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Peer-Review Record

An Efficient Resource Allocation Algorithm for OFDM-Based NOMA in 5G Systems

Electronics 2019, 8(12), 1399; https://doi.org/10.3390/electronics8121399

by Omar A. Saraereh¹

, Amer Alsaraira²

, Imran Khan³

and Peerapong Uthansakul^4,*

Reviewer 1: Anonymous

Reviewer 2: Anonymous

Reviewer 3: Anonymous

Electronics 2019, 8(12), 1399; https://doi.org/10.3390/electronics8121399

Submission received: 15 October 2019 / Revised: 15 November 2019 / Accepted: 21 November 2019 / Published: 23 November 2019

(This article belongs to the Section Microwave and Wireless Communications)

Round 1

Reviewer 1 Report

The paper proposes an optimization algorithm for a NOMA system. Although the contribution of the paper is very poor, overall the work is fine. At the same time, I like to provide a couple of comments to improve the manuscript.

1. The paper title is not appropriate. Please change it to something like

"An Efficient Resource Allocation Algorithm for OFDM-based NOMA in 5G systems".

2. As a part of the system model, provide a diagram of an OFDM-based downlink NOMA system and explain that so that it can be easily understood.

3. Include a few more recent references on general NOMA. For example,

"Non-Orthogonal Multiple Access (NOMA): How It Meets 5G and Beyond" (2019)

Author Response

Comments from Reviewer 1

Comments and Suggestions for Authors

The paper title is not appropriate. Please change it to something like

"An Efficient Resource Allocation Algorithm for OFDM-based NOMA in 5G systems".

Author Response: We would like to thank the reviewer for the valuable suggestions and recommendations which improved the manuscript. We have changed the paper title with the recommended title.

As a part of the system model, provide a diagram of an OFDM-based downlink NOMA system and explain that so that it can be easily understood.

Author Response: Thank you very much for your encouraging comments. We have added a diagram (Fig.1) of the proposed OFDM-based downlink NOMA system which further improved the readability and understanding of the proposed study.

Include a few more recent references on general NOMA. For example,

"Non-Orthogonal Multiple Access (NOMA): How It Meets 5G and Beyond" (2019)

Author Response: Thank you very much for your constructive comments. We have added more recent relevant references to the manuscript including the above recommended reference on general NOMA.

Reviewer 2 Report

References list shows 27 references has been used. They do not all appear in the text if they have been used. For example references from 1-5 do not appear to have been used. Similarly there are others that are not used. Lines 37-48 seems unclear “in tradition OMA, a single user can only allocate a single resource …”. Is it the user who is responsible to allocate the resource? Again there are issues in referencing that need looking at mainly in section 1 and subsequent sections where necessary. Line 148 “specific steps of GA scheme”. What is GA? I appreciate that algorithm is described using steps, however, it will be lot useful to add a flowchart of the algorithm. A flowchart will provide much better understanding of the algorithm. Same applies to algorithm 2. Please include a flowchart. In results comparisons from figure 1 onward, please elaborate clearly why the algorithms performs better than its counterparts. For example, line 260 to 263 discuss about the comparison of algorithms. Please elaborate why the proposed algorithm performs better. Also, table 1 shows the channel estimation parameter as “Ideal”. How the proposed algorithm is better from [17]. Lines 263 to 265 especially discuss the evaluation of the algorithm based on the channel quality. Please elaborate this point in the discussion. The attenuation factor was chosen as 0.2, was there any particular reason for this? Line 316” When the performance better to the exhaustive algorithm is obtained, the search range is reduced…” is unclear.

Author Response

Comments from Reviewer 2

Comments and Suggestions for Authors

Author Response: Thank you very much for your constructive comments which improved the manuscript. We have corrected the references list and properly cited them in the text.

Lines 37-48 seems unclear “in tradition OMA, a single user can only allocate a single resource …”. Is it the user who is responsible to allocate the resource?

Author Response: Thank you very much for your encouraging comments. We have rephrased the sentence which correctly reflect the actual meaning of the terms. Actually, in OMA, a single resource is allocated to a single user.

Again there are issues in referencing that need looking at mainly in section 1 and subsequent sections where necessary.

Author Response: Thank you very much for your solid technical comments. The referencing is corrected in Section 1 and in the rest of the paper.

Line 148 “specific steps of GA scheme”. What is GA?

Author Response: Thank you very much for your remarkable comments. The abbreviation of GA is greedy algorithm which is highlighted in the corresponding sentence.

I appreciate that algorithm is described using steps, however, it will be lot useful to add a flowchart of the algorithm. A flowchart will provide much better understanding of the algorithm. Same applies to algorithm 2. Please include a flowchart.

