected Dominating Set (GAMCDS) strategy and GA based Load Balanced Connected Dominating Set (GALBCDS) strategy for the test CCS protocols which are used as topological backbone for other protocols and applications.

Dynamic and Quantitative Method of Analyzing Clock Inconsistency Factors among Distributed Nodes

Designing appropriate clock synchronization schemes and maintaining time consistency among many sensor nodes are crucial for novel distributed applications environments such as Internet of Thing (IoT). However, analyzing the various factors leading to clock inconsistency should be conducted first. The traditional analysis methods are primarily experiential and qualitative, and dynamic disturbances existing among the factors are not considered; moreover, the emerging IoT is rapidly evolving in terms of large-scale feature, service-oriented trend, complexity, and dynamics. Such developments present difficulties in the use of traditional methods in IoT for the analysis of factorial effects on system clocks. To remedy these problems, we propose a novel dynamic evolution model called clock finite state automata (CFSA) using formal methods, exhibiting the overall changing processes of global clock states. We also develop a clock consistency evolution algorithm using CFSA to quantitatively evaluate the influencing factors. The experimental evaluation shows that network delay (41.4% on average) is the greatest impact factor; the frequent entry and exit of the sensor nodes (29.9%) are the second greatest, and the oscillator jitter of computers (11.1%) is the least impact factor. Compared with traditional analysis methods, our method has good feasibility, effectiveness, and novelty. The analysis results can guide the designers of new clock synchronization algorithms for distributed sensor nodes in IoT.

Efficient and Discrete Gradient Synchronization

Gradient clock synchronization is a particular synchronization scheme in distributed systems that requires neighboring nodes to be more tightly synchronized than far away nodes. Up until now, two gradient clock synchronization algorithms have been proposed in the literature which are optimal in terms of worst-case synchronization error among neighboring nodes. In this article, we focus on these algorithms and reveal their drawbacks: The first algorithm requires continuous decision making, which makes it unsuitable for discrete computing systems. Although the second one is a discrete algorithm, it performs computation at every tick of the clock which increases its computational complexity drastically. In addition, both algorithms share the drawback of increasing memory requirements with the network density. Considering these drawbacks, we devise a new discrete gradient clock synchronization algorithm whose communication and computation events are synchronized with clock tick events. The proposed algorithm is lightweight in terms of computational overhead since its computation steps are simple and they are not performed at each clock tick. Moreover, it has constant space complexity that is independent from the network density.

소프트웨어 기반 의사위성 시각동기 기법 성능평가를 위한 오차 요소 분석

This paper proposes three methods of the time synchronization for Pseudolite and GPS and analyzes pseudolite time synchronization error factors for software based performance evaluation on proposed time synchronization methods. Proposed three time synchronization methods are pseudolite time synchronization station construction method, method by using UTC(KRIS) clock source and GPS timing receiver based time synchronization method. Also, we analyze pseudolite time synchronization error factors such as errors of pseudolite clock and reference clock, time delay as clock transmission line, measurement error of time interval counter and error as clock synchronization algorithm to design simulation platform for performance evaluation of pseudolite time synchronization.

A TIME SYNCHRONIZED HYBRID VEHICULAR AD HOC NETWORK OF ROADSIDE SENSORS AND VEHICLES FOR SAFE DRIVING

VANET is a type of ad hoc network in which the moving vehicles act as nodes. There has been lot of research for using VANETs in many applications. One of the main applications is the use of VANETs to improve driving safety. In any safety related applications, the vehicular nodes have to constantly communicate with each other and the roadside equipments. For e.g., the roadside units sense real time information about road conditions, road blocks or animals straying on the road and passes the message to the approaching vehicles. The alert message enables the driver to take timely decisions in preventing accidents or delay. However there are two issues in the above system. One problem is that VANETs are subject to frequent network disconnections especially in low traffic areas. Due to this some events in the road may go undetected while the detected events may not be transmitted on time. The second issue it with maintaining a synchronized clock within the network. Only then the messages communicated between the nodes will be meaningful. To overcome the above issues and make the system more reliable we propose to include roadside wireless sensor nodes along with the vehicular nodes in the network. The roadside wireless sensor nodes can be deployed at fixed distances and communicate wirelessly with the vehicular nodes. They play an important role in keeping the network connected and guarantee message transmission. We also propose a Hybrid Clock Synchronization (HCS) algorithm to synchronize the clocks of all the nodes. This integrated network which is also time synchronized is called the Hybrid VANET (H-VANET). The proposed H-VANET was simulated and tested using GrooveNet. On comparing our system with the conventional VANET implementing RBS for synchronization, it was seen that our model has better performance and reliability.

