Energy-efficient Time Synchronization Research Articles

EcoSync: An Energy-Efficient Clock Discipline Data Synchronization in Wi-Fi IoMT Systems

The growth of the Internet of Medical Things (IoMT) and healthcare data analytics allows wearable Wireless Body Area Networks (WBANs) and ambient sensors to collect the large quantities of physiological signals necessary for better patient diagnostics and treatments. Artificial intelligence and machine learning algorithms frequently require precisely synchronized signals from multiple sensors, which in turn require time-consuming and energy-inefficient synchronization methods with constant wireless network connectivity. We propose ecoSync, a highly energy-efficient time synchronization algorithm for Wi-Fi devices in IoMT applications. We demonstrated that ecoSync can correct the time difference error to ±42 µs with an hour between resynchronizations, using only 658 millijoules of energy. This is an 87% improvement in time difference error and a 99.93% reduction in energy usage over using TSF for synchronization alone over a 1 h period. Wireless synchronization of sensors allows placement of physiological sensors on objects of everyday use (Smart Stuff), which in turn allows seamless collection of physiological status data every time we interact with smart objects in an IoMT environment.

New timestamp mark–based energy efficient time synchronization method for wireless sensor networks

Aimed at the demands of wireless sensor networks for high energy-efficient time synchronization, the reduction of synchronization energy consumption is studied from the aspects of both accurate timestamps marking and synchronous information transmission mechanism. First, the network is divided into several parent–child groups periodically. The group-wise pair selection algorithm is used to select the network’s pairwise synchronization nodes, and chain-type network topology is thus generated. Second, the sequential multi-hop synchronization algorithm is introduced to realize the synchronization information exchange among pairwise synchronization nodes. The overhearing synchronization (OS) nodes obtain the synchronization information packet based on a one-way overhearing mechanism. Moreover, the accurate acquisition of the synchronization ack packet’s timestamp is carried out through the use of receiving-time-plus-fixed-delay mode. Third, the joint maximum likelihood method and the minimum variance unbiased estimation method are used to estimate the clock offsets of pairwise synchronization nodes and overhearing nodes to the parent nodes, respectively, based on which the child nodes adjust their local virtual clocks. Periodically, the pairwise synchronization nodes initiate the network’s time synchronization, estimate, and broadcast the relative offset to the gateway node, assisting the upper layer child nodes in synchronizing to the gateway node. Simulation results show that the proposed method not only achieves the millisecond level synchronization accuracy but also reduces the synchronization energy consumption and thus improves the network lifetime.

Improving Multi-Hop Time Synchronization Performance in Wireless Sensor Networks Based on Packet-Relaying Gateways With Per-Hop Delay Compensation

Based on the reverse asymmetric time synchronization framework, we have proposed several schemes with a major focus on the energy efficiency and computational complexity of a large number of battery-powered, low-cost sensor nodes in wireless sensor networks (WSNs). To address the cumulative end-to-end synchronization error, we have also introduced an idea of compensating for the processing delays at packet-relaying gateways as an energy-efficient way of multi-hop extension of WSN time synchronization schemes. In this paper, we present a comprehensive analysis of the multi-hop extension of WSN time synchronization schemes based on packet-relaying gateways with the per-hop delay compensation and the results of extensive experiments for the energy-efficient time synchronization schemes based on the reverse asymmetric time synchronization framework together with the flooding time synchronization protocol as a representative of existing schemes. Experimental results based on a real testbed demonstrate that the multi-hop extension based on packet-relaying gateways with the per-hop delay compensation greatly improves the performance of time synchronization of all the schemes considered compared to the multi-hop extension based on the conventional time-translating gateways.

Per-Hop Delay Compensation in Time Synchronization for Multi-Hop Wireless Sensor Networks Based on Packet-Relaying Gateways

Multi-hop time synchronization is essential to large-scale deployment of IoT and wireless sensor networks. Its performance, however, is affected by the processing delays at intermediate gateway nodes, which cause cumulative synchronization error. To address this, we propose a per-hop delay compensation scheme as a simple and effective multi-hop extension option based on packet-relaying gateway nodes for energy-efficient time synchronization in wireless sensor networks. Experimental results on a real testbed demonstrate that the per-hop delay compensation scheme significantly improves the multi-hop time synchronization performance when applied to the state-of-the-art beaconless asymmetric energy-efficient time synchronization scheme and the conventional flooding time synchronization protocol.

