• Journal of Institute of Control, Robotics and Systems
• /
• v.14 no.6
• /
• pp.608-614
• /
• 2008

This paper describes a location tracking system to guide landing process of an Unmanned Helicopter(UMH) exploiting MIT Cricket nodes. For automatic landing of a UMH, a precise positioning system is indispensable. However, GPS(Global Positioning System) is inadequate for tracking the three dimensional position of a UMH because of large positioning errors. The Cricket systems use Time-Difference-of-Arrival(TDoA) method with ultrasonic and RF(Radio Frequency) signals to measure distances. They operate in passive mode in that a listener attached to a moving device receives distance signals from several beacons located at fixed points on ground. Inevitably, this passive type of implementation causes large disturbances in measuring distances between beacons and the listener due to wind blow from propeller and turbulence of UMH body. To cope with this problem, we proposed active type of implementation for positioning a UMH. In this implementation, a beacon is set up at UMH body and four listeners are located at ground area at least where the UMH will land. A pair of Ultrasonic and RF signals from the beacon arrives at several listeners to calculate the position of the UMH. The distance signals among listeners are synchronized with a counter value appended to each distance signals from the beacon.

• Journal of electromagnetic engineering and science
• /
• v.11 no.3
• /
• pp.213-219
• /
• 2011

Simulative target generators are needed for testing and calibrating various radar systems. The generator in this study discriminates the transmitting frequency from a radar and simulates parameters like target range, range rate, and atmospheric attenuation using the digital RF memory technique. The simulative target echo is then sent to the radar for testing and evaluation. This paper proposes a novel architecture for controlling the digital RF memory so it continually writes ADC data to the memory and reads it for the DAC with increasing one step address in order to control the delay of target range in a simple way. The target echo is programmed according to various preprogrammed scenarios and is generated in real time using a wireless local area network (LAN). To analyze the detected and generated target information easily, the system times for the radar and simulative target generator are synchronized using a global positioning system (GPS).

• The Transactions of The Korean Institute of Electrical Engineers
• /
• v.65 no.12
• /
• pp.2113-2118
• /
• 2016

The precise detection of electric leakage point of underground power cable is very important to reduce cost and time of maintenance and prevent electric shock accident through expedite repair of electric leakage point. This paper proposes a electric leakage point detection system underground power cable using of half-period modulated transmission waveform and earth electric potential measurement. The developed system is composed of transmitter to generate the wanted pulse waveform, receiver to measure and display earth electric potential by the transmitted pulse in electric leakage point and PC Software program to display of GPS coordinate on detection cable line. The performance of the electric leakage point detection system was tested in the constructed underground cable leakage detection test bed. The test results on signal generation voltage precision of signal transmitter, mean detection earth voltage, mean detection leakage current and electric leakage point detection error showed the developed system can be used in electric leakage point detection underground power cable.

• Proceedings of the Korean Association of Geographic Inforamtion Studies Conference
• /
• 2008.06a
• /
• pp.322-324
• /
• 2008

재난재해 등 긴급 상황이 발생했을 때 신속한 대응 체계 수립을 위해 비 접근 및 난접근 지대, 목표물 감시대상지역에 대한 공간정보를 신속하게 취득할 수 있는 실시간 공중모니터링 체계의 구축이 시급한 실정이다. 이에 본 연구에서는 긴급한 재난 상황과 혹은 이와 유사한 여러 상황에 신속하고 유연하게 운용될 수 있는 무인헬기 기반의 실시간 공중 모니터링 체계에 적용할 멀티 센서 시스템의 설계를 목표로 한다. 이를 위해 먼저 실시간 공중모니터링 임무 및 운용 시나리오를 크게 4가지로 설정하고 이에 적합한 디지털 카메라, 레이저 스캐너, GPS/IMU 및 무인헬기 플랫폼의 요구사항을 각각 도출하였다. 또한, 기술 동향 및 규격 조사결과를 바탕으로 도출된 요구사항에 가장 적합한 각각의 센서 및 플랫폼을 선정하였다. 마지막으로 시스템 설계의 최적화를 위하여 시뮬레이션을 통해 설정된 임무에 부합하는 품질의 공간정보 성과물이 선정된 멀티센서 시스템으로부터 취득 가능한가를 검증하였다. 본 연구를 통해 소형무인헬기기반의 멀티 센서시스템에 대한 최적 설계의 방법론을 정립할 수 있었고, 향후 설계의 결과는 임무로부터 도출된 요구사항에 최적화된 맞춤형 시스템 구축에 적용들 예정이다.

• Journal of Positioning, Navigation, and Timing
• /
• v.3 no.4
• /
• pp.155-161
• /
• 2014

The purpose of this study is to develop precise point positioning (PPP) algorithms based on GLONASS code-pseudorange, verify their performance and present their utility. As the basic correction models of PPP, we applied Inter Frequency Bias (IFB), relativistic effect, satellite antenna phase center offset, and satellite orbit and satellite clock errors, ionospheric errors, and tropospheric errors that must be provided on a real-time basis. The satellite orbit and satellite clock errors provided by Information-Analytical Centre (IAC) are interpolated at each observation epoch by applying the Lagrange polynomial method and linear interpolation method. We applied Global Ionosphere Maps (GIM) provided by International GNSS Service (IGS) for ionospheric errors, and increased the positioning accuracy by applying the true value calculated with GIPSY for tropospheric errors. As a result of testing the developed GLONASS PPP algorithms for four days, the horizontal error was approximately 1.4 ~ 1.5 m and the vertical error was approximately 2.5 ~ 2.8 m, showing that the accuracy is similar to that of GPS PPP.

