• Korean Journal of Optics and Photonics
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• v.16 no.6
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• pp.494-499
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• 2005

We have demonstrated a fiber short-wavelength filter with a good cut-off property using dissimilar dispersive properties between? a thermally expanded cored fiber and an external medium. Side-polishing is applied to coupling between the fiber and the external medium. The experimental results revealed that the bend edge wavelength can be adjusted by controlling the degree of core expansion. Futhermore, the sharpness of wavelength response? was significantly? improved by employing expanded core fiber instead of a conventional single mode fiber. Tuning range of the band edge wavelength exceeded 400 m based on thermo-optic effect of the external medium.

• Journal of Advanced Marine Engineering and Technology
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• v.37 no.2
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• pp.199-204
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• 2013

Marine data communications still look for a novel data communication system at sea because of the restriction of bandwidths and costs of current carriers. In order to make the most efficient use of the broadband land carriers at sea, this paper proposes a routing scheme (MCS-NTC) at a marine MANET model. The routing scheme optimizes the route by choosing optimal nodes and carriers among the traditional and land carriers based on normalized transmission characteristics of applications and carriers. The performance is compared with the max-win method (OMH-MW) scheme considering the specific values of transmission characteristics. The result shows that our scheme derives more efficient routes than the previous one in terms of the transmission characteristics such as bandwidth, cost, delay, the number of hops and carriers.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.40 no.1
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• pp.202-208
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• 2015

A wireless ship area network is required to configure and control various sensors and electrical instruments embedded or boarded in a ship. In such environment, wireless communication protocol adopting relaying function is needed because direct link or communication between two nodes is hardly guaranteed due to spatial constraints in a ship. In this study, we introduce and analyze a WiMedia Distributed MAC (D-MAC) based approach considering throughput and energy constraint of wireless communication module. Performance evaluation results demonstrate that the relay-based wireless communication protocol improves reliability of wireless communication network in a ship.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.1A
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• pp.7-15
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• 2008

In this paper, it is investigated that the limitation due to the asymmetry of optical power with respect to optical phase conjugator(OPC) in mid-span spectral inversion(MSSI) for compensating optical signal distortion due to group velocity dispersion(GVD) and nonlinearities generated in fiber by combining with lumped dispersion management(DM) technique into MSSI. Two kinds of lumped DM configuration(configuration A and configuration B) are considered and compared each other in this research. Configuration A consists of two dispersion compensating fiber(DCF) span positioned after transmitter and before receiver, respectively. Configuration B consists of two dispersion compensating fiber(DCF) span positioned before and after OPC placed at middle of total transmission link, respectively. It is confirmed that the transmission performances are more improved by the configuration A combined with MSSI than configuration B. Also, it is confirmed that the best performance of overall channels are obtained by making net residual dispersion(NRD) to have positive value in self phase modulation(SPM)-limited WDM transmission systems, irrelevant to the configuration of DM.

• The Journal of Korea Institute of Information, Electronics, and Communication Technology
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• v.13 no.5
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• pp.344-352
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• 2020

Covertness and performance are very important design goals in the underwater communications. To satisfy both of them, we proposed efficient underwater communication model which combined multiband and direct sequence spread spectrum method in order to improve performance and covertness simultaneously. Turbo coding method with 1/3 coding rates is used for channel coding algorithm, and turbo equalization method which iterately exchange probabilistic information between equalizer and decoder is used for receiver side. After optimal threshold value was set in Rake processing, this paper analyzed the performance by varying the number of chips were 8, 16, 32 and the number of bands were from 1 to 4. Through the simulation results, we confirmed that the performance improvement was obtained by increasing the number of bands and chips. 2~3 dB of performance gain was obtained when the number of chips were increased in same number of bands.

• Communications for Statistical Applications and Methods
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• v.17 no.3
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• pp.413-421
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• 2010

In this study, we considered bivariate conditional auto-regressive model taking into account spatial association as well as correlation between the two dependent variables, which are the counts of murder and burglary. We conducted likelihood ratio test for checking over-dispersion issues prior to applying spatial poisson models. For the real application, we used the annual counts of violent crimes at 25 districts of Seoul in 2007. The statistical results are visually illustrated by geographical information system.

• The Journal of the Acoustical Society of Korea
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• v.40 no.4
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• pp.359-369
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• 2021

In underwater communications, to compensate performance degradation induced from rapidly changing channel transfer characteristic, multi-band communication method which allocate the same data to different frequency bands is used. However, the multi-band configuration may have worse performance than the single-band one because performance degradation in a particular band affects the output from the entire bands. This problem can be solved through a receiving end that analyzes error rates of each band, sets threshold values and allocates lower weights to inferior bands. Therefore, this paper proposed a weighting algorithm based on estimated Bit Error Rate (BER) which analyzes reliability of received data based on the performance difference between demodulated and decoded data. Employing turbo codes with coding rate of 1/3, we evaluate the performance of the proposed weighted multi-band transmission model in real underwater environments based on optimal simulation parameters. Through the sea trial experiment, we confirmed error performance was improved by applying the proposed weighting algorithm.

• Journal of IKEEE
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• v.23 no.2
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• pp.599-605
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• 2019

Ferrite cores are used as a soft magnetic material in the fabrication of couplers for inductive powerline communication (PLC). However, it is difficult to adjust the size freely according to the power-line and power-grid environment. In this paper, we report that a nano-crystalline alloy with higher permeability than ferrite can be used as an inductive coupler for non-contact PLC. Since nano-crystalline are produced in the form of a thin ribbon, the size of the coupler can be freely controlled by the number of ribbons wound on the toroidal core. It was fabricated with induction type coupler and showed to be suitable for non-contact power line communication. Experimental results show that the communication bandwidth is 45 Mbps for 100 m and 8 Mbps for 200 m under the current fluctuation of less than 100 A, and the reception ratio is 100%.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.25 no.10
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• pp.1353-1358
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• 2021

IoT (Internet of Things) emerges from various technologies such as communications, micro processors and embedded system and so on. The IoT has also been used to UAV (Unmanned Aerial Vehicle) system. In manned aircraft, a pilot and co-pilot should control FCS (Flight Control System) with FBW(Fly By Wire) system for flight operation. In contrast, the flight operation in UAV system is remotely and fully managed by GCS (Ground Control System) almost in real time. To make it possible the communication channel should be necessary between the UAV and the GCS. There are many protocols between two systems. Amongst them, MAVLink (Macro Air Vehicle Link) protocol is representatively used due to its open architecture. MAVLink does not define any securities itself, which results in high vulnerability from external attacks. This paper proposes the method to enhance data security in GCS network by applying cryptographic methods to the MAVLink messages in order to support safe UAV operations.

• 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.