A Beaconless Asymmetric Energy-Efficient Time Synchronization Scheme for Resource-Constrained Multi-Hop Wireless Sensor Networks

The ever-increasing number of WSN deployments based on a large number of battery-powered, low-cost sensor nodes, which are limited in their computing and power resources, puts the focus of WSN time synchronization research on three major aspects, i.e., accuracy, energy consumption and computational complexity. In the literature, the latter two aspects have not received much attention compared to the accuracy of WSN time synchronization. Especially in multi-hop WSNs, intermediate gateway nodes are overloaded with tasks for not only relaying messages but also a variety of computations for their offspring nodes as well as themselves. Therefore, not only minimizing the energy consumption but also lowering the computational complexity while maintaining the synchronization accuracy is crucial to the design of time synchronization schemes for resource-constrained sensor nodes. In this paper, focusing on the three aspects of WSN time synchronization, we introduce a framework of reverse asymmetric time synchronization for resource-constrained multi-hop WSNs and propose a beaconless energy-efficient time synchronization scheme based on reverse one-way message dissemination. Experimental results with a WSN testbed based on TelosB motes running TinyOS demonstrate that the proposed scheme conserves up to 95% energy consumption compared to the flooding time synchronization protocol while achieving microsecond-level synchronization accuracy.

A Robust Time Synchronization Scheme for Industrial Internet of Things

Energy-efficient and robust-time synchronization is crucial for industrial Internet of things (IIoT). Some energy-efficient time synchronization schemes that achieve high accuracy have been proposed recently. However, some unsynchronized nodes namely isolated nodes exist in the schemes. To deal with the problem, this paper presents R-Sync, a robust time synchronization scheme for IIoT. We use a pulling timer to pull isolated nodes into synchronized networks whose initial value is set according to level of spanning tree. Then, another timer is set up to select backbone node and its initial value is related to the distance to parent node. Moreover, we do experiments based on simulation tool NS-2 and testbed based on wireless hardware nodes. The experimental results show that our approach makes all the nodes get synchronized and gets the better performance in terms of accuracy and energy consumption, compared with three existing time synchronization algorithms TPSN, GPA, STETS.

On Detection of Sybil Attack in Large-Scale VANETs Using Spider-Monkey Technique

Sybil security threat in vehicular ad hoc networks (VANETs) has attracted much attention in recent times. The attacker introduces malicious nodes with multiple identities. As the roadside unit fails to synchronize its clock with legitimate vehicles, unintended vehicles are identified, and therefore erroneous messages will be sent to them. This paper proposes a novel biologically inspired spider-monkey time synchronization technique for large-scale VANETs to boost packet delivery time synchronization at minimized energy consumption. The proposed technique is based on the metaheuristic stimulated framework approach by the natural spider-monkey behavior. An artificial spider-monkey technique is used to examine the Sybil attacking strategies on VANETs to predict the number of vehicular collisions in a densely deployed challenge zone. Furthermore, this paper proposes the pseudocode algorithm randomly distributed for energy-efficient time synchronization in two-way packet delivery scenarios to evaluate the clock offset and the propagation delay in transmitting the packet beacon message to destination vehicles correctly. The performances of the proposed technique are compared with existing protocols. It performs better over long transmission distances for the detection of Sybil in dynamic VANETs' system in terms of measurement precision, intrusion detection rate, and energy efficiency.

Efficient, Single Hop Time Synchronization Protocol for Randomly Connected WSNs

This paper develops a fast, accurate and energy-efficient time synchronization protocol in wireless sensor networks that operate in harsh environments. The suggested protocol concept is based on an electrical physical metaphor. The protocol treats the nodes times as the states of an unconditionally stable discrete dynamical system that uses only single hop communication. The system can terminate at a low number of message exchanges while still in the transient phase. It can yield high quality time estimates with accuracies that are fractions of the clock at which node communication takes place. The synchronizer is developed and its capabilities are demonstrated by simulation and physical experiments on the MICA-Z wireless sensor network

Energy Efficient Optimized Protocols for Wireless Sensor Network

We consider energy-efficient time synchronization in a wireless sensor network where a head node is equipped with a powerful processor and supplied power from outlet, and sensor nodes are limited in processing and battery-powered. It is this asymmetry that our study focuses on; unlike most existing schemes to save the power of all network nodes, we concentrate on battery-powered sensor nodes in minimizing energy consumption for time synchronization. We present a time synchronization scheme based on asynchronous source clock frequency recovery and reverse two-way message exchanges combined with measurement data report messages, where we minimize the number of message transmissions from sensor nodes while achieving sub microsecond time synchronization accuracy through propagation delay compensation. We carry out the performance analysis of the estimation of both measurement time and clock frequency with lower bounds for the latter. Simulation results verify that the proposed scheme outperforms the schemes based on conventional two-way message exchanges with and without clock frequency recovery in terms of the accuracy of measurement time estimation and the number of message transmissions and receptions at sensor nodes as an indirect measure of energy efficiency.