Research on Spacecraft Attitude Control Simulation Technology Based on Multidisciplinary Integration

The design of spacecraft attitude control is important during the manufacture of spacecraft, and it is need to be validated adequately. To get the digital simulation validation of attitude control system, this paper discussed the spacecraft attitude control simulation system based on STK, Matlab and ADAMS. Based on the simulation frame, the paper analyzed the simulation model inter-clock. and realized the simulation system clock synchronization mechanism and algorithm. Based on the method of clock synchronization, the clock synchronization and logic correctness of message among multi-disciplinary simulation models could be ensured.

Simulation Analysis on the Delay of Clock Synchronization Algorithm Based on Adaptive Fuzzy Control Technology

The knowledge economy is knowledge-based economy, which is a new type of vibrant economic form, and brand marketing is the core of business development. Because our country is being in the economic system in-between period, we need through the development and construction to boost domestic demand, so in the era of knowledge economy, brand building has become particularly important. Through the analysis of the knowledge economy innovation structure, this paper puts forward own brand marketing strategys marketing model, namely combined with the clock information transmission and working mechanism optimization PTP clock node model to construct the rand marketing strategy model. In order to verify the practicability of the model, we have built network simulation structure and made simulation of synchronous networking accuracy test based on FTP data flow. The results show that the model has strong practicability and wide availability. Its idea applied in the research of brand marketing strategy in knowledge economy era has the advantages that are not available in other model.

Stability and Performance Analysis of Clock Synchronization in FlexRay

This paper presents a case study on the performance of a distributed clock synchronization algorithm used in FlexRay, a communication protocol designed to meet the requirements of dependable, fault-tolerant real-time applications. The FlexRay industry consortium drives forward the standardization of a fault-tolerant communication system for advanced automotive applications. In this case study we will analyze two different configurations for typical automotive applications by means of simulation. The focus of the simulation experiments is the assessment of performance and stability of the FlexRay clock synchronization algorithm in the presence of varying clock drift rates. For the analysis we will use SIDERA, a simulation model for time-triggered distributed systems

Analysis and Simulation on Clock Resynchronization in Time Triggered Architecture

An improved clock synchronization algorithm for time triggered architecture has been proposed in this paper. A single reference real time is added in the system, so periodically calibration to real time can be achieved. This algorithm is based on the classical Welch-Lynch[1] fault tolerant clock synchronization process. Systematic clock drift problem has been solved by using the algorithm. Formal analysis is presented, and verification is taken on Matlab/Simulink platform. Simulation result has verified the performance of the algorithm, and the clock difference is bounded as expected.

Network Clock Synchronization Based on the Second-Order Linear Consensus Algorithm

In this paper a distributed algorithm for clock synchronization is proposed. This algorithm is based on an extension of the linear consensus algorithm which is able to synchronize a family of identical double integrators. Since in reality the various clocks may have different drifts, the algorithm needs to be designed in such a way that it works correctly also in case of heterogeneous double integrators. We start by reviewing an unrealistic synchronous implementation of the clock synchronization algorithm, that has been recently proposed in the context of noisy double integrators. The main contribution of this paper is to propose a realistic pseudo-synchronous implementation of this algorithm. This pseudo-synchronous algorithm is shown to be a perturbation of the synchronous one and so, through arguments related to the center manifold theorem, it is proved to be locally convergent under the assumption of absence of process noise, measurement noise and propagation delays. However, through numerical simulations, the performance of this algorithm is evaluated also in the case the communication delays are not negligible, the clock drifts are time-varying and the communication channels are unreliable. Moreover, again through numerical simulations, the strategy we propose in this paper is compared with other fully distributed strategies recently proposed in the literature. While being slightly slower to reach the asymptotic synchronization, our strategy seems to significantly outperform the other strategies in terms of robustness to process and measurement noises and time-varying clock drifts.

