• Journal of the Korean Society of Industry Convergence
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• v.25 no.5
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• pp.853-859
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• 2022

In this study, we analyzed the instantaneous trajectory generation capability and target arrival rate of a mobile robot by changing the parameter of the TEB (Timed Elastic Band) Local Planner among local planners that affect the instantaneous obstacle avoidance ability of the mobile robot using ROS (Robot Operating System) simulation and real experience. As a result, we can expect a decrease in the target arrival time of the mobile robot through a decrease in the parameter values of the TEB Local Planner's min_obstacle_dist, inflation_dist, and penalty_epsilon. However, if this parameter is reduced too much, the risk of obstacle collision of the moving robot is increases, so it is important to combine the appropriate values to construct the parameter.

• ETRI Journal
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• v.44 no.4
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• pp.543-559
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• 2022

To determine a suitable waveform for Internet of Things (IoT) transmission over low-Earth orbit (LEO) satellites, this paper reports the results of a performance comparison between chirp spread spectrum (CSS)-based LoRa and direct sequence spread spectrum (DSSS)-based Ingenu. The performance of both waveforms was measured in terms of the packet error rate, throughput, and packet loss rate, considering the Doppler effect caused by the high speed of LEO satellites and the interference among multiple terminals. Simulation results indicate that the DSSS scheme is more suitable than the CSS scheme for high-traffic IoT services because of its robustness against interference among multiple terminals. However, the CSS scheme is more suitable than the DSSS scheme for high-mobility IoT services because of its robustness against the Doppler effect. We discuss various solutions, such as the preprocessing of Doppler effect and avoidance of packet collision, to enhance the performance of the DSSS and CSS schemes. The simulation results of the proposed solution show that the enhanced DSSS scheme can be a proper waveform in IoT transmission over LEO satellites for both the high-traffic and high-mobility services.

• Journal of Communications and Networks
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• v.15 no.1
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• pp.77-86
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• 2013

Cognitive radio (CR) has emerged as one of effective methods to enhance the utilization of existing radio spectrum. Main principle of CR is that secondary users (SUs) are allowed to use the spectrum unused by primary users (PUs) without interfering PU's transmissions. In this paper, PUs operate on a slot-by-slot basis and SUs try to exploit the slots unused by PUs. We propose OSA protocols in the single channel and we propose an opportunistic spectrum access (OSA) protocols in the multi-channel cognitive radio networks with one control channel and several licensed channels where a slot is divided into contention phase and transmission phase. A slot is divided into reporting phase, contention phase and transmission phase. The reporting phase plays a role of finding idle channels unused by PUs and the contention phase plays a role of selecting a SU who will send packets in the data transmission phase. One SU is selected by carrier sense multiple access / collision avoidance (CSMA/CA) with request to send / clear to send (RTS/CTS) mechanism on control channel and the SU is allowed to occupy all remaining part of all idle channels during the current slot. For mathematical analysis, first we deal with the single-channel case and we model the proposed OSA media access control (MAC) protocol by three-dimensional discrete time Markov chain (DTMC) whose one-step transition probability matrix has a special structure so as to apply the censored Markov chain method to obtain the steady state distribution.We obtain the throughput and the distribution of access delay. Next we deal with the multi-channel case and obtain the throughput and the distribution of access delay by using results of single-channel case. In numerical results, our mathematical analysis is verified by simulations and we give numerical results on throughput and access delay of the proposed MAC protocol. Finally, we find the maximum allowable number of SUs satisfying the requirements on throughput and access delay.

• The Journal of Korean Institute of Electromagnetic Engineering and Science
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• v.29 no.3
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• pp.214-224
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• 2018

Continuous space development increases the occurrence probability of space hazards such as collapse of a satellite and collision between a satellite and space debris. In Korea, a space surveillance network with optical system has been developed; however, the radar technology for an independent space surveillance needs to be secured. Herein, an L-band phased array radar system for the detection and tracking of space objects is proposed to provide a number of services including collision avoidance and the prediction of re-entry events. With the mission analysis of space surveillance and the case analysis of foreign advanced radar systems, the radar parameters are defined and designed. The proposed radar system is able to detect a debris having a diameter of 10 cm at a maximum distance of 1,576 km. In addition, we confirmed the possibility of using the space surveillance mission for domestic satellites through the analysis of the detection area.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.7 no.1
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• pp.1-21
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• 2013

The release of IEEE 802.15.4e specification significantly develops IEEE 802.15.4. The most inspiring improvement is the enhancement for medium access control (MAC) sublayer. To study the performance of IEEE 802.15.4e MAC, in this paper we first present an overview of IEEE 802.15.4e and introduce three MAC mechanisms in IEEE 802.15.4e. And the major concern here is the Time Slotted Channel Hopping (TSCH) mode that provides deterministic access and increases network capacity. Then a detailed analytical Markov chain model for TSCH carrier sense multiple access with collision avoidance (CSMA-CA) is presented. Expressions which cover most of the crucial issues in performance analysis such as the packet loss rate, energy consumption, normalized throughput, and average access delay are presented. Finally the performance evaluation for the TSCH mode is given and we make a comprehensive comparison with unslotted CSMA-CA in non-beacon enabled mode of IEEE 802.15.4. It can validate IEEE 802.15.4e network can provide low energy consumption, deterministic access and increase network capacity.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.48 no.7
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• pp.529-536
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• 2020

Reaction Control System of the third stage of the Korean Space Launch Vehicle II conducts roll control and 3 axis control throughout third stage engine start, satellite separation, and collision and contamination avoidance maneuver. Reaction control system consumes its propellant in each thruster operation. Hence, loading of proper amount of the propellant is important for mission success. It is needed to have a rough estimation method of propellant consumption during the flight. In this paper, we developed a energy equation using pressure and temperature data which are acquired in the on-board reaction control system. We constructed a test system which is similar with the on-board reaction control system to verify the energy equation. Test results using deionized water were compared with estimated propellant consumption. We also conducted an error analysis of the energy equation. We also presented the propellant consumption result of a system level operation test.

