• 한국해양공학회지
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• 제36권1호
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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.

• 한국멀티미디어학회논문지
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• 제20권12호
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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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• 제36권3호
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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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• 제17권1호
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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.

• 디지털산업정보학회논문지
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• 제16권1호
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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.

• 한국정보과학회논문지:정보통신
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• 제35권4호
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• pp.337-344
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• 2008

음파를 이용한 수중 센서 네트워크는 지상에서의 무선 네트워크 환경과 다르게 긴 전파 지연과 낮은 전송 속도를 가진다. 따라서 기존의 선 네트워크에서 사용되는 프로토콜을 수중 센서 네트워크에 적용될 경우 매우 제한적이며 비효율적으로 사용될 수 있다. 본 논문에서는 수중 센서 네트워크에서 에너지 효율과 처리율 향상을 위한 MAC 프로토콜을 제안한다. 제안된 프로토콜은 슬롯 기반의 경쟁 기법을 사용하며 데이타 패킷을 전송하기 위해 사전에 슬롯을 예약하게 된다. 제안된 프로토콜에서는 경쟁방식에 의하여 노드간의 충돌이 발생할 수 있으나 예약방식에 의하여 인접 노드의 채널을 미리 인지함으로써 충돌을 최소화하고 노드의 불필요한 에너지 소모를 줄임과 동시에 처리율 향상을 가져온다. 제안된 프로토콜에 대한 성능을 평가하기 위해 시뮬레이션을 수행하며 소모된 에너지, 충돌횟수, 채널효율, 처리율과 전송지연시간에 대하여 평가한다. 또한 기존의 MAC 프로토콜과 비교함으로써 제안된 프로토콜이 기존의 프로토콜에 비해 성능이 우수함을 보인다.

• 한국통신학회논문지
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• 제36권7B호
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• pp.886-891
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• 2011

본 논문은 수중 센서 네트워크에서 효율적인 하향링크 멀티캐스트 데이터 전송기법을 제시하였다. 기존에 센서 네트워크에서 많은 멀티캐스트 전송 기법이 제안되었지만, 배터리를 지속적으로 공급받거나 충전시키기 어려운 환경에 있는 수중 센서 네트워크에 특화된 멀티캐스트 기법은 없었다. 본 논문에서는 이를 위하여 수중 센서 네트워크에서의 멀티캐스트 두 가지 특성을 파악하여 이를 알고리즘에 적용하였다. 싱크 노드에서 목적지 노드들의 위치 정보를 가공하여서 각도 정보를 추출하였고, 이렇게 추출한 목적지 노드들의 각도 정보를 바탕으로 가상의 유클리디언 스테이너 포인트를 이용한 최적의 멀티캐스트 전송 알고리즘을 제안하였다. 본 알고리즘은 저 계산 능력과 제한된 전송파워를 가지는 수중 센서 네트워크에서 구동하기에 알맞음을 시뮬레이션을 통하여 확인하였다. 제안한 방식은 기존의 방식들에 비하여 감소된 전송 전력과 감소된 라우팅 계산량을 보였다.

• 한국인터넷방송통신학회논문지
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• 제8권6호
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• pp.97-103
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• 2008

최근에 제안된 수중 음향 센서 네트워크용 MAC 프로토콜인 T-Lohi는 저가형 음향 모뎀들이 밀집되어 구성된 네트워크에서 사용되도록 설계된 프로토콜이다. 그러나 T-Lohi는 각 노드들이 모든 노드들의 신호를 수신할 수 없어 멀티 홉 라우팅이 필요한 네트워크에서 사용될 때 hidden terminal 문제로 인해 많은 패킷 충돌이 발생한다. 본 논문에서는 T-Lohi처럼 톤을 사용하여 전력 소모에 있어서의 경제성을 추구하면서도 RTS/CTS handshaking을 통해 hidden terminal 문제를 해결한 새로운 MAC프로토콜을 제안한다. 모의실험 결과는 새로운 MAC프로토콜이 T-Lohi와 비교했을 때 패킷 손실을 훨씬 줄이면서도 좋은 네트워크 활용률을 달성할 수 있음을 보여준다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제11권7호
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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.

• 대한임베디드공학회논문지
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• 제7권4호
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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.