Chuan Sun

Bio: Chuan Sun is an academic researcher from Shanghai Jiao Tong University. The author has contributed to research in topics: Synchronization & Underwater acoustic communication. The author has an hindex of 2, co-authored 3 publications receiving 10 citations.

Multi-hop time synchronization for Underwater Acoustic Networks

Abstract: Time synchronization plays an important role in UANs, which need fine-grained coordination among nodes. Precise time synchronization is also needed for a variety of other coordinate tasks in UANs such as data fusion, TDMA scheduling, localization, power-saving and so on. Recently, time synchronization protocol for point-to-point with high propagation delay has been proposed, while time synchronization for multi-hop UANs is still an open issue. In this paper, we propose a multi-hop time synchronization scheme for Underwater Acoustic Networks (MSUAN). MSUAN includes three stages. In the first stage, we assign each node a level by establishing a path to the reference node. During the second phase, nodes realize synchronization by receiving synchronization packets both from it's parent node and neighboring nodes. The third stage re-synchronizes nodes because the clock may drift away without synchronization for long time. Mathematical analysis of MSUAN's synchronization error shows that the more time-stamps we get, the more accurate skew we will get. At the end, we use OPNET to simulate MSUAN, and the simulation result under pyramid topology shows that even the hop accumulates to 8, for MSUAN, the average offset error is maintained at about 58us and the average skew error is below 2ppm.

Improved multi-hop time synchronization for Underwater Acoustic Networks

Abstract: Time synchronization is important for many distributed applications in Underwater Acoustic Networks (UANs) with large propagation delay, such as precise scheduling, target tracking and energy conservation. In this paper, we prove that the accuracy of time skew estimation increases as the number of overheard packet exchange from other neighboring nodes increases, and propose a light-weighted synchronization algorithm for multi-hop UANS, named as Improved Multi-hop time Synchronization for Underwater Acoustic Networks(IMSUAN). IMSUAN consists of three parts. The first one is to establish a time synchronization tree with the reference node as the root, and assign each node a tree level as low as possible. The second one is to synchronize with the parent node by dedicated three-time handshake and overhear exchange packets from parent and neighboring nodes. The third is to filter the inaccurate time-stamps of the overheard synchronization packets. In the paper, we establish a simulation platform in OPNET to evaluate the performance of IMSUAN. Simulation results show that the performance of extended Tri-message, MSUAN and IMSUAN are the same when no overhearing exists. However, when overhearing is possible in a random topology, the performance of IMSUAN can be 60% better than extended Tri-Message and 40% better than MSUAN.

Modeling and Simulation of Multi-hop Time Synchronization for Underwater Acoustic Networks Based on OPNET

Abstract: Time synchronization is important for Underwater Acoustic Networks (UANs) to achieve precise scheduling, localization and low energy consumption. Although time synchronization for UANs has been studied for years, corresponding simulation has not been researched in detail. UANs simulation faces some special challenges, such as the accurate channel model and the complex state machine of UANs synchronization algorithm. This paper provides details of the implementation of a multi-hop time synchronization scheme for Underwater Acoustic Networks (MSUAN) based on OPNET. By modifying the pipeline stages of Propdel-Stage, Power-Stage and Bkgnoise-Stage, we make our scheme applicable for underwater channel, and design a project to evaluate synchronization performance of MSUAN.

Reverse Flooding: Exploiting Radio Interference for Efficient Propagation Delay Compensation in WSN Clock Synchronization

Abstract: Clock synchronization is a necessary component in modern distributed systems, especially Wireless Sensor Networks (WSNs). Despite the great effort and the numerous improvements, the existing synchronization schemes do not yet address the cancellation of propagation delays. Up to a few years ago, this was not perceived as a problem, because the time-stamping precision was a more limiting factor for the accuracy achievable with a synchronization scheme. However, the recent introduction of efficient flooding schemes based on constructive interference has greatly improved the achievable accuracy, to the point where propagation delays can effectively become the main source of error. In this paper, we propose a method to estimate and compensate for the network propagation delays. Our proposal does not require to maintain a spanning tree of the network, and exploits constructive interference even to transmit packets whose content are slightly different. To show the validity of the approach, we implemented the propagation delay estimator on top of the FLOPSYNC-2 synchronization scheme. Experimental results prove the feasibility of measuring propagation delays using off-the-shelf microcontrollers and radio transceivers, and show how the proposed solution allows to achieve sub-microsecond clock synchronization even for networks where propagation delays are significant.

