kumoh national institute of technology
Networked Systems Lab.

Mohtasin Golam, Williams-Paul Nwadiugwu, Rubina Akter and Dong-Seong Kim, "Brownian Motion Based UAV-assisted Energy Harvesting Scheme for Internet of Battlefield Things", IEEE Communication Letters 2019. (R)
By : Mohtasin Golam
Date : 2019-11-19
Views : 238

Dear Author(s):

The review of the referenced manuscript, CL2019-2209, entitled Brownian Motion Based UAV-assisted Energy Harvesting Scheme for Internet of Battlefield Things, is now complete. I regret to inform you that based on the enclosed reviews and my own reading of your manuscript, I am unable to recommend its publication in IEEE Communications Letters.

Your paper may not be resubmitted for review. The reasons for this are as follows:
- Poor and confusing problem formulation.
- Very weak and unclear contributions.
- Lack of relevant literature review making it hard to judge the claimed contributions.
- The problem formulation and system model are incomplete and confusing.
- The mathematical model is missing main convincing proof/derivation steps and cannot be justified.
- The selected benchmarking system are not justified/clarified.
- Poor paper writing and confusing disorganized flow.

Additional comments include:

The abstract is not well presented nor well structured
The literature survey doesnt cover the existing relevant work; i.e., trajectory optimization for energy harvesting UAVs, which is a very rich literature. Hence, the contrast of claimed contributions versus state-of-the-art is missing.
The problem definition in Section II is quite shallow and confusing due to several missing details such as who is sending energy and who is harvesting (drone or IoT), what are the involved components (IoT ground devices, drone, ...etc.), what is the main issue, ...etc.
What is the justification of using FBM with Hurst 1/2 for modeling the system at hand?
Equations (6) & (7) are confusing and have no reference nor justification.
Equation (12) & (13) are very awkward since they have P_{Trans(max)} and P_{Trans(min)} appearing in the Nominator and Denominator in both cases, respectively. This doesnt always guarantee a maximum or a minimum value!
Equation (15) has no justification nor derivation and it is supposed to be a main finding in this work!
The selected benchmarking techniques are not justified and the compared parameters are not clear (what is the Energy %? It is percentage of what?).
The structure of the paper and relations between different sections as well as the follow are very confusing.
The writing of the paper is very poor and has many spelling and grammatical mistakes.

The reviewers' comments are found at the end of this email.

Thank you for submitting your work to the IEEE Communications Letters.


Prof. Tamer Khattab
Associate Editor
IEEE Communications Letters

Reviewer: 1

Comments to the Author
This paper discusses a trajectory optimization approach of an unmanned aerial vehicle (UAV) node, where the authors propose the addition of the energy harvesting (EH) constraint of several ground nodes in a battlefield environment. The authors have modeled the movement of the UAV to follow a Brownian motion model, and then attempted to optimize the amount of harvested energy of the ground nodes.

The paper is not clearly presented. For instance, the Simultaneous Transmission and Energy-Harvesting Scheme sub-section and most of the System Model section are taken from reference [9] in the paper, and the Fractional Brownian Motion (FBM) subsection is taken from reference [10] in the paper. The most important part of the paper, which is Eq. (15), is not discussed at all. Hence, it is not clear to me how does the Brownian motion of a UAV is involved in this work. Is the UAV forced to follow a Brownian motion model to maximize EH, or is this a practical modeling of the UAVs trajectory? Moreover, it seems to me from the results, particularly the result depicted in Fig. 4, that the UAV follows a much longer path when compared with the benchmark trajectory, thus compromising the energy efficiency of the UAV. Perhaps if the paper was significantly re-structured, the contributions could be clearer.

A few more comments regarding the presentation of the paper are below:

In general, it is quite challenging to read the paper as the language can be improved.
Some acronyms are not defined, e.g. SWIPT and WPT.
There is a problem with the references in the paper. For instance, the reference mentioned in Page 1, line 58, second column does not discuss Eq. (2) at all. The same for the reference mentioned in Page 2, line 20, left column.
In Page 2, left column, line 22: The reference (Mandelbrot and Van Ness 1968) has the wrong format and not mentioned in the references.
Page 2, left column, line 2: \lambda is the wavelength and not the efficiency parameter. I think you meant \eta instead.
Page 2, left column, line 34: this is not the definition of the Gamma function.
In Eq. (12), shouldnt the denominator be a function of P_{Trans(max)} instead of P_{Trans(min)}? The same for Eq. (13), shouldnt the denominator be a function of P_{Trans(min)}?
Some parameters in Eq. (15) are defined after mentioning them, and others are not even defined.
Some parameters in Table II are not defined in the text (Dropout, Conv 2D).
What are the Benchmark methods in Fig. 3. What does Iterations mean for the x-axis?
What is the unit of time in Fig. 5?

Reviewer: 2

Comments to the Author
Authors have utilized UAVs as a hub-point between base station and IoT devices in a battle environment. In such a scenario, authors argued that a major concern is the energy requirement of the IoT devices, thus, they proposed an energy-harvesting technique along with trajectory optimization of the UAVs to ensure the longevity of IoT devices.

Mainly, because of the poor writing style, it is difficult to follow the presented concepts. The authors have claimed in the contributions that they have presented an energy harvesting scheme along with the trajectory optimization. In the system model, they have presented such a technique in eq (15), however, it is not properly stated that how they have optimized this equation. Thus, the solution of the presented idea is unclear.

The eqs from (4-8) related to brownian motion were stated, however, unused in relation to the maximization problem.

The optimal solution presented in Fig. 3 is compared with two benchmark techniques, however, the authors have not mentioned those techniques with proper references anywhere in the paper.

In Table 2, authors have mentioned Conv 2D and Dropout values, however, they have not explained their use in any equation. Usually such terms belong to neural networks (NNs), however, there is no mention of these NN tools.

I feel that it is very difficult for the readers to follow the presented ideas in the article due to poor presentation of the ideas and writing style. Moreover, authors should clearly mention the equation of their main optimization problem and then explain the technique to solve that problem. The explanation of the simulation setup needs improvement.

Other than the above mentioned major concerns, following are some editorial comments.

- line 49, 1st column, page 1, full form of SWIPT at its first mention is missing.
- line 11, 2nd column, page 1, energy proficiency of?
- line 38, 2nd column, page 1, state clearly, what do you mean by increasing communication? is it communication time?
- eq 1, define X, R and R_opt
- line 2-5, 1st column, page 2, re-write clearly
- line 16, 1st column, page 2, re-write the sentence clearly
- eq4, define t and s
- Explain the equations 4 and 5
- eq 8, define sigma
- differentiate the notation of X for a set of time slots (line 36, 2nd column, page 2) and eq 2
- Fig 2 is unclear due to undefined notations

Reviewer: 3

Comments to the Author
While this paper tackles an important subject, I believe it suffers from major issues:
1- The paper is poorly written and is full of both grammatical mistakes and structural ones.
2- The contribution of the paper is not well articulated, especially when it comes to the distribution of the nodes on the ground.
3- The use of Brownian motion to model the UAV movement is not well presented nor justified in the paper.
4- The whole idea of using a UAV to charge ground nodes in a broadcast fashion might be questionable.
5- I don't see the relation for section II.A. The cited equation doesn't exist in reference [8].
6- Equation (15) which seems to be essential for the paper comes with no derivation or justification.
7- Details about the other schemes used for comparison is missing which raises doubts about the validity of the comparison.
8- Ref [10] is not cited in the paper.
In summary, while the topic of the paper is important, and the idea of using Brownian motion for modeling the UAV movement might be promising, the paper needs major effort to have it ready for publication.