• 한국통신학회논문지
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• 제35권9A호
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• pp.874-881
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• 2010

수중 통신에서 사용되는 음향 신호의 감쇠는 노드 사이의 거리는 물론 사용 주파수 대역에도 크게 영향을 받는다. 또한 음향 신호는 긴 전송 지연을 가지므로 복잡한 절차와 많은 제어 메시지를 필요로 하는 매체 접속 기법은 사용하기에 적합하지 않다. 본 논문은 이처럼 열악한 수중 환경에서 코드 분할 다중 접속 기법의 적용 방법을 제시하고 그 성능을 분석한다. 수중 음향 센서망 구조는 데이터 수집형 트리 구조를 가정하며 에너지 절약을 위해 트리 구조에서 계층간 엇갈림 깨어남 패턴을 사용한다. 성능 분석을 위해 다양한 사용 주파수 대역에서 계층별 데이터 전송률을 수학적으로 도출한다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2000년도 춘계학술대회 논문집 전자세라믹스 센서 및 박막재료 반도체재료 일렉트렛트 및 응용기술
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• pp.168-171
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• 2000

Underwater acoustic communications have made considerable advances in the past decade. The purpose of this paper is to achieve the underwater communication by ultrasonic sensors and to investigate conditions of good underwater acoustic communicators. As a result of this experiments, the ultrasonic sensors, MA40E7R/S, made by Nicera can be used as ultrasonic transducers for underwater communication using AM(Amplitude Modulation) signal and Transmission Loss is 17.328[dB] at 65[cm]. To make a good underwater communicator, proper diameter of disk PZT transduers is the one of most important factors, because radiation of acoustic wave depends on proper diameter of transduers and the transmission loss strongly depends on the spreading loss.

• International Journal of Naval Architecture and Ocean Engineering
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• 제11권2호
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• pp.865-874
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• 2019

A controller for an underwater glider is presented. Considered underwater glider is a torpedo-shaped autonomous underwater vehicle installing adjustable buoyancy bag and movable battery in it. The controller is composed of an LQR controller to maintain zigzag vertical movement for gliding and two PD controllers to control elevator/rudder angles. The LQR controller controls the pumping speed into the buoyancy bag and the moving speed to locate the battery. One of the PD controller controls the elevator angle to assist the LQR controller, and the other controls the rudder angle to adjust the direction of the underwater glider. A reduced order Luenberger observer is adopted to estimates the center of gravity of the glider and the buoyancy mass that are essential but cannot be measured. Mathematical simulation using Matlab proved the validity of the proposed controller to obtain better performance than conventional LQR only controller under the influence of sea current.

• 한국통신학회논문지
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• 제36권4B호
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• pp.405-411
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• 2011

최근 해양 환경 모니터링과 해양 개발에 대한 관심이 증대됨에 따라 수중 무선센서네트워크 구성 및 이를 위한 저전력 수중 통신 모뎀에 대한 연구의 필요성이 제기되고 있다. 이에 본 논문에서는 초소형 무지향성 트랜스 듀서를 탑재한 수중 음향 통신 모뎀을 설계하고 구현한다. 또한, 개발한 모뎀을 사용하여 수조와 실외 환경에서 공급 전압과 통신 거리에 따른 성능 실험을 실시하고 결과를 분석한다. 실외 환경에서의 실험 결과에 의하면, 개발한 모뎀에 12 V를 공급하였을 때 40 m 거리에서 200 bps, $10^{-3}$ 비트오율로 단방향 수중 무선 통신이 가능하였다. 본 논문에서 구현한 모뎀은 초소형, 저전력, 무지향성 특성을 가지므로 수중 무선센서네트워크에 기반한 다양한 응용 시스템에 적용될 수 있을 것으로 기대된다.

• Journal of information and communication convergence engineering
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• 제8권2호
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• pp.163-167
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• 2010

In underwater acoustic communication, acoustic signals from transducers or hydrophones are used. And the underwater acoustic communication channels are very complicated, because of vertical distribution of acoustic velocity according depths, and reflections from boundaries like as surface or bottom. For the implementation of the underwater acoustic communication channel, the image method or ray tracing method have been used. In this paper, we introduce a new approach for implementation of underwater acoustic communication channel using the simulation of the Transmission Line Matrix Modeling and cross-correlations from the input and output signals.

