Measurement Time Synchronization Research Articles

A Baseband Wireless VNA for the Characterization of Multiport Distributed Systems

Frequency characterization of spatially large structures has become increasingly required, mostly in the fields of structural health monitoring (SHM) and communication systems based on nonconventional media. When the ports of the system under measurement are far apart, methods based on traditional wired instruments become unattractive for field applications, due to the increased complexity, cost, and signal integrity-related issues. Aiming toward removing the wired connection from the ports of the system under test and the elaboration unit (EU), the main issue to be dealt with is the time synchronization of measurements at the ports. This contribution proposes a solution to such an issue by presenting a Wireless Vector Network Analyzer (WVNA), suitable for the characterization of distributed systems. For this purpose, a wireless synchronization scheme is proposed, which is based on the disciplining of the signal sampling clock from the 1-pulse/s reference signal. The proposed synchronization method reduces clock jitter at different ports at 1.13 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\mu \text{s}$ </tex-math></inline-formula> over a 300-s observation interval. The hardware and software implementation of the system are detailed and experimental results proving its operation are provided.

A Robust State Estimation Framework Considering Measurement Correlations and Imperfect Synchronization

This paper develops a robust power system state estimation framework that accounts for correlations and imperfect time synchronization of the measurements. In this framework, correlations of the measurements obtained from the supervisory control and data acquisition (SCADA) system and the phasor measurement units (PMUs) are separately calculated through the unscented transformation and a vector auto-regression (VAR) model. Specifically, the PMU measurements during the waiting period of two successive SCADA measurement scans are buffered via a VAR model whose parameters are robustly estimated using the projection statistics. The latter take into account their temporal and spatial correlations and provide the needed measurement redundancy to suppress bad data and mitigate imperfect time synchronization. In the case where the SCADA and the PMU measurements do not arrive simultaneously at the control center, yielding imperfect measurement time synchronization, either the forecasted PMU measurements or the prior SCADA measurements from the latest state estimation run are leveraged to restore system observability. Finally, a robust generalized maximum-likelihood (GM)-estimator is extended to integrate the measurement error correlations and to handle the outliers, also known as bad data. Simulation results that stem from a comprehensive comparison with other alternatives under various conditions demonstrate the benefits of the proposed framework.

Development and Evaluation of a WSN for Real-time Structural Health Monitoring and Testing

In this work, a detailed analysis of a low-cost wireless sensor network for structural health monitoring and testing is provided. Differently from other works available in literature, main goals simultaneously pursued in the design of the wireless sensor network are the scalable sampling rate, the time synchronization of measurements and the limited amount of computational and memory resources. In order to minimize power consumption, still offering a real-time behavior, a star topology has been considered. The star center also behaves as a gateway towards most popular wired and wireless communication protocols; thus, cloud computing services can be adopted for analyzing data coming from monitored sites. The proof-of-concept solution physically implemented is capable to collect data from 16 nodes simultaneously with a sampling rate in the 10Hz range and a 1- year lifetime using conventional batteries.

Feedback-Based Clock Synchronization in Wireless Sensor Networks: A Control Theoretic Approach

Most wireless sensor networks (WSNs) employ a sleep clock to enable sensor on-off mode to save energy. Since the sleep clock usually works at a relatively low frequency, it is important to correct the long-term synchronization error caused by instability and nonlinearity. In this paper, the time synchronization issue in a WSN is formulated as a closed-loop control problem. Using the proportional-integral (PI) control principle, we propose a feedback-based synchronization (FBS) scheme to compensate the clock drift caused by both internal perturbation and external disturbance. Synchronization accuracy and FBS dynamics are analyzed in terms of response time and overshoot. We also derive a formula to determine the controller parameters for different synchronization accuracy and response-time requirements. Extensive experiments have been conducted to evaluate this synchronization scheme. The results indicate that FBS is much more robust than the delay measurement time-synchronization (DMTS) protocol in different synchronization durations and sensor node configurations. It is shown that FBS achieves almost the same accuracy as the flooding time-synchronization protocol (FTSP) when synchronization period P is less than 60 s, and it outperforms FTSP when P is longer than 60 s. Furthermore, the experimental results reveal that FBS's response to an external disturbance is faster than that of FTSP in one- or two-hop WSN scenarios. In addition, FBS consumes fewer resources than FTSP.

RLG Trapping 신호처리 기법의 성능개선에 관한 연구

본 논문은 RLG의 신호처리 기법인 Trapping 기법 적용시 각속도와 가속도의 측정시점 불일치에 의해 발생되는 오차를 보상하는 기법에 관한 연구이다. RLG의 대표적인 신호처리 기법인 Stripping 신호처리 기법과 Trapping 신호처리 기법에 대하여 각 기법의 오차요인을 분석하고 이에 대한 모델링을 수행하였다. 그리고 Trapping 기법 적용시 각속도와 가속도 측정시점 불일치에 의해 발생되는 오차에 대한 모델링을 통하여 항법오차에 미치는 영향을 분석하였으며 이를 감소시키기 위한 새로운 신호처리 기법을 제안하고 시뮬레이션 및 시험을 통하여 이에 대한 성능분석 결과를 제시하였다. 성능 분석결과 본 논문에서 제시한 신호처리 기법이 기존의 방법에 비하여 항법오차를 크게 감소시키는 것을 확인할 수 있었다. In this paper, we propose the new method to decrease the navigation error by measurement time synchronization error in RLG Trapping signal processing. There are two methods to eliminate the dither motion in RLG. One is the stripping signal processing method. Another is the trapping signal processing method. This two methods have various error sources in measurement output. We perform the error modelling and analysis for the measurement time synchronization error between angular rate from RLG and acceleration from accelerometer in the trapping signal processing method. And we verify the navigation performance through simulation and experiment. Results of simulation and experiment show that the proposed method is very effective in decreasing the navigation error.