Secure and self-stabilizing clock synchronization in sensor networks

Global synchronization is important for many sensor network applications that require precise mapping of collected sensor data with the time of the events, for example, in tracking and surveillance. It also plays an important role in energy conservation in MAC layer protocols. This paper describes four methods to achieve global synchronization in a sensor network: a node-based approach, a hierarchical cluster-based method, a diffusion-based method, and a fault-tolerant diffusion-based method. The diffusion-based protocol is fully localized. We present two implementations of the diffusion-based protocol for synchronous and asynchronous systems and prove its convergence. Finally, we show that, by imposing some constraints on the sensor network, global clock synchronization can be achieved in the presence of malicious nodes that exhibit Byzantine failures.

SpaceWire fiber-optic Bus is a development of the SpaceWire ECSS-E-50-12C standard. Its transmission rate can reach 2 Gbps. However, it suffers from the problems of imprecise clock synchronization and link blocking in networks. Therefore, we analysis the problems and propose following methods. Firstly, we design clock synchronization algorithms to guarantee the precision of clock synchronization. Furthermore, we design static time distribution scheduling table which takes time-triggered traffic for real-time messages. Through simulation verification, the time precision can be within 58 ns while using clock synchronization algorithm. The use of scheduling table can effectively avoid network conflicts and reduce the delay of data transmission. The improved scheduling method can meet the real-time requirements of SpaceWire fiber-optic Bus systems, and will effectively promote the space application of fiber-optic technology.

In this paper, a consensus-based clock synchronization algorithm is presented and its resilience to frequency displacement estimation errors as well as communication noise is analyzed. The synchronization-enforcing control that is to be applied to clock periods is derived upon re-casting the consensus problem into a convex optimization problem and solving it in a distributed fashion via alternating direction method of multipliers. Conversely, plain consensus is used for reaching agreement on clock values. The proposed algorithm achieves higher convergence rates and equivalent noise resilience with respect to algorithmic solutions based on the only plain average consensus. The superior clock synchronization performance is corroborated via numerical tests.

年图灵奖获得 者 Lamport 教授就指出时钟同步是分布式系统的关键依赖性条件 [4] .随着 21 世纪科学技术的高速发 展, 人们对网络化系统中分散时钟的有效同步提出了更高要求, 这正是因为网络化系统日益渗透到不 同行业

Time synchronization is critical to sensor networks at many layers of its design and enables better duty-cycling of the radio, accurate localization, beamforming and other collaborative signal processing. While there has been significant work in sensor network synchronization, measurement based studies have been restricted to very short-term (few minutes) datasets and have focused on obtaining accurate instantaneous synchronization. Long-term synchronization has typically been handled by periodic re-synchronization schemes with beacon intervals of a few minutes based on the assumption that long-term drift is too hard to model and predict. Thus, none of this work exploits the temporally correlated behavior of the clock drift. Yet, there are incredible energy gains to be achieved from better modeling and prediction of long-term drift that can provide bounds on long-term synchronization error across a sensor network. Better synchronization can lead to significantly lower duty-cycles of the radio, simplify signal processing and can enable an order of magnitude greater lifetime than current techniques.We measure, evaluate and analyze in-depth the long-term behavior of synchronization skew and drift on typical Mica sensor nodes and develop an efficient long-term time synchronization protocol. We use four real time data sets gathered over periods of 12-30 hours in different environmental conditions to study the interplay between three key parameters that influence long-term synchronization - synchronization rate, history of past synchronization beacons and the estimation scheme. We use this measurement-based study to design an online adaptive time-synchronization algorithm that can adapt to changing clock drift and environmental conditions while achieving application-specified precision with very high probability. We find that our algorithm achieves between one and two orders of magnitude improvement in energy efficiency over currently available time-synchronization approaches.

Clock parameters in wireless sensors experience slow changes due to low‐cost construction and environmental conditions. In this paper, a filter‐based distributed protocol, called FBP, is proposed to dynamically achieve clock synchronization for wireless sensor networks. The idea of FBP is derived from a first‐order filter which is robust to environmental noises. The proposed protocol is fully distributed, meaning that each node relies only on its local clock readings and reading announcements from its neighbouring sensor nodes. This will allow the proposed protocol applicable to large sensor networks. By applying FBP, the compensated clock skews can be bounded into a small steady‐state error. Numerical simulations show that the proposed protocol yields better performances in both convergence property and synchronization accuracy.

