• Journal of Positioning, Navigation, and Timing
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• v.5 no.3
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• pp.137-144
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• 2016

In this paper, the performance of ranging measurement, which is generated using two receiver clock offsets in one receiver, was analyzed. A spoofer transmits a counterfeited spoofing signal which is similar to the GPS signal with hostile purposes, so the same tracking technique can be applied to the spoofing signal. The multi-correlator can generate two receiver clock offsets in one receiver. The difference between these two clock offsets consists of the path length from the spoofer to the receiver and the delay of spoofer system. Thus, in this paper, the ranging measurement was evaluated by the spoofer localization performance based on the time-of-arrival (TOA) technique. The results of simulation and real-world experiments show that the position and the system clock offset of the spoofer could be estimated successfully.

• Management Science and Financial Engineering
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• v.15 no.2
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• pp.23-52
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• 2009

This study compares the cycle times of handling operations of yard cranes under different sequencing rules. An operation cycle was divided into several elementary movements and formulas for the expectation and the variance of each elementary movement were analytically derived. The expected waiting time of trucks was estimated based on the given arrival rate of trucks. The previous studies focused on developing a method to make an efficient schedule of operations for yard cranes. This paper introduces several sequencing rules, such as first-come-first-served, unidirectional travel, and Z pick travel rules. In addition, a formula for estimating the cycle times of yard cranes under each sequencing rule is derived, and the performance under the different sequencing rules are compared with each other.

• Proceedings of the Safety Management and Science Conference
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• 2000.05a
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• pp.339-349
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• 2000

Inchon Port is the second largest import-export port of Korea, and has the point at issue such as the excessive logistics cost because of the limits of handling capacity and the chronic demurrage. There are few research activities on the analysis and improvement of the whole port operation, because Inchon Port not only has the dual dock system and various facilities but also handles a various kind of cargo. The purpose of this paper is to develop the simulation program as a long-term strategic support tool, considering the dual dock system and the TU(Terminal Operation Company) system executed since March, 1997 in Inchon Port. The basic input parameters such as arrival intervals, cargo tons, service rates are analyzed and the probability density functions for these parameters are estimated. The main mechanism of simulation model is the discrete event-driven simulation and the next-event time advancing. The program is executed based on the knowledge base and database. From the simulation model, it is possible to estimate the demurrage status through analyzing various scenarios and to establish the long-term port strategic plan.

• Proceedings of the Safety Management and Science Conference
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• 2000.11a
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• pp.95-99
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• 2000

The domestic ports become less competitive for the out of dated equipments and inefficient information system. Specially, Inchon Port, which is the second largest port of Korea, has the point at issue such as the excessive logistics cost because of the limit of handling capacity and the chronic demurrage. In this paper to develope the simulation programs the basic input parameters such as arrival intervals, cargo tons, service rates are analyzed and the probability density functions for there variable are estimated. Also to perform the conception of continuous berth utilization, the berth and cargo classification is reconstructed. And the more actual simulation is realized by using more detailed depth representation of water The simulation model is executed based on the knowledge base and database, and is constructed using Visual Basic and Access database. Simulation results reveal that this study suitably reflect the real berth operation and waiting time of ships is shortened.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2014.10a
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• pp.39-41
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• 2014

최근 유가인상, 운임하락, 온실가스규제 등의 복합적인 요인으로 선박의 운항 효율 관리를 위한 직 간접적인 방법이 개발되고 있으며, 실제로 이를 지원하는 시스템의 탑재사례가 늘고 있다. 본 논문에서는 이러한 경제운항지원시스템들 중에서 실시간 기상정보와 그에 기초한 선박의 부가저항을 고려한 최적의 추천경로를 제공하는 최적 항로 지원 시스템에 대해 기술하고자 한다. 본 시스템은 주어진 ETA (Estimated Time of Arrival) 범위 내에서, 기상예보를 바탕으로 연비관점에서의 최적의 경로 및 엔진출력을 제안하며, 추천경로 및 실제운항경로 사이의 효율비교와 함께 항해정보분석까지 가능한 것을 특징으로 한다. 이러한 시스템은 선박의 연료절감과 함께 운항경로 전반에 대한 포괄적인 이해에 도움을 줄 것으로 기대한다.

