Abstract
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.
Highlights
In many sensorics applications, the data gathered by different devices must be fused in order to perform some task as a whole, e.g., localization [1], monitoring/surveillance [2], remote sensing [3], and many more
The data gathered by different devices must be fused in order to perform some task as a whole, e.g., localization [1], monitoring/surveillance [2], remote sensing [3], and many more. Time synchronization among these sensor devices, that are usually connected through non-deterministic media, is a fundamental requirement for this purpose: data from different sources should share a common notion of time, i.e., a unique and consistent reference clock, in order to be correctly merged
As a more detailed example of the use of our statistical analyses for selecting a two-clock synchronization method, let us consider a particular case in robotics taken from the general paradigm of UC2: the CRUMB robot, a mobile system we employ in our research based on a Kobuki platform augmented with a manipulator and other sensors (Figure 3)
Summary
The data gathered by different devices must be fused in order to perform some task as a whole, e.g., localization [1], monitoring/surveillance [2], remote sensing [3], and many more (see for example surveys [4,5]). This statistical analysis has identified which method performs better in each aspect, and which parameters of the scenario, i.e., the particular sensory system, have the strongest influence on these measures Using these results, we contribute with some guidelines to select the best synchronization method for each situation, and illustrate them with a number of practical sensory applications where two-clock synchronization appears. A rigorous, thorough statistical comparison of a number of representative two-clock synchronization methods run in simulated environments synthetically generated from the previous characterization and evaluated with a set of performance measures that cover their applicability, quality of estimation and existence of hard guarantees. We highlight the main conclusions of this work and outline future lines of research
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