• The Magazine of the IEIE
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• v.22 no.8
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• pp.33-43
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• 1995

생산시스템 분야에서의 다중로봇시스템에 대한 필요성이 증가되고 있기 때문에, 이에 대한 시스템 성능분석이 우선적으로 필요하다. 본 논문에서는 다중로봇시스템의 성능평가를 위한 컴퓨터 시뮬레이션 방법을 제시한다. 먼저 오류회복 기능만을 고려한 다중로봇시스템에 대하여 여러 가지의 모델링 방법 중에서 확장 페트리 네트 모델을 기초로 하여 컴퓨터 시뮬레이션 하는 과정을 제시하고 제시된 시뮬레이션 방법의 유효성을 입증하기 위하여 부가적으로 큐잉모델을 기초로 한 해석적 수식을 유도하여 두 가지의 결과를 비교해 본다. 그 다음, 오류회복 기능에 덧붙여서 충돌회피 기능을 고려한 다중로봇시스템은 해석적 수식을 유도하기 위해서는 강력한 가정들이 필요하며 이러한 가정들 때문에 실제 시스템을 정확히 모델에 반영하기 어려워진다. 따라서, 그 유효성이 입증된 컴퓨터 시뮬레이션을 이용하면 필요한 최적의 운용 변수를 용이하게 선택할 수 있을 것이다. Since there are Increasing demands for multirobot interconnection systems(MRIS) in Industrial manufacturing system, the performance evaluation of the MRIS is first needed. This thesis presents a computer simulation technique for the performance evaluation of the MRIS. First, we consider a error recoverable MRIS. We adopt the extended Petri net model as a computer simulation model that allows an easy evaluation of the performance. To verify the significance of the proposed computer simulation method, mathematical analysis, which is based on the given queueing model, is carried out with some design issues for the MRIS. In addition to this, it is required to analyze the MRIS considering collision avoidance as well as error recovery. In this case, methematial analysis needs hard assumptions which are the constraints for the precise description of real environment. Thus, we present a computer simulation model and its results suggest an optimal operational strategy for the MRIS under given conditions.

• Convergence Security Journal
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• v.23 no.3
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• pp.65-71
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• 2023

The importance of combat drones has been highlighted through the recent outbreak of the Russia-Ukraine war. The combat drones play a significant role as a a game changer that alters the conventional wisdom of traditional warfare. Many pundits expect the role of combat swarm drones would be more crucial in the future warfare. In this regard, this paper aims to analyze the development of artificial intelligence-enabled combat swarm drones. To transform the human-operated swarm drones into fully autonomous weaponry system our suggestions are as follows. Developments of (1) AI algorithms for optimized swarm drone operations, (2) decentralized command and control system, (3) inter-drones' mission analysis and allocation technology, (4) enhanced drone communication security and (5) set up of ethical guideline for the autonomous system. Specifically, we suggest the development of AI algorithms for drone collision avoidance and moving target attacks. Also, in order to adjust rapidly changing military environment, decentralized command and control system and mission analysis allocation technology are necessary. Lastly, cutting-edging secure communication technology and concrete ethical guidelines are essential for future AI-enabled combat swarm drones.

• Journal of Astronomy and Space Sciences
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• v.32 no.4
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• pp.411-417
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• 2015

Several optical monitoring strategies by a ground-based telescope to protect a Geostationary Earth Orbit (GEO) satellite from collisions with close approaching objects were investigated. Geostationary Transfer Orbit (GTO) objects, Inclined GeoSynchronous Orbit (IGSO) objects, and drifted GEO objects forced by natural perturbations are hazardous to operational GEO satellites regarding issues related to close approaches. The status of these objects was analyzed on the basis of their orbital characteristics in Two-Line Element (TLE) data from the Joint Space Operation Center (JSpOC). We confirmed the conjunction probability with all catalogued objects for the domestic operational GEO satellite, Communication, Ocean and Meteorological Satellite (COMS) using the Conjunction Analysis Tools by Analytical Graphics, Inc (AGI). The longitudinal drift rates of GeoSynchronous Orbit (GSO) objects were calculated, with an analytic method and they were confirmed using the Systems Tool Kit by AGI. The required monitoring area was determined from the expected drift duration and inclination of the simulated target. The optical monitoring strategy for the target area was analyzed through the orbit determination accuracy. For this purpose, the close approach of Russian satellite Raduga 1-7 to Korean COMS in 2011 was selected.

• Journal of the Korean Society of Marine Environment & Safety
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• v.18 no.3
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• pp.221-226
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• 2012

This research presents an analysis of algorithm for ship track-keeping along a given trajectory. The maneuver of a free running model ship guiding through a simple path are presented. In order to solve the above problem, a desired trajectory is usually determined by GPS points in a pre-fixed place then these points are set in a pre-programmed navigation so that the ship would be automatically tracked. Proportional-Derivative(PD) control which is useful for fast response controllers was used in this program as a course keeping system. A high accuracy GPS receiver was installed on the model ship that could provide positions frequently, the system will compare and give out the remaining distance and heading to the target way-point. The results of ship auto track-keeping experiment will be explained in order to illustrate the adjustment in controlling parameters. These results can be utilized as a preliminary step to carry out the experiment of ship collision avoidance system and automatic berthing in the future.