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Open AccessArticlePost Publication Peer ReviewVersion 1, Original

Static and Dynamic Evaluation of an UWB Localization System for Industrial Applications (Version 1, Original)

1
Normandie Univ, UNIROUEN, ESIGELEC, IRSEEM, 76000 ROUEN, France
2
SIAtech SAS, 73 RUE MARTAINVILLE 76000 ROUEN, France
*
Authors to whom correspondence should be addressed.
Received: 18 September 2019 / Accepted: 28 October 2019 / Published: 31 October 2019
Peer review status: 3rd round review Read review reports

Reviewer 1 Gabriele S. De Blasio Instituto Universitario de Ciencias y Tecnologías Cibernéticas, Universidad de las Palmas de Gran Canaria, Campus de Tafira, 35017, Las Palmas de Gran Canaria, Spain Reviewer 2 Francisco Molina Martel Fraunhofer Institute of Optronics, System Technologies and Image Exploitation IOSB, Gutleuthausstraße 1, 76275 Ettlingen, Germany, Institute of Astronomical and Physical Geodesy, Technical University of Munich, Arcisstrasse 21, 80333 Munich, Germany Reviewer 3 Dries Van Baelen Department of Information Technology, Ghent University/imec, Technologiepark-Zwijnaarde 15, 9052 Ghent, Belgium
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Version 2
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Version 3
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Version 3, Approved
Published: 3 April 2020
DOI: 10.3390/sci2020023
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Version 2, Revised
Published: 29 February 2020
DOI: 10.3390/sci2010007
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Version 1, Original
Published: 31 October 2019
DOI: 10.3390/sci1030062
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Many applications in the context of Industry 4.0 require precise localization. However, indoor localization remains an open problem, especially in complex environments such as industrial environments. In recent years, we have seen the emergence of Ultra WideBand (UWB) localization systems. The aim of this article is to evaluate the performance of a UWB system to estimate the position of a person moving in an indoor environment. To do so, we implemented an experimental protocol to evaluate the accuracy of the UWB system both statically and dynamically. The UWB system is compared to a ground truth obtained by a motion capture system with a millimetric accuracy. View Full-Text
Keywords: indoor localization; Ultra WideBand (UWB); range estimation indoor localization; Ultra WideBand (UWB); range estimation
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Delamare, M.; Boutteau, R.; Savatier, X.; Iriart, N. Static and Dynamic Evaluation of an UWB Localization System for Industrial Applications. Sci 2019, 1, 62.

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1

Reviewer 1

Sent on 29 Dec 2019 by Gabriele S. De Blasio | Approved with revisions
Instituto Universitario de Ciencias y Tecnologías Cibernéticas, Universidad de las Palmas de Gran Canaria, Campus de Tafira, 35017, Las Palmas de Gran Canaria, Spain

Authors have improved the overall quality of the work with respect to the former submission, but some minor details should be corrected:

- In my opinion, authors must mention in the abstract that a contribution of their work is "...to define if UWB localization sensors can be used for gesture recognition in 3D space", as it is said in the Introduction.

- Subsection 3.4.3. Dynamic Measurement Evaluation and Precision of Mapping: "The third test is to realize a mapping of the inner area (Figure 5a) and outer area (Figure 5a)" ==> please correct according to the captions of those figures.

Response to Reviewer 1

Sent on 04 Aug 2020 by Mickaël Delamare, Remi Boutteau, Xavier Savatier, Nicolas Iriart

This is the ultimate aim of the whole study but the article presented here is a first step that does not fully answer that question. Therefore, it should be deleted from the introduction. We removed "for gesture recognition" so the sentence becomes: to see if UWB can be used to obtain an accurate 3D trajectory.

Fixed

Reviewer 2

Sent on 12 Jan 2020 by Francisco Molina Martel | Approved with revisions
Fraunhofer Institute of Optronics, System Technologies and Image Exploitation IOSB, Gutleuthausstraße 1, 76275 Ettlingen, Germany, Institute of Astronomical and Physical Geodesy, Technical University of Munich, Arcisstrasse 21, 80333 Munich, Germany

The authors resume several localization technologies and methods, while focusing on UWB systems. They show an experimental setup with four to six anchors and one tag. The ground truth position of the UWB devices is measured with a motion capture system. Both measured ground truth positions and the estimated UWB tag positions are expressed in a common reference frame, which transformation is calculated using a Singular Value Decomposition (SVD).

