• Journal of Institute of Control, Robotics and Systems
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• v.20 no.12
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• pp.1204-1208
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• 2014

As required performance of UAV (Unmanned Aerial Vehicle) becomes more complex and complicated, required positioning accuracy is becoming more and more higher. GPS is a reliable world wide positioning providing system. Therefore, UAV generally acquires position information from GPS. But when GPS is not available such as too weak signal or too less GPS satellites environments, UAV needs alternative positioning system such as network positioning system. RSSI (Received Signal Strength Indicator) based positioning, which is one method of network positioning technologies, determines its position using RSSI measurements containing distance information from AP (Access Point)s. In that method, a selected AP's configuration has strong and tight relationship with its positioning errors. In this paper, for, we additionally account AP's configuration information by adopting DOP (Dilution of Precision) into AP selection procedures and provide more accurate RSSI based positioning results.

• Journal of the Korean Institute of Intelligent Systems
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• v.16 no.5
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• pp.525-530
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• 2006

This paper presents an efficient input variable selection method using both fixed-point independent component analysis(FP-ICA) and adaptive partition mutual information(AP-MI) estimation. FP-ICA which is based on secant method, is applied to quickly find the independence between input variables. AP-MI estimation is also applied to estimate an accurate dependence information by equally partitioning the samples of input variable for calculating the probability density function(PDF). The proposed method has been applied to 2 problems for selecting the input variables, which are the 7 artificial signals of 500 samples and the 24 environmental pollution signals of 55 samples, respectively The experimental results show that the proposed methods has a fast and accurate selection performance. The proposed method has also respectively better performance than AP-MI estimation without the FP-ICA and regular partition MI estimation.

• Journal of KIISE:Information Networking
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• v.41 no.4
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• pp.192-201
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• 2014

User scheduling boosts the Multi-User Multi-Input Multi-Output (MU-MIMO) gain by selecting an optimal set of users to increase the 802.11 Wi-Fi system capacities. Many kinds of user scheduling algorithms, however, fail to realize the advantages of MU-MIMO due to formidable Channel State Information (CSI) overhead. In this paper, we propose a user scheduling method considering such CSI exchange overhead and its MAC protocol, called ACE (Active CSI Exchange based User Scheduling for MU-MIMO Transmission). Unlike most proposals, where user scheduling is performed after an Access Point (AP) receives CSI from all users, ACE determines the best user set during the CSI exchange phase. In particular, the AP broadcasts a channel hint about previously scheduled users, and the remaining users actively send CSI reports according to their Effective Channel Gains (ECGs) calculated from the hint. Through trace-driven MATLAB simulations, we prove that the proposed scheme improves the throughput gain significantly.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.35 no.2A
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• pp.142-152
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• 2010

When a mobile station(MS) performs a handover, in the IEEE 802.11 WLAN, MS's channel scanning for discovering new available APs is the dominating factor in handover latency, accounting 90% of overall latency. In order to reduce such a scanning latency, we focus on the method for reducing the number of channels for the MS in handover process to scan. With the help of IEEE 802.21 information server(IS), a proper order of groups of channels to be scanned is offered by the current AP depending on the information of neighbor APs in terms of the distance from serving AP, traffic load and network topology. By using this scanning order, the passive scanning of a MS in normal operation enables the MS to filter out the unavailable channels, and thus to classify the candidate channels of neighbor APs into three groups. Then, a handover-imminent MS can perform the active scanning from the most reliable group of channels. Simulation results show that the proposed scanning scheme reduce the scanning latency in comparison with the conventional scheme.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2014.10a
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• pp.595-598
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• 2014

In order to provide the Mobile Stations operating in IEEE 802.11 Wireless LAN network with seamless handover, a comprehensive study on the functions of handover considering various networking environments and characteristics of Mobile Stations is required. Note that the channel scan process finding a new AP takes the major portion of handover time, and this is the most significant issue with seamless handover for real-time multimedia service in WLAN environment. In this paper the functions required to provide seamless handover in IEEE 802.11 WLAN network are identified, and a new scanning technique is proposed with which the Mobile Stations can selectively scan the channels to reduce the channel scan time in various network environments. Here each Mobile Station awares of the channels the neighbor APs are using by scanning them in advance according to the proposed technique. Afterwards, when handover is actually required, the optimal AP is decided quickly by scanning only the predetemined group of channels and order of scan without unnecessary scan of all the channels. In addition, proposes to enter the Scan Trigger Value and Handover Threshold Value in mobile phones in order to prevent the phenomenon can not handover.

