A Comprehensive Signal Quality Assessment for BDS/Galileo/GPS Satellites and Signals

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Reviewer: The manuscript presents an analysis and comparison of new BDS-3 signals with BDS-2, GPS and Galileo in terms of carrier-to-noise ratio, code noise and multipath with different types of receivers. It is well written and very interesting for readers of remote sensing. However, there are many minor mistakes in the manuscript, for which the authors should make careful corrections. The following minor modifications should be made:

[1] Try to use different colors with strong with strong contrast in all figures.

[2] The font of the first paragraph is incorrect

[3] p.1 line 14: a complete signal quality assessment method... -> change ‘complete’ to 'comprehensive'

[4] p.1 line 28: As of September 2022, the data of 30 BDS-3 satellites... -> describe to the latest status, such as ‘As of May 2024’

[5] p.3 table 2: please explain the acronym ‘G’, ‘E’, and ‘C’.

[6] p.3 line 87: …are usually used for indicated the signal quality... -> change ‘indicated’ to 'indicating'

[7] p.3 line 91: …the transformation coordinate value between  between the earth... -> remove ‘between ’

[8] Eq. 2 is incorrect

[9] the symbol of Eq. 7 should correspond to Eq.5 and Eq.6

[10] the symbol of Eq. 9 should correspond to Eq.5

[11] p.5 line 141: When no cycle slip appears in the carrier phase observations... ->remove the sentence which is repeated with the following sentence

[12] Eq. 13 is incorrect

Comments on the Quality of English Language

Minor revision

Author Response

#Reviewer:

The manuscript presents an analysis and comparison of new BDS-3 signals with BDS-2, GPS and Galileo in terms of carrier-to-noise ratio, code noise and multipath with different types of receivers. It is well written and very interesting for readers of remote sensing. However, there are many minor mistakes in the manuscript, for which the authors should make careful corrections. The following minor modifications should be made:

1. Try to use different colors with strong with strong contrast in all figures.

Response: Thanks for the reviewer's suggestion. The captions for some figures  in the article may not accurately describe the content of the figures. Therefore, the captions for all the figures in the article have been carefully revised to provide a detailed description of the figure.

2. The font of the first paragraph is incorrect

Response: Thanks for the reviewer's suggestion, and the mistake has been corrected in the contribution.

3. p.1 line 14: a complete signal quality assessment method... -> change ‘complete’ to 'comprehensive'

Response: Thanks for the reviewer's suggestion, and the mistake has been corrected in the contribution.

4. p.1 line 28: As of September 2022, the data of 30 BDS-3 satellites... -> describe to the latest status, such as ‘As of May 2024’

Response: Thanks for the reviewer's suggestion.The author consulted relevant materials, learned about the latest status of BDS-3, and made corrections

5. p.3 table 2: please explain the acronym ‘G’, ‘E’, and ‘C’.

Response: Thanks for the reviewer's suggestion. A description of the acronym ‘G’, ‘E’, and ‘C’ has been added, and other similar situations in the article have been simultaneously modified

6. p.3 line 87: …are usually used for indicated the signal quality... -> change ‘indicated’ to 'indicating'

Response: Thanks for the reviewer's suggestion, and the mistake has been corrected in the contribution.

7. p.3 line 91: …the transformation coordinate value between  between the earth... -> remove ‘between ’

Response: Thanks for the reviewer's suggestion, and the mistake has been corrected in the contribution.

8. Eq. 2 is incorrect

Response: Thanks for the reviewer's suggestion, and the mistake has been corrected in the contribution.

9. the symbol of Eq. 7 should correspond to Eq.5 and Eq.6

Response: Thanks for the reviewer's suggestion, and the mistake has been corrected in the contribution.

10. the symbol of Eq. 9 should correspond to Eq.5

Response: Thanks for the reviewer's suggestion, and the mistake has been corrected in the contribution.

11. p.5 line 141: When no cycle slip appears in the carrier phase observations... ->remove the sentence which is repeated with the following sentence

Response: Thanks for the reviewer's suggestion, and the mistake has been corrected in the contribution.

12. Eq. 13 is incorrect

Response: Thanks for the reviewer's suggestion, and the mistake has been corrected in the contribution.

Reviewer 2 Report

Comments and Suggestions for Authors

With the rapid development of BDS-3, it is important and interesting to evaluate its performance, especially for the new signals. The author comprehensively compares and analyzes its signal performance with other systems, and the results are clear and instructive. The paper can be potentially acceptable once the following remarks have been appropriately taken care of.

1. The references in the article are not completed (only up to 2022), and the latest references need to be added.

2. Authors analyze the multipath combination in equation (9), but it is not able to see the receiver-environment for the receivers? This is particularly important when comparing the multipath root-mean-squares between different types of receivers. How can one make conclusions about multipath without presenting this essential information?

