Fast distributed multi-hop relative time synchronization protocol and estimators for wireless sensor networks

The challenging problem of time synchronization in wireless sensor networks is considered in this paper, where a new distributed protocol is proposed for both local and multi-hop synchronization. The receiver-to-receiver paradigm is used, which has the advantage of reducing the time-critical-path and thus improving the accuracy compared to common sender-to-receiver protocols. The protocol is fully distributed and does not rely on any fixed reference. The role of the reference is divided amongst all nodes, while timestamp exchange is integrated with synchronization signals (beacons). This enables fast acquisition of timestamps that are used as samples to estimate relative synchronization parameters. An appropriate model is used to derive maximum likelihood estimators (MLE) and the Cramer-Rao lower bounds (CRLB) for both the offset-only, and the joint offset/skew estimation. The model permits to directly estimating relative parameters without using or referring to a reference' clock. The proposed protocol is extended to multi-hop environment, where local synchronization is performed proactively and the resulted estimates are transferred to the intermediate/end-point nodes on-demand, i.e. as soon as a multi-hop communication that needs synchronization is initiated. On-demand synchronization is targeted for multi-hop synchronization instead of the always-on global synchronization model, which avoids periodic and continuous propagation of synchronization signals beyond a single-hop. Extension of local MLE estimators is proposed to derive relative multi-hop estimators. The protocol is compared by simulation to some state-of-the-art protocols, and results show much faster convergence of the proposed protocol. The difference has been on the order of more than twice compared to CS-MNS, more than ten times compared to RBS, and more than twenty times compared to TPSN. Results also show scalability of the proposed protocol concerning the multi-hop synchronization. The error does not exceed few microseconds for as much as 10 hops in R4Syn, while in CS-MNS, and TPSN, it reaches few tens of microseconds. Implementation and tests of the protocol on real sensor motes confirm microsecond level precision even in multi-hop scenarios, and high stability (long lifetime) of the skew/offset model

Structural Damage Detection Robust Against Time Synchronization Errors

Structural Damage Detection based on Wireless Sensor Networks Can Be Affected Significantly by Time Synchronization Errors among Sensors. Precise Time Synchronization of Sensor Nodes Has Been Viewed as Crucial for Addressing This Issue. However, Precise Time Synchronization over a Long Period of Time is Often Impractical in Large Wireless Sensor Networks Due to Two Inherent Challenges. First, Time Synchronization Needs to Be Performed Periodically, Requiring Frequent Wireless Communication among Sensors at Significant Energy Cost. Second, Significant Time Synchronization Errors May Result from Node Failures Which Are Likely to Occur during Long-Term Deployment over Civil Infrastructures. in This Paper, a Damage Detection Approach is Proposed that is Robust Against Time Synchronization Errors in Wireless Sensor Networks. the Paper First Examines the Ways in Which Time Synchronization Errors Distort Identified Mode Shapes, and Then Proposes a Strategy for Reducing Distortion in the Identified Mode Shapes. Modified Values for These Identified Mode Shapes Are Then Used in Conjunction with Flexibility-Based Damage Detection Methods to Localize Damage. This Alternative Approach Relaxes the Need for Frequent Sensor Synchronization and Can Tolerate Significant Time Synchronization Errors Caused by Node Failures. the Proposed Approach is Successfully Demonstrated through Numerical Simulations and Experimental Tests in a Lab. © 2010 IOP Publishing Ltd

A Time Synchronization Protocol for TDMA Based Wireless Sensor Networks

학위논문 (석사)-- 서울대학교 대학원 : 전기공학부, 2013. 8. 이정우.There has been much interest in wireless sensor networks recently, due to their diverse range of possible applications. Although there have been much research in MAC layer protocols for wireless sensor networks, these works are mainly focussed on the power savings and efficiencies of the protocols. For sensor networks which are in-situ and do not require much flexibility, such as a battery management system, energy is not always the most important factor, but rather reliability and scalability (where sensing periods are known). As such, a traditional TDMA protocol can be considered as a good option. Time synchronization in wireless sensor networks have also been considered by many academics, but work related to time synchronization in TDMA networks have been much less popular. In this thesis, a time synchronization protocol for TDMA based wireless sensor networks is proposed, Propagating Chain Time Synchronization. Propagating Chain Time Synchronization is a novel protocol for synchronizing TDMA based networks. The scheme achieves improved synchronization errors compared to traditional beacon synchronization methods, through skew correction estimated from chained two-way message exchanges, which employ piggybacking and overhearing.1 Introduction 1 1.1 Wireless Sensor Networks 1 1.1.1 Challenges in Designing Wireless Sensor Networks 2 1.2 Thesis Motivation 7 1.2.1 Wireless Sensor Networks in Battery Management Systems 7 2 Time Synchronization 10 2.1 Overview 10 2.2 Models of Clock Synchronization 11 2.2.1 Typical Synchronization Errors 13 2.3 Related Work 14 2.3.1 Sender-Receiver Synchronization 14 2.3.2 Receiver-Receiver Synchronization 16 2.3.3 Receiver-Only Synchronization 17 2.3.4 Clock Skew Estimation and Correction 18 2.3.5 Clock Synchronization in TDMA Based Networks 19 3 Propagating Chain Time Synchronization for TDMA Based Wireless Sensor Networks 21 3.1 Overview 21 3.2 System Model 21 3.2.1 Basic Assumptions 22 3.2.2 Topology 22 3.2.3 Chained Synchronization 23 3.2.4 Overhearing and Piggybacking 24 3.2.5 Propagating Skew Correction 28 4 Theoretical Error Analysis 31 4.1 System Models 31 4.2 Node Clock Modelling 32 4.3 TSF 34 4.4 Chained Synchronization 36 4.5 Two-Way Message Exchange Synchronization Error 38 5 Simulation 42 5.1 Simulation Parameters 42 5.2 Simulation Results 46 6 Conclusion 52 Bibliography 54Maste

