Capacity Improvement of 3D-OCDMA-PON Hybrid System Next Generation Using Weight Zero Cross Correlation Code

Round 1

Reviewer 1 Report

The present paper focuses on a novel 3D spectral/temporal/spatial zero cross-correlation code for optical code division multiple access (OCDMA).

 

The paper is based on 31 reference titles, most of them very actual.

 

- On my opinion, all the step-by -step explanations for building the 3D-SWZCC is way too long. There are also inconsistencies there – for instance I do not understand why the Zero matrix has to be presented (eq. 6), who are the sub-matrices ?1, ?2, and ?3, that are further divided in are divided into ?21, ?22, 199 and ?23 – but the b matrices are not defined. If this part has already been described in other work, just cite the source and give the result. This is a research paper not a master course.

 

- The example given in Table 1 (by the way, why is it split in two parts?) is also trivial

 

- Regarding Table 2. The 3D-SWZCC code cross correlation, I don’t really see the need of inserting a table for that; it is obvious that if a code is correctly constructed the cross-correlation is 0 and auto-corelation is 1, Eqn. (11, 12) suffice.

 

- Regarding User (1,1,1), g Figure 1. 3D spectral/temporal/spatial OCDMA system. – please explain what User (1,1,1), … ,User (L1,L2,L3) represents (i.e. the numbers)

 

- In section 4. 3D-SWZCC System Performance, formulas (14, 15,  ….  28) seems to be taken from existing literature. Then just give the final result and make a reference to the source. Also, if a eqn. is written on 3 rows, you don’t need to number it as three eqns. (like 18-20,22-24)

 

Regarding 5. Numerical Results – since this seems to be the main contribution of the authors, they should explain in more detail the simulation setup and parameters. The results are interesting, but in order to give them more credit they should be compared against other similar ones existing in the literature

 

In 6.1. Principle of 3D-OCDMA-PON – you start to describe the system again. This is the same system as the one described in section 3. System Function? Is different?

 

In 6.1 sees to have a different implementation of the same system – but the results are expressed differently (based on the eye diagrams and the values of Q factors versus distance). Is there any connection between the simulation results shown in sections 5 and 6? From all those eye diagrams, can’t you extract some conclusions?

 

Finally there are lot of issue with alignment of the text, spacing between the lines is different in several section – overall the text have a disordered and unkempt aspect.

 

But, the main issue is that I do not see the novelty of this approach. The authors performed simulations in two different simulators, but the two simulations seems not to be connected to one another. Furthermore, there is no comparison with other similar papers already publish to validate the results.

More than that, the Turnitin plagiarism detector reported a similarity factor of 34% (very high, on my opinion), especially in the theoretical part (see attached)   

Comments for author File: Comments.pdf

Author Response

Capacity Improvement of 3D-OCDMA-PON Hybrid System Next Generation Using Weight Zero Cross Correlation Code

Dear Editor;

First, we thank the editor and the journal team for their efforts to improve and develop scientific
research, second we would like to thank the reviewers for the appreciation given to our work, also for their valuable comments and relevant suggestions. We have provided detailed answers to their comments and mentioned the changes brought according to their suggestions. The reviewers’
comments are in black font and the answers are in blue font, revisions on the manuscript are in green.

We hope we have correctly addressed the questions recommended by the reviewers.

Reviewers Comments:

Reviewer 1:

We thank the reviewer for his questions that help us improve the paper.

Question 1:

 

1.1.  In my opinion, all the step-by-step explanations for building the 3D-SWZCC are way too long.

Answer

We have provided more details on the construction of the code so that it is easily understood by the researchers.

1.2. There are also inconsistencies there – for instance, I do not understand why the Zero matrix has to be presented (eq. 6)

Answer

The zero matrix is given for its filling by the sub-matrices , , and  given in (Eq.5).

1.3. Who are the sub-matrices ?1, ?2, and ?3, that are further divided in are divided into ?21, ?22, and ?23 – but the b matrices are not defined. If this part has already been described in other work, just cite the source and give the result.

Answer

This is an error that occurred while writing and has been corrected as follows:

?1                         ?2                       ?3                              

?21                     ?22                   ?23    

 

 ,and  are defined in Eq.5 as sub matrices

 

Question 2:

 - The example given in Table 1 (by the way, why is it split in two parts?) is also trivial

Answer

Table 1 presents an example of a three-dimensional coding sequence for =2, =3, and =3, in addition, the example is given to give how to do the 3D coding between the spectral, temporal, and spatial components respectively where component X (parte 1) is a spectral sequence, Y and Z (parte 2) are a temporal and spatial sequences respectively and  ( is the 3D coding result or the 3D-SWZCC code.

