Tag Archives: Clock Synchronization

Simultaneous localization and synchronization (SLAS) for multiple agents, with a nice state of the art including both SLAS for individual and multiple agents

June 30, 2017 10:59 ,

B. Etzlinger, F. Meyer, F. Hlawatsch, A. Springer and H. Wymeersch, “Cooperative Simultaneous Localization and Synchronization in Mobile Agent Networks,” in IEEE Transactions on Signal Processing, vol. 65, no. 14, pp. 3587-3602, July15, 15 2017. DOI: 10.1109/TSP.2017.2691665.

Cooperative localization in agent networks based on interagent time-of-flight measurements is closely related to synchronization. To leverage this relation, we propose a Bayesian factor graph framework for cooperative simultaneous localization and synchronization (CoSLAS). This framework is suited to mobile agents and time-varying local clock parameters. Building on the CoSLAS factor graph, we develop a distributed (decentralized) belief propagation algorithm for CoSLAS in the practically important case of an affine clock model and asymmetric time stamping. Our algorithm is compatible with real-time operation and a time-varying network connectivity. To achieve high accuracy at reduced complexity and communication cost, the algorithm combines particle implementations with parametric message representations and takes advantage of a conditional independence property. Simulation results demonstrate the good performance of the proposed algorithm in a challenging scenario with time-varying network connectivity.

Posted in: Communication networks , Tagged:

Reducing error in time synchronization for multisensor arrangements in aerial applications, with interesting formulae for the clock drift of IMUs

June 19, 2017 12:18 ,

J. Li, L. Jia and G. Liu, “Multisensor Time Synchronization Error Modeling and Compensation Method for Distributed POS,” in IEEE Transactions on Instrumentation and Measurement, vol. 65, no. 11, pp. 2637-2645, Nov. 2016. DOI: 10.1109/TIM.2016.2598020.

An airborne distributed position and orientation system (POS) is high-precision measurement equipment that can accurately provide multinode time-spatial reference for novel remote sensing system as multitask imaging sensors and array antenna synthetic aperture radar. However, it is difficult for multisensor to precisely acquire information at the same moment and result in data fusion error. Thus, the measurement precision is severely degraded. To solve the problem, a multisensor time synchronization error modeling and compensation method is proposed. Based on the component and operation principles of distributed POS, the time synchronization mechanism is analyzed. Multisensor time synchronization error models that include time delay error, random error, and time-varying error are established. A time synchronization error compensation method of the distributed POS is proposed. The experiment results show that the proposed method can accurately calibrate and compensate for the time synchronization error, and improve the measurement precision of the distributed POS. It verified the validity of the proposed method.

Posted in: Real-Time Systems , Tagged:

A novel clock synchronization architecture for networked systems based on forcing the synchronization, with a nice summary of uses of clock synchronization and of existing synchronization architectures

June 8, 2017 10:13 ,

S. Bolognani, R. Carli, E. Lovisari and S. Zampieri, “A Randomized Linear Algorithm for Clock Synchronization in Multi-Agent Systems,” in IEEE Transactions on Automatic Control, vol. 61, no. 7, pp. 1711-1726, July 2016. DOI: 10.1109/TAC.2015.2479136.

A broad family of randomized clock synchronization protocols based on a second order consensus algorithm is proposed. Under mild conditions on the graph connectivity, it is proved that the parameters of the algorithm can always be tuned in such a way that the clock synchronization is achieved in the probabilistic mean-square sense. This family of algorithms contains, as particular cases, several known approaches which range from distributed asynchronous to hierarchical synchronous protocols. This is illustrated by specializing the algorithm for the well-known broadcast and gossip scenarios in wireless communications, and for the standard hierarchical protocol used in the context of wired communications in data networks. In these cases, we show how the feasible range for the algorithm parameters can be explicitly computed. Finally, the performance of this strategy is validated by actual implementation in a real testbed and by numerical simulations.

Posted in: Communication networks , Tagged:

Improvement on the classical regression-based estimation algorithm of the relative clock frequency of two remotely connected clocks for better behaviour under outliers, and a good related works section on the estimation of clock relative frequency

December 22, 2015 17:57 ,

Oka Saputra, K.; Wei-Chung Teng; Tsung-Han Chen, Hough Transform-Based Clock Skew Measurement Over Network, in Instrumentation and Measurement, IEEE Transactions on , vol.64, no.12, pp.3209-3216, Dec. 2015, DOI: 10.1109/TIM.2015.2450293.

The accurate clock skew measurement of remote devices over network connections is crucial to device fingerprinting and other related applications. Current approaches use the lower bound of offsets between the target device and the measurer to estimate clock skew; however, the accuracy of estimation is severely affected when even a few offsets appear below the crowd of offsets. This paper adopted the Hough transform to develop a new method, which searches for the densest part of the whole distribution. This method is effective in filtering out the upper and lower outliers such that the skew values derived from the remaining offsets are stable, even when lower outliers occur, or when the measuring time is not long enough for current approaches to achieve stable results. The experimental evaluation of the proposed method has been conducted in order to compare its performance with that of linear programming algorithm (LPA) and two other approaches. During the five consecutive measurements of 1000 offsets each, skews of the proposed method varied within the range of 0.59 ppm, whereas LPA resulted in the range of 0.89 ppm. Both ranges increased to 1.34 and 63.93 ppm, respectively, when the lower bounds encountered interference from lower outliers.

Notes:

  • They assume there is no NTP running in the background; however, their results seem to come from a conventional TCP/IP network, where it is difficult not to find NTP enabled.
Posted in: Communication networks, Real-Time Systems , Tagged: ,

A new algorithm for clock synchronization in wireless sensor networks with bounded delays, that includes interesting references to surveys

July 27, 2015 10:26 ,

Emanuele Garone, Andrea Gasparri, Francesco Lamonaca, Clock synchronization protocol for wireless sensor networks with bounded communication delays, Automatica, Volume 59, September 2015, Pages 60-72, ISSN 0005-1098, DOI: 10.1016/j.automatica.2015.06.014.

In this paper, we address the clock synchronization problem for wireless sensor networks. In particular, we consider a wireless sensor network where nodes are equipped with a local clock and communicate in order to achieve a common sense of time. The proposed approach consists of two asynchronous consensus algorithms, the first of which synchronizes the clocks frequency and the second of which synchronizes the clocks offset. This work advances the state of the art by providing robustness against bounded communication delays. A theoretical characterization of the algorithm properties is provided. Simulations and experimental results are presented to corroborate the theoretical findings and show the effectiveness of the proposed algorithm.

Posted in: Communication networks, Real-Time Systems , Tagged: , ,

Mathematical model of quartz crystal clocks and Kalman Filter estimation for clock synchronization

January 23, 2015 17:46 ,

Giorgi, G., An Event-Based Kalman Filter for Clock Synchronization, Instrumentation and Measurement, IEEE Transactions on , vol.64, no.2, pp.449,457, Feb. 2015, DOI: 10.1109/TIM.2014.2340631

The distribution of a time reference has long been a significant research topic in measurement and different solutions have been proposed over the years. In this context, the design of servo clocks plays an important role to get better performances by smoothing the influence of noise sources affecting a synchronization system. A servo clock is asked to provide an adaptive and conservative measure of the time distance between the local clock and the time reference by minimizing, if possible, the energy consumption. In this paper, we propose a servo clock based on an efficient implementation of the Kalman filter (KF), called in the following event-based KF that allows to overcome drawbacks of existing KF-based servo clocks with furthermore a significant reduction of the computational cost. An in-depth analysis of the synchronization uncertainty has been reported to completely characterize the proposed solution; and finally, some guidelines on how to correctly initialize the KF are provided.

Posted in: Networked telerobots , Tagged: ,