• Journal of the Korea Institute of Information and Communication Engineering
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• v.20 no.7
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• pp.1229-1236
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• 2016

In underwater acoustic multipath channel, a performance of underwater acoustic (UWA) communication systems is affected by dynamic variation of boundary and high temporal and spatial variability of the channel conditions. Time and spatial variations of UWA channel induce a carrier frequency offset (CFO) since a phase and a frequency of received signal mismatch with a transmitting signal. Therefore, a performance of a phase shift keying underwater acoustic communication system is degraded. In this study, we have analyzed a performance of CFO estimation and compensation using a phase code in time and spatial variation channel. A constant amplitude zero autocorrelation (CAZAC) signal is applied as a phase code signal and its performance is evaluated in water tank. The bit error rate of a quadrature phase shift keying (QPSK) system with a phase code is improved about 4 to 10 times better than that without a phase code.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.19 no.10
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• pp.2247-2255
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• 2015

In very shallow water acoustic communication channel, underwater acoustic (UWA) communication signal is observed as frequency selective fading signal due to time-varying multipath. This induces a time and frequency dependent inter-symbol-interference (ISI) and degrades the UWA system performance. There is no study about how the performances of the error correction codes are related to a multipath fading statistics in very shallow water. In this study, the characteristics of very shallow water multipath fading channel is analyzed and the performances of two different forward error correction (FEC) codes are compared. The convolution code (CC) and Reed-Solomon (RS) code are adopted. Sea experimental results show that RS code is better choice than CC in frequency selective channel with fading.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2008.05a
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• pp.929-932
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• 2008

W3C(World Wide Web Consortium)는 2007년 상반기부터 웹 기술을 PC를 넘어 휴대폰, PDA, 정보가전, 로봇 등 모든 디바이스로 적용이 확대하기 위해 유비쿼터스 웹 응용을 위한 표준 개발을 시작하였다. 이를 담당하고 있는 유비쿼터스 웹 응용 워킹그룹은 탁상용 컴퓨터뿐 아니라 사무용품, 가정 매체 기구, 이동 전화, RFID나 바코드를 포함하는 센서나 이펙터(effector) 등의 유비쿼터스 기기들이 다양하게 흩어져 있는 환경에서 쉽게 웹 응용 개발을 가능하게 하는 표준 개발을 목표로 한다. 본 워킹그룹의 활동의 중요한 표준화 아이템 중의 하나는 Delivery Context: Client Interfaces(DCCI)로 이는 다양한 디바이스들의 기능들의 접근을 위한 표준 인터페이스를 정의하는 것이다. DCCI가 중요한 이유는 현재 웹 환경에서 오픈 API를 이용하여 개발되고 있는 다양한 매쉬업 응용에 GPS와 같은 단말을 기능을 매쉬업을 제공할 수 있는 기반이 되기 때문이다. 본 논문에서는 최근에 W3C의 UWA(Ubiquitous Web Application) WG에서 추진되고 있는 DCCI에 대한 표준화 동향을 설명한다.

• The Journal of the Korea institute of electronic communication sciences
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• v.5 no.5
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• pp.509-515
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• 2010

Such as disaster rescue in deep water, undersea exploration and monitering for environmental pollution, many applications require the acoustic communication for high data rate over underwater acoustic channel. As underwater channel is very complex and is time-varying, conventional single carrier communication has good performance. In this paper, An adaptive OFDM system is analyzed for high data rate and reliability and rubust service over UWA channels. Through the adaptive system, we show threshold switching for an adaptive algorithm.

• Proceedings of the Korea Information Processing Society Conference
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• 2015.10a
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• pp.851-854
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• 2015

수중음파통신은 물속에서 지상과는 달리 음파를 사용하여 통신한다. 또한 제한된 전력과 자원을 사용하기 때문에 최소한의 연산으로 본래의 목적을 수행해야만 하는 조건이 따른다. 따라서 수중음파통신에 보안을 적용하기 위해서는 기밀성과 안전성도 중요하지만 무엇보다 가용성을 고려한 보안설계가 중요하다. 본 논문은 제한된 전력과 자원 환경에서 동작하는 수중음파통신용 MAC 프로토콜에 가용성이 부각할 수 있는 LEA 블록암호알고리즘의 적용방안을 논하고자 한다. 또한 기존의 AES(Advanced Encryption Standard)와 ARIA(Academy, Research Institute, Agency) 블록암호알고리즘과의 성능분석을 통해 LEA의 우수성과 수중음파통신에 적합성을 보이고자 한다.

