A Deep Echo State Network-Based Novel Signal Processing Approach for Underwater Wireless Optical Communication System with PAM and OFDM Signals
Round 1
Reviewer 1 Report
In this manuscript, authors propose and demonstrate the application of DeepESNs for channel equalization in high- speed UWOC systems to enhance system performance with both PAM and QPSK-OFDM modulation. By the experiment, achieve error-free underwater transmission over 40.5 meters with data rates up to 167 Mbps. The results will be helpful in the design of UWOC links employing PAM and QPSK-OFDM. The detailed comments are as follows:
1. What is the core innovation in inferring DeepESNs from other communication systems to UWOC system?
2. Figure 2 shows that the trend of changes in the curve is different under different receiving power. What is the reason for this?
3. I want to know what is the maximum distance? Is the UWOC system capable of only reaching 40.5 meters with data rates 167 Mbps?
4. I hope the author can increase the analysis of the relationship between maximum transmission distance and communication rate.
5. I suggest the author verify the following description of the first time, ‘In this paper, DeepESN is, for the first time applied in optical communication signal processing to minimize noise and distortion effects while enhancing the signal-to-noise ratio (SNR) in signals received from UWOC channels’.
Minor editing of English language required.
Author Response
Please see the attachment.
Author Response File: 
Author Response.docx
Reviewer 2 Report
The authors proposed and demonstrated the application of Deep Echo State Networks (DeepESNs) for channel equalization in high speed UWOC systems to enhance system performance with both PAM and QPSK-OFDM modulations. Their experimental results demonstrate the effectiveness of DeepESNs in UWOC systems achieving error-free underwater transmission over 40.5 meters with data rates up to 167 Mbps. The results are interesting for underwater wireless optical communication. However, some issues need to be clarified before publication
1. Significant absorption and scattering loss in underwater channels will seriously affect the performances of underwater wireless optical communication. Under different absorption and scattering losses, how are the performances of underwater wireless optical communication using DeepESNs?
2. What are the recovery waveforms of these signals PAM and QPSK-OFDM?
3. What type of laser is 520nm LD. What are its rate-equations?
4. How to modulate these signals PAM and QPSK-OFDM to the laser?
Author Response
Please see the attachment.
Author Response File: Author Response.docx
Reviewer 3 Report
The authors propose and demonstrate the application of Deep Echo State Networks (DeepESN) for channel equalization in high-speed UWOC systems to improve system performance with PAM and QPSK-OFDM modulations, the article is interesting due to the investigation of the transmission of data underwater so the article becomes interesting.
1. The authors could show a comparison table with different works with propagation distances in Underwater Wireless Communication Technology and maximum number of bits transmitted underwater
2. The authors could explain more about the dispersion of the signal underwater.
3.-Could you explain how reliable the transmission system is if there are signal distortions?
Author Response
Please see the attachment.
Author Response File: Author Response.docx
Reviewer 4 Report
Dear authors,
In this article, the authors proposed the use of Deep Echo State Networks for channel equalization in underwater wireless optical communication systems. The results obtained during experimental tests proved the high efficiency of DeepESN in systems of this type of communication, which achieved error-free underwater transmission over 40.5 meters with a data transfer rate of up to 167 Mb/s.
The article is well structured and enjoyable to read.
Remarks:
1. I think the title is too long. Is it justified to include the obtained bit transmission rate and range in the title? Please think deeply about it?
2. In the "Introduction" chapter, lines 92-94 mention - "The DeepESN method has been improved and applied in multiple fields to solve different problems after its proposal [34, 35, 36, 37, 38]." There are no references to uses in this method of data transmission. Is it in line with current developments?
3. There is no detailed information about the conduct of experimental tests. Repeating the experimental tests by the readers of the article is impossible.
Author Response
Please see the attachment.
Author Response File: Author Response.docx
Round 2
Reviewer 2 Report
Authors have well responsed the issuses concerned by reviewers. The manuscript in current form is suggested to be published
Reviewer 4 Report
Dear authors,
Thank you for your comprehensive answers. I believe that the changes introduced will increase the attractiveness of your work.
