• 한국통신학회논문지
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• 제40권5호
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• pp.809-811
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• 2015

In this paper, for the purpose of providing high data rate services, the multi-hop frame structure is designed for the underwater acoustic (UWA) short-range system which is proposed as a part of ocean surveillance and tracking network (OSTN). Under the measured underwater channel environment, the link-level system performance are also evaluated. Simulation results show not only the packet error rate (PER) comparisons, but the optimal modulation and coding scheme (MCS) levels for the orthogonal frequency division multiplexing (OFDM) based short-range UWA communications network.

• 한국음향학회지
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• 제30권2호
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• pp.86-91
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• 2011

In the underwater communications, the acoustic channel is in poor communication conditions, such as long propagation delay, narrow bandwidth, and high bit-error rate. For these bad acoustic channels, we propose an efficient automatic repeat request (ARQ) for multi-hop underwater network by using the concepts of concurrent bi-directional transmission, multiple sub-packets, and overhearing data packet instead of the acknowledgement signal. Our results show that the proposed ARQ significantly reduces the transmission latency especially in high BER compared with the existing Stop and Wait ARQ.

• 한국해양공학회지
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• 제33권4호
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• pp.358-363
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• 2019

The acoustic power is used as a primary index characterizing underwater sound sources and could be defined by its source level. The source level has been assessed using various experimental techniques such as the reverberation time method and reverberant tank plot method. While the reverberation time method requires reverberation time data extracted in a preliminary experiment in a reverberant water tank, the reverberant tank plot method only needs acoustic pressure data directly obtained at the reverberation water tank. In this research, these experimental techniques were studied in comparative experiments to estimate the source levels of underwater sources in a reverberant water tank. This paper summarizes the basic theories and procedures of these experimental techniques and presents the experimental results for an underwater source in a long cuboid water tank using each technique, along with a discussion.

• 한국정보처리학회:학술대회논문집
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• 한국정보처리학회 2011년도 추계학술발표대회
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• pp.97-100
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• 2011

Underwater Wireless Acoustic Sensor Networks have become an important area of research over the recent decades. Designing an underwater network, especially a media access control (MAC) protocol, faces many challenges due to the peculiarities of underwater environment. One of the most important problems is resulted from long and variable propagation delay of the acoustic wave. In this paper, we propose a new method, namely Dynamic Timeout over Multiple Access with Collision Avoidance (DT/MACA), which is designed to handle long and high variable propagation delay in underwater acoustic sensor networks. In this proposed method, the difference timeout intervals are evaluated and applied to each network transmission. Simulation results show that our work not only improves the network throughput, but also decreases the unnecessary retransmission and end-to-end delay.

• 한국통신학회논문지
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• 제37C권12호
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• pp.1328-1336
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• 2012

수중 음향통신 환경에서는 지상 RF 통신에 비하여 제한된 대역폭, 높은 페이딩효과, 높은 수중음파 전달지연과 같은 제약이 있다. 본 논문에서는 이러한 수중 음향통신의 제약을 극복하여 효과적인 대규모 수중감시시스템의 구축을 가능케 하는 계층적 네트워크 구조를 제안한다. 제안하는 네트워크구조는 수중센서, 클러스터헤드, 수중/해상 싱크 및 수중무인기를 포함하며, 패킷의 전송성공률을 최대화하고 센서노드의 전력소모를 최소화시키기 위하여 복수의 수중무인기를 이용한 하이브리드 형태의 데이터라우팅을 제공한다. 즉, 클러스터 내부에서 클러스터멤버들은 Tree구조기반 라우팅을 사용하여 클러스터헤드에게 데이터를 전송하며, 궤도 이동을 하는 수중무인기는 클러스터헤드로부터 병합된 센싱데이터를 수집하고 Store-carry-forward 방식으로 싱크노드에게 데이터를 전달한다. 수중무인기의 최장 궤도이동 시간을 최소화하기 위하여 Integer Linear Programming 기반의 알고리즘이 사용된다. 시뮬레이션을 이용한 성능분석을 통하여 제안하는 수중센서네트워크 구조가 기존의 Gradient 기반 라우팅과 Geographical Forwarding 방식에 비해 높은 전송성공율과 낮은 전력소모를 획득할 수 있음을 보인다.