 

Question 3:

- Regarding Table 2. The 3D-SWZCC code cross correlation, I don’t really see the need of inserting a table for that; it is obvious that if a code is correctly constructed the cross-correlation is 0 and auto-corelation is 1, Eqs. (11, 12) suffice.

Answer

Table 2 presents the cross correlation values of our 3D-SWZCC code. Moreover, the Table is given to clarify the results in the other cases

( ,).

Question 4:

 - Regarding User (1,1,1), g Figure 1. 3D spectral/temporal/spatial OCDMA system. – please explain what User (1,1,1), … ,User (L1,L2,L3) represents (i.e. the numbers)

Answer

Figure 1 shows the 3D coding mechanism using the SWZCC code for the OCDMA system,  Each user's data is modulated by an external modulator using an optical source, resulting in an optical signal at the output of the modulator, thus, User (1,1,1), …, User (L1, L2, L3) blocs represent the output of modulator (the optical signal resulting from each user).

Question 5:

 - In section 4. 3D-SWZCC System Performance, formulas (14, 15,  ….  28) seems to be taken from existing literature. Then just give the final result and make a reference to the source. Also, if a eq. is written on 3 rows, you don’t need to number it as three eqns. (like 18-20,22-24)

Answer

Your recommendations have been taken into account and the equations have been corrected.

Question 6:

6.1/  Regarding 5. Numerical Results – since this seems to be the main contribution of the authors, they should explain in more detail the simulation setup and parameters. The results are interesting, but in order to give them more credit they should be compared against other similar ones existing in the literature.

6.1. Answer

This section considers the performance of a system employing a three-dimensional single-weight zero cross-correlation (3D-SWZCC) code using two terms: the bit error rate (BER), in terms of the number of concurrent users, amount of received power, data bit rate, optical bandwidth, and the quality factor (Q), in terms of the number of concurrent users, with the assistance of MATLAB software. For numerical calculation, we set the data bit rate
, the PD sensitivity  , the Optical bandwidth
 , the effective source power , the load resistor at receiver
 , the receiver noise temperature , the electron charge c, and the Boltzmann constant .

In the simulation and results section, the work is divided into two sections: a section of numerical simulation using MATLAB software and a section of validation of the results obtained in the first section using Optisystem software.

By using the parameters listed in Table 3, the proposed 3D-SWZCC code shows better performance compared to 3D-PD, 3D-PD/MD, 3D-DCS/MD, 3D-PTZCC codes, and the same code in 1D and 2D domains (1D-SWZCC and 2D-SWZCC) and this is due to ZCC property which completely suppresses the PIIN noise which leads to the elimination of the MAI. Moreover, to give more credibility to these results our code is also studied in section 6 using the parameters of Table 4 where the results indicate that the proposed 3D-SWZCC code satisfies the needs of the optical transmission and respects the conditions of optical communication. For better understanding, we summarize the results obtained in sections 5 and 6 in the following table:

