Lun Shao

Bio: Lun Shao is an academic researcher from Chongqing University of Posts and Telecommunications. The author has contributed to research in topics: Clock synchronization & Wireless sensor network. The author has an hindex of 5, co-authored 6 publications receiving 58 citations.

Estimation of Clock Skew for Time Synchronization Based on Two-Way Message Exchange Mechanism in Industrial Wireless Sensor Networks

Abstract: Time synchronization is indispensable for convenient network management, device monitoring, security, and other fundamental operations in industrial wireless sensor networks (IWSNs) Over the past few decades, a wide variety of highly accurate clock synchronization protocols have been investigated by employing powerful statistical signal processing techniques However, most two-way exchange estimation schemes do not readjust the node's local clock upon every resynchronization before the clock parameters are estimated And it may not be appropriate in IWSNs where time synchronization is consistently required Based on the two-way message exchange mechanism, this paper investigates the clock synchronization schemes of active node and overhearing node with immediate clock readjustment The maximum-likelihood estimators of the clock skew and the corresponding Cramer–Rao lower bounds are derived assuming Gaussian delays Simulation and experimental results validate the performance of the proposed estimators

Estimation of Frequency Offset for Time Synchronization With Immediate Clock Adjustment in Multihop Wireless Sensor Networks

Abstract: The clock synchronization problem for wireless sensor networks (WSNs) is inherently related to parameter estimation. Nowadays, extensive studies on time synchronization have been conducted by adopting statistical signal processing methods. However, most estimation schemes do not readjust clock offset during the process of synchronization parameter estimation, and it would lead to unsatisfactory clock accuracy during synchronization. Thus, the applications of these methods are greatly limited in WSNs. This paper analyzes time synchronization of sensor nodes with immediate clock adjustment at every cycle under multihop scenario, and presents an estimator of clock skew under the Gaussian linear delay model and the corresponding algorithms for finding the estimator in detail. Simulation results verify that the proposed estimator is efficient.

Clock synchronization frequency deviation estimation method applicable to multi-hop wireless sensor network

Abstract: The invention relates to a clock synchronizing frequency deviation estimation method applicable to a multi-hop wireless sensor network, and belongs to the technical field of the wireless sensor network. In the clock synchronizing frequency deviation estimation method, two methods, including, a forwarding method and an unvarnished transmission method, are provided based on demands of a node for synchronization precision: A, in the forwarding method, a node in an intermediate layer initiates synchronous interaction with a node in the next layer at the same time interval after every correction time; and B, in the unvarnished transmission method, the processing time of the node in the intermediate layer is regarded as an additionally introduced fixed time delay and random time delay, and the node directly establishes a synchronization relationship with a root node. According to the estimation method provided by the invention, the node can correct the local clock in each synchronous information interaction process, the synchronization precision error of the node is enabled to be always kept at a relatively low level, and the problem of synchronization precision uncontrollability in a synchronization parameter estimation process is accordingly overcome.

A Global Clock Skew Estimation Scheme for Hierarchical Wireless Sensor Networks

Abstract: Time synchronization is extremely important for wireless sensor networks (WSNs). For large-scale WSNs, hierarchical clock synchronization, which can effectively save energy by reducing communication overhead, has become an attractive approach in practical networks. Based on the hierarchical network, in this paper, we present a global clock skew estimation scheme with immediate clock adjustment. The maximum likelihood estimator and corresponding Cramer–Rao lower bound of the clock skew are derived under the Gaussian delay model, and the simulation results verify that the proposed method is efficient.

OPC UA Message Transmission Method over CoAP

Abstract: OPC Unified Architecture (OPC UA) is a data exchange specification that provides interoperability in industrial automation. With the arrival of Industry 4.0, it is of great importance to implement the exchange of semantic information utilizing OPC UA Transmitting in CoAP. This document provides some transmission methods for message of OPC UA over CoAP.

TMSRS: trust management-based secure routing scheme in industrial wireless sensor network with fog computing

Abstract: Based on fog computer, an industrial wireless sensor network (F-IWSN) is a novel wireless sensor network in the industry. It not only can more efficiently reduce information transmission latency, but also can more beneficially achieve the real-time control and the rapid resource scheduling. However, similar to other distributed networks, it also faces enormous security challenges, especially those internal attacks. The differences from those traditional security schemes are that, one is the trade-off between security, transmission performance and energy consumption to meet the requirements of information convergence and control, the other constructs a multi-dimensional selective forwarding scheme to achieve the real time transmission. In this paper, we propose a Gaussian distribution-based comprehensive trust management system (GDTMS) for F-IWSN. Furthermore, in its trust decision, the grey decision making is introduced to achieve the trade-off between security, transmission performance and energy consumption. The proposed trade-off can effectively select the secure and robust relay node, namely, a trust management-based secure routing scheme. In addition, the proposed schemes are also applicable to defending against bad mouthing attacks. Simulation results show that, the comprehensive performance of GDTMS is better than other similar algorithms. It can effectively prevent the appearance of network holes, and balance the network load, promote the survivability of the network.

Protocol interoperability of OPC UA in service oriented architectures

Abstract: Industrial Internet of Things covers all aspects of networked intelligent manufacturing systems. This means covering a wide array of application domains and user requirements. In such scenarios it is not feasible to define a single protocol for all situations. Hence, a multi-protocol approach is required. OPC UA has strong backing from Industry 4.0 as the protocol for the Industrial Internet of Things. Interoperability of OPC UA has been investigated in the context of migration from legacy and with protocols such as DPWS. Additionally HTTP and CoAP have been investigated as possible transport mediums. However, OPC UA interoperability has not been investigated within a multi-protocol settings and no generic protocol translation exists. This paper proposes an OPC UA translator following the service translator model proposed in the Arrowhead project. Utilizing a mapping to intermediate format, it can be used along side CoAP, HTTP and MQTT protocols.

Rapid-Flooding Time Synchronization for Large-Scale Wireless Sensor Networks

Abstract: Accurate and fast-convergent time synchronization is very important for wireless sensor networks. The flooding time synchronization converges fast, but its transmission delay and by-hop error accumulation seriously reduce the synchronization accuracy. In this article, a rapid-flooding multiple one-way broadcast time-synchronization (RMTS) protocol for large-scale wireless sensor networks is proposed. To minimize the by-hop error accumulation, the RMTS uses maximum likelihood estimations for clock skew estimation and clock offset estimation, and quickly shares the estimations among the networks. As a result, the synchronization error resulting from delays is greatly reduced, while faster convergence and higher-accuracy synchronization is achieved. Extensive experimental results demonstrate that, even over 24-hops networks, the RMTS is able to build accurate synchronization at the third synchronization period, and moreover, the by-hop error accumulation is slower when the network diameter increases.

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

Abstract: 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.