• The KIPS Transactions:PartC
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• v.17C no.3
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• pp.251-258
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• 2010

In an indoor localization method taking the lateration-based approach, the location of a target is estimated with the location of anchor points (APs) and the approximated distances between the target and APs using received signal strength (RSS) measurements. The accuracy of distance estimation affects the localization accuracy of a lateration-based method. Since a radio propagation environment varies randomly in time and space, the highest RSSs do not necessarily give the best estimation of the distances between a target and APs. Thus, all APs hearing a target have been used for localization. However, the accuracy of a lateration-based method degrades if more APs beyond a certain threshold are used because the area of polygon with the APs increases. In this paper, we focus on reducing the size of the polygon to further increase the localization accuracy. We use the centroid of the polygon as a reference point to estimate the relative location of a target in the polygon. Once the relative location is estimated, only the APs which are closest to the target are used for localization to reduce the area of the polygon with the APs. We validate the proposed method by implementing an indoor localization system and evaluating the accuracy of the proposed method in the various experimental environments.

• Proceedings of the Korea Information Processing Society Conference
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• 2014.11a
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• pp.244-246
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• 2014

본 논문에서는 이기종 무선망 환경에서 AP를 이용한 단절시간 계산을 통해 새로운 타겟 네트워크를 선정하는 기법을 제안하였다. 본 논문에서는 단절시간이라는 새로운 개념을 이용하여 기존 기법들이 가지는 방법과는 다른 방향으로 접근을 시도하였다. NS-2 시뮬레이션 결과, 제안한 기법이 단절시간이 짧은 네트워크를 선택함으로써 처리량이 향상됨을 확인하였다.

• Journal of the Korea Society of Computer and Information
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• v.25 no.1
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• pp.63-69
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• 2020

In this paper, we propose an indoor positioning technique using the landmark based on relative Access Point (AP) signal strengths. The absolute values of AP signals are used to conventional indoor positioning technologies, but they may be different because of the difference of the measuring device, the measuring environment, and the timing of the measurements. However, we found the fact that the flow of the AP's RSSI in certain places shows almost constant patterns. Based on theses characteristics, we identify the relative strength between the APs and store the certain places as landmarks where they show certain patterns. Once the deployment of the landmark map is complete, system calculate position of user using the IMU sensor of smartphone and calibrate it with stored landmarks. Our system shows 75.2% improvement over technology that used only sensors, and 39.6% improvement over technology that used landmarks that were selected with absolute values.

• Proceedings of the Korea Information Processing Society Conference
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• 2010.04a
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• pp.463-466
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• 2010

길이가 긴 질의에는 검색에 불필요한 단어가 포함되어 있어서 사용자가 원하지 않는 문서가 검색결과에 포함된다. 질의에서 불필요한 단어를 제거하고 핵심 단어만 선택한다면 검색에 효율을 높일 수 있다. 본 논문에서는 질의 조합을 기반한 클러스터를 이용해 핵심 단어를 찾고 핵심 단어와의 근접도를 이용해 상위 문서의 정확율을 향상시키는 기법을 제안한다. 실험은 뉴스 집합인 TREC AP 문서를 검색한 결과를 제안한 알고리즘으로 재순위화하여 초기 검색 결과의 상위 문서의 정확율을 비교함으로써 제안된 알고리즘의 유효성을 검증한다.

• The KIPS Transactions:PartC
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• v.16C no.5
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• pp.645-652
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• 2009

Location-based service providing the customized information or service according to the user's location has attracted a lot of attention from the mobile communication industry. The service is realized by means of several building blocks, a localization scheme, service platform, application and service. The localization scheme figures out a moving target's position through measuring and processing a wireless signal. In this paper, we propose an adaptive localization scheme in an indoor localization system based on IEEE 802.15.4 standard. In order to enhance the localization accuracy, the proposed scheme selects the best reference points and adaptively reflects the changes of propagation environments of a moving target to approximate distances between the target and the reference points in RSS(Received Signal Strength) based localization system using triangulation. Through the implementation of the localization system, we verify the performance of the proposed scheme in terms of the localization accuracy.