• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.39C no.3
• /
• pp.275-281
• /
• 2014

Recently, the need for various underwater application systems targeting efficient resource exploration and aquatic ecosystem monitoring is rapidly increasing in littoral sea and inland waters. In this paper, we focus on the research and development of digital module of acoustic micro modem which can be used for underwater mobile communication systems and underwater sensor network systems. Specifically, a digital module of acoustic modem embedding digital signal processor is designed and implemented. On top of the developed hardware platform, physical layer frame generation and recovery and channel coding algorithms are mounted and tested in a water tank and a pond to verify its functionality and performance. According to experimental results, less than 1 percent of total computational power is consumed in the processing of frame control and convolutional code with the data rate of 1 kbps. Thus, the performance of micro modem could be improved by loading efficient baseband algorithms into the processor while maintaining the implemented hardware.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.40 no.8
• /
• pp.1631-1636
• /
• 2015

With the advance of wireless communication technology in terrestrial area, underwater communication is also evolving very fast from a simple point-to-point transmission to an elaborate networked communications. Underwater acoustic channel has quite different features comparing with the terrestrial radio channel in terms of propagation delay, Doppler shift, multipath, and path loss. Thus, existing technologies developed for terrestrial communication might not work properly in underwater channel. Especially medium access control (MAC) protocols which highly depend on propagation phenomenon should be newly designed for underwater network. CSMA/CA has drawn lots of attention as a candidate of underwater MAC protocol, since it is able to resolve a packet collision and the hidden node problem. However, a received signal could be degraded by the interferences from the nodes locating outside the receiver's propagation radius. In this paper, we study the effects of interference on the CSMA/CA based underwater network. We derived the SNR with the interference using the sonar equation and analyzed the degradation of the RTS/CTS effects. These results are compared with the terrestrial results to understand the differences. Finally we summarized the design considerations in CSMA/CA based underwater network.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.21 no.12
• /
• pp.2394-2402
• /
• 2017

The frequency selective fading by multipaths determines a performance of underwater acoustic communication system in shallow littoral ocean. In this study, a characteristics of underwater acoustic channel and performance of multi-carrier system is evaluated in littoral ocean with a 50m deep water, an effective wave height of 0.5m and sandy mud bottom near Busan city. A multipath delay spread and time and frequency domain are presented as a function of a transmitter-to-receiver range. A bit-error-rate of a 5 channel 4FSK(Frequency Shift Keying) with a transmission rate of 1kbps, is examined and RS(Reed-Solomon) code is also adopted to remove a burst error due to time domain fading. A number of multipath are less than four and a bit-error-rate is decreased as an increase of a transmitter-to-receiver range which gives a congestion of multi-paths resulting in a decrease of time and frequency domain fading. The measured bit-error-rate is about 10-4 at greater than 600m of transmitter-to-receiver range.

• Proceedings of the Korean Society of Coastal and Ocean Engineers Conference
• /
• 2001.08a
• /
• pp.163-171
• /
• 2001

• IEMEK Journal of Embedded Systems and Applications
• /
• v.12 no.5
• /
• pp.343-350
• /
• 2017

Underwater glider with a single buoyancy engine could generally obtain propulsive forces by moving the center of buoyancy and gravity. Futhermore, The hull and internal structure of underwater glider are designed according to the purpose of long-time operation, high speed and a wide variety of payloads (sensors, communications and etc.). In this paper, Ray-type underwater glider featuring flatfish is considered in view of hydrodynamics. The hull design is especially performed by the analysis of fluid resistance and dynamic performance. The resistance performance is analyzed using the Computational Fluid Dynamics (CFD). In addition, a simulation program is implemented in order to verify the validity of dynamics modeling and dynamic performances.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.34 no.6A
• /
• pp.437-444
• /
• 2009

Underwater sensor networks (USN) for ocean development and disaster prevention have been emerged as one of interesting research topics recently. Since a high-speed and inexpensive communication modem is a prerequisite for deployment of USN, we design and implement an underwater modem by utilizing general-purpose waterproof ultrasonic sensors in this paper. We also make experiments in indoor and outdoor environment with two modems facing each other to conduct a point-to-point communication. According to the experiments, we can achieve the data rates of 1.5 kbps in a water tank and 2 kbps in a pond. Also, the maximum communication distance between two modems is about 30 meters. Besides, we conduct a point-to-multipoint experiment imitating USN by deploying a gateway, a sink node and three sensor nodes in a water tank.

• Journal of the Korea Institute of Information and Communication Engineering
• /
• v.16 no.11
• /
• pp.2397-2404
• /
• 2012

Underwater acoustic communication has multipath error because of reflection by sea-level and sea-bottom. The multipath of underwater channel causes signal distortion and error floor. In order to improve the performance, it is necessary to employ an iterative coding scheme. Among the iterative coding scheme, turbo codes and LDPC codes are dominant channel coding schemes in recent. This paper concluded that turbo coding scheme is optimal for underwater communications system in aspect to performance, coded word length, and equalizer combining. Also, decision directed phase recovery was used for correcting phase offset induced by multipath. Based on these algorithms, we confirmed the performance in the environment of oceanic experimentation.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.36 no.4B
• /
• pp.399-404
• /
• 2011

For the underwater wireless sensor networks, we propose the packet transmission method which distinguishes more important packet than others. Because the ocean underwater transmission environments are extremely unstable, we use SON(Self Organizing Network) techniques to adapt to the constantly varying underwater acoustic communication channels and randomly deployed sensor nodes. Especially we suppose two kinds of packets which have different priorities, and through the simulations we show that high priority packets arrive at the source node faster than lower priority packets with a proposed scheme.

• Journal of Ocean Engineering and Technology
• /
• v.34 no.6
• /
• pp.475-480
• /
• 2020

Underwater operating platforms face difficulties regarding power supply and communications. To overcome these difficulties, this study proposes a hybrid surface and underwater vehicle (HSUV) and presents the development of the platform, control algorithms, and results of field tests. The HSUV is capable of supplying reliable power to the unmanned underwater vehicle (UUV) and obtaining data in real time by using a tether cable between the UUV and the unmanned surface vehicle (USV). The HSUV uses global positioning system (GPS) and ultra-short base line sensors to determine the relative location of the UUV. Way point (WP) and dynamic positioning (DP) algorithms were developed to enable the HSUV to perform unmanned exploration. After reaching the target point using the WP algorithm, the DP algorithm enables USV to maintain position while withstanding environmental disturbances. To ensure the navigation performance at sea, performance tests of GPS, attitude/heading reference system, and side scan sonar were conducted. Based on these results, manual operation, WP, and DP tests were conducted at sea. WP and DP test results and side scan sonar images during the sea trials are presented.

• The Journal of the Acoustical Society of Korea
• /
• v.25 no.5
• /
• pp.239-245
• /
• 2006

Time-reversal processing (TRP) has been shown as an effective way to focus in both time and space. The temporal focusing properties have been used extensively in underwater acoustics communications. Recently. adaptive time-reversal processing (ATRP) was applied to the simultaneous multiple focusing in an ocean waveguide. In this study. multiple focusing with ATRP is extended to the underwater acoustic communication algorithm for multiple receiving locations. The developed algorithm is applied to the underwater acoustic communication to show, via simulation and real data, that the simultaneous self-equalization at multiple receiving locations is achieved.