• The Journal of the Korea institute of electronic communication sciences
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• v.11 no.5
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• pp.451-458
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• 2016

Urban railway can be divided into ground and underground sections. In particular, the center of the metropolitan has been built mostly underground stations and tunnels. Underground section is difficult to measure the position because GPS signal is unavailable, so it is necessary to apply the indoor positioning technology. For this purpose, we analyzed the positioning technologies which are based on Wi-Fi and mobile base stations. The positing technology for smart phone which uses mobile base station' information is developed in the underground area of urban railway where the core technique is to implement base station ID into the positing technology by considering hand-off point.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.15 no.2
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• pp.404-420
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• 2021

In this paper, an automatic system of locating the indoor area with weak or no mobile signal was proposed and demonstrated experimentally by using the Internet of Things (IoT) technology. Nowadays, the technicians of mobile services providers need to go along with numerous heavy equipment to measure and record the mobile signal strength at outside environment. Recently, there are systems proposed to do such measurement at outdoor area by using the IoT technology automatically. However, these works could not be applied in the indoor area since there are difficulties to do the indoor mapping and positioning. In this work, the Bluetooth Low Energy (BLE) was used to tackle these two difficulties. After a proper placement of BLE in the testing site, while the technician walk around with a handheld analyzer, the data can be obtained accordingly for further analysis in the proposed system which includes the construction of floor plan, detection of mobile signal strength and suggestion of indoor base stations. The gift wrapping and centroid algorithms were used during the analysis. The experimental results showed that the proposed system successfully demonstrated the indoor mapping, positioning of weak mobile signal area and suggestion of indoor base stations for the normal rectangular rooms with an area of 100 m² on single floor.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.33 no.6A
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• pp.624-634
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• 2008

The mobile station which is about to do handover in IEEE 802.16e networks scans its neighboring base station channels to decide its next target base station. However, due to the lack of location information of its subscribers, the serving base station cannot provide any reliable candidate channel which is actually attachable by the scanning mobile stations, which makes the mobile station suffer from the long scanning time. Sometimes, long scanning time may cause the degradation of quality of service due to repeatable scan-duration or failure to start the handover procedure in time. To overcome these problems, in this paper, we propose a new protocol so called fast group scanning scheme, in which multiple mobile stations form a group to scan their neighboring base station channels simultaneously. Main contribution of this proposal is to find and decide a reliable target base station within a short scanning time. The fast group scanning scheme can be deployed to the cell network of the serving base station with a dynamic neighboring base station list management.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.5B
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• pp.475-488
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• 2003

To prevent performance degradation of TCP due to packet losses in the smooth handoff by the route optimization extension of Mobile IP protocol, a buffering of packets at a base station is needed. A buffering of packets at a base station recovers those packets dropped during handoff by forwarding buffered packets at the old base station to the mobile user. But, when the mobile user moves to a congested base station in a new foreign subnetwork, those buffered packets forwarded by the old base station are dropped and TCP transmission performance of a mobile user in the congested base station degrades due to increased congestion by those forwarded burst packets. In this paper, considering the general case that a mobile user moves to a congested base station, we analyze the influence of packet buffering on TCP performance according to handoff arrival distribution for Drop-tail and RED (Random Early Detection) buffer management schemes. Simulation results show that RED scheme can reduce the congestion increased by those forwarded burst packets comparing Drop-Tail, but RED scheme cannot avoid Global Synchronization due to forwarded burst packets by the old base station and new buffer management scheme to avoid it is needed in Mobile IP based networks.

• The Journal of Korea Robotics Society
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• v.6 no.4
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• pp.344-352
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• 2011

A mobile manipulator is a system with a robotic manipulator mounted on top of a mobile base. It has both indoor and outdoor applications for transporting or transferring materials. When a user gives commands, they are usually at high levels such as "move the object to the table," or "tidy the room." By intelligently decomposing these complex commands into several subtasks, the mobile manipulator can perform the tasks with a greater efficiency. One of the crucial subtasks for these commands is the pick-and-place task. For the mobile manipulator, selection of a good base position and orientation is essential to accomplishing this task. This paper presents an algorithm that determines one of the position and orientation of a mobile manipulator in order to complete the pick-and-place task without human intervention. Its effectiveness are shown for a mobile manipulator with 9 degrees-of-freedom in simulation.

