Evaluation of the Digital Data Performance Transmission on a Fiber-Radio System

Round 1

Reviewer 1 Report

The paper is well written, clear and well presented. 

I think it can be improved just adding some comments on:

1) the fact that the used sequence is not of any influnece on the final resul;

2) the introduction of debugging and normalization of the data to eliminate spurious peaks is it needed? It seems that this process is similar to a direct application of the original sequence to the transmitter. So, why simulating also the optical section? This is not clear to me. It is also not too clear the difference between Fig. 4 (a) and Fig. 5 data sequences.

Please note that in Eq 2 there is a superscript after CCI that is probably not needed.

Author Response

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Author Response File: Author Response.pdf

Reviewer 2 Report

The paper studies the digital data performance transmission of optical fiber radio system, and the following problems exist:

1 Note the repeatability between Figures 1 and 2.

2. The amplitude of the received QPSK signal is 10-11 power. How can such a small signal be detected? Has the influence of signal-to-noise ratio been considered?

3 There is a problem in the calculation of the bit error rate of the author. The calculation of the bit error rate is too large, such as 20% - 40%. The actual bit error rate calculation is only meaningful when it is below 10-6.

4. Some language expressions and descriptions must be further improved and refined. Also note the format of the references.

Author Response

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Reviewer 3 Report

This paper studies the performance of digital data transmission in a Fiber-Radio System using numerical simulations. However, I think the novelty of this paper is not enough, and the performance evaluation is not thorough and clear. Specifically:

1. In “Introduction”, several applications of fiber-radio schemes are listed before introducing the proposed system. However, I cannot tell the novelty of this paper from the literature review. The proposed system is a standard Fiber-Radio System, with a typical modulation format. Although it is stated that “To the best of our knowledge, this is the first time that a fiber-radio system is numerically evaluated by using two different Software.” However, I don’t think this statement is convincing, as the two software are commonly used together to evaluate the performance of a communication system by taking advantage of the excellent packages in each software.

2. In the Optical and wireless transmission schemes, the main parameters of each module, such as DFB, MZM, fiber parameters, PD parameters, etc., should be listed in detail to help the reviewer check if the simulation is practical. For example, for the DFB laser, which module is used in VPI (as VPI provides several modules for the optical sources), and what are the main parameters, such as linewidth, etc? For the 25km SM-SF, which module is used? What are the settings of dispersion, dispersion slope, nonlinear effects and attenuation? For the PD, what is the responsivity? Is PIN or APD used? All these main parameters for VPI simulation should be provided in the paper. To be honest, it seems the result in Figure 4 (b) is a little ideal.

3. The unit is missing in the simulation parameters of Table 1.

4.  In “simulation results”, a waveform that contains a short sequence is provided in Figures 4-7. I don’t think the waveform analysis is enough to evaluate the system performance. How about the eye diagram, RF spectrum, signal constellation, and bit error rate for this system? These basic performances should be provided in the numerical simulation, as the performance evaluation is the main focus of this paper.

5. The analyses of Figures 8-10 are too brief. Besides, I don’t quite catch the bit error rate % description in Figure 8. How many bits are used for the bit error rate calculation?

6. Please check that the abbreviations are clarified when they appear for the first time. Also, please check the reference format, as different formats are found in the “References”.

 

Author Response

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Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

The author has carefully revised

Author Response

English language and style were verified.

Reviewer 3 Report

I appreciate the authors for revising the paper. My comments are as follows.

1. About point 1: The novelty of this paper is still not clarified by only removing the statement. Please highlight the novelty of this paper.

2. About point 2: Please replace the part of "VPI photonics" with the real VPI simulation diagram (e.g. the schematic shown in the.vtmu file in VPI) in figure 2. The VPI simulation is one of the essential parts of the simulation scheme, a list of modules is not enough. It deserves clarification to show how these modules are connected. Besides, as the table has clearly shown the widening of these pulses, it is better to directly include this table to quantify the pulse widening values presented in figure 4 (b), as it is not clear to observe the pulse widening in figure 4 (b) even with the description "a small widening of the recovered pulses".

3. About point 4: It is stated that "This data undergoes a debugging and normalization process to remove spurious peaks; in this process, the first three “0” bits and the “1” bit are removed". Could the author clarify why the spurious peaks and flat bottoms are generated, and how to debug to remove these spurious peaks? Besides, as the QPSK signal is transmitted, the received signal constellation is better to provide to show the two-dimensional signal quality after transmission.

Author Response

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Author Response File: Author Response.pdf