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

A new cutting tool is always well-defined and sharp at the onset of the metal cutting process and gradually losses these properties as the machining process advances. Similarly, at the beginning of the machining process, amplitude of tool vibrations is considerably low and it increases gradually and peaks at the end of the service period of the cutting tool while machining. It is significant to provide a corresponding real-time varying damping to control this chatter, which directly influences accuracy and quality of productivity. This paper aims to review the literature related to the application of smart fluid to control vibration in metal cutting and also focused on the challenges involved in the implementation of active control system during machining process.,Smart dampers, which are used as semi-active and active dampers in metal cutting, were reviewed and the research studies carried out in the field of the magnetorheological (MR) damper were concentrated. In smart materials, MR fluids possess some disadvantages because of their sedimentation of iron particles, leakage and slow response time. To overcome these drawbacks, new MR materials such as MR foam, MR elastomers, MR gels and MR plastomers have been recommended and suggested. This review intents to throw light into available literature which exclusively deals with controlling chatter in metal cutting with the help of MR damping methods.,Using an MR damper popularly known for its semi-active damping characteristics is very adaptable and flexible in controlling chatter by providing damping to real-time amplitudes of tool vibration. In the past, many researchers have attempted to implement MR damper in metal cutting to control vibration and were successful. Various methods with the help of MR fluid are illustrated.,A new cutting tool is always well-defined and sharp at the onset of metal cutting process and gradually losses these properties as the machining process advances. Similarly, at the beginning of the machining process, amplitude of tool vibrations is considerably low and it increases gradually and peaks at the end of service period of cutting tool while machining. Application of MR damper along with the working methodology in metal cutting is presented, challenges met are analyzed and a scope for development is reviewed.,This study provides corresponding real-time varying damping to control tool vibration which directly influences accuracy and quality of productivity. Using an MR damper popularly known for its semi-active damping characteristics is very adaptable and flexible in controlling chatter by providing damping to real-time amplitudes of tool vibration.,This study attempts to implement smart damper in metal cutting to control vibrations.,It is significant to provide corresponding real-time varying damping to control tool vibration which directly influences accuracy and quality of productivity.

Application of smart fluid to control vibration in metal cutting: a review

A Smith predictor-Taylor series-based LQG (STLQG) control to compensate time delay of a semiactive suspension system is newly presented. This control consists of a Taylor series-based LQG (TLQG) control and a Smith predictor based on the TLQG. The TLQG control compensates one half of time delay to decrease magnification from whole time delay compensation. The Smith predictor based on the TLQG compensates the other half to decrease horizontal shift from whole time delay compensation using the Smith predictor-based LQG. Finally, a practical case illustrates advantages of the STLQG control.

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Smith Predictor-Taylor Series-Based LQG Control for Time Delay Compensation of Vehicle Semiactive Suspension

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

Time-delay of magnetorheological elastomer bearing (MRB) can bring structural response menace to bridges. This paper investigates a bridge pier-bearing semi-active-coupling control method based on model predictive control (MPC). The presented strategy takes the structure prediction model to predict the state responses of the controlled plant in a period of future time. Then, the control law can be determined by solving a finite horizon optimization problem. The peak shearing force of pier top, the displacement and the acceleration of beam are chosen as control goals, and the vibration isolation rate is applied to characterize the vibration isolation effect. It is noted that MPC method naturally takes the time-delay and uncertain interference into consideration, and significantly improves the control performance of the system. Finally, the numerical example is described and the seismic response of isolated bridge based on MRB is analyzed. The simulation results show that predictive control can be used to control the time-delay of bridge system in different degrees. The best control performance is at 0.4 s. Even if the time-delay reaches 2 s, it is still good. Therefore, the control method significantly reduces the adverse effects of time-delay on the system, and has a good vibration isolation performance.

Tang Xiao-ming

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

Semi-Active Predictive Control of Isolated Bridge Based on Magnetorheological Elastomer Bearing