3. Authors need to explicitly guide the reader to the figure so they can understand your conclusions and see it for themselves at the corresponding row and panel (e.g. top, middle and bottom row, left, middle, right panel). This applies to all he figures, please read through your manuscript.

4. Several formulas in the text have errors (e.g. Eq. 2 and Eq. 13), and many formula symbols are inconsistent. The authors should carefully check all the equations.

5. There are many small errors in the article, and the author needs to read and polish the entire text to correct them.

Comments on the Quality of English Language

With the rapid development of BDS-3, it is important and interesting to evaluate its performance, especially for the new signals. The author comprehensively compares and analyzes its signal performance with other systems, and the results are clear and instructive. The paper can be potentially acceptable once the following remarks have been appropriately taken care of.

1. The references in the article are not completed (only up to 2022), and the latest references need to be added.

2. Authors analyze the multipath combination in equation (9), but it is not able to see the receiver-environment for the receivers? This is particularly important when comparing the multipath root-mean-squares between different types of receivers. How can one make conclusions about multipath without presenting this essential information?

3. Authors need to explicitly guide the reader to the figure so they can understand your conclusions and see it for themselves at the corresponding row and panel (e.g. top, middle and bottom row, left, middle, right panel). This applies to all he figures, please read through your manuscript.

4. Several formulas in the text have errors (e.g. Eq. 2 and Eq. 13), and many formula symbols are inconsistent. The authors should carefully check all the equations.

5. There are many small errors in the article, and the author needs to read and polish the entire text to correct them.

Author Response

#Reviewer:

With the rapid development of BDS-3, it is important and interesting to evaluate its performance, especially for the new signals. The author comprehensively compares and analyzes its signal performance with other systems, and the results are clear and instructive. The paper can be potentially acceptable once the following remarks have been appropriately taken care of.

1. The references in the article are not completed (only up to 2022), and the latest references need to be added.

Response: Thanks for the reviewer's suggestion, and I have added the latest references in the first section Introduction. The details are as follows.

‘Furthermore, when studying the combination positioning of BDS-3 and other systems, the increase of BDS-3 new signals can significantly improve the positioning performance of BDS/GPS/Galileo [29-30]. However, it is found that the inter-system bias (ISB) between BDS-3 and other GNSS systems cannot be ignored. Even ISB exists between BDS-3 and BDS-2 [31-32].’

 

32. Ma, Z.; Cui, J.; Liu, Z.; Su, X.; Xiang, Y.; Xu, Y.; Deng, C.; Hui, M.; Li, Q. Influence of Inter-System Biases on Combined Single-Frequency BDS-2 and BDS-3 Pseudorange Positioning of Different Types of Receivers. Remote Sens. 2024, 16, 1710. https://doi.org/10.3390/rs16101710
33. Dang, X.; Yin, X.; Zhang, Y.; Gao, C.; Wu, J.; Liu, Y. Improved MediumBaseline RTK Positioning Performance Based on BDS/Galileo/GPS Triple-Frequency Only Observations. Remote Sens. 2023, 15, 5198. https://doi.org/10.3390/ rs15215198
34. Xiao, K.; Sun, F; Zhu, X; Zhou, P; Ma, Y; Wang, Y.Assessment of overlapping triple-frequency BDS-3/BDS-2/INS tightly coupled integration model in kinematic surveying.GPS Solutions. 2024, 28,DOI:10.1007/s10291-024-01637-3.
35. Shu, B.; Tian, Y.; Qu X.; Li, W.; Huang, G.; Du, Y.; Zhang, Q. Estimation of BDS‑2/3 phase observable‑specific signal bias aided by double‑differenced model: an exploration of fast BDS‑2/3 real‑time PPP. GPS Solutions. 2024, 28, 88.
36. Authors analyze the multipath combination in equation (9), but it is not able to see the receiver-environment for the receivers? This is particularly important when comparing the multipath root-mean-squares between different types of receivers. How can one make conclusions about multipath without presenting this essential information?

Response: Thanks for the reviewer's suggestion, and I have added the description of the receiver-environment for the receivers in the second section Data and Methods. The details is as follows.

‘All the selected stations are installed in an open sky environment, and pictures of these stations can be found in http:// www.igs.org.’

3. Authors need to explicitly guide the reader to the figure so they can understand your conclusions and see it for themselves at the corresponding row and panel (e.g. top, middle and bottom row, left, middle, right panel). This applies to all he figures, please read through your manuscript.

Response: Thanks for the reviewer's suggestion. The captions for all the figures in the article have been carefully revised to provide a detailed description of the figure.

4. Several formulas in the text have errors (e.g. Eq. 2 and Eq. 13), and many formula symbols are inconsistent. The authors should carefully check all the equations.

Response: Thanks for the reviewer's suggestion, and the mistake has been corrected in the contribution.

5. There are many small errors in the article, and the author needs to read and polish the entire text to correct them.

Response: Thanks for the reviewer's suggestion, and the author has read the entire text, and corrected any mistakes therein.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript compares the performance of different receivers in processing transmissions from several different GNSS constellations.

