Motivated by the importance of the clock synchronization in wireless sensor networks (WSNs), due to the packet loss, the synchronization error variance is a random variable and may exceed the designed boundary of the synchronization variance. Based on the clock synchronization state space model, this paper establishes the model of synchronization error variance analysis and design issues. In the analysis issue, assuming sensor nodes exchange clock information in the network with packet loss, we find a minimum clock information packet arrival rate in order to guarantee the synchronization precision at synchronization node. In the design issue, assuming sensor node freely schedules whether to send the clock information, we look for an optimal clock information exchange rate between synchronization node and reference node which offers the optimal tradeoff between energy consumption and synchronization precision at synchronization node. Finally, simulations further verify the validity of clock synchronization analysis and design from the perspective of synchronization error variance.

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Clock Synchronization in Wireless Sensor Networks: Analysis and Design of Error Precision Based on Lossy Networked Control Perspective

Synchronizing time between the sensors of wireless sensor network has vital importance. It helps in maintaining a consistent and reliable frame of time across the network. Two clocks are stated to be synchronized when their frequency source runs with equal rate and their offsets are set identical. Basically, due to the manufacturing difference there is slight variation in their clock oscillator which affects the degree of frequency source and accuracy. Therefore this leads to the problem of synchronizing time between the sensor clocks. To attain time synchronization in a network typical contention-based message passing techniques are used. In this paper two-way message passing scheme is utilized. It proposes a statistical tool based on the maximum probability theory for selecting the reference clock offset for time synchronization protocols. It also proposes a subset selection algorithm to support the proposed statistical tool. The results obtained consist of the selection of most probable estimate for clock offset. The proposed algorithm utilizes the two-way message passing scheme for the exchange of timing messages within the network. The proposed algorithm is compared with the existing algorithms for estimation of clock offset. It was observed that the proposed works gives better results in terms of efficiency i.e. 99.8% efficient.

Time synchronization problem of wireless sensor network using maximum probability theory

This paper discusses the synchronization issues of the unilateral TDoA method applied in ultra-wideband (UWB) localization systems. Focus of the paper is on implementation aspects of the synchronization. At first, the structure of unilateral TDoA method is explained and a method for synchronization is proposed. In the next step, typical implementation challenges of synchronization such as rounding effect, outliers, filtering, packet loss detection and thermal dependencies are discussed and for each problem a solution is provided. A set of experiments have been performed on different clock sources to study their effect on the accuracy of synchronization. The results of the experiments confirm that the voltage and temperature compensated oscillator has the highest accuracy, lowest frequency jitter but longest steady state time among the other variants applied. At the end, the performance of the synchronization solution in real experiments are demonstrated. The results prove that the proposed methods can successfully reduce the negative effects of clock inaccuracies. According to the results, localization accuracy of 3cm in average is achieved when a proper oscillator is used.

Implementation Challenges of Synchronisation of UWB Nodes in TDoA Structures

In the cyber-physical environment, the clock synchronization algorithm is required to have better expansion for network scale. In this paper, a new measurement model of observability under the equivalent transformation of minimum mean square error &#x0028 MMSE &#x0029 is constructed based on basic measurement unit &#x0028 BMU &#x0029 , which can realize the scaled expansion of MMSE measurement. Based on the state updating equation of absolute clock and the decoupled measurement model of MMSE-like equivalence, which is proposed to calculate the positive definite invariant set by using the theoretical-practical Luenberger observer as the synthetical observer, the local noncooperative optimal control problem is built, and the clock synchronization system driven by the ideal state of local clock can reach the exponential convergence for synchronization performance. Different from the problem of general linear system regulators, the state estimation error and state control error are analyzed in the established affine system based on the set-theory-in-control to achieve the quantification of state deviation caused by noise interference. Based on the BMU for isomorphic state map, the synchronization performance of clock states between multiple sets of representative nodes is evaluated, and the scale of evaluated system can be still expanded. After the synchronization is completed, the state of perturbation system remains in the maximum range of measurement accuracy, and the state of nominal system can be stabilized at the ideal state for local clock and realizes the exponential convergence of the clock synchronization system.

Scalable clock synchronization analysis: A symmetric noncooperative output feedback tubes-MPC approach

\n\n In recent research, time synchronization has a great importance in the various\napplication of wireless sensor network. Localization, tracking, message passing using contention-based\nschemes and communication are some of the fields where synchronization between sensor clocks is\nhighly required. Therefore, several algorithms were designed to achieve a rational and reliable frame of\ntime within the wireless sensor network. Patents related to time synchronization in WSN were also analyzed.\n\n\n\n This paper discusses the powerful statistical tool using maximum probability theory for synchronizing\nthe time within the sensor's clock. In this paper, maximum probability theory is applied to\nestimate the best value of clock offset between two sensor clocks. The proposed algorithm is analyzed\nby exchanging timing messages between nodes using two-way message exchange schemes.\n\n\n\nThe proposed algorithm is also implemented along with a Time-Sync Protocol for Sensor Network.\nIt reduces error deviation from 2.32 to 0.064 ms as compared with Time-Sync Protocol for Sensor\nNetwork without proposed works.\n\n\n\n It was observed that for a small network, proposed work gives better and efficient results\nwith Time-Sync Protocol for Sensor Network.\n

A Statistical Tool for Time Synchronization Problem in WSN

Motivated by the importance of the clock synchronization in wireless sensor networks (WSNs), this paper proposes a new research approach and model approach, which quantitatively analyzes clock synchronization from the perspective of modern control theory. Two kinds of control strategies are used as examples to analyze the effect of the control strategy on clock synchronization from different perspectives, namely, the single-step optimal control and the LQG global optimal control. The proposed method establishes a state space model for clock relationship, thus making dimension extension and parameter identification easier, and is robust to changes under the condition of node failures and new nodes. And through the design of different control strategies and performance index functions, the method can satisfy various requirements of the synchronization precision, convergence speed, energy consumption and the computational complexity, and so on. Finally, the simulations show that the synchronization accuracy of the proposed method is higher than that of the existing protocol, and the former convergence speed of the synchronization error is faster.

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Cai Chun-yang

Papers

Clock Synchronization in Wireless Sensor Networks: Analysis and Design of Error Precision Based on Lossy Networked Control Perspective

Clock Synchronization in Wireless Sensor Networks: A New Model and Analysis Approach Based on Networked Control Perspective