• The Journal of the Acoustical Society of Korea
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• v.34 no.4
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• pp.295-302
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• 2015

Acoustic channels are characterized by long multipath spreads that cause inter-symbol interference. The way in which this fact influences the design of the receiver structure is considered. To satisfy performance and throughput, we presented consecutive iterative BCJR (Bahl, Cocke, Jelinek, Raviv) equalization to improve the performance and throughput. To achieve low error performance, we resort to powerful BCJR equalization algorithms that iteratively update probabilistic information between inner decoder and outer decoder. Also, to achieve high throughput, we divide long packet into consecutive small packets, and the estimate channel information of previous packets are compensated to next packets. Based on experimental channel response, we confirmed that the performance is improved for long length packet size.

• Journal of IKEEE
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• v.25 no.1
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• pp.95-100
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• 2021

If we know the location of the hull block and the welding feeder in the shipyard, we can easily obtain the location information of the worker. That data is very useful for implementing a workplace safety monitoring system. However, it is difficult to apply a fixed communication network to the workplace due to the specificity of the hull structure and welding process. In this study, inductive power line communication, which can replace dedicated communication line, was reviewed. A ferrite core was used as an inductive coupler to be installed on the power cable of the welding machine, and a nano-crystalline core was applied as a coupler to be fastened to the support rod of the metal block. In order to visualize the operating principle of the proposed couplers, 3D modeling and finite element analysis were performed with the COMSOL AC/DC module. In the communication performance test using an aluminum profile, when the communication channel was formed by the contact of the welding electrode, the bandwidth was kept above 6 Mbps.

• The Journal of the Acoustical Society of Korea
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• v.41 no.2
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• pp.218-226
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• 2022

The main characteristics of the underwater acoustic channel have varying multipath and fast fading. Especially, Frequency Shift Keying (FSK) signals with multiple frequency bands caused loss of information bits allocated on the specific frequencies due to selective fading phenomenon. Therefore, this paper proposes frequency gain control algorithm based on preamble error rates. The proposed algorithm estimates optimal gain value in the range of preamble error rate with less than 10 % for specific faded frequency. By employing turbo equalized FSK signals with rate of 1/3, the experiment was conducted on a lake in Munkyeong city with distance of 300 m to 500 m. The result confirms that packets are decoded successfully by applying proposed algorithm as increasing number of iterations.

• Journal of Advanced Navigation Technology
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• v.28 no.1
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• pp.123-128
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• 2024

When mid-span spectral inversion (MSSI), which inverts the propagated wave into phase-conjugated wave in the middle of the entire transmission distance, is combined with dispersion-managed link, it is very effective in compensating for the wavelength division multiplexed (WDM) signal distortion due to chromatic dispersion and nonlinear effects. In this MSSI combined dispersion-managed link, the shape of the dispersion map, channel data rate, channel wavelength and wavelength spacing, etc. affect the compensation and, consequently, determine the transmission distance and capacity of the WDM signal. In this paper, the compensation according to the extinction ratio of the return-to-zero (RZ) pulse that constitutes the WDM signal in the MSSI combined distributed control link was numerically analyzed. As a result of the simulation, it was conformed that the extinction ratio to obtain the best compensation should be determined depending on the shape of the dispersion map and the size of the residual dispersion per span, which determines the specific shape of the dispersion map. These results show a significant difference from the results in a general optical transmission system, where as the extinction ratio increases, the power difference between the '1' and '0' signals increases, thereby improving reception performance.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.28 no.2
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• pp.63-93
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• 2023

This study aims to examine the history of naming the strait between the Yellow and East China Seas and the East Sea to suggest a consistent nomenclature and to demarcate the geographic region of the strait. Although the strait is internationally known as 'Korea Strait', it is commonly referred to as the 'South Sea' in Korean common usage. This review ultimately recommends the use of 'Korea Strait' as an appropriate geographical name for this area. To support this recommendation, the historical boundaries typically assigned to the Korea Strait were investigated. We also analyzed the evolution of geographical labels assigned to Korea Strait and to the Western and Eastern Channels (labels given to the two maritime areas surrounding Tsushima). Resources for this analysis included historic maps and charts, International Hydrographic Organization Special Publications (S-23), and maps published in the Ocean Science Journal (OSJ) and Journal of Oceanography (JO), which are two international journals representing Korean and Japanese sources, respectively, from 2005 to 2021. In these two international journals, the most frequently used names assigned to the strait of interest were Korea Strait (appearing 42.9% of OSJ maps, and 7.5% of JO maps), and Tsushima Strait (appearing 60.4% of JO maps, and 0% of OSJ maps). Other names were South Sea and Korea Strait/Tsushima Strait. On maps in the two reviewed journals, the boundaries of Korea Strait were defined explicitly or implicitly in five different ways: a broad region between the Yellow and East China Seas and Ulleung Basin (Type 1), the region between Ulleung Basin and Tsushima (Type 2), the western channel of the strait (Type 3-1), the eastern channel of the strait (Type 3-2), and both the western and eastern channels of the strait (Type 4). Overall, Type 1 was the most frequently used boundary, taking up 71.4% of OSJ and 60.4% of JO maps. Lastly, we suggest in this paper that the current flowing through Korea Strait from the East China Sea to the East Sea should be labeled the 'Korea Strait Warm Current' to indicate its full path through the strait. Currently, this current is internationally referred to as the 'Tsushima Warm Current', which does not link well to the commonly used geographic name of the strait.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2007.12a
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• pp.141-142
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• 2007

