• Journal of Ocean Engineering and Technology
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• v.36 no.1
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• pp.61-81
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• 2022

The available underwater acoustic spectrum is limited. Therefore, it is imperative to avoid frequency interference from overlapping frequencies of underwater acoustic equipment (UAE) for the co-existence of the UAE. Cognitive technology that senses idle spectrum and actively avoids frequency interference is an efficient method to facilitate the collision-free operation of multiple UAE with overlapping frequencies. Cognitive technology is adopted to identify the frequency usage of UAE to apply cognitive technology. To this end, we investigated two principle underwater acoustic sources: UAE and marine animals. The UAE is classified into five types: underwater acoustic modem, acoustic positioning system, multi-beam echo-sounder, side-scan sonar, and sub-bottom profiler. We analyzed the parameters of the frequency band, directivity, range, and depth, which play a critical role in the design of underwater acoustic cognitive technology. Moreover, the frequency band of several marine species was also examined. The mid-frequency band from 10 - 40 kHz was found to be the busiest. Lastly, this study provides useful insights into the design of underwater acoustic cognitive technologies, where it is essential to avoid interference among the UAE in this mid-frequency band.

• Journal of Korea Multimedia Society
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• v.20 no.12
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• pp.1940-1950
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• 2017

The security threat types in underwater communication networks environment are almost the same as the terrestrial, but the security of mechanisms the terrestrial RF-based networks environment can not be directly applied due to not only the limited resources of each node but also unsafe channel such as low propagation delay, high bit error rate etc. Nevertheless there has not been much research on the security of underwater acoustic communication networks. Therefore, in this paper analyzes the differences between the terrestrial communication networks and underwater acoustic communication networks, and identifies issues that are the starting points of underwater communication networks security research.

• ETRI Journal
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• v.36 no.3
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• pp.506-509
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• 2014

This paper studies the energy efficiency power allocation for cognitive radio networks based on uplink orthogonal frequency-division multiplexing. The power allocation problem is intended to minimize the maximum energy efficiency measured by "Joule per bit" metric, under total power constraint and robust aggregate mutual interference power constraint. However, the above problem is non-convex. To make it solvable, an equivalent convex optimization problem is derived that can be solved by general fractional programming. Then, a robust energy efficiency power allocation scheme is presented. Simulation results corroborate the effectiveness of the proposed methods.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.17 no.1
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• pp.239-260
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• 2023

The underwater acoustic wireless communication networks are generally formed by the different autonomous underwater acoustic vehicles, and transceivers interconnected to the bottom of the ocean with battery deployed modems. Orthogonal frequency division multiplexing (OFDM) has become the most popular modulation technique in underwater acoustic communication due to its high data transmission and robustness over other symmetrical modulation techniques. To maintain the operability of underwater acoustic communication networks, the power consumption of battery-operated transceivers becomes a vital necessity to be minimized. The OFDM technology has a major lack of peak to average power ratio (PAPR) which results in the consumption of more power, creating non-linear distortion and increasing the bit error rate (BER). To overcome this situation, we have contributed our symmetry research into three dimensions. Firstly, we propose a machine learning-based underwater acoustic communication system through long short-term memory neural network (LSTM-NN). Secondly, the proposed LSTM-NN reduces the PAPR and makes the system reliable and efficient, which turns into a better performance of BER. Finally, the simulation and water tank experimental data results are executed which proves that the LSTM-NN is the best solution for mitigating the PAPR with non-linear distortion and complexity in the overall communication system.

• Journal of Korea Society of Digital Industry and Information Management
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• v.16 no.1
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• pp.93-98
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• 2020

Research on underwater sensor networks is increasing due to such reasons as marine resource management, maritime disaster prediction and military protection. Many underwater sensor networks performs wireless communication using an acoustic sound wave band signal having a relatively low frequency. So the digital part of their modem can take charge of carrier band signal processing. To enable this, the sampling rate of the baseband band signal should be increased to a sampling rate at which carrier band signal processing is possible. In this paper, we designed a sampling rate increasing circuit based on a CIC interpolator for underwater sensor nodes. The CIC interpolator has a simple circuit structure. However, since the CIC interpolator has a large attenuation of the pass band and a wide transition band, an inverse sinc LPF is added to compensate for frequency response of the CIC interpolator. The proposed interpolator was verified in time domain and frequency domain using ModelSim and Matlab.