Author Response: Thank you very much for your encouraging comments. As followed by majority of researchers, the step-wise description of the algorithm is more effective. Therefore, we have also followed this trend. As this step wise and flowchart description provides the same meaning of the technique, therefore, it has been added. However, if its still mandatory then we can add it in the second round of revision.

In results comparisons from figure 1 onward, please elaborate clearly why the algorithms performs better than its counterparts. For example, line 260 to 263 discuss about the comparison of algorithms. Please elaborate why the proposed algorithm performs better.

Author Response: Thank you very much for your solid technical comments. As indicated by the numerical results of Fig. 2 (updated after adding Fig. 1 of system model), the total system throughput increases with the number of users for all the algorithms. However, it is clear that the proposed algorithm gives better throughput for each number of users than the existing state-of-the-art algorithms. For example, when the number of users is 20, then the throughput given by the proposed algorithm is 5.4 Mbit/s, whereas the throughput given by references [29], [20] and [21] is 5.1Mbit/s, 4.8Mbit/s, 4.2Mbit/s respectively.

In Fig. 3, the total system throughput is compared with the total number of cellular users. As can be seen that the proposed algorithm gives a better throughput performance for each number of cellular users as compared with the references [30] and [31] algorithms. For example, when the number of cellular users is 20, then the throughput given by the proposed algorithm is 4.16Mbit/s whereas the throughput given by reference [30] and [31] is 3.9Mbit/s and 3.7Mbit/s respectively.

In Fig. 4, the total system throughput is compared against the power allocation factor for the algorithms. As can be seen from the results that the throughput of the proposed algorithm decreases less than the existing references [30] and [31] algorithms for each power allocation factor value. This gives us idea that the proposed algorithm is robust against power allocations and is more reliable in variable power allocation scenarios. For example, for power allocation factor of 6, the proposed algorithm gives a throughput of 3.18Mbit/s whereas references [30] and [31] gives a throughput of 2.95Mbit/s and 2.75Mbit/s respectively.

In Fig. 5, another important result is compared: the achievable sum rate against the power-to-noise ratio for the algorithms. It can be obvious from the results that the proposed algorithm gives better achievable sum rate for all values of the power-to-noise ratio as compared with references [29], [20], [21] and OMP algorithms. For example, when the power-to-noise ratio is 35 dB, then the achievable sum rate given by the proposed algorithm is 375bps/Hz, whereas the achievable sum rate given by references [29], [20], [21] and OMP algorithms is 3.51bps/Hz. 340bps/Hz, 330bps/Hz and 310bps/Hz respectively.

In Fig. 6, the sum rate is evaluated against the number of iterations for the algorithms. As for a good algorithm, it requires lesser number of iterations to reach the maximum sum rate performance; same is given by the proposed algorithm. As indicated from the results, the proposed algorithm gives a sum rate of 5.95bps/Hz when number of iterations is only 3 whereas the reference [29] gives its peak sum rate of 5.54bps/Hz when the number of iterations is 11. For the reference [20] algorithm, it requires 40 number of iterations to reach to its peak sum rate of 4.8bps/Hz. For the reference [21] algorithm, it requires 40 number of iterations to reach its peak sum rate of 3.9bps/Hz. Finally, the traditional OMA scheme requires 40 number of iterations to reach its peak sum rate of 3.3bps/Hz respectively. In summary, the proposed algorithm gives better sum rate and reaches quickly to its peak value with a smaller number of iterations required. This makes the proposed algorithm simple to implement with a smaller number of signal processing required.

Also, table 1 shows the channel estimation parameter as “Ideal”. How the proposed algorithm is better from [17].

Author Response: Thank you very much for your remarkable comments. It was mistakenly mentioned as ideal whereas it is actually the attenuation factor.

Lines 263 to 265 especially discuss the evaluation of the algorithm based on the channel quality. Please elaborate this point in the discussion.

Author Response: Thank you very much for your encouraging comments. It is rephrased and the correct term CSI is used.

The attenuation factor was chosen as 0.2, was there any particular reason for this?

Author Response: Thank you very much for your solid technical comments. No, there was no particular reason as this value is mostly used by the existing literature for numerical experimentations analysis, therefore, following their trend, we have also chosen this value for our simulation experiments.

Line 316” When the performance better to the exhaustive algorithm is obtained, the search range is reduced…” is unclear.

Author Response: Thank you very much for your constructive comments. It has been rephrased with clear understanding.

Reviewer 3 Report

Major comments

This paper deals with algorithm development for non-orthogonal multiple access wireless networks. Overall, the scope and timeliness of the contribution are good. Description of the previous and parallel literature in the theme of the manuscript is well covered. Own contributions have been motivated and numerically compared against the selected state-of-the-art schemes. Presented numerical results demonstrate that the proposed algorithm is clearly functional and competitive in performance. There are no major flaws to be mentioned but some minor issues are raised below (mainly language/typographical in nature) with respective correction proposals.

