• Communications of the Korean Mathematical Society
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• v.33 no.3
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• pp.929-933
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• 2018

In this paper we show that complete noncompact harmonic Finsler manifolds with minimal horospheres are flat.

• Journal of Navigation and Port Research
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• v.28 no.4
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• pp.305-309
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• 2004

The problem for parameters estimation of the received signals impinging on array sensors has long been of great research Interest in a great variety of applications, such as radar, sonar, and land mobile communications systems. Conventional subspace-based algorithms, such as MUSIC and ESPRIT, require an extensive computation of inverse matrix and eigen-decomposition In this paper, we propose a new parameters estimation algorithm via nonlinear minimization, which is simplified computationally and estimates signal parameters simultaneously.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2012.06a
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• pp.80-81
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• 2012

Our society consist of many country's critical infrastructure such as production and distribution of electric power systems, communications technology, tele-communications, financial system, transportation systems when those systems are operated efficiently and normally. Country's critical infrastructure and its application fields of this magnitude rely on more and more P.N.T (Positioning, Navigation. Timing) systems, in which the tele-communications(Timing), financial market(Timing), logistics (Positioning, Navigation, Timing), transportation(Positioning, Navigation. Timing) is shoring. Reliability concerned about the exact position and timing of these critical national infrastructure rely on ability to provide a stable from GPS.

• Journal of Advanced Marine Engineering and Technology
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• v.36 no.6
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• pp.823-829
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• 2012

Data communications networks at sea in the future can be modelled by overlapped MANET networks with Broadband Wireless Access carriers. A novel routing scheme (CPLR) is proposed in this paper, which finds out an optimal route by selecting an optimal carrier for each hop in routes based on carrier preferences of each application, and locations of ships as well. As distances between each ships and destination ships are considered in this scheme, routing can be done much faster. Performance is compared with that of the CPR (only Carrier Preference-based Routing Scheme), and it shows some improvements.

• ETRI Journal
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• v.43 no.4
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• pp.660-673
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• 2021

To efficiently use frequency resources, the next 6th generation mobile communication technology must solve the problem of out-of-band emission (OoBE) of cyclic prefix (CP) orthogonal frequency division multiplexing (OFDM), which is not solved in 5th generation technology. This study describes a new zero insertion technique to replace an existing filtering scheme to solve this internal problem in OFDM signals. In the development of the proposed scheme, a precoder with a two-dimensional structure is first designed by generating a two-dimensional mapper and using the specialty of each matrix. A spectral shaping technique based on zero insertion instead of a long filter is proposed, so it can be applied not only to long OFDM symbols, but also very short ones. The proposed method shows that the transmitted signal is completely blocked at the bandwidth boundaries of signals according to the current standards, and it is confirmed that the proposed scheme is ideal with respect to bit error rate (BER) performance because its BER is the same as that of CP-OFDM. In addition, the proposed scheme can transformed into a real time structure through vectorizing process with minimal complexity.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.16 no.5
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• pp.906-912
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• 2012

A ship ad-hoc network (SANET) can provide ships with diverse multimedia services by replacing expensive satellite communications. While ITU-R M. 1842-1, standards for maritime VHF band digital communications, can be used as the specifications of physical layer for SANETs, no standards are specified for higher layers of SANETs. In this paper, we propose a ship ad-hoc communication (SAC) protocol for SANETs, based on medium access control (MAC) and routing protocols for terrestrial ad-hoc networks. SAC protocol is a cross-layer protocol which combines MAC and routing into one algorithm and considers maritime environments, including the existence of neighboring ships, the possibility of routing to a destination, and changing the communication mode in case of VHF channel failure.

• Journal of Navigation and Port Research
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• v.31 no.10
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• pp.833-837
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• 2007

In this study, we have fabricated a gain flattened erbium-doped optical fiber amplifier. Gain flattening filters were realized by the strain-induced long period fiber gratings, which are made of periodically arrayed metal wires. Using the filter of $550{\mu}m$ period, spontaneous emission amplified at C-band wavelength by a 980nm pumping laser was flattened within 1dB of gain ripple. The performance of the simultaneous multi channel amplification was measured using a fabry-perot laser diode. Amplification ratio was above 20dB. This amplifier can be applied to the long distance transmission system based on a wavelength division multiplexing for boosting an attenuated signal.

• Journal of IKEEE
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• v.23 no.3
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• pp.777-784
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• 2019

A pre-fire awareness and automatic notification system are required because it is possible to minimize the damage if the fire situation is precisely detected after a fire occurs in a place where people are unusual or in a mountainous area. In this study, we developed a RaspberryPi-based fire recognition system using Faster-recurrent convolutional neural network (F-RCNN) and single shot multibox detector (SSD) and demonstrated a fire alarm system that works with power line communication. Image recognition was performed with a pie camera of RaspberryPi, and the detected fire image was transmitted to a monitoring PC through an inductive power line communication network. The frame rate per second (fps) for each learning model was 0.05 fps for Faster-RCNN and 1.4 fps for SSD. SSD was 28 times faster than F-RCNN.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.41 no.3
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• pp.371-378
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• 2016

We have studied on the maritime navigation with functions of navigation route search and maritime safety information for small-size fishery ships, fishing boats, yachts, and boats in coastal seas. We have designed a smart phone application which is more exact information on marine obstacles of islands, aquafarms, and rocks by using land navigation techniques. Our navigation system is relatively easy to be used for costal navigation and may be a substitute for expensive ECDIS(Electronic Chart Display and Information System). Our system consists of maritime navigation databases to manage necessary maritime data and a mobile application to support maritime navigation for operators. We believe that our research findings can improve safety navigation in coastal seas by supporting lower cost, no time-consuming installation and maintenance, and easy-to-use operations.

• Strategy21
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• s.43
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• pp.57-88
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• 2018

Security situations are fundamentally and rapidly changing on the Korean Peninsula. Above all, as North Korea(NK) is heightening its nuclear and missile capabilities, Republic of Korea(ROK) is facing an existential threat. At the same time, as China's economic, diplomatic and military power is quickly rising, the balance of power is shifting and strategic competition between the Unite States(US) and China is accelerating in the Asia-Pacific region. Under the pressure of development of these situations, ROK seems to face allegedly the most serious crisis in its national security since the end of the Korean War. In the current grim geopolitical situation, maritime security may become the most difficult security challenge for ROK in the years to come. The purpose of this paper is to compare major changes in maritime security affairs of the ROK during last twenty years from 1998 until now(2018). 1998 was when this journal 『Strategy 21』 was published for the first time by the Korea Institute for Maritime Strategy. Then, this paper tries to identify challenges and risks with which this country has to deal for its survival and prosperity, and to propose some recommendations for the government, the Navy, and the Coast Guard as they are responsible for the maritime security of the country. The recommendations of this paper are as follows: strengthen ROK-US alliance and expand security cooperation with regional powers in support of the maintenance of the current security order in the region; building-up of maritime security capacity in preparation for crisis on the maritime domain with the navy targeting to acquire 'a non-nuclear, balance-of-terror capability, to improve interoperability with the Coast Guard based on 'a national fleet,' and to actively pursue innovation in naval science and technology. Finally, this paper proposes that naval capability the country needs in another twenty years depends on how effectively and rigorously the navy put its utmost efforts towards building 'a strongest navy' today.