• 로봇학회논문지
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• 제13권2호
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• pp.79-85
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• 2018

This study focuses on autonomous exploration based on map expansion for an underwater robot equipped with acoustic sonars. Map expansion is applicable to large-area mapping, but it may affect localization accuracy. Thus, as the key contribution of this paper, we propose a method for underwater autonomous exploration wherein the robot determines the trade-off between map expansion ratio and position accuracy, selects which of the two has higher priority, and then moves to a mission step. An occupancy grid map is synthesized by utilizing the measurements of an acoustic range sonar that determines the probability of occupancy. This information is then used to determine a path to the frontier, which becomes the new search point. During area searching and map building, the robot revisits artificial landmarks to improve its position accuracy as based on imaging sonar-based recognition and EKF-SLAM if the position accuracy is above the predetermined threshold. Additionally, real-time experiments were conducted by using an underwater robot, yShark, to validate the proposed method, and the analysis of the results is discussed herein.

• 한국해양공학회:학술대회논문집
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• 한국해양공학회 2003년도 춘계학술대회 논문집
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• pp.319-323
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• 2003

In this paper, we propose a hybrid transceiver for underwater acoustic communication, which allows the system to reduce complexity and increase robustness in time variant underwater channel environments. It is designed in the digital domain except for amplifiers and implemented by using a multiple digital signal processors (DSPs) system. The digital modulation technique is quadrature phase shift keying (QPSK) and frame synchronization is an energy (non-coherent) detection scheme based on the quadrature receiver structure. DSP implementation is based on block data parallel architecture (BDPA). We shaw experimental results in th? underwater anechoic basin at KRISO. The results indicate that the frame synchronization is performed without PLL. Also, we shaw that the adaptive equalizer can compensate frame synchronization error and the correction capability is dependent on the length of equalizer.

• 한국음향학회지
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• 제40권4호
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• pp.314-319
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• 2021

수중운동체의 수중방사소음을 측정하기 위해서는 수중음향 최근접점 거리의 계산과 해표면 반사 등에 의한 음향간섭이 음향준위에 미치는 영향이 고려되어야 한다. 그러므로 본 논문에서는 해표면 반사에 의한 음향간섭으로 발생하는 로이드 미러 효과가 수중운동체의 수중방사소음 측정 결과에 미치는 영향을 분석하고자 하였다. 수중운동체의 수중방사소음 측정결과에 로이드 미러 효과에 의한 주파수스펙트럼 레벨의 변동이 나타나는 것을 확인하였고, 이론식으로부터 예측한 로이드 미러 패턴이 측정결과와 일치됨을 확인할 수 있었다. 확인된 로이드 미러 패턴으로부터 수중운동체의 최근접점거리를 추정하였으며, 표면 간섭으로 나타나는 로이드 미러 효과가 수중운동체의 수중방사소음 준위 분석에 영향을 미치는 것을 확인하였다.

• 로봇학회논문지
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• 제7권4호
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• pp.231-242
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• 2012

This paper proposes particle filter(PF) method using acoustic signal for localization of an underwater robot. The method uses time of arrival(TOA) or time difference of arrival(TDOA) of acoustic signals from beacons whose locations are known. An experiment in towing tank uses TOA information. Simulation uses TDOA information and it reveals dependency of the localization performance on the uncertainty of robot motion and senor data. Also, comparison of the PF method with the least squares method of spherical interpolation(SI) and spherical intersection(SX) is provided. Since PF uses TOA or TDOA which comes from measurement of external information as well as internal motion information, its estimation is more accurate and robust to the sensor and motion uncertainty than the least squares methods.

• 한국음향학회지
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• 제31권8호
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• pp.569-579
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• 2012

압전 세라믹을 이용한 전형적인 Tonpilz형 수중 음향센서는 외부에서 들어오는 음향 신호를 이에 상응하는 전압으로 변환해 스칼라 양인 음압의 크기만 측정할 뿐 외부에서 들어오는 신호의 방향은 파악할 수 없는 한계가 있다. 이와 같은 문제점을 해결하고자 본 논문에서는 Tonpilz형 트랜스듀서를 이용해 단일 센서만으로도 음압의 크기와 방위각 방향을 동시에 분석해 낼 수 있는 새로운 벡터 센서 구조를 제안하고, 제안된 구조의 타당성을 수식 및 유한요소해석을 통해 검증하였다.