Motivated by the importance of the clock synchronization in wireless sensor networks (WSNs), this paper proposes a new research approach and model approach, which quantitatively analyzes clock synchronization from the perspective of modern control theory. Two kinds of control strategies are used as examples to analyze the effect of the control strategy on clock synchronization from different perspectives, namely, the single‐step optimal control and the LQG global optimal control. The proposed method establishes a state space model for clock relationship, thus making dimension extension and parameter identification easier, and is robust to changes under the condition of node failures and new nodes. And through the design of different control strategies and performance index functions, the method can satisfy various requirements of the synchronization precision, convergence speed, energy consumption and the computational complexity, and so on. Finally, the simulations show that the synchronization accuracy of the proposed method is higher than that of the existing protocol, and the former convergence speed of the synchronization error is faster.

A PI consensus controller with gossip communication for clock synchronization in wireless sensors networks

Distributed time synchronization is an important part of sensor networks. Due to the limited battery capacity of the sensor nodes, applicable schemes should concern the energy consumption of the networks. To achieve better efficiency, an event-triggered time synchronization scheme (ETTS) is presented, which aims at providing on-demand time synchronization in sensor networks. The scheme is composed of two phases: skew correction phase and estimation of offset phase. When timestamps from different clocks need to be compared, they can be reconciled after the event. ETTS removes the need to predict application requirements in advance, which means that the synchronization energy is only expended after an event has occurred. Compared to traditional schemes, for example, TPSN, simulation results show that ETTS achieves desired energy efficiency when the frequency of event is low.

Clock synchronization is a mechanism for providing a standard time to various devices across a network. This monograph provides a comprehensive overview of recent developments for clock synchronization protocols built on two-way message exchanges. Several clock synchronization protocols are available in the literature for distributing time from high-cost, high-stability clocks (termed masters) to low-cost, low-stability clocks (termed slaves) via an interconnecting network. A number of clock synchronization protocols are built on two-way message exchanges. These include the timing protocol for sensor networks (TPSN), lightweight time synchronization (LTS) protocol, tiny-sync and mini-sync, network time protocol (NTP) and the IEEE 1588 precision time protocol (PTP). The messages traveling between the master and slave nodes can encounter several intermediate switches and routers, accumulating delays at each node. The main factors contributing to the overall delay are the fixed propagation and processing delays at the intermediate nodes along the network path between the master and slave, as well as the stochastic queuing delays at each such node. Popular probability density function (pdf) models for modeling the stochastic delays include Gaussian, exponential, gamma, Weibull, and log-normal. Although these pdf models for the stochastic queuing delays apply to several scenarios, they might not be suitable in specific scenarios such as cellular base station synchronization using mobile backhaul networks and IEEE 1588 in 4G Long Term Evolution (LTE) networks. Further, there could be possibly unknown asymmetries between the fixed path delays in the forward master-to-slave path and the reverse slave-to-master path. These unknown asymmetries could arise from various sources, including delay attacks or incorrect modeling. In this monograph, we present recent developments for clock synchronization protocols built on the two-way message exchange. After an introduction to the basic concepts and mathematical models, the optimum estimators are presented for estimating the clock skew and offset that are applicable for any pdf model of the stochastic delays. Robust algorithms that can also handle unknown path asymmetries are presented next. The focus is on techniques that consider practical, relevant measurement models in order to guide the reader from physical observations to the actual synchronization of the clocks at the slave and master.

