On the practical implementation of propagation delay and clock skew compensated high-precision time synchronization schemes with resource-constrained sensor nodes in multi-hop wireless sensor networks

In wireless sensor networks (WSNs), implementing a high-precision time synchronization scheme on resource-constrained sensor nodes is a major challenge. Our investigation of the practical implementation on a real testbed of the state-of-the-art WSN time synchronization scheme based on the asynchronous source clock frequency recovery and the reverse two-way message exchange, which can compensate for both propagation delay and clock skew for higher precision, reveals that its performance on battery-powered, low-complexity sensor nodes is not up to that predicted from simulation experiments due to the limited precision floating-point arithmetic of sensor nodes. Noting the lower computational capability of typical sensor nodes and its impact on time synchronization, we propose an asymmetric high-precision time synchronization scheme that can provide high-precision time synchronization even with resource-constrained sensor nodes in multi-hop WSNs. In the proposed scheme, all synchronization-related computations are done at the head node equipped with abundant computing and power resources, while the sensor nodes are responsible for timestamping only. Experimental results with a testbed based on TelosB motes running TinyOS demonstrate that the proposed time synchronization scheme can avoid time synchronization errors resulting from the single-precision floating-point arithmetic of the resource-constrained sensor nodes and achieve microsecond-level time synchronization accuracy in multi-hop WSNs.Comment: 20 pages, 10 figure

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.Comment: 12 pages, 16 figure

On the Practical Implementation of Propagation Delay and Clock Skew Compensated High-Precision Time Synchronization Schemes with Resource-Constrained Sensor Nodes in Multi-Hop Wireless Sensor Networks

In wireless sensor networks (WSNs), implementing a high-precision time synchronization scheme on resource-constrained sensor nodes is a major challenge. Our investigation of the practical implementation on a real testbed of the state-of-the-art WSN time synchronization scheme based on the asynchronous source clock frequency recovery and the reverse two-way message exchange, which can compensate for both propagation delay and clock skew for higher precision, reveals that its performance on battery-powered, low-complexity sensor nodes is not up to that predicted from simulation experiments due to the limited precision floating-point arithmetic of sensor nodes. Noting the lower computational capability of typical sensor nodes and its impact on time synchronization, we propose an asymmetric high-precision time synchronization scheme that can provide high-precision time synchronization even with resource-constrained sensor nodes in multi-hop WSNs. In the proposed scheme, all synchronization-related computations are done at the head node equipped with abundant computing and power resources, while the sensor nodes are responsible for timestamping only. Experimental results with a testbed based on TelosB motes running TinyOS demonstrate that the proposed time synchronization scheme can avoid time synchronization errors resulting from the single-precision floating-point arithmetic of the resource-constrained sensor nodes and achieve microsecond-level time synchronization accuracy in multi-hop WSNs

Time Synchronization and Its Applications in Wireless Sensor Networks

Time synchronization is an essential component of wireless sensor networks (WSNs) that play a key role in the thriving Internet of Things (IoT), supporting IoT applications from large-scale monitoring & event detection to collaborative interactions. The large-scale applications based on resource-constrained sensor nodes promote the development of WSN time synchronization towards the three major aspects of lower energy consumption, lower computational complexity, and higher multi-hop time synchronization accuracy. It is these three aspects that we focus on in our contributions to the development of WSN time synchronization, which are presented in this thesis together with their applications to optimal bundling and node identification

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 Survey of Clock Synchronization Over Packet-Switched Networks

Clock synchronization is a prerequisite for the realization of emerging applications in various domains such as industrial automation and the intelligent power grid. This paper surveys the standardized protocols and technologies for providing synchronization of devices connected by packet-switched networks. A review of synchronization impairments and the state-of-the-art mechanisms to improve the synchronization accuracy is then presented. Providing microsecond to sub-microsecond synchronization accuracy under the presence of asymmetric delays in a cost-effective manner is a challenging problem, and still an open issue in many application scenarios. Further, security is of significant importance for systems where timing is critical. The security threats and solutions to protect exchanged synchronization messages are also discussed

Outlier Identification in Sensor Network Clock Synchronization

We first present a survey of clock synchronization research that describes the problem and various challenges to implementing an efficient protocol for clock synchronization in sensor networks. We then present several changes to an existing protocol that we believe will enhance the accuracy. These changes are implemented in a software simulation and a large experiment is conducted that involves several runs of the simulation using various parameters for error bounds and outlier detection. We present our results and show that modifying the outlier detection range used by many existing algorithms can improve network clock accuracy and provide a stabilized average error