• Journal of KIISE:Information Networking
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• v.35 no.4
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• pp.337-344
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• 2008

Underwater acoustic sensor networks exhibit characteristics such as high propagation delay and low data rates, which are different from those of terrestrial wireless networks. Therefore, the conventional protocols used in wireless networks can be restrictive and inefficient when applied to underwater acoustic sensor networks. In this paper, we propose a medium access control protocol (MAC) to enhance the energy efficiency and throughput in underwater acoustic sensor networks. The proposed protocol employs a slot-based competition mechanism that reserves a time slot to send a data packet in advance. In the proposed protocol, collision between nodes can occur due to competition to obtain a slot. However, the proposed protocol minimizes the collisions between nodes because the nodes store the reservation information of the neighboring nodes, this reduces unnecessary energy consumption and increases throughput. We perform a simulation to evaluate the performance of the proposed protocol with regard to the energy consumption, the number of collision, channel utilization, throughput and transmission delay. We compare the proposed protocol with the conventional protocol, and the performance results show that the proposed protocol outperforms the conventional protocol.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.36 no.7B
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• pp.886-891
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• 2011

Multicast has been a key routing service for efficient data dissemination in underwater acoustic sensor networks. In sensor networks, there are several multicast routing protocol which reflects sensor network nature. However, existing routing scheme was not targeted at underwater acoustic sensor networks which is hard to provide battery continually. Therefore, a specialized routing algorithm is essential for acoustic sensor networks. In this paper, we propose angle aided multicast routing algorithm for decreasing routing computation complexity, including virtual Euclidean Steiner point. Simulation results show better performance than exist routing Position Based Multicast, Geographic Multicast Routing. such as low computation capability and limited power consumption.

• The Journal of the Institute of Internet, Broadcasting and Communication
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• v.8 no.6
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• pp.97-103
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• 2008

T-Lohi, a MAC protocol for underwater acoustic sensor networks, has been designed to support dense networks consisting of short-range acoustic modems. However when T-Lohi is applied to large networks in which multi-hop routing is necessary, it suffers a lot of packet collisions due to the hidden terminal problem. To combat this problem, we propose a new MAC protocol which employs RTS/CTS handshaking. To our knowledge, this protocol is the first to adopt both a tone-based approach and RTS/CTS handshaking for dense underwater acoustic sensor networks. Simulation results show that this new protocol drastically reduces packet collisions while achieving good network utilization.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.11 no.7
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• pp.3329-3350
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• 2017

Installing caching and computing facilities in mobile edge networks is a promising solution to cope with the challenging capacity and delay requirements imposed on future mobile communication systems. The problem of optimal facility placement in mobile edge networks has not been fully studied in the literature. This is a non-trivial problem because the mobile edge network has a unidirectional topology, making existing solutions inapplicable. This paper considers the problem of optimal placement of a fixed number of facilities in a mobile edge network with an arbitrary tree topology and an arbitrary demand distribution. A low-complexity sequential algorithm is proposed and proved to be convergent and optimal in some cases. The complexity of the algorithm is shown to be $O(H^2{\gamma})$, where H is the height of the tree and ${\gamma}$ is the number of facilities. Simulation results confirm that the proposed algorithm is effective in producing near-optimal solutions.

• IEMEK Journal of Embedded Systems and Applications
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• v.7 no.4
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• pp.187-191
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• 2012

In these days, there are huge increases of concerning underwater acoustic sensor networks (UWASNs) to explore marine resources and to monitor climate change. To collect information from sensor nodes which are randomly deployed in underwater, Multi-Dimensional Scaling (MDS) based locating methods have been recently introduced, which consider sound speed to be constant in underwater. However, underwater sound speed tends to vary depending on underwater environment factors, such as depth, temperature, and salinity. In this paper, we propose a method considering environment factors, can influence upon sound speed in underwater, and introduce experimental setup which can follow up environmental factors.