• Journal of Advanced Navigation Technology
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• v.20 no.4
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• pp.367-373
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• 2016

We propose an improved direction of arrival (DoA) estimation algorithm based on co-prime array and propagator method. The propagator method with co-prime array does not require singular value decomposition (SVD) requiring much less computational complexity but exhibiting somewhat worse performance in comparison with MUSIC based on co-prime array. We notice that one cause of the performance degradation was in the avoidance of the usage of the diagonal elements of the signal autocorrelation matrix that contains the noise power spectral density. So we propose an algorithm with the diagonal elements of the signal autocorrelation matrix based on the fact that the noise power spectral density can be estimated using noise observation over a long period of time. We observe, through simulations, that the proposed scheme in this paper improves the performance, with 4 times more computational requirement, by signal-to-noise ratio of 1.5dB and by DoA resolution of $0.7^{\circ}$ at the detection probability of 95% compared with the previously introduced co-prime array propagator scheme, resulting in performance much closer to that of co-prime array-based MUSIC scheme.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2018.05a
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• pp.318-320
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• 2018

When a ship sails on sea, it may be influenced by the environmental disturbance such as wind, wave, sea surface temperature, etc. These affect on the ship's speed, fuel consumption, safety and operating performance. It is necessary to find the optimal weather route of a ship to avoid adverse weather conditions which can put the crews in serious danger or cause structural damage to the vessel, machinery, and equipment. This study introduced how to apply A* algorithm based on sea trial test data for determining the optimal ship routes. The path cost function was modelled as a function of minimum arrival time or minimum energy depending on the time of various environment conditions. The specially modelled path-cost function and the safety constraints were applied to the A* algorithm in order to find the optimal path of the ship. The comparison of ship performances estimated by real sea trial's path and estimated optimal route during the voyage of the ship was investigated. The result of this study can be used to create a schedule to ensure safe operation of the ship with short passage time or minimum energy. In addition, the result of this study can be integrated into an on-board decision supporting expert system and displayed in Electronic Chart Display and Information System (ECDIS) to provide all the useful information to ship master.

• ETRI Journal
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• v.43 no.5
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• pp.941-949
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• 2021

In this study, a spatial spectrum method is proposed to cope with the pilot spoofing attack (PSA) problem by exploiting the of uplink-downlink channel reciprocity in time-division-duplex multiple-input multiple-output systems. First, the spoofing attack in the uplink stage is detected by a threshold derived from the predefined false alarm based on the estimated spatial spectrum. When the PSA occurs, the transmitter (That is Alice) can detect either one or two spatial spectrum peaks. Then, the legitimate user (That is Bob) and Eve are recognized in the downlink stage via the channel reciprocity property based on the difference between the spatial spectra if PSA occurs. This way, the presence of Eve and the direction of arrival of Eve and Bob can be identified at the transmitter end. Because noise is suppressed by a spatial spectrum, the detection performance is reliable even for low signal-noise ratios and a short training length. Consequently, Bob can use beamforming to transmit secure information during the data transmission stage. Theoretical analysis and numerical simulations are performed to evaluate the performance of the proposed scheme compared with conventional methods.

• The Transactions of the Korea Information Processing Society
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• v.2 no.5
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• pp.768-776
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• 1995

In a distributed computer system with star topology, the processing power of central node may be greater than that of peripheral nodes and the job arrival rate of each node may be different. The performance of load balancing may be very different according to the selection of sender criteria and receiver criteria for job transfer. But the optimal decision of sender and receiver criteria is very difficult in heterogeneous distributed computer systems. In this paper we propose effective destination decision policies using dynamic criteria such as mean job response time of a node and estimated response time of a job, instead of fixed threshold for dynamic load balancing.

• The Journal of the Convergence on Culture Technology
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• v.3 no.2
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• pp.31-35
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• 2017

Recently, Many deliveries have sprung up and those are beginning to receive much attention from consumers. Like this, the application makes our lives more comfortable. Now, the delivery food application uses only static information of the user and the users only makes oder. In this thesis, however, the studies suggested that designed food application uses the user's location for mesuring a distance of delivery and estimated arrival time is displayed in the delivery application and The application provides a graphical view of the location of the user in real time.