• The Transactions of the Korea Information Processing Society
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• v.7 no.8S
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• pp.2748-2756
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• 2000

IMT-2000 시스템(International Mobile Telecommunications-2000 system)은 음성, 화상, 및 데이터 서비스등 멀티미디어 서비스 제공을 목표로 기존의 디지털 이동통신 시스템에 적용된 기본 기술에 새로운 시스템 개념과 각종 응용기술 및 망 기술이 접목된 차세대 이동통신 시스템이다. 본 논문에서는 동기방식의 IMT-2000 시스템의 핵심 시스템인 제어국(BSC : Base Station Controller)의 무선 트래픽 및 신호접속기능, 이동호 제어기능 및 운용보전기능의 설계 및 구현에 대하여 논하고자 한다. 또한, IMT-2000 시스템의 호처리 절차 및 핸드오프 처리절차를 제시한다. 주로 BSC의 서브시스템인 AIS(ATM Interconnection Subsystem), BIS(BTS Interface Subsystem), SDS(Selector Distribution Subsystem), CSS(Control & Signal Subsystem) 및 BEMS(Base station Element Management Subsystem)의 구조와 기능, 그리고 MS(Mobile Station),BTS(Base Station Transceiver Subsystem), BSC 및 MSC(Mobile Switching Center)간의 호처리 기능, 절차(핸드오프 기능 포함)를 설계, 구현하였다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.5 no.5
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• pp.1069-1084
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• 2011

This paper considers an optimal base station clustering problem for designing a mobile (wireless) communication network. For a given network with a set of nodes (base stations), the problem is to optimally partition the set of nodes into subsets (each called a cluster) such that the associated inter-cluster traffic is minimized under certain topological constraints and cluster capacity constraints. In the problem analysis, the problem is formulated as an integer programming problem. The integer programming problem is then transformed into a binary integer programming problem, for which the associated linear programming relaxation is solved in a column generation approach assisted by a branch-and-bound procedure. For the column generation, both a heuristic algorithm and a valid inequality approach are exploited. Various numerical examples are solved to evaluate the effectiveness of the LP (Linear Programming) based branch-and-bound algorithm.

• The Journal of Korea Robotics Society
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• v.16 no.4
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• pp.313-318
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• 2021

This paper proposes a new method to generate inverse reachability maps that are more efficient for mobile manipulators than the previous algorithms. The base positioning is important to perform the given tasks. Using the inverse reachability method, we can know where to place the robot's base for given tasks. For example, the robot successfully performed the task with relocation, even when the target is initially in a low manipulability area or outside the workspace. However, there are some inefficiencies in the online process of the classical inverse reachability method. We describe what inefficiencies appear in the online phase and how to change the offline process to make the online efficient. Moreover, we demonstrate that the proposed approach achieves better performance than usual inverse reachability approaches for mobile manipulation. Finally, we discuss the limitations and advantages of the proposed method.

• Journal of Information Processing Systems
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• v.10 no.4
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• pp.581-588
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• 2014

To facilitate the implementation of a wide variety of context-aware applications based on mobile devices, general-purpose context-aware framework that applications can use by calling is needed. The context-aware framework is a middleware that performs the sensing, reasoning, and retrieving based on the knowledge base. The knowledge base must systematically represent the information required on the behavior of the context-aware framework, such as context information and reasoning information. It must also provide functions for storage and retrieval. To date, previous research on the representation of the context information have been carried out, but studies on the unified representation of the knowledge base has seen little progress. This study defines the knowledge base as the unified context information, and proposes the UniOWL, which can do a good job of representing it. UniOWL is based on OWL and represents the information that is necessary for the operation of the context-aware framework. Therefore, UniOWL greatly facilitates the implementation of the knowledge base on a context-aware framework.

• Journal of Communications and Networks
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• v.9 no.3
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• pp.254-264
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• 2007

A promising approach to improve the performance of mobile location system is the use of antenna arrays in both transmitter and receiver sides. Using advanced array signal processing techniques, such multiple-input multiple-output (MIMO) communication systems can offer more mobile location information by exploiting the spatial properties of the multipath channel. In this paper, we propose a novel approach to determine the position of mobile terminal based on estimated multipath signal parameters using only one base station in MIMO communication systems. This approach intends to minimize the error occurring from the estimation of multiple paths and gives an optimal estimation of the position of mobile terminal by simultaneously calculating a set of nonlinear location equations. This solution breaks the bottleneck of conventional mobile location systems which have to require multilateration of at least three base stations.