Simulation	Results
Numerical Results	·         Our proposed code can accommodate a greater number of users, up to 454, while the 1D and 2D cases can accommodate just 68  and 157 users, respectively. As a result, the system cardinality has been optimized by about 6.67 and 2.89 times from transitioning from 1D to 3D and from 2D to 3D, respectively. Additionally, the OCDMA system based on the 3D-SWZCC code has outperformed the 3D-PD, 3D-PD/MD, 3D-DCS/MD , and 3D-PTZCC codes, for the same code lengths, by about 4.24, 3.72, 3.22 and 1.32 times, respectively, where the system cardinality for each code is 107, 122, 141 and 354 users, respectively. This means that the system can potentially meet the demands of optical networks. ·         3D-SWZCC has a greater SNR because of the high output current resulting from the photodiode (SDD technique) compared with dark current noise. Additionally, in view of the inverse relevance between the SNR and dark current, this contributes to increasing the SNR value. ·         Both 3D ZCC codes, SWZCC and MD, produce greater SNRs compared to other codes, but the dominant code is always our proposed code. This can be seen from the SNR values at K=150, which were 30.79, 1.63.2, 1191, 99.97, 141.1, 136.9, and 773 for the 1D, 2D, and 3D SWZCC codes and the PD, PD/MD, DCS/MD, and PTZCC codes, respectively. ·         Our proposed code can satisfy optical communication needs with an optical bandwidth of 0.03  THz, while the 3D-PD, 3D-PD/MD, 3D-DCS/MD, 3D-PTZCC and2D-SWZCC codes force the OCDMA system to access optical bandwidths of 4.6, 4, 3.7, 0.07 and 1.68 THz, respectively. Employing the 3D-SWZCC code enables the OCDMA system to decrease its use of the bandwidth of the light source by 4.75, 3.97, 3.67, and 0.04 THz compared with the 3D-codes PD, PD/MD, DCS/MD, and PTZCC, respectively; additionally, 1.65 THz of bandwidth is saved by moving from 2D to 3D. ·         Employing our proposed code enables each user in the OCDMA system to require only minor power at the receiver level and saves around -9.1 and -1.1dBm compared with the 3D-DCS/MD and 3D-MD codes, respectively. In addition, the transitions from 1D to 3D and from 2D to 3D save around -8.3 and -4.6 dBm, respectively. ·         Employing our proposed code in an OCDMA system can supply a great data rate, nearly 5 Gbps, while other codes cannot reach 1 Gbps, with the exception of the 3D-MD code. This optimization can be explained by the ZCC property of our code, which positively and effectively optimizes the OCDMA system performance. Additionally, the 1D and 2D SWZCC codes enable each user in the OCDMA system to exploit up to 0.12 and 0.67 Gbps, respectively
Network Results	·         First, note that the eye diagrams of eight active users shown in Figure 16 are all different, and none of them are similar to each other. Moreover, the Q-factor values of the users are between 9 and 12 dB, which means that our proposed code offers good results in spite of high data rates, up to 8 Gbps. The 3D-SWZCC code has the ability to detect and restore the desired signals. ·         Second, the performance of the 3D-SWZCC code is also estimated at different data rates and characterized by referring to the BER and the eye diagram patterns, as shown in Figure 17. It is clear that the SWZCC code gives the 3D-OCDMA system a good performance; this can be observed through the resulting BER and Q-factor values. The BER values are: ,  and  and the Q-factor values are 18.84, 11.09, 8.51 and 7.05 for data rates of 0.622, 1, 1.5 and 2 Gbps, respectively.

The results above demonstrate that the 3D-SWZCC code is capable of outperforming the other codes tested in this investigation, making it more flexible and convenient for meeting optical communication demands and being used in an NG-3D-OCDMA-PON network.

6.2/  In 6.1. Principle of 3D-OCDMA-PON – you start to describe the system again. This is the same system as the one described in section 3. System Function? Is different?

6.2. Answer

Section 3 is devoted to describing the 3D-SWZCC-OCDMA system, while Section 6.1 is devoted to using the OCDMA system based on the 3D-SWZCC code for a PON and solving the aforementioned problems.

Section 6.1 offers a novel scheme for the WTS-OCDMA system by relocating the SCs in order to diminish the power decline and extent of the fibers among the transmitter (Te) and receiver (Re) nodes. The proposed architecture is able to significantly emulate the conventional scheme of a PON while keeping the great cardinality and capacity of a 3D-SWZCC-based OCDMA system.

Although there are a lot of fibers used between OLT and ONUs, PON is employed to save the number of fibers but this number is necessary to achieve spatial encoding as FBG and delay lines are needed to achieve the spectral and temporal encoding respectively.

 

The advantages of the proposed OCDMA- PON compared to such state-of-art PON technologies. The optical CDMA technique is a point-to-multipoint technology where each end-user picks up its own message from the broadcast signal. Similarly, PON architecture is also point-to-multipoint access technology with passive components, such as splitters, couplers, fiber optics, etc., where potentially the cost is reduced.

As the amount of energy that can be consumed by an AON is more than that consumed by a PON. Therefore, a PON is considered overall to be an energy saver.  This contributes to saving the power consumed by the OCDMA system if the OCDMA and PON have emerged in the same network.

 

In order to obtain results that can be described as near the practical performance of such a system, some factors should be taken into consideration, such as the non-linearity characteristics of a single-mode fiber (SMF) and noise sources, represented by the thermal noise coefficient.

 

Question 7:

In 6.1 sees to have a different implementation of the same system – but the results are expressed differently (based on the eye diagrams and the values of Q factors versus distance). Is there any connection between the simulation results shown in sections 5 and 6? From all those eye diagrams, can’t you extract some conclusions?

Answer

 

Section 5 is dedicated to translating the mathematical modeling of our system in terms of BER, SNR, Q factor,....etc, where the simulation results demonstrate that the 3D-SWZCC code is able to outperform the other codes tested in this section investigation, making it more flexible and convenient to meet optical communication demands.

 

In order to confirm the obtained results (section 5), the system function is provided by exhibiting the architecture of the transmitter and receiver in the PON context (section 6), where the proposed code demonstrates its effectiveness in meeting optical communication requirements based on 3D-OCDMA-PON by producing a high quality factor (Q) equals to 18.8 and low bit error rate (BER) of  over a long distance which can reach 30 Km for a data rate of 0.622 Gbps.