• Journal of Institute of Control, Robotics and Systems
• /
• v.17 no.5
• /
• pp.429-435
• /
• 2011

This paper presents a sensor fusion-based estimation of heading and a Bezier curve-based motion planning for unmanned ground vehicle. For the vehicle to drive itself autonomously and safely, it should estimate its pose with sufficient accuracy in reasonable processing time. The vehicle should also have a path planning algorithm that enables to adapt to various situations on the road, especially at intersections. First, we address a sensor fusion-based estimation of the heading of the vehicle. Based on extended Kalman filter, the algorithm estimates the heading using the GPS, IMU, and wheel encoders considering the reliability of each sensor measurement. Then, we propose a Bezier curve-based path planner that creates several number of path candidates which are described as Bezier curves with adaptive control points, and selects the best path among them that has the maximum probability of passing through waypoints or arriving at target points. Experiments under various outdoor conditions including at intersections, verify the reliability of our algorithm.

• Journal of Institute of Control, Robotics and Systems
• /
• v.16 no.5
• /
• pp.433-439
• /
• 2010

This paper proposes a beacon color code scheduling algorithm for the localization of multiple robots in a multi-block workspace. With the developments of intelligent robotics and ubiquitous technology, service robots are applicable for the wide area such as airports and train stations where multiple indoor GPS systems are required for the localization of the mobile robots. Indoor localization schemes using ultrasonic sensors have been widely studied due to its cheap price and high accuracy. However, ultrasonic sensors have some shortages of short transmission range and interferences with other ultrasonic signals. In order to use multiple robots in wide workspace concurrently, it is necessary to resolve the interference problem among the multiple robots in the localization process. This paper proposes an indoor localization system for concurrent multiple robots localization in a wide service area which is divided into multi-block for the reliable sensor operation. The beacon color code scheduling algorithm is developed to avoid the signal interferences and to achieve efficient localization with high accuracy and short sampling time. The performance of the proposed localization system is verified through the simulations and the real experiments.

• Journal of the Institute of Electronics Engineers of Korea TC
• /
• v.44 no.12
• /
• pp.44-53
• /
• 2007

In this paper, we focus on the developments of complex location awareness algorithms for real-time location based service and precise/stable localization in the outdoor. In the case of using galileo satellite system along with GPS, several error factor such as the ionosphere can be reduced for an increment of used frequency and visible satellites. Therefore, localization estimation error is no longer having problems with location awareness. But, chips synchronization error induces the error of acquisition and tracking, and the performance of receiver can be decreased. In order to solve this problem, this paper proposes a correlator for performance improvement of receiver in the precise localization.

• IEMEK Journal of Embedded Systems and Applications
• /
• v.4 no.1
• /
• pp.42-49
• /
• 2009

Most Vehicular Ad hoc Network (VANET) applications rely heavily on broadcast transmission of traffic related information to all reachable nodes within a certain geographical area. Among various broadcast approaches, flooding is the first broadcasting technique. Each node rebroadcasts the received message exactly once, which results in broadcast storm problems. Some mechanisms have been proposed to improve flooding in Mobile Ad hoc Networks (MANET), but they are not effective for VANET and only a few studies have addressed this issue. We propose two distance-based and timer-based broadcast suppression techniques: 15P(15percent) and slotted 15P. In the first (distance based) scheme, node's transmission range is divided into three ranges (80%,15%and5%). Only nodes within 15% range will rebroadcast received packet. Specific packet retransmission range (15%) is introduced to reduce the number of messages reforwarding nodes that will mitigate the broadcaststorm. In the second (timer-based) scheme, waiting time allocation for nodes within 15% range isused to significantly reduce the broadcaststorm. The proposed schemes are distributed and reliedon GPS information and do not requireany other prior knowledge about network topology. To analyze the performance of proposed schemes, statistics such as link load and the number of retransmitted nodes are presented. Our simulation results show that the proposed schemes can significantly reduce link load at high node densities up to 90 percent compared to a simple broadcast flooding technique.

• International Journal of Internet, Broadcasting and Communication
• /
• v.10 no.3
• /
• pp.42-50
• /
• 2018

The majority of existing falling recognition techniques provide service by recognizing only that the falling occurred. However, it is important to recognize not only the occurrence of falling but also the situation before and after the falling, as well as the location of the falling. In this paper, we design and propose the falling notification service system to recognize and provide service. This system uses the acceleration sensor of the smartphone to recognize the occurrence of a falling and the situation before and after the falling. In order to check the location of falling, GPS sensor data is used in the Google Map API to map to the map. Also, a crosswalk map converted into grid-based coordinates based on the longitude and latitude of the crosswalk is stored, and the locations before and after falling are mapped. In order to reduce the connection speed and server overload for real-time data processing, fog computing and cloud computing are designed to be distributed processing.