• International Journal of Computer Science & Network Security
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• v.21 no.4
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• pp.277-283
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• 2021

The objective of this project is to conduct an underwater survey. The primary goal is to develop a device that can achieve the desired output under test conditions. For this reason, certain practical considerations must be taken into account, and the implementation is then developed to be carried out to obtain stable performance with the available hardware based on that experiment. The experiment was performed via BlueROV2 (Remotely Operated Vehicle) using RaspberryPi and softwares such as QGC (QGroundControl) and ArduPilot. This paper explains the work, the results with the collected data and how we implemented the work is presented in the end. The intention of this experiment is to connect two PCs using RaspberryPi with MAVLink communication using a Commercial-Off-The-Shelf device.

• Journal of the Institute of Electronics and Information Engineers
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• v.49 no.11
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• pp.211-216
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• 2012

Such as disaster rescue in deep water, undersea exploration and monitering for environmental pollution, many applications require the acoustic communication for high data rate over underwater acoustic channel. As underwater channel is very complex and is time-varying, In this paper, The proposed OFDM system with synchronization errors and multipath delay spread is analyzed for high data rate and reliability and rubust service over UWA channels.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.792-798
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• 2008

CPT 시험은 지난 30여년 동안 지반조사 분야에서 널리 이용되어 왔다. CPT 콘의 근입은 항타말뚝의 근입방법과 유사하기 때문에, CPT 콘의 선단저항력을 이용하여 말뚝의 지지력을 산정하려는 연구가 많이 수행되어 왔다. 본 연구의 목적은 기존에 제안된 CPT 선단지지력 공식의 적용성을 분석하는 것이다. 이를 위해 낙동강 하구 대심도 연약지반에서 수행된 항타 PHC 말뚝에 대한 총 172개의 PDA 시험자료와 80개소의 CPT 자료를 수집하였다. PDA시험의 CAPWAP분석에서 얻어진 선단지지력과 각 CPT 지지력 공식에서 산정된 선단지지력을 비교함으로써 각 공식의 적용성을 분석하였다. 분석에 이용된 CPT 지지력 공식은 Aoki 방법, Meyerhof 방법, Penpile 방법, Philpponnat 방법, LCPC 방법, Schmertmann 방법, Zhou 방법, ICP 방법, Eslami & Fellenius 방법, 그리고 UWA-05 방법의 총 10가지이다. 분석결과, Aoki 방법, Phillipponnat 방법, ICP 방법 그리고 LCPC 방법 순으로 그 적용성이 높은 것으로 나타났다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.13 no.5
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• pp.2400-2413
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• 2019

Doubly-selective (DS) fading channel is often occurred in many orthogonal frequency division multiplexing (OFDM) communication systems, such as high-speed rail communication systems and underwater acoustic (UWA) wireless networks. It is challenging to provide an accurate and fast estimation over the doubly-selective channel, due to the strong Doppler shift. This paper addresses the doubly selective channel estimation problem based on complex exponential basis expansion model (CE-BEM) in OFDM systems from the perspective of distributed compressive sensing (DCS). We propose a novel DCS-based improved sparsity adaptive matching pursuit (DCS-IMSAMP) algorithm. The advantage of the proposed algorithm is that it can exploit the joint channel sparsity information using dynamic threshold, variable step size and tailoring mechanism. Simulation results show that the proposed algorithm achieves 5dB performance gain with faster operation speed, in comparison with traditional DCS-based sparsity adaptive matching pursuit (DCS-SAMP) algorithm.

• Journal of Communications and Networks
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• v.18 no.3
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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.