 

The performance of the system is noticed by the vertical opening of the eye diagram, if the vertical opening is maximum, the system performs better and the data is received under better conditions, which causes a low error rate on bits and achieves good transmission quality at a long distance, and if the vertical opening of the eye diagram is minimal, the system becomes bad and the data transmitted at the receiver are perturbed.

 

As shown in Figures 17 to 19, it can be seen that the vertical opening of the eye diagram of the proposed code is maximum, which indicates that the data from the transmitter is received almost perfectly despite a long SMF distance. Thus, our system can be used in optical systems that support transmission over long distances.

Question 8:

 

Finally, there are a lot of issues with the alignment of the text, spacing between the lines is different in several sections – overall the text has a disordered and unkempt aspect.

 

Answer

 

Your recommendations have been taken into account and have been corrected

 

Question 9:

But, the main issue is that I do not see the novelty of this approach. The authors performed simulations in two different simulators, but the two simulations seem not to be connected to one another. Furthermore, there is no comparison with other similar papers already publish to validate the results.

Answer

This paper proposes a novel three-dimensional (3D) spectral/temporal/spatial single-weight zero cross-correlation (3D-SWZCC) code for optical code division multiple access (OCDMA) systems. The proposed code could potentially be used by the next generation of passive optical networks (NG-PONs) providing a 3D-SWZCC-OCDMA-NG-PON system in order to:

1. Completely suppress the multiple access interference (MAI) effects that constitute a main drawback for OCDMA systems
2. Diminish the power decline and extent of the fibers among the transmitter (Te) and receiver (Re) nodes.
3. Saving the power consumed by the OCDMA system if the OCDMA and PON have emerged in the same network.

The proposed system is already compared to other systems, as indicated in section 5.

By using the parameters listed in Table 3, the proposed 3D-SWZCC code shows better performance compared to 3D-PD, 3D-PD/MD, 3D-DCS/MD, 3D-PTZCC codes, and the same code in 1D and 2D domains (1D-SWZCC and 2D-SWZCC) and this is due to ZCC property which completely suppresses the PIIN noise which leads to the elimination of the MAI.

Moreover, to give more credibility to these results, our code is also studied in section 6 using the parameters of Table 4 where the results indicate that the proposed 3D-OCDMA-PON code satisfies the needs of the optical transmission and respects the conditions of optical communication.

Answer:  plagiarism detector

Concerning the anti-plagiarism software, it detects several technical words in addition to our emails, the names of the authors and of our university, we do not have the possibility of rewriting them in other words, so it is irreplaceable, this are technical words and the name of our university and my email

: we quote for example:

*/ code for optical code division multiple access (OCDMA)

*/the next generation of passive optical networks (NG-PONs)

*/characterized by a high capacity and a zero cross-correlation property

of the 3D-SWZCC

*/Three-dimensional, Single weight zero cross correlation (SWZCC)

*/ 3D-PD/multi-diagonal (3D-PD/MD) code

*/ University of Saida. Algeria

*/ mon email:

Correspondence: [email protected]

 

Author Response File: Author Response.pdf

Reviewer 2 Report

The paper presents a novel 3D coding scheme for optical CDMA systems. The code is based on a 1D scheme. The authors explain the code construction in a systematic and detailed manner. The system in which the code is used is also explained. The performances of the coding scheme are then analyzed through simulations. Several results are given for various scenarios and parameter values. The results demonstrate the advantage of the new coding scheme over ither similar schemes. The authors then use the coding scheme in a network simulation software in order to obtain more practical results. Again, the performances of the new scheme are shown to be very good.

 

 

The paper is in general well written. However, there are several typos and formatting issues.

 

Line 166: “a constant weight… exactly one” is repeated.

 

Line 222: “X” is missing (X, Y, and Z)

 

Line 316: “where” (lowercase “w”, this error is present in several places in the text).

 

In several places, words are not separated by spaces, as in line 424.

 

In the text, do not put a “.” after “Figure”.

 

Line 550: what are the parameters?

 

Line 578: rewrite the phrase. “and” before “PON” ?

 

Line 583: no verb in the phrase.

 

Line 738: sills?

 

Line 770: “of than 6 dB”?

Author Response

Capacity Improvement of 3D-OCDMA-PON Hybrid System Next Generation Using Weight Zero Cross Correlation Code

Dear Editor;

First, we thank the editor and the journal team for their efforts to improve and develop scientific
research, second we would like to thank the reviewers for the appreciation given to our work, also for their valuable comments and relevant suggestions. We have provided detailed answers to their comments and mentioned the changes brought according to their suggestions. The reviewers’
comments are in black font and the answers are in blue font, revisions on the manuscript are in green.