We study the fundamental problem of distributed clock synchronization in a basic probabilistic communication setting. We consider a synchronous fully-connected network of $n$ agents, where each agent has a local clock, that is, a counter increasing by one modulo $T$ in each round. The clocks have arbitrary values initially, and they must all indicate the same time eventually. We assume a pull communication model, where in every round each agent receives an $\ell$-bit message from a random agent. We devise several fast synchronization algorithms that use small messages and are self-stabilizing, that is, the complete initial state of each agent (not just its clock value) can be arbitrary. We first provide a surprising algorithm for synchronizing a binary clock ($T=2$) using $1$-bit messages ($\ell = 1$). This is a variant of the voter model and converges in $O(\log n)$ rounds w.h.p., unlike the voter model which needs polynomial time. Next we present an elegant extension of our algorithm that synchronizes a modulo $T=4$ clock, with $\ell = 1$, in $O(\log n)$ rounds. Using these two algorithms, we refine an algorithm of Boczkowski et al.~(SODA'17), that synchronizes a modulo $T$ clock in polylogarithmic time (in $n$ and $T$). The original algorithm uses $\ell=3$ bit messages, and each agent receives messages from two agents per round. Our algorithm reduces the message size to $\ell = 2$, and the number of messages received to one per round, without increasing the running time. Finally, we present two algorithms that simulate our last algorithm achieving $\ell < 2$, without hurting the asymptotic running time. The first algorithm uses a message space of size 3, i.e., $\ell =\log_2(3)$. The second requires a rough upper bound on $\log n$, and uses just 1-bit messages. More generally, our constructions can simulate any self-stabilizing algorithm that requires a shared clock, without increasing the message size and by only increasing the running time by a constant factor and a polylogarithmic term.

This paper addresses the problem of estimating the temporal synchronization in mobile sensors' networks, by using image sequence analysis of their corresponding scene dynamics. Unlike existing methods, which are frequently based on adaptations of techniques originally designed for wired networks with static topologies, or even based on solutions specially designed for ad hoc wireless sensor networks, but that have a high energy consumption and a low scalability regarding the number of sensors, this work proposes a novel approach that reduces the problem of synchronizing a general number $$N$$ N of sensors to the robust estimation of a single line in $${\mathbb {R}}^{N+1}$$ R N + 1 . This line captures all temporal relations between the sensors and can be computed without any prior knowledge of these relations. It is assumed that (1) the network's mobile sensors cross the field of view of a stationary calibrated camera that operates with constant frame rate and (2) the sensors trajectories are estimated with a limited error at a constant sampling rate, both in the world coordinate system and in the camera's image plane. Experimental results with real-world and synthetic scenarios demonstrate that our method can be successfully used to determine the temporal alignment in mobile sensor networks.

Since the announcement of Industry 4.0 (I4.0), the concepts and ideas behind this revolution have been overturning. On the communication side however, all scenarios can be reduced to similar requirements. I4.0 communication requires real-time capability, reliability and interconnectivity of many clients. The realization of these requirements is already made possible by the IEEE standardized TSN technology. A key enabler for the realization of these requirements is a common time understanding of all involved instances, in order to coordinate the complexity arising in such a scenario. For this purpose, clock synchronization is an essential component of TSN. However, there is another essential feature that many I4.0 use cases have in common, which is the spatial dynamics of clients that only wireless communication can provide. This paper presents an approach based on WLAN, which is also able to meet these requirements. The essential points of clock synchronization as used in TSN are analyzed and transferred to WLAN and further concepts and optimizations will be introduced. These concepts are evaluated and analyzed in simulations. The result is a communication concept, which is able to exceed the performance of wired TSN as shown by various KPIs.

Time synchronization is a critical component in many wireless sensor network applications. Although several synchronization protocols have recently been developed, they tend to break down when implemented on networks of heterogeneous devices consisting of different hardware components and operating systems, and communicate over different network media. In this paper, we present a methodology for time synchronization in heterogeneous sensor networks (HSNs). This includes synchronization between mote and PC networks, a communication pathway that is often used in sensor networks, but has received little attention with respect to time synchronization. In addition, we evaluate clock skew compensation methods including linear regression, exponential averaging, and phase-locked loops. Our HSN synchronization methodology has been implemented as a network service and tested on an experimental testbed. We show that a 6-hop heterogeneous sensor network can be synchronized with an accuracy on the order of microseconds.KeywordsSensor NetworkSensor NodeWireless Sensor NetworkTime SynchronizationSynchronization ErrorThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

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.