One-way Speed of Light Using Interplanetary Tracking Technology

Light transmission in the Sun-Centered Inertial (SCI) frame is considered within a flat space-time metric of relativity theory. It is shown that this metric which is used to derive the Langevin metric that generates the accurate clock synchronization algorithm used in the Global Positioning System (GPS), also predicts one-way light speed anisotropy in an inertial frame that contradicts the principle of light speed constancy. This finding is tested and confirmed in the SCI frame using the range equations employed in the tracking of planets and spacecrafts moving within our solar system. These equations are based on the observation that light travels in the SCI frame at a constant speed c and have been extensively tested and rigorously verified. The results suggest a modification of the Lorentz Transformations that yields new transformations that are consistent with the observed light speed anisotropy and which better accord with the physical world.

A New Design of Clock Synchronization Algorithm

The introduction of Ethernet makes the distributed network system more flexible and efficient, but it also makes nodes which are far apart from each other unable to work in the same time basis due to the long distance. This is not allowed for the high performance requirements of the system synchronization, such as high-precision multiaxis machining system. This paper presents a high-precision network clock synchronization algorithm, namely, optimal PI clock servo, which imposes a PI controller in order to compensate for the clock drift of each network node. Then a simulation platform established by the toolbox TrueTime is used to verify the stability of the algorithm and compare it with the clock synchronization algorithm of EtherCAT. The results show that the new synchronization algorithm has higher synchronization precision and faster convergence rate.

A Comparison of Clock Synchronization in Wireless Sensor Networks

The recent advances in microelectro devices have led the researchers to an area of developing a large distributed system that consist of small, wireless sensor nodes. These sensor nodes are usually equipped with sensors to perceive the environment. Synchronization is an important component of almost all distributed systems and has been studied by many researchers. There are many solutions for the classical networks, but the traditional synchronization techniques are not suitable for sensor networks because they do not consider the partitioning of the network and message delay. Additionally, limited power, computational capacity, and memory of the sensor nodes make the problem more challenging for wireless sensor networks. This paper examines the clock synchronization issues in wireless sensor networks. Energy efficiency, cost, scalability, lifetime, robustness, and precision are the main problems to be considered in design of a synchronization algorithm. There is no one single system that satisfies all these together. A comparison of different clock synchronization algorithms in wireless sensor networks with a main focus on energy efficiency, scalability, and precision properties of them will be provided here.

Improvement of Physical Clock Synchronization Algorithm by Two-Level Synchronization

Synchronization of the clocks is one of the essential thing for many applications in distributed systems. Clock synchronization is very important because they improve the performance and reliability of distributed systems. The main purpose of clock synchronization algorithms is to provide the common time to essential parts of the distributed systems. In this paper the problem considered is synchronization of clock with bounded clock drift and proposing a two level synchronization algorithm which synchronizes the processors local clocks by combining both internal and external clock synchronization.

Distributed Clock Skew and Offset Estimation in Wireless Sensor Networks: Asynchronous Algorithm and Convergence Analysis

In this paper, we propose a fully distributed algorithm for joint clock skew and offset estimation in wireless sensor networks based on belief propagation. In the proposed algorithm, each node can estimate its clock skew and offset in a completely distributed and asynchronous way: some nodes may update their estimates more frequently than others using outdated message from neighboring nodes. In addition, the proposed algorithm is robust to random packet loss. Such algorithm does not require any centralized information processing or coordination, and is scalable with network size. The proposed algorithm represents a unified framework that encompasses both classes of synchronous and asynchronous algorithms for network-wide clock synchronization. It is shown analytically that the proposed asynchronous algorithm converges to the optimal estimates with estimation mean-square-error at each node approaching the centralized Cramer-Rao bound under any network topology. Simulation results further show that {the convergence speed is faster than that corresponding to a synchronous algorithm.