In recent years, the rate of mean sea level rise is increasing rapidly from the phenomena of global warming, together with the increasing trend of the storm scale. The issue of sea level rise is multifaceted and produces a range of environmental problems. Especially, high tides and the tidal currents become higher, and wave base increases, so the energy received at the coastal boundary may increase. This brings that many coastal environments go into disequilibrium, such as damages to the structures, erosion, and deposition Similarly it was known that the problems of nearshore processes and damage of berth and counter facilities during storm period had appeared at the small fishery port. Here we try to analyze the impact of the rearrangement of counter facilities and berth layout adopted for tranquility of its'inner harbor. Because this harbor is being connected to channel and open sea, the rearrangement of the structures might affect to the current speed and direction and wave height, so do to the sea bottom undulation. Therefore, we made model test for the several layouts of the berth and breakwater in this area.

• Journal of the Korean Society of Marine Environment & Safety
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• v.14 no.1
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• pp.45-54
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• 2008

"Summer Deadweight Tonnage(SDWT)" is used as the criteria of the berthing capacity when establishing port entry limits under current guideline. The important factors affecting to the maximum ship size of possible berthing are mass, length and breath of the ship rather than deadweight. Therefore this guideline should be modified to ensure safety and efficient operation of berth. This study aimed to propose a rational guideline to adjust the berthing capacity. In order to decide proper berthing capacity, three berths of Port of Ulsan were selected and systematic evaluations for the safety of passage transit, berthing maneuvers, ship motions at berth and stabilities of structures were conducted. Small changes of ship size had little effect on those characteristics and little significant differences were found according to the increase of ship size at the same displacement. The evaluation results of the increasement of 50% of berthing capacity at 20,000 DWT, 25% at 40,000 DWT and 13% at 150,000 DWT were within the design criteria in which the berths were built. Therefore, if the channel width, diameter of turning circle, berth length and mooring arrangements are satisfied with the criteria, the current berth limitations should be adjusted by the displacement. as substitute for the deadweight.

• Geophysics and Geophysical Exploration
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• v.9 no.2
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• pp.139-147
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• 2006

We had conducted a numerical modeling to investigate seismic properties of gas hydrate with field parameters acquired over the East sea in 1998. We used a 2-D staggered grid finite difference method to generate synthetic elastic seismograms for multi-channel seismic survey, OBC (Ocean Bottom Cable) survey and VCS (Vertical Cable Seismic) survey. The results of this study showed that the method using staggered grid yielded stable results and could be used to seismic imaging. We could find out the high amplitude anomaly and the phase reversal phenomenon of reflection wave at interface between the gas hydrate layer and free gas layer such a BSR (Bottom Simulating Reflector) which is the evidence for existence of gas hydrate in seismic reflection data. And we computed the reflection coefficients at the incident angles corresponding to offset distance with the synthetic seismograms. The reflection coefficients acquired from the numerical modeling were nearly consistent with the reflection coefficient computed by Shuey's equation.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• v.1
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• pp.433-438
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• 2006

When we consider to develop a new harbor, the most important factor, we think, is the lowest water depth of waterway and approaching channel for safe navigation of vesse. The existing harbors have been being dredged to meet the international trend of jumbo sized vessels by adopting the new design criteria. As the dredged materials over the expected at the design level were common and there are still lack of land based reclamation area, we have no choice to discharge the dredged materials in open sea area. In this study, we analysed the behavior of discharged materials at the dumping area of offshore open sea, which were collected from the dredging work at the waterway in Busan New Port. We measured the tidal currents and analyzed the waters of dumping site after the dumping work. these were used to evaluate the numerical models. Suspended Solids(SS) were introduced to the diffusion model. Because of the characteristics of the dumping site, the speed of initial diffusion and settle down of the discharged materials was so fast. Therefore, we believe that the dumped materials do not cause a significant impact to the marine environment.

• Journal of Navigation and Port Research
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• v.37 no.4
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• pp.375-381
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• 2013

In order to establish eLoran system it needs the betterment of a receiver and a transmitter, the add of data channel to loran pulse for loran system information and the differential Loran for compensating Loran-c signal. Precise ASF database map is essential if the Loran delivers the high absolute accuracy of navigation demanded at maritime harbor entrance. In this study we developed the ASF mapping method using predicted ASFs compensated by the measured ASFs for maritime in the harbor. Actual ASF is measured by the legacy Loran signal transmitted from Pohang station in the GRI 9930 chain. We measured absolute propagation delay between the Pohang transmitting station and the measurement points by comparing with the cesium clock for the calculation of the ASFs. Monteath model was used for the irregular terrain along the propagation path in the Yeongil Bay. We measured the actual ASFs at the 12 measurement points over the Yeongil Bay. In our ASF-mapping method we estimated that the each offsets between the predicted and the measured ASFs at the 12 spaced points in the Yeongil. We obtained the ASF map by adjusting the predicted ASF results to fit the measured ASFs over Yeungil bay.