• Journal of Communications and Networks
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• 제18권3호
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• pp.387-396
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• 2016

Multiuser communication has been an important research area of underwater acoustic communications and networking. This paper studies the use of adaptive orthogonal frequency-division multiple access (OFDMA) in a downlink scenario, where a central node sends data to multiple distributed nodes simultaneously. In practical implementations, the instantaneous channel state information (CSI) cannot be perfectly known by the central node in time-varying underwater acoustic (UWA) channels, due to the long propagation delays resulting from the low sound speed. In this paper, we explore the CSI feedback for resource allocation. An adaptive power-bit loading algorithm is presented, which assigns subcarriers to different users and allocates power and bits to each subcarrier, aiming to minimize the bit error rate (BER) under power and throughput constraints. Simulation results show considerable performance gains due to adaptive subcarrier allocation and further improvement through power and bit loading, as compared to the non-adaptive interleave subcarrier allocation scheme. In a lake experiment, channel feedback reduction is implemented through subcarrier clustering and uniform quantization. Although the performance gains are not as large as expected, experiment results confirm that adaptive subcarrier allocation schemes based on delayed channel feedback or long term statistics outperform the interleave subcarrier allocation scheme.

• The Journal of the Acoustical Society of Korea
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• 제24권2E호
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• pp.61-66
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• 2005

Experimental work in underwater acoustic communications using passive phase conjugation has shown that the demodulation error depends on the relative drift rate between the source and receiver [Rouseff et al., IEEE J. Oceanic Eng. 26, 821-831 (2001)]. The observed effect involves the mismatch between the initial impulse response and the subsequent response after the source or receiver has changed locations. In the present work, the effect of drifting source is analyzed by numerical simulations and compared to the experimental results. The communications bit error rate is qualified as a function of drift rate, drifting direction, and source-receiver range.

• 한국정보통신학회:학술대회논문집
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• 한국해양정보통신학회 2010년도 춘계학술대회
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• pp.258-261
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• 2010

기존의 수중음향통신모뎀은 상용 제품들을 기반으로 개발되어 수중음향통신모뎀의 기능 및 성능 구현은 가능하지만 개발 시스템을 제품화하기에는 시스템의 크기나 개발 비용 등에서 단일 플랫폼으로의 시스템 구현이 필수적으로 요구되었다. 따라서 본 논문에서는 수중음향통신모뎀의 단일 하드웨어 플랫폼을 구현함에 있어 중요한 역할을 하는 신호처리 모듈을 TigherSHARC DSP 칩을 이용하여 설계 및 구현하고자 한다.

• 제어로봇시스템학회논문지
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• 제18권10호
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• pp.928-933
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• 2012

In this paper, the IR and compass sensors for the underwater system were used. The walls of the water tank have been recognized and avoided treating the walls as obstacles by the bio-mimetic underwater robot. This paper is consists of two parts: 1.The hardware part for the IR and compass sensors and 2.The software part for obstacle avoidance algorithm while the bio-mimetic robot is swimming with the obstacle recognition. Firstly, the hardware part controls through the RS-485 communications between a microcontroller and the bio-mimetic underwater robot. The software part is simulated for obstacle recognition and collision avoidance based upon the data from IR and compass sensors. Actually, the bio-mimetic underwater robot recognizes where is the obstacle as well as where is the bio-mimetic robot itself while it is moving in the water. While the underwater robot is moving at a constant speed recognizing the wall of water tank as an obstacle, an obstacle avoidance algorithm is applied for the wall following swimming based upon the IR and compass sensor data. As the results of this research, it is concluded that the bio-mimetic underwater robot can follow the wall of the water tank efficiently, while it is avoiding collision to the wall.

• 제어로봇시스템학회논문지
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• 제20권2호
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• pp.132-137
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• 2014

In this paper, An LQR controller is proposed for way-point tracking of AUV (Autonomous Underwater Vehicle). The LQR controller aims at tracking a series of way-points which operator registers arbitrarily in advance. It consists of a depth controller and a steering controller and AUV's surge speed is assumed varying to consider the dynamic environment of the underwater. In order to show the performance, a conventional state feedback controller is compared with the proposed controller by the simulation using Matlab/Simulink. The parameters of AUV developed by the author's laboratory are used. In the simulation, we verify that the LQR controller can track all the way-points within 1 m error range under the varying surge speed, which proves the robustness of the LQR controller.