Blockchain-Based Spectrum Sharing Algorithm for UAV-Assisted Relay System

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This paper studies spectrum sharing algorithm with UAVs act as relays. While the topic is timely, there are a number of concerns need to be addressed.

 

1.     Why we need “security guarantees for spectrum sharing”? Please clearly explain. 

2.     Would blockchain causes significant delay?

3.     In p.2, it is stated that there is hardware limitation of UAVs. But then later in that paragraph, it is stated that “UAVs engage in spectrum sharing by leasing and purchasing spectrum from BS, and spectrum transactions between the PU system and the SU system are realized through Stackelburg games, constructing a blockchain-based transaction model …….”. If the hardware of UAVs is limited, how can UAVs perform so many tasks? Is there a contradiction here?

4.     Why the power allocation is done by greedy algorithm? As power is a continuous variable, why not use conventional optimization method [R1] or projected gradient descent [R2]? Please justify in the paper why other methods are not used.

5.     What is the difference between cellular users and ground terminal users?

6.     How the equations (4) and (5) reflect the NOMA operation? In general, the SINR expression in NOMA formulation should depend on the decoding order, see [R1][R2].

7.     In UAV positioning problem (P4), how many UAVs are there? From Fig. 1, there are multiple UAVs. If multiple UAVs are positioned at the same time, should there be a minimum separation UAVs to ensure safety? Why there is no such constraint in (P4)?

8.     Any relationship between Algorithm 1 and Algorithm 2? If no, why the two problems are studied independently? Why not perform joint optimization?

 

 

[R1] ``NOMA-based Pervasive Edge Computing: Secure Power Allocation for IoV," IEEE Trans. on Industrial Informatics, 2021.

[R2] ``Massive Access in Secure NOMA under Imperfect CSI: Security Guaranteed Sum-rate Maximization with First-order Algorithm," IEEE Journal on Selected Areas in Communications (JSAC), 2021.

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Abstract

 

The topic is very interesting and valuable since UAVs have more and more applications. What is really innovative is the challenge of spectrum scarcity. This is not only a technical but also an economic issue. So the paper proceeds with a utility function methodology to define an optimal algorithm. On top of that the authors do a Spectrum trading between PUs and Sus which modeled as a Stackelberg game and further to ensure security they suggest a blockchain algorithm. So this is a paper with a lot of work that includes a lot of interesting ideas and suggests practical solutions in a novice and forward thinking manner.

 

Introduction

 

The paper starts very precisely and the arguments are solid. However, in some parts elaboration could be beneficial and further strengthen the scope of the paper. For example, lines 26-29 could be extended to a small paragraph to provide some context and why UAV are ‘becoming and essential tool’ Trends, statistics and other empirical evidence can be useful. Also lines 29-32 could be expanded to a small paragraph, not only mentioning scarcity but what are the negative effects of scarcity and the problems it creates.

Lines 36-50 are very good describing spectrum sharing. Then the analysis flows very well, identifying security as a challenge and consequently blockchain as a solution and highlights the limitations of previous work.

Then the authors lay out (one of) their contribution ‘On the other hand, a reasonable and secure spectrum sharing mechanism is needed, including the process of spectrum leasing, bandwidth allocation, and fair pricing. We propose a blockchain-based spectrum sharing algorithm for the UAV cooperative communication system’. The economic element in this work is critical and is appreciated. Some more analysis focusing on some costs etc. could be a useful addition.

 

In line 92 the authors say ‘The specific innovations are as follows’ That is fine, but if the authors add ‘contributions’ and mention briefly the literature gaps and add some phrases what is unique, lines 94-132.

 

Before system model I would advice a short Literature review highlighted important studies and key arguments related to the model before proceeding to it.

 

System Model

 

Figure 1 on the system model is very illustrative. The rest of the models looks good.

In lines 187-188 ‘To maximize the utility of both users, we employ greedy and Nelder Mead algorithms for optimizing the UAV's position and transmission power.’ This needs some more explanation, why is this algortm useful? Who has used it before? Are there any more options, and why is the Nelder Mead algorithm the best option?

Lines 194-198 This is a general description of Blockchain – which blockchain technology are you going to use? Have you considered hyper ledgers, it might be better for such system. Moreover, blockchain can add much computing burden on the communications – and you have to analyse that later.

 

Spectrum Sharing

 

The models and equations seem right. For the Utility Function some more justification can be useful. Does it correspond to other Utility Functions? Is there any related literature? Why have you picked this function? I can provide some arguments against it, but in general I think it is good, but needs some more justification. The rest of the optimization process seems effective, but it is not my expertise and other reviewers can better comment on hat.

 

Blockchain

 

The use of blockchain is critical and it is a valuable contribution of this paper.

I understand that it is more of a theoretical paper but some practical implications should be taken into consideration. This is effectively highlighted in ‘Given the insufficient putting and storage capabilities of UAV devices to uphold and preserve the entire block chain ledger, lightweight algorithms are indispensable’ – Absolutely right, you do not want to miss the previous benefits of the optimization and therefore blockchain should not add much burden. This is an issue that should be analyzed more and provide also some practical recommendations on the use of blockchains.

 

Simulation

 

The simulations solves some other comments I could have suggested. Excellent analysis and rigorous work.

 

Overall Opinion.

This is an excellent paper. An interesting topic, well-structured and well executed A lot of work in various parts that are synthesized effectively. Especially the simulation provides much rigour and validity to the previous theoretical analysis. The paper can be accepted in the current form, but I believe it can benefit from minor revisions.

Comments for author File: Comments.pdf

Author Response

Please see the attachment

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

This version addressed my concerns satisfactorily.