We hope we have correctly addressed the questions recommended by the reviewers.

Reviewers Comments:

Reviewer 2:

We thank the reviewer for his questions that help us improve the paper.

 

The paper is in general well written. However, there are several typos and formatting issues.

 

Question 1 :

 

Line 166: “a constant weight… exactly one” is repeated.

 

Answer:

 

Your recommendations have been taken into account and have been corrected as much as possible

 

Question 2 :

 

Line 222: “X” is missing (X, Y, and Z)

 

Answer:

 

Your recommendations have been taken into account and have been corrected as much as possible

 

Question 3 :

 

Line 316: “where” (lowercase “w”, this error is present in several places in the text).

 

Answer:

 

Your recommendations have been taken into account and have been corrected as much as possible

 

Question 4:

 

In several places, words are not separated by spaces, as in line 424.

 

Answer:

 

Your recommendations have been observed and corrected as much as possible

 

Question 5:

 

In the text, do not put a “.” after “Figure”.

 

Answer:

 

Your recommendations have been observed and corrected

 

 

Question 6:

 

Line 550: what are the parameters?

 

Answer:

The parameters are values of different variables used in the simulation according to the mathematical analysis

Question 7:

 

Line 578: rewrite the phrase. “and” before “PON” ?

 

Answer:

 

Your recommendations have been observed and corrected

 

Question 8:

 

Line 583: no verb in the phrase.

 

Answer:

 

Your recommendations have been observed and corrected

 

Question 9:

 

Line 738: sills?

 

Answer:

 

Your recommendations have been observed and corrected

 

Question 10:

 

Line 770: “of than 6 dB”?

 

Answer:

 

Your recommendations have been observed and corrected

 

 

 

Author Response File: Author Response.pdf

Reviewer 3 Report

The work proposes a novel three-dimensional (3D) spectral/temporal/spatial single-weight zero cross-correlation (3D-SWZCC) code for optical code division multiple access (OCDMA) systems. From the abstract to the conclusions, all sections are easy to understand, well-structured, and developed. The study of state of the art is complete. The results and comparisons are clear and precise, and their discussion is quite relevant. My congratulations on the work done. 

Author Response

Capacity Improvement of 3D-OCDMA-PON Hybrid System Next Generation Using Weight Zero Cross Correlation Code

 

 

Dear Editor;

First, we thank the editor and the journal team for their efforts to improve and develop scientific research, second we would like to thank the reviewers for the appreciation given to our work, also for their valuable comments and relevant suggestions.

 

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The paper is clearer now with respect to its previous version, an its quality improved. However 

 

 

- regarding section 5, the authors still need to explain in more detail the simulation setup and parameters (the Matlab software is run on a computer with the following characteristics A, B, etc)

 

- In section [5] the results are compared with the  3D-PD, 3D-PD/MD, 3D-DCS/MD  and 3D-PTZCC (references are needed for each code).

 

- Also at line 402 “curves of the codes that belong to ZCC families (1D, 2D, 3D-SWZCC, and 3D-MD codes) have greater SNR values than the others” (references are needed for each ZCC family).

 

 

- Also at line 444 “… compared with the3D-DCS/MD and 3D-MD codes, respectively” (references are needed)

 

- Also at line 455 “ …For the BER threshold, our proposed code can satisfy optical communication needs with an optical bandwidth of 0.03 THz, while the 3D-PD, 3D-PD/MD, 3D-DCS/MD, 3D-PTZCC and 2D-SWZCC …” (references are needed)

 

 

- at line 493 “OCDMA system cardinality is 454, 354, 157, 493

141, 122, 107 and 68 for the 3D-SWZCC, 3D-MD, 2D-SWZCC, 3D-DCS/MD, 3D-PD/MD, 3D-PD, and 1D-SWZCC codes, respectively” (references are needed)

 

 

- at line 526 “To confirm this, the values of the PIIN at ??=-25 dBm are 3.9 × 10−18, 5.4 × 10−18, 3.13 × 10−15and 8.3 × 10−15 A for the 3D codes SWZCC, PTZCC, DCS/MD, PD and PD/MD respectively.” (references are needed)

 

 

- Figures 14, 15 are blurred. Please replace them with a clearer version.

 

- Figures 16, 17 are unclear. The text cannot be read clearly, even if increasing the zoom at 400%. Please replace them with a better version.

 

 

 

 

 

Author Response

Please see the attachment.

Author Response File: Author Response.pdf