Energy-Efficient Time Synchronization Based on Asynchronous Source Clock Frequency Recovery and Reverse Two-Way Message Exchanges in Wireless Sensor Networks

We consider energy-efficient time synchronization in a wireless sensor network where a head node (i.e., a gateway between wired and wireless networks and a center of data fusion) is equipped with a powerful processor and supplied power from outlet, and sensor nodes (i.e., nodes measuring data and connected only through wireless channels) are limited in processing and battery-powered. It is this asymmetry that our study focuses on; unlike most existing schemes to save the power of all network nodes, we concentrate on battery-powered sensor nodes in minimizing energy consumption for time synchronization. We present a time synchronization scheme based on asynchronous source clock frequency recovery and reverse two-way message exchanges combined with measurement data report messages, where we minimize the number of message transmissions from sensor nodes, and carry out the performance analysis of the estimation of both measurement time and clock frequency with lower bounds for the latter. Simulation results verify that the proposed scheme outperforms the schemes based on conventional two-way message exchanges with and without clock frequency recovery in terms of the accuracy of measurement time estimation and the number of message transmissions and receptions at sensor nodes as an indirect measure of energy efficiency.

STETS: A novel energy-efficient time synchronization scheme based on embedded networking devices

Time synchronization is essential in the implementation of large-scale Wireless Sensor Networks (WSNs). However, many approaches of time synchronization suffer from high communication overheads when pursuing high accuracy. Such overheads cause significant shrinkage of the lifetime of WSNs since frequent data communications consume much energy which is extremely limited in each sensor node. The energy consumption increases rapidly with the growth of WSNs density. In this paper, we present a Spanning Tree-based Energy-efficient Time Synchronization (STETS) which effectively incorporates two time synchronization schemes: Sender to Receiver Protocol (SRP) and Receiver to Receiver Protocol (RRP). It reduces the communication overheads while still maintaining high accuracy. In our approach, backbone sensor nodes form a spanning tree and they get synchronized layer by layer through SRP. Other nodes get synchronized through RRP by only listening to the communication between backbone sensor nodes. We evaluated the performances by simulating our approach on NS-2 and implementing it on embedded networking devices STM32W108 with simple MAC protocol stack. The experiment results show that our approach is efficient in both energy consumption and accuracy of time synchronization. Especially, it can get better performances in densely connected WSNs.

Infrastructures for Secure Data Aggregation, use of Wireless Sensor Networks for Industrial Monitoring and its Application in Networks Monitor Transportation

With the help of this paper we come to know that need for accurate time synchronization in the order of 0.6 − 9 μs every few minutes is necessary for data collection and analysis. Two-stage energy-efficient time synchronization is proposed in this paper. Firstly, the network is divided into clusters and a head node is elected using Low-Energy Adaptive Clustering Hierarchy based algorithm. Later, multiple packets of different lengths are used to estimate the delay between the elected head and the entire network hierarchically at different levels Wireless sensor networks (WSNs) have not only become an attractive solution for low power implementations and embedded systems but also for the Power transmission and distribution. Research is ongoing to develop an innovative power source to facilitate the running of advanced sensing and communications technology in hazardous areas using WIFI to Power Sensors, Energy Harvesting using novel MEMS Electromagnetic Transducers, Powering sensors with Pipeline heat.

Cluster-based and energy-efficient hierarchical time synchronization algorithm for multi-hop wireless sensor network

Concerning the problem that typical time synchronous algorithms used in multi-hop Wireless Sensor Network(WSN) mainly focus on increasing the network synchronization precision,but ignore such issues as the network energy,path hop and error accumulation,a cluster-based and energy-efficient hierarchical time synchronization algorithm was proposed based on a cluster hierarchical network structure.In this algorithm,a cluster node was selected to take a two-way synchronization with the cluster head,and its neighbor nodes achieved bidirectional synchronization indirectly through the passive monitoring mode.In such a way,the number of the packet's transmission was reduced while the digital signature pattern ensured the safety of transmission.In addition,the cycle update coefficient of synchronous group delay was quoted to further reduce the consumption of synchronization packets.The simulation results show that the algorithm reduces the energy consumption and prolongs the network life time,therefore this algorithm has certain practicability.

