Simple Ultrasonic-Based Localization System for Mobile Robots

Round 1

Reviewer 1 Report

1.It is suggested to add a brief introduction to existing ultrasound-based positioning systems. The reason is that the system is based on ultrasound, there is no relevant content introducing ultrasound-based systems in the introduction.

2. Please add a reason for choosing the trilateration-based method. This paper frequently refers to the trilateration-based method for determining the robot's position. However, it lacks a detailed explanation of the reason why choose this method.

3. Please check the font format in Figure 2, Please check the font format of the vertical axis in Figure 4 which should be consistent with the format in Figure 3. It is suggested to choose a similar color for T2 and AVGT2 in Figure 17.

4. The paper mentions the generation of ultrasonic signals when processing high-frequency signals received by beacons. It states that the period of these ultrasonic signals has been experimentally verified, but the specific experimental validation process is not described in the subsequent text. The detailed explanations on this matter should be provided.

5.It is suggested to conducting comparative experiments between this system and other system to highlight these benefits.

Author Response

Thank you for all your comments on the article. We must state that the article has been revised
based on your feedback.
1. Table No. 1 presents comparisons of various localization technologies including ultrasonic
(US) systems such as DOLPHIN and LOSNUS. Not all systems listed in the table are described
in the text to avoid overloading the content of the article.
2. Reasons for using trilateration have been added to Chapter 3 following your comments.
3. The font style in Figures 2, 3, and 4 has been adjusted to conform with the article's text format.
The color for AVGT2 has been changed. Figure 2 was inserted with improved resolution.
4. Regarding the generation of 20 periods of the ultrasonic signal by beacons, a more detailed
description of the experimental validation process has been added to Chapter 3.
5. The conclusion has been supplemented with information about the methodology for dynamic
measurement we are preparing. In future work, we will likely compare this also with other
systems.
Best regards.

Author Response File: Author Response.pdf

Reviewer 2 Report

This paper presents a real-time localization system (RTLS) for use by robotics within indoor environments, the system is trilateration-based which utilizes the time-of-flight (TOF) principle of ultrasonic waves, it achieves an update frequency of 10 hz and a standard deviation accuracy of up to 15 mm.

Ultrasound-based Localization has high accuracy (due to its ability to mitigate interference), is robust (can penetrate obstacles), is flexible and cost effective (it doesn’t rely on either existing nor expensive infrastructure).

The basic principle is based on sending ultrasonic waves from a battery-powered transmitter (Beacon) to a receiver (Tag) and measuring the distance between them by determining the time it takes for the ultrasonic signal to travel this distance. In the case of placing at least three beacons somewhere on the ceiling, it is possible to determine the 3D coordinates of the tag using trilateration calculations. The beacon always dictates the basic clock. It also determines which of the tags should send the ultrasonic signal. Therefore, synchronization is ensured using this principle.

The tag must be capable of communicating and triggering the transmission of ultrasonic waves from the beacons at the most precise timing for synchronization facilitated by a transceiver. Meanwhile, in the beacon, the received HF signal is processed, and a number of periods (determined through experimental verification) of the ultrasonic signal with a frequency of 40kHz are generated, a processor (power efficient microcontroller) in the tag evaluates the distance (using a Fast Fourier Transform) and sends a request to the next beacon. The conversion of distance from the measured results was possible by creating an arithmetic progression method of calculated magnitudes for a given time interval.

During the measurements, the repeatability of the measurement principle was crucial, which can be determined using the standard deviation. This should ensure measurement accuracy after calibration to precise distances, the smallest standard deviations were measured (2.13mm to 2.49mm). The results for the results of points within the valid range, all had a standard deviation no higher than 15mm on all axes: x, y, z.

Comments: Everything about science is solid, but the presentation is overly verbose, the paper needs to be condensed and trimmed down, empirical data should be tabulated instead of being talked about in large free-flowing paragraphs the just pad out the pages.

Author Response

Thank you for all your comments on the article. We must state that the article has been revised based on your feedback.
Under some of the graphs, the discussion was shortened to exclude data that are visible from the graphs, as you mentioned in your comments.
Best regards.

Author Response File: Author Response.pdf

Reviewer 3 Report

Some comments are the following:

1. The quality of the figures can be improved, specifically Figures 2 and 5.

2. Define the acronyms meaning before using them in the text. For instance, Fast Fourier Transform (FFT)

3. Use consistent metric units. 

4. In (1) the term $mag_max$ is not defined

5. In line 335 d1, d2 and d3  should be d_1, d_2 and d_3. The same applies to x1, x2 and x3 in line 332.

6. In (7) the term 1500y_3^2, should be 1500^2.

The english language can be improved. There are several grammatical errors.

Author Response

Thank you for all your comments on the article. We must state that the article has been revised based on your feedback.
1. The quality of Figures 2 and 5 has been improved to ensure readability.
2. Definition of Fast Fourier Transform (FFT) has been added.
3. The calculations were presented as they are computed by the system. We acknowledge that this is not entirely correct, but we wanted to describe everything as it was designed.
4. A definition has been added for the variable mag_max.
5. The changes you suggested regarding indexing have been implemented.
6. Yes, you are correct, y_3 should not be there. It has been corrected.
Best regards

Author Response File: Author Response.pdf

Reviewer 4 Report

This paper suggests a method based on trilateration for a real-time localization system employing ultrasonic waves for mobile robotics.  The approach is adequately described and the conclusions are supported by the results.

This paper is recommended for publication with a few minor improvements. 

1. Redraw Figure 2 in better quality

2. The legend in Figure 3 is not complete

3. Add 3D Tags position in figures 10,11,12 and 14,15 and 16, to getter a better sense of distances, and it may help clarify some of the observed patterns in std results

4. Discuss the challenges that may face this method in a dynamic target case

5. Discuss existing low-cost real-time localization methods based on signal mapping such as: "Updatable indoor localization based on BLE signal fingerprint", "Phone application for indoor localization based on Ble signal fingerprint" an "Calibration cost reduction of indoor localization using bluetooth low energy beacon"

Author Response

Thank you for all your comments on the article. We must state that the article has been revised based on your feedback.
1. The image has been adjusted and inserted into the article in better quality.
2. In Figure 3, the vertical axes display dimensionless numbers. We have added this information to the text below the figure. This is because it involves direct measurement of voltage using an ADC, where it is not necessary to convert an 8-bit number to voltage since we are looking for the peak of the envelope. The magnitude is also calculated directly from this number.
3. Figures 10, 11, 12, and 14, 15, 16 were generated from Figures 9 and 13. We understand what you mean. We tried various ways to add beacons to these figures, but the result was that these figures lost clarity. Therefore, Figures 5, 6, 7 are included in the article to explain the beacon positions above the measured points from different perspectives in more detail.
4. Regarding the measurements of the moving tag under the beacons, we are currently preparing the measurement methodology and planning a series of measurements. Therefore, we do not want to get ahead of ourselves, and in this article, we focused primarily on verifying the repeatability of measurements at various points distributed in space. We have also added a discussion on the challenges of dynamic measurements.
5. The introduction mentions some other methods for indoor position measurement, both more and less precise. We primarily focused on ultrasonic systems. Following your suggestion, we decided to supplement the article with results from using a BLE system and have also updated the literature list.
Best regards.

Author Response File: Author Response.pdf