The presentation would be very significantly improved if the authors edited the test to address these points:

1. The question of detecting and removing cycle slips would benefit from more discussion. This is especially important when the ionosphere-free combinations are computed, since cycles slips that occur at the same time on multiple frequencies can be difficult to detect, especially for the case when the signs of the slips in the two frequencies are different.  This problem would seem to be particularly serious in the estimate of the contribution of multipath, which has terms both in the sum and the difference of phase data.

2. The analysis is based on data that is about 5 years old. Therefore, it is very likely that all of the contemporary receivers in the study would have firmware that has been upgraded -- possibly more than once. It would help if the authors indicated the version of the firmware that was used in the different receivers that they studied. This would certainly be an improvement, but it does not really address the problem that the firmware used in the analysis is very likely no longer available, and the newer firmware for each receiver may not perform the same as the version used in the test. This would be a significant problem for a reader who had newer versions of the hardware that was tested. Since the data in the study are about 5 years old, this is very likely to be the general case.

3. The captions for the figures should be expanded to explain what is being displayed, and the units for the axes should be added when they are not already present. This latter comment is especially relevant for figures that have two types of data displayed on the same axes.

Author Response

#Reviewer:

The manuscript compares the performance of different receivers in processing transmissions from several different GNSS constellations.

The presentation would be very significantly improved if the authors edited the test to address these points:

1. The question of detecting and removing cycle slips would benefit from more discussion. This is especially important when the ionosphere-free combinations are computed, since cycles slips that occur at the same time on multiple frequencies can be difficult to detect, especially for the case when the signs of the slips in the two frequencies are different.  This problem would seem to be particularly serious in the estimate of the contribution of multipath, which has terms both in the sum and the difference of phase data.

Response: Thanks for the reviewer's reminder. I strongly agree with the reviewer's viewpoint. When analyzing the impact of multipath, the author also noted the impact of cycle slips. In the specific experimental process, when encountering situations with cycle slips, the author will segment the data.

	(10)
	(11)

In the formulas 10 and 11 above, due to the influence of cycle silps, the values of the term B may vary in the segmented data. Considering this, the author adopts the method of subtracting the average value in each segment to eliminate the influence of B, and the obtained result can reflect the influence of multipath.

2. The analysis is based on data that is about 5 years old. Therefore, it is very likely that all of the contemporary receivers in the study would have firmware that has been upgraded -- possibly more than once. It would help if the authors indicated the version of the firmware that was used in the different receivers that they studied. This would certainly be an improvement, but it does not really address the problem that the firmware used in the analysis is very likely no longer available, and the newer firmware for each receiver may not perform the same as the version used in the test. This would be a significant problem for a reader who had newer versions of the hardware that was tested. Since the data in the study are about 5 years old, this is very likely to be the general case.

Response: Thanks for the reviewer's reminder. I strongly agree with the reviewer's viewpoint. As time goes by, the receiver firmware version will be upgraded. The author's original intention was to analyze the impact of receiver types and firmware version upgrades on BDS-3 signal performance from 2019 to 2024, as well as the impact on the inter-system bias between BDS-3 and other systems. The author has used 2015-2018 data to analyze the impact of receiver firmware version upgrades on the inter-system bias between BDS-2, GPS, and Galileo at overlapping frequency points. Please refer to the author's paper ‘Estimating inter-system biases for tightly combined Galileo/BDS/GPS RTK’ for details^[1]. In the experiment, the author first analyzed the 2019 data that could initially process BDS-3 satellite signals. As interesting experimental results were discovered, the author wrote this article first. Due to time constraints, the author has not yet completed the experimental analysis from 2020 to 2024. Further analysis of BDS-3 signal performance and system bias will be conducted using the data from 2020 to 2024. Thank you for your suggestion. In addition, additional explanations have been provided in the text as follows:

‘The earlier use of data here is because BDS-3 data is just available at this time, and BDS-2 data is also relatively complete, laying a solid foundation for subsequent BDS performance analysis.’

 

[1] Tian, Y.; Sui, L.; Xiao, G.; Zhao, D.; Chai, H.; Liu, C. Estimating inter-system biases for tightly combined Galileo/BDS/GPS RTK. Advances in Space Research, 2020, 65,  1:572-585.DOI:10.1016/j.asr.2019.09.003.

3. The captions for the figures should be expanded to explain what is being displayed, and the units for the axes should be added when they are not already present. This latter comment is especially relevant for figures that have two types of data displayed on the same axes.

Response: Thanks for the reviewer's suggestion. The captions for all the figures in the article have been carefully revised to provide a detailed description of the figure.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have improved the text by adding units and captions to the figures wherever needed. The author has also addressed the problem of cycle slips, although the method that is used may not be adequate in all circumstances. It is certainly an improvement.

The results could be useful, although the analysis uses data that are about 5 years old. I noted this in my previous comments.