무선 센서네트워크에서의 시각동기를 위한 실시간 클럭 스큐 추정

Time synchronization is crucial in wireless sensor networks such as Wireless USB and WBAN for diverse purposes from the MAC to the application layer. This paper proposes online clock skew estimators to achieve energy-efficient time synchronization for wireless sensor networks. By using recursive least squares estimators, we not only reduce the amount of data which should be stored locally in a table at each sensor node, but also allow offset and skew compensations to be processed simultaneously. Our skew estimators can be easily integrated with traditional offset compensation schemes. The results of simulation and experiment show that the accuracy of time synchronization can be greatly improved through our skew compensation algorithm.

웨어러블 컴퓨터 시스템을 위한 WUSB over WBAN 프로토콜의 에너지 효율적인 시간 동기 기술

본 논문에서는 웨어러블 컴퓨터 시스템을 위한 WUSB over WBAN 프로토콜에서 요구되는 에너지 효율적인 시간동기 알고리즘을 제안한다. 이를 위해 전력 소모를 최소화 하면서 정밀한 시간 동기가 이루어지는 알고리즘을 제안한다. 본 논문에서 제안하는 시간 동기 알고리즘은 웨어러블 컴퓨터의 주변 장치를 구성하는 WUSB over WBAN 프로토콜 기반 센서 노드에서, 계층적인 구조를 구성하고 Time Stamp 패킷을 송수신하는 방식으로 빠르게 실행되어 전력소모를 최소화한다. In this Paper, we propose an Energy Efficient Time Synchronization technique based on WUSB (Wireless USB) over WBAN (Wireless Body Area Networks) protocol required for Wearable Computer systems. For this purpose, the proposed Time Synchronization algorithm minimizes power consumption and estimates time information with accuracy. It is executed on the basis of WUSB over WBAN protocol at each sensor node comprising peripherals of a wearable computer system. It minimizes power consumption by exchanging time stamp packets and forming a hierarchical structure.

SAEP: Secure, Accurate and Energy-Efficient Time Synchronization Protocol in WSNs

Existing time synchronization schemes in sensor networks were all developed to be energy-efficient, precise, and robust, but none of them were developed with security in mind. We have developed a secure, accurate and energy-efficient time synchronization protocol (SAEP). SAEP achieves accurate time synchronization service with significantly reducing the number of message exchanges. Also, it safeguards against Byzantine failure, in which nodes drop, modify, or delay time information in an attempt to disrupt the time synchronization service in multi-hop networks. SAEP takes a distributed approach where each sensor independently makes decisions based only on the information collected from multiple adjacent nodes, thus achieving a high level of resistance to various attacks while minimizing the energy cost. We investigate the misbehavior of a maliciously compromised node and analyze how SAEP can combat these attacks. In our experiment SAEP outperforms the existing time synchronization protocol in accuracy, energy consumption and it is even resilient to multiple capture attacks.

Energy-efficient and rapid time synchronization for wireless sensor networks

To synchronize clocks of nodes with low energy use and in short time in WSNs, this paper focuses on the reduction of the number of transmissions and on the message forwarding amongst sensor nodes. And we present a method, which is called EETS (Energy-Efficient Time Synchronization). The EETS method decreases the number of messages for the time synchronization and the messages could be rapidly passed through the network. Additionally, the WSNs are finally able to save energy. Through the performance comparisons of existing algorithms and the EETS with a network simulator and analysis, we show the performance evaluations of the EETS and the improved energy efficiency of the proposed algorithm for the Time Synchronization in the WSNs.

EETS: AN ENERGY-EFFICIENT TIME SYNCHRONIZATION ALGORITHM FOR WIRELESS SENSOR NETWORKS

High precision and real-time communications are increasingly becoming important in Wireless Sensor Networks as such networks are required to support highly time-critical applications. The sensor nodes need to communicate data to each other at the correct time. However, the clocks of sensor nodes run at different speed and very often drift from the real time value. In this paper we are proposing EETS, an energy efficient time synchronization algorithm. Energy efficiency is achieved by synchronizing only nodes that are communicating with each other when an event occurs. EETS is performed in two phases namely the Level discovery phase and the Synchronization phase. A simulation study has been carried out and the results shows that EETS is more energy efficient than other existing algorithms. Particularly, EETS has been compared to Network Wide Time Synchronization (NWTS) which is a widely used algorithm for time synchronization in WSN. Simulation results have shown that NWTS uses about 10% more energy than EETS. NWTS synchronizes 90% of the network nodes but reduces the lifetime of the network considerably while EETS synchronizes only nodes that need to be synchronized and thus saving energy. Keywords: Time Synchronization, Energy Efficiency, Sensor Networks, Clock Drift, Network Delay