Time synchronization in wireless sensor networks

Time synchronization is basic requirements for various applications in wireless sensor network, e.g., event detection, speed estimating, environment monitoring, data aggregation, target tracking, scheduling and sensor nodes cooperation. Time synchronization is also helpful to save energy in WSN because it provides the possibility to set nodes into the sleeping mode. In wireless sensor networks all of above applications need that all sensor nodes have a common time reference. However, most existing time synchronization protocols are likely to deteriorate or even be destroyed when the WSNs attack by malicious intruders. The recently developed maximum and minimum consensus based time synchronization protocol (MMTS) is a promising alternative as it does not depend on any reference node or network topology. But MMTS is vulnerable to message manipulation attacks. In this thesis, we focus on how to defend the MMTS protocol in wireless sensor networks under message manipulation attacks. We investigate the impact of message manipulation attacks over MMTS. Then, a Secured Maximum and Minimum Consensus based Time Synchronization (SMMTS) protocol is proposed to detect and invalidate message manipulation attacks

Signal processing techniques for synchronization of wireless sensor networks

Plenary PaperClock synchronization is a critical component in wireless sensor networks, as it provides a common time frame to different nodes. It supports functions such as fusing voice and video data from different sensor nodes, time-based channel sharing, and sleep wake-up scheduling, etc. Early studies on clock synchronization for wireless sensor networks mainly focus on protocol design. However, clock synchronization problem is inherently related to parameter estimation, and recently, studies of clock synchronization from the signal processing viewpoint started to emerge. In this article, a survey of latest advances on clock synchronization is provided by adopting a signal processing viewpoint. We demonstrate that many existing and intuitive clock synchronization protocols can be interpreted by common statistical signal processing methods. Furthermore, the use of advanced signal processing techniques for deriving optimal clock synchronization algorithms under challenging scenarios will be illustrated. © 2010 SPIE.published_or_final_versio

Hybrid Approach for Energy-Aware Synchronization in Sensor Networks

This book chapter discusses a time synchronization scheme for wireless sensor networks that aims to save sensor battery power while maintaining network connectivity for as long as possible

Dynamic Voltage Scaling Techniques for Energy Efficient Synchronized Sensor Network Design

Building energy-efficient systems is one of the principal challenges in wireless sensor networks. Dynamic voltage scaling (DVS), a technique to reduce energy consumption by varying the CPU frequency on the fly, has been widely used in other settings to accomplish this goal. In this paper, we show that changing the CPU frequency can affect timekeeping functionality of some sensor platforms. This phenomenon can cause an unacceptable loss of time synchronization in networks that require tight synchrony over extended periods, thus preventing all existing DVS techniques from being applied. We present a method for reducing energy consumption in sensor networks via DVS, while minimizing the impact of CPU frequency switching on time synchronization. The system is implemented and evaluated on a network of 11 Imote2 sensors mounted on a truss bridge and running a high-fidelity continuous structural health monitoring application. Experimental measurements confirm that the algorithm significantly reduces network energy consumption over the same network that does not use DVS, while requiring significantly fewer re-synchronization actions than a classic DVS algorithm.unpublishedis peer reviewe

Precision timing in TDMA - based Wireless Sensor Network through IEEE 1588 standard

This paper proposes an energy-efficient time synchronization scheme for Wireless Sensor Networks(WSNs) based on the IEEE 1588 standard. Although a number of methods have been studied for time synchronization of WSNs, some applications require high precision time synchronization with very low power consumption. This paper presents a reduced implementation of IEEE 1588 precision time protocol (PTP) for WSNs. Within the proposed synchronization approach, a sensor node is synchronized using the timing message generated by a master node synchronized with GPS. This paper also presents experiments to evaluate the performance of the precision time synchronization of a slave-master pair of sensor nodes.Peer ReviewedPostprint (published version