Minor comments

Abstract, page 1, line number 22: … to solve … -> … to be solved … Abstract, page 1, line numbers 25-26: … and reduced complexity performance than the existing state-of-the-art algorithms. -> … than the existing state-of-the-art algorithms and reduced complexity performance. Introduction, page 1, line number 32: … needs … -> … need … Introduction, page 1, line number 34: … has been difficult … -> … has got difficulties … Introduction, page 2, line numbers 49-50: The expression beginning as ‘Multi-user separation …’ should be revised as in the present form it is not a complete sentence. Introduction, page 2, line number 59: From this point onwards the word ‘literature’ has been used excessively in conjunction with references. However, it associates to a larger entity than an individual reference. Therefore, I suggest to use alternative formulations in citations (baseline … reference []). Introduction, page 2, line number 71: … transmits power is equally distributed … -> … transmits power equally distributed … or … transmit power is equally distributed … Introduction, page 2, line number 83: … to solve separately … -> … to be solved separately … Introduction, page 2, line number 87: … are allocated power … -> … having power allocated … or … that have been allocated power … Introduction, page 2, line number 92: … Algorithms and its principle are analyzed. -> … algorithms and their principles are analyzed. Section 2, page 3, line numbers 101-103: Ensure that all equations are fully embedded and integrated into surrounding phrases with proper punctuation. In this case the colon before the equation is unnecessary. After the equation the word where (not capitalized) should continue the sentence being indented to the left. This principle applies to the rest of manuscript and requires revisions in many places. Section 2, page 4, line number 129: … equation(7) … -> … equation (7) … Section 4, page 7, line number 233: … K , then … -> … K, then … Section 4, page 7, line number 236: … sub-addition … -> … sub-additions … Section 4, page 7, line number 237: … multiplication … -> … multiplications … Section 4, page 7, line number 238: … addition … -> … additions … Section 4, page 7, line number 238: … multiplication … -> … multiplications … Section 4, page 7, line number 241: … than the iterative … -> … than in the iterative … Section 5, page 8, line number 243: … NMA … -> … NOMA … Section 5, page 8, line number 259: … 0.2 . … -> … 0.2. … Section 5, page 11, line number 295: … increase … -> … increases … Section 5, page 11, line numbers 298-299: In my opinion the claim that the proposed algorithm is more robust than the reference schemes is not substantiated by the results of Fig. 4. All curves have almost identical shape and thus respond similarly to the changes in power to noise ratio. In a matter of fact, the proposed algorithm seems to more sensitive (less robust) than others in the regime 0 … 5 dB that can be considered the noisy environment in this plot. Section 5, page 11, line number 299: … a noisy environments … -> … noisy environments … Section 5, page 11, line number 299: … scheme. -> … schemes. Section 5, page 11, line number 309: … algorithms. -> … algorithm’s. Section 6, page 12, line number 322: … it’s … -> … its …

Author Response

Comments from Reviewer 3

Comments and Suggestions for Authors

Major comments

Minor comments

Abstract, page 1, line number 22: … to solve … -> … to be solved …

Author Response: Thank you very much for your solid technical comments. The correction has been made.

Abstract, page 1, line numbers 25-26: … and reduced complexity performance than the existing state-of-the-art algorithms. -> … than the existing state-of-the-art algorithms and reduced complexity performance.

Author Response: Thank you very much for your constructive comments. The correction has been made.

Introduction, page 1, line number 32: … needs … -> … need …

Author Response: Thank you very much for your encouraging comments. The correction has been made

Introduction, page 1, line number 34: … has been difficult … -> … has got difficulties …

Author Response: Thank you very much for your remarkable comments. The correction has been made.

Introduction, page 2, line numbers 49-50: The expression beginning as ‘Multi-user separation …’ should be revised as in the present form it is not a complete sentence.

Author Response: Thank you very much for your solid technical comments. The sentence has been revised.

Introduction, page 2, line number 59: From this point onwards the word ‘literature’ has been used excessively in conjunction with references. However, it associates to a larger entity than an individual reference. Therefore, I suggest to use alternative formulations in citations (baseline … reference []).

Author Response: Thank you very much for your encouraging comments. The corrections have been made.

Introduction, page 2, line number 71: … transmits power is equally distributed … -> … transmits power equally distributed … or … transmit power is equally distributed …

Author Response: Thank you very much for your encouraging comments. The correction has been made.

Introduction, page 2, line number 83: … to solve separately … -> … to be solved separately …

Author Response: Thank you very much for your encouraging comments. The correction has been made.

Introduction, page 2, line number 87: … are allocated power … -> … having power allocated … or … that have been allocated power …

Author Response: Thank you very much for your constructive comments. The correction has been made.

Introduction, page 2, line number 92: … Algorithms and its principle are analyzed. -> … algorithms and their principles are analyzed.