Reverse Flooding: exploiting radio interference for efficient propagation delay compensation in WSN clock synchronization

Abstract: Clock synchronization is a necessary component in modern distributed systems, especially Wirless Sensor Networks (WSNs). Despite the great effort and the numerous improvements, the existing synchronization schemes do not yet address the cancellation of propagation delays. Up to a few years ago, this was not perceived as a problem, because the time-stamping precision was a more limiting factor for the accuracy achievable with a synchronization scheme. However, the recent introduction of efficient flooding schemes based on constructive interference has greatly improved the achievable accuracy, to the point where propagation delays can effectively become the main source of error. In this paper, we propose a method to estimate and compensate for the network propagation delays. Our proposal does not require to maintain a spanning tree of the network, and exploits constructive interference even to transmit packets whose content are slightly different. To show the validity of the approach, we implemented the propagation delay estimator on top of the FLOPSYNC-2 synchronization scheme. Experimental results prove the feasibility of measuring propagation delays using off-the-shelf microcontrollers and radio transceivers, and show how the proposed solution allows to achieve sub-microsecond clock synchronization even for networks where propagation delays are significant.

Simulation and Performance Analysis of the IEEE1588 PTP with Kalman Filtering in Multi-hop Wireless Sensor Networks

Abstract: As the wireless sensor networks (WSNs) find wider and wider applications, time synchronization has emerged as a key technology to improve network performance and enable WSNs in time-sensitive applications. The recently proposed IEEE 1588 Precision Time Synchronization Protocol (PTP) has shown its capability for the wired Ethernet, but its performance in multi-hop WSNs is still an open question. This is because of the non-negligible asymmetric delays caused by the wireless media access control protocol, low-cost crystal oscillators and time-stamping uncertainties due to limited resources in WSNs nodes. This paper studies the performance of the IEEE 1588 in a multi-hop WSNs by state-space modeling and realistic simulation. Furthermore, the Kalman filter is introduced to improve the offset and skew estimation. The realistic simulator was developed on the OMNeT++ discrete event simulation platform and the simulation results show that the proposed Kalman filtering improves the performance of time synchronization in multi-hop WSNs in terms of offset and skew estimation

Implementation of multi-hop time synchronization on miniature test-bed setup of underwater acoustic sensor network

Abstract: Time synchronization is an important part of any distributed networked embedded system. It is essentially the process of achieving and maintaining common time base among all network nodes of the system. This task is quite challenging for the systems or applications like sensor networks, since these systems are highly resource constrained, yet need to process time-sensitive data in collaborative manner. Though many protocols have been suggested for terrestrial sensor networks (RSB, TPSN, FTSP and LTS) and they perform reasonably well, very few protocols (THSL, Tri-message) have been suggested for the high-latency underwater acoustic networks, since achieving time-synchronization for high-latency networks is even more challenging issue. Here we describe a very simple extension and implementation of Tri-message time synchronization protocol for multi-hop Underwater Acoustic Sensor Network (UASN) on the miniature test-bed setup.

Joint Algorithm for Multi-Hop Localization and Time Synchronization in Underwater Sensors Networks Using Single Anchor

Abstract: In this study, an effort to synchronize and localize the underwater sensors simultaneously in a multi-hop environment is considered. Underwater Sensor Networks (UWSNs) has limited range and connectivity due to propagation delay and limited bandwidth. By using a multi-hop environment, we can extend the range and enhancing the network connectivity for providing more accurate localization and synchronization technique. We have established a connection between sensors point to point directed links and then analytically construct the model for the synchronization as a function of range, delay, and timestamps. Secondly, we have formulated the unconstrained optimization problem for localization by using a gradient technique. The proposed research scheme first synchronizes and then localizes the unknown nodes with known depth by using the single anchor node in a multi-hop scenario. According to the literature survey, this joint effort has never been addressed before; both localization and time synchronization for multi-hop scenarios are addressed separately. The proposed algorithm will also calculate the propagation delay that will be generated during message propagation for both localization and time synchronization. The numerical results are compared with some well-known techniques in terms of the number of nodes, localization error, synchronization error, total processing time up to four hops. Experimental results show that the proposed model outperforms in terms of localization and synchronization accuracy, but since this work has never been done before therefore, we compare our results with the techniques that had separately address this problem having some constraints.