While adequately described up to this point, there seem to be some flaws in the Tests and Evaluation section (3.4).

-Missing explanation of how the estimate of the tag UWB position (Theta_i) is calculated.

-On the Z Anchor Change Test (3.4.4):  Having coplanar anchors can result in a very high (bad) VDOP. Furthermore, depending on how the position of the tag is calculated, there can be two valid solutions: One below the plane formed by the 4 anchors and one above them. Changing the position of the z-axis of the anchors, should reduce the VDOP value and thus the standard deviation error in the z-axis. This is especially true for unbiased distance measurements (mean error near zero). It is easy to calculate the DOP values in order to verify this. Placing one anchor high and one low should provide you a good VDOP value.

-It is not clear to me why the results between static and dynamic measurements should differ, and if the anchor setup is the same, why the bad VDOP does not affect the solution. Is it possible that an error in time synchronization between the UWB data and the ground truth data is increasing the actual UWB localization error?

-The performance with more anchors should in theory be better (again you can calculate DOP values). There is something probable wrong there, for example some NLOS situation or some offset errors in the distance measurement(s).

There are some english grammar errors in the text that should be adressed.

Response to Reviewer 2

Sent on 04 Aug 2020 by Mickaël Delamare, Remi Boutteau, Xavier Savatier, Nicolas Iriart

The objective of the article is to evaluate an existing system, and the location data is provided directly by this system. The algorithm is implemented by Decawave and uses Time of fight calculation. We added the clarification: We use the two-way ranging (TWR) standard algorithm embedded by Decawave.

In theory the results should be better, but the manufacturer's recommendations are to place the anchors in a coplanar configuration. This hypothesis should therefore be used in their algorithms and this explains the results obtained experimentally. We will take into account the remarks on DOP in future works where we will develop our own algorithms.

In the static case we have calculated a mean error while in the dynamic case we calculate an instantaneous error for each point. This is the main reason for the increase of the error in the dynamic case.

We agree that it should be better in theory. However, when we increased the number of anchors, we placed them in a non-coplanar configuration to try to increase the Z-accuracy. Not following the configuration recommended by the manufacturer may explain this slight increase in error. Moreover, the variation is small compared to the announced accuracy of the system and is therefore not significant.

We have tried to correct as many mistakes as possible.

Reviewer 3

Sent on 08 Jan 2020 by Dries Van Baelen | Not approved
Department of Information Technology, Ghent University/imec, Technologiepark-Zwijnaarde 15, 9052 Ghent, Belgium

How are the estimated values from the UWB system obtained? Which algorithm is used on which acquired data to achieve this? Please elaborate.

For comparison, the measurements should also be done in conditions with less multipath, such as an outdoors environment or an anechoic chamber.

In which way has the cart been moved? Was it self-propelled with a remote control, or was it pushed by a person? Did this influence the measurements?

Please clarify whether NLOS scenarios been investigated.

More care should be invested in the text, language-wise. This English is often sloppy and multiple typos exist.

There is a lot of repetition in the content between paragraphs 1 and 2. This can and should be done more concise.

The document needs improvements. Multiple additional questions and suggestions have been added in the attached file.

Response to Reviewer 3

Sent on 04 Aug 2020 by Mickaël Delamare, Remi Boutteau, Xavier Savatier, Nicolas Iriart

The objective of the article is to evaluate an existing system, and the location data is provided directly by this system. The algorithm is implemented by Decawave and uses Time of flight calculation. We added the clarification: We use the two-way ranging (TWR) standard algorithm embedded by Decawave.

This is a good point, but the aim of our work is to evaluate the system in real conditions, not in perfect conditions. This is why we have carried out these tests in conditions representative of an industrial environment.

The cart was being pushed by a person. We first assessed the impact of the person on the accuracy. We found that there was no in uence because the person was far enough away from the UWB tag. We added the clarification: To limit interference, we placed the tag on a wooden cart pushed by a person far enough away from the tag.

For this study, NLOS tests were not performed because it is more difficult to obtain a ground truth since the VICON system also requires LOS conditions. We are working on an evaluation under these conditions on an industrial environment (production line) with NLOS conditions, but this will be the subject of another study.

The have amended the article accordingly.

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