kumoh national institute of technology
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Review Comment

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Hoa T.D, Dong-Seong Kim: "Efficient Relay Selection Algorithm for Cooperative Routing in Underwater Acoustic Sensor Networks", IET Journal
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Date : 2018-02-27
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Dear Prof. Kim


Efficient Relay Selection Algorithm for Cooperative Routing in Underwater Acoustic Sensor Networks

Thank you for submitting your paper to IET Networks. The peer review process is now complete. I regret to say that the referees and I feel your paper is unsuitable for consideration in the journal. Under the circumstances I have decided to decline your paper.

I appreciate that this decision will be a disappointment but would like to thank you for your interest in IET Networks.

Yours sincerely

Dr. Han-Chieh Chao
IET Networks

Reviewer: 1

Comments to the Author
This manuscript proposes a relay selection algorithm when both routing relays (RR) and cooperative relays (CR) are present in the cooperative underwater acoustic sensor networks (UW-ASNs). The topic is very interesting. However, the reviewer has several comments on this work.

1) The proposed scheme is based on the update of neighbor tables frequently (what is the exact frequency? what is the frequency concerned with?), yet what is the cost of this action (including the energy consumption and processing time)? Since in the underwater acoustic (UWA) environment, it is not easy to do the update so frequently due to the limited energy supply and long time transmission delay. The authors should evaluate the balance of the benefit and the cost.

Also in section 3.2.1, what is the time cost of initialization? The UWA channels may change after long waiting.

2) The authors should add some references about the work of relay selection when existing both RR and CR are in the terrestrial radio channels. And point out that why it could apply to UWA channels. Also, more research paper could be cited about cooperative communications in UWA channels, especially from journals such as JOE and JASA. Here are some examples:
[A] S. Al-Dharrab, et al. Cooperative Underwater Acoustic Communications, IEEE Communications Magazine, vol. 51, no. 7, pp. 146-153, Jul. 2013
[B] Y. Chen, et al, FDM modulated dynamic coded cooperation in underwater acoustic channels, IEEE Journal of Oceanic Engineering, vol. 40, no. 1, pp. 159-68, Jan. 2015.
[C] Y. Zhang, et al, Dynamic Node Cooperation in an Underwater Data Collection Network, IEEE Sensors Journal, vol. 16, no. 11, pp. 4127-4136, Jun. 2016
[D] PC Sofotasios, et al, Relay Selection Based Full-Duplex Cooperative Systems under Adaptive Transmission,IEEE Wireless Communications Letters, 2017 , PP (99) :1-1

3) The authors said Eq. 2 is valid for 100 Hz
From Eq. 1, the transmission loss is related to the transmission distance, and the ambient noise is related to the frequency from Eq.7. Then the SNR is only related to the distance from Eq.8 once the frequency is fixed at 30 kHz. Hence, both ToA(is) and SNR(is) are only related to the distance. In this case, it seems that it only considers the distance for each hop transmission and it can not reflect the difference between ToA and SNR in Table 2.

4) During the simulation, it is better to present the performances (average end-to-end delay, energy consumption, etc.) vs. the number of relays (fix the source-to-destination distance).

5) How to define the packet delivery ration in Fig. 6 and how to calculate the energy consumption in Fig. 7? The authors should present the formulas.

6) The authors should pay more attention to the writing, such as:
---In Eq. 8, B(r,f) should be B_T(r,f) as mentioned in Eq. 1.
---In the end of section 3.2.3, the authors said Since GPS or localization information of nodes are considered in this paper; however, in the conclusion part, the authors said Thus, our method can be easily implementedwithout requiring additional hardware components, i.e., GPS.

Reviewer: 2

Comments to the Author
In this paper, the authors considered the routing design for underwater acoustic sensor networks. With the consideration of the poor acoustic link quality,they did a cross-layer design of physical layer and network layer, where when a routing relay node was selected, a cooperative relay node was also chosen for each hop. However, details of the implementation of this design were not described, such as how to design the time slot length for the cooperation. and performance evaluation for this design is not enough. And the conclusion that this proposed routing algorithm could improve the performance of UASNs with regard to average end-to-end delay, packet delivery ratio and energy consumption should be carefully derived. What was your cost of your proposed design?
Moreover, some descriptions should be checked. The authors mentioned that the this formula for attenuation approximation in (2) was valid for 100Hz < f < 3kHz, while in the simulation setup, the sensor nodes all operated at 30kHz.