Extended Spatial-Index LED Modulation for Optical MIMO-OFDM Wireless Communication
Round 1
Reviewer 1 Report
In the paper, the author proposes a novel ESI-LED modulation scheme. Compared to the previous schemes, it doesn’t have the limitation of number of LEDs and the bit rate increases semi-non-linearly with the number of LEDs. The author introduces the model of the system and does the simulation and compare the proposed scheme with GLIM and FGIS in terms of data rate, error rate at different SNR levels of different system configurations. The analysis of calculation complexity is also presented in the paper.
In general, the topic is of good research interest, the system has pretty good novelty and the presentation is well organized. I think the paper may be strengthened in the below aspects:
How the QAM signals looks like at different noise levels by providing some eye/constellation diagrams. The paper will be greatly strengthened with a simple experimental demonstration/measurement on top of the simulation.Author Response
First of all, the authors would like to deeply thank the editors and the reviewers for their valuable comments to improve the clarity, the presentation, and the novelty of our paper. The authors have revised the paper based on the reply to the reviewers as follows. The modifications and corrections are highlighted by yellow color in the revised manuscript.
Kindly find the point by point reply in the attached file
Author Response File: 
Author Response.pdf
Reviewer 2 Report
This research presents an interesting approach to a problem in wireless technology using visible light communication (VLC) by increasing the channel capacity with spectral efficiency. However, there are several presentation styles, inconsistency, errors and unclear points in the paper as detailed in the comments to the authors. Also, for the evaluation section, the authors should investigate the complexity analysis of their proposal and their previous work, as well as the related work.
The overall recommendation is major revision and the current version of the paper should be improved for the next review round for the potential publication in this journal.
Major
-Correct the Eq 16.
Line 335 and line 356 what is the difference between these two abbreviation RA and RS also the PD has two meaning photodiode and photo dector.
-Paper organization
Section 2 only includes 1 subsection (Subsection 2.1) expected to further include some more sub-section in this Section. Also, the system model and the proposed methods should be separated to improve the readability and the organization structure of the paper.
-Evaluation section
The paper, in my opinion, does not make a fair comparison of Computational Complexity in the evaluation section. Specifically, the proposed method should be compared with the author’s previous work FGIS and other relevant works because, in GLIM, the achievable Data rate is steady even when the number of LEDs increases. I suggest if possible conducting an evaluation of ESI-LED with FGIS.
Minor
Line 19 should add abbreviation (VLC)
Line 139 spite should be split.
In the figure5,6 and 7 should but in x-axis SNR dB.
Author Response
First of all, the authors would like to deeply thank the editors and the reviewers for their valuable comments to improve the clarity, the presentation, and the novelty of our paper. The authors have revised the paper based on the reply to the reviewers as follows. The modifications and corrections are highlighted by yellow color in the revised manuscript.
Kindly find the point by point reply in the attached file
Author Response File: Author Response.pdf
Reviewer 3 Report
In this paper, a novel optical MIMO-OFDM communication modulation scheme termed as extended
spatial-index light-emitting diode (ESI-LED) modulation is proposed. A detailed analysis of ABER and CC is presented.
My main concern is the practicality of the concept for ESI/ FGIS SM, in simulations, the concept works for selected configuration, e.g, see as in Fig 2 (a-C), however, for practical point view at system level, it is difficult to achieve the same performance metrics, e.g, ABER, data rates, SNR etc. It is due to high channel correlation/ channel cross talk and noise, I will highly recommend the authors to explore the practical implementation for the proposed modulations, if the concept works, and it will be very interesting and valued. The SE of the ESI is improved by varying both the power weight allocation and the positions of the complex OFDM time domain components several times over the same active LEDs indices and active LEDs indices are utilized many times with different power allocation values for OFDM real and imaginary components, no analysis is shown how does this helps to distinguish the LEDs? Does it increase the reliability of wireless channel if the channel is highly correlated? This could be better written, I suggest to rewrite it, not clear “Moreover, the number of active LEDs are changed from the situation where only two LEDs are activated to the situation where multiple/all LEDs are activated”? Figure 2, the configuration are not realistic for a MIMO receiver (RX), how could one practically implement. Let’s take an laptop example, in MIMO RX receiver, the PDs must be few cm to mm apart from each other, however, this could increase the channel correlation, that could increase the error in spatial domain bits and signal domain too, I suggest to check this and redo simulations, which are more realistic? There is no technical discussions, on Fig 4 (a-c), the required SNR decreases to achieve the same ABER for channel A-C, is it because of the channel gain or less cross talk/ channel correlation?. For 4x4, GLIM and 3x3 ESI, figure 4, why the SNR is same to achieve the same ABER in all channel A-C. There not much improvement in performance metric, SNR and ABER. Figure 5 (a-c) the performance difference for 5x5 is suddenly big and shows that ESI performance is better, which is not consistent with 4x4, provide your reasons? What happened if a large MIMO is considered such as 8xNr, 16xNr and so on???
Author Response
First of all, the authors would like to deeply thank the editors and the reviewers for their valuable comments to improve the clarity, the presentation, and the novelty of our paper. The authors have revised the paper based on the reply to the reviewers as follows. The modifications and corrections are highlighted by yellow color in the revised manuscript.
Kindly find the point by point reply in the attached file
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
please see attached file
Comments for author File: Comments.pdf
Author Response
First of all, the authors would like to deeply thank the editors and the reviewers for their valuable comments to improve the clarity, the presentation, and the novelty of our paper. The authors have revised the paper based on the reply to the reviewers as follows. The modifications and corrections are highlighted by yellow color in the revised manuscript.
Kindly find our point to point replay to the respected reviewer comments in the attached file.
Author Response File: Author Response.pdf
