Phase Correlation Single Channel Continuous Wave Doppler Radar Recognition of Multiple Sources
Round 1
Reviewer 1 Report
In this paper, a phase tuning approach has been implemented to detect the physiological parameters in a multi-target scenario.
The topic is very interesting and well suited to MDPI Sensors journal.
I really appreciated the technical content of the contribution. My only comment concerns the reported reference list: 11 out of 18 citations are self-citations. In my opinion is a too high rate.
I suggest to add additional recent works concerning multi-target physiological parameters detection both at the same or different range. I reported an example list, hereafter.
Cardillo, C. Li and A. Caddemi, "Millimeter-Wave Radar Cane: A Blind People Aid With Moving Human Recognition Capabilities," in IEEE Journal of Electromagnetics, RF and Microwaves in Medicine and Biology, doi: 10.1109/JERM.2021.3117129.
Liu, B.; Chen, B.; Yang, M. Constant-Modulus-Waveform Design for Multiple-Target Detection in Colocated MIMO Radar. Sensors 2019, 19, 4040. https://doi.org/10.3390/s19184040.
Jia, Y.; Guo, Y.; Yan, C.; Sheng, H.; Cui, G.; Zhong, X. Detection and Localization for Multiple Stationary Human Targets Based on Cross-Correlation of Dual-Station SFCW Radars. Remote Sens. 2019, 11, 1428. https://doi.org/10.3390/rs11121428.
Cardillo and A. Caddemi, "Radar Range-Breathing Separation for the Automatic Detection of Humans in Cluttered Environments," in IEEE Sensors Journal, vol. 21, no. 13, pp. 14043-14050, 1 July1, 2021, doi: 10.1109/JSEN.2020.3024961.
Ishtiaq, X. Wang and S. Hassan, "Detection and tracking of multiple targets using dual-frequency interferometric radar," IET International Radar Conference (IET IRC 2020), 2020, pp. 468-475, doi: 10.1049/icp.2021.0646.
Author Response
The authors would like to thank the reviewers for their insightful comments to improve the quality of the manuscript. The reviewers’ comments have been addressed in the revised manuscript, as indicated below.
Reviewer 1
We thank the reviewer for bringing the issue of high number of self-citations to our attention. In the revised manuscript we have removed five self-citations and added 8 new references as following:
- Four references suggested by Reviewer 1 have been added: references 5, 12, 13, and 14.
- Four new references were added: references 1, 6, 7, and 18.
- References 5, 9, 10, 14, and 17 (self-citations) from the original manuscript were removed.
Reviewer 2 Report
See the attached file.
Comments for author File: 
Comments.pdf
Author Response
The authors would like to thank the reviewers for their insightful comments to improve the quality of the manuscript. The reviewers’ comments have been addressed in the revised manuscript, as indicated below.
Reviewer 2
- Line 148: ASPPT 2998 from Antenna Specialist is used in this work. The system diagram
shows in Figure 3 involves a number of modules. How do these modules relate to ASPPT
2998? It is good to provide some background information of the modules and its connection
with the entire system used in this work
Fig. 3 has been revised to indicate ASPPT 2998, and the text was revised accordingly (line 144).
- Compared to other methods mentioned in the introduction which require some specific
signal processing algorithms (e.g. MUSIC) as mention in the introduction, the proposed
method is fairly simple. Towards the end of the article, it is good if the authors are able to
comment the pros and cons of the proposed algorithm over existing algorithms such that
the merits of the algorithm become apparent to the readers.
Following text has been added in conclusions (lines 235-238):
Proposed phase tuning technique with FFT does not require significant hardware complexity not significant computational resources. However, this technique does rely on frequency separation of sources, thus for overlapping frequency spectra other signal processing technique such as MUSIC or empirical mode decomposition (EMD) may be explored in the future.
- Is there any fundamental limitation of the algorithm (e.g. the number of possible sources at
the same range)? Is it possible to separate the breathing of two people at the same range?
Following text has been added:
Number of sources that can be separated will be limited by the resolution of the phase shifter. (lines 225-226)
Since human targets are likely to present different surface configurations and breathing dynamics, and thus different initial phase even at the same radar range, this method is promising for separation of physiological signals from multiple individuals. (lines 243-245)
