Fernández-Madrigal Juan-Antonio, Navarro Angeles, Asenjo Rafael, Cruz-Martín Ana
Department of System Engineering and Automation, University of Málaga, 29016 Málaga, Spain.
Department of Computer Architecture, University of Málaga, 29016 Málaga, Spain.
Sensors (Basel). 2020 Aug 26;20(17):4808. doi: 10.3390/s20174808.
Time synchronization among sensor devices connected through non-deterministic media is a fundamental requirement for sensor fusion and other distributed tasks that need a common time reference. In many of the time synchronization methods existing in literature, the estimation of the relation between pairs of clocks is a core concept; moreover, in applications that do not have general connectivity among its devices but a simple pairwise topology, such as embedded systems, mobile robots or home automation, two-clock synchronization is actually the basic form of the time estimation problem. In these kinds of applications, especially for critical ones, not only the quality of the estimation of the relation between two clocks is important, but also the bounds the methods provide for the estimated values, and their computational effort (since many are small systems). In this paper, we characterize, with a thorough parameterization, the possible scenarios where two-clock synchronization is to be solved, and then conduct a rigorous statistical study of both scenarios and methods. The study is based on exhaustive simulations run in a super-computer. Our aim is to provide a sound basis to select the best clock synchronization algorithm depending on the application requirements and characteristics, and also to deduce which ones of these characteristics are most relevant, in general, when solving the problem. For our comparisons we have considered several representative methods for clock synchronization according to a novel taxonomy that we also propose in the paper, and in particular, a few geometrical ones that have special desirable characteristics for the two-clock problem. We illustrate the method selection procedure with practical use-cases of sensory systems where two-clock synchronization is essential.
对于通过非确定性介质连接的传感器设备而言，时间同步是传感器融合以及其他需要公共时间基准的分布式任务的一项基本要求。在文献中现有的许多时间同步方法里，时钟对之间关系的估计是一个核心概念；此外，在其设备之间没有一般连通性而是具有简单成对拓扑结构的应用中，比如嵌入式系统、移动机器人或家庭自动化，双时钟同步实际上是时间估计问题的基本形式。在这类应用中，尤其是对于关键应用，不仅两个时钟之间关系估计的质量很重要，而且方法为估计值提供的界限以及它们的计算量（因为许多是小型系统）也很重要。在本文中，我们通过全面的参数化来描述需要解决双时钟同步的可能场景，然后对场景和方法进行严格的统计研究。该研究基于在超级计算机上运行的详尽模拟。我们的目标是根据应用需求和特性提供一个合理的基础来选择最佳的时钟同步算法，并且推断在解决该问题时一般哪些特性是最相关的。为了进行比较，我们根据本文中还提出的一种新颖分类法考虑了几种具有代表性的时钟同步方法，特别是一些对于双时钟问题具有特殊理想特性的几何方法。我们用双时钟同步至